July 2007 Edition

CUTTING TOOLS

The Right Cutting Tool Helps a Shop Across the ‘Finish Line’

Keeping parts within surface finish specifications was a contest a shop was losing until it found the right tool

The top and bottom halves of the anthrax detector require an 8 rms finish in 6061 aluminum

When a Baltimore job shop decided to retool an aluminum milling job to meet a surface finish specification of 8 rms, it found unexpected cost-savings as well.

“And, we’re not done yet,” Jeff Grueninger, milling foreman of Excel Machine and Fabrication, said.

Surface finishes on the part are so far within the specification, the company eliminated one inspection step. Moreover, cycle time for the milling operation was reduced by half. Insert indexing time dropped from half an hour to minutes. But, since the edges last more than ten times longer, indexing time has become a non-issue.

What made this possible was Ingersoll Cutting Tool’s Aluminator face mill.

“With the retooling, the process is under control,” Grueninger said.

Ingersoll Aluminator cutting tools solved Excel Machine and Fabrication’s surface finish requirement and provided additional benefits as well

The workpiece is a housing for airborne contaminant detection systems, such as anthrax detectors. Consisting of mating halves made of 6061 aluminum, the housings hold filter media that captures contaminants. Assembled housings measure about the size of a paperback book. Each half contains eight, deep, intricately-machined pockets to hold the filter media; more than a dozen variously sized holes in two different planes; and a gasket channel.

The Smooth and Flat Challenge

The key machining problem was to achieve an 8 rms finish and a 0.0005" flatness on surfaces in the machined gasket channel, without taking an extraordinary length of time. The channel goes around three sides of the housing.

Specifications precluded hand working. The customer needed 125 complete housings each week, which left no time for hand work either.

Excel first tried a 2" wiper-type face mill with four inserts, but even at a 42 ipm or less feed, surface finish ranged from 7 rms to 35 rms, so every piece needed a profilometer check. Scrap and rework rates were unacceptable.

After testing, cutting speeds that were less than 42 ipm with unacceptable surface finishes were raised to 80 ipm with surface finishes so well within specifications that part inspection could be reduced

To add to the difficulty, insert edges lasted less than 100 pieces. Indexing involved handling three different types of inserts that took more than 30 minutes each time.

“It took rocket science to index the thing,” Grueninger said.

He tried another cutter with triangular inserts without any improvement, and cutting loads were up to 120 percent of spindle capacity, so he kept looking.

Jim Smith, an Ingersoll Cutting Tools, Rockford, IL, field engineer, suggested a new face mill for aluminum, the Aluminator. He set up a test using Excel’s Kitamura CNC machine. The cutter consistently delivered surface finishes in the rms 4 range at higher cutting rates.

To test the cutter’s limits, Grueninger ran tests at 265 ipm. Surface finish still remained within specifications, spindle load remained within limits, and inserts endured the machining.

But, Grueninger and Smith knew there’s a big difference between tests and the real world.

Results with the insert are so consistent that profilometer spot checks replaced 100 percent inspection

Measured Risks

“We can take risks in a one-time test that we can’t in day-to-day shop practice,” Grueninger said. “The test gives us a road sign on the way to a more robust process that produces in-spec parts every time.”

In fact, Excel never ran the previous cutter in operation as hard as Smith did in the test, and it didn’t push the new cutter to its limits in testing. Feedrates with previous cutters were closer to 25 ipm, and depth of cut was 0.200", not 0.250".

Currently, Grueninger keeps the feedrate at about 80 ipm.

“Once we’re sure the retooled process meets finish and flatness specs every time, we’ll tweak the feedrate,” he said.

“The test gave us a good basis for setting expectations, but we’ll take it a step at a time. Besides, a consistent 4 rms finish in aluminum with a non-balanced three-insert cutter running at 80 ipm is nothing to sneeze at.”

After several months, surface finish has remained so well within limits that Excel dispensed with 100 percent part inspection, saving additional dollars.

“The operation runs twice as fast as before, yet surface finish remains steady and the edges seem as good as new,” Grueninger said.

According to Ingersoll’s Smith, the Aluminator’s performance stems from a combination of ground and polished inserts and a high-positive rake presentation geometry.

“The ground-and-polished inserts deliver a better finish. The free cutting geometry delivers lower spindle loads and longer edge life,” Smith said.

“Add to that the Aluminator standard cutter and inserts cost much less, too,” Grueninger said. In total, savings from all sources arising from the retooling to the Aluminator saved Excel more than $10,000 a year on this job alone.

“More importantly, we’ve met the tight surface finish and flatness specs so well that I can sleep at night again,” Grueninger said.

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