Cylindrical, centreless, and surface grinding are getting pushed aside by hard turning and milling, right? Hardly. PHOTO courtesy Norton/St. Gobain Abrasive
By Kip Hanson
Polycrystalline cubic boron nitride (PCBN) inserts work wonders when turning hardened steels, as do whisker-reinforced ceramics. Polycrystalline diamond (PCD) is the go-to for high-volume machining of most non-ferrous alloys. And anyone who’s watched a solid ceramic end mill plow through a chunk of Inconel at cutting speeds that would destroy carbide will say to themselves, “I have to get me some of that.” That is, once they’re done looking for the nearest fire extinguisher.
There’s no argument that these and other high-performance cutting tools are edging into grinding territory, but CNC grinders aren’t ready for retirement. Far from it. In fact, Shane Farrant, national grinding machines product manager for Jtekt Machinery Americas Corporation, will tell you that the grinding market is alive and well, thank you, and that’s not about to change.
Let me count the ways
“To suggest that we’re seeing a decrease in the amount of grinding work is incorrect, and I would say it’s just the opposite, actually,” says Farrant. “Over the past year, we’ve enjoyed significant demand, some of which is thanks to the aerospace industry, although the lion’s share is still in automotive. The work in this sector includes the usual suspects like gears, cams, and crankshafts, but the biggest increase has been in the electric vehicle market. We’re seeing quite a few applications in this area.”
Whether to grind, turn, or mill ultimately comes down to the dollars and cents a manufacturer pays for a component, he adds, and grinding is often the most cost-effective solution—fortunately for Jtekt and other CNC grinder manufacturers, there’s no shortage of such parts in a battery electric vehicle (BEV).
One example of this is the motor’s rotor shaft, which requires grinding of its various bearing journals and main body. There is also an intermediate gear that helps transfer power from the motor to the output, as well as various other gear components based on the manufacturer’s design. (though far fewer than are needed in a vehicle with an internal combustion engine, or ICE, with its multispeed transmission).
But Farrant points to additional grinding requirements beyond these vehicle components, such as the cylinders needed to roll sheets of anode, cathode, and copper to “extremely precise” thicknesses and surface quality, which are then used to make batteries.
Yet Jtekt doesn’t limit itself to automotive grinding. For instance, the ballscrews that raise and lower hospital beds are finished on Jtekt grinders, as are hydraulic cylinders, plastic injection mold components, pump shafts, and countless other machined parts that touch our daily lives. And Jtekt Machinery offers silicon wafer disk grinders to meet the needs of the growing semiconductor industry.
Goodbye, black arts
Some have said that grinding is a black art that requires years of experience to master and no small amount of tribal knowledge. Yet much of grinding’s continued—and in some cases, increased—popularity is because Jtekt and its competitors are keeping up with CNC lathe and machining centre manufacturers in terms of current technology.
Machinists can now rely on intelligent controls and onboard sensors to tell them it’s time to dress the wheel, that they’re feeding too aggressively (and vice-versa), or that the coolant temperature is rising, and they should take corrective action. “We’re able to monitor everything about the grinding process and give the machine operator recommendations to keep them in the sweet spot,” says Farrant.
What it won’t tell you is when to switch to a different type of grinding wheel. That’s the job of Alfredo Barragan, senior corporate application engineer for superabrasives North America at Norton/Saint-Gobain Abrasives, who might suggest moving to a wheel filled with one of the materials listed at the start of this article, whether it’s CBN, diamond, or ceramic.
Anyone who’s shopped for one of these “superabrasive” wheels will tell you they’re quite expensive. Barragan counters that argument by telling shops to look at the big picture—whether the customer pays for a premium wheel or sticks with a low-cost commodity product depends on many factors, starting with the cost per part.
“In many applications, superabrasives reduce cycle time by significantly boosting metal removal rates,” he says. “They also require less dressing, further increasing throughput, and provide more consistent part quality. So while they might not be for everyone, shops struggling to reduce their rejection rates or overall production costs should definitely evaluate superabrasives.”
Back to school
They should also take a class or receive intensive instruction from the grinding wheel manufacturer. As with investing in a modern grinder, those who’ve purchased superabrasives need to learn all they can about wheel selection, preparation and dressing techniques, and how to apply the wheel to various materials.
“If you’re paying for a state-of-the-art CNC grinder, you need to do everything possible to maximize its capabilities, and that starts with proper application of a premium grinding product,” Barragan explains.
Increasingly, such wheels are not optional. Shops producing aerospace parts know all about the uber-tough, often extremely hard nickel-based superalloys in this industry. Here, only a superabrasive can cut the mustard. Similarly, it might be time for these shops looking at a new grinder to go with it—as Barragan points out, “it’s all a system.”
“I’m not saying you can’t run a superabrasive wheel on an older piece of equipment, but the results will not compare to what’s possible on one of today’s new machines. When you apply a premium wheel on a modern CNC grinder, where you have proper coolant delivery and filtration, the right fixturing, and rigid, high-performance motion control, the results are beautiful.” SMT