Rotary Transfer Machine’s Flexibility Spurs Shop’s Growth
Initially purchased for a high-volume job, this rotary transfer machine proves an efficient tool for short- to medium-run family-of-parts jobs as well.
Metal Essence, Inc. is a small machine shop in Sanford, Florida. Owner Al Stimac is the embodiment of the immigrant-makes-good story. He came to this country as a teenager from Croatia and, after 25 years of working in the metalworking industry, opened his own precision machining shop in 1986.
Like most shops, Metal Essence mostly handles small- and medium-volume jobs. Mr. Stimac is always alert to new opportunities, however, and when he learned about a high-volume part being produced in Detroit, Michigan, that was headed to Mexico to be manufactured there instead, he decided to bid on it. He bid the job with the expectation of producing it on a rotary transfer machine, even though he didn’t have one; he would buy one if he won the job, and he did win the job.
The job called for 6 million parts annually. Mr. Stimac did the math: Working at 92 percent efficiency, the rotary transfer machine would have to operate around the clock, 7 days a week, producing a part every 3.5 seconds. He took the job to Hydromat Inc. (St. Louis, Missouri), who, after analyzing the machining requirements for the part, advised him that it would require a 4.5-second cycle time and that two machines would be needed to satisfy the annual production requirements.
The problem was, Metal Essence is a small, privately-owned shop with limited resources; it could not afford to buy two machines to run the job. Mr. Stimac approached Hydromat again and asked if they would be willing to work with him to get the cycle time for the part down to 3.5 seconds so he could run the job on one machine.
The request came to the attention of Hydromat President Bruno Schmitter, who saw it as an opportunity to provide a customer with a precision machining solution. He accepted the challenge and committed his company to work with Metal Essence to find ways to reduce the cycle time for the part. Each firm would concentrate on specific areas: Hydromat would make adjustments to the machine where appropriate; Metal Essence would work on the tooling and workholding aspects of the job.
Hydromat’s task was perhaps the most challenging because the design and operation of its rotary transfer machine had been refined through the years to improve performance. Any changes, therefore, could be expected to bring about only modest improvements. For example, by shortening the pusher travel of the bar feed on Metal Essence’s machine, Hydromat was able to shave a tenth of a second from the cycle time. Timings were adjusted to achieve similar savings. The part inverter station was modified to flip the part faster, and so on.
Metal Essence’s efforts resulted in a more dramatic payback. The part requires an operation that takes a hefty roughing cut yet leaves an acceptable surface finish. To ensure that the aggressive feed rate for the operation would not cause premature tool wear and compromise surface finish, Mr. Stimac contacted a diamond tooling source in the Orlando area to design a diamond tool for the application. “Most sources require a 4-week lead time for a tool,” he notes. “The shop we worked with was willing to come up with a tool in 1 week and agreed to make the modifications needed to improve the performance of the tool. They made the tool, we tested it and requested changes…there was a lot of back and forth. Through trial and error, we finally found the right geometry. It produced well-formed chips and provided the surface finish we needed (less than 16 microinches) at the high machining speed we needed if we were going to make the 3.5-second cycle time.”
Another consideration was the raw material used for the aluminum part. One of Mr. Stimac’s favorite methods for minimizing machining requirements for a part is to use a near-net-shape blank when possible. When the part is made of aluminum and its configuration permits, Mr. Stimac starts with a blank sawn from an aluminum extrusion designed with a profile very close to that of the machined part. (During Production Machining’s visit to the shop, we saw numerous extruded aluminum blanks being mounted in multiples on tombstone fixtures mounted on the shop’s horizontal machining centers.)
Mr. Stimac used that same approach for the high-volume job running on the rotary transfer machine. The extrusions from which the discrete blanks for the parts are produced can be seen loaded on the rotary transfer machine’s magazine-type bar feeder (see photo above). Where profile dimensions of aluminum extrusions are usually accurate within a few thousandths, the company requires its local extruder to hold even closer tolerances to minimize machining requirements on the periphery of the part.
When Mr. Stimac took delivery of the rotary transfer machine, the required cycle time and surface finish of the machined part was close but still short of the goal. However, as a result of the close collaboration between his company and Hydromat, he was confident that ongoing work would achieve the desired results. He felt confident that Hydromat would provide any additional support that he might require—an important consideration in light of the fact that this was the shop’s first encounter with a rotary transfer machine. “We are just a small job shop without a lot of investment capital,” he explains. “The rotary transfer machine represented a major investment for us, and if for some reason we failed to produce the parts, the consequences could be disastrous for our company. It was comforting to know that we could rely on Hydromat’s constant support.”
