Revisiting An Intriguing CNC Multi-Spindle Experiment

When Production Machining visits a company to write an article about the benefits of a new machine tool, programming software, high-pressure coolant system, inspection machine and so on, we seldom get the chance to revisit the company to track ongoing success with the investment. When PM Editor-in-Chief Chris Koepfer asked me to check back with Otto Engineering (Carpentersville, Illinois), a manufacturer that he had written about in the September/October 2004 issue, I contacted John Lang, machine shop supervisor for the company, to arrange another visit to his shop. (I had been there before to assist in the cover photo shoot for that issue.)

Otto Engineering is a manufacturer of mechanical switches and related products. The vertically-integrated company has its own machine shop, which produces many of the switch components that supply the company’s assembly lines. Like most other manufacturing firms, Otto was looking for ways to cut costs and improve the efficiency of its manufacturing operations. To reduce inventory costs, the company wanted its machine shop to produce parts for its assembly lines on more of a just-in-time basis. “We were asked to find a way to reduce the inventory in our assembly area by 75 percent,” Mr. Lang explained in the previous article. “The math was simple. Our current inventory turn for a given family of parts was about 1 month. We had to find a way to get that down to about 1 week.”

Producing the different switch components in smaller quantities would not only require more frequent setups on the shop’s existing CNC single-spindle lathes, but also additional lathes would be needed to permit more part numbers to be produced at the same time. However, adding more machines meant having to expand the machine shop and incur higher overhead costs.

A visit to a shop that was running multi-spindle screw machines started Mr. Lang and others at the company thinking about purchasing a CNC multi-spindle machine as an alternative to more CNC single-spindle turning centers. Multi-spindle machines have traditionally been used for applications involving long runs of parts in very high volumes. Could such a machine be used to efficiently produce numerous part numbers in small quantities?

Otto approached DMG America Inc. (Schaumburg, Illinois) to ask if its Gildemeister multi-spindle screw machine could be configured to meet Otto’s high-mix, small-lot requirements. The builder responded to the challenge and agreed to work with the company to come up with a multi-spindle solution for its production needs. The solution turned out to be a Gildemeister GMC 35 ISM CNC multi-spindle turning center, configured especially for small-lot production.

The machine uses single-point, indexable insert tooling exclusively to minimize tool changes from job to job. Tools are preset offline to keep unavoidable tool change times short. The machine is equipped with a bundle loader capable of holding hundreds of bars at a time. No time is lost changing out bars when going from one job to the next because Otto has standardized on a single bar diameter for the machine.

Configuring the machine to minimize change-over times was important, but Mr. Lang realized that the key to succeeding with the multi-spindle is organizing Otto’s part mix into families of parts. Doing so would enable the machine to go from one part in a family to another with little or no change-over time. The purpose of our revisit was to see how well he had succeeded.

"We were able to organize many of our parts into four families of parts,” Mr. Lang reports. “We schedule jobs to run on the multi-spindle by family to minimize change-over times from job to job. Going from one part to another within a family, our setup time averages about 3 minutes.

"After we have run all the parts in one family, we set up the machine for the next family,” he continues. “That usually takes about 60 minutes. It takes us about 2 weeks to go through the four families of parts, and then we start all over again.

"When we bought the Gildemeister, I was sure we’d reduce our running time for the parts, but I was worried that we’d only have about 300 hours of work per month for it,” he continues. “We are currently at 500 hours of work per month (a two-shift operation) for the machine.”

Otto is currently running 200 part numbers on its CNC multi-spindle. Mr. Lang expects the number to grow to 300 parts within the next 6 months. The timing of the Gildemeister purchase couldn’t be better. Otto enjoyed a 20 percent increase in business last year and is expecting a 30 percent increase this year because of increased sales of existing products and expansion of its product line.

Although Otto has not yet met its 75 percent inventory-reduction target, it has made a significant dent in the amount of parts in the pipeline. “We are running lean to the point where if this machine were to stop running, I would have to send home some of our people on the assembly line,” Mr. Lang says.

Finally, Otto’s success with the multi-spindle as a short-run machine hasn’t ruled out its use for longer runs. “I regard our multi-spindle as a 24/7 machine,” he explains. “Not all of our jobs involve small quantities. When we get a large order, I try to schedule it to run over the weekend. The machine virtually runs itself and, if no change-overs are required, is capable of running untended for long periods. When we get a large order, we can run the job over the weekend with no one in the building.” Short runs and long runs—that kind of flexibility is hard to beat.