A common question asked by Design Engineers in concurrent engineering is whether a particular hole in a part is castable? To answer that question requires an analysis of the four dimensional components that constitute the description of the hole: diameter, length, diametrical tolerance and locational tolerance.
First, I should be very clear that the casting of holes is a “good thing”. Holes are the type of part detail that can generally be provided by the investment casting process at negligible cost to a customer. Cast holes can also be of benefit to the foundry as they enhance the dimensional stability of a casting.
Straight through-holes are more easily cast than are blind holes. For the purposes of this essay we’ll confine our attention to straight holes that are open from both ends. I shall address the special circumstances of casting blind holes and internal cores in other blogs.
Roundness: Let’s begin with an understanding that the form, or shape, of a cast hole is never “perfect” (but neither is a machined hole) and will vary slightly in size and shape along its length. This loss of perfection is induced by the contraction of the hot metal as it cools in the casting. As a result the diameter of a cast hole can be pulled out of shape as areas around it solidify and become smaller. A second phenomenon concerns holes cast through a thin thickness of metal tending to nonfill unevenly around the diameter. The measurement of the location of a cast hole can sometimes be difficult as any loss of accuracy in determining the centerline of an imperfect shape also diminishes the accuracy of the measurement.
Diametrical Tolerance: The tolerance on the diameter of a hole must conform to Standard Investment Casting tolerances (approximately ±.005 inch/inch) as do all cast features. Additional tolerance will required dependent on the length of hole being cast.
Diameter to Length Ratio: To reproduce a feature it is necessary for investment casting to build a minimum number layers of ceramic shell in or about it. In the case where a hole diameter is too small relative to its length the ceramic will be unable to fully form and the shell will fail when cast with metal. The ratio between the diameter and length of the hole will determine if the feature is castable.
The smaller the diameter of a through-hole the shorter the length that can be cast. For example a hole diameter of Ø.06” can be cast up to two diameters in length where a Ø.25” hole can be cast up to five diameters in length.
In instances where the diameter to length ratio is too small there is an alternative option to produce the hole from a preformed ceramic core. Preformed ceramic core add expense to the casting but are a very viable option for the manufacture of fine detail that can’t be otherwise be produced directly by the investment casting process. For more information about ceramic cores please see a related blog on the casting of blind holes and internal cores.
Locational Tolerance: The locational tolerance for a hole is more often an issue than is its form tolerance. The locational tolerance of holes must be in accordance with Standard Investment Casting Tolerances (approximately ±.005 inch/inch). As locationally important holes can be machined to a much higher tolerance cast through-holes are most often used for less critical features such as fluid flow passages, wire feeds or for ventilation.
A Designer can, however, sometimes mitigate a locational tolerance with some creative dimensioning. For example, cast holes might require less tolerance if dimensioned to nearby “local” features rather than directly to the datums.
O’Fallon Casting publishes an Investment Casting Design Guide that is available for free download on its website. The Design Guide contains tables that delineate the castable sizes of holes. Please download the Design Guide and in the event that your requirements are inside of the industry recommendations contact your O’Fallon Casting Sales Engineer to verify if a design is manufacturable.
Monday 14 December 2015
Friday 11 December 2015
Model Based Definition – Advantages & Disadvantages
Prior to the widespread integration of CAD systems in the 1980’s part drawings were filled with leader lines to features delineated by dimensions for size and location with independent tolerances. CAD systems have made the designing of parts both better and quicker and have a positive impact downstream from product design. Also known as Digital Product Definition (DPD) the MBD revolution in design has had both good and bad repercussions for the foundry industry.
O’Fallon Casting has been at the industry forefront in adopting technologies that support Model Based Definition designs. OFC can tool, manufacture and inspect its manufactured castings to a customer solid model without the need of a 2D drawing.
OFC Customers have varying degrees of MBD implementation. Some provide a solid model with a fully dimensioned drawings others with partially dimensioned and sometimes with drawings that contain no dimensions whatsoever. O’Fallon Casting has found that limited dimension drawings, especially for larger sizes of castings, are an effective way for an engineer to convey information regarding the important features of a part design.
Model Based Definition has helped reduce the cycle time from receipt of a design to the shipment of product. Toolmaking has become faster and more accurate as has the inspection of first articles. The First Pass Yield of MBD parts is better than it is for castings from tooling manufactured from fully dimensioned drawings.
The manufacture of Rapid Prototyping has greatly expanded with the advent of CAD solid model files. As the use of rapid prototypes has increased the materials, processes and equipment to produce them has also improved. Additive manufactured patterns from SLA, SLS or Voxeljet technologies are used to produce 1-off quantities or even low rates of production directly from a customer CAD file. (It should be noted, however, to successfully manufacture rapid prototypes the supplied CAD solid models must be complete with fillet radii; a detail that is frequently omitted by engineers because of the modeling time required and size of the resultant files.)
Laser scanning inspection of castings to their Solid Models is both less expensive and more informative as compared to the normal inspection of a fully dimensioned drawing. Traditionally the inspection of a part surface to a dimensioned drawing is made by the measurement of a series of points along the surface. By comparison a laser scan accumulates millions of points per square inch and so is capable of detecting small variations in the surface that would remain undetected by a traditional “point” methods. The wealth of data from a laser scan makes the dimensional analysis of a casting better and aids the ability of an engineer to discern in-process deviations from tooling errors.
The variety of available CAD formats can be challenging to a supply chain especially among smaller subcontractors. Parasolid (.x_t) and Step (.stp) file formats are generally well supported across the industry. Iges (.igs) files can be universally read but can be difficult to use as they seem to be very prone to file errors. Formats other than Parasolid, Step or Iges are likely to be translated to a locally readable format at some point along the supply chain. The use of other than the generally excepted CAD formats can also serve to limit the number of available subcontractors and may increase the cost for services.
More the case in the past, but still true today, Document and Data control of MPD CAD files has been found to be “difficult”. Part drawings and associated CAD files can sometimes go out of “sync” with each other and obsolete revision files have been mistakenly distributed. As a result of bad experiences some customers have become reticent to supply their CAD files for fear they are not up-to-date.
Tooling subcontractors, however, have become dependent on their receiving a customer solid model for their design and manufacture of tooling. Without a supplied customer CAD file it often becomes necessary for a toolmaker to first create their own Solid Model of the part. This extra step adds time and expense to the procurement of the tool and any latent errors found in toolmaker developed CAD file can also contribute to delays in product deliveries.
Model based definition products have become the norm in the investment casting industry. MBD possesses advantages in speed and accuracy of a designed product that far outweigh the challenges to downstream users of the files.
O’Fallon Casting is very familiar with the manufacture of nonferrous investment castings to their CAD solid models. If you have any questions regarding Model Based Definition please contact your O’Fallon Casting Sales Engineer.
O’Fallon Casting has been at the industry forefront in adopting technologies that support Model Based Definition designs. OFC can tool, manufacture and inspect its manufactured castings to a customer solid model without the need of a 2D drawing.
OFC Customers have varying degrees of MBD implementation. Some provide a solid model with a fully dimensioned drawings others with partially dimensioned and sometimes with drawings that contain no dimensions whatsoever. O’Fallon Casting has found that limited dimension drawings, especially for larger sizes of castings, are an effective way for an engineer to convey information regarding the important features of a part design.
Model Based Definition has helped reduce the cycle time from receipt of a design to the shipment of product. Toolmaking has become faster and more accurate as has the inspection of first articles. The First Pass Yield of MBD parts is better than it is for castings from tooling manufactured from fully dimensioned drawings.
The manufacture of Rapid Prototyping has greatly expanded with the advent of CAD solid model files. As the use of rapid prototypes has increased the materials, processes and equipment to produce them has also improved. Additive manufactured patterns from SLA, SLS or Voxeljet technologies are used to produce 1-off quantities or even low rates of production directly from a customer CAD file. (It should be noted, however, to successfully manufacture rapid prototypes the supplied CAD solid models must be complete with fillet radii; a detail that is frequently omitted by engineers because of the modeling time required and size of the resultant files.)
Laser scanning inspection of castings to their Solid Models is both less expensive and more informative as compared to the normal inspection of a fully dimensioned drawing. Traditionally the inspection of a part surface to a dimensioned drawing is made by the measurement of a series of points along the surface. By comparison a laser scan accumulates millions of points per square inch and so is capable of detecting small variations in the surface that would remain undetected by a traditional “point” methods. The wealth of data from a laser scan makes the dimensional analysis of a casting better and aids the ability of an engineer to discern in-process deviations from tooling errors.
The variety of available CAD formats can be challenging to a supply chain especially among smaller subcontractors. Parasolid (.x_t) and Step (.stp) file formats are generally well supported across the industry. Iges (.igs) files can be universally read but can be difficult to use as they seem to be very prone to file errors. Formats other than Parasolid, Step or Iges are likely to be translated to a locally readable format at some point along the supply chain. The use of other than the generally excepted CAD formats can also serve to limit the number of available subcontractors and may increase the cost for services.
More the case in the past, but still true today, Document and Data control of MPD CAD files has been found to be “difficult”. Part drawings and associated CAD files can sometimes go out of “sync” with each other and obsolete revision files have been mistakenly distributed. As a result of bad experiences some customers have become reticent to supply their CAD files for fear they are not up-to-date.
Tooling subcontractors, however, have become dependent on their receiving a customer solid model for their design and manufacture of tooling. Without a supplied customer CAD file it often becomes necessary for a toolmaker to first create their own Solid Model of the part. This extra step adds time and expense to the procurement of the tool and any latent errors found in toolmaker developed CAD file can also contribute to delays in product deliveries.
Model based definition products have become the norm in the investment casting industry. MBD possesses advantages in speed and accuracy of a designed product that far outweigh the challenges to downstream users of the files.
O’Fallon Casting is very familiar with the manufacture of nonferrous investment castings to their CAD solid models. If you have any questions regarding Model Based Definition please contact your O’Fallon Casting Sales Engineer.
Wednesday 9 December 2015
Laser Engraved Part Marking
O’Fallon Casting provides its customers with a better alternative and consistently legible option for the application of variable part marking information on castings: Laser Engraved Part Marking. This OFC technology eliminates customer complaints and rejections of castings for poor legibility of manually applied vibro-peened or ink stamped part marking.
