Peter Zelinski has been a writer and editor for Modern Machine Shop for more than a decade. One of the aspects of this work that he enjoys the most is visiting machining facilities to learn about the manufacturing technology, systems and strategies they have adopted, and the successes they’ve realized as a result. Pete earned his degree in mechanical engineering from the University of Cincinnati, and he first learned about machining by running and programming machine tools in a metalworking laboratory within GE Aircraft Engines. Follow Pete on Twitter at Z_Axis_MMS.
Manufacturers now succeeding with additive manufacturing have begun to see what its ultimate impact might be. I had a chance to speak to that here. This video summarizes some of the ideas and promises related to AM that were not clear at first, but now are becoming apparent.
“Your comment that the Japanese do not listen to music while working reminded me of a video that we show in our shop to new employees. Despite what people think about their ability to multitask, the human mind can really only focus on one task at a time. You can either listen to music or work with your hands. Take a few minutes to watch this YouTube video [embedded above].”
He went on to say: “I have been showing this video for a couple of years. The reason: our millennials. I have watched our youngest employees bouncing to the music in their headphones while either punching offsets into the controls of our very expensive CNC production equipment or ensuring the quality of our customers’ parts. We want them to enjoy their time at work, but they also need to understand their responsibility to our stakeholders to be productive in an extremely competitive global market.
“I banned the headphones. They are a distraction as well as a safety concern. While I have not banned cell phone use in the building, I have stressed that its use should be appropriate to work. Focus!
“That focus is important. We stress to the staff that anyone with several million dollars can buy every piece of equipment we own. There is nothing unique about the Tornos Deco, Tsugami, Index, Euroturn or Miyano equipment that we own. The only competitive advantage that we have is each team member’s brain working in conjunction with the brains of their co-workers.”
Mitsui Seiki is a machine tool builder that aims to excel in the area of precision. It provides machines, often custom-engineered, to meet machining challenges related to high-value parts with particularly demanding tolerances. Therefore, the company’s introduction of additive manufacturing as a capability it can now deliver might seem like an odd fit. Additive manufacturing—building up parts or features through a controlled process of adding material in layers—cannot by itself achieve anything like the fine tolerances that machining can.
But Robb Hudson, technology and business development manager for the company, says additive manufacturing is an addition to machining that brings both design freedom and process efficiency to complement machining’s precision. And by consolidating more of a part’s processing into a single machine, it potentially reduces part handling, which facilitates precision as well. During the past year or more that the company has been preparing to come to market with additive capability, he says, it has been experimenting with how to use metal cutting and metal deposition effectively within the same machine tool, without having to compromise the effectiveness or promise of either capability.
Mr. Hudson says essentially any of the company’s machines can now be made available as a hybrid system, capable of both additive and subtractive operations. A hybrid model of the company’s Vertex five-axis machining center will now be a standard product. The additive capability comes from the company’s partnership with Hybrid Manufacturing Technologies, a firm jointly based in Texas and the UK that offers a system for integrating additive manufacturing capability into an existing machine tool. The Hybrid head performs metal additive manufacturing through laser cladding, feeding metal powder into a pool that is melted by a laser. The head mounts in the machine’s spindle using a toolholder, and when it is not in use, it waits in the machine’s carousel alongside other tools.
A hybrid additive/subtractive version of this machining center is now available as a standard product, but the company says essentially any of its machines can now be made available as hybrids.
Yet integrating additive capability into the machine is not as simple as adding this head. The machine itself is also modified for safe use of the laser, as well as to enable powder flow. And if the full machining capabilities are to remain available, then new processing techniques along with other machine modifications are in order, too.
For example, what about coolant? Generally, coolant and lasers don’t mix, Mr. Hudson observes. But as part of the testing of additive/subtractive processing at Mitsui Seiki’s headquarters in Japan, the company has refined a process for using flood coolant extensively within a cycle that also includes additive layering. In this process, an air blow-off operation removes much of the volume of coolant still clinging to the part, followed by the laser applied at a wide focus to evaporate the rest. The surface dried in this way is ready for a new feature to be grown onto it through laser cladding.
A similarly important consideration is protection of the machine. Because some metal powder invariably escapes, preserving the machining precision demands ensuring that the powder does not affect sensitive mechanical systems such as the ballscrews and ways. Here, the company was able to draw on extensive prior experience, Mr. Hudson says. Guarding and other kinematic protections the company has engineered for machining centers used in precision graphite milling have been adapted to protecting the machine against metal powder.
