by Jim Barnes
Attitudes are changing toward tooling and tough alloys
There are two types of machine shops, says one expert: those that do a lot of high-temperature superalloy and titanium alloy work, and those that shy away from it due to long cycle times and short tool life.
The latter might be due for an update. Advances in tooling are making these jobs more productive and profitable. “These metals are more difficult to machine than carbon alloy steel – but perhaps not as difficult as people think,” says Steve Geisel, senior product manager, non-rotating products, Iscar Canada, Oakville, ON.
In fact, progress in tool coatings, geometries and machining procedures has been significant.
New PVD (physical vapor deposition) coatings have been developed for nickel, iron, and cobalt-based superalloys. “The heat-resistance and wear resistance that you get from the aluminum oxide [coatings] has proven to be excellent,” says Kurt Ludeking, product manager, turning at Walter AG in Waukesha, WI. Advantages include improving control of work hardening and heat, keeping cutting edges sharp and better tool life. “With PVD aluminum oxide, you can run at over 200 sqm and have the same or better tool life than you had running slower with other tools,” he says.
Speed improvements can be dramatic. One example is Iscar’s IC806 grade (a TiAlN PVD-coated grade). “We are machining Inconel between 200 and 240 sfm, maintaining the same depth of cut and feed rate – and seeing triple the tool life,” says Geisel. “You’re talking about double the spindle speed, so you are cutting your production time in half.”
For titanium alloys, uncoated grades are most common, so geometries are the focus of innovation. “The new geometries are specifically geared toward titanium and combat crater wear and improve chip control,” says Ludeking. “You can run faster – 20 or 30 per cent – and also feed at a higher rate.”
“We’ve adjusted the form of the cutting edge to be effective in these types of alloys. They are more robust, but still maintain a sharp cutting edge,” he adds. The result is a reduction in work hardening and 60 to 100 per cent increases in tool life.
Other innovations include Iscar’s P290 serrated cutting edged insert. “You’re getting increased tool life and you can push a little bit faster, too,” says Thomas Hagan, product manager, milling, Iscar Canada. The HM 390 is a three-sided insert with a dovetail pocket. “It’s a lot more secure and it clamps better. We’re seeing 15 to 20 per cent more productivity,” he says.
Ceramic inserts can provide dramatic productivity improvements, says Ludeking.
Whiskered ceramics are gaining a lot of interest in roughing. “They can run at five to ten times the surface speed of carbide. Typically, if you’re running at 150 to 200 sfm with carbide, you could be running at 1,000 sfm with a ceramic,” says Ludeking.
Iscar’s IW7 grade whisker-reinforced ceramic inserts are suitable for nickel-and cobalt-based superalloys, says Geisel. “Now, you’re talking about machining Inconel at crazy spindle speeds, like 400 to 600 sfm,” he says.
The need for speed
Many shops misunderstand speed requirements when machining superalloys, our experts said.
When faced with a problem, it seems to be human nature to back off and slow things down to find out what is going on. However, with current-generation inserts, that could actually make your problems worse. “All inserts are designed to run at a certain minimum speed. You need to create enough heat within the cutting zone for the inserts to work effectively, says Ludeking.
Attitudes are due for review. “People are still stuck with the model of using a high depth of cut and lots of coolant, and let it go,” says David Vetrecin, product manager, holemaking at Iscar. “We like to come in with an approach where we make a light, radial depth of cut and many passes. The metal removal rate is higher than the other method and the tool life is better.”
“If you’re doing any appreciable amount of high temperature alloy work, you really want the right coolant,” says Ludeking, who recommends talking to a cutting-fluid specialist.
High-pressure coolant may help speed things up on some jobs. Iscar’s JETHP toolholders support coolant pressures of up to 5,000 psi. “Increasing your coolant pressure up to 1,000 psi might allow you to increase your spindle speed or feed or depth of cut on high-temperature alloys by 40 per cent or more,” says Geisel.
“If you combine the new coatings and geometries with high-pressure coolant, you can cut superalloys under conditions comparable to those of carbon and alloy steel,” he adds.
People are seldom satisfied with five-year old computers or cellphones. “Why are they content with their five-year old tooling?” asks Geisel.
Upgrading is not a question of slapping a new insert line into your existing machines and methods. A systems approach is key to productivity and profitability with these tough metals.
“To get a real improvement in throughput, you have to look at the whole system,” says Hagan. Iscar is prepared to walk customers through the whole machining operation, including machines, programming and workholding–almost like spec’ing a turnkey machining system. The firm describes these exercises as “total projects,” based on hard, international machining data. At the end of it all, the shop owner gets exact data on costs and running the system productively.
“It doesn’t matter what material people are cutting,” says Geisel. “The biggest thing Canadian shops should be doing is to review the tooling they use at least once a year. [The industry] is constantly releasing new technology to the marketplace.” SMT
Jim Barnes is a contributing editor.[email protected]