No matter how many Teslas or Bolts you may see along your commute, eMobility—moving vehicles through the use of electricity rather than the internal-combustion engine—is still in its infancy. However, the fact that the traditional car makers as well as startups are showing a commitment to the transition is already making a big impact on how components such as gears are being designed and produced.

“eMobility is changing the gear worlds quite a lot, and for several reasons,” said Antoine Türich, director product management, hard finishing solutions for Munich, Germany-based Gleason Corp. “First of all, there are fewer gears required to drive electric cars than a combustion-engine car. But those gears have much, much higher requirements in terms of quality and noise characteristics as well as torque characteristics. It’s fewer gears, higher quality.

“Also, because an electric motor makes much less noise than a combustion engine, the gearbox itself can become a problem if the gears within the gearbox are noisy. None of the sound is masked by the familiar sound of a gasoline-powered engine.”

In addition, the speed at which the electric-drive gears are turning are magnitudes higher than in a gas engine, Türich pointed out.

“A combustion engine runs at a maximum of 4,000–5,000 rpm and typically, when you’re cruising on the highway, is running at maybe 2,000–3,000 rpm. In contrast, in an electric drive there are systems that reach 20,000 or even 30,000 rpm. Much higher input rpm from the motor compared to a combustion engine also means higher speed on at least the first gear in the in the gear reduction,” he said.

Walter Friedrich, president and CEO, German Machine Tools of America (GMTA), Ann Arbor, Mich., pointed out another change. While the electric drive train itself requires fewer gears, the trend is also for a greater variety in the gears themselves, meaning that part runs are becoming shorter.

“Up until recently, we’d build a machine for an automaker such as General Motors and the machine would be slated for a single part number,” he said, “and that’s all the machine would do for the next four or five years. That doesn’t happen any longer.

“The runs are shorter. But generating gears for GM on their E drive technology, for example, we see ring gears that are very similar, but they come in different variations for different ratios. One comes with, say, 40 teeth. Another one comes with 50 teeth. So, we see a lot of changeover in the machine. Before they bought a machine just for one part, where now they buy a machine for five or six or seven different parts in a part family.”

Ryan W. Moore, sales director of gear technology at EMAG LLC, Farmington Hills, Mich., noted that on top of those trends, the automakers and suppliers are also trying to meet more stringent environmental expectations. “They’re under the microscope to make their processes more environmentally friendly, for the sake of the ecosystem and the health of their own employees—their most valuable resource.” All this is on top of the constant global marketplace pressure of improving throughput and lowering the total cost of production, he noted.

The makers of gear-generating equipment are addressing these challenges in a variety of ways.

Traditionally, gears are ground in a “wet” process, with oil-based coolant used to reduce friction, discharge heat and evacuate the chips. But the use of coolant comes with costs, which EMAG’s Moore enumerated: “You have the cost of the coolant supply unit; you need an oil mist separator; anytime you have oil in the process, you have to wash the gears afterwards. And you usually have additional automation equipment that’s required because you’re going to connect to that washing machine. Also, a separate chiller for the coolant is required.

“Along with the purchase costs of all of these are the costs associated with maintenance; and then there’s added costs for the disposal of the coolant itself and of contaminated chips. All of this takes much more floor space too—and there’s the cost of preventing adverse health and environmental impacts.”

Finally, he noted, the equipment dedicated to the oil treatment—the tanks, high-pressure pumps, filtration unit, etc.—absorb 75 percent of the total energy consumed by a grinding machine.

The traditional grinding approach typically has two passes—roughing and finishing—and the majority of that coolant is needed for the roughing pass, Moore said. “Because after you heat-treat that part, you have distortion in the gear tooth, which makes for unequal stock removal. The grinding wheel has to remove more material from one flank than the other.”

EMAG’s solution is the SU SG 160 Sky Grind machine, which replaces the coolant-assisted grinding-wheel roughing pass with a dry cutting process. Instead of grinding, most of the stock allowance is removed on the first pass with a hobbing tool, which has the advantage of not heating the workpiece excessively.

“We use the carbide skiving hob to remove the bulk of the material versus a roughing pass of the grinding wheel. That leaves a very minimal stock, like 10 µm per side, for the finished pass,” he said. Subsequently, for the finishing pass, a grinding wheel removes the remaining stock without causing problems of overheating the workpiece—a completely dry process.

