Multitalented MACHINE TOOLS

Manufacturing Engineering, Jan 2005 by Aronson, Robert B

They do everything but make the coffee

The path to survival in the face of overseas competition favors those companies that can provide added value to a product. That means more precise, complex products. At the same time small companies are looking for greater product diversity, but without major investment. And this has favored the development of multifunction machine tools.

Here are some of the pluses:

* Fewer, sometimes single, setups.

* Complex parts don't have to be made on several machines.

* Minimized part handling.

* Fewer machines-don't need as much costly floor space.

Machine tool manufacturers have approached this expanding market in two ways. The most obvious is to be able to do more than one process. Machines are now available that offer a combination of milling, drilling, tapping, turning, grinding, welding, and balancing.

The other less obvious way to be more versatile is to make the machine more productive by improving or accelerating part handling, chiefly through the addition of robots or part-handling mechanisms within a single machine or cell.

Another factor promoting interest in multifunction machine tools is the trend of major auto and aerospace manufacturers to minimize their own manufacturing, and instead require suppliers to deliver ready-to-assemble modules. Analysts see large companies faced with warranty issues and aging equipment getting away from high-volume precision work. Some high-volume jobs are now being broken into smaller lots and given to a number of suppliers.

Here are a few examples:

Grinding is now part of the machine tool cell. Makino (Mason, OH) has concentrated on developing grinding technology. Initially they offered plated CBN grinding wheels in conventional machining centers. But, according to Makino's Mark Waymouth, "This technology has been greatly expanded. In addition to grinding with plated CBN, grinding with vitrified grinding wheels is now being done with machining centers. When machining hard nickel-based alloy materials, grinding has now become the primary roughing operation, in addition to the traditional final finishing operation. This has been a dramatic transformation and offers the flexibility of having both machining and grinding capabilities in one machine.

"We take a standard machining center platform and offer unique grinding option packages. In addition to plated CBN wheels we now offer a grinding option package that enables the use of vitrified wheels. Plus, we have added special coolant circuits and wheel dressing capabilities to support the grinding functionality. A second spindle carries a diamond dressing roll to support continuous dress grinding.

"That includes both continuous and intermittent dress systems that are mounted within the machine tool's work zone. The ability to supply continuous dress improves productivity and quality because sharp abrasive is continuously exposed and the wheel has very good form-holding capability. The wheel profile can be changed simply by calling up a different dressing roll and grinding wheel from the tool magazine, analogous to the way in which a machining center performs a tool change.

"The single most important aspect to control is coolant application. If too much is applied, the wheel hydroplanes; too little and you not only reduce the cutting rate, you are likely to burn the part. There is a separate set of nozzles for milling, plus through-thespindle coolant, where needed.

"We can position a high-pressure nozzle 360° around the grinding wheel. Utilizing this programmable nozzle, high-pressure coolant is injected into a porous wheel ahead of the grind. Centrifugal force pushes the fluid out of the wheel. There is enough fluid to flush the swarf from the wheel and keep the part cool. With this system and continuous dressing we can remove up to 12 in.3 [33 cm^sup 3^] in hard nickel alloys."

Modular design is critical. Emag (Farmington Hills, MI) is unique in that it is vertically integrated and makes virtually all of its own machine tool components. "We have a number of basic machine platforms that can be modified to meet specific requirements," says Vice President Gary Hulihan. "Most of our machines are custom-built using add-on modules. For example, one of our best-selling machines is the verticalspindle chucking machine. With it we can do green turning, hard turning, grinding, nobbing, hardening, assembly, and laser welding. "

When they get an order, designers first derive a solution for the customer's production situation, then create a machine or line of machines that can do the work. This may be a single-purpose (grinding, milling, etc.) machine. But more often it requires a multifunction design that can include: milling, drilling, turning, grinding, thread rolling, hobbing, tapping, welding, gaging, and part balancing in one machine. "We don't get the easy jobs!" says Hulihan.

Key design features include:

*Short strokes. That is, minimal travel between the part and cutting element.

*Ambient cooling. The machine is kept at ambient temperature, not at some arbitrary value. The best results will be achieved if the part being made and the machine are at the same temperature. An internal system circulates fluid to all heat sources within the machine, including motors and bearings.