A new turn for spinning

Spinning is an established, well-known form of metalworking. It typically involves a mandrel rotating at high speeds, which is pressed into a metal blank. Simply put, it is the process of turning a single, flat piece of metal on a lathe around a pattern, which then allows the metal to form into a desired, three dimensional shape. A good example of a Canadian company in this area is M.W. Metal Spinning Ltd. in Downsview, ON.

“We design table bases,” says Annette Goldstein, the owner of M.W. Metal Spinning. “And we also do a lot of industrial parts—we have CNC, PNC, as well as hydraulic and manual.”

Most in the industry are familiar with CNC, but perhaps less so with PNC, which stands for “Playback Numerical Control.” Despite the use of these technologies, spinning has not changed very much over the years, and still requires experienced workers who are good with their hands and understand the importance of playing back to perfect the form.

“With spinning you can’t just program it and stick in a disc,” says Goldstein. “There are too many steps. Sometimes you have to literally spin by hand and then play it back.”

Goldstein has spun aluminum, stainless steel, brass, copper, even titanium. There are challenges with each grade; for example, stainless steel will often work harden, risking a crack in the middle of the part. Nonetheless, the advantage of spinning technology—it produces hardened metal—results in significant savings potential of material and weight. And, as we shall see later in this article, the simple act of spinning can be a natural heat dissipater, though with power spinning, lubricants are usually necessary to control the heat build-up on the mandrel.

But spinning is a non-cutting manufacturing process. What if you could take the “spinning” of a typical milling tool and combine it with the advantages of a fixed turning tool?

Spinning, milling, and turning–in one

A few years ago Greg Hyatt was working at Kennametal, where he wanted to conceive of a way to leverage the abilities of a multi-tasking machine to combine the advantages of a mill and a lathe. When he moved to Mori Seiki, (he is vice president of engineering and chief technical officer of the company now known as DMG/Mori Seiki USA) he was in a good position to get the two companies together to realize his vision. The result has been a spinning turning tool jointly developed by Mori Seiki and Kennametal.

“When I was an employee at Kennametal I was director of their disruptive technology group,” says Hyatt. “We had a tool that no machine could support, so it made sense that, when I joined Mori Seiki I gave Kennametal a call.”

What he came up with was a turning spinning tool designed to distribute heat and wear more effectively than a single-point lathe cutter.

“In some ways the idea is not as revolutionary as it appears,” says Hyatt. “The first patent for a rotating lathe tool came out in the 1920s, and it was reinvented many times over the years. But the problem with the original concept is that they were self-propelled–-the cutting force itself propelled the rotation of the tool.”

This solved one set of problems, only to create another. It was impossible to precisely control the speed of rotation, which also made it impossible to control the thermodynamic cycle, and without control over the heating/cooling cycle, thermal cracking then became the dominant issue.

“Our innovation was to realize that we could use the milling spindle,” says Hyatt. “We conducted research to understand the thermodynamics of the tool in order to manage the heat cycle. We can now eliminate fatigue while also attacking the classic thermal modes of failure.”

Specifically, the technology developed by Hyatt uses a turning insert similar to a full radius insert. Typically, this would be mounted on a turning holder. The specialized insert, however, is mounted at the bottom of a cylindrical tool shank and held in a rotary spindle that spins at high speeds. Though a completely different form of metalworking from the non-cutting process mentioned above, the “spinning” in this context also serves to dissipate heat.

The results have been impressive. By using the tool’s rotation to distribute heat and wear around the tool’s entire diameter, Mori Seiki has found that the spinning tool can increase productivity by up to 500 per cent and tool life by up to 2,000 per cent.

“We see these improvements because conventional tooling can’t do 3,000 sfm,” says Ruy Frota, manager product engineering, tooling systems, at Kennametal. “These are extremely high speeds that would normally generate too much heat.”

When the spinning turning technology first came out, CAM developer DP Technology performed a test cut on a steel workpiece mounted on a Mori Seiki NT4200. The test was run without coolant and included roughing and finishing operations. Because the tool has no single point of contact, the test found that it was excellent for heat dissipation and wear. As well, because it directed most of the cutting forces axially into the spindle, vibration and chatter were reduced. The test also found that the tool was good at back-and-forth-cutting, as well as taper and arc moves.

“By being able to cut on the YZ plane you don’t have the heat and wear limitations presented by single point inserts,” says Dave Bartholomew, technical marketing specialist for DP Technology. “Mori Seiki’s research also found that a 20° angle is the best angle to cut at.”

The next generation

Hyatt and his team are now working on a second generation of the tool.

“We are targeting the most difficult and challenging applications such as large work pieces, where you often can’t get through a single cut without tool failure,” he says. “Tool replacement interrupts the process, is labour intensive, and creates opportunity for operator error.”

This second generation of the tool is part of an on-going learning process. One of the new challenges relates to chip formation.

“What we know from conventional turning does not necessarily apply,” says Scott Etling, manager, global threading, grooving & cut-off at Kennametal. “The way you orient the tool to the workpiece is critical; this is one of the variables that we don’t have in conventional turning—it changes chip formation. It is easy with this technology to produce very long chips, which are hard to break.”

Because of the orientation of the tool, conventional chip breakers don’t work. The plan is to optimize the parameters and geometries based on the spinning tool, with chip breakers around the inserts. The second generation will also be coolant-capable, with the fluid coming through the holder and delivering coolant to the cutting edge radially.

“It uses a hollow insert with coolant passages,” says Hyatt. “It delivers coolant directly to the cutting edge, with no external nozzles required.”

In some ways, the development of the next generation is made more complex by the very capabilities a spinning turning tool can deliver, such as the fact that the cutting conditions are no longer limited by heat generation, but by the power available in the machine.

“As a general rule, the tool can handle more power than the machines can deliver,” says Hyatt. “To fully utilize it, we will have to start making more powerful machines. The low hanging fruit was in structural and stainless steels–which can still be challenging–but the greatest benefit will come with Inconel, titanium, and other high-temperature alloys.”

The advantages of higher removal rates and improved productivity (of essentially doing more with less) likely won’t be overlooked in the market.

“Our customers are looking at the technology and saying ‘This is cool’,” says Etling from Kennametal. “With coolant delivery and the chip breaker, it feels like the sky is the limit in terms of what we can do with this.” CM

Tim Wilson is a regular contributor and freelance writer based in Peterborough, ON.