Inserts Improve Milling Of Tough Steel Castings For Missouri Manufacturer

When a Laurel, Missouri manufacturer of industrial equipment identified problems in their two machining operations on high alloy steel casting, they solved them with an insert and a cutter switch.

Case Study From: 3/1/1997 Modern Machine Shop

When a Laurel, Missouri manufacturer of industrial equipment identified problems in their two machining operations on high alloy steel casting, they solved them with an insert and a cutter switch. Laurel Machine and Foundry, Co., experienced edge wear facemilling and boring steel alloy castings. They swapped their conventional square carbide facemilling inserts for indexable, round, carbide inserts with pressed-in positive rake. The new inserts, made out of a tougher carbide, also had a more advanced coating. To accommodate the new inserts, they switched cutters as well. The inserts and cutter body were made by Sandvik Coromant, in Fairlawn, New Jersey.

The switch paid off. They improved throughput 35 percent and decreased stoppages for edge changes by 20 to 1, using the Sandvik CoroMill 200 cutter in combination with Waveline inserts in grade GC 4030

Each alloy steel casting requires two operations: boring and facemilling. They bore a 6.459-inch and facemill adjacent surface areas in a large casting weighing several hundred pounds. Facemilling involves removing between 0.125 inch and 0.188 inch of material in two passes. "We had trouble with these parts," says I.B. Wash, CNC shop foreman at Laurel Machine. "The inserts were breaking and there was a significant amount of vibration."

Laurel Machine operators were using a carbide facemilling cutter with conventional 235 coated carbide, square, indexable inserts. They had to index them every 6 to 10 pieces because of edgewear.

Machining at 350 feet per minute with the feed rate of 4 inches per minute, they were able to turn out only about six piece per hour.

When the low throughput and frequent stoppages for insert change started troubling Mr. Wash, he called on Sandvik sales representative Jamie Price for a remedy. Mr. Price recommended positive rake, round, indexable inserts coated by titanium nitride versus the flat, square inserts Laurel was using. "I recommended that these guys use the round inserts because these inserts can take higher loads," Mr. Price recalls. There was also another asset to these inserts. The operator can easily lock the insert in every time he indexes it because of mating notches on the insert and the cutter body.

When he told me that we should use round inserts, I was very skeptical," recalls Mr. Wash. "We've used round inserts before and they didn't hold up very well, so basically I've written them off. Honestly, I didn't expect them to do a very good job."

Laurel agreed to at least run tests on suggested inserts. Mr. Price offered to help Mr. Wash with tests on the troublesome workpiece.

The round Waveline inserts in grade GC 4030 for high alloy steel differ from the conventional square inserts in four ways. The first is their shape. The round inserts are said to be stronger than square inserts because there are no corners to cause stress cracks.

The second difference accounting for the better insert life is in the coatings. The outer coating of the new insert consists of outer layer titanium nitride (TiN), while the inner layer is made out of titanium carbonitride (TiCN). This combination adds to the edge life of the insert and the ability to run at higher speeds which in turn increases throughput.

The third difference is the carbide material itself. The tungsten carbide microstructure creates a more wear-resistant edge with more shock resistant core.

The fourth and final difference, is the top geometry. The pressed-in positive rake of the round inserts exhibits lower cutting forces than zero rake of the flat square-shoulder inserts.

For testing purposes, Mr. Wash set the new cutter at a slightly higher speed of 450 feet per minute versus the previous 350. This resulted in a change of number of components per insert went from 10 with the 235 inserts, to 200 with the CoroMill 200 with Waveline GC 4030 inserts. The total time per component changed as well, from 11 minutes to 8 minutes. Based on these results, Mr. Wash standardized on the new tooling not long afterward.

Since then, Laurel increased their throughput 35 percent and reduced dead time 65 percent, running the cutter at the cutting speed of 450 feet per minute with a feed rate of 9.0 inches per minute. Mr. Wash says, "With this new breed of inserts, we are putting more speed on the cutter. Because of higher speed, we've managed to increase productivity." Since the switch, they are machining eight pieces per hour versus the previous six. They also decreased line stoppages for insert change 20 to 1, getting 200 pieces per edge.

The company found that the operations run more smoothly due to an improved stability of the cutter. The screw mounted inserts in the cutter and an open chip pocket allow for a free chip flow. As a result, Mr. Wash experiences less downtime for indexing inserts than he did previously.

Mr. Wash and the rest of Laurel Machine and Foundry operators are happy with their new tooling. "Originally, I hoped these tools would at least last longer," comments Mr. Wash. "The fact that we can run them faster was an unexpected bonus." With the new tooling, Laurel Machine And Foundry came out a winner both ways MMS

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