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:

• 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.

With easily machined alloys, such as aluminum, the One-Piece advantage is of greater significance than is Near-Net-Shape.

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.

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.

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:

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

www.investmentcasting.org

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.

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.