Taking on the Tough Stuff

It may not be as marvelous as learning that the COVID-19 vaccines are over 90 percent effective, but here's some good pandemic news: Some of the key players in grinding used the break from constant selling to finish the development and testing needed to introduce exciting new technology. Let's start with improvements to continuous dress creep feed grinding (CDCF), and its longstanding effort to supplant milling for tough applications.

As Phil Wiss, regional sales manager for the profile grinding division of United Grinding North America, Miamisburg, Ohio, explained, CDCF delivers a high material removal rate (MRR) in difficult-to-machine materials, while virtually eliminating the need for deburring. "Any time you have hardened materials, creep feed grinding can beat out other approaches that force you to combine applications," he said. For example, rather than mill soft material, then heat treat, and then finish grind, "you can cut right to the chase and do a creep feed grind. You don't have to add different operations." And while Wiss recognized that manufacturers struggle with justifying an investment in an expensive creep feed grinder versus paying a "$15 an hour deburring guy," he said the choice is getting clearer. "It's harder and harder to find that guy who's willing to pick up a deburring tool and try to clean up a part."

Wiss offered a perhaps more clearcut case of CDCF beating out milling: a 24 × 0.4" (610 × 10.16 mm) medical part that ate up milling tools. There are two versions, Wiss explained. "One is similar to a nickel alloy and the other is a titanium derivative. Both are very difficult to machine." The part has a tight tolerance down the entire length, and milling tools wouldn't last through the cut without limiting them to a very light pass, necessitating multiple cuts and frequent tool changes. And yet the scrap rate was over 20 percent, Wiss added. "It was just a very slow process, and expensive from a tooling standpoint." The situation became intolerable when required part volumes increased, so the company switched to CDCF grinding. Now they tackle the part in one pass.

"Another unique thing about continuous dress creep feed grinding," offered Wiss, "is that you know exactly what your tooling costs are. On a continuous dress application, you feed the diamond roll into the grinding wheel at a set rate, let's say at a seven millionths per revolution. And if you’ve got a 20" long [50.8 cm] cut at 20 ipm, you can calculate exactly what your wheel wear will be for that length of cut. Therefore, you can assign a specific tooling cost to that part, because you know exactly how many parts you’ll get per wheel. There are no surprises. It's a very calculated process and you can pass on those costs to whoever you’re selling that part to."

At Norton | Saint-Gobain Abrasives in Worcester, Mass., the company is helping lead the charge with new wheels for CDCF applications, plus new superabrasives. Corporate Applications Engineer Dave Goetz explained that the company's older ceramic wheel, "the SG, as we called it, needs a lot of horsepower, grinding energy, and force to fracture the grain. So it wasn't optimal in some applications. Our new Norton Quantum Prime is a friable ceramic grain. The grain itself micro-fractures and self-sharpens a lot more readily. But it has the cut rate and the life of the SG wheels. So, you have higher stock removal rates, you can get more parts per wheel, and usually you can cut cycle time with it."

Naturally, he's delighted the name itself suggests Q-prime! In one OD bearing grind, in which the material was 62 Rockwell 100Cr6, the new Quantum Prime was able to cut 9.3 seconds from the cycle time and boost the number of parts per dress by 150 percent versus the previous generation ceramic wheel.

Goetz said the Quantum Prime is also finishing better than the original version. "When you’re trying to achieve a specific Ra or Rz, you often have to go to a finer grit size to get the finish, with a corresponding loss of the larger stock removal. Let's say an 80 grit should have been able to achieve the finish, but you had to go to 100 or 120 because of the way the grains fractured. The Quantum Prime grain is behaving like a true 80 grit. So now we can go down and get the same finish, and the same stock removal rates, and not have to play with, or adjust, the grit size to achieve all the objectives."

