GETTING IN GEAR

When a rebuilt CMM from the 1970s that was being used for gear inspection lost its repeatability, this specialty transmission manufacturer replaced it with a bridge-type CMM equipped with inspection software and a level of basic gear measuring capability that optimized the inspection process and improved measurement variation by over 200 percent.

Cotta Transmission Company LLC (Beloit, WI) is a privately-held manufacturer of precision-engineered transmissions, speed increasers and reducers, direct- or remote-mount transfer cases, split shaft power take offs, creep and heavy-duty pump drives, custom transmissions, and reversing drives for vocational trucks, defense, off-highway, aerospace, heavy industry, well-drilling, mining, marine and other applications.

Its 70,000 sq ft facility is a showcase of lean manufacturing capabilities, 5S techniques, efficiency and process flow that all come together to improve standardization and ensure the delivery of the company’s most important product: quality. Cotta designs in accordance with American Gear Manufacturers Association standards, so adherence to a rigid Supplier Certification and Selection program ensures constant control of material quality. In fact, quality is monitored systematically and comprehensively throughout the entire operation. First-piece inspection is conducted on every machining sequence, focusing on quality at the source to support a “zero-defect” policy. Every transmission is assembled and tested and backed by an excellent standard warranty.

With such an intense focus on quality, it may come as a surprise that only two years ago the shop was still using a rebuilt coordinate measuring machine (CMM) from the 1970s for gear inspection. “When I joined the company, the organization was already extremely discontent with their current CMM equipment,” states quality manager Todd Wells. “The CMM operators were actually using the old DCC CMM as a manual machine because of fears it would crash. They would often re-inspect a product multiple times because they had little confidence in the results.”

A team was assembled to rectify the situation. “The old CMM that we were using had been rebuilt once already, and when we conducted an accuracy study it was obvious it was not repeatable anymore,” recalls Wells. “For example, we performed one study where the same part was inspected several times on a program that was written to run in automatic mode. The measurement results varied more than 220 percent from the required design tolerance.”

With this new knowledge of the rebuilt machine’s inability to repeat, the team mandated sub-contracted CMM inspection for specific parts with tolerances that were too critical for the old CMM until a new system could be purchased. “We estimated that our work level would require an expenditure of at least $100,000 over the next 12 months to accommodate sub-contracting to an outside CMM service,” says Wells. “We needed a new CMM to insure our commitment to meet the needs of our customers and to continue to deliver a competitively priced quality product on time.

After reviewing several systems, the team wanted to purchase a Wenzel LH 12.30.10 bridge-type CMM with a measuring envelope of 1200 mm x 3000 mm x 1000 mm that provides adequate table capacity for some of the larger transfer cases that Cotta produces. With this equipment design the Y-axis guideway is machined directly into the granite base plate, providing optimal long-term accuracy and stability. The machine can reach a 3D measuring speed of 700 mm/sec with maximum acceleration of 2,000mm/sec². It is equipped with a Renishaw PH10M probing system and a HT400 teach pedant that eliminates the tedious keyboard interaction necessary with conventional CMM teach pendants.

The team also wanted OpenDMIS software, but they were not confident that their budget or timing requirements would permit it. So they contacted Xspect Solutions (Wixom, MI), the Wenzel operation in North America and wholly-owned subsidiary of Wenzel GmbH of Germany that is the number three supplier of both traditional CMMs and GMMs (gear measuring machines) to the North American metrology market. They discussed their situation with regional sales manager Nick Moceri and Keith Mills, the president of Xspect.