by Kip Hanson
A new breed of hybrid additive equipment promises to cut a wide swath in the machining world
Bananas and peanut butter, milk and cookies, oil and vinegar: some things are made to go together. But for the past few decades, additive manufacturing—also known as 3D printing—has remained firmly in the hands of service bureaus and prototype houses, complimentary to but separate from traditional machining.
That distinction is undergoing a dramatic sea change as a handful of prominent machine builders introduce equipment that combines 3D metal printing capabilities with conventional metal cutting CNC machine tools. The additive technology used in these machines varies, but all share a common goal—to make feasible the creation of parts and tooling that were once difficult or downright impossible to manufacture.
Get to bed
One of these is the Lumex Avance-25, from Matsuura Machinery Inc., distributed in North America by MC Machinery Systems, Wood Dale, IL. The Lumex combines powder bed fusion additive manufacturing technology, with high speed three axis machining, to deliver a machine aimed at the mouldmaking market.
Like drawing your name in a sandbox, powder bed fusion uses a laser to fuse the topmost layer of a metal powder bed. As each layer is completed, the bed drops a small amount, a wiper bar distributes a fresh layer of powder, and the laser again goes to work. The process is repeated until the workpiece is complete. The difference with a hybrid additive system is that those layers can be machined as soon as they’re built, cleaning away rough edges and providing far greater accuracy than powder bed technology alone.
Greg Langenhorst, technical marketing manager for MC Machinery, explains the process. “We use a 400 watt fiber laser to melt layers of 45 micron spherical powdered steel or titanium. Every 10 layers or so, at a thickness of roughly 0.5 mm (0.02 in.), a milling cutter is used to semi-finish the top 10-layer level, and a special relieved “neck back” cutter reaches past the top level to finish the one directly beneath it.”
This manufacturing approach allows for moulds with internal water channels that are more efficient at cooling than those made with existing methods, and for porous “breathable” moulds that speed up the injection process. Both of these attributes reduce moulding times. And Langenhorst points out another big advantage of hybrid machines. “If you find something in the finished workpiece that you want to change, it’s easy to put it back in the machine, mill down to that level and rebuild it.”
Adding to “Done in One”
Some hybrid machines are designed for part feature generation as well as component repair, thus eliminating the need to manufacture parts from scratch. Mazak Corp., Florence, KY, is introducing a hybrid machine that provides both capabilities. The Integrex i-400AM is a multi-tasking machine with a twist. “By adding a laser system to the Integrex, we’re able to perform what we call laser metal depositioning,” says Joe Wilker, product manager for Mazak multi-tasking machines in North America. “The AM machine uses a fiber optic laser to melt powdered metal, which is sprayed on the workpiece directly ahead of the laser. This allows us to lay beads of material on top of one another, which in turn creates machinable 3D geometries on existing components.”
Combining in-process metal-deposition technology with mill/turn capability creates numerous manufacturing possibilities. Turbine blade repair becomes an iterative process: measure the damaged blade with an inline probe, machine away the affected area, apply replacement material and then re-machine the component to size. It also allows new features to be “added on” to machined parts—a threaded boss, for example, could be built up on the outside of a cylinder, or a titanium wear surface added to a steel engine component.
Wilker says stand-alone powder bed sintering systems produce very accurate and detailed parts, but at a price. “Those systems are slow,” he says. “Our process is basically four to five times faster. We achieve a workable balance between additive speed and accuracy, then finish machine the parts afterwards. Ultimately this provides shorter cycle times.”
The laser optics and powder delivery system on the Integrex i-400AM are housed in a unit small enough to fit in the machine’s tool changer. Once mounted in the machine spindle, the head engages with an external unit that supplies power to the laser, powder to the cladding head, and shielding gas such as argon or nitrogen.
To accomplish this, Mazak worked in partnership with UK-based Hybrid Manufacturing Technologies, the developer of the Ambit metal deposition heads used in the i-400 additive machine. Jason Jones, Hybrid’s chief executive officer, says hybrid additive machines resolve the dilemma that’s plagued additive manufacturing for more than three decades. “If you want fine-featured resolution, you pay the penalty of building up parts in really thin layers. Hybrid machines eliminate this problem.”
