Meeting in the Middle
- Published: March 30, 2018
Hybrid machine tools present manufacturers with unique challenges as well as opportunities
The fear that 3D metal printing once brought to the mind of machinists and machine shop owners–that CNC milling and turning machines would soon be as obsolete as paper tape–has finally been put to rest as knowledge of this disruptive new technology has grown. Additive manufacturing is now seen as a complementary process, reducing costs and development times while opening radical new doors for product designers.
Yet for all its awesome capabilities, 3D printing suffers some serious limitations. For starters, it’s not very accurate, at least by machining standards. It’s also slow–even the most tired, underpowered machine in the shop can remove metal faster than a 3D printer can print it. And scaffold-like structures are needed to support 3D printed metal parts as they’re being built, to prevent the twisting and warping that occurs when a laser beam melts powdered metal (although this is not typically the case with the hybrid machines).
Taking a powder
Machine tool builders recognize this, and have taken steps to leverage the flexibility and potential of 3D printing while minimizing its drawbacks. By equipping a CNC lathe or machining centre with a high powered laser along with a means of applying successive layers of metal powder, parts can be built up, machined to size, built up, machined to size, on and on one section at a time, until the workpiece is completed.
Despite the apparent novelty of this approach, Gregory Hyatt, senior vice president and chief technical officer at DMG MORI, says the technology of metal powder deposition is nothing new. What is new is the presence of a computer controlled milling cutter or turning tool in the same–now hybrid–CNC machine tool.
DMG MORI and its competitors have a distinct advantage over the original developers of blown powder technology. Not only are machine tools much better today, but so too is laser technology. The price per kilowatt has come down dramatically, as has its reliability and ease-of-use; put it all together and hybrid additive is, for the first time ever, commercially feasible.
The result in DMG Mori’s case is advancing additive in powder nozzle and powder bed techniques. This concept is used in DMG MORI’s five axis Lasertec 65 3D hybrid and Lasertec 4300 3D hybrid machines. Both machines are designed for the manufacture of large components such as complex turbine components. Another machine, the Lasertec 30 SLM, is a powder bed design that uses different materials, while an intelligent powder module concept allows the changeover in under two hours and gives users the ability to manufacture small, complex filigree parts.
Changing it up
Aside from building and machining complex parts from scratch, many hybrid machines can repair turbine blades, or fix damaged tooling, such as forging and stamping dies. That’s cool stuff, but Hyatt points to the ability of some hybrids to include multiple metals in a single part build as one more example of its game-changing potential. To take advantage of it, though, product designers will need to look at things from a new perspective.
“Additive and especially hybrid additive is capable of things that no traditional manufacturing process can do, and if we only look at existing part designs for its use we’re not leveraging those capabilities. Consider bimetallic materials–you can’t pour two different alloys in a casting at the same time and control precisely where each goes. But you can with hybrid technology. You have a machine tool that can add material wherever necessary, change alloys mid-build, and machine critical features within the part that would normally be impossible to reach. It’s the metallurgical equivalent of building a ship in the bottle.”
David Fischer, product specialist at Okuma America Corp., says the company is enjoying great interest in its MU-V Laser EX and Multus U Laser EX series of machines from several areas.
“There’s a lot of research and development at the university level, but there are also a number of customers looking to develop new products that they couldn’t make before.”
Hybrid technology brings two big things to the table, he notes. The first is material freedom, in that product designers can “put the material they want, where they want it,” and machine away the excess. Secondly, and no different than any other additive process, it gives them geometric freedom, to create shapes that would be very difficult if not impossible to produce using conventional manufacturing technology.
“For example, you might want to create a mesh-style part feature, switch to solid mid-part, then go back to mesh,” says Fischer. “This helps to limit heat transfer between components, and also reduces part weight. And the repair side is huge. By probing worn parts in the machine, you can very quickly determine what material has to come off—you can then machine the damaged area out, add material back in, and bring it back to size very quickly. In the past, much of this was done manually, so hybrid brings a great deal more accuracy to the process.”
Okuma has partnered with machine builder and laser developer TRUMPF for its laser needs. According to Fischer, the company’s disk-style solid state laser offers lower investment costs in multi-machine scenarios, as a single laser can power up to six machine tools. “Quite often, you’ll use the laser for only a small percentage of the total cycle time. This approach lets shops make better use of an expensive asset.”
Whatever laser is used and however many machines its used for, Fischer and DMG Mori’s Hyatt agree that proper application of laser power is needed in any additive manufacturing scenario. “For example, the biggest laser we offer is a 10 kW direct diode laser capable of depositing upwards of ten kg per hour of stainless steel or nickel-based alloy,” Hyatt explains. “On parts with thin walls or delicate features, however, you can’t use all of the available power, just as you can’t use a twelve-inch diameter face mill at 50 horsepower to machine those same features. It takes a relatively robust part to sustain very high deposition rates.”
The hybrid machines discussed so far work by spraying metal powder onto the workpiece while simultaneously laser melting it, a process that is referred to as DED (Directed Energy Deposition), cladding, or laser metal deposition. An alternative type of hybrid additive machine exists, one that uses the powder bed design seen in some “traditional” 3D printers but is equipped with a high speed machining spindle as well. Here, a layer of metal powder is laid down, sintered with the laser beam, then machined as needed to achieve the desired accuracy and geometry.
Get to bed
One example of this is the Lumex. Tom Houle, director of Matsuura Machinery’s lineup of hybrid machines, says the Lumex was initially designed for the manufacture of conformal cooling channel-equipped inserts used in plastic injection moulds, but adds that its use has expanded into various other industries, including tooling and turbine blade repair.
“One area that’s receiving a lot of attention is titanium, which is pretty much the holy grail of aerospace and medical implants,” he says. “Having the ability to sinter this and other metal powders and cut it in the same machine is opening a lot of doors for manufacturers everywhere.”
The problem is the gas. Because titanium is reactive, a special atmosphere is needed to prevent well, explosions. “You have this metal powder that you’re hitting with a laser beam, so it’s important to flood the chamber with an inert gas such as argon,” says Houle. “That’s pretty easy to accommodate in a purely additive environment, but when you introduce a spindle and a tool changer, you run into the situation where leakage can occur. We’ve gone to great lengths to avoid that.”
DMG MORI claims its “Reactive Metals Package” uses a safe titanium powder. The company says in tests inhalation, exposure was less than 10 per cent of safety thresholds, eliminating the concerns of ignition or powder inhalation.
Despite the nuances that accompany any new technology, the programming and operation of hybrid equipment is surprisingly straightforward, and anyone with some level of additive experience (and good knowledge of machining) will pick up on this brave new technology with little difficulty. SMT