Changing times for gear milling

With its new hob concept, CoroMill 176, Sandvik Coromant has taken a large step forward in gear milling technology and performance
Cutting tool solutions underpin the gear milling revolution“What was seen as impossible 18 months ago is now a reality, performed on a daily basis,” said Kenneth Sundberg, Global Business Development Manager, Gear Milling Solutions, Sandvik Coromant. This summarises the company’s development efforts in a technology area that is relatively new to this leading cutting tool manufacturer.
Sandvik Coromant saw the need and potential for a performance shift in gear milling around 2005. Sure enough, machine tool and software technology as well as industry applications began to evolve, so did cutting tool solutions. The driving motivation for this shift from solid HSS tools to indexable insert tools was higher productivity, increased tool life and the elimination of re-grinding and recoating.
Changing the gameWith its new hob concept, CoroMill 176, Sandvik Coromant has taken a large step forward in gear milling technology and performance. A higher level of tool precision and rigidity has been achieved through a new patent-pending interface between insert and tool that also enables higher metal removal rates and enhanced surface quality.“The level of rates we now run at is completely new to the gear milling industry,” emphasised Mr Sundberg. “In fact, we can double or in some cases triple output with CoroMill 176. We are also making use of the Coromant Capto tool holding to add strength and stability to gear milling tools.”
Product developments such as CoroMill 176 have emerged after close collaboration with a select number of leading manufacturers and machine tool makers, all of which have set very high requirements. Such companies appreciate increased competition among tool manufacturers and especially the fact that indexable insert tools are now being offered to accommodate a far bigger range of gears.
Sandvik Coromant can now offer solutions for most gear milling applications, including transmission components in industries such as wind power, mining, marine, industrial gearboxes, agriculture, land moving and heavy vehicles. With regard to the latter, some are sceptical that the tight precision demands required for the high-speed transmissions deployed in many heavy vehicles can be met using indexable insert tools.
“While the ambition was there from the start, I was doubtful that we would be able to offer solutions for this application as early as during 2012, mainly because we have been competing with solid, precision-ground HSS tools,” stated Mr Sundberg. “But actually, we now meet quality 9 (according to DIN) on a regular basis. Under favourable conditions we can even achieve quality 8.”
Part of this impressive performance is because Sandvik Coromant tools are delivered with mounted inserts, and with a measurement protocol according to DIN 3968. Naturally, subsequent insert indexing requires a clean environment and skilled operators to reach these levels consistently.
Fresh approachSandvik Coromant enters the gear milling arena with a new outlook, a strong technology base and a long experience as a leader in metal cutting to challenge existing means and methods. Another advantage Sandvik Coromant can offer is a dedicated gear milling team able to provide global support. Manufacturers of gears can rely on the company to support their business from initial investment through to the day-to-day running of machinery.
“Of course, the ambition is to expand the offer as quickly as possible and to supply even further improved service levels,” said Mr Sundberg. “The target is to have the absolute best offer on the market by the end of 2012 and to have the ability to give specialist support to the gear milling industry anywhere in the world.”
Today Sandvik Coromant can cover hobbing from module 4 up to 18. By the end of 2012, the company aims to cover from module 3 up to 30 with indexable solutions. Disc-type milling cutters will also be available from module 3 up to 40.
Initially, Sandvik Coromant wants to give customers the opportunity to take full advantage of CoroMill 176, which is being made available from module 3 to 9. There is huge savings potential with the application of this concept. In most cases, around 50 per cent cycle time reductions can be achieved compared with existing industry solutions. Moreover, these results are attained with lower costs as tool life is increased 300-500 per cent, making the transition to indexable insert technology very advantageous. With the hobbing of smaller gears, where basically only HSS cutters are available today, the gains are much bigger. In addition, the expensive and cumbersome logistics associated with re-grinding and recoating can be eliminated.
uP-wards and onwardsSandvik Coromant already has an extensive gear milling offer. For instance, the new uP-Gear and InvoMilling methods are proving of great interest to manufacturers with small to medium size batches as they offer machining flexibility at high productivity levels with low costs using standard or standard-like tooling.
“We started to work closely with machine tool maker Heller and manufacturer Voith Turbo in 2009 to develop a solution for bevel gear machining,” explained Mr Sundberg. “This resulted in the flexible uP-Gear milling solution, introduced in the middle of 2010. Like the InvoMilling method, which is our own development, this is a very interesting alternative to existing solutions. As of September 2011, Gleason took over the sales of this solution on Heller machines and we are the exclusive cutting tool partner. Solutions such as uP-Gear and InvoMilling are already attracting a broad range of manufacturers who machine gears and/or components featuring integral gears. These methods have the potential to revolutionize this type of gear manufacturing.”
And more on this front is in the pipeline. In order to explore and develop gear milling solutions, Sandvik Coromant has access to state-of-the-art machines from Höfler and Heller at its application centre in Sandviken. The company also has a close collaboration with Zeiss regarding metrology and is working closely with some leading providers of software solutions within tool design.
The gear manufacturing industry is highly specialised, and Sandvik Coromant has learnt that it is all about generating specific gear profiles. The company needs to offer the means to machine these profiles, which leads to all tools being engineered. However, a few standard profile inserts for hobbing according to DIN have been introduced, along with some standard inserts for roughing with disc cutters.
Huge savings“Ultimately we can see enormous gains when replacing tools on existing equipment,” said Mr Sundberg. “In some cases, we have witnessed machining time reductions of 80 per cent. The upshot is that we can offer gear manufacturers who need more capacity a new tool instead of having to buy an additional machine. Then we are talking real cost savings.”
The mass production of gears through hobbing offers productivity increases, the elimination of re-grinding and recoating and the possibility to introduce dry machining. Machining without coolant has been met with a positive response as it further reduces costs and improves the operator environment. Another motivation is that dry chips mean higher scrap material prices.
“The reason why a shift from HSS to indexable insert tooling has not taken place for gear hobbing previously is that the technology has not been available, but it is now,” Mr Sundberg concluded.

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