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Reviving a Staple: How Additive Manufacturing Changes the Investment Casting Process

- January 08, 2018
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Reviving a Staple: How Additive Manufacturing Changes the Investment Casting Process

Investment casting is a long standing legacy in manufacturing. Its simplicity and competency in creating metal pieces from jet engine components to Oscar trophies for the Academy Awards have made it a staple in the manufacturing industry. The customary process starts with a piece sculpted by hand or machined. Now, additive manufacturing is shaking up the process of investment casting, bringing a new streamlined approach to foundries to create intricate metal parts.

The Scoop on the Scope of DMLS Metals

Traditionally, investment casting starts with the master pattern – a sculpted, machined or molded piece of wood or wax that’s shaped and designed like the final product. Depending on the part, the process could take weeks or even months to complete. Once the master pattern is sent to a foundry, it’s attached to a gate and dipped in ceramic slurry and refractory grain silica. When the slurry and grain silica hardens, the wax or wood is burned out of the shell and molten metal is poured into the mold to fill the negative indentation left behind. After the metal cools, the ceramic is blasted away to reveal the final part.

Stratasys Direct Manufacturing offers an advanced solution for investment casting right from the beginning – highly accurate master patterns built in a matter of hours or days with Stereolithography (SL) technology.

The Effective Build

The goal for investment casting patterns is to use as little material as possible while maintaining shape, accuracy and handling at the foundry. SL offers excellent internal structures, thin walls, surface finish and ideal resolution.

SL builds components with a UV laser to cure and solidify thin layers of resin. Stratasys Direct Manufacturing has developed a particular build style that is perfect for investment castings. Our patterns are built with a honeycomb, hollow structure and thin walls, creating a durable pattern with complete internal draining and ideal final surface sealing.

The resulting investment casting pattern is up to 25% lighter than conventional SL parts, which translates to higher yield in the casting process and makes the piece easier to ship and more durable in transit than a wax pattern that might warp.

After the SL pieces are built, complete drainage of uncured liquid material is key to complete pattern burnout and reducing residual ash. They are expertly sealed and leak-checked to ensure not even the smallest crack in the pattern’s surface exists that could cause substandard casting. The pattern is then selectively smoothed and assembled, if necessary, before shipping.

The Perfect Material

Another important factor in an effective SL master pattern is the right material. Stratasys Direct Manufacturing builds with two photopolymers developed specifically for investment casting patterns that meet our high yield rate standards. Patterns built with these materials are much lighter and leave a reduced amount of burn-out ash.

SC 1000P (an updated SC 1000) is a photopolymer material that provides great accuracy with high stability. The material has low deformation do to shrink and high strength with the added benefits of low moisture absorbtion and MRI image clarity. Dimensionally stable, SL master patterns from SC 1000P are durable during handling and have a high burnout with significantly less ash.Cast

Additionally, we now offer Somos® Element, an antimony-free photopolymer developed specifically for foundry applications. The material uses a proprietary photo-initiator system that lacks antimony. Previously, foundries would have to account for antimony in their process depending on the final metal. This material removes that concern.

Reviving a Staple

Investment casting is a tried-and-true manufacturing method sure to produce metal parts for years to come. By providing an upgrade to the process with unique SL builds and tailored materials, Stratasys Direct Manufacturing can streamline your next production in a major way.

After 30 years of experience with Stereolithography technology, we have refined this process and accomplished one of the highest yield rates in the industry.