Rapid process casts stainless-steel parts

Nov. 3, 2005
A newly developed process casts stainless-steel parts without the costs associated with investment casting and machining.

Mark Two Engineering designed and cast all at one time this stainless-steel bell, which has text on the inside and outside and a working clapper. The bell has an electropolish satin finish.

The developer says multiple-part assemblies can be cast in one step, details usually left for secondary operations can be included, and turnaround cuts weeks off traditional manufacturing methods.

The 4th Dimension Technology process from Miami-based Mark Two Engineering Inc. (marktwo.com), involves producing a composite master pattern from 3D CAD data. The pattern is made in a way similar to stereolithography but with smoother surfaces. Patterns require no further rework, such as sanding. The pattern is then coated with a proprietary ceramic and baked in an industrial oven to harden it and burn out the pattern. This leaves a cavity for casting stainless steel. Tolerances are held to ±0.003 on most dimensions. Tighter ones are possible. Small features such as holes and text typically require no secondary operations.

The firm produces components in quantities from one to about 1,000 in alloys including 304L, 316L, and 17-4 PH stainless steel, as well as F-75, chrome-cobalt combinations and nickel superalloys. Finishes such as electropolish or passivation and surface textures are applied if necessary.

"The technology is well suited to complex components," says Dennis L. Steffen, designer, Plantation Key Design Inc., Tavernier, Fla. "One example is a retractor used in surgical procedures. The retractors have two jaws attached to a forceps that hold incisions open. Making a mold for investment casting could cost $40,000. And because designers must account for how the two halves of the mold separate, they must incorporate draft angles in parts to ensure there are no undercuts." In contrast, ceramic molds from the new technology are sacrificial, so mold costs are minimal. Designers can also add radii and other features to give components added strength or a refined finish. These details were typically avoided because of cost.

If engineers designed the retractors for machining, lead time would be four to six weeks, or more, and part cost would be high. In contrast, the new technology has a lead time of about two weeks from receipt of 3D data to completed component. Also, there are no machine-setup charges or tooling costs and the technology avoids machined-in stresses and unintentional material work-hardening.

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