Factors that can impede hard turning include lack of machine tool rigidity, lack of workholding rigidity, lack of tooling rigidity and lack of part rigidity. Sheehy believes that many of the problems associated with hard turning should be blamed on the machinist, not the machine.
He notes that Hardinge’s Super Precision series of CNC lathes, “are an ideal choice for hard turning due to the rigid structure of the machines, collet ready spindles and 0.1 micron control resolution offered on these models.” The majority of hard turning is performed dry, resulting in decreased expense in coolant disposal … there can be a substantial cost savings from increased throughput via faster metal removal rates and decreased cost of equipment, when compared to grinding, while maintaining comparable tolerances and quality,” adds Sheehy. “Most customers that inquire to Hardinge in regards to hard turning are looking for faster throughput, accuracy, process and machine flexibility, reduction in set-up times as well as multiple operations in a single set-up, all of which reduce the cost of the finished component. “Hardinge has been hard turning for over 20 years and has extensive process and cutting tool knowledge… additionally, Hardinge has been conducting hard turning seminars for 10 years or more, to assist our customers in getting up to speed in this area,” says Sheehy. Tom Sheehy, manager of applications engineering at Hardinge, Inc., of Elmira, New York, takes a considerably different tack. That said, the most robust process is still a grinder and will be for the foreseeable future,” he says, adding that hard turning has been cited as a growing trend “for decades” and still hasn’t achieved widespread acceptance. “Progress continues to be made with hard turning and turning centers continue to improve in accuracy. Still, Fischer can’t accept Hembrug’s premise that hard turning is the wave of the future. A grinder will be consistent with finish where a turning center will change as the tool wears.” Fischer is willing to concede that, “hard turning does tend to be more environmentally friendly since you eliminate swarf disposal.” He also notes that “hard turning can be done on any of Okuma’s turning centers” including the new HJ-250E horizontal lathe with a FANUC control. “Finish is another area that can be an issue. Typically, a lathe will have to be constantly monitored and the offsets constantly adjusted. I can run the grinder for days on end and never have to get fussy with the offsets to maintain size. “The grinder is a more robust platform when parts have to be held to millionths.
“Anyone who thinks a turning center can be more accurate than a grinder must have used a seriously bad grinder … turning centers can be very accurate, but grinders are in a different category,” says David Fischer, lathe product specialist at Okuma America Corp. Some industry experts think Hembrug is on to something, while others dismiss the Dutch firm as way off base. It’s important to ask, what do the big players think of hard turning?Īs it stands, opinions range all over the map. Multiple operations can be done in one set up (saving time and money) while the whole process is environmentally friendly (hard turning can be done ‘dry’), adds the site.Īll very well, but Hembrug is still a relatively small fish in the machine tool market. “In factories throughout the world, hard turning is replacing grinding, cutting costs and raising productivity,” boasts .Īccording to this site, hard turning offers several advantages over grinding, including greater accuracy, flexibility and productivity (hard turning is three to four times faster than cylindrical grinding). Hembrug operates two websites, a corporate site (which describes Hembrug as “the hard turning company”) and a separate site (found at solely devoted to the glories of hard turning. Hembrug corporate literature, on the other hand, comes in flawless English and a singular point-of-view. The doctor’s English was shaky, which made it difficult for him to make his point.
“Well, what I’ve noticed-people are getting more and more familiar with hard turning,” said Nefkens, interviewed at the Hembrug booth at Chicago’s recent International Manufacturing Technology Show (IMTS). The process is hard turning-defined in Hembrug literature as “single point cutting of hardened part pieces between 55 and 68 HRC.”
Robert Nefkens, managing director of Hembrug Machine Tools from the Netherlands, is a fervent believer in what many still consider a niche process.