Blind holes and pockets are common features of investment casting designs. They serve to lighten the part, provide designed clearances and are examples of the type of detail that can often be provided by the investment casting process at negligible cost to a customer.
For any feature to be castable, it is necessary for an IC foundry to build a minimum number layers of ceramic shell in or about it. The ratio between the diameter of a hole and its depth determines if the ceramic shell will fully form. By definition blind holes & pockets are open from only one end and are more difficult to build layers of ceramic than are through-holes that are open from two ends. As blind holes are more difficult it follows that the castable ratio between the diameter and depth is different than it is for through holes (see the OFC Blog on Through Holes for more information).
The greater the diameter of the blind hole the greater the depth that it can be cast. For example a Ø.12” diameter blind hole can be cast .12” in depth (1x) whereas a Ø.50” diameter blind hole can be cast .75” in depth (x1½). O’Fallon Casting publishes an Investment Casting Design Guide that is available for free download on its website. The Design Guide contains a table that delineates the castable sizes of blind holes.
All blind holes & pockets must have a fillet radius around the base of the feature. A fillet is critical as a sharp corner can potentially cause a failure in the casting process to produce the feature (see the OFC Blog on Fillet radii for more information). A minimum fillet radius of .06”R is recommended or a full spherical radius with Ø.12” or smaller diameter blind holes.
Investment casting wax patterns are produced with injection molds and blind holes and pockets are “positive” features in a mold. As the injected pattern wax cools and contracts the pattern will tend to adhere to those positives. A small amount of draft angle on pocket walls can sometimes help to facilitate the removal of the wax pattern from the mold. Although a draft angle is not generally required for investment casting designs an allowance to tool blind pockets with up to a 1° of draft may benefit the manufacturability of the part.
Working within the recommendations in the Design Guide will help to prevent cast features from becoming a cost drivers. Should it be necessary to design a feature outside those recommendations we suggest that you consult a foundry to determine if there is any impact on part manufacturability and of any cost implications. It is very likely that a foundry can suggest changes that will improve a part’s castability without impacting its cost.
If you have any questions regarding the casting of Blind Holes & Pockets, contact your O’Fallon Casting Sales Engineer.
Showing posts with label Investment Casting Design Guide. Show all posts
Showing posts with label Investment Casting Design Guide. Show all posts
Tuesday, 3 May 2016
Monday, 14 December 2015
Investment Casting “Through-holes”
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.
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.
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
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.
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