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Threads erratically tore out or ran oversize in this aluminum gear housing, resulting in an unacceptable scrap rate.
Fairris Dean is machining division manager at Ward Corporation (Ft. Wayne, Indiana), a supplier of aluminum parts and components to the automotive, marine, motorcycle, recreational equipment and heavy truck industries. The company is entirely vertically integrated (there are four divisions: pattern engineering, foundry, machining and heat-treat), allowing for complete and total control over process and quality. Raw material literally goes in one end of the company and finished aluminum parts and assemblies come out the other.
So when Mr. Dean attempted to fix a persistent—and erratic—tapping problem that was causing unacceptable levels of scrap, he found himself searching for a cause and not finding one.
“I looked at everything—all the process parameters— and not only did nothing jump out as the cause of the problem, there appeared to be no cause whatsoever, says Mr. Dean. There was no discernable pattern; no rhyme or reason.”
Mr. Dean says that some 300,000 lbs of aluminum are machined annually by the division, which employs 50 people and runs three shifts, 5 days a week. Machining takes place in 40,000 square feet arranged on two floors of a five-story building. As many as 486 different part numbers are machined each year in runs ranging from 100 to 200,000 pieces. Process operations include milling, drilling, tapping, reaming, finish turning and form tapping. Actual stock removal varies up to 0.750 inch. Typical materials are 356 and 319 cast aluminum. Tolerances are consistently tight, in the 0.0001-inch to 0.0005-inch range.
There were four jobs in which the erratic tapping problem occurred: A gear housing, two fuel filter heads and a transmission case. All four of the workpieces had threaded holes and tight tolerances on true position.
“On the gear housing,” Mr. Dean says, “we were holding a 0.0007-inch true position off a 2" datum bore with a diameter tolerance of ±0.0005 inch to another datum bore with the same diameter tolerance over a length of 14 inches. Holding 0.0007 inch on a piece that long is really very tough—the aluminum tends to stress, to warp and to bend, and to spring back from the hydraulic fixture. Fluctuations in temperature can radically affect it, too. This is an expensive part, and a 6 to 7 percent scrap rate is just not acceptable. To try to get at the root of the problem, I had to begin at the beginning, at the base line and work backward.” Mr. Dean notes that the nature of the tapping problem was particularly frustrating. The company would run three good threads and then the fourth would rip out. Then numbers five, six, seven and eight would run fine, only to have number nine rip out or go oversize. Then ten and 11 would be okay, but 12 would fail. Every parameter checked seemed to be exactly as it should: the tooling was fine, the tapping and speeds were fine, the fixture and the machine were fine, the coolant flow was fine—and yet the rip-out or oversize problem kept occurring with no predictability.
Mr. Dean says that with a tapping problem in aluminum, it’s natural to look into the mechanics of the process for a cause. But when that failed to produce a result, he began to “think out of the box” for an answer. The alternative—accepting the scrap rate and living with it—was a position Mr. Dean was unwilling to accept. He began to suspect that the tooling was gumming up and sticking, resulting in torn and oversize threads. His focus now became the metalworking fluid used in all four jobs.
“I contacted our local ... Milacron distributor, and asked if there wasn’t a fluid with better lubricity than what we were using, that was designed for aluminum work and specifically tapping,” Mr. Dean says. He discovered that Milacron (Cincinnati, Ohio) was releasing Cimstar 3890, and that it might meet his needs.
Milacron paid Mr. Dean a visit and introduced him to Cimstar 3890, a biostable, chorine-free, high-lubricity fluid formulated for aluminum machining, threading and finishing applications. The two agreed to a controlled test on a single machine. Nothing has changed for the test—it's the same machine, fixture, tooling, speeds, feeds—except the fluid. The results, Mr. Dean says, were nothing short of remarkable.
“I’ve been in the trade for 25 years,” Mr. Dean says, “and during that time I’ve had people try to sell me everything from allen wrenches to multi-million dollar robotic systems. But whatever the product, the proof has always been in the performance, and that’s what we’re getting with Cimstar 3890.”
Mr. Dean reports that his scrap rate for the gear housing has fallen from 6 to 7 percent to less than 1 percent. The thread problem has simply disappeared. Tool life has increased a full 12 percent. And he’s seen a significant increase in productivity. “I’ve been able to increase my feeds and speeds,” he says, “where before, because I was ripping out thread, I had to slow the machines down. Now we’re running up where we should be.”
Mr. Dean also notes that he’s able to “recycle” the Cimstar 3890, which saves time and money. He says, “Usually the water evaporates before I have to do anything. We just add more water and concentrate, then adjust the fluid concentration to the proper refractometer reading. We don’t have to completely flush the entire system, as we do with other fluids—disposing of the spent fluid, cleaning out the sump, adding new fluid and recharging the system. With the Cimstar 3890, we just recycle and add makeup with no resulting loss in fluid effectiveness.
“Our customers are very intolerant of defects, and very understandably so,” Mr. Dean continues. “They’re pushing for 100 parts per million—not just for the machining division but for the entire corporation. For a foundry, heat-treat and machining facility, 100 parts per million is a very big issue. Everything we do has to work toward eliminating any potential for error and that includes even the seemingly small stuff—like solving what appeared to be an unsolvable thread tapping problem.
Mr. Dean notes that today he uses Cimcool Cimstar metalworking fluid 3800 on all the other machines and the Cimstar 3890 on three high-precision horizontal machining centers that run the tough threading jobs. And even though the CIMSTAR 3890 costs more than the 3800, Mr. Dean justifies the investment because it has paid for itself in extended tool life and the elimination of thread-related scrap.
“It takes just as much money to run bad parts as it does to run good ones,” Mr. Dean says. “Same operating costs, same labor costs. But no one wants to run bad parts. In this business, you get the performance you pay for. We buy top of the line machining centers, fixturing, tooling and fluids. And the proof is sown on the floor with the operators. What is their reaction to the change in the fluid? No odor, no skin irritation, no spotting or finish problems—and no more torn or oversized threads. That’s all the proof I need.”blog comments powered by Disqus