Twin Disk doubled grinding output of drive shafts for marine and other types of transmissions.
Twin Disc of Racine, Wis., needed to change its transmission driveshaft grinding operations that were too labor intensive [PI1]and involved moving shafts from one process and machine to the next. What the shop wanted was a grinder with a full B axis that would combine processes on a single machine flexible enough to handle various different shaft types.
As a manufacturer of transmissions for watercraft, over-the-road heavyduty trucks and military vehicles, Twin Disc produces about 1,200 different types of transmission drive shafts, with order quantities ranging from one to 500 pieces. Shafts measure between 8 in. and 48-in. long with diameters of 0.500 in. to 10 in., can weigh anywhere from 1 lb to 350 lb, and can have several different tapers[PI2]. Surface-finish requirements run between 10 Ra and 40 Ra for the shafts, made mostly from 1144, C1144, 4145, 4140, 8620 and some stainless.
When the shop started searching for a grinder, Terry Andersen, team leader, programmer and machine operator in Twin Disc's grinding area, says there were not many to choose from, mainly because the dimensions of some of the shafts, especially those weighing 350 lb, eliminated a lot of possibilities right off the bat. The machine that did finally fulfill the shop's demands was a Kellenberger Kel-Varia cylindrical grinding system from Hardinge (www.hardinge.com) with a Heidenhain GRINDplusIT control. Andersen reports that since the shop runs so many different shaft types, changeovers and setups are common occurrences, a task he finds easy to perform on the Kel-Varia. "Depending on what's involved, we can changeover from shaft to shaft in about 10 min, especially if we're not changing centers, and it's strictly a matter of moving the tailstock and changing the driver. If we have to change centers and drivers and other things, then we may be up and grinding in 20 min or less, which is pretty amazing when you consider the volume and variety of shaft work we do here, day in and day out."
The Kel-Varia also handles Twin Disc's tapering operations, which involve tolerances of 0.0002 in. to 0.001 in. The shop runs about five different shaft tapers that, for some jobs, is nothing more than a press fit. Andersen says the tapers are absolutely critical and must be done on a machine that can repeatably and consistently hold extremely tight tolerances. Most taper surfaces are 40 Ra, but some tapers have angles of 30 to 1, less than a one-degree taper. About a year after purchasing the shop's first Kellenberger grinder, Gary Pope, plant manager at Twin Disc, bought a second Kel-Varia with a hydraulic tailstock for handling even heavier shaft work. "We used to have two grinding cells, and the process was slow and labor intensive," says Pope. Operators had to fixture and refixture shafts from O.D. grinders to a plunge grinder that did shaft tapers, a step that caused bottlenecks and hindered the shop's ability to improve productivity.
The two Kel-Varias reside within a single production cell, and one operator handles both machines, pumping out twice as much product as before. Two shafts run simultaneously and come off the machines that are working six days a week, 24 hours a day, completely and accurately finished.
Powerful motors and fast control systems on the grinders ensure high dynamic unround and threadgrinding operations. The machines also feature absolute measuring in the B axis, incremental distance-coded scales in the X and Z axes, ultrahigh resolution in the C axis and expansion options with the addition of a second B axis for dimensional stability and profile accuracy.