The concept of laser cladding in a machine tool isn’t new. Jones says the Ambit began as an academic project roughly seven years ago, one designed to bring cladding technology into a package small enough for integration into any machine tool. “One of the challenges is the harsh environment. Laser cladding heads have delicate optics, and don’t respond well to bumps and crashes. We also wanted the option of multiple heads, so that different beam profiles or metal powders could be used in a single machine. It took a good deal of testing to get it right.”
Apparently, they were successful. The company received the International Additive Manufacturing Award from the Association For Manufacturing Technology (AMT) and The German Machine Tool Builders’ Association (VDW), an award that signifies Hybrid’s advancement in additive processes and applications.
Looking through a LENS
Another company seeing success is Optomec Corp., which was recently awarded a contract by America Makes, the National Additive Manufacturing Innovation Institute, “to deliver additive technology that fits inside virtually any CNC machine tool,” says Ken Vartanian, vice president of marketing at Optomec. “We’re adopting an open approach. We don’t care what machine tool it is, whether it’s new or used. Our goal is to give manufacturers the ability to upgrade their machine tools with additive capability.”
The Albuquerque, NM, company has been developing additive manufacturing technology since the mid-90s, when it licensed a metal cladding process developed by Sandia National Laboratories. Optomec dubbed it LENS (Laser Engineered Net Shaping), and has since commercialized the technology. Now with its LENS Print Engine, Optomec is expanding into the hybrid market.
One example of this is Optomec’s recent retrofit of a Fadal machining centre with a pair of LENS-equipped powder feeders and a cladding head. The hybrid machine is currently in beta testing at TechSolve, a consulting firm in Ohio. “By leveraging existing equipment, it saves a lot of time for us, and money for our customers,” he says. “This is very important to the adoption cycle.”
Raw materials are also important. Vartanian and other experts say the metal produced by cladding exhibits mechanical properties very similar to and in some cases better than cast material. Also, new alloys can be created on the fly. “We can start building with material A, and gradually switch over to material B to form functionally-graded materials, or mix them in uniform proportions during the printing process,” Vartanian says. “This lets us develop new alloys very quickly, and do so on top of existing machined workpieces.”
Do me a solid
Greg Hyatt, chief technical officer at DMG MORI, prefers the term “powder spray” to cladding. “Cladding implies a single layer of material, whereas we’re doing an awful lot of complete builds of complex features. Our technology is geared towards larger parts—heavy equipment, oil fields, and other industries frustrated because they couldn’t leverage additive manufacturing due to the size of their workpieces.”
DMG MORI offers two machines—the Lasertec 65 3D hybrid machining centre, and the NT 4300 Additive Manufacturing mill-turn machine. Both use a diode laser to achieve deposition rates best measured in kilograms per hour, a rate substantially faster than pure additive machines. According to Hyatt, high deposition rates together with in-process machining capability make hybrid additive machines competitive with traditional casting processes.
“The cost of additive has been furiously debated,” Hyatt says. “Compared to casting, the sprues, runners, and risers are all eliminated, so the mass of that metal does not need to be melted. Even though additive manufacturing has a minor loss/drawback regarding heat generation compared to other technologies, this is offset by the fact that we can add material to a workpiece, thus building up features that could not otherwise have been cast or forged. This reduces energy consumption, and dramatically shortens the build time.”
For those who cringe at the thought of a high-priced machine tool sitting idle while a laser builds up material, Hyatt says don’t be. “Because we can deposit material very accurately, we virtually eliminate rough machining operations and proceed directly to finishing. So while we’re adding process time for material deposition, we’re also subtracting time from cutting.”
Like additive manufacturing once was, hybrid machine tools are a paradigm shift. Product designers must learn to think differently, as do process engineers, programmers, and machinists. Thermal effects and metallurgical properties become relevant when material is fused to a workpiece during the machining cycle. Internal stresses must be considered, and the build process analyzed to avoid scrap and achieve efficiency in manufacturing
Another consideration is capital equipment cost, which varies widely based on machine capability as well as the machine tool builder itself—for example, a retrofit solution can easily cost $300K, while a factory-built hybrid machine might cost three times that amount or more. Whatever the price, you can be sure of one thing: hybrid additive manufacturing is here to stay. SMT
Kip Hanson is a contributing editor. [email protected]