Ask the Expert: Additive Manufacturing

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by Kip Hanson

Additive manufacturing is quickly becoming mainstream. Is your shop ready for it?

I came across an article recently, titled “3D printing or machining: the duel?” I’ve spoken with the company that published it several times over the years and have a great deal of respect for their equipment, but to suggest that there’s some kind of competition between additive manufacturing (AM) and its subtractive counterpart is ridiculous. That would be like saying that CNC lathes will one day replace cylindrical grinding operations, or that machining centres can eliminate the need for jig boring. 

Oh, wait. I guess that company has a point. The duel really is on. 

Seriously, though, additive manufacturing, a.k.a 3D printing, is just another process. Yes, it can replace machining in certain circumstances, but for the most part, the two complement one another. In fact, 3D-printed parts—especially those made of metal—often require a trip to the machine shop for support removal and machining of tight-tolerance features. CNC machining, it seems, isn’t going anywhere.

But neither is 3D printing, and machine shops that embrace this versatile technology can make faster prototypes, build jigs and fixtures in record time, and quite possibly open the door to new work. The question then becomes: which one do you need?

The answer depends on what you want to print. Most of the hugely complex and intricate metal parts you see in magazines like this one were produced via laser powder bed fusion (LPBF), equipment that can easily cost a million dollars to implement and many months to learn. Examples include machines from SLM Solutions, Velo3D, and Concept Laser (now GE Additive). 

Lower-cost alternatives from companies like Markforged and Desktop Metal also produce metal parts, as well as ones made of carbon fiber-reinforced polymers (although not in the same machine). Such industrial-level 3D printers are an attractive option for shops serious about metal printing, but without the massive investment. 

On the polymer side, fused filament fabrication (FFF) is a popular choice. Also known as fused deposition modeling (FDM), it works on the principle behind a hot glue gun, extruding a thin stream of molten polymer to build up parts one layer at a time. Then there’s the grandfather of all 3D printing, stereolithography. Invented in 1984 by 3D Systems founder Chuck Hull, it remains one of the most important of all AM technologies and is capable of producing both prototype and limited end-use parts. 

So is selective laser sintering, or SLS. Similar in function to LPBF and other forms of metal powder bed printing, SLS uses a laser to fuse individual particles of polymer powder the consistency of flour or fine sand. Like LPBF, it can create fully functional end-use parts with geometries impossible to produce via traditional means. And binder jet sprays a polymer binder onto a bed of metal, ceramic, or plastic powder, fusing the particles together. Depending on the material, a secondary sintering or curing step may be required. 

The point here is simple: shops wishing to take the next step in manufacturing have plenty of options, from $5000 (or less) desktop machines to multi-million-dollar laser systems. All they have to do is ask questions, kick some tires, break out the checkbook or credit card, and get printing. SMT

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