Q&A with Stefan Scherbarth

Manager—Automotive Application Development Center
Sandvik Coromant

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I’ve heard a great deal of buzz about InvoMilling™. How did the idea come about?

I was visiting a big machine tool maker in Germany, and we were having a deep discussion about gear milling with the technicians and the president of the company. If you look back at our (Sandvik’s) history, we’ve always been in a very close relationship with machine tool makers. All of these discussions centered on difficulties machining larger module gears on their multi-tasking machines. You see, multi-talking machines are quite stable, but there is no counter-spindle, so you have a free-flying tool. With a free-flying tool, you have difficulty going into a hobbing process with bigger modules.

That seems simple enough. But the challenge evolved, didn’t it?

Yes. Once I dug deeper into the situation, I found that if you use the hobbing process, the last cut would nearly always give you full engagement.
So we started researching how we could split the cuts, and InvoMilling was born. With InvoMilling, you can easily work with different cuts—a roughing cut and a finishing cut, and you can split the process. For most gears, it’s just these two cuts. But for bigger modules—we once did a module 27—you will end up doing more than just two.

InvoMilling is a unique approach to milling spur and helical gears using indexable insert cutters. It opens up new, cost-efficient ways to produce geared components without dedicated hobbing machines. Since complete components can now be machined with just one set-up in just one machine, overall production times can be reduced dramatically. And a new generation of indexable carbide insert gear cutters will increase cutting data and lower the cost per machined gear wheel significantly.

It’s really quite simple. All machines are flexible, because iron is flexible. Of course, our MTM has methods to improve their machines and add stiffness, but you cannot improve the stability of a machine endlessly. The components of the machine are getting too heavy and, of course, expensive. In many cases, the only way to improve precision is to reduce the power of the cutting forces. The best way to do that is to make a finishing cut. InvoMilling is flexible and, at the same time, very productive. The method is “green” since the machining is performed dry, instead of with cutting oil.

If you use big tradition gear milling machines with hobs for small batch sizes, it’s not very efficient. In this case, with a large module, InvoMilling is superb, because you can do it on a machine center if it’s a spur gear, or you can use a multi-task machine if you have a helical gear. It makes the process much more flexible.
Gear quality is normally related to the module size. You have wider tolerances on big gears. With big modules, specifically, you have an extremely good gear quality with InvoMilling.

What about programming?

The programming is a combination of intelligent CNC programming with precision cutters. It’s been adapted by Mori Seiki to the machine control software Mori-AP in order to simplify programming of different gear sizes and modules.

So now your mission is to take InvoMilling to the manufacturing world, right?

We are spreading it out to all machine tool makers. At the moment, we have more requests than we can serve. More or less all, machine tool makers who are producing multi-tasking machines have requested that we implement InvoMilling on their machines. That will be our first task: to make InvoMilling available on all machine tools worldwide. That’s the biggest step we can take to promote it. We’re really concentrating and putting a lot of resources into it.

MORE INFORMATION: Visit www.sandvik.coromant.com.