Shop Solutions: Milling Titanium Faster on Light-Duty Machines
When bidding large titanium jobs with a lot of stock removal, you’d better get everything right, from the bidding numbers to the actual machining rates. Otherwise you may either lose the bid or end up waving goodbye to a bundle of bucks when the parts actually run.
TEM Inc., a progressive 40-man shop in Buxton, ME, sure has gotten it right with a fleet of 34 light-duty CNC mills running 16/5 machining titanium. TEM rough mills an airframe forging literally five times faster than is possible with conventional cutters—on a light-frame CNC with a 20-hp (14.9-kW) spindle. The key is high-feed milling with a 3" (76-mm) Hi-Quad-F mill from Ingersoll Cutting Tools (Rockford, IL), featuring an improved PVD surface coating on the inserts. TEM completes the parts in just five hours, compared with 26 hours with conventional mills or 10 hours with competing high-feed cutters.
Unlike a lot of Maine-coast job shops, TEM serves a national client base which includes stainless steel work for oil and gas companies. So the company has been all too familiar with milling high-temp metals for years and has had decent success with some older Ingersoll high-feed mills in those applications.
It was last November when TEM decided to go after titanium aerospace jobs. Their first job involved removing 80 lb (36 kg) of stock from a 200-lb (90.7-kg) fuel tank mounting bracket made of forged TI6Al4V. Besides skinning off about 1" (25.4 mm) of stock, specs require hogging out several pockets measuring 4" deep by 8" wide by 11" long (100.6 × 203 x 279 mm).
TEM was already thinking high-feed practices at the time, but wanted to be sure they were using the latest and best. So at the bid stage, TEM considered the possibilities with Ingersoll’s David Gradie because of the company’s deep knowledge base in high-feed machining. In high-feed milling, stock is removed in shallower, faster passes, which enables higher metal removal rates (MRR) with lower cutting forces. This helps run material fast on 40-taper machines without stalling the spindle.
Gradie estimated that the new Ingersoll Hi-Quad-F cutter with new insert grade IN4030 could rough the parts in less than 15 hours, with a set of inserts lasting through an entire piece. Most important, the removal rate was about double what conventional milling cutters could deliver on a 40-taper machine.
TEM had ballparked the job using conventional tooling, and came up with about 25 hours per part. Maximum possible parameters for a 40-taper machine were 125 sfm (38 m/min), 6.6 ipm (167 mm/min), 0.100" (2.5 mm) DOC. “Had we run a conventional tool any faster on our equipment, either the inserts would rupture or the spindle would overload,” TEM said. So the high-feed approach definitely seemed the way to go.
TEM got the job, with initial runs on the new tool coming out better than predicted. Parameters were 125 sfm (38 m/min), 0.040" (1 mm) DOC, 30 ipm (0.76 m/min), yielding a cycle time of about 12 hours, with a single set of inserts lasting all the way through. These are roughly the numbers on which TEM started machining.
Next, TEM started to push the envelope, ramping up the parameters, and found that with the new IN4030 coating, it would withstand a lot higher sfm without wearing the inserts. They were able to run 243 sfm (74 m/min), and by maintaining the same chipload, feed rate went to 59 ipm (1.5 m/min). That was almost double the starting point, and it cut cycle time to five hours. Insert edges still lasted through the entire part. These are now TEM’s standard parameters for roughing all titanium jobs.
“High-feed machining works because the cutter’s positive presentation geometry creates a shearing and chip thinning action, which enables very high feeds without excessive cutting forces,” said Gradie. “The cutting forces are resolved axially rather than radially, reducing pressure on the bearings in 40-taper spindles.”
Extra durability of the new IN4030 grade oxide insert coatings results largely from the different way it is deposited. First, the substrate surface is etched to create a larger gripping area. Next, the alumina coating is deposited by physical vapor deposition (PVD), which runs cooler than chemical vapor
deposition (CVD). The lower temperature reduces microcracks, leaving a smoother surface with fewer stress raisers.
“We’ve worked with high-feed mills in the past, and the performance of this new Ingersoll Hi-Quad-F mill has been surprisingly impressive,” said TEM. “The geometry fulfills the full potential of high-feed machining practice. Moreover the coating enables us to crank up the surface speed beyond what we believed possible.”
In fact, TEM is in the process of converting all their 34 mills over to the new Hi-Quad-F for roughing. We’re doing this also to take advantage of the Ingersoll ‘free cutter’ promotion running throughout 2014,” said TEM.
Based on actual results on the titanium job, TEM expects to save at least $500,000 a year in machining costs when all 34 machines are retooled this way. “More important, it will boost our overall production capacity. We can take on more work without having to buy larger taper equipment, especially more titanium work which puts us in a much more competitive bidding environment. Now, shops with 40-taper machines can compete for titanium work.” ME
For more information from Ingersoll Cutting Tools, go to www.ingersoll-imc.com, or phone 815-387-6600.
This article was first published in the May 2014 edition of Manufacturing Engineering magazine. Click here for PDF.
Published Date : 5/1/2014