Moreover, the system uses two spindles actuated by linear motors, and the use of more channels simultaneously enable a time of chip-to-chip of less than two seconds—faster than traditional dual table grinding machines, according to Moore. The no-coolant-needed system is characterized by a smaller footprint and a lower cost of investment for auxiliary equipment. “Just as important, by totally eliminating the need for cutting oils, the machine is [more] environmentally friendly,” Moore said.

According to GMTA’s Walter Friedrich, the company’s Scudding machine line was designed for making internal ring gears as quickly and more economically than the traditional method of broaching. This S line includes models with one or two spindles in either a horizontal or vertical configuration, and in two sizes—the S 240 and the larger S 300.

“Broaching is a fast and reliable process,” Friedrich noted. “But it’s also an expensive process as far as the tooling is concerned. Our system can produce the same quality of internal ring gears—but with a tool that will cost only a fraction of what a broach bar costs.”

At the same time, the two-spindle configuration enables production speed that matches broaching, and the scudding process can be adjusted as needed to compensate for dimensional changes in the part from heat treatment (as described above)—something that broaching isn’t able to do, he pointed out.

In recent years, it’s the vertical models that are proving to be the most in demand with the automotive manufacturers.

“Vertical has a big advantage for round, flat parts because the machine itself can be used as a pickup machine,” he said. “Automation makes it a lot easier to load and unload because the spindle actually goes over to the conveyor and picks up the part,” eliminating a need for intermediate transfer stations.

“For shaft-type applications the horizontal orientation makes more sense. You can load a shaft much easier in a horizontal machine than in a vertical machine.”

As far as Friedrich knows, GMTA is the only company that offers vertical, twin-spindle scudding machines. “That has made the last two years very successful for us. We have had a lot of orders from General Motors and from Magna for the twin-spindle machines,” he said.

A big advantage of the twin-spindle machine is its smaller footprint, taking up much less floor space than two single spindle machines, Friedrich noted.

That’s on top of the volume increase made possible with two spindles doing operations instead of one. But twin spindles enable more than increasing the throughput for a single operation, he pointed out. Two spindles able to double the time it takes to do one operation is good—but even better is the way the system can pass the part from spindle to spindle for successive operations.

“What we do for some applications—at Magna, as an example—is transfer the part between the two spindles for successive operations in order to produce a finished part,” he said.

Gleason’s HFC (for hard finishing cell) system uses a robotic loader to handle the workpiece and employs integrated modules for auxiliary processes, part loading, threaded wheel grinding, washing, marking, measuring and part handling in a palletizer, according to Gleason’s Antoine Türich.

It also shows one of the advantages of in-line part inspection, which eliminates the cost of time needed to remove a part from a machine, taking it to a stand-alone measurement device, inspecting it, and returning it to its next spot in the production process.

That’s the most obvious benefit. Another one is that in-line inspection actually has the effect of loosening those tight tolerances from what they are when using statistical process control to ensure quality.

As Friedrich explained, statistical process control is what enables a manufacturer to get away with only inspecting maybe five percent of the gears they produce and still have the expectation of quality. The only way such a small sample can be adequate is if you ramp up the tolerance requirements way, way beyond what’s needed for the actual operation of the gear.

“So, if your drawing allows you, say, a tolerance of 10 µm and you want to be sure with a sampling of just a few parts that you are 99.9-something percent certain that all inspected gears are within tolerance, then within the sampling you have to use a much tighter tolerance—maybe 5 µm.”

But as the requirements of those high-rpm, silent-running gears increase, the required tolerances get tighter, he said. “And when using statistical process control, we can only use a very small bandwidth. It is really becoming a tough goal because now we are talking about tolerances of about 2 µm. And if you are taking the 2 µm of drawing tolerance and reducing it again by half because of statistical error, then you are within a micron—and then you are getting to the limits of inspection machines.

“That’s why people are looking for inline inspection for up to 100 percent of the parts. Inspecting almost every part to really make sure that they are within the required tolerance for the gear’s functionality removes the need for statistical process control and the burden of even tighter tolerances that it requires.”

However, 100-percent part inspection only makes practical sense if it can be done as fast as the parts are being produced. Gleason’s inspection system, called GRSL, is a gear-rolling system combined with laser scanning that meets that requirement, he said.

The GRSL’s advanced waviness analysis of measurement data is also able to check for critical noise issues, he said. “We’re able to inspect not only for standard geometrical quality issues but also for critical noise topics.