The reward for all of this development will be the opportunity to deliver much more manufacturing capability within a single cycle, and bring much more of a part’s production into a single machine. CNC machining is the solution for tight precision, while additive manufacturing is potentially the solution where a high level of geometric complexity is needed. Those two benefits need not be separate—a part that includes geometrically challenging features is now also a part that can be machined to tight tolerances, without any handling or travel needed to transition between those objectives.
Indeed, that promise is particularly beneficial to manufacturers in the aerospace industry, Mr. Hudson says. A large portion of the machine tool builder’s customers are in this sector. “Their aim is often the buy-to-fly ratio, or how much material they have to purchase versus how much is left once all of the part’s machining is done,” he says. Buy-to-fly ratios are often high to machine elaborate aircraft components out of solid billet or even out of forgings, meaning material waste is high. But hybrid manufacturing offers a solution here as well. That is, instead of an oversize workpiece going into the machine to get much of its material cut away, what if a workpiece that was actually incomplete went into the machine instead? For material efficiency, some of this part’s features would still be produced through machining, while other features—narrow fins and other projections, for example—could instead be produced cost-effectively by additively building them on.
Jon Kulikowski, president of Blum-Novotest Inc., responded to that commentary to carry my argument even further. The manufacturer of measurement technology, including laser toolsetting systems for machine tools, routinely uses 3D printing to make prototypes of mounting brackets tailored to particular machine tools before committing expensive production equipment to making this hardware. However, the company president went on to point out that “small” does not have to be limiting when it comes to a 3D printer. Blum-Novotest personnel build prototypes that are much larger than the printer by building them in pieces and bonding the smaller segments together.
Mr. Kulikowski says, “We routinely make prototypes 5 to 10 times the capacity of our 3D printer, a Stratasys Fortus machine with travels of 250 × 250 × 300 mm, by chopping up the model and putting ‘joints’ in it. We then print the parts and glue them together. The result is a prototype that is surprisingly accurate—within 200 microns—and amazingly strong. When we made our first one, I put it through my crude but effective ‘smash’ test, and it passed. Then my engineer who put it together started breathing again.”
Is this the key to expanding a 3D printer’s prototyping size? Blum-Novotest is not making functional parts, just prototypes to validate the design. Still, jointed prototypes pasted with acrylics glue have proven both accurate and strong.
The photo at the top of the page shows an example. Company engineer Brandon Rau holds the prototype for a bracket that will integrate laser toolsetting with a large Toshiba horizontal boring mill. The prototype will allow Blum-Novotest and its customers to be confident in the design and to discover any potential interference points at the machine.
“The prototype has a material cost of about $500. The final bracket priced out at just over $3,200. Obviously, finding mistakes with a $500 mock-up beats making a $3,000-plus bracket two times. It also lets the customer know exactly what they’re getting and how it will affect the machining envelope,” Mr. Kulikowski says.
Meanwhile, there is another benefit beyond the engineering efficiency. “Going to a customer with a 3D print is a marketing tool as well,” he says. “Some are more fascinated with the model than they are with the final product.”
A large, complex bracket can encounter interferences that can only be discovered in the actual assembly. Better to seek out those problems with a cheap prototype, says Mr. Kulikowski, rather than taking the risk of having to manufacture the same bracket twice.
Relatively few shops perform frequency response measurements (like the one shown in the photo) to determine the optimal, chatter-free spindle speeds and depths of cut for their machines.
However, a much larger share of shops do run at something like these optimal parameters, because they eventually arrive at these parameters through the trial-and-error process of adjusting a machine’s speed until the chatter stops, and then cutting as deep as they can at that speed. The difference is: Measuring to find these parameters can get the shop to the optimal process faster, without so many parts being cut inefficiently along the way.
Jerry Halley of Tech Manufacturing experienced this. He was looking for a machining center that would perform well in heavy cutting of aluminum using a ¾-inch or 1-inch tool. For each of the machine models he considered, he went to where that machine was in use so he could measure to find the machine’s chatter-free milling speeds with these tools. (That measurement is often called a “tap test.”) A machine from SNK gave him the best performance he measured with the tools he wanted to use.
He shared this information with the machine’s user, the shop he was visiting to measure the machine. That is, he told team members at this shop the exact spindle speed at which they could run the machine to get the best efficiency with a 1-inch tool.
They said, essentially, “That sounds right.” The staff here had already figured out that this particular speed was best.
Mr. Halley nevertheless says there is an important point here that illustrates the value of the frequency response evaluation. In questioning the staff members further, he learned that they had fine-tuned the machine’s cutting parameters over the course of several months before coming to the correct findings that they did. By contrast, he came to the same correct conclusion with a measurement that took 15 minutes. Measurement and experience arrived at the same place, but measurement made it there much more quickly.
Learn more about measuring machine tools to find chatter-free cutting conditions here and here.