Minimizing Parts And Designing Components Solves Several Needs

Milltronics Manufacturing Company, a CNC (computerized numerical controls) machine tool builder located in Waconia, Minnesota, is a major manufacturer and marketer of high quality, cost effective machining centers, toolroom and bridge mills and toolroom lathes sold both in the United States and abroad.

During its nearly 25-year history, Milltronics has changed its marketing philosophy several times to survive in a very competitive business. Originally, they manufactured and marketed CNC systems (a computer programmed with dimensional information which commands the movements of milling machines) to domestic machine tool builders. As more and more imports entered the market, U.S. manufacturers dropped out, convinced they could no longer compete.

With a decreasing number of domestic builders, Milltronics started selling turnkey products, installing their own CNCs on imported machines. Additional government sanctions nearly depleted their source for machines, as well as the iron source for the few customers they had remaining. At that point, their only remaining choice was to build the machines themselves. It was a path that many had tried earlier, and failed. The difference was how they did it. Milltronics credits much of its success to keeping the number of parts in their machines to a minimum and designing components that solve several needs.

They named their new product line "Partner," which defines the company's overall attitude. Milltronics developed "partnerships" with its employees, vendors and customers. This strategy, in turn, influenced the technical capability, competitive pricing and redefinition of an entire segment of machine tools.

It was through this company/vendor partnership that Milltronics solved a troubling engineering problem that was threatening the quality and future design of one of its most popular product lines--the CNC machining centers. The company was installing brush-type DC servomotors on the machines which could not offer the technical and performance superiority of AC servomotors.

When the machine tool builder decided to install brushless motors on the VM17 series machining center, Robert Page, an electrical engineer who is responsible for servodrives and motors, became an integral part of this engineering change. "We had determined at the start of this project that the market was demanding brushless systems," says Mr. Page, "mainly because of its speed and reliability." There were some fast brush-type DC motors on the market but, compared to newer brushless technology, were considered old-fashioned. "In general," Mr. Page notes, "brushless motors are faster and the need to change brushes or worry about commutation limits is eliminated."

The company experimented with various combinations of servodrives and motors from various manufacturers over an 18-month period. In some cases, they tested products from the same manufacturer; in other cases, they mixed and matched. "Our results weren't all that good," Mr. Page states. "We still were having problems and continued to research options that were easier to use and more reliable."

The company began looking at the Sigma Servo System from Yaskawa Electric (Northbrook, Illinois), a compact, high performance combination of brushless servomotors matched with flexible, all-digital amplifiers. The Sigma family of products provided higher torque to inertia, higher torque per length and higher torque per dollar than other systems they analyzed.

Peter Gennuso, regional sales manager, Yaskawa Machine Tool Sales Group, arranged for delivery of brushless servo- motors, drives and cables to Milltronics for installation on a machining center scheduled for shipment to the IMTS trade show in September 1996. "I was very impressed with the speed and overall performance of this prototype model," states Mr. Page. "It generated tremendous interest from customers at the show who were becoming more astute at that time to AC digital brushless motor technology and performance."

Yaskawa's technical representatives were also very supportive. "Whenever we asked for help, they immediately showed up here to work with our people. I know one technician spent two days at our facility to make sure the drives were totally matched appropriately," Mr. Page said "The support has always been very good—one of the things we liked from the beginning. They went out of their way to provide us with different Yaskawa Sigma servo models for testing in our prototype units, and didn't hesitate to take back those we didn't choose. Yaskawa gave us the tools we needed to make the initial discovery and get things going. The learning curve was quick because of their engineering effort and the technical knowledge they provided in the plant."

"Our engineering tests using the brushless servomotors and drives showed excellent results," Mr. Page added. "They performed exactly the same way every time they're turned on—from one machine to the next. It has made my life much easier because now I don't have to fine tune the servomotors and drives. They are absolutely uniform and always work."

Lately, Milltronics has been doing much more rigorous testing to ensure that its machines are accurate. One of the most rigorous is the Renishaw bar ball test. The machine is programmed to cut a circle which is measured for circularity to see how close it is to being theoretically perfect. This is a difficult operation for machine tool motors to drive and control. It's comprehensive, since it measures all aspects of the machine. According to Mr. Page, the brushless servo motors are delivering round, smooth circles—every time.

System set-up, parameter setting, auto-tuning, performance monitoring and troubleshooting are made much easier with SVMON, the Sigma System's software package. "It's very easy to use," Mr. Page noted. "SVMON allows you to plug an RS-232 cable into the front of the drive, and download the parameters in about 15 seconds. A parameter file is maintained for each axis of these machines, so we just power up the drives, download the parameters, and they're ready to go."

