Investment Casting with a 3D Printer

Fused Deposition Modelling (FDM) provides an alternative method for producing investment casting patterns that can provide dramatic time and cost savings.

The Investment Casting with a 3D Printer is great for:

Investment casting or lost wax casting is a process in which a pattern, also known as a master or master pattern, traditionally made of wax, is covered with a ceramic slurry. The wax pattern is normally produced with injection molding. The wax is melted out of the ceramic shell, which is pre-heated before molten metal is poured into it. After the metal cools, the ceramic is vibrated and blasted from the metal casting. Investment casting generally provides higher accuracy (+/- 0.005 inch (0.127 mm) tolerance is normal) and surface finish (typically 125 micron RMS (3.125 micron Ra)) than other casting processes. It is generally used in applications that have relatively low production quantities and changing product designs. 

3D Printing Invetsment Cast

Fused Deposition Modelling (FDM) provides an alternative method for producing investment casting patterns that can provide dramatic time and cost savings. FDM technology is an additive manufacturing process that builds plastic parts layer by layer, using data from CAD files. FDM makes it possible for the foundry to produce a pattern that can also serve as a prototype for form and fit evaluation. In one day, the foundry can provide the customer with a prototype that provides a perfect match to the casting that would be produced if it becomes the pattern. The strength of the materials used in the FDM process makes it possible to put the FDM component into an assembly and perform testing. If any problems are discovered, the foundry can usually make the changes requested by the customer and build a new pattern in about 24 hours.

As soon as the customer approves the prototype, the foundry can move into production by using the FDM parts as patterns for investment casting. Since FDM is an additive process, the pattern can be as complex as needed without any impact on cost. (With injection molding increasing pattern complexity often requires a more complex and more expensive tool).

Other advantages of FDM patterns are that they have greater strength, toughness and accuracy than wax or other additive manufacturing technologies. This durability is important because it prevents damage that often occurs in the transportation and handling of patterns made of wax or other materials.

Process Overview

FDM patterns are direct replacements for traditional patterns that are injection molded with foundry wax. One significant difference is that FDM material does not melt like wax. It burns, which leaves a small amount of ash, typically 0.021 percent, in the shell cavity. The ash is later removed in a shell washing operation. Venting should be added to the ceramic shells to speed the burnout of the FDM pattern.

Investment casting patterns need to be produced to close tolerances and with an excellent surface finish because any defects are reproduced in the finished part. The Stratasys Finishing Touch Smoothing Station uses a semi-automated process to improve the surface finish of FDM parts to near injection molded quality without the labor or cost associated with traditional finishing. Advancements in finishing technology have improved FDM parts to the point that hand finishing is no longer needed, making FDM a much stronger competitor in the investment casting market.

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