A Counterintuitive Approach to Printing Metal Parts

Hybrid additive/subtractive systems for printing and finishing metal parts have been around for years now. With these systems, a part is completely printed and then is brought to necessary tolerances (i.e., edges, details, surface finish) through machining. It’s always been “first build it, then cut and polish it.”

A process developed by 3DEO Inc. (3deo.co) uses a radically different hybrid method.

3DEO’s process makes metal 3D printed production parts to spec in a counterintuitive way. The company’s Intelligent Layering system, like other liquid binder systems, applies a binder to a bed of metal powder to build a part that will eventually be sintered in a furnace. While some systems apply the binder only where it is needed to build up the part, Intelligent Layering instead goes wide: the binder is applied uniformly over the entire powder bed.

This isn’t even low-resolution—it’s no-resolution.

Then, micro CNC mills that are part of the 3DEO system deploy to precisely cut the outline and interior cavities. Another thin layer of powder is applied, followed by the binder spray, and the mills come out again.

In the fight to get as close as possible to net shape prior to CNC machining, 3DEO goes straight to CNC machining from the start.

To reach the best tolerances, the part can be cut a layer at a time. But up to ten layers can be built up before cutting, which saves time and also enables 2.5-D features to be included. The machine can also cut at depths of less than a full layer’s thickness to create intralayer features and enable finer tolerances than the printer could unaided.

The result is a “green” part that needs to be sintered in a furnace after loose powder is removed. Furnace-sintered parts lose some volume, but it’s a well-understood process and can be compensated for at the outset. The sintered parts come out of the furnace with a density of over 99 percent and with a finish of about 100µin. R_a. They meet the MPIF Standard 35 for quality. The current system has an 8 × 8i-n. build area and can print 17-4PH and MIM 316L stainless steel, with more types of metal to follow.

The system offers cost-savings benefits, like using standard metal injection molding (MIM) powders. Another cost-saver: cutting unsintered bound metal powder is a lot easier on a cutting tool edge than cutting solid metal, so much so that, after cutting over 10,000 parts (on three different machines), the company says it has not yet had to replace a cutting tool.

3DEO isn’t selling the system itself—or at least not yet. Rather, it’s a service provider, using the system to print parts for customers on demand.