MACHINING CENTERS FOR GEAR MAKING

According to Mitsui Seiki USA, Inc. (Franklin Lakes, NJ), several of its customers are successfully cutting 10 to 14 class ring gears in low- to mid-volume applications, such as for aerospace and power generation, on its CNC vertical and horizontal machining centers.

Traditionally, manual gear hobbers or CNC gear cutting machines are employed, however compelling benefits are surfacing in certain applications using highly precise machining centers. In particular, Mitsui Seiki's Vertex machine is suitable for ring gears up to 16 in, and a special gear-making model incorporates a rotary trunnion table for the finish turning operations.

"This machine can turn the gear faces, the final profile of the internal bore, and generate the gear teeth," says Mark Speier, sales engineer at Mitsui Seiki.

"One of the benefits of producing gears on that machine is that the relative gearboxes or gear cases, and even reduction gear boxes, can also be processed on this one machine," adds Speier. "The gear housing is a critically precise piece. The accuracy of both parts has a direct correlation to the transmission performance over the life of the motor. The end product reliability is a positive factor, too. Further, the gear is mounted flat and then turned up 90 deg (or another angle) so that the end mills can cut at the optimum attitude to the gear profile. This results in excellent roughing efficiencies. For finishing, ball nose end mills generate the final profile before heat treating."

Mitsui Seiki's initial foray into gear cutting involved cutting the gear teeth, roughing, and semi-finishing operations prior to heat treating. Now, by adding turning operations to the Vertex machine, accuracies have improved through the single setup for all operations. The company anticipates turning functionality will be available on the HU80A-5X in about 6 months.

"The traditional gear cutting machines may run faster," concedes Speier, "However, the tooling economics, improved accuracy through one setup machining, and improved process control, the overall cost may be advantageous, especially in low volume runs. Plus, this application may enable our current gear making customers to get more use out of their Mitsui Seiki 5-axis machining centers. Our knowledge base is growing exponentially in this area."

One of the key aspects to successful gear cutting on a Mitsui Seiki machining center is software. CNC Software, Inc., developers of Mastercam has generated the optimum toolpaths for spiral bevel gear cutting and has been an integral partner in this area with Mitsui Seiki.

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