Ground to order: Inspection Efficiency

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END USER: General Broach Co., (517) 458-7555, www.generalbroach.com. CHALLENGE: Increase capacity and maintain quality while grinding broaches for aerospace applications. SOLUTION: CNC surface and creep-feed grinder with auxiliary grinding head and large work volume. SOLUTION PROVIDERS: United Grinding Technologies Inc., (937) 847-1214, www.grinding.com; and Tooling Systems Sales Inc., (248) 656-2035

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General Broach Co., Morenci, Mich., designs and manufactures broaching tools and machines and provides broaching services. GBC puts special emphasis on tools and machines to broach aerospace parts.

In broaching, a tool with a series of progressively larger teeth is drawn through or across a workpiece to create a feature, usually an irregular shape such as a keyway or spline. In succession, the teeth rough, semifinish and finish the desired form. Broaching generally is performed on a specialized broaching machine in a single pass. “The broach kind of whittles away at the part,” said Larry Stover, general manager of GBC’s broach tool division.

Courtesy of General Broach

General Broach employs a Blohm Planomat CNC surface and profile grinder to produce broach tool segments with complex “fir-tree” profiles.

Typical of the aerospace part features cut with GBC broaches are slots in titanium or nickel-base alloy turbine engine compressor discs. The slots hold turbine blades around the disc periphery and are generally broached to an irregular V-shape that resembles a fir tree. A single turbine disc may require 90 to 100 slots.

View this brief video to see an animated demonstration of slot broaching.

Depending on the disc being machined, a full set of broaches may consist of eight to 10 segments of tools that together measure 100 ” to 300 ” in length. Individual segments range from 4 ” to 39 ” long, 0.6250 ” to 2.5 ” wide and 1.0 ” to 2.5 ” high. In the first segments in a set, the teeth usually are simple shapes. In succeeding segments, the teeth become larger, change form and eventually reach the final fir-tree configuration. The tools usually are ground from PMT-15 P/M alloy, Stover said, adding that they are rarely coated because most are titanium-based coatings, which chemically react with titanium workpieces.

A few years ago, GBC had been grinding turbine broach segments on a manual 6 “×18 ” Gardner surface grinder fitted with a CNC wheel dresser. As demand for the broaches grew, production speed and capacity became an issue. Stover, then production manager at GBC, set out to find a way to increase capacity.