O’Fallon Casting’s Laser Engraved Part Marking provides a .0001 - .0003” deep permanent marking that eliminates the variability of manually applied marking and replaces traditional techniques such as ink stamping, vibro-peening or electrochemical etching. Although not intended to replace “personal” ink stamps, such as Inspection Stamps, Laser Engraved Part Marking is a versatile technology for marking a cast surface with variable product information such as Melt & Heat Treat lot numbers, Part Serialization, or even a 2D Matrix barcode.
Laser Engraved Part Marking is recognized in standard marking specifications MIL-STD-130 (Table II) and AS478 (15A).
To eliminate a needless cause of Customer Dissatisfaction, O’Fallon Casting encourages Engineers to specify Laser Engraved Part Marking as a part marking option for the marking of variable information on their castings.
For more information about Laser Engraved Part Marking contact your O’Fallon Casting Sales Engineer.
O’Fallon Casting’s Laser Engraved Part Marking provides a .0001 - .0003” deep permanent marking that eliminates the variability of manually applied marking and replaces traditional techniques such as ink stamping, vibro-peening or electrochemical etching. Although not intended to replace “personal” ink stamps, such as Inspection Stamps, Laser Engraved Part Marking is a versatile technology for marking a cast surface with variable product information such as Melt & Heat Treat lot numbers, Part Serialization, or even a 2D Matrix barcode.
Laser Engraved Part Marking is recognized in standard marking specifications MIL-STD-130 (Table II) and AS478 (15A).
To eliminate a needless cause of Customer Dissatisfaction, O’Fallon Casting encourages Engineers to specify Laser Engraved Part Marking as a part marking option for the marking of variable information on their castings.
For more information about Laser Engraved Part Marking contact your O’Fallon Casting Sales Engineer.
Thursday 19 November 2015
Geometric Dimensioning and Tolerancing of Castings
There is nothing really new about Geometric Dimensioning and Tolerancing so I was surprised by a question an engineer asked recently concerning GD&T. I had just finished speaking to a group of engineers about investment casting design and the first question asked was to express my opinion of “GD&T casting drawings”. Admittedly confused I lamely answered with something akin to “I’m good with it” and felt fortunate that there was no follow-up question on the same subject.
Truthfully, I am so accustomed to working with Geometric Dimensioning & Tolerancing (ASME Y14.5) that I likely haven’t given it much thought for a couple of decades. Now having revisited the subject I believe my initial response the GD&T questions wasn’t too bad after all because I am “good with it” but didn’t provide much insight. So, in my opinion GD&T is the better method for an engineer to define part requirements than was the old Plus / Minus system. It is, however, a more difficult system to learn and interpret and as a consequence there seem to be greater numbers of errors made with GD&T.
I also believe that GD&T paved the way for dimensionless drawings that have created a much larger quandary for designers of cast products. (This, perhaps, with a little clarification, might have been the true subject of the question being asked of me?) However, for the purposes of this essay I’ll confine my attention to addressing Geometric Dimensioning and Tolerancing of a fully dimensioned casting drawing.
If you’ve worked with castings you likely realize that dimensional variation accumulates in the longer dimensions. The Investment Casting Institute has published a Linear Tolerance Table* that translates roughly to ±.005 inch of tolerance per inch of length. Therefore, a dimension of 2-inches would require a ±.010 tolerance and a 4-inch dimension ±.020. It is important to remember that a linear dimension is the distance between two points such as can be measured with a pair of Vernier calipers.
Let’s compare the two methods as to how one would dimension and tolerance three coplanar holes on a surface. One point of clarification: The following example considers a casting in an ideal state and so is presumed to be perfectly flat and square. As already discussed a linear dimension is the distance between two points and not a point to a (datum) plane. In the “real world” tolerance consideration is 3-dimensional (-X-, -Y-, -Z-) and must also include the size and shape of the datum plane.
In a Plus / Minus drawing the dimensions to three coplanar cast holes might be tolerance as follows:
In GD&T drawing the locational dimensions become Basic and the feature (hole) is designated with a True Position (feature location) tolerance linked to a Maximum Material Condition:
GD&T True Positions have circular tolerance zones where the tolerance zones in a Plus / Minus system are rectangular, so the GD&T system does provide a “smidge” of additional tolerance. Otherwise these two systems are pretty much equivalent.
Note, however, that a ±.010 locational tolerance is roughly equivalent to a true position of .028. Rookie engineers sometimes make the mistake of presuming that a .020 inch (±.010) of a Plus / Minus tolerance zone is the same size as .020 of True Position geometric tolerance where in actuality there quite a bit of difference. Geometric dimensions originate from the nexus or 0,0 point of the -X- and -Y- datums (it’s Pythagorean’s value of c in the a2 + b2 = c2) where Plus / Minus systems dimensions are measured along an axis perpendicular to the datum plane (a & b).
It is readily apparent from the above tables that the dimensions furthest from the datums require significantly more tolerance in either system. This emphasizes the point that datum selection is an important consideration for the Tolerancing of a part regardless of the system being used. I can suggest that one way to help mitigate the stack up of tolerance is to centralize the datum structure.
Let’s revisit the previous scenario but this time with the nexus of -X- and -Y- datums better centralized and being coincident with the centerlines of Hole A
In the Plus / Minus system dimensions and tolerances for the three holes become:
In the GD&T system the dimensions and tolerances become:
As you can see, the effect of centralizing the two datums is to average the cumulative deviation bilaterally, in two directions, instead of unilaterally and shifting all of the tolerance requirements to the “far end”. The centralized –X- and –Y- datums should create a more acceptable tolerance condition for the designer.
The ±.005 inch/inch linear tolerance was established by the Investment Casting Institute as a guideline to assist companies in the design manufacturable castings for its member foundries. O’Fallon Casting and many other Institute members manufacture castings to tolerances tighter than those being recommended by the ICI. We suggest that in instances where a designer is being driven to work inside of the ICI recommended tolerances, that they confer with a foundry to confirm their capability.
The use of Geometric Dimensioning and Tolerancing on a fully dimensioned drawing should not present an issue to a foundry. In any dimensioning system the size of the part and the location of the datum planes will have a direct impact on the amount of tolerance necessary for a manufacturable and affordable casting. Centralized datums will prevent the stack-up of part variation from manifesting itself in one side of the casting by averaging the deviations in two directions.
If you have any questions regarding Geometric Dimensioning and Tolerancing of castings, please contact your O’Fallon Casting Sales Engineer.
*The Investment Casting Handbook published by the Investment Casting Institute, copyright 1997.
Truthfully, I am so accustomed to working with Geometric Dimensioning & Tolerancing (ASME Y14.5) that I likely haven’t given it much thought for a couple of decades. Now having revisited the subject I believe my initial response the GD&T questions wasn’t too bad after all because I am “good with it” but didn’t provide much insight. So, in my opinion GD&T is the better method for an engineer to define part requirements than was the old Plus / Minus system. It is, however, a more difficult system to learn and interpret and as a consequence there seem to be greater numbers of errors made with GD&T.
I also believe that GD&T paved the way for dimensionless drawings that have created a much larger quandary for designers of cast products. (This, perhaps, with a little clarification, might have been the true subject of the question being asked of me?) However, for the purposes of this essay I’ll confine my attention to addressing Geometric Dimensioning and Tolerancing of a fully dimensioned casting drawing.
If you’ve worked with castings you likely realize that dimensional variation accumulates in the longer dimensions. The Investment Casting Institute has published a Linear Tolerance Table* that translates roughly to ±.005 inch of tolerance per inch of length. Therefore, a dimension of 2-inches would require a ±.010 tolerance and a 4-inch dimension ±.020. It is important to remember that a linear dimension is the distance between two points such as can be measured with a pair of Vernier calipers.
Let’s compare the two methods as to how one would dimension and tolerance three coplanar holes on a surface. One point of clarification: The following example considers a casting in an ideal state and so is presumed to be perfectly flat and square. As already discussed a linear dimension is the distance between two points and not a point to a (datum) plane. In the “real world” tolerance consideration is 3-dimensional (-X-, -Y-, -Z-) and must also include the size and shape of the datum plane.
In a Plus / Minus drawing the dimensions to three coplanar cast holes might be tolerance as follows:
| Hole A: | Ø.50 ±.005 | 5.00 ±.025 from -X- | 5.00 ±.025 from -Y- |
| Hole B: | Ø.50 ±.005 | 2.00 ±.010 from -X- | 2.00 ±.010 from -Y- |
| Hole C: | Ø.50 ±.005 | 10.00 ±.050 from -X- | 10.00 ±.050 from -Y- |
In GD&T drawing the locational dimensions become Basic and the feature (hole) is designated with a True Position (feature location) tolerance linked to a Maximum Material Condition:
| Hole A: | Ø.50 ±.005 | 5.00 Basic from -X- | 5.00 Basic from -Y- | 070 True Position MMC |
| Hole B: | Ø.50 ±.005 | 2.00 Basic from -X- | 2.00 Basic from -Y- | 028 True Position MMC |
| Hole C: | Ø.50 ±.005 | 10.00 Basic from -X- | 10.00 Basic from -Y- | 140 True Position MMC |
GD&T True Positions have circular tolerance zones where the tolerance zones in a Plus / Minus system are rectangular, so the GD&T system does provide a “smidge” of additional tolerance. Otherwise these two systems are pretty much equivalent.
Note, however, that a ±.010 locational tolerance is roughly equivalent to a true position of .028. Rookie engineers sometimes make the mistake of presuming that a .020 inch (±.010) of a Plus / Minus tolerance zone is the same size as .020 of True Position geometric tolerance where in actuality there quite a bit of difference. Geometric dimensions originate from the nexus or 0,0 point of the -X- and -Y- datums (it’s Pythagorean’s value of c in the a2 + b2 = c2) where Plus / Minus systems dimensions are measured along an axis perpendicular to the datum plane (a & b).
It is readily apparent from the above tables that the dimensions furthest from the datums require significantly more tolerance in either system. This emphasizes the point that datum selection is an important consideration for the Tolerancing of a part regardless of the system being used. I can suggest that one way to help mitigate the stack up of tolerance is to centralize the datum structure.
