March 2008 Edition

MACHINING CENTER

Loyalty On Its Own Terms

Because of performance — not a force of habit — a tool manufacturer invested in several machining centers from the same company

There is a difference between being brand loyal and using a brand based on high-quality performance.

"Many people buy a particular brand of machine tool because they've always bought that brand," John Powers, manufacturing vice president, Branson Ultrasonics Corp., said. "Not because it's the best machine, or because previous iterations have performed well. In our shop there are 13 or 14 machining centers and about 20 Bridgeports. Our latest VMCs are Bridgeport 760XP3s and a Bridgeport 610XP3. They were ordered within a seven-month span."

The Danbury, CT, company builds tooling for the automotive, medical, surgical, and consumer markets, including toys, remote controls for TVs and stereos, and video and DVD packaging.

"We build acoustic tools, horns, and fixtures to support our customers' product welding," Powers said. "We don't weld plastic parts; we build the tooling our customers use to ultrasonically weld their parts. Our customer list includes most of the Fortune 500."

"We build tons of tooling for all those types of things," he said. "But ours isn't a volume business. We're primarily a one-of-a-kind shop. That makes time-to-market critical. Occasionally, we'll build a tool or fixture used in production runs, but all of our lots are small — one or two pieces.

"However, these pieces must be precise to provide a perfect weld. Most work — 65 percent — is in titanium followed by aluminum, about 35 percent, so machining time varies from hours to days, depending upon the size and complexity of the tool. This is why selecting the right machining center is critical."

Bridgeports, but Not out of Habit

Powers said the Bridgeport machining centers, from Hardinge Inc., Elmira, NY, fit his company's one-of-a-kind operation. According to Powers, they are flexible, fast, easy to change over, precise, and rigid. He also said the machines' power is not just in cutting, but in manipulating large data files — some in the 40 Mb range — which are routine with contour work. Contours are like injection molds. About 90 percent of the jobs at Branson are contour work.

Powers said most contours his company makes are about the size of a quarter. However, some in the range of 3"×5" or 6"×5" require a large data file. Larger still are contours that can be 14" to 16" long by 3" wide — such as surgical equipment or diver snorkels. These can have huge data files.

"One thing about these parts is that they must have a fine finish," Powers said. "The better the finish, the easier it is for us to polish. If you've seen injected molded tools, they've got a mirror finish. And that's what we do; we replicate that type of finish by hand polishing."

He said the Bridgeports let them create a tight, dense point cloud, so the step-over from slice to slice going across is small. That makes a finer finish and reduces polishing time. The Bridgeports bring accuracy and repeatability as well as data transfer speed to contour work.

"The control on both new machines — a Fanuc 18i MB — is a real advantage in quick data transmission," he said.

Speed, with a Great Finish

"Two Bridgeports replaced two Japanese machines, which frankly couldn't keep up with the data, nor could they produce as fine a finish," Powers said.

Like the Bridgeports, the Japanese machines had 12,000 rpm spindles, but were less effective processing machining data; they developed a bottleneck in machining the contours of some horns.

"The Bridgeports are much faster," Powers said. "The control technology of the previous machines couldn't keep up. For one thing, they were drip fed data. The program was in a PC, and we'd feed blocks of data across to the machine tool through a wire."

The machine tool had a specific baud rate, a speed at which it could interpret data. The machine would have to slow because the machine controls couldn't digest the fine increments of data as fast as the machine could act. The company would take a part and create a point cloud of the shape, from point to point that might be 0.00003" or 0.00004". The data would be fed to the machines, and they would go into starvation because the information could not be fast enough to keep the spindles turning.

With the Fanuc 18i MBs on the Bridgeports, Branson Ultrasonics no longer has machine starvation. The data moves from the control to the spindle, maintaining productivity and reducing process interruption.

Powers said he can run at 80 ipm to 100 ipm, where with the other machines ran at 35 ipm to 40 ipm with worry about starvation alarms going off. The Bridgeports are up to twice as fast, he said.

Another advantage of the machines, according to Powers, is the finish on the titanium horns.

"We don't machine to a tolerance, like an aircraft shop might," he said. "We fit the part so that when they're welding there's no marking on the surface of the plastic. Parts have to fit exactly; a real challenge."

As in producing an injection mold, hand polishing is the last step. Branson employees massage the data into the machine tool program, machine the part, and then hand polish. They then match the fit of the part from the original injection mold.

"We can hold 0.00003" or 0.00004" on most of our contours with a surface finish of 8 Ra or 10 Ra, but then when it's all polished, any marking is eliminated completely. That's why the finer the finish, the less polishing."

Powers said that when Branson used Japanese machines the amount of polishing in finishing might take up to 90 minutes. With the Bridgeports, polishing takes about 30 minutes to get the same result. On average, hand finishing was cut from 50 percent to more than 66 percent, compared to the former process.

"The results are better because there's less marking on the parts. We're getting a superior finish before polishing," Powers said. "This, too, is due to more accurate transmission of data. What we transmit and what we see at the machine tool spindle are much more accurate."

Ultrasonic Welding

Powers said that Branson is a time-to-market business and builds to customer order. In some cases he might get an order that's due in three to four days. Depending on material availability, the design of the tool, and machine time, he said he will take the job.

But, there are times that he can't meet the deadline because the job involves more machining than can be done by the deadline. Creation of some ultrasonic welding tools may take up to four weeks. Spraying on carbides and grinding them, by an outside finisher, may add another week or more.

"Some of the tools last for years," Powers said, "depending on the stress put on the tool and the application. We make four varieties of tools: 15 kHz, 20 kHz, 30 kHz, and 40 kHz."

Most of the applications created by Branson are 20 kHz jobs. A 20 kHz tool vibrates at 20,000 times a second. That melts the plastic and welds the part. Welding cycles are less than a second. Weld cycles can be longer, but a well-designed plastic joint would weld in between 300 and 500 milliseconds. There's no contamination, and it's environmentally friendly, but unforgiving.

"We have to produce perfect tooling," Powers said. "Which means we must rely on the precision, accuracy, repeatability, and data crunching speed.

"A chunk of titanium might be worth $4,000 — not a great deal of money — but when you consider how much titanium we go through, we cannot afford to scrap out even one job," Powers said.

And Then There Were More

"I've submitted an appropriation request for two more machines," Powers said. "I'm not sure if it will be two Bridgeport 760 XP3s, two 610 XP3s, or one of each. I have another project that would require a larger VMC, probably an 1000XP3. So, it looks like we'll probably buy three more."

Powers cautions against buying the same name brand just because that's what's always been purchased. As with any equipment, especially capital equipment, he said homework must be done to make sure a company is getting good value in return for its investment.

"Above all," Powers said, "make the vendor sell his machine. Sending a brochure and a spec sheet doesn't cut it for a five-figure investment. We're buying three Bridgeports not through just brand loyalty. We've done our homework." Hardinge Inc.

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