Additive manufacturing, aka 3-D printing, has many advantages. It allows designers to create optimal designs without restrictions from conventional manufacturing processes. Parts can be made from scratch at lower cost. Products can be lighter. A part that previously required multiple components can now be designed as one unit, eliminating assemblies. Fixture and jigs, sales demos and working prototypes can be quickly made.
But, 3-D printing does have some disadvantages. Not all finished goods can be 100 percent completed with the materials – and technology – currently at hand. Another disadvantage, from a high-production standpoint, is that AM can be a slow process.
However, 3-D printing is evolving with new materials, including a range of metals, and better software, lasers, and other technologies critical to the AM process allowing a range of new finished-part possibilities, made at faster rates, and within tighter tolerances.
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One of the newest companies to help drive this evolution is Methods3D Inc., a subsidiary of Methods Machine Tools, Inc., established through a partnership between 3D Systems, a supplier of 3D printing products, and Methods Machine Tools Inc., a supplier of precision machine tools and automation. Benjamin Fisk, general manager for Methods3D, says that the new subsidiary is about more than just 3-D printers; it’s about developing production “ecosystems” that incorporate traditional subtractive technologies with 3-D technologies to produce better parts faster.
Fisk says the goal is to take additive technology and move away from the traditional non-scalable mode, which for the most part is where additive has been entrenched. Therefore, the overriding approach is to explore the best ways to manufacture products.
“How do I take all of the pieces that are required to go from the raw design and material through a finished part and not have to do a load and unload and all of these manual or semi-manual operations that have been at the heart of additive for the last 20 to 30 years?” he says. “That is the question.”
One example of this concept was the company’s Figure 4 workcell showcased at the International Manufacturing Technology Show 2016 in Chicago. The workcell module featured six print engines that simultaneously printed different parts on different plates, using different materials. Aided by Fanuc robots, the parts were loaded and offloaded as parts were built.
After production, components were moved to post-processing stations including two different cleaning stations, an air blast and a wash module, a final cure station, and then inspected with imaging technology.While the parts were undergoing these subsequent steps, other parts were in the machine being built.
Essentially, this autonomous assembly line took bottled resin and transformed it into a finished part with little human involvement other than during programming.
While Figure 4 was a plastic-based production process, Fisk says that similar production cells using metal materials can be modularly designed. At the heart of these metal-based processes is the company’s ProX line of direct metal printers (DMP).
“We are using the same type of thought process and applying that to the metals,” he says. “We are taking the concept of full automation that we do here [at Methods Machine Tools] on the machine tool side, applying that same type of concept to the additive side, and using those systems to load, unload, and transfer or convey products over to the other processes.
“Now, we’re improving what some people might say is the inefficiency of the printing process itself,” Fisk adds. “If I can keep moving products through the printer at a regular pace where I don’t have hours of downtime when the laser is not firing, while I’m unloading and cleaning and doing all those steps, , then all of my systems are working in concert, and I’m starting to break down the barriers of speed.”
The company’s DMP machines use a high-precision laser that is directed to metal powder particles in order to selectively build up thin, horizontal metal layers. Materials that can be printed include titanium, nickel super alloys, stainless steel, tool (maraging) steel, non-ferrous alloys, precious metals and alumina. The metal powder particles pinpointed by the laser fully melt so that the new material properly attaches to the previous layer, without glue or binder liquid, and ensures a dense and homogeneous material structure. CAD file programs drive the machine without requiring any clamping or tooling. In this way, the most complex part shapes can be produced, including recesses, ribs, cavities and internal features.
The ability to create these complex, internal features using maraging steel has been a key to one of the most promising applications for metal 3-D printing.
“Right now, there’s been a significant amount of activity across the industry in creating advanced thermal cooling for injection molding,” Fisk says. “If I can put conformal cooling lines into a mould, then I get a much better thermal behavior of the die. With this improvement, cycle times are significantly reduced driving up throughput and productivity. Since product costs are directly tied to throughput, customers are reaping the benefits with lower operating costs and more competitive product pricing.” ”
To keep production going, and, equally important, to make sure that parts are built to within tolerances, the ProX DMP 320 machine utilizes software to track the entire process from beginning to end. Software will take the CAD file and “slice” the entire build into discreet layers each typically 30 to 60 microns in depth and then analyze each layer to ensure accuracy and precision.
“It’ll look at that layer and say, ‘Does it look right? Does it see issues?” says Fisk. “The software will determine whether there might be a potential problem in producing the required geometry. It will determine if there are any metallurgy concerns or if there are thin sections or walls next to a bulk section. Has the program created an overhang that I wasn’t aware of that might have less of an optimal surface finish or other characteristic? Once you get through all that, then the software will actually send the file to the 3-D printer.”
During production, the ProX DMP system will continually monitor the process checking the support structure, how subsequent layers are laid down and will track the orientation of the part relative to the powder bed as it builds the part layer-by-layer. According to Fisk, the system is not only looking at the layer just built, but also at previous and subsequent layers, and it adjusts the laser power, scan speed and other parameters in real-time to achieve “the most homogeneous material structure, the best surface finish, and the best tolerance or dimensional goal.
“That may mean dropping the laser power way down in certain areas to build very fine features or going slower to make sure you get the proper melt,” he explains. “In big bulk sections, it can increase the laser power and move the laser faster to melt more powder quicker. When it finishes that layer, it simply repeats this process. You have a recoater [that lays down the metal powder] that comes across again, the laser fires up and, eventually, you have built thousands of layers of a part.”
At the end of the build, the part is raised and the unmelted powder is collected for recycling. At this point, the part will then go through any required post-processing steps, such as a thermal processing, machining, and finishing. Most metals, such as tool steels or Inconels, need a stress relief due to the significant amount of residual stress contained within the part. Failure to perform this step will result in dimensional distortion when removed from the build plate.
To do this, the printed part may go into a heat treat module situated within the production cell. After that, the part is moved to the EDM step where it is cut off the build plate and moved to other post processing steps such as surface finishing, turning or milling.
The part built from Methods3D’s DMP process will have a dense and homogeneous material structure. Density achieved using the DMP process is between 99.5 to 99.9 percent, which Fisk says is in the same density range as other forms of metal forming such as casting and forging.
The best you’re ever going to achieve is 99.9 percent. There’s no such thing as a 100 percent truly dense product. There’s always some level of porosity,” he says.
According to Fisk, the additive industry has worked incredibly hard to get to this level. In the past, when metals typically started out, you were lucky if you hit 50 percent. Then it was 75 percent.
“It slowly matured,” he says. “In the past five plus years, it has really ramped up. Today, for all intents and purposes, we have achieved a theoretically fully dense material.”
This improvement, he says, was accomplished through improved software that controls how and when to fire the laser and other parameters such as the optimal laser, what are the power settings, as well as the improved material that are being used and the system’s ability to uniformly spread control-consistent layer thicknesses.
“If you look at the material properties, you look at the work that’s been done on the metals additive processes, especially our powder bed, and you’ll see we have come a remarkably long way,” Fisk says, “and now, we are producing material that rivals more traditional methods.”