Let’s revisit the previous scenario but this time with the nexus of -X- and -Y- datums better centralized and being coincident with the centerlines of Hole A
In the Plus / Minus system dimensions and tolerances for the three holes become:
| Hole A: | Ø.50 ±.005 | 0.00 ±.000 from -X- | 0.00 ±.000 from -Y- |
| Hole B: | Ø.50 ±.005 | 3.00 ±.015 from -X- | 3.00 ±.015 from -Y- |
| Hole C: | Ø.50 ±.005 | 5.00 ±.025 from -X- | 5.00 ±.025 from -Y- |
In the GD&T system the dimensions and tolerances become:
| Hole A: | Ø.50 ±.005 | 0.00 Basic from -X- | 0.00 Basic from -Y- | ..000 True Position MMC |
| Hole B: | Ø.50 ±.005 | 3.00 Basic from -X- | 3.00 Basic from -Y- | .042 True Position MMC |
| Hole C: | Ø.50 ±.005 | 5.00 Basic from -X- | 5.00 Basic from -Y- | .070 True Position MMC |
As you can see, the effect of centralizing the two datums is to average the cumulative deviation bilaterally, in two directions, instead of unilaterally and shifting all of the tolerance requirements to the “far end”. The centralized –X- and –Y- datums should create a more acceptable tolerance condition for the designer.
The ±.005 inch/inch linear tolerance was established by the Investment Casting Institute as a guideline to assist companies in the design manufacturable castings for its member foundries. O’Fallon Casting and many other Institute members manufacture castings to tolerances tighter than those being recommended by the ICI. We suggest that in instances where a designer is being driven to work inside of the ICI recommended tolerances, that they confer with a foundry to confirm their capability.
The use of Geometric Dimensioning and Tolerancing on a fully dimensioned drawing should not present an issue to a foundry. In any dimensioning system the size of the part and the location of the datum planes will have a direct impact on the amount of tolerance necessary for a manufacturable and affordable casting. Centralized datums will prevent the stack-up of part variation from manifesting itself in one side of the casting by averaging the deviations in two directions.
If you have any questions regarding Geometric Dimensioning and Tolerancing of castings, please contact your O’Fallon Casting Sales Engineer.
*The Investment Casting Handbook published by the Investment Casting Institute, copyright 1997.
Monday 16 November 2015
Integrally Cast Lettering & Marking
One of the primary benefits provided by the Investment Casting process is that part detail can very often be furnished at negligible additional cost. Engineers frequently take advantage of this “free” capability by incorporating cast lettering and marking into their part designs. Marking can be almost anything from letters, numbers, logos, trademarks or be simply decorative.
There are basically two types of cast marking, “Integral” or “Applied”. Integral-marking is embedded into a pattern mold so that the identical marking appears on each part cast. Applied-marking such as that made by laser, vibro-etch or ink stamping is applied to the finished product and used most often to identify castings with information that changes part-to-part or lot-to-lot such as serial numbers or heat treat lot data. We will devote our attention here to integral-marking.
Integral-marking, being permanently cut into the pattern mold, is somewhat difficult to alter. Although there are methods by which to integrally cast variable information this does add an element of cost to the casting and so is better suited for one of the applied-marking methods.
Integral-marking can be either raised or depressed on the casting surface but given a choice foundries tend to prefer that marking be raised. The reason for this preference is that positive features on a part are the inverse in the pattern mold. Thus a depressed part marking will be raised on the surface of the mold so will be very susceptible to damage from handling of the mold. A designer desiring a depressed integral-marking (thus raised in the pattern mold) should consider designing the depressed lettering to be on a “raised pad” with the pad height being taller than the marking is deep. In this manner, in the pattern mold, the “pad” will be deeper in the mold than the lettering is high so the lettering be somewhat more protected from damage when the mold is being handled.
Though commonplace, whether integral-marking be raised or depressed, there are other challenges that can be mitigated with good design. With investment casting it is important that integral-marking be sufficiently substantial in height and stroke-width that the process will robustly reproduce them. If marking is too shallow it will not be legible on the cast part or if too deep the integral-marking may suffer from metal penetration so, for example, the loops of a letter “B” fill with metal to then more resemble a letter “D”.
O’Fallon Casting suggests that the raised height or depth of the integral-marking be .010 - .015” from the casting surface depending on the choice of characters or fonts. Characters and forts will cast optimally without any sharp edges or corners.
Incorporating Integral-marking into designs is one way to take advantage of the investment casting’s ability to provide part detail at minimal expense. If you have any question if an integral-marking should be included in your casting design, please consult your O’Fallon Casting Sales Engineer.
There are basically two types of cast marking, “Integral” or “Applied”. Integral-marking is embedded into a pattern mold so that the identical marking appears on each part cast. Applied-marking such as that made by laser, vibro-etch or ink stamping is applied to the finished product and used most often to identify castings with information that changes part-to-part or lot-to-lot such as serial numbers or heat treat lot data. We will devote our attention here to integral-marking.
Integral-marking, being permanently cut into the pattern mold, is somewhat difficult to alter. Although there are methods by which to integrally cast variable information this does add an element of cost to the casting and so is better suited for one of the applied-marking methods.
Integral-marking can be either raised or depressed on the casting surface but given a choice foundries tend to prefer that marking be raised. The reason for this preference is that positive features on a part are the inverse in the pattern mold. Thus a depressed part marking will be raised on the surface of the mold so will be very susceptible to damage from handling of the mold. A designer desiring a depressed integral-marking (thus raised in the pattern mold) should consider designing the depressed lettering to be on a “raised pad” with the pad height being taller than the marking is deep. In this manner, in the pattern mold, the “pad” will be deeper in the mold than the lettering is high so the lettering be somewhat more protected from damage when the mold is being handled.
Though commonplace, whether integral-marking be raised or depressed, there are other challenges that can be mitigated with good design. With investment casting it is important that integral-marking be sufficiently substantial in height and stroke-width that the process will robustly reproduce them. If marking is too shallow it will not be legible on the cast part or if too deep the integral-marking may suffer from metal penetration so, for example, the loops of a letter “B” fill with metal to then more resemble a letter “D”.
O’Fallon Casting suggests that the raised height or depth of the integral-marking be .010 - .015” from the casting surface depending on the choice of characters or fonts. Characters and forts will cast optimally without any sharp edges or corners.
Incorporating Integral-marking into designs is one way to take advantage of the investment casting’s ability to provide part detail at minimal expense. If you have any question if an integral-marking should be included in your casting design, please consult your O’Fallon Casting Sales Engineer.
Thursday 12 November 2015
Surface Texture of Investment Castings
The Investment Casting Institute’s “The Investment Casting Handbook” states that a 125 RMS surface texture is typical (for steel castings) and that no other casting process produces a finer surface finish than does investment casting. Although “The Investment Casting Handbook” says Typical, a 125 RMS is commonly cited by the industry and a 125 RMS Max has become a common callout on many investment casting drawings. As the surface texture provided by O’Fallon Casting is generally much better than a 125 RMS Max requirement it is not considered to be an issue at Contract Review. However, every few years a profilometer inspection of an as-cast surface texture will find and reject some area of a part for being in excess of a 125 RMS Max drawing requirement.
Because of these occasional incidents I argue against placing a surface texture requirement on a casting drawing unless the texture is important to the function of the part. My thoughts are echoed in ANSI/ASME B46.1 Appendix B on the Control & Production of Surface Texture. Appendix B1 states that: “Surface characteristics should not be controlled on a drawing…” as “Unnecessary restrictions may increase production costs…”. Since the surface texture of a casting is a function of a given foundry process, the options available to improve the native surface texture will entail some nature of secondary operation that will add expense to the cost of the product.
ANSI/ASME B46.1 Appendix B reinforces this notion by further stating that “Surface texture is the result of the processing method…” In effect a Sand Casting will have a sand cast surface texture while a Die Casting will have a die cast surface texture and an Investment Casting an investment casting surface texture.
An accompanying Figure (B1) in ANSI/ASME B46.1 shows the normal ranges of surface texture by processing method which for Investment Castings is 60 – 200 RMS. Designers should consider 60 – 200RMS as an appropriate range of variation when specifying a surface texture requirement and also deciding if a given surface should be machined to a finer finish or remain as-cast.
The occasional rejection of castings to a 125 RMS Max requirement is also in part explained by ANSI/ASME B46.1 where it states that “Castings are characterized by random distribution of nondirectional deviations from the nominal surface.”
ANSI/ASME B46.1 further states that “Surface characteristics of castings should never be considered on the same basis as machined surfaces.” An inspection of an as-cast surface texture with a profilometer is in itself an inappropriate method for a foundry product. The inspection of Surface texture as-cast surfaces should instead be performed by visual comparison to a standard. GAR Electoforming (http://garelectroforming.com) manufactures a “C-9 Cast Microfinish Comparator” that can be used as a standard for visual and tactual comparison to a cast surface consistent with ASNI/ASME B46.1. The use of this type of Comparator is highly recommended for the evaluation of an as-cast surface texture.
Overall it is recommended that a Surface Texture should only be specified on a drawing when it is important to the function of the end product. The surface texture of a casting will be representative of its manufacturing process and it should be inspected visually to an appropriate surface texture gage.
Because of these occasional incidents I argue against placing a surface texture requirement on a casting drawing unless the texture is important to the function of the part. My thoughts are echoed in ANSI/ASME B46.1 Appendix B on the Control & Production of Surface Texture. Appendix B1 states that: “Surface characteristics should not be controlled on a drawing…” as “Unnecessary restrictions may increase production costs…”. Since the surface texture of a casting is a function of a given foundry process, the options available to improve the native surface texture will entail some nature of secondary operation that will add expense to the cost of the product.
ANSI/ASME B46.1 Appendix B reinforces this notion by further stating that “Surface texture is the result of the processing method…” In effect a Sand Casting will have a sand cast surface texture while a Die Casting will have a die cast surface texture and an Investment Casting an investment casting surface texture.
An accompanying Figure (B1) in ANSI/ASME B46.1 shows the normal ranges of surface texture by processing method which for Investment Castings is 60 – 200 RMS. Designers should consider 60 – 200RMS as an appropriate range of variation when specifying a surface texture requirement and also deciding if a given surface should be machined to a finer finish or remain as-cast.
The occasional rejection of castings to a 125 RMS Max requirement is also in part explained by ANSI/ASME B46.1 where it states that “Castings are characterized by random distribution of nondirectional deviations from the nominal surface.”
ANSI/ASME B46.1 further states that “Surface characteristics of castings should never be considered on the same basis as machined surfaces.” An inspection of an as-cast surface texture with a profilometer is in itself an inappropriate method for a foundry product. The inspection of Surface texture as-cast surfaces should instead be performed by visual comparison to a standard. GAR Electoforming (http://garelectroforming.com) manufactures a “C-9 Cast Microfinish Comparator” that can be used as a standard for visual and tactual comparison to a cast surface consistent with ASNI/ASME B46.1. The use of this type of Comparator is highly recommended for the evaluation of an as-cast surface texture.
