Custom cutters control costs.
High-volume manufacturers of heavy equipment traditionally employ transfer lines using specialized tooling designed to ensure maximum efficiency on long production runs. The development of special tools is often aided by manufacturers' representatives who initiate and facilitate the process.
In a challenging application at a major U.S. producer of diesel engines, manufacturer's representative Dave O'Brien of Tech Reps, Zionsville, lad., coordinated the development of milling cutters that reduced tooling costs and production downtime.
The operation, which took place on a Lamb transfer line, involved milling two sets of radii in bosses on a ductile iron engine head. The radii hold rocker arm shafts of two different diameters. Two different cutters, mounted together on an arbor, finish-milled the bosses. One cutter was 10.921" in diameter and 1.378" thick, and the other was 10.0 in diameter and 1.717" thick. Each cutter had 24 carbide blanks brazed into a steel body.
After an OD grinder created the radii on the carbide teeth, the teeth received a clearance grind. Generating the clearance without affecting the radius form was difficult and time consuming. Grinding the complex form was difficult, because it "was a radius on a helix," O'Brien said. "It would be much easier to do if each tooth [had a] 0░ helix and 0░ radial rake, but that isn't the case with these cutters. You've got all this compound geometry going on."
Correct radius form was crucial in meeting the tolerance requirement of ▒50Ám. Although it was possible to adjust the cutter up and down and side to side in the machine, "there was no way to adjust the form that you were cut ting," O'Brien said.
Tolerance of the finished radii was measured by gaging the finished heads with a coordinate measuring machine. Cutters typically finished bosses on 3,000 to 3,500 heads before wear made regrinding of the carbide teeth necessary.
Mounting the cutters on the arbor and installing them in the machine was a lengthy process, making long tool life a key to minimizing downtime.
The engine manufacturer discussed with O'Brien the possibility of developing a replaceable-insert cutter that would reduce the cost of tool fabrication and regrinding. O'Brien approached special toolmaker Continental Carbide Ltd., Clinton Township, Mich. "With the expertise and equipment they had, [Continental] wanted to give it a shot," he said.
Development of the insert cutter evolved over a period of about 9 months. In the first design, one insert cut half the radius and the following insert milled the other half. That arrangement, however, was found to produce an irregularity in the radius at the point where the two cuts merged. A subsequent attempt to grind inserts that produced a full-radius cutting edge resulted in a smooth-but inaccurate-radius.
To solve the problem, Dinos Karagounis, Continental Carbide's vice president, asked the engine manufacturer to provide CMM data that showed where the radius form was out of tolerance. He used the information to "tweak" the radius form. "We used their CMM data to help us program our CNC grinder," he said. "We were able to dial in our process to yield for them what they were asking."
The new insert cutters produce significant savings in tooling costs. Buying a Continental cutter loaded with fresh inserts costs less than regrinding a brazed tool.
The insert cutters consistently achieve the required 50Ám tolerance. "Typically, at tool change, we are in the high teens," O'Brien said.
An added benefit is increased tool life. Using the same cutting parameters as those used for the brazed cutters, tool life of the insert cutters has, on occasion, reached 7,000 heads. Typically they produce 4,000 to 5,000 parts, which reduces the number of required tool changes by more than 20 percent.
To ensure maximum precision and consistency, worn cutters are returned to Continental Carbide for inspection, maintenance and insert replacement. To accurately preset the inserts, the toolmaker developed a gage that employs Mylar overlays viewed at extreme magnification.
Karagounis noted that every time a cutter is returned for indexing and presetting, it is checked for pocket-floor damage and hub wear. The cutters are marked with serial numbers so any in consistencies in performance can be tracked to a specific cutter.