For all their industry-changing capabilities, most additive manufacturing (AM) technologies have a problem. They produce parts that are far from complete. Getting printed parts to a finished state is more difficult the stronger the printed material is, and for parts made of metal, this means that when the build cycle ends, a host of post-processing steps are required, including depowdering, separation from the build plate, support removal, heat treatment, non-destructive testing (NDT) and, most commonly, costly, and time-consuming of all, a trip to the milling department.
“There’s always unfinished business once you’re done with the printing step,” says Jason Jones, PhD, the CEO and co-founder of Hybrid Manufacturing Technologies. “Because of this, secondary post-processing operations are a very non-trivial portion of the additive process.”
He explains that these flies in the metal AM ointment often account for half of the finished part cost. And for safety-critical components or those that require extensive machining, post-processing expenses can be much higher. Worse, it can be difficult, or even impossible, to reach deep inside the complex cavities and internal passages for which metal AM is prized, potentially affecting part performance.
One increasingly popular solution to all this is hybrid manufacturing, which combines additive and subtractive processes in one machine. Here, metal powder or wire feedstock is deposited onto the workpiece while a focused energy source—a laser or plasma arc, typically—melts the material, fusing it to the part surface. A milling cutter is then used to finish machine part surfaces and features as needed, either intermittently or after the part is printed. Hybrid machines also automate many other post-processing steps including the removal of supports and several types of inspection. For many materials, parts leave the machine ready for use.
Jones and team have led the way in commercializing hybrid manufacturing alongside the likes of DMG Mori, Okuma, Mazak and a handful of other CNC equipment builders that have jumped on the hybrid additive bandwagon in a big way, thus extending the “done in one” mantra to a whole new level. But what about machine shops, OEMs and research organizations that need custom combinations of heads or would like to add it to an existing CNC for cost reasons?
Jones recognizes this need, and for the past 11 years has worked to bring AM to the subtractive masses. The company’s AMBIT line of interchangeable, multi-material directed energy deposition (DED) and material extrusion heads deliver the capabilities just described, but can be installed on practically any CNC machining center or lathe.
“We’ve built a suite of tools that allows even commodity machines to produce finished parts and perform repairs on worn or damaged blades, mold cavities, bearing surfaces and the like,” he says. “That’s been our goal since the company’s founding. What’s new is that we’re able to deliver complete workflows that are under digital control, all in a single machine. Nobody else has ever done that.”
He’s talking about the unique ability to not only add metal to a workpiece, but inspect it immediately after deposition. “Because DED is a thermal process, it can lead to cracking. Our solution is to use an eddy current probe to go in and look for those cracks during the build process, greatly reducing the potential for failures that wouldn’t normally be found until the part is complete.”
Hybrid Manufacturing Technologies’ AMBIT lineup also includes ultrasound and laser scanning heads. As Jones points out, making NDT an integral piece of the hybrid manufacturing process avoids the need for standalone, significantly more expensive inspection equipment and all that it entails. By incorporating eddy current and other inspection technology into the CNC machine tool, operators can check parts as frequently as they want.
In some cases, “we can use one of our ultrasound heads to avoid post-build CT scanning, which is a lengthy, expensive process,” he says. “In many ways, hybrid manufacturing is an automation solution enabling costs to go down because you don’t have to pay for a robot or skilled operator to shuttle parts from machine to machine, while the workflow becomes both simpler and more controllable.”
Detecting and then mitigating cracks during the build is a big win, but what about stress relieving, hardening and hot isostatic pressing (HIP)? Don’t most 3D-printed metals still require some level of machining after heat treatment? It depends on the application, says Jones.
“If you’re using casting alloys intended for global heat treatment, then this workflow might not apply. But if you can utilize the laser for localized heating during the build process, either with the original material or by moving to a welding alloy able to withstand a very dynamic thermal cycle, then global heat treatment can become unnecessary. Further, a whole new generation of alloys is under development, many of them commercially available right now, that respond favorably to the localized heat treatment possible on hybrid additive machines.”
The possibilities for hybrid manufacturing go much further, however. Rather than make an entire part out of heat-treatable tool steel, why not print its critical sections from an alloy like Inconel or cobalt and the balance from cast iron or other inexpensive material? Doing so would not only deliver a better end product, but one that provides a lower cost and shorter lead time.
Similarly, polymers and metals might be combined in the same build, greatly improving part performance. There’s no natural bond between these materials, but his team has demonstrated how machining a dovetail channel, and then extruding plastic into it, makes a fastener-free mechanical joint. More examples come from Iowa State University, which used one of HMT’s polymer deposition heads on a CNC machining center to accomplish just that in a variety of forms. The result was a polymer composite airfoil that would have been far more difficult to produce via conventional means.
And because many hybrid additive systems can print blended powders or even multiple metals simultaneously—AMBIT included—it eases the development of novel alloys and bonded materials that would otherwise remain out of reach. The trick, Jones suggests, is determining which ones will work most effectively with which substrate. “We as an industry are just beginning to get our feet wet here, but I see that machine learning and artificial intelligence will play a huge role in optimizing these material combinations and bonding methods.”
Jones is a founding member of the ASTM F42 standards committee. He has served as chair of the SME AM technical community and received the organization’s Dick Aubin Award for Additive Manufacturing Innovation in 2014. He and business partner Peter Coates have built a successful business with dozens of patents between them. When asked how the two met, his answer was at first surprising.
“It was true love,” he laughs. “My wife wanted to study the history of 19th century British painting for her graduate work, and London was the right place to pursue that. So of course I followed her. I thought we’d only be there for a couple of years, but we ended up leaving 10 years later with two master’s degrees, a PhD from the University of Warwick, and a few children to boot. And during this time, I met my co-founder Peter Coates and we started Hybrid Manufacturing Technologies. It was a very productive decade for all of us.”
Jones’ interest in manufacturing began long before that. His family was in the construction business, so it was only natural that the much younger Jones liked to build things. In his university days, CNC machining captured his interest and he worked as a part-time machinist while studying engineering. It wasn’t until he went to the U.K. and started working for an engineering firm there that he expanded his skills to laser cutting and decided to learn all he could about manufacturing. And when the company’s managing director added a 3D printer to its CNC machinery lineup, Jones was hooked.
“That led to a discussion with De Montfort University’s Innovation Centre, which did research using 10 3D printers and also had a CNC machining center that no one knew how to operate,” he says. “When I started working there part-time as a research fellow, they were literally afraid of it. ... Getting the CNC machine running is when collaboration between myself and my co-founder first began which would ultimately develop into a company.”
A lot has changed since then. Jones notes that 3D printing has been around for nearly 40 years now, but it hasn’t been until the last 10 or so that it’s become a relatively mature manufacturing process. The time has come to make it part of the team.
“Everybody in this industry continually—and rightfully so—talks about the promise of 3D printing and whether it’s real,” Jones says. “Look at the financial cycles that go with 3D printing and you’ll see that we’ve been through at least two hype cycles and crashes—one right around the time we started the company and another more recently. So again, will this promise ever be fulfilled? My answer is yes, it will be, but first we have to recast 3D printing not as a solo performer, but as a very valuable player within the team of manufacturing. It’s a perfectly ripe time to do exactly that.”
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