Overall it is recommended that a Surface Texture should only be specified on a drawing when it is important to the function of the end product. The surface texture of a casting will be representative of its manufacturing process and it should be inspected visually to an appropriate surface texture gage.
Tuesday 3 November 2015
In-Process Weld Rework
Castings are susceptible to having small discontinuities such as inclusions, voids, cracks, etc. that are cosmetically unappealing or potentially even a cause of end product failure. In-process weld rework of castings, sometimes also referred to as “cosmetic weld repair”, is a routine and commonplace foundry activity that is used to mend such casting discontinuities. A casting that has been welded and blended will be dimensionally, physically, chemically and metallurgically compliant to drawing requirements.
Foundry customers derive both direct and indirect benefit from weld rework as it helps make castings more affordable and improves foundry on-time delivery. Foundries factor a casting-yield in their production runs which is an allowance for some quantity of scrap. A poorer than predicted yield of castings will jeopardize a customer delivery, burden the foundry with the cost for the unanticipated scrap, and also the additional expense for a re-run of parts. In-process weld rework provides a foundry with an opportunity to salvage parts that might otherwise be scrap and so protect the customer delivery. Foundries won’t perform unnecessary amounts of weld rework as the cost can easily exceed the value of a casting. In effect weld rework stabilizes foundry yields which, in turn, improves the delivery and the overall affordability of a casting.
The practice for in-process weld rework is well established and presents no deleterious risk to the quality of a casting. A properly performed weld, because of its rapid solidification, is likely stronger than the base metal of the casting.* If you think about it prosaically, the welding of a casting is essentially a “local re-liquefaction” of something that was formerly all liquid.
For the heat treatable alloys to be metallurgically compliant the weld rework of castings must be performed prior to any heat treatment. Post treatment welding will destroy the effect of the heat treatment and so is often called “green welding”. Green welding should only be conducted with the express written permission of the customer.
Weld rework of commercial castings is generally performed by foundries without reservation. Military and aerospace drawings, however, are likely to contain an AMS or ASTM material specification that will prohibit weld rework of castings without first having written customer authorization. Drawing notes are frequently used to convey the required permission to the foundry. In instances where an in-process weld authorization is not automatically being flowed a foundry should identify this at contract review issue and formally request a rework authorization from its customer.
Welding of castings should be referred to as an in-process weld “rework” instead of “repair”. In aerospace and perhaps in other industries as well, the word “Repair” alludes to a very specific and closely controlled activity. Unfortunately, the foundry industry does often identify the procedure as a “Weld Repair”. In aerospace vernacular an in-process weld rework being performed prior to heat treatment it is not considered to be a “Repair” and use of the term should be discouraged.
The most commonly referenced specification for the weld rework of investment castings is AMS2694. Titled “In-Process Welding of Castings” the “Purpose” of AMS 2694 is to define “the requirements for in-process correction of foundry discontinuities by manual welding of castings.” A discontinuity is further defined as a casting nonconformance such as a crack, damage, hot tear, cold shut, shrinkage, porosity, gas hole, inclusion, etc. Weld rework may not be used to correct dimensional discrepancies, discontinuities found during machining, or to fabricate portions of castings unless specifically authorized by a customer. AMS2694 requires that weld rework must be performed by qualified welders and that the welds must be blended and inspected to the requirements of the drawing. Residual linear indications are never acceptable.
In-process weld rework is a routine foundry operation that enhances the affordability and delivery of cast products. If you have any questions concerns regarding weld rework please contact your O’Fallon Casting Sales Engineer.
*There are a number of studies that attest to this fact. See Paper presented by Authors Gerald Gagel, Daniel Hoefert, Joseph Hirvela, & Randy Oehrlein at AFS CastExpo 2013 on the “Effect of Weld Repair on Static and Dynamic Tensile Properties of E357-T6 Sand Castings” and concludes that the researchers found that “…repair welding had no detrimental effects on tensile or fatigue properties.”.
Foundry customers derive both direct and indirect benefit from weld rework as it helps make castings more affordable and improves foundry on-time delivery. Foundries factor a casting-yield in their production runs which is an allowance for some quantity of scrap. A poorer than predicted yield of castings will jeopardize a customer delivery, burden the foundry with the cost for the unanticipated scrap, and also the additional expense for a re-run of parts. In-process weld rework provides a foundry with an opportunity to salvage parts that might otherwise be scrap and so protect the customer delivery. Foundries won’t perform unnecessary amounts of weld rework as the cost can easily exceed the value of a casting. In effect weld rework stabilizes foundry yields which, in turn, improves the delivery and the overall affordability of a casting.
The practice for in-process weld rework is well established and presents no deleterious risk to the quality of a casting. A properly performed weld, because of its rapid solidification, is likely stronger than the base metal of the casting.* If you think about it prosaically, the welding of a casting is essentially a “local re-liquefaction” of something that was formerly all liquid.
For the heat treatable alloys to be metallurgically compliant the weld rework of castings must be performed prior to any heat treatment. Post treatment welding will destroy the effect of the heat treatment and so is often called “green welding”. Green welding should only be conducted with the express written permission of the customer.
Weld rework of commercial castings is generally performed by foundries without reservation. Military and aerospace drawings, however, are likely to contain an AMS or ASTM material specification that will prohibit weld rework of castings without first having written customer authorization. Drawing notes are frequently used to convey the required permission to the foundry. In instances where an in-process weld authorization is not automatically being flowed a foundry should identify this at contract review issue and formally request a rework authorization from its customer.
Welding of castings should be referred to as an in-process weld “rework” instead of “repair”. In aerospace and perhaps in other industries as well, the word “Repair” alludes to a very specific and closely controlled activity. Unfortunately, the foundry industry does often identify the procedure as a “Weld Repair”. In aerospace vernacular an in-process weld rework being performed prior to heat treatment it is not considered to be a “Repair” and use of the term should be discouraged.
The most commonly referenced specification for the weld rework of investment castings is AMS2694. Titled “In-Process Welding of Castings” the “Purpose” of AMS 2694 is to define “the requirements for in-process correction of foundry discontinuities by manual welding of castings.” A discontinuity is further defined as a casting nonconformance such as a crack, damage, hot tear, cold shut, shrinkage, porosity, gas hole, inclusion, etc. Weld rework may not be used to correct dimensional discrepancies, discontinuities found during machining, or to fabricate portions of castings unless specifically authorized by a customer. AMS2694 requires that weld rework must be performed by qualified welders and that the welds must be blended and inspected to the requirements of the drawing. Residual linear indications are never acceptable.
In-process weld rework is a routine foundry operation that enhances the affordability and delivery of cast products. If you have any questions concerns regarding weld rework please contact your O’Fallon Casting Sales Engineer.
*There are a number of studies that attest to this fact. See Paper presented by Authors Gerald Gagel, Daniel Hoefert, Joseph Hirvela, & Randy Oehrlein at AFS CastExpo 2013 on the “Effect of Weld Repair on Static and Dynamic Tensile Properties of E357-T6 Sand Castings” and concludes that the researchers found that “…repair welding had no detrimental effects on tensile or fatigue properties.”.
Tuesday 27 October 2015
The O’Fallon Casting University
To underscore its commitment to its customers and to contribute to our mutual success, O’Fallon Casting has founded “The O’Fallon Casting University”.
Castings present a cost effective solution for the manufacture of complex shapes that reduce part count and improve the affordability, manufacturability and reliability of an engineered product. However, successful casting design does require a specialized expertise.
The O’Fallon Casting University is a collection of educational resources that will help educate and train casting professionals in the “Specialized Expertise” necessary for successful casting design. Some of these OFC provided resources of the O’Fallon Casting University include:
O’Fallon Casting’s “Investment Casting Design Guide” is a continuously updated and downloadable reference that is posted on ofalloncasting.com. OFalloncasting.com is also home to O’Fallon Casting’s Technical Papers and for Blogs that share experiences and opinions pertaining to investment casting.
Concurrent Engineering is a one-on-one active review of customer casting designs by OFC Engineers to catch errors and provide design recommendations, hopefully, “before the ink is dry”. Concurrent Engineering activities also serves to mentor and improve the skill of customer casting designers.
Good casting design translates into both direct savings from lower manufacturing cost and reduced part count and also from indirect savings from higher levels of quality, more reliable deliveries and lower administrative costs.
The O’Fallon Casting University is a free service to the customers of O’Fallon Casting. Detailed information about all of these resources is available on ofalloncasting.com.
To commence your educational benefit, please contact your O’Fallon Casting Sales Engineer or email to: sales@ofalloncasting.com
Castings present a cost effective solution for the manufacture of complex shapes that reduce part count and improve the affordability, manufacturability and reliability of an engineered product. However, successful casting design does require a specialized expertise.
The O’Fallon Casting University is a collection of educational resources that will help educate and train casting professionals in the “Specialized Expertise” necessary for successful casting design. Some of these OFC provided resources of the O’Fallon Casting University include:
- O’Fallon Casting’s Investment Casting Design Guide
- IC-101 Class on the considerations for investment casting design
- IC-201 Course on the manufacture of investment castings
- Concurrent Engineering Service
- Ofalloncasting.com
- Technical Papers
- Blogs
O’Fallon Casting’s “Investment Casting Design Guide” is a continuously updated and downloadable reference that is posted on ofalloncasting.com. OFalloncasting.com is also home to O’Fallon Casting’s Technical Papers and for Blogs that share experiences and opinions pertaining to investment casting.
Concurrent Engineering is a one-on-one active review of customer casting designs by OFC Engineers to catch errors and provide design recommendations, hopefully, “before the ink is dry”. Concurrent Engineering activities also serves to mentor and improve the skill of customer casting designers.
Good casting design translates into both direct savings from lower manufacturing cost and reduced part count and also from indirect savings from higher levels of quality, more reliable deliveries and lower administrative costs.
The O’Fallon Casting University is a free service to the customers of O’Fallon Casting. Detailed information about all of these resources is available on ofalloncasting.com.
To commence your educational benefit, please contact your O’Fallon Casting Sales Engineer or email to: sales@ofalloncasting.com
Wednesday 14 October 2015
Edge & Corner Radii
Edges & Corners are external features such as you would see on any cube such as a child’s Alphabet Block. Structurally Edges & Corners have little impact on the strength of a casting. However, Edges and Corners are still an important consideration of casting design.