Goetz added that Norton | Saint-Gobain Abrasives is also having success with extruded, shaped grains that it calls TQ and TQX. In a typical abrasive, he explained, the crystals are grown as a sheet, fractured, and then sorted by diameter with a mesh. "There's no real control over the shape of the grain. The only thing you control is the particle size. But the shape of that grain is controlled by how that initial crystal fractured." Conversely, the Saint-Gobain division that supplies the TQ grain can control the diameter of the crystal as it's grown and extruded into shape and then, to a certain extent, control the length of the grain as it's broken.

Goetz described TQ as "like a cake sprinkle, or a piece of broken spaghetti," and said the grain achieves higher stock removal because "when the broken pieces of noodle mix, they are all in various orientations. So, when they come through your grind zone, there's at least one sharp cutting point. In the tests I’ve done, we’re finding significant improvement in stock removal over other ceramics."

Norton's Paradigm diamond wheel is "old news" in the world of grinding carbide cutting tools, but United Grinding's Wiss said it's now coming into play for producing other non-ferrous parts, including applications in CMC (ceramic matrix composite) and silicon. "We’ve been doing some test grinds on the silicon material used for making microchips," recounted Wiss. "It's a very difficult-to-machine material, a dusty swarf type material, that is also a bit difficult to grind. But with a Paradigm wheel we were able to cut it like butter. We were able to grind through this material with deep cuts, fast speeds, and very little to any grinding wheel wear."

Goetz explained that Paradigm is a "unique, dressable metal bond. So you can true it and dress it online, if your machine is capable, using particular CVD-reinforced dressing rolls. That allows you to maintain the wheel profile and face condition. It's very free cutting. And, because it holds the grain so long and so well, it allows you to use the full diamond grain to its maximum benefit. Then, by the time your grain starts to dull, you’re already breaking down and removing the bond to bring the next cutting layer to the surface. So, extended wheel life is a huge benefit. And it's very consistent from beginning to end. You don't see nearly as much change in diameter as it wears, like you do in some conventional wheels."

For ferrous applications using CBN, Norton | Saint-Gobain Abrasives has developed a new bond for superabrasive CBN wheels called Vitron 7 (sold under the Norton Winter brand). According to Goetz, this new technology has contributed to a move from conventional to superabrasives. "You go to a higher priced wheel, but you’re running the wheel so much longer, at higher stock removals, at far more parts per dress, such that the lower operating cost of converting to the superabrasive more than outweighs the price of the wheel," as Goetz put it. The company reports wheel life gains of up to 40 percent over existing products and says "Vitron7 wheels also grind cooler due to a lower specific grinding energy that ensures minimal residual stress, for superior part quality with surface roughness degradation reductions of up to 30 percent."

Wiss cautioned that the dressing cycle for these wheels is intermittent (unlike CDCF), and it's virtually impossible to predict the rate of wear on the dressing disk, so you need a way to monitor the process. United Grinding's preferred approach is to measure the part and use that data to interpret changes to the grinding wheel and dressing disk. This can be done either by "probing the part in the machine, or by having a closed-loop system in which you take the part out, measure it in a CMM next to the machine, and then feed that data back to the machine as you’re grinding the next part," explained Wiss. "We see a big push among customers—especially those with high-volume manufacturing of the same part—to integrate the CMM into the cell. It can be robot loaded, or manually loaded, but you have to have that feedback going back to the machine for critical features."

Wiss reported that another trend is the increasing adoption of grinding machines that can also mill, drill, and threadmill. He attributed this to the general loss of craftsmen, programmers, and skilled operators, which is pushing manufacturers to "ask machine tools to do a lot more than they have in the past." The more you can do in one setup, the less you’re counting on your operators to do multiple setups perfectly, and the less time spent moving parts from machine to machine. While United Grinding has offered some degree of multitasking for about 10 years, Wiss said the company learned over that time, and current models benefit from that experience. That includes features like through-spindle coolant (which wasn't necessary for grinding) and a second control at the toolchanger in back, enabling the operator to switch out grinding wheels and cutting tools without interrupting the job in progress.

Another thing United Grinding learned in adding milling capability was the need for higher spindle speeds than those typically used in grinding, said Wiss. The company's premier multitasking platforms are its Mägerle MFP 30, 50, 51, 100 machines, all of which are fast, five-axis, high-torque high-power machines (with over 100 hp in some cases). While going to higher speeds necessitates some sacrifice in power, Wiss said 40 hp was sufficient in multitasking machines.