Tim Rashleger, chief operating officer, thought early in the testing phase that the Sigma Servo brushless motors and drives and, concurrently, the higher technology level it provides, would be too expensive—that it was going to cost too much, and the learning curve might be too long to get the product going. But it turned out to be quite the contrary. "The cost of going with the Yaskawa Sigma Servo motors was actually less than the previous effort," he said. "I think it falls into four categories. First, the curve to get the product up to speed and ready to go was very quick. Second, the price was better than we thought. When the price was factored into our volume figures, they were easy to justify. Third, technically on the floor, the Sigma Servo motors and drives assemble quicker and test faster. Troubleshooting is minimal because they work. And fourth, when they get out into the field we don't have replacement and service costs and, consequently, unhappy customers. So, it turns out that the overall cost of using Yaskawa Sigma Servos is favorable against what might be lower technology.

Milltronics' product line is divided into machining centers and toolroom machines. Two-thirds of its business is from the machining centers' product line and one-third is generated from the toolroom products. There are six Milltronics machining center models, ranging from 25- by 16- inch to 100- by 30-inch table travels, and up to 20 horsepower for heavy-duty machining. All of these, with the exception of an entry-level model, are manufactured with Sigma Servo motors and drives. "From a manufacturing standpoint, it has been very productive for us to build several models with the same servomotors," Mr. Rashleger says. "Previously, we had to buy several different sizes of DCs in higher quantities to get better pricing, and then carry a large inventory. Because of Yaskawa's value in the 40- and 50-inch range, we're able to cover several machine models with one servo product."

The rapid traverses of the VM16 machine with DC servodrives is 400 inches-per-minute (ipm). Most other machine centers in the product line that use Yaskawa are substantially higher—about 800 ipm being typical. "When you're selling a machine with 400 ipm versus a machine that features 800 ipm, that's the difference the Yaskawa AC servos make compared to the brush-type DCs," explains Mr. Rashleger. "We're not really pressing either technology past reasonable, and the reliability of both technologies, quite honestly, is very good. However, a customer who needs production from a machine, or is doing high-speed cornering, is going to look at the 800 ipm feature favorably.

"Also, the cornering feed rate when actually cutting metal is expanded on the AC digital servos. This would be very demanding for the DCs. On the other hand, the AC servos, because of their lower inertia and very high performance, excel in projects requiring high speed processing and three-dimensional machining.

"We've had Yaskawa Sigma servos in the field now for over six months, so there are a significant number in use," Mr. Rashleger notes, "and I have never had a single report of one being undersized. Whatever they publish, the specification tends to be very conservative. Sometimes, there were questions previously about the thrust of the machine when the same size of DCs were used, but that hasn't been a consideration with brushless Sigma servos and drives. And that's significant.

"The reliability of these products has been exceptional—above any we've ever used in terms of usage. Our service department reported no field failures in the first six months of shipments which, quite honestly, is phenomenal.

"We noticed some of our competitors have started manufacturing some of their own servos," Mr. Rashleger said. "We have reviewed this option, and it just doesn't make sense. To learn this technology—to master and maximize it—just isn't an expertise we feel we should be spending our resources on. The products are very competitive. Yaskawa is far more versed in producing this product technically correct than any private machine tool company could. In our viewpoint, it isn't feasible to design and make this ourselves, and we'll continue to source this part of the machine tool. To make the heart of our machining centers the best pos-sible, we have selected Yaskawa servos.

"We've already determined that switching to brushless Sigma servos was a very good decision for the company," stated Mr. Rashleger. "We're very excited about what it has done for us. We just wish we had made the change six months earlier, because we're paying prices for other decisions. The fact that 100 percent of our AC digital drive usage is Yaskawa really states the confidence we have in the product and the business relationship."

Toolroom machines are incredibly competitive, so every dollar counts in this product line. The requirements on these machines typically are in the realm of DC technology.

Milltronics manufactures its own CNC systems, so the technical advancements in the Yaskawa products are really appreciated," says Mr. Rashleger. Milltronics recently introduced a high-speed Centurion control with state-of-the-art technology, including such features as 3D color graphics and high-speed contouring. But it still wouldn't perform to its maximum performance unless it was matched to a servo with the same upgraded technology. Incorporating the two technologies has given Milltronics a leading edge in performance. Machining centers with this level of performance have typically cost double.

"What is exciting about our company is that there is real manufacturing being done," Mr. Rashleger said. "We're proving that the technology exists in America for a blue chip company to successfully manufacture quality, value-oriented products and market them worldwide. We think the manufacturing base is the most exciting thing happening." MMS