Investment Castings will naturally exhibit a .008” - .012” radius along an edge even when tooled “sharp”. I often say that foundries “don’t cast razor blades” (but then even razor blades are not truly “sharp” either). The freezing of the wave front and back pressure from air in the cavity prevent the liquid metal from achieving a truly “sharp” edge. Casting Designers should provide for this condition on their designs with an allowance of at least a .015” R Max along cast edges & corners.
Foundries, however, generally prefer not to have “sharp” edges and corners on cast parts. In Investment Casting a sharp edge can create a weak point in the ceramic shell mold. (If you’ve ever tried to paint a sharp corner you’ll understand that it can be very difficult to build thickness along a sharp edge.) A vulnerable “thin” area in the ceramic shell that may cause the shell to crack from the stress of the De-Wax operation or fail as the mass of the hot metal is being cast. O’Fallon Casting recommends that a radius roughly equivalent to the wall thickness be allowed on all external Edges & Corners.
OFC also recommends that dimensions for Corner & Edge radii have an R-Max tolerance applied. An R-Max tolerance provides flexibility to the pattern mold designer to strategically omit the Edge Radii along parting planes in the mold. Omitting an edge Radii allows the parting plane in the pattern mold be located at the top of features which simplifies the design of the mold and makes it less expensive to design and build. Cosmetically, in this manner, the parting lines on the casting will blend with the “Sharp” edge. (Edges along non-parting surfaces in the pattern mold will be cut with the full radii.) An R-Max allows for a Sharp Edge at parting planes that will reduce the cost of the Pattern Mold and also improve the cosmetic appearance of a casting.
If for the function of the casting it is necessary for edges and corners have a radius this can certainly be accommodated. A design includes a ± tolerance (rather than an R-Max) for the Edge Radii the parting planes then need to be placed adjacent to the root of the Edge Radius rather than at the top of features. This requirement will increase both the design and construction time of a pattern mold and so also its expense. Also a casting produced from a tool cut with an edge radius at the parting surfaces will exhibit a residual parting line adjacent the root of the edge radius and that will likely grow heavier as the pattern mold wears.
Edge and Corner radii are an important consideration for casting design. Even when tooled sharp, castings will display a slight radius that should be noted on a drawing as .015 R Max. Foundries prefer that casting designs permit an Edge Radius equivalent to the wall thickness and recommend that they be designated with an R-Max tolerance so that the radius may be omitted from parting surfaces in the pattern mold.
Investment Castings will naturally exhibit a .008” - .012” radius along an edge even when tooled “sharp”. I often say that foundries “don’t cast razor blades” (but then even razor blades are not truly “sharp” either). The freezing of the wave front and back pressure from air in the cavity prevent the liquid metal from achieving a truly “sharp” edge. Casting Designers should provide for this condition on their designs with an allowance of at least a .015” R Max along cast edges & corners.
Foundries, however, generally prefer not to have “sharp” edges and corners on cast parts. In Investment Casting a sharp edge can create a weak point in the ceramic shell mold. (If you’ve ever tried to paint a sharp corner you’ll understand that it can be very difficult to build thickness along a sharp edge.) A vulnerable “thin” area in the ceramic shell that may cause the shell to crack from the stress of the De-Wax operation or fail as the mass of the hot metal is being cast. O’Fallon Casting recommends that a radius roughly equivalent to the wall thickness be allowed on all external Edges & Corners.
OFC also recommends that dimensions for Corner & Edge radii have an R-Max tolerance applied. An R-Max tolerance provides flexibility to the pattern mold designer to strategically omit the Edge Radii along parting planes in the mold. Omitting an edge Radii allows the parting plane in the pattern mold be located at the top of features which simplifies the design of the mold and makes it less expensive to design and build. Cosmetically, in this manner, the parting lines on the casting will blend with the “Sharp” edge. (Edges along non-parting surfaces in the pattern mold will be cut with the full radii.) An R-Max allows for a Sharp Edge at parting planes that will reduce the cost of the Pattern Mold and also improve the cosmetic appearance of a casting.
If for the function of the casting it is necessary for edges and corners have a radius this can certainly be accommodated. A design includes a ± tolerance (rather than an R-Max) for the Edge Radii the parting planes then need to be placed adjacent to the root of the Edge Radius rather than at the top of features. This requirement will increase both the design and construction time of a pattern mold and so also its expense. Also a casting produced from a tool cut with an edge radius at the parting surfaces will exhibit a residual parting line adjacent the root of the edge radius and that will likely grow heavier as the pattern mold wears.
Edge and Corner radii are an important consideration for casting design. Even when tooled sharp, castings will display a slight radius that should be noted on a drawing as .015 R Max. Foundries prefer that casting designs permit an Edge Radius equivalent to the wall thickness and recommend that they be designated with an R-Max tolerance so that the radius may be omitted from parting surfaces in the pattern mold.
Thursday 8 October 2015
Why Castings need a Fillet Radii
By definition a Fillet Radii is a rounding of an interior corner and are employed on castings to increase their load bearing strength and to improve both manufacturability and quality. For those reasons a fillet radius should be a standard allowance on every casting design.
A Fillet Radius makes a structure stronger because it redirects stresses from being concentrated at a sharp interior corner and distributes them over the broader volume of the fillet. The effect of the Fillet Radius is to mitigate a potential weak point of cast structure making transitions within a structure, especially between right angled walls, stronger.
Because of this faculty to mitigate stress concentrations a Fillet Radius also improves the manufacturability of a casting. Castings often require a mechanical “Straightening” operation to restore flatness, perpendicularity and parallelism to the part and a filleted corner is less prone to cracking during this operation. Better casting manufacturability provides a foundry with control of its costs and promotes more consistent deliveries.
The foundry industry works diligently to avoid turbulence in the flow of hot metal as their products are being cast. Turbulence can cause a mixing of the metal with air to trap gas or lead to the formation of oxides that may become embedded in the casting. Fillet radii help to minimize the turbulence in the metal as it flows through the cavities of the mold thus inhibiting the formation defects from oxides and trapped gas and so contributes to the better quality of a cast product.
In the Investment Casting process a thickness of ceramic shell is formed about a pattern assembly by repeated dips of the assembly into slurry. Sharp internal corners in a part configuration can provide nucleation sites onto which bubbles of air form and adhere to the pattern while the slurry is being applied. Air bubbles on the pattern will become small voids in the ceramic shell that will subsequently fill with metal and become positives on the surface of the casting. A fillet radius improves the ability for the pattern to shed air bubbles as the slurry is applied thus reducing the propensity of casting to exhibit positive metal.
A general “Rule of Thumb” for an aluminum investment casting is to apply a fillet radius equal to 1x to 1.5x of the wall thickness with a recommended minimum of .06”R. It is also advisable to specify fillet radii with a Max tolerance.
Customers of O’Fallon Casting are provided a free Concurrent Engineering service to assist in their design and improve their use of castings. If you have questions regarding Fillet Radii or other investment casting design considerations call your O’Fallon Casting Sales Engineer for assistance.
A Fillet Radius makes a structure stronger because it redirects stresses from being concentrated at a sharp interior corner and distributes them over the broader volume of the fillet. The effect of the Fillet Radius is to mitigate a potential weak point of cast structure making transitions within a structure, especially between right angled walls, stronger.
Because of this faculty to mitigate stress concentrations a Fillet Radius also improves the manufacturability of a casting. Castings often require a mechanical “Straightening” operation to restore flatness, perpendicularity and parallelism to the part and a filleted corner is less prone to cracking during this operation. Better casting manufacturability provides a foundry with control of its costs and promotes more consistent deliveries.
The foundry industry works diligently to avoid turbulence in the flow of hot metal as their products are being cast. Turbulence can cause a mixing of the metal with air to trap gas or lead to the formation of oxides that may become embedded in the casting. Fillet radii help to minimize the turbulence in the metal as it flows through the cavities of the mold thus inhibiting the formation defects from oxides and trapped gas and so contributes to the better quality of a cast product.
In the Investment Casting process a thickness of ceramic shell is formed about a pattern assembly by repeated dips of the assembly into slurry. Sharp internal corners in a part configuration can provide nucleation sites onto which bubbles of air form and adhere to the pattern while the slurry is being applied. Air bubbles on the pattern will become small voids in the ceramic shell that will subsequently fill with metal and become positives on the surface of the casting. A fillet radius improves the ability for the pattern to shed air bubbles as the slurry is applied thus reducing the propensity of casting to exhibit positive metal.
A general “Rule of Thumb” for an aluminum investment casting is to apply a fillet radius equal to 1x to 1.5x of the wall thickness with a recommended minimum of .06”R. It is also advisable to specify fillet radii with a Max tolerance.
Customers of O’Fallon Casting are provided a free Concurrent Engineering service to assist in their design and improve their use of castings. If you have questions regarding Fillet Radii or other investment casting design considerations call your O’Fallon Casting Sales Engineer for assistance.
Saturday 3 October 2015
How an Investment Casting is Manufactured
Investment Casting is a cost effective method for the production of precise, near-net-shape and complex metal parts. Although Investment Casting is relatively ancient in origin it is today a highly sophisticated manufacturing process.
By definition Investment Casting is a foundry process by which a metal casting is produced from a ceramic mold that was formed by a disposable pattern. Much as Sand Castings are produced from sand molds and Die Castings from metal dies, the Investment Casting process name originates from the ceramic “Investment” in which parts are cast.
There are eight basic steps for the manufacture of an Investment Casting:
By definition Investment Casting is a foundry process by which a metal casting is produced from a ceramic mold that was formed by a disposable pattern. Much as Sand Castings are produced from sand molds and Die Castings from metal dies, the Investment Casting process name originates from the ceramic “Investment” in which parts are cast.
There are eight basic steps for the manufacture of an Investment Casting:
- The first step of the process is the production of a Disposable Pattern. Generally Investment Casting patterns are made of Wax and produced by an aluminum injection mold. However, Investment Casting patterns might alternatively be produced from a rubber or soft metal molds or formed by an Additive Manufacturing process such as SLA, SLS, or Voxeljet.
- Once the wax pattern has been formed it is attached to a Runner System. The runner system is also comprised of wax that is cut to size from injected or extruded stock and is “wax-welded” together. A complete and “Assembled” part & runner system is referred to as a “Sprue” or “Tree” and may be comprised of many multiple Wax Patterns.
