Incredible speeds and metal removal rates will define milling in the future
The future of milling will be notable for the ability to machine thermal resistant materials at high speeds. The accuracy will improve, but so will many of the challenges, the biggest of which will be the requirement for phenomenal rates of metal removal.
“These materials have high cutting resistance,” says Yusuf Altintas, NSERC-P&WC industrial research chair coordinator of the Mechatronics Option at the University of British Columbia (UBC). “If you try to cut too deep, machine tools will vibrate, and then chip thickness grows.”
Tool companies must adjust to these increasingly challenging materials. CBN (cubic boron nitride) will likely become the norm for finishing applications, because of its thermal stability, chemical inertness, and high wear resistance. CBN is not new, but it has been pricey, and has only recently come into wide adoption as a coating. That’s good news, because the trend toward hardened steels is here to stay.
“Machining hardened steels is a trend that has developed in recent years and will only increase in the years to come,” says Craig Ramsey, product manager for OSG Canada. “These materials include P20, H13 and D2 and can range from 28-65 Rc hardness.”
Ramsey says that, in the past, milling these materials has often been an expensive and slow process, both in tooling cost and, most importantly, in machining time. Given that new end mills and coatings have the capability to cut harder and harder steel, there is less of a need for electric discharge machining (EDM) for metal removal. Advanced tooling can assume those functions. We’ll likely see more solid carbide end mills with a sub micron carbide substrate, such as OSG’s Exocarb-WXS.
“These end mills are designed for hard machining applications,” says Ramsey. “The WXS nanotechnology coating has a much higher oxidation temperature. This allows for higher cutting speeds, which generate more heat that actually increases surface lubricity and extends tool life.”
Ramsey says that high speed machining (HSM) with spindle speeds of 15,000-45,000 RPM will only become more popular as global competition increases. At present, aluminum provides an example of where we might be headed with milling harder metals and alloys.
“In aircraft, you can take a 1,000 kilogram aluminum block, and mill it down to only 10 to 15 kilograms,” says Prof. Altintas. “You have to cut fast, and have fast removal rates, to justify the cost.”
Prof. Altintas’s research group is the largest in Canada, with 25 people working on all aspects of metal cutting and machine tools.
“We develop technology to predict the proper speed and depth of cut,” says Altintas. “We also work on special tooling techniques to improve productivity for metal removal.”
Prof. Altintas notes that advanced industries like aerospace rely heavily on titanium and inconels, and that one of the biggest challenges – now and in the future – is temperature. Without heat dissipation, the tool will fail. As a result, milling these thermal resistant alloys has always been at very low speeds, but that will change in the future.
“In the early ’80’s a spindle would burn at 7,000 RPM,” says Prof. Altintas. “Now we are milling at 60,000 RPM, and already at 200,000 RPM for micro-machining.”
It is possible that the speeds we are seeing in micro-machining could apply to larger parts in the future, because milling speeds are much easier to scale than are turning speeds, where there is always the risk that the part will be thrown from the chuck.
