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Grinding thin-wall cylinders.

Grinding thin-wall cylinders

A complete rebuild program for a 20-yr-old centerless grinder, including CNC control, precision servo drives, and closed-loop inspection features, provided higher quality and production rates for cylinder liners for an engine manufacturer. The early stages of processing hardened cast-iron liners had proved that thin-walled cylindrical components and centerless grinding don't always mix. The pressure of the regulating wheel and grinding wheel on the liner compressed the part in nearly every case, causing it to spring back egg-shaped.

This condition might have been acceptable if the parts were within size specifications, but this could not be accomplished even when a dwell was added at the end of the grinding cycle. A major contributor was the inability of the 20-yr-old grinding machine with a hydraulic drive system to accurately repeat to a set zero feed point during the dwell.

One option was purchasing new equipment. The second was to contact Grinders Clearing House, specialists in rebuilding and remanufacture of grinding equipment, for an evaluation of the existing machine. After a thorough review, GCH proposed and was given approval for a rebuild program that included precision electrical servo drives, load monitor, closed-loop in-process and post-process gaging, two-axis CNC wheel dressing, and a variable-speed transmission, all tied to the latest Allen-Bradley CNC.

Where previously the parts were as much as 0.0025" out-of-round and with up to 0.001" of taper, the "new" machine grinds liners to within 0.0006" and 0.0003" limits, respectively. Much of the credit is due to the rebuilt machine's feed repeatability of 0.000 050" provided by the servo drives. Also, exact dwell times and pressure is regulated by data relayed to the control by inprocess gaging for consistent output, while surface speeds are modified accordingly via the adjustable transmission. Load sensors continually monitor parts so the CNC can make automatic alterations in feeds and speeds when excess grind stock is encountered.

Post-process gaging inspects parts for taper. When set limits are approached, the CNC activates an automatic dressing of the grinding wheel. This controls taper, and because wheel dressing is done during the load cycle, adds no downtime.

Although higher quality was the primary incentive here, productivity should not be overlooked. Liners are now ground at a rate of three/min compared to an average of one/min previously. Since both output and quality improved at a cost of two manufacturer is confident it chose the right option.

For more information, Grinders Clearing House Inc, 13301 East Eight Mile Rd, Warren, MI 48089 or circle 382.
COPYRIGHT 1989 Nelson Publishing
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Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Publication:Tooling & Production
Date:Nov 1, 1989
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