- The Assembled wax Sprue is then ready to be “Invested” or coated with ceramic. The most prevalent method to “Invest” a wax sprue is the Ceramic Shell Process. In the Ceramic Shell Process a sprue will dipped multiple times into vats of specialized slurry and refractory sand to form a Shell. The shell is allowed dry time after each layer is applied and once a sufficient layers of ceramic have been applied to the sprue the completed shell is allowed to dry fully.
- Once the shell is dry a DeWax operation is performed, generally with a steam autoclave, to melt and eliminate the wax from the sprue.
- With the wax removed the shell is Fired in an oven to create a crystalline ceramic structure that will withstand the weight and thermal shock of the metal to be cast into it.
- Once the shell has been fired molten metal is then Cast to fill the cavities in the sprue that had been formed by the wax pattern & runner system.
- After the metal has solidified the ceramic is removed from the Sprue with high pressure water or some other form of knockout system.
- With the ceramic removed the metal parts are cut–off from their runner system with a saw or other cutting method such as a laser.
Thursday 1 October 2015
The Five Part Solution
My introduction to the subject of Part Count Reduction came about as an observation of the results of a Design Project in my sophomore year of college. I’ve come to refer to the anecdote as “The Five Part Solution” which might have been long forgotten had the saga not come with an accompanying lesson in humility.
The Design Project was a first instance of being challenged for an original engineering solution and I recall “enthusiastically” devoting several weekends to research and then to developing a concept for my proposal. With some degree of pride I completed my design, an electro-mechanical masterpiece replete with springs, hinges, micro-switches, transformers, etc. Accompanying my submission was a full set of Assembly & Detail drawings of each part and included a 40 (or perhaps 50) piece Parts List.
On entering the classroom to submit my proposal I noted that a group of students were chatting excitedly in a corner of the room. Their attention had been drawn by another student who was busily demonstrating the operation of his design proposal on a mock-up he’d constructed of wood in his garage. His design was a stunning contrast to my own elaborate proposal as it contained only five mechanical members and required no external power to operate; the Five Part Solution.
I still remember being struck by the elegant simplicity of the Five Part Solution which has garnered even greater appreciation as I’ve grown to understand the full impact of engineering decisions on the cost of a product. Had my product design competed with the Five Part Solution in the “Real World” one manufacturer (his) would hold a significant price advantage and so enjoyed much greater success in the marketplace.
The story of the Five Part Solution demonstrates why Castings and in particular Investment Castings are such an effective manufacturing method. Castings offer a unique capability to combine multiple features into a unitized structure that reduces the total part count of an assembly and improves the overall affordability of an engineered product. We encourage that Engineers take advantage of the opportunity that castings present and to write their own Five Part Solution.
The Design Project was a first instance of being challenged for an original engineering solution and I recall “enthusiastically” devoting several weekends to research and then to developing a concept for my proposal. With some degree of pride I completed my design, an electro-mechanical masterpiece replete with springs, hinges, micro-switches, transformers, etc. Accompanying my submission was a full set of Assembly & Detail drawings of each part and included a 40 (or perhaps 50) piece Parts List.
On entering the classroom to submit my proposal I noted that a group of students were chatting excitedly in a corner of the room. Their attention had been drawn by another student who was busily demonstrating the operation of his design proposal on a mock-up he’d constructed of wood in his garage. His design was a stunning contrast to my own elaborate proposal as it contained only five mechanical members and required no external power to operate; the Five Part Solution.
I still remember being struck by the elegant simplicity of the Five Part Solution which has garnered even greater appreciation as I’ve grown to understand the full impact of engineering decisions on the cost of a product. Had my product design competed with the Five Part Solution in the “Real World” one manufacturer (his) would hold a significant price advantage and so enjoyed much greater success in the marketplace.
The story of the Five Part Solution demonstrates why Castings and in particular Investment Castings are such an effective manufacturing method. Castings offer a unique capability to combine multiple features into a unitized structure that reduces the total part count of an assembly and improves the overall affordability of an engineered product. We encourage that Engineers take advantage of the opportunity that castings present and to write their own Five Part Solution.
Sunday 27 September 2015
Concurrent Engineering
Customers of O’Fallon Casting are entitled to a free Concurrent Engineering Service to assist in their design of affordable cast products. Concurrent Engineering is remarkably easy to accomplish and is time well spent. O’Fallon Casting hopes that, as a result of Concurrent Engineering, its customers will design better castings and so be more inclined to engineer other parts as foundry products.
The effectiveness of Concurrent Engineering is of course greatest when initiated very early in the design process. Experience tells us that once the component part designs become finalized it becomes difficult to affect change.
The primary benefit of Concurrent Engineering is to design a more manufacturable product that minimizes cost drivers. Concurrent Engineering also offers the foundry an opportunity to make suggestions such as combining multiple parts into the single cast piece that will enhance the total value of the product.
In addition to the direct benefit of designing a more affordable product the Concurrent Engineering process also serves to grow a customer’s internal expertise. When armed with an appreciation for the capabilities of the investment casting process customer designers will more readily identify opportunities to optimize the configuration of their engineered assemblies.
Investment Casting provides the most freedom and is the most straightforward foundry process for which to design. This flexibility is in-part because a draft angle need not be taken into consideration but also because the process is less restrictive in producing configuration such as undercuts and cored holes.
O’Fallon Casting’s Concurrent Engineering Service is an efficient and effective method for Engineers to obtain that specialized expertise that will help them design affordable and manufacturable cast products. For more information please contact O’Fallon Casting.
The effectiveness of Concurrent Engineering is of course greatest when initiated very early in the design process. Experience tells us that once the component part designs become finalized it becomes difficult to affect change.
The primary benefit of Concurrent Engineering is to design a more manufacturable product that minimizes cost drivers. Concurrent Engineering also offers the foundry an opportunity to make suggestions such as combining multiple parts into the single cast piece that will enhance the total value of the product.
In addition to the direct benefit of designing a more affordable product the Concurrent Engineering process also serves to grow a customer’s internal expertise. When armed with an appreciation for the capabilities of the investment casting process customer designers will more readily identify opportunities to optimize the configuration of their engineered assemblies.
Investment Casting provides the most freedom and is the most straightforward foundry process for which to design. This flexibility is in-part because a draft angle need not be taken into consideration but also because the process is less restrictive in producing configuration such as undercuts and cored holes.
O’Fallon Casting’s Concurrent Engineering Service is an efficient and effective method for Engineers to obtain that specialized expertise that will help them design affordable and manufacturable cast products. For more information please contact O’Fallon Casting.
Wednesday 23 September 2015
The Characteristics of an Aluminum Investment Casting
The Investment Casting process provides two primary cost benefits to its customers. First is its Near-Net-Shape capability that stems from the dimensional precision of the process and because no draft angle is required. Secondly the Investment Casting process provides an ability to combine multiple pieces into a One-Piece structure with few design constraints and without a major impact to cost.
Based upon those inherent advantages Investment Casting should be considered as a manufacturing method if:
A great example of a One-Piece casting design is the American Foundry Society / Metal Casting Design & Purchasing Magazine’s “2013 - Casting of the Year”. The multiplicity of features that are combined into this lightweight yet rigid structure imparts great value to its customer both in direct savings from reduction of assembly time and indirectly from part-count reduction.
Designing a One-Piece product can necessitate a certain level of skill on the part of product engineers. To assist our customers develop their internal casting design expertise O’Fallon Casting offers both a 3-Hour IC-101 Class and a 3-Day IC-201 Course. These two classes provide the customer / students an overview of the investment casting process, insight as to its strengths & weaknesses and an understanding for good design practices.
O’Fallon Casting also provides its customers with a free Concurrent Engineering Service. Through Concurrent Engineering OFC Engineers will appraise the castability of a customer design and make recommendations to improve its manufacturability.
Investment Casting castings present a cost effective solution for the manufacture of complex shapes that reduce part count and improve the affordability, manufacturability and reliability of an engineered product. If you have any questions, pleased to not hesitate to call your O’Fallon Casting Sales Engineer.
Based upon those inherent advantages Investment Casting should be considered as a manufacturing method if:
- There is an opportunity to eliminate assembly operations with a One-Piece casting.
- The Alloy or Configuration is difficult to machine.
- The Configuration needs to be lightweight.
- There is a need for a precision casting without a draft angle.
- There are undercuts or detail that cannot be cast by another foundry process.
- There is a need for good and uniform cosmetic appearance.
A great example of a One-Piece casting design is the American Foundry Society / Metal Casting Design & Purchasing Magazine’s “2013 - Casting of the Year”. The multiplicity of features that are combined into this lightweight yet rigid structure imparts great value to its customer both in direct savings from reduction of assembly time and indirectly from part-count reduction.
Designing a One-Piece product can necessitate a certain level of skill on the part of product engineers. To assist our customers develop their internal casting design expertise O’Fallon Casting offers both a 3-Hour IC-101 Class and a 3-Day IC-201 Course. These two classes provide the customer / students an overview of the investment casting process, insight as to its strengths & weaknesses and an understanding for good design practices.
O’Fallon Casting also provides its customers with a free Concurrent Engineering Service. Through Concurrent Engineering OFC Engineers will appraise the castability of a customer design and make recommendations to improve its manufacturability.
Investment Casting castings present a cost effective solution for the manufacture of complex shapes that reduce part count and improve the affordability, manufacturability and reliability of an engineered product. If you have any questions, pleased to not hesitate to call your O’Fallon Casting Sales Engineer.
Sunday 20 September 2015
Introducing IC100 ToughMet®
ToughMet® is a popular copper-nickel-bronze alloy that is available from Materion Corporation in the form of wrought plate, sheet, rod, wire, and tubing. ToughMet has many highly desirable material properties that have made it a successful selection for rigorous applications such as bushings that are subjected to heavy loads. ToughMet is a strong, stiff, corrosion resistant, and galling resistant bronze alloy. It possesses the additional attributes of being very low friction and resistant to wear.
For example, ToughMet bushings may last three to five times longer than equivalent steel bushings do. In addition, ToughMet exhibits stable properties over a wide range of temperatures and contains no lead, beryllium, or other hazardous materials.
Over the course of four years, metallurgical engineers from Materion and O’Fallon Casting collaborated to develop a cast ToughMet alloy that could provide these same characteristics in the form of investment cast shapes. The result was O’Fallon Casting’s IC100 ToughMet. SAE International has issued AMS 4863 specification for IC100.
