Over 90 years ago, Harley-Davidson began a journey of continuous improvement. More recently, the company made a commitment to reaching a production capacity of 100,000 motorcycles per year. To achieve this, management recognized that world class manufacturing practices were key.
To accomplish these goals, many processes have been streamlined and improved. All three manufacturing facilities have been extensively redesigned and reconfigured to improve productivity, material flow, product quality and the environment. Components were identified as "core competencies" in production, meaning Harley-Davidson would develop the process, become experts in their continuous improvement and keep in-house all responsibility for these areas.
One core competency that has undergone major change is gear production. Current European law mandates more strict noise control. To meet regulations set forth, Harley-Davidson motorcycles were required to reduce noise output. Anticipating that this would soon become standard in other coun-tries as well, the company modified its transmission to include gear ratio changes and high contact tooth geometry.
The new design dictated changes to the manufacturing process. Using Harley-Davidson's "concurrent product development methodology" adopted to achieve the 100,000 unit goal, a team was formed to spearhead the design, manufacturing and equipment changes. According to project engineer Ron Ackerman, the 100,000 unit goal factors out to 430 transmissions per day and with ten gears per transmission, the company will produce about one million gears per year.
Team members from product development, manufacturing, metallurgy, quality control and purchasing began to explore how to produce 12 different parts made of 4615 material. The complex profiles with 20-42 teeth and the need for tight tolerances ruled out the traditional machining method of hobbing, shaving and heat treating. Hard honing was not considered to be developed enough for Harley-Davidson's production requirements. Gear grinding using the CBN method was also investigated, but had no track record for this type of application. The team pursued an answer that would allow extremely precise grinding of very tough heat-treated material. Never before had Harley-Davidson ground gears.
A supplier considered to be a grinding expert had met with success grinding similar materials using a gear grinding machine from Reishauer Corp. (Elgin, Illinois), the Reishauer RZ 301AS. The RZ 362A was developed to grind especially hard materials economically. This method for grinding on the RZ 362A was new to the United States and Harley-Davidson was the first US user in full production.
Applying the principle of shift grinding, which can be compared with continuous dressing or creep feed, the machine continuously presents new parts of the grinding worm to the gear as it is ground. This continuous shift process is used for both roughing and finishing passes even on precision gears. For this application, a modification in the coolant nozzle eliminates any burning.
During Phase I of the transition to the new gear design, Harley-Davidson selected a supplier to grind the gears and train operators on the gear grinder. By the time Harley-Davidson took delivery and installed its first five machines (in Phase II of the transition), the operators were ready. "When our machines were put into service we already knew they would meet our requirements on reliability, repeatability and productivity," said Mr. Ackerman. "We planned for these machines to be in operation...and we had no time for process development once they were in."
Features Mr. Ackerman pointed out as advantageous on the RZ 362A machines are automatic fine balancing of the wheel which provides outstanding repeatability, flexibility in the dressing tool, coupled with the RP1SW dressing unit, and quick changeover time on the six diamond dressing rolls. A new stock divider design has eliminated the possibility of violating case depth specifications and assures even stock removal. Because this is accomplished accurately "on the fly," production is not slowed.
ABB (Asea Brown Boveri) robotics coupled with an automated part identification probe has increased quality and productivity up to 30 percent in Harley-Davidson's process. "We weighed the advantages of equipping each machine with its own robot versus sharing one robot between two machines," states Mr. Ackerman. "Our team conducted a cost analysis that made it clear to us that idling the capital investment of the grinding machines to wait for the much less costly robot was not cost efficient. This way, all machines stay in production with very little idle time, making it less complicated for us to meet productivity requirements." Unproductive time is virtually eliminated because load and unload sequencing happens simultaneously.
The oversized robots, designed to accommodate future gear design, are able to pick up an entire basket of parts to load the washer. The result is door-to-door cycle time of 11.3 seconds, and overall grinding time of 56 seconds.
A final, important component in the company's world class manufacturing practices is its commitment to protecting the environment. "Housekeeping is a direct reflection on quality," notes Mr. Ackerman. Modifications to the machine to reduce oil carryout are in place and continuously being improved. Process heat is redirected to provide heat for work areas. In addition, an energy credit was realized because of high efficiency motors and pumps as well as roof-mounted condensers to service the machine. MMSblog comments powered by Disqus