Metal casting at foundries is one of many tried and true manufacturing processes that have been impacted by 3D printing. Stratasys Direct Manufacturing has for more than 20 years worked to introduce the benefits of 3D printing to numerous foundries. This experience has led the company to develop proprietary build styles and processes for superior 3D printed investment casting patterns and other important production applications such as custom tools and manufacturing aids.
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.
Traditionally, investment casting starts with the master pattern – a sculpted, machined or moulded 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. Next, the structure is heated to melt the wax cores, leaving a void that can receive molten metal. Once the metal is solidified, the ceramic mould is broken and the casting is released.
3D printing investment casting patterns
3D printing offers an effective tool-less solution for investment casting patterns with Stereolithography (SL). As an alternative to wax and wood, SL builds patterns with a UV laser that cures and solidifies thin layers of resin. Stratasys Direct builds SL investment casting patterns in a nearly hollow structure with a sparse internal lattice structure and thin walls. This proprietary build style translates to proportionately less ash and minimised thermal expansion forces during flash firing.
Using a polymer formulation instead of wax, Stratasys Direct Manufacturing is offering accuracy, flexibility, and functionality to match certain foundries’ particular techniques
Having partnered last year with Somos, a specialist provider of SL materials Stratasys Direct Manufacturing has beta-tested a second-generation antimony-free formulation, Somos Element, “to validate and ensure it would deliver acceptable patterns as far as accuracy, robustness and shipping.”
Stratasys Direct utilises two Stereolithography materials for investment casting patterns. SC 1000P is a custom photopolymer formulation developed for low cost investment casting patterns. SC 1000P has low water absorption, and patterns built with this material are less prone to dimensional distortion. Somos® Element is a newer antimony-free formulation for investment casting patterns. This material is specifically used when a project calls for casting with reactive metal alloys where antimony may contaminate the cast metallurgical properties.
Stereolithography offers a new design freedom, unbound to tooling. Designs can be easily altered and gating systems can be proven out prior to tooling. SL delivers excellent pattern accuracy and repeatability, at less expense than conventional methods. These benefits translate to higher yields in the casting process and make the piece easier to ship and more durable in-transit than a wax pattern.
The compatibility of metalcasting and additive manufacturing remains a matter of finding common applications. With diecasting and permanent mould casting there isn’t much impact yet from additive manufacturing. Sand casting is a slow-developing market for AM, because the costs of the technology do not match well with the cost structures of sand casting foundries.
Foam patterns can be produced with SL systems, but Stratasys Direct said the group has not identified the “value proposition” of supplying lost foam casting foundries.
And then there is the possibility of producing printed metal parts. According to Stratasys Direct, that AM technology is an opportunity, and a threat to investment casting operations.
“Direct metal is a good option for much smaller, complex parts and systems than investment casting may allow. Investment casting foundries should be aware of direct metals when speaking to customers, because it’s great for verifying design and helping their customers get to market faster.”
This is a guide of the shifting landscape in metalcasting and additive manufacturing, and in the evolving universe where the future high technology and precision parts is taking shape.