Investment casting is versatile and a cost effective foundry process for the manufacturing of accurate, near-net-shape cast parts that minimize the need for secondary machining and can reduce the part count of engineered assemblies. With IC100, O’Fallon Casting can now manufacture cast configurations from ToughMet that are difficult or impossible to machine from wrought stock. Moreover, investment casting holds the promise for combining multiple components into single piece castings.
As of today, the attributes of Materion’s ToughMet bronze are now available from investment cast IC100 through O’Fallon Casting.
For additional information please refer to the ToughMet page available on the Materion website.
ToughMet® is a registered trademark of Materion Corporation.
For example, ToughMet bushings may last three to five times longer than equivalent steel bushings do. In addition, ToughMet exhibits stable properties over a wide range of temperatures and contains no lead, beryllium, or other hazardous materials.
Over the course of four years, metallurgical engineers from Materion and O’Fallon Casting collaborated to develop a cast ToughMet alloy that could provide these same characteristics in the form of investment cast shapes. The result was O’Fallon Casting’s IC100 ToughMet. SAE International has issued AMS 4863 specification for IC100.
Investment casting is versatile and a cost effective foundry process for the manufacturing of accurate, near-net-shape cast parts that minimize the need for secondary machining and can reduce the part count of engineered assemblies. With IC100, O’Fallon Casting can now manufacture cast configurations from ToughMet that are difficult or impossible to machine from wrought stock. Moreover, investment casting holds the promise for combining multiple components into single piece castings.
As of today, the attributes of Materion’s ToughMet bronze are now available from investment cast IC100 through O’Fallon Casting.
For additional information please refer to the ToughMet page available on the Materion website.
ToughMet® is a registered trademark of Materion Corporation.
Tuesday 8 September 2015
Standard Investment Casting Linear Tolerances
Relative to other foundry processes Investment Casting is a very precise method to produce a Near-Net shape cast product. This capability stems both from the repeatability of the process and that a draft angle need not be added to cast surfaces. As with all manufacturing processes there will exist some part-to-part variation that needs to be accommodated by a dimensional tolerance.
The standard design guidelines for the industry have been established by the Investment Casting Institute. This includes standards for linear tolerance as published by the ICI in the Investment Casting Handbook. Their recommendations for linear tolerances are shown in the following table:
To correctly apply the tolerances from this table it is first important to have a clear understanding of what constitutes a linear dimension. If we first understand that cubic inch is a volume of 1” x 1” x 1” and then that a square inch is an area of 1” x 1” then it follows that a linear inch a length defined as the distance between two points (1”).
Therefore, any dimension to a feature that can be measured with a ruler or a pair of calipers should have applied a linear tolerance from the table.
However, properly applying the table can be confusing for Designers when tolerancing non-linear features. Castings, for example, are frequently measured from a datum structure that is established by datum points. When measuring a casting from datum points we no longer have a linear point-to-point measurement but a non-linear point-to-plane dimension and the size and shape (flatness & perpendicularity) of the plane must now be taken into account.
Take the instance of a table top. If we were to measure the thickness of the table top with a pair of calipers we then have a linear dimension to which a linear tolerance should be applied. However, if we instead to measure the height of the table top from the floor and run an indicator across the area of table top we would expect to receive a much wider measurement variation because the table top is not perfectly flat nor square to the floor and the amount of variation would be relative to the size of the table top.
When measuring a casting from a datum structure the size of the feature and the distance from the datum both need to be taken into account in the tolerance. So in addition to the linear tolerance per the table an allowance for .005”/inch of tolerance must be provided to account for variations flatness, perpendicularity and parallelism of the casting.
As a general rule of thumb Engineers should consider the farthest feature that being measured from the 0,0,0 point of the three perpendicular datums. If the longest measurement was for example 10” the tolerance from the table for that linear segment would be ±.037” or an equivalent profile tolerance of .074” of the part from the datums.
For instances where it is necessary that a design include a tolerance of a feature that is tighter than the industry standard it is important consult with a foundry to assure that the desired capability is manufacturable. Even if the foundry feedback is negative or perhaps finds that additional tooling will be required, it is always better to engineer a manufacturable design than to deal with the cost and consequences of one that isn’t.
For further information contact O’Fallon Casting.
To purchase a copy of the Investment Casting Handbook contact the Investment Casting Institute:
The standard design guidelines for the industry have been established by the Investment Casting Institute. This includes standards for linear tolerance as published by the ICI in the Investment Casting Handbook. Their recommendations for linear tolerances are shown in the following table:
|
LINEAR TOLERANCE
|
|||
|
|
DIMENSIONS
|
NORMAL
|
PREMIIUM
|
|
|
up to 1"
|
± .010"
|
±.005
|
|
|
up to 2"
|
± .013"
|
±.010
|
|
|
up to 3"
|
± .016"
|
±.013
|
|
|
up to 4"
|
± .019"
|
±.015
|
|
|
up to 5"
|
± .022"
|
±.017
|
|
|
up to 6"
|
± .025"
|
±.020
|
|
|
up to 7"
|
± .028"
|
±.022
|
|
|
up to 8"
|
± .031"
|
±.024
|
|
|
up to 9"
|
± .034"
|
±.026
|
|
|
up to 10"
|
± .037"
|
±.028
|
|
> 10" allow ±.005" per inch
|
|||
To correctly apply the tolerances from this table it is first important to have a clear understanding of what constitutes a linear dimension. If we first understand that cubic inch is a volume of 1” x 1” x 1” and then that a square inch is an area of 1” x 1” then it follows that a linear inch a length defined as the distance between two points (1”).
Therefore, any dimension to a feature that can be measured with a ruler or a pair of calipers should have applied a linear tolerance from the table.
However, properly applying the table can be confusing for Designers when tolerancing non-linear features. Castings, for example, are frequently measured from a datum structure that is established by datum points. When measuring a casting from datum points we no longer have a linear point-to-point measurement but a non-linear point-to-plane dimension and the size and shape (flatness & perpendicularity) of the plane must now be taken into account.
Take the instance of a table top. If we were to measure the thickness of the table top with a pair of calipers we then have a linear dimension to which a linear tolerance should be applied. However, if we instead to measure the height of the table top from the floor and run an indicator across the area of table top we would expect to receive a much wider measurement variation because the table top is not perfectly flat nor square to the floor and the amount of variation would be relative to the size of the table top.
When measuring a casting from a datum structure the size of the feature and the distance from the datum both need to be taken into account in the tolerance. So in addition to the linear tolerance per the table an allowance for .005”/inch of tolerance must be provided to account for variations flatness, perpendicularity and parallelism of the casting.
As a general rule of thumb Engineers should consider the farthest feature that being measured from the 0,0,0 point of the three perpendicular datums. If the longest measurement was for example 10” the tolerance from the table for that linear segment would be ±.037” or an equivalent profile tolerance of .074” of the part from the datums.
For instances where it is necessary that a design include a tolerance of a feature that is tighter than the industry standard it is important consult with a foundry to assure that the desired capability is manufacturable. Even if the foundry feedback is negative or perhaps finds that additional tooling will be required, it is always better to engineer a manufacturable design than to deal with the cost and consequences of one that isn’t.
For further information contact O’Fallon Casting.
To purchase a copy of the Investment Casting Handbook contact the Investment Casting Institute:
Investment Casting Institute
136 Summit Avenue
Montvale, NJ 07645-1720
136 Summit Avenue
Montvale, NJ 07645-1720
Wednesday 5 August 2015
Casting Conversions
I was looking at an Investment Casting Institute publication entitled Case Studies and Applications which elaborates on the substantial savings realized when fabricated assemblies are converted to One-Piece castings. In that Investment Casting is such an effective manufacturing method for realizing this type of savings one wonders why companies don’t place greater emphasis on achieving them. Perhaps their not knowing a good place to look to find a casting conversion candidate is the answer.
The Investment Casting process provides two main cost benefits to its customers. First is its Near-Net-Shape capability that stems from the dimensional precision of the process and that no draft angle is required. Secondly the Investment Casting process provides an ability to combine multiple pieces into a One-Piece structure with few design constraints and without a major impact to cost. With easily machined alloys, such as aluminum, the One-Piece advantage takes on a greater significance than does Near-Net-Shape.
Considering this, then the most ready opportunities to realize a significant savings from a conversion to an aluminum investment casting is to find situations where components are being assembled together either with a fastener, braze or weld. Weldments and Dip Brazed assemblies are obvious candidates to becoming Investment Castings.
The direct savings from the elimination of an assembly operation can be substantial but the indirect savings from a reduction of Part Count can be even larger. One-Piece cast structures also lower the risk of assembly point failures with the additional benefit of the Near-Net-Shape precision of the investment casting process and potential for component weight reduction.
Investment Castings present a cost effective method for the manufacture of complex and near-net shapes. Replacing fabricated structures with One-Piece castings is a good starting point to achieve substantial savings.
The Investment Casting process provides two main cost benefits to its customers. First is its Near-Net-Shape capability that stems from the dimensional precision of the process and that no draft angle is required. Secondly the Investment Casting process provides an ability to combine multiple pieces into a One-Piece structure with few design constraints and without a major impact to cost. With easily machined alloys, such as aluminum, the One-Piece advantage takes on a greater significance than does Near-Net-Shape.
Considering this, then the most ready opportunities to realize a significant savings from a conversion to an aluminum investment casting is to find situations where components are being assembled together either with a fastener, braze or weld. Weldments and Dip Brazed assemblies are obvious candidates to becoming Investment Castings.
The direct savings from the elimination of an assembly operation can be substantial but the indirect savings from a reduction of Part Count can be even larger. One-Piece cast structures also lower the risk of assembly point failures with the additional benefit of the Near-Net-Shape precision of the investment casting process and potential for component weight reduction.
Investment Castings present a cost effective method for the manufacture of complex and near-net shapes. Replacing fabricated structures with One-Piece castings is a good starting point to achieve substantial savings.
Monday 27 July 2015
O'Fallon Casting Publishes Design Guide
O’Fallon Casting has published its first “Investment Casting Design Guide” which is now available for free download on the OFC Website (www.ofalloncasting.com/design guide/).
Investment Casting is a cost effect method for the manufacture of complex, near-net-shape, products but some specialized expertise is required for their design. The Design Guide is a natural offshoot of O’Fallon Casting’s “IC-101” class on the basics for the design of Investment Casting and addresses that need for information of best design practices.
