Accelerated grinding

Adapting a CNC grinder with conventional abrasives to use Meister CBN grinding wheels improved productivity 15-fold in plunge-grinding close-tolerance aerospace parts. The Rockford, Illinois, plant of Woodward Inc. successfully addressed this manufacturing bottleneck while reducing projected expenditures for additional grinding equipment to make similar parts. Additionally, it received a payback on equipment modifications in less than a year.

These results came from modifying the manufacturing process for an aerospace pump gear made of soft A11 tool steel hardened to 75HRc.

According to Steve Dietrich, pump gear-manufacturing cell operator, the specifications for this part leave no room for burning or microscopic cracking as revealed by eddy current testing. Since the original ceramic wheel used in this application tended to load quickly and generate excessive heat, it was necessary to operate the grinder at very slow speeds and to stop the process frequently to dress the wheel. Those conditions cut the grinder’s cycle time to one part every 2-1/2 hours.
 

Moving carefully

Blackhawk Industrial, Woodward’s manufacturing supplies integrator, initially approached Woodward with the concept of improving grinding efficiency by retrofitting selected conventional-abrasive grinders with cubic boron-nitride (CBN) wheels. Blackhawk then introduced Woodward’s manufacturing engineers to Meister Abrasives USA, in North Kingstown, Rhode Island, which provided wheels, dressers, and technical support as the company converted an existing Okuma grinder to CBN capabilities.

Tim Vinz, account manager for Blackhawk says, “The success of that project gave the company the confidence to move forward on the aerospace project, which had a much higher potential for dramatic productivity improvements. Woodward worked closely with Meister throughout several months, carefully developing process, wheel, and dresser specifications for its retrofitted CBN wheel process.”

Meister’s Midwest Sales/Applications Engineer Tom Cappadona notes that adapting the CBN wheel for use on the Studer S33 shaft and gear-grinding machine required the addition of several pieces of peripheral equipment.

Acoustic sensors provide a real-time indication of wheel pressure during grinding to indicate the quality of dress based on the consistency of noise generated by the dresser moving across the wheel. A high frequency dresser with programmable speed control was added. A chiller keeps coolant temperature at 73°F to assure repeatable high surface finishes (3Ra to 4Ra), even while operating at high grinding surface speeds. Finishing the machine additions were an auto balancer for the grinding wheel and a CBN wheel and diamond dresser – a Meister vitrified CBN wheel and rotary hybrid diamond dresser (hDD). The retrofitted equipment added approximately $55,000 in up-front costs to the project.

Economic analysis

Woodward Manufacturing Engineer Geoff Means says, “Within days of installing the new process, it was clear that it would achieve significant productivity improvements without burning or cracking the parts. We went from making less than one part an hour to up to 15 an hour. Those were our most dramatic results. However, we are running several families of similar parts and getting very good machine cycles with them as well.”

Means adds that one of the biggest surprises “was that the per-part wheel costs for CBN versus ceramic for this application was significantly less, even though the CBN wheel cost us about $7,000 compared to $600 for the ceramic product. The CBN wheel was still in good condition after 6 months and is likely to last more than a year.”

The Meister rotary hDD dresser produced a free cutting wheel after precisely removing a thin layer of material from the CBN wheel face. Dietrich reports that this fine incremental dressing process has resulted in better dimensional control, reducing the amount of time the operator has to spend watching over and adjusting the equipment.

Means says engineers at this plant are now looking at other applications that could benefit from using a CBN wheel on a conventional-abrasive grinder, and they are not the only ones. Word of process improvements travels fast at Woodward, and engineers at the company’s facility in Ft. Collins, Colorado, are making a similar assessment.

Meister Abrasives USA
www.meister-abrasives-usa.com

Woodward Inc.
www.woodward.com