ROCKFORD, IL— Adapting a CNC grinder with conventional abrasives to use Meister CBN grinding wheels has resulted in a 15x productivity improvement for plunge grinding close tolerance aerospace parts at Woodward, Inc., producer of high-precision components and systems for the Aerospace and Energy Industries. This innovative process change has broken a perplexing manufacturing bottleneck, reduced multi-year projected expenditures for acquiring additional grinding equipment to make similar parts, and has resulted in a payback on necessary equipment modifications in less than a year.
Steve Dietrich: “The specifications for this part leave absolutely no room for burning or microscopic cracking.”
These results were achieved by modifying the manufacturing process for an aerospace pump gear made of “soft” A11 tool steel and hardened to 75 HRc. According to Steve Dietrich, who operates the pump gear manufacturing cell, the specifications for this part leave absolutely 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 up quickly and generate excessive amounts of heat, it was necessary to operate the grinder at very slow speeds and to stop the process frequently to dress the wheel. Under these conditions the grinder was producing only one part every 2 ½ 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 CBN wheels. Blackhawk then introduced the Woodward Manufacturing Engineers to Meister Abrasives USA, (North Kingstown, RI) which provided wheels, dressers, and technical support as the company tested the approach by converting an existing Okuma grinder to CBN capabilities.
Tim Vinz, Account Manager for Blackhawk said: “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 over several months, carefully developing process, wheel, and dresser specifications for its retrofitted CBN wheel process.”
Meister’s Midwest Sales/Applications Engineer, Tom Cappadona explained how adapting the CBN wheel for use on the Studer S33 shaft and gear grinding machine required the addition of several pieces of peripheral equipment to the machine:
- Acoustic Sensor: Provides a real time indication of wheel pressure during grinding and indicates the quality of dress based on the consistency of noise generated by the dresser as it moves across the wheel.
- High Frequency Dresser with programmable speed control.
- Chiller: To keep coolant temperature at a consistent 73°F to assure repeatable surface finishes (3 – 4 Ra) even while operating at high grinding surface speeds.
- Auto Balancer for the grinding wheel.
- CBN Wheel and Diamond Dresser: Meister vitrified CBN wheel and rotary hDD (Hybrid Diamond Dresser).
This retrofitted equipment added approximately $55 thousand in up-front costs to the project.
The full CBN retrofit cost $55 thousand, but reduced the total cost per part from $202 to $11.
Economic Analysis
The new process went on line in November of 2012. Woodward Manufacturing Engineer, Geoff Means said, “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 a 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.”
To illustrate this point, Woodward and Meister USA collaborated on a 6-month study to evaluate the economic benefit of switching from ceramic to CBN wheels for this process. The following table summarizes some particularly impressive results on one of Woodward’s most challenging parts.
Table 1: Economic Impact of Replacing Ceramic Wheel with CBN Wheel and Rotary Diamond Dresser
| Ceramic Wheel | CBN wheel & hDD dresser | |
| Cycle Time (min) | 150 | 10 |
| Parts ground/hour | 0.4 | 6 |
| Dressing frequency | 32 dresses/part | 8 parts/dress |
| Parts per wheel | 16 | 4444 |
| Wheel cost/part | $31 | $1.60 |
| Dresser cost/part | $0.7 | $0.07 |
| Grind time cost/part | $137 | $9 |
| Dress cycle cost/part | $24 | $0.11 |
| Wheel change cost/part | $2.58 | $0.01 |
| Total cost per part | $ 202 | $11 |
“One of the things that surprised us the most,” said Means, “was that the per part wheel costs for CBN vs Ceramic for this application was significantly less, even though the CBN wheel cost us about $7000 [plus 1 backup wheel and a dressing disk] compared to $6oo for the ceramic product. The CBN wheel was still in good condition after 6 months and is likely to last more than year.”
The Meister rotary hDD dresser produced a very 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 said engineers at this plant are now looking at other applications that could benefit from the use of 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, CO are making a similar assessment.