Engineers prefer Investment Casting as it provides them with more freedom and is the most straightforward foundry process for which to design. The Guide provides recommendations for allowances and other considerations that are generally necessary for the successful design of an investment cast product. Basic information on topics such as linear tolerance, fillet radii allowance, and castable hole sizes, etc. are included in the guide.
The Design Guide does not supplant the need for Concurrent Engineering with a foundry. Castings are cost effective in combining features into One-Piece casting designs that reduce the Part Count of an assembly and consultation with a foundry remains the best way to achieve the most affordable configuration of a cast product.
OFC hopes that the information in the O’Fallon Casting “Investment Casting Design Guide” will assist Engineers take better advantage of the strengths of the investment casting process to design more affordable products for their customers.
Investment Casting is a cost effect method for the manufacture of complex, near-net-shape, products but some specialized expertise is required for their design. The Design Guide is a natural offshoot of O’Fallon Casting’s “IC-101” class on the basics for the design of Investment Casting and addresses that need for information of best design practices.
Engineers prefer Investment Casting as it provides them with more freedom and is the most straightforward foundry process for which to design. The Guide provides recommendations for allowances and other considerations that are generally necessary for the successful design of an investment cast product. Basic information on topics such as linear tolerance, fillet radii allowance, and castable hole sizes, etc. are included in the guide.
The Design Guide does not supplant the need for Concurrent Engineering with a foundry. Castings are cost effective in combining features into One-Piece casting designs that reduce the Part Count of an assembly and consultation with a foundry remains the best way to achieve the most affordable configuration of a cast product.
OFC hopes that the information in the O’Fallon Casting “Investment Casting Design Guide” will assist Engineers take better advantage of the strengths of the investment casting process to design more affordable products for their customers.
Tuesday 23 June 2015
The Design Engineer's Role in Casting Procurment
It is a well-known axiom that 70% - 90% of the cost of a product is the result of design decisions. Although we might debate as to the preciseness of this estimation the fact remains that design is key element to the manufacturability, availability, reliability and overall affordability of any manufactured product.
Castings are inherently a cost effective method to manufacture shapes that reduces the part-count of an assembly and therefore improves the affordability of that product. However, casting design does require some specialized expertise and appreciation of the strength and weaknesses of the foundry process.
Any poorly designed product as a consequence will incur unnecessary or unexpected costs. For example, the cost of poor product manufacturability might be reflected in late deliveries, short shipments or frequent rejections. These types of design related issues will drive a rise of both Inventory and Administrative costs.
Less obvious is the cost of a missed opportunity where the product might have been manufactured via a superior method. Poor design choices can threaten both the reputation and profitability of an enterprise.
Good casting design accomplishes two things. First the combining multiple parts into a one-piece cast structure will reduce the amount of assembly required to manufacture a product. Such Part-Count Reduction favorably impacts not only the direct manufacturing cost but also reduces inventory and administrative costs. Secondly, because of the Near-Net-Shape capability, castings reduce the cost for secondary machining. Investment Casting is an effective foundry process by which to take advantage of both capabilities.
The Designing of Investment Castings is a relatively straightforward process as there are few constraints on configuration and it requires no consideration of a draft angle. Therefore, anytime two separate members need be assembled together presents an opportunity to combine them into a 1-piece cast structure. Obvious candidates for conversion to casting are dip-brazed or welded assemblies.
Admittedly there are a few casting design “Rules of Thumb” that do need to be taken into consideration and knowledge of those aspects will help to avoid any unintended “Designed–In” costs. O’Fallon Casting readily assists its customers with several services to help enhance the value of their casting designs. First O’Fallon Casting provides its customers a Concurrent Engineering Service to critique their casting designs and offer recommendations for improvement. Secondly, OFC offers to conduct a 3-Hour, IC-101, class on the basics of Investment Casting design at Customer facilities. Thirdly, O’Fallon Casting also offers a 3-Day, IC-201, class held at O’Fallon Casting for customers desiring an in-depth exposure to Investment Casting.
Castings provide an opportunity to enhance the affordability of customer designed products. O’Fallon Casting wants to assist its customers in making the most effective use of castings in their products.
For more information please call your OFC Sales Engineer.
Castings are inherently a cost effective method to manufacture shapes that reduces the part-count of an assembly and therefore improves the affordability of that product. However, casting design does require some specialized expertise and appreciation of the strength and weaknesses of the foundry process.
Any poorly designed product as a consequence will incur unnecessary or unexpected costs. For example, the cost of poor product manufacturability might be reflected in late deliveries, short shipments or frequent rejections. These types of design related issues will drive a rise of both Inventory and Administrative costs.
Less obvious is the cost of a missed opportunity where the product might have been manufactured via a superior method. Poor design choices can threaten both the reputation and profitability of an enterprise.
Good casting design accomplishes two things. First the combining multiple parts into a one-piece cast structure will reduce the amount of assembly required to manufacture a product. Such Part-Count Reduction favorably impacts not only the direct manufacturing cost but also reduces inventory and administrative costs. Secondly, because of the Near-Net-Shape capability, castings reduce the cost for secondary machining. Investment Casting is an effective foundry process by which to take advantage of both capabilities.
The Designing of Investment Castings is a relatively straightforward process as there are few constraints on configuration and it requires no consideration of a draft angle. Therefore, anytime two separate members need be assembled together presents an opportunity to combine them into a 1-piece cast structure. Obvious candidates for conversion to casting are dip-brazed or welded assemblies.
Admittedly there are a few casting design “Rules of Thumb” that do need to be taken into consideration and knowledge of those aspects will help to avoid any unintended “Designed–In” costs. O’Fallon Casting readily assists its customers with several services to help enhance the value of their casting designs. First O’Fallon Casting provides its customers a Concurrent Engineering Service to critique their casting designs and offer recommendations for improvement. Secondly, OFC offers to conduct a 3-Hour, IC-101, class on the basics of Investment Casting design at Customer facilities. Thirdly, O’Fallon Casting also offers a 3-Day, IC-201, class held at O’Fallon Casting for customers desiring an in-depth exposure to Investment Casting.
Castings provide an opportunity to enhance the affordability of customer designed products. O’Fallon Casting wants to assist its customers in making the most effective use of castings in their products.
For more information please call your OFC Sales Engineer.
Monday 20 April 2015
AFS Metalcasting Supply Chain & Design Summits
O’Fallon Casting had the pleasure of addressing both the American Foundry Society’s Metalcasting Supply Chain Summit and Metalcasting Design Summit held in Chicago on February 3rd and 4th. The AFS held these two Summits as a vehicle to update users of cast metal products as to the State of the Industry and to learn of innovation within the industry. The two summits also provided forums for Industry Experts to interact with the Supply Chain and Engineering Professionals in roundtable discussions of pertinent issues such as Lead Times, Casting Conversions, and Specifications.
At the Metalcasting Supply Chain Summit O’Fallon Casting presented a paper entitled: “Cost Factors of Aluminum Investment Castings”. This presentation provided an overview of the Investment Casting process, summed the major issues as regard to cost and suggested ways that users might optimize the value in their cast metal products.
At the Metalcasting Design Summit O’Fallon Casting presented a paper entitled: “The Role of the Design Engineer in the Supply Chain”. The paper argued that 70% – 90% of Product Cost is the result of Design Decisions and demonstrated how effective casting design can reduce the Part Count and thus the cost of secondary machining and assembly operations in their engineered products. This point was reinforced with an analysis of the exquisite casting design of O’Fallon Casting’s AFS/MCDP “2013-Casting of the Year”.
At the Metalcasting Supply Chain Summit O’Fallon Casting presented a paper entitled: “Cost Factors of Aluminum Investment Castings”. This presentation provided an overview of the Investment Casting process, summed the major issues as regard to cost and suggested ways that users might optimize the value in their cast metal products.
At the Metalcasting Design Summit O’Fallon Casting presented a paper entitled: “The Role of the Design Engineer in the Supply Chain”. The paper argued that 70% – 90% of Product Cost is the result of Design Decisions and demonstrated how effective casting design can reduce the Part Count and thus the cost of secondary machining and assembly operations in their engineered products. This point was reinforced with an analysis of the exquisite casting design of O’Fallon Casting’s AFS/MCDP “2013-Casting of the Year”.
Friday 9 January 2015
Investment Casting (Al/SiC) Metal Matrix Composites
The particulate Silicon Carbide reinforcement in Aluminum Alloy Metal Matrix Composite enhances this lightweight material with improved mechanical property attributes for stiffness, vibration dampening, wear resistance, high thermal conductivity, and low coefficient of thermal expansion. With its unique set of properties MMC alloys have been employed in diverse applications such as moving structures in high speed equipment for manufacturing, brake rotors for vehicles, heat sinks for electronics and as housings & mirrors for optics.
In the 1980’s and 1990’s cast shapes from MMC ingot was envisioned to be a major enabling technology for manufacture of MMC metal components. This prompted the development of foundry processes and specialized techniques to overcome the natural tendency of the SiCp particles to clump or to precipitate from the aluminum matrix. The inherent abrasiveness of the Silicon Carbide particulates in the alloy, perhaps unfairly, also gave MMC a reputation of being difficult and expensive to machine. For a myriad reasons a broad market for cast and other process shapes has not developed and so despite its many attributes MMC remains an underutilized material option.
As it is with other difficult to machine materials, the near-net-shape capability Investment Casting is an effective counterbalance to help mitigate the cost for machining aluminum MMC. With effective casting designs this capability, combined with the refinements in the alloy and of the secondary machining, makes investment cast aluminum alloy / silicon carbide particulates a viable and affordable option for engineers to incorporate lightweight MMC shapes into their products.
In the 1980’s and 1990’s cast shapes from MMC ingot was envisioned to be a major enabling technology for manufacture of MMC metal components. This prompted the development of foundry processes and specialized techniques to overcome the natural tendency of the SiCp particles to clump or to precipitate from the aluminum matrix. The inherent abrasiveness of the Silicon Carbide particulates in the alloy, perhaps unfairly, also gave MMC a reputation of being difficult and expensive to machine. For a myriad reasons a broad market for cast and other process shapes has not developed and so despite its many attributes MMC remains an underutilized material option.
As it is with other difficult to machine materials, the near-net-shape capability Investment Casting is an effective counterbalance to help mitigate the cost for machining aluminum MMC. With effective casting designs this capability, combined with the refinements in the alloy and of the secondary machining, makes investment cast aluminum alloy / silicon carbide particulates a viable and affordable option for engineers to incorporate lightweight MMC shapes into their products.
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