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Edge Prep Boosts Tool Life

Oct. 19, 2006
As a manufacturer of automobile axle assemblies, the Getrag Axle Plant in Newton, N.C., produces about 1,800 assemblies daily for customers such as GM and Daimler-Chrysler.

EMG tool-edge-preparation reduces gear machine downtime at Getrag.

As a manufacturer of automobile axle assemblies, the Getrag Axle Plant in Newton, N.C., produces about 1,800 assemblies daily for customers such as GM and Daimler-Chrysler. At the heart of the axle assemblies are ring and pinion gears that are machined in a dry gear-generating process. The dry process saves Getrag Axle a significant amount in the purchase and disposal costs of coolants, but it is extremely hard on tooling, and often causes premature tool failure.

According to Tony Trimm, a gear-cutting engineer at Getrag Axle, the shop's largest cost was carbide stick blades. The life of those tools had to be improved to reduce downtime on the gear-generating machine. In one year, Trimm says the shop replaced gear-cutting heads 1,250 times, chewing up about 40 min for each replacement. "We needed to extend carbide blade tool life to minimize this downtime, boost the use of our expensive gear-generating equipment and reduce unproductive labor activity spent changing out and regrinding tools," says Trimm. The shop carried an inventory of carbide worth more than $220,000. However, the diminished use of gear machines was the most significant cost. Trimm says Getrag Axle was losing $600,000 to $1 million per machine each year because of downtime.

Getrag Axle tried to extend blade life in several ways, using different carbide grades, various coatings and different honing techniques, but to no avail. While some of the honing techniques improved tool life, they were not consistent.

What finally delivered consistent tool life improvement for Getrag Axle was an edge-preparation technology called Engineered Micro-Geometry (EMG) from Conicity Technologies ( EMG uses dense silicon-carbide filament brushes applied with computer numerical control (CNC) to consistently and precisely shape tool edges to tolerances of 0.0002 in., an order of magnitude more precise than most conventional honing methods, Conicity says.

After initially outsourcing tool-edge preparation to Conicity and consistently achieving a 50 percent increase in blade life, Getrag Axle installed its own Conicity GXM-50A EMG edge-preparation machine. The system hones 100 blades per hour, taking them directly from Getrag Axle's grinding machines to shorten lead times.

Since incorporating the EMG process, Getrag Axle's use of gear machines has increased so significantly that Trimm says the shop will not need to buy as many new gear machines as it expands capacity, saving millions of dollars in equipment costs. Axle assembly production is expected to grow to 3,000 per day, and the shop now can produce that volume with two or three fewer gear-generating machines. In addition, Getrag Axle's labor cost for changing out blades, regrinding and blade inspection is less, as are blade inventory and replacement costs.

Software within the EMG system's CNC manages all critical process variables for applying the same edge preparation tool after tool at Getrag Axle. Moreover, the shop can apply optimal micro geometries precisely according to the particular requirements of each cutting application. "For our gear-generating application, Conicity determined the optimal edge preparation as a slight radius for good chip roll and making the tool cut more efficiently with less heat generated and less material trapped between the tool and workpiece," says Trimm.