Making ultrasonic welding tools for joining nearly all things plastic is partially art and partially science (the larger part is science, as in the nearly imperceptible perfection of the process of producing the “horn,” the acoustic tooling used in the plastic joining process). At heart is the machining center. Here’s why...
DANBURY, CT — John Powers, vice president, manufacturing, Branson Ultrasonics Corp.: “We build acoustical tools, horns and fixtures to support our customers’ product welding,”
he says. “We do not weld plastic parts; we build the tooling our customers use to ultrasonically weld their parts. Our customer list is very, very long — including most of the Fortune 500.”
Powers says they build tooling without discrimination: for small shops and large, local companies and global. Their tooling can be found in automotive, medical and surgical, toys (and more toys), consumer products, remotes for TVs and stereos, tooling for encapsulating bubble wrap, and packaging that a video or DVD might come in. They also make the tooling for the hard plastic wrapping that no one can ever possibly get open. (“I had to wrestle with this just today,” Powers says. “I had to try to open the packaging for a small calculator. I could see the calculator there in its clear seamless hard package wrap. The package itself held no clues for opening. I finally had to resort to my pocket knife to cut the packaging apart.”)
“We build tons of tooling for all those types of things,” he says. “But ours is not a volume business. We’re primarily a one-of-a-kind business, which makes time-to-market very critical. Occasionally, we’ll build a tool or fixture that will be used in long production runs, but all of our lots are small — one or two pieces. However, these pieces must be very precise in order to provide a perfect weld in the end. The material we work in most is titanium (65 percent) followed by aluminum (35 percent), and the machining time varies from hours to days, depending upon the size and complexity of the tool. Which is why selecting the right machining center becomes absolutely critical.”
BRIDGEPORTS, NOT OUT OF HABIT
“Many people will buy a particular brand of machine tool because they’ve always bought that brand,” Powers says. “Not because it’s the best machine, or because previous iterations have performed well. Or, because, well . . . for a number of reasons. If you looked around our shop you’d see 13 or 14 machining centers, most of which are high-end Japanese machines. However, our latest investment in VMCs include a pair of machines from Bridgeport’s top-end line, the Bridgeport 760XP3 and Bridgeport 610XP3 (marketed today as the Bridgeport XR 760 and XR 610), both ordered within seven months of each other.”
Flexible, fast, easy to change over, very precise and rigid, that’s how Powers describes his newest Bridgeport vertical machining centers. Very powerful as well — not just in cutting chips, but also in the manipulation of huge data files (some are 30 to 40 megs) which is routine with contour work. The contour is very much like an injection mold; it’s the shape that must fit the shape of the plastic part. Typically, about 90 percent of the work Powers does on his new Bridgeports is contour work.
Powers notes that a cross section of parts Branson makes may be very small, some the size of a quarter. However, contours that are 3.00” x 5.00” or 6.00” x 5.00” square can require a data file that’s quite large. Larger still are contours that can be 14.00” to 16.00” long by 3.00” wide — like some surgical instruments or a snorkel for divers. These can have data files that are absolutely huge.
“One thing about these parts is that they must have a very good finish,” says Powers. “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. What the Bridgeports allow me to do is create a very tight, dense point cloud, so the step-over from slice to slice as we’re going across is very, very small, and that makes a finer finish and reduces polishing time significantly. The big advantage the Bridgeports bring to contour work, other than accuracy and repeatability, is their speed — speed in transferring data. The control on both new machines — a Fanuc 18i MB — is a real advantage to us in transmitting data very quickly.”
POWER AND DATA
Powers says that they had developed a bottleneck in machining the contours of some of their horns. “These two Bridgeports replaced two high-end Japanese machines, which frankly couldn’t keep up with the data, nor could they produce as fine a finish,” commented Powers.
“The Bridgeports are just so much faster,” Powers says. “The control technology of the previous machines simply 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 certain baud rate, a speed at which it could interpret data. What would happen is that we would have to slow the machine down because the machine controls couldn’t digest the fine increments of data as fast as the machine could act on them. We’d take a part and create a point cloud of the shape and from point to point that might be 0.00003” or 0.00004”. We’d feed that information across to the machines, and they’d go into starvation mode because we couldn’t feed information fast enough to keep the spindles turning.”
With the new Bridgeports, machine starvation is nonexistent. The data literally flies from the control to the spindle, keeping productivity up and helping to reduce the chance of process interruption. Powers notes that as a result he can run at 80 to 100/ipm, where with the other machines he’d run at 35 to 40/ipm and still be worried about starvation alarms going off at that rate. The Bridgeports are literally twice as fast.
Powers remarks that another advantage of the Bridgeports is the finish they produce machining the titanium horns. “We don’t machine to a tolerance, like an aircraft shop might,” he says. “What we have to do is fit the part so that when they’re welding there’s no marking on the surface of the plastic part. The requirement is that our part has to fit precisely and exactly. This is very hard to do. Just as in producing an injection mold, hand polishing is always the last step. We massage the data into the machine tool program, machine the part and then hand polish. What we do is match the fit of the part from the original injection mold. Sure, we can hold 0.00003” or 0.00004” on most of our contours with a surface finish of 8 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.”