For example, in getting to the 3.5-second cycle time with the diamond tooling, the shop was creating such a load on one of the spindles that it was overheating. A Hydromat representative called in to diagnose the problem determined that the load created by the aggressive machining called for a larger spindle motor. So the representative installed a larger motor, which solved the overheating problem.
Hydromat also provides Metal Essence with a remote machine monitoring service that keeps tabs on the performance of the rotary transfer machine. “Its engineers can call in and see what we are doing with the machine,” Mr. Stimac explains. “They can even make changes to the machine. We monitor the effects of the changes on cycle time and surface finish at our end and communicate with them if other problems arise.”
Three Seconds And Falling
The shop has had its rotary transfer machine for about 2 years now. In that time, it has reduced the cycle time for the high-volume part to 3 seconds and is currently working on getting it down to 2.9 or 2.8 seconds. Reduction of the cycle time for the job created a modest amount of open time on the rotary transfer machine, and the company looked for ways to fill that open time with other shorter-run work. To accomplish that, the company began to focus on ways to reduce setup times for the machine.
“When we bought the rotary transfer machine, we had the same impression that a lot of people have, which is that the machine is only good for high-volume jobs,” Mr. Stimac confesses. “Over the last 2 years, however, we have discovered ways to reduce setup times so that we can use the machine to process smaller quantities of similar parts—families of parts—where the changes involved in changing over from one part to another are relatively minor. In some cases, we can go from one job to another in as little as 2 to 3 hours.
“Using tool presetters, for example, we can preset the tooling off the machine so that tool changes can be made quickly,” he explains. “The biggest part of the setup time for us when going to an entirely different part is having to change the chuck jaws in all 12 stations of the machine and the lining for the bar feeder to accommodate the different extruded bar profiles, and we are presently working with Hydromat to find ways to reduce those times. Right now, however, we are concentrating on getting things ready for the next job while the current job is still running. Our experience has shown that having everything in readiness for the next job saves our people 30 to 60 minutes on a setup.”
To date, Metal Essence has used its rotary transfer machine to produce seven jobs totaling 11 million parts. However, Mr. Stimac is quick to point out that the seven jobs are from three different part families. He explains that in cases where only minor changes are needed to go from one part to another in a family of parts, he can economically run lot sizes of less than 5,000 pieces on his rotary transfer machine.
A Second Machine After All
The shop’s rotary transfer machine is currently running at 100 percent of capacity and accounts for 20 to 25 percent of the shop’s total sales. Where two years ago, Mr. Stimac couldn’t afford to buy a second machine, today he is getting ready to accept delivery of his second Hydromat, and he already has work scheduled for the machine. “The job involves a family of about 30 different parts, each of which requires the drilling of a slightly different side hole,” Mr. Stimac explains. “Lot sizes range from 5,000 to 10,000 parts per month.”
Mr. Stimac notes that the second machine will be a hydraulic machine, just like the first one. “We have found the hydraulic machine to be very reliable,” he explains. “It is a workhorse, producing parts every day, non-stop.
“However, we are purchasing the second machine with one CNC station to accommodate the different side holes from part to part,” he continues. “Hydromat built the CNC unit especially for our requirements. We saw the unit in operation machining several different parts from the family, and we are confident that the unit will do the job for us.”
Metal Essence is still very much a Mazak shop, but Mr. Stimac’s experience with the rotary transfer machine for the last 2 years has opened his eyes to other possibilities. “The rotary transfer machine provides a higher margin than any other machine in the shop,” he notes. “One reason is the cost of labor. For example, I have a lot of horizontal machining centers, which are highly productive machines. However, they still depend on a person loading and unloading parts, and if that person forgets to tighten a workpiece I’ve got parts flying, broken tools, possible damage to the fixture or machine…it can get costly. The rotary transfer machine avoids those problems; once the workpiece material is loaded in the bar feed, it is automatically loaded into the machine and machined parts are automatically ejected. The machine can run practically untended until it runs out of material.
“Right now, I think I could be very successful with two or three rotary transfer machines, using them for both high-volume, long-running jobs and for family-of-parts type jobs involving relatively small lot sizes,” he continues. “With the many techniques available for reducing setup times, the family-of-parts type work represents a whole new and profitable way of using the machine.”
Mr. Stimac first began thinking about a rotary transfer machine in order to win a job that was headed for Mexico. Purchasing the machine enabled him to keep the job here in the United States. In the 2 years that the machine has been in operation at Metal Essence, more than 90 percent of the parts produced on it have been exported to customers in Brazil, Mexico, Spain and the Czech Republic. How’s that for reversing the flow?
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