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Viewpoints: Do You Really Need a Special-Purpose Machine?

 Vincent Trampus

By Vincent Trampus
Vice President
Heller Machine Tools LP
Troy, MI

When you consider the progress in machining technology, you might wonder if the special-purpose machine has seen its day.

Not quite yet, but sooner rather than later.

The characteristics of the machining center today greatly broadens its scope, allowing it to work with tooling and fixturing that only a few years ago would not be considered likely. Gear-cutting, mill-turning, full five-axis simultaneous machining for contouring, and NC feed-out tooling for turning operations allow the machining center to be effectively assigned many more tasks than milling, drilling, tapping, and reaming.

This new range of options is made possible by machining centers designed and built from a clean sheet of paper with the operations in mind. They feature very stiff structure to assure volumetric accuracy under load, ample horsepower and torque, and full five-axis simultaneous machining.

Particularly in the automotive machining arena, special machines have been designed to take on special purposes that standard machines were not designed or equipped to accomplish. But the machining center, perhaps with roots in the horizontal boring mill, has developed to the point where it can take on most of the tasks for which special machines were called upon.

And machining centers can be reprogrammed or repurposed for new assignments as part designs change or volumes ramp up or down.

A flexible machining-center solution also offers the advantage in many cases of a lower initial cost than special machines. With machining centers, manufacturers can enjoy more capability for a similar investment in special machines—but with the flexibility of reprogramming or retooling and repurposing. For example, Heller today is retooling several automotive manufacturing systems that include customer machining centers from earlier programs, not all of which are Heller machines.

Although machining centers are likely to be assigned operations on prismatic parts, they can now perform operations on round parts such as gears, completing the machining in one setup. Key to this new range of assignments is full five-axis simultaneous machining by a highly dynamic, rigid machining center.

Heller, in cooperation with Sandvik and train builder Voigt, has developed a process to produce large bevel gears on a Heller five-axis HMC. With this process, Voigt can avoid the need to purchase a special-purpose machine—a hobber—and apply the machining center to low-volume production of the gears, achieving all the quality required. What’s more, the machining center can be tasked with other assignments as the need arises.

Considering turning operations, a machining center, equipped with an NC feedout axis, driven by the machine control through the spindle, can accomplish what used to require a special boring spindle with fixed tooling: creating precision bores, such as those in an engine block or pump housing.

This new machining strategy enables the user to perform two or more different machining processes on the same machining center in a single setup, including facing, grooving, milling, as well as boring. In a recent application, the results have been a 50% reduction in net machining time, reduced tooling cost, and an increase in process dependability.

Again, with innovative tooling in a highly rigid machine, many different operations can be included in a single setup. The right machining center is more flexible than ever.

The potential cost benefit to manufacturers is large. Combine 95% or greater spindle uptime with the ability to perform all necessary operations in one fixture, eliminating midcycle part handling, and you can dramatically reduce the cost of each workpiece while increasing the quality of the work and throughput rates. And should part details change or part volumes adjust, the machining centers can respond in a very short time.

The advantages are compelling. So much so that re-thinking the process on existing production parts could justify an investment in high-capability machining centers, using fewer machines to deliver the production than may be the case currently, while positioning the factory floor to successfully take on the challenges ahead.

But the keystone is the machining center. It must combine high dynamic stiffness and a high-torque spindle with full five-axis capability for complex, difficult-to-machine parts in a single setup. ME


This article was first published in the August 2011 edition of Manufacturing Engineering magazine.  Click here for PDF 




Published Date : 8/1/2011

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