Improving Milling Throughput By 50 Percent With 'Wrong' Insert

Parker Hannifin's Quick Coupling Division (Lincoln, Nebraska) will save at least $87,500 per year by changing over to positive rake cutter and inserts for milling a family of ductile iron couplings. Cycle time per part has dropped one third, elevating production from four to six parts per hour.

The "gummy" ductile iron workpieces exacted heavy penalties on the previous zero rake cutter with flat carbide inserts. The main problems were heavy burring and short tool life. "We perform 12-15 operations per part in this setup," says Al Joseph, manufacturing engineer. "At a yearly production volume of 25,000 parts, extra manual deburring steps and poor tool life inherent in the old method were significant time and cost burdens."

Parker Hannifin switched to the Sandvik Coromant CoroMill 200 cutter with round Waveline inserts in June of 1996. Although the 16-degree positive rake Waveline insert was developed mainly for steel, it worked fine for ductile iron despite its different machining characteristics.

With the new tooling, Parker Hannifin reduced deburring time by 40 percent. Insert life more than doubled, going from 24-32 parts per edge to 64.

The shop also netted an unexpected dividend: higher productivity. The gain arose by starting with the higher recommended speeds and feeds for the new tooling, then pushing beyond them. "Al was really smart to push the tool to its limits," says Lyle Schneider, Sandvik salesman. "The recommended data that comes with the tooling should be thought of as a starting point only."

The combined impact from less deburring time, longer tool life, and improved throughput account for a $3.50 savings per part.

A closer look at the improved operation reveals that: Parker Hannifin runs the couplings continuously three shifts per day on a dedicated 855 horizontal CNC. The castings are made of ductile iron D65-45-12 HB180. The housings measure 1.900 inches thick by 5.5 inches long by 6.75 inches wide. Tolerances are ±0.005 inch. The operation consists of milling three faces—front, top and bottom. Surface finish specifications are 100 RMS. Depth of cut is 0.070 inch. Machining is dry to avoid thermal cracking.

Parker Hannifin's previous cutter had zero-degree seat rake and eight rectangular inserts with zero degree rake. Inserts lasted from 24 to 32 parts per edge.

The CoroMill 200 cutter has positive-rake seat pockets and holds five round inserts with eight edges each. The Waveline insert itself is an RCKT 190600 PM 4030 with sixteen degree top rake. The change to the positive geometry milling arrangement reduced cutting forces, accounting for the increased edge life and reduced burrs.

The doubling of edge life with the Waveline insert translated to a 50 percent reduction in work stoppages for edge changes. "Many shop managers equate longer tooling life only with lower tooling costs, when the more important benefit is the added productivity due to fewer stoppages," says Mr. Schneider. "The value of productivity gains from longer edge life usually outweighs the tooling cost savings by ten to one."

The previous deburring operation, consisting of filing and sanding, has been replaced by one quick step. With the tap of a file, the operator dislodges any small burrs on the surface of the workpiece. This is why deburring time is down by 40 percent.

Why did the steel insert work for the gummier ductile iron? "The extra positive rake of the Waveline insert requires lower cutting forces, thereby generating less heat, and introduces more of a cleaving action at the cutting point. And the insert itself is more wear-resistant," says Mr. Joseph. He says it holds up well to the cutting action.

In addition to the expected results, Parker Hannifin had a few pleasant surprises, which contributed to its overall throughput gains.

The productivity gain was a "plus" Mr. Joseph did not expect. The new tooling enabled him to increase feed from 70 ipm to 90 ipm and spindle speeds from 2500 rpm to 3000 rpm. At the same time, operators are achieving 50 to 60 RMS finish on the part, well within the 100 RMS part specification.

The CoroMill 200 multi-purpose milling cutter is a rugged, highly productive cutter designed for general milling, aerospace applications and die/mold making. The cutter body features open chip pockets and a large clearance for free chip flow. This makes it possible to machine in any direction.

New RCKT family of inserts was developed especially for these cutters and features new Waveline geometries for medium and heavy milling. The round inserts are stronger than square inserts because there are no corners to cause stress raisers. They are screw mounted, and the insert seats in the cutters are protected by thick carbide shims. The insert's faceted design provides quick, distinct indexing for up to eight indexes. The steel milling grade is the CoroKey GC4030.

"The investment we made in the CoroMill 200 is really insignificant in comparison to the extraordinary gains we got in throughput and productivity," added Mr. Joseph. "We started with some very definite objectives in mind, and got more results than we ever thought possible."