Shop Solutions: Gearmaker Wins with Advanced Grinding
Milwaukee Gear (Milwaukee, WI) was founded in a small downtown Milwaukee one-story brick building by two men in 1918, Emil Borisch and Walter Kohls, who were the company’s salesmen, machinists, order clerks and inspectors. By 1953, the family-owned company had moved to its current sprawling 180,000 ft2 (16,722-m2) facility. It was acquired by a private equity group in 2008 and subsequently sold in early 2012 to Regal Beloit Corp. Today Milwaukee Gear employs about 220 and operates as a unit of Regal Beloit America Inc.
“We manufacture gears and pinions for a variety of industries—air and gas compression, oil, gas and coal mining, construction equipment, cranes and hoists, different types of air-moving equipment, fans and blowers, refrigeration chillers and speed reduction/increase gear cases,” said Joe Leone, manager quality control/gear grind. “Customers come to us with their designs. Our engineering group uses the latest gear ratings software to optimize their applications, and then we manufacture the gearing to spec for them. In some cases, we will manufacture housings and do complete gearbox assembly. However, most of the time our customers do their assembly in their own facilities and we supply the loose gearing.”
Milwaukee Gear basically works from the raw material stage to a finished component, including machining, heat treat and all the processes in between. “We work in steel, typically a carburizing grade of 9310, 4320, 8620 or 17Cr Ni Mo6 bearing quality. I’d say 90% of our gearing is carburized and hardened,” said Leone. “We’ll use bar stock, die forgings, hand-hammered forgings in many different steel configurations. We purchase the raw material, do all the pre-heat treat machining, turning of surfaces, drilling and threading, and machine keyways or splines if required. We have full in-house heat-treating capability and metallurgical control. The case-hardening process involves gas carburizing and polymer or oil quench in an atmosphere-controlled integral furnace. And then we do all of the post-heat treat machining, which includes OD/ID grinding, and, of course, gear tooth grinding, which is our core competency.”
Milwaukee Gear prides itself on always having the very best equipment and being second to none in investment in advanced technology. In 2005, the company acquired a Studer S40 universal grinder from United Grinding Technologies (Miamisburg, OH). “Not only is it still running today, seven years after first being installed, but the S40 is still operating as our primary OD grinding machine. Many of the parts that we manufacture have a dimensional size requirement of ±0.0002" [0.005 mm], which is one of our tightest size tolerances. We confine the Studers to only our highest precision gears, pinions and shafts, because once you attain size, the Studers are reliable and accurate and amazingly repeatable—piece after piece after piece. The size range on the Studer S40 is 15" [381 mm] in diameter by 63" [1.6 m] in length.” A Studer S33 universal grinder with a size range of 2.9" (74-mm) diameter and a length of 39.4" (1 m) was purchased later to do a specific line of products.
Both CNC universal cylindrical grinders are designed for grinding medium-sized workpieces in individual and series production. They feature a solid Granitan S103 machine base and Studer Grind software with proven pictogramming that allows even less-experienced users to quickly optimize the potential of the machine and enables efficient programming of special applications, such as form and thread grinding. Changeover from grinding between centers to live spindle grinding is easy on the Studers. Only a few movements are needed to withdraw the tailstock to its “park” position and free up space required for internal grinding. Reference points from grinding wheels to dressing tool and workpiece can be registered very quickly with the help of Quick-Set, Studer’s software-controlled setup device.
“The Quick-Set programming allows us to grind any part as long as we have a program for it,” said Venu “Vinny” Gupta, Studer operator and setup man. “With Quick-Set, you put the part in, bring the program down, offsets up and run the part. I can change from one part to another in 30 minutes. This is especially true if we’re doing similar or a family of parts. Whether you’re running an S40, or S33, all the software is identical, so an operator can go from an S40 to the S33 with virtually no retraining. The Studers are a very precise and reliable machine. On surface finishes we can get 8, 6 or 4 micro—you name it, the Studers can deliver. Generally we’re getting a 6 micro requirement on surface finish.”
Milwaukee Gear chose the S40 “largely because of Studer’s strong reputation for quality, precision and repeatability,” said Leone. “What really swung the decision was the Quick-Set package, which allows us to set up and start running a job sooner. Keep in mind we’re a job shop. We aren’t running the same product line day after day as you might find it in the automotive industry. We have lots of setups and part turnovers. Because of our small lot sizes, setup and changeover are not just measurements in time, but an indicator of our overall efficiency. That’s what sold us on the purchase of the S40 and later the S33.”
“The B axis on the S40 can swivel in any direction with a positioning resolution of 0.0001° to grind tapers, angles, contours and whatever you need, you can grind,” said Gupta. “We have two grinding wheels on both machines, so we can put different size wheels with different radii configurations, thus giving us considerably more capability and adding to our overall efficiency.”
“We produce gearing for the high-speed compressor industry, which is one quality level down from aerospace gearing,” Leone said. “To get maximum efficiency, the OEM will utilize a drive ratio with a 1 1/2" [38-mm] diameter gear tooth pinion driven with a 35" [889-mm] diameter gear. These pinions can run up to 75,000 rpm. There are impellers assembled and precision balanced, and there are very tight fits within the housing of the compressors, so the diameter sizes have to be tightly toleranced and controlled. Again, ±0.0002" [0.005 mm] is a common tolerance for these pinions, and concentricity of these diameters is 0.0002" as well. A surface finish of 6 µin. (0.15240 µm) is common. There is an electronic probe (vibration sensor) assembled into the compressors so if the bearings start to wear, and these pinions start to shimmy and shake, when they reach a certain threshold, the compressor will shut down. For that industry the tolerances are critical, and this is probably some of the tightest tolerance work we do here. Again, being a job shop, we do a lot of compressor gearing for different OEMs.”
“In our process,” Leone said, “we are doing OD grinding on both Studers. The S40 was purchased as a universal grinder to do many different types of parts, while the S33, which is more of a base machine, was purchased to do a specific line of parts. Gear-tooth grinding is done on an entirely different machine, one specifically designed to grind precision gear teeth.” ME
For more information from United Grinding Technologies, go to www.grinding.com, or phone 937-847-1229; from Milwaukee Gear go to www.milwgear.com, or phone 414-395-4122.
This article was first published in the October 2013 edition of Manufacturing Engineering magazine. Click here for PDF.