by Jim Barnes
Machine shop cuts milling time in half with new inserts
Most shop owners are skeptical when a tool vendor offers to cut their machining time in half.
However, checking out a new line of inserts showed AFI Hydro Inc. of Paris, ON, that changing your technology can really pay off.
AFI Hydro makes massive, steel components for its customers in the hydroelectric power generation sector. Milling is a key operation and the two boring mills in use have axis travels of 48 ft (15 m) and 27 ft (8 m) respectively.
Some workpieces are huge mating parts that have to be precision-milled to ensure water tightness. For example, “one piece of stainless is 52 ft (16 m) long and about four by 12 in. (101 by 305 mm),” says Joe Felice, lead hand for the machine shop at AFI Hydro. “It’s a three-piece weld, fully welded. It takes 220 passes to weld one side,” and these parts must be machined on three sides.
Complicating matters, these parts are bowed. “Figuring out the right chip rate was difficult. In some spots, you could take almost a quarter inch. In other spots, you are only taking 20 thou., says Daz McLeod, sales engineer at distributor Tool and Cutter Supply, London, ON.
AFI had been using an octagonal cutter from another supplier, but was unhappy with the results. “They were taking two passes and the passes were taking about 45 minutes apiece, taking a 60 thou. cut,” says Felice. On top of that, tool life on the inserts seemed to be short.
The welds were another concern. “[The cutters] would hit the weld and just burn out,” says Felice. He decided to touch base with Tool and Cutter Supply.
“Joe Felice is all about ‘let’s get the latest technology, let’s get things done quicker,’” says McLeod. “The shop is very busy.”
Tool and Cutter represents Walter, which recommended a couple of grades, according to Ray Vander Kooy, team leader, Central Canada, Walter Canada, Brampton, ON. The SNMX 1205ANN-F57 grade WKP35S is for steel and the SNMX 120512-F67 grade WSP 45 is for stainless. The steel grade has a TiCN + Al2O3 coating, while the stainless grade has a TiAlN+ Al2O3 coating. These 45°, negative/positive milling cutters are heavy metal removal tools, according to Vander Kooy. They have a fine pitch, with many teeth on the cutter. The insert is negative in the cutting pocket but has a positive cutting range because of its geometry. That permits high metal removal rates with a high horsepower milling machine.
“Boring machines… seem like they’re stable, but when you are milling and pushing a lot of material off, there is a lot of bouncing and vibration,” says Vander Kooy.
“A lot of people use 45° high shear positive/positive cutters in applications like that,” he adds. “That positive geometry tends to hold the part away from the fixture. It has great, positive shearing action, but it causes vibration.
“Holding the workpiece down into the fixturing, combined with the grade, is an advantage. The positive/negative geometry tends to push the workpiece in the Z axis, but the positive allows for the free cutting action”.
The test data and the performance of the tools in production amazed Felice. “With the new cutters, we could do two cuts in a half hour apiece at a 200 thou. depth… With a feed of 20 ipm (508 mm/min) and an rpm of 200, the chips were just flying.” He says he was able to double metal removal rates.
The application combines a roughing insert with a wiper. “The wiper gives us a two-thou. finish that more than meets the customer’s spec,” says Felice.
The horsepower of the milling machine was one constraint. “We had to go way more aggressive than they were before. Because of the machine, we still could not push it to what we wanted to do,” says McLeod.
As well, there is a 90° cutter on the machine for the end faces. It has a gear ratio, so it gears down, further reducing available horsepower. “The main objective was to get them the most free cutting cutter,” says McLeod.
The welds were another issue. At first, the tools were sparking when they hit the welds. “We were only taking about 20 thou. at that point because of the bow,” says McLeod. The cutter is not made for a 20 thou. depth of cut, it is made for 120 to 240 thou. depth of cut. The next cut we did was full engagement, and we went through the weld with no problem.”
Felice was stumped when we asked him if there had been any wrinkles in making the switch. He says at one point he was having problems with the wipers. “There are two different kinds of inserts and I had put the wrong one on it. It was my fault. Ray (Vander Kooy) came in to look at it and found the problem right away.”
Adds Felice, “the new cutters really changed our process, how long it takes to get things done. The improvement in deliveries made the plant manager happy.” The huge savings in machine time paid for the inserts almost immediately, according to Felice.
That is in addition to the savings resulting from the longer tool life. The running joke between McLeod and Felice is that Tool and Cutter will not get repeat business on the inserts–because they last so long. SMT
Jim Barnes is a contributing editor[email protected]