Reducing risk: the metallurgical considerations of 3D printing

From a raw material perspective, manufacturing life was once much simpler. If you worked in a job shop or fabrication house, for example, customers would send you a print, tell you how many parts they wanted, how soon they needed them (usually next week), and if you were lucky, a target price.

There in the title block would be listed 316 SS or 6061-T6, neatly spelling out whatever metal the bolts, brackets, or cabinets should be made of. You’d call the local steel house, get a price, figure out what the parts will cost to produce, and send in your quote. Easy.

Once it came time to make the part, there were no concerns about things like tensile strength and grain structure. Whatever metal went into the machine tool emerged a few minutes or hours later, different in shape but essentially unscathed from a metallurgical perspective. You couldn’t feed too fast or bend too hard, and as long as you kept a copy of the supplier’s material certs on file, any product failure due to porosity or stress cracks five years from now was the steel mill’s problem, not yours.

Not anymore. As the 3D printing industry transforms itself from a prototype-only industry to one of end-use, often mission-critical part production, its practitioners are finding themselves held accountable for far more than a product’s accuracy; they are also increasingly responsible for its structural integrity.

Think about it: Unlike most CNC machine tools, where “pouring on the coals” to increase throughput might lead to a broken end mill or perhaps a part sailing across the shop, cranking up the print speed on a metal-powder-bed additive machine will almost certainly create porosity, delamination, or residual stress. If you’re lucky, these failure modes will generate nothing more than a scrapped workpiece, but they could also lead to a critical failure years down the road.

What then?

Don’t get me wrong. I’m not patting myself on the back for recognizing this potential problem. I’m sure medical, industrial, and especially aerospace engineers the world over grapple with this concern every day, hence the strict emphasis on rigid process control, including robust build software, inline metrology, and strict material-handling procedures. It’s also why CT scanning of flight-critical additive parts is now routine, because identifying internal defects is only possible through nondestructive testing.

Similar arguments can be made about polymer parts, although the stakes are probably less high than with metal. Whatever the case, the message should be clear: If you or your shop’s owner is thinking about investing in 3D printing for prototyping, tooling, or low-risk, low-volume production, have at it. Doing so still requires no small amount of learning, but learning is always a good thing (at least that’s what Mom said).

But if you have visions of being the next 3D-printed part supplier to Boeing or Halliburton or Johnson & Johnson, tread carefully. There are lives on the line.