Using a polymer formulation instead of wax,3D-print is offering accuracy, flexibility, and functionality to match certain foundries’ particular techniques.
In the end, it’s the shape that matters, which may be why so many different methods of metalcasting proliferate. Over thousands of years, craftsmen, laborers, and now engineers have filled molds with metal, and the variations in their techniques are the origins for many debates, endless research, and boundless innovation. In the past decade, much of the innovation in metalcasting has been prompted by the industrialization of additive manufacturing.
Of course, additive manufacturing is a wholly separate industry, and like metalcasting it consists of numerous methods and techniques. Even so, there are a number of points — e.g., printing sand molds and cores; forming or repairing molds or tools — where metalcasting and AM technologies coincide. One point of recent convergence involves investment casting patterns, and the materials and processes additive manufacturing can offer for those.
Recall that investment casting is a high-cost, high-value approach to metalcasting. The parts are formed to achieve exquisite precision in form — thin walls, internal shapes and voids; and/or function — turbine engine parts, valves, and surgical implants; and often in critical or exotic alloys.
Time and effort add to the cost of investment casting. The part’s final shape is formed in full detail, typically in wax. This shape, or multiple versions of it, are attached to a “tree”, and then dipped in ceramic slurry that coats and hardens around the wax form. This process is repeated until a hard ceramic shell forms.
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 mold is broken and the casting is released.
This is simplified, but the plain fact is that investment casting takes time to carry out properly, and time is money. Additive manufacturing (or, 3D-printing) can be done in many ways, and one of the most common is “stereolithography” (SL or SLA.). In this process, CAD files are converted to .STL format to guide a “printer” (the SL system) to build a 3D structure in successive layers, each one bonded to the preceding one. 3D Systems is one of the primary suppliers of SL technology, with machines capable of producing layers as narrow as 0.002-in., for finished parts with superior dimensional tolerances, smooth surfaces, and fine feature details.
So, it’s becoming clearer why, and how, 3D-printing is making investment casting its target market. —Tooling costs associated with wax patterns are eliminated when investment casting patterns are made with stereolithography.The bigger and more complex the pattern, the better the value proposition for choosing SL versus wax. Complex parts generally take only one or two weeks to deliver. This allows for foundries to help their customer get to market much faster and at a lower cost.