FMSes uncork bottlenecks: Turning Performance

Many shops follow a well-worn growth path. The owner buys an affordable 3-axis, 40-taper vertical machining center, works long days and weekends until the business is stable, and then continues adding one VMC after another until a long row of verticals stands along one wall. Every machine or two has an operator standing in front of it or them. Countless hours have been spent building tooling and programming parts. Everyone knows which job goes where and how to set it up, and the shop mentality is firmly entrenched in “vertical thinking.”

There’s a lot to be said for this approach. It’s relatively safe and steady, and thanks to the popularity of VMCs, finding a qualified machinist is probably easier than for other, less common machines. Yet it’s far from perfect. Machining multiple sides of a workpiece on a VMC requires an indexer or trunnion, which increases costs and consumes table real estate. Unless a pallet system is incorporated (another expense), the spindle is idle while parts are loaded.

Within 4 years of installing its first flexible manufacturing system, Steelville Manufacturing employed three times as many workers. Image courtesy of Steelville Manufacturing.

Moreover, chips fall back onto the part, making chip recutting a concern. And while a robot might be used for unattended loading and unloading, it mandates automated fixturing, which is impractical unless part quantities are in the thousands.

Tripled Growth

“Before our first FMS, we did everything on our verticals,” said John Bell, vice president of engineering at Steelville (Mo.) Manufacturing Co., a machine shop specializing in aerospace parts. “To be fair, we did have a stand-alone horizontal machining center, and we loved it for all the obvious reasons. But when one of our customers asked if we’d be interested in a prove-it-and-move-it program, which meant replicating their FMS line so we could take over production following an internal runoff, we jumped at the chance.”

For those unfamiliar with the concept, in this context, an FMS line is comprised of one to six, or more, horizontal machining centers attached to a linear pallet system (LPS). The flow of work to each HMC is managed by a cell controller, which receives scheduling and priority instructions from its human master. Each machine tool has hundreds of tool positions, and the LPS contains perhaps hundreds of pallets, each with a fixture or tombstone.

When the controller instructs the FMS to load a new job, the system’s rail-mounted robot retrieves the appropriate pallet and carries it to whichever machine is available. The same robot brings completed pallets to a load/unload station, where a human or another robot removes finished parts and loads raw material for the next job.

When presented with an opportunity to purchase an FMS, don’t approach it lightly, Bell warned. “Know your costs, really figure out what you’re doing, and then explore all the options. And be prepared for growth. When we installed our first FMS 10 years ago, we had around 55 people. Within 4 years, we employed three times that. And a large part of that is because of the switch to flexible manufacturing.”

It wasn’t a matter of just hiring 100 more machine operators. Steelville needed more programmers, manufacturing engineers, shipping and receiving people, and even janitors. “When you buy an FMS, it’s pretty incredible what happens,” Bell said. “The business just expands upon itself. But you do need to change your mind-set to get the full value.”

Some examples include changes to workholding, setup procedures and programming.

Any Part, Any Machine, Anytime

Today, Steelville has two FMS lines, with a total of 10 machines between them. Bell said spindle utilization averages 80 percent throughout the year, with periods of 97 percent utilization not being unusual.

Morgan Hill, Calif.-based Micro-Mechanics Inc., a multinational supplier to the semiconductor and other high-tech industries, has seen similar results with its pair of FMS lines.