The investment casting process, specifically the “lost wax” process, is a means of producing precision quality castings. It is an old process which date back more than three thousand years. The process as it is known today came about during World War II when the need for a practical production tool arose to economically produce various parts with complex shapes or configurations which were difficult or impossible to machine. These parts also require close tolerances, a good finish, and difficult materials. Investment casting provided the solution to these problems while paying a dividend of reduced costs in many instances. Since that time investment casting has grown to a significant part of the metal working industry with more and more applications in industrial and commercial usage being realized every day. Investment casting’s primary advantage to its users are reduced costs, increase precision and improved products.


WHEN TO CONSIDER INVESTMENT CASTING
The answer to when do you consider investment casting is sometimes easy – when you can’t make the part any other way. More specifically, the investment casting process may well be the answer to your production problems or contemplated design, if your component fits into one or more of the following categories:
  • Your component has a complicated design or contour not easily machined or fabricated

  • Section thickness as low as 0.025 inch are specified, or where sudden changes in cross-section are desired

  • Two or more fabricated components can be reduced to a single, integral casting

  • Tolerance control of ±.005 inch per inch is satisfactory on most dimensions or where closer tolerances can be obtained without excessive secondary operations

  • Uniform physical properties in all grain directions are desirable

  • Alloy specified or desired is difficult or impossible to machine or fabricate

  • Resistance to corrosion, abrasion, heat and/or other unusual physical properties is needed

  • Surface finish as fine as 60-90 micro inches are desired. Overall design is reasonably small – preferably two pound or less and is under 5-6 inches in maximum dimension

  • Sales appeal is enhanced by improved functioning of appearance
Investment casting can provide answers to many production problems, however, the process is not a panacea to all problems that may arise in the production of various components. In so many cases investment casting will not be economically feasible if your component can be made on a screw machine, by die casting, or as a simple stamping, sand casting, or forging without secondary machining. In some specific cases improved product performance has resulted in the use of investment casting over these other methods.

Any doubts that may arise about specific designs you have under consideration, Schuber & Sons, Inc. will be more than happy to supply realistic, honest information to help you determine the best method of producing the part. We evaluate hundreds of new designs, and normally make our recommendations within a few days.


SOME BASIC DESIGN RULES
The best results for the lowest cost are attained in investment casting as in any production mode, when you design for the process. Curved and blended contours make for stronger designs than straight lines and abrupt angles, and usually cost less. Nevertheless, if part function calls for the latter type of design – it can be investment cast.

Designing for the process is also desirable where surfaces aren’t critical. When they are, leave ample stock so that you can get below the as-cast surface with your finishing operation. Allow 0.010 inch for a grinding finish. For a small part to be machine finished, allow 0.032 inch if warpage or out-of-roundness is not involved.

Picking the best metal or alloy for the job should be a primary consideration. The amount of money you save by using a lower grade metal amounts at most to a few pennies per casting. Skimping here is throwing away investment casting’s advantage of freedom in alloy selection.


TOLERANCES
Always remember that you get the best results for the lowest cost if you design for the process. Try to avoid specifying needlessly close tolerances in non-critical areas. The rule-of-thumb investment casting tolerance of ±0.005 inch per inch produces a low-cost casting, but a tolerance of ±0.010 inch per inch is even better. If you want an extremely small casting, we can often hold even finer tolerances than ±0.003 inch per inch.


A WORD TO PURCHASERS
Customers play a very important part in achieving the closest possible customer-vendor relations. In order for Schuber & Sons, Inc. to supply castings that are metallurgically sound, dimensionally accurate, and at the best possible price, we need to know the following:
  • How close tolerances have to be for the function intended

  • Closer tolerances than are required increase the price unnecessarily

  • Complete details on material and processing specifications. All drawings and/or requests for quotation that call for “in-house” specifications and standards should be accompanied by a copy of those specifications. This will prevent delay and possible future misunderstanding

  • All requirements that will be performed by Schuber & Sons, Inc. such as heat treating, penetrant or magnetic inspection, x-ray, test specimens, chemical analysis, etc., should be clearly defined. We can then determine the best production methods, set up proper controls and estimate the price correctly

  • Usage figures are very helpful in deciding the type of tooling that should be used. The datum and/or tooling points, as well as the checking fixtures to be used. By using the same methods of checking as the customer does, Schuber & Sons, Inc. can guarantee the castings will be dimensionally correct upon receipt
Schuber & Sons, Inc. guarantees that all of its products will meet with the customer’s specifications and satisfaction or they will be corrected or replaced at no additional cost to the customer.