Caution Advised On 3D Printed Metal Proposal

A Kickstarter campaign is under way to fund a project to produce metal-filled filaments for use in 3D printers.

The second and third sentences in the proposal state: “The 3D Printer will replace the Plastic Injection Molding Machine in the Metal Injection Molding [MIM] process, and later with Oxide and non-Oxide ceramic filled filaments in  the Ceramic Injection Molding Process [CIM]. The MIM and CIM processes currently produce  $1.6 Billion Dollars of intricate small industrial metal and ceramic parts.”

Not surprisingly a few writers in the 3D printing sphere jumped on this story. To me, this proposal seems like dotcomism. That is, hyperbole aimed at taking advantage of 3D printing hype.

3D printers, at least based on current and foreseeable technology, will not replace injection molding machines. Injection molding machines produce parts in seconds and minutes. 3D printers produce parts in hours and hours. As a CEO famously said recently, watching parts made in a 3D printer “is like watching ice melt”.

Can 3D printers produce metal parts with the densities and mechanical properties required for the very demanding MIM market? What types of tolerances can be achieved? There’s not even a sniff of engineering data to answer these questions.

And, of course, it’s ridiculous to thing that “makers” would be willing to invest in the extensive downstream equipment for debinding and baking the parts that are necessary to make them ready for use.

The Sinterhard proposal states: “We are planning a crowd funded, low cost, table top debind and sinter furnace project as soon as the Sinterhard Metal Filled Filament Project is launched and product is delivered.” Also, Sinterhard acknowledges that post part processing will be required to achieve net shape. OK, so you’re going to need some machine tools as well.

Use of additive manufacturing technology is well developed to make very high tolerance metal parts using lasers. In fact it dates to the late 1980s in work done both in Texas and in Germany. It’s a very expensive, capital-intensive process that produces high-tolerance, complex parts such as dental implants.

Another point: the binders used in the MIM process have been carefully formulated over several years for optimum results. One popular binder consists of paraffin wax, polypropylene and stearic acid. A typical binder by volume is 40 percent of the MIM compound, according to Russell M. German’s authoritative text on powder injection molding. Sufficient binder is needed to fill all the voids between the particles. The stearic acid is a lubricant that allows particles to slide during the injection molding process. Viscosity of the mixture is critical.

Sinterhard is working with filament  materials available from commercial suppliers: ABS and PLA, the two most commonly used 3D printer plastics. Two metal powders are initially targeted.

If BASF and MIT or Hoeganaes and Caltech announced they were launching an exploratory campaign to explore the potential for 3D printed metal parts, I’d say, OK, maybe this could be interesting. Also, I can see the potential of the Arburg FreeForming process as a possible way—down the road, way down the road—to make 3D printed metal parts. Arburg is one of the premier technology companies in the plastics processing field and is now shipping FreeFormers that probably cost in the neighborhood of a quarter million each.

But here’s what Sinterhard has to offer: “Are others more qualified to do this? Maybe, but: We have a Masters Thesis done on how additives affect flow properties in thermoplastics during injection molding” and 30 years experience in debinding.

There are some real world challenges and problems in the proposal, but not enough and they’re buried too deep.



About Doug Smock

Former Chief Editor at Plastics World and Senior Technical Editor Design News
Additive manufacturing

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