Five-axis multitasking also necessitates 3D simulation, observed Wiss, to "make sure that a wheel pack fits into the machine and we have enough clearance around the fixtures to grind and machine the part." And like most five-axis work, shops generally want to program offline with a skilled engineer using a good CAD/CAM package. For United Grinding's Mägerle and Blohm surface and profile grinders, Siemens NX is the natural "bridge," as Wiss put it. The machines have Siemens controls, and, in addition to benefiting from NX to program feeds and speeds for the milling operations, United Grinding provides a suite of grinding macros for NX, which includes continuous dress functions.

The big news at JTEKT Toyoda Americas Corp. is an extremely accurate roll grinder for electric vehicle batteries. To be specific, this new machine grinds the rolls that are used to generate the aluminum and copper sheets that go into the cathode and anode of the battery cells. As Shane Farrant, national product manager for grinding machines at Arlington Heights, Illinois-based JTEKT Toyoda explained, "any imperfections in the roll translate back to those sheets when they’re rolled out, so we are achieving surface finishes of 0.15 μm Ra and cylindricities of half a micron per meter over the entire length of the roll, which could be four meters."

The details of how Toyoda achieves these numbers are secret, except to say that it started with one of its most popular large machines for high-accuracy grinding and included NC steady rests and Toyoda's hydrostatic technologies in the spindle, ways system, and subassembly components. But the new machine, called the GR7, is "designed specifically for grinding of those rolls," said Farrant. He added that the machine's special features also ensure the tolerances can be maintained over extended periods of time, as well as proprietary software to reduce operator setup time.

Beyond the GR7, Farrant said he's seeing an increase in requests for large grinders in general. "We see it in cutting dye manufacturing, or rolls that are used for printing or paper manufacturing. We’re seeing it for electrical motor shafts. For compressors and things of that nature." Toyoda offers machines for these applications that go up to 157.4" (4 m) between centers with almost 26" (660 mm) of swing. One model has a weight capacity of 6,600 lb (3,000 kg) between centers. For applications like large printing rolls, which don't have the extreme tolerances of the EV battery rolls, "we would generally go to a piece of equipment like the GE6," said Farrant.

In another example of making the most of the pandemic to finish an important development, Danobat's new generation of OD/ID grinders, called CG machines, can apply conventional abrasives at wheel speeds of 80 m/s (16,000 sfpm), using standard equipment. This boosts productivity up to 20 percent in many applications.

That's according to Danel Epelde, Danobat's business development director, based in Elgoibar, Spain and Humble, Texas. He said the CG also offers nearly 100 percent availability, thanks to smart engineering that reduces component count, remote diagnostics, predictive maintenance, and Danobat's experience in producing machines for high-volume production. What's more, the CG's unusual cross-slide design and swiveling B-axis wheelhead make it capable of grinding a wide variety of part sizes and geometries (including non-round parts) in a compact space.

A number of additional factors contribute to the CG's ability to achieve this rare combination of benefits, explained Epelde. "We use linear motors for all linear axes and direct drive motors for all the rotary axes. And Danobat also uses natural granite for the machine base, which is better than synthetic granite or other materials in terms of vibration dampening, temperature stability, and stiffness. The machine can also be customized to suit specific needs. You can choose from a wide range of wheelhead configurations and add measuring systems, conventional or self-centering steady rests, counter spindles, automatic taper correction, super-finishing stations, deburring systems, laser gauges, and more." Applications range from gears and shafts to CV joints, drills, and screw compressors.

As U.S. distributor Daniel Rey, of Rey Technologies, St. Charles, Illinois put it, "the CG is a perfect fit for the U.S. market, because most customers here want a versatile solution, even if they’re sure the current job will run for a long time. And everyone loves the higher throughput you can get from these wheel speeds. We look forward to showing off the new machine at our demo center near Houston."

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