Saturn Industries grinds a lot gears, and the company uses GU4-R universal grinder to ensure and face surfaces run true to each other
This bearing cage with numerous blended angles and radii on both its I.D. and O.D. are no problem for Merrill Tool’s Toyoda GU4 universal grinder.
Toyoda universal grinders get their rigid vibration-dampening spindles from the company's Stat bearing design, which metal contact.
Manufacturing these tank-engine seals would have been a job Saturn Industries turned down if it weren’t for its GU4-R grinder.
Some jobshops continue to shy away from CNC universal grinding machines. They expect them to be complicated and time-consuming, often having multiple diamond locations and requiring users to keep track of three different wheels. In addition, programming is usually thought of as difficult and taking longer than the part cycle time itself. However, new developments in the machine and CNC minimize these negative aspects of universal grinding.
Three of those technological developments include single diamond location, position memory in the software, and controllers with pre-programmed cycles for tracking wheel diameters in every mode. And because of the affordability of technology, says Steven Ewers of Toyoda, Wixom, Mich., universal grinding is indeed becoming the norm for shops with more than one type of application.
Manual or automatic
The wheelhead on a universal grinding machine swivels one of two ways, either manually or controlled automatically through the machine's CNC. With a manual-type head, operators, during a pause in the part program, open the door and index the wheelhead to the needed. These grinders offer the flexibility to complete O.D., I.D., and angle-head work machine. As compared to a fixed-wheel CNC machine with an I.D. attachment, universal grinders deliver much more capibility, which is exactly why & Merrill Tool & Machine (MTM) Inc. of Merrill, Mich., purchased its Toyoda GU4 manual-type universal grinder.
Primarily, the jobshop produces various parts and subassemblies for OEMs and initially acquired the grinder for a bearing-race prototype job for Delphi. MTM went universal because it wanted a single ma-chine that did complete parts accurately and consistently.
The company previously ground the races on manual machines but needed volumes — the wanted 1,500 pieces MTM also had to have quick changeovers. The GU4's indexing head, automatic contour wheel dressing, and easy programming, says Jeff Yackel, vice president of MTM, make job changeovers fast.
The GU4's head accurately indexes in 5° increments from 0 to 180° (180° being the back I.D. wheel). "It is versatile," says MTM GU4 operator Bill Schimdt. "In-stead of having to tilt a machine's head or the part, we simply program these moves into the new grinder." For tapers, such as on the bearing cages, the shop would have had to turn the heads on its other grinders and then sine them into place.
According to Yackel, in a job-shop environment doing "onesytwosy-type" jobs, cutting cycle time is not always as crucial as being able to quickly set up for the next job. "If we were running 10,000-piece jobs, then cycle time would matter more, and we probably would have opted for an automatic swiveling wheelhead," he says.
Before going universal for the bearing cages, the shop had to manually dress a wheel radius, grind it on the part, dress the next radius, grind it, and so on. In addition, operators had to use a readout, which the shop installed on the machine, to repeat back to original locations.
"Just dressing a wheel could take as long as 1 1 /2 hours," says Yackel. "That's longer than it takes to grind a bearing race, which takes about 10 min. Now with the GU4, we grind the part in 2 min and dress in 5 min." Operators simply generate points from a CAD system and plug them into the machine's CNC to automatically contour wheels. This, he says, is why wheel shape is so repeatable with the GU4.
As far as programming is concerned, MTM does a lot at the machine, and the GU4, fill-in-the-blank-type programming makes it easy. All essential data for grinding conditions are input at one time and on one screen. The machine automatically determines parameters for both external and internal grinding, but these can be modified based on an operator's know-how.
Yackel says that the biggest hurdle involved with universal grinders is justifying that type of machine for jobs with between 5 and 12 parts. But, in the long run, he believes the machine's versatility will let the shop take on other jobs.
"Jobshops are somewhat reluctant to move beyond old-style mechanical or hydraulic-type machines," he says. "But what happens is that, once part numbers increase, CNC universal grinding machines become more attractive."
Increased part numbers, along with a need for multiple part-surface trueness, are precisely the reasons Saturn Industries Inc. in Warren, Mich., made the transition to a universal grinding machine. About 95% of the shop's work is for the military, and the amount of parts per job is quite high, according to Saturn President James Campeau.
"Having a CNC-controlled B axis (auto-swivel wheelhead) makes large production runs feasible. With wheel changing automated and included in the part program, shops such as Saturn can complete lots numbering in the thousands, which is simply not practical with manual changes," says Campeau.
"Larger jobshops can not necessarily control their workloads at all times," says Toyoda's Ewers. "They may have a period of time where 80% of what they are doing is O.D. grinding, and a few weeks or months later, their production schedules require 70% I.D. work. Universal grinders provide that type of flexibility for a moderate additional investment. So the primary benefit from the automatic-swivel wheel-head capacity to address I.D. and O.D. wheels in chucking."
At Saturn, gearboxes, hydraulic gear pumps, and sophisticated assemblies make up the bulk of the shop's military work. And when it comes to the internal gears for the pumps, it is critical that the I.D.s and face surfaces run completely true to each other. "This is why we needed the I.D./O.D.-combination head of a universal machine, and in particular, one with a head that swivels automatically," states Campeau. The shop runs the gears on a Toyoda GU4-R, which uses a servomotor together with a precision coupling to accurately swivel its wheelhead. For O.D. wheels, the head's spindle is a rigid hybrid type with Toyoda's Stat bearing design, which has no metal-to-metal contact and high vibrationdampening qualities.
At rest, hydrostatic pressure firmly holds the spindle at its center position. While rotating, both hydrostatic and hydrodynamic pressures provide rigidity and dampen vibration.
Operators at Saturn chuck a gear and kiss the face surface with the machine's head angled. Then the head automatically indexes, and they grind the I.D. Previously, the shop would farm out these parts and end up reworking about 30% of them. According to Campeau,part types vary at Saturn, and operators must often changeover the GU4-R. Its CNC, relieves operators of many decisions as compared to running manual-type grinders.
Jobs done on the new grinder often consist of a few hundred pieces, but they involve a great deal of intricate grinding. For example, total tolerance on a tank-engine seal machined at Saturn must be held within 0.0002 in. The 430 stainless steel part is first heat treated then ground, and once again, diameter and face surfaces must run true to a center hole.
The shop grinds all the part features on the GU4-R, and, comments Campeau, the shop wouldn't have dreamed of tackling such a job if it didn't have universal grinding capabilities. "The more that can be done in one chucking the better," he adds, "because most parts will match up with other parts." Having accurately ground parts, of course, makes final assemblies more precise and fit together smoothly.
According to Gabe Boucher, plant manager at Saturn, part setups on the GU4-R take one-fifth the time as compared to a manual machine. The shop's programmer enters in the numbers, and the machine's control does all the complicated trigonometry. In addition, the machine automatically dresses wheels at certain programmed intervals, and afterwards makes the necessary offset adjustments to accommodate the dressing amount.