The finish may in fact be closer than described above, says Powers. He notes that when they used Japanese machines the amount of polishing in finishing might take 60 to 90 minutes. With the Bridgeports, polishing takes 30 to 40 minutes to get the same results — about half the time of the old process. “As a matter of fact,” Powers says, “the results are better because there’s less marking on the parts. With the Bridgeports we’re getting a far superior finish — before polishing. This again is due to more accurate transmission of data. What we transmit and what we see at the machine tool spindle are much more accurate with the Bridgeports.”
Powers reminds us 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, which depending upon material availability and the design of the tool and machine time, he’ll probably do. But there are times that he won’t be able to meet the deadline because there’s more machining in the part than can be done in three to four days. Some tools may take three to four weeks to obtain, and when the part requires outside finishing to allow certain carbides sprayed on and ground, that may take another week or so.
“Some of these tools last for years,” Powers says, “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 we see are 20 kHz jobs. What a 20 kHz tool does is vibrate back and forth 20,000 times a second. That’s what creates the energy when it contacts the part. The friction melts the plastic and welds the part. Welding cycles are typically less than a second. There can be times when the weld cycle is longer, but a well-designed plastic joint would weld in between 300 and 500 milliseconds. It’s a very fast, very quick process. There’s no contamination. It’s very environmentally friendly. It’s also pretty unforgiving. We have to produce perfect tooling, which means we must rely on the precision, accuracy, repeatability and data crunching speed of the Bridgeports.”
MATTER OF VALUE
John Powers reflects on the decision to buy the new Bridgeport 610XP3 and 760XP3. Setup, he says, is very quick and easy. One of the options he’s particularly pleased he chose are the two Renishaw® probes, one for tool setting and the other for workpiece inspection. “If you look at a chunk of titanium sitting on the bed waiting to be machined into an ultrasonic welding horn, the piece might be worth $3000 to $4000 — 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 says. “We use one Renishaw probe to locate exactly where the contour is going, and it makes setup very simple and easy. We do one-offs and go from one part to another, and 15 minutes later we’re cutting the next part. This is very quick for us.”
Many of the things Powers’ team does are simple, common sense things. For example, they keep the same tools in the same pockets in the ATC, so they become “standard” tools and are always in the machine. The Bridgeport 610XP3 has a 24 tool ATC and the Bridgeport 760XP3 has a 30 tool ATC. Both change tools in four seconds, chip-to-chip. “The Renishaw tool probes make it easy to change from a worn tool to a new one,” Powers says, “and if you consider that we’re cutting titanium for 7, 8, or 9 hours on a single job, we use multiple, redundant tools to remove the chance of breaking a tool halfway into an 8 or 10 hour job. The Renishaw probe tells us when to change, and we change out tools pretty frequently.”
Powers says that when they looked at the new Bridgeports, he thought the price was reasonable, but when he looked closely at the specs, he was surprised at the value for the dollar. “The control and all the drives are top of the line Fanuc — bullet proof,” he says. “The overall construction, the large ball screws, everything seemed rigid, stable, very robust. In fact, we run them lights out. We put the large contours on when the guys from the day shift are leaving, and we’ll run those contours overnight. We needed a machine we could rely on, because we’re running nearly a three-shift operation here, and these machines are cutting chips all day long.”
COOLANT - GETTING IT IN, KEEPING IT CLEAN
Another huge advantage offered by the new Bridgeports is through-spindle coolant at 290 psi, according to Powers. “We machine some really deep contours, and we’re able to use this option to get coolant into places we never thought we could, and this makes a significant difference in the quality of the finish machined part.”
One of the things that Powers hadn’t planned on was fine shavings and slivers in the coolant. He explains: “We’re using small tools, perhaps a 0.0625” ball nose endmill to get into the little, fine, tight corners and small areas — perhaps a 0.0060” or a 0.0090” tool — we’ve actually run a 0.0040” endmill. Most of the time, we’ll run from 0.0625” to 0.500”, and most of the time the finished work is done with a small tool, perhaps a 0.125”. Consequently, we started seeing little, fine chips which eventually would plug up the coolant supply. Hardinge designed and installed an inline filter, much like your car’s oil filter, and it traps these fine shavings and slivers. End of problem.”
AND THEN THERE WERE MORE
“Right now I’ve got an appropriations request in for two more machines,” Powers says. “I’m not sure if we’re talking about two Bridgeport 610 XP3s or two Bridgeport 760 XP3s or one of each. Plus, I have another project that would take a larger VMC, probably the Bridgeport 1000XP3. So, it looks like we’ll probably buy three more.” However, Powers again cautions against buying the same name brand just because you’ve done so in the past. Doing your homework is a must when buying capital equipment — any equipment. Are you getting good value in return for your investment? “Above all,” Powers says, “make the vendor sell you on his machine. Sending you a brochure and a spec sheet doesn’t cut it when you’re parting with tens of thousands of dollars. Yes, we’re buying another three Bridgeports, but it’s not because we’re loyal to the brand — partial, maybe yes. But we’ve done our homework. We’ve watched our most recent Bridgeports and feel we’re on very solid ground. The value for the dollar is exceptional.”