Open CNC powers machining center rebuild

Many old computer numerical control (CNC) machines have a solid mechanical structure, but out-of-date controls. Retrofitting an old machine with new controls and rebuilding its mechanical hardware, such as ball screws and ways, can make it run like a new machine. HM Dunn (Euless, Tex.) specializes in manufacturing aerospace components.

06/01/2001


Many old computer numerical control (CNC) machines have a solid mechanical structure, but out-of-date controls. Retrofitting an old machine with new controls and rebuilding its mechanical hardware, such as ball screws and ways, can make it run like a new machine.

HM Dunn (Euless, Tex.) specializes in manufacturing aerospace components. One of its Matsuura MV1000 machining centers had been in storage for two years, when the company realized it needed a number of parts the machine could produce. MV1000 is a vertical, two-spindle machine that had a Fanuc 3000C control. In April 2000, Red Fultz of HM Dunn approached Mark Rice, president of Mark's Industrial (Bedford, Tex.), to rebuild the machine.

The machine ran programs for titanium parts, with profiling done via keller-type cutting. These numerical control (NC) programs included many very small linear moves at high feed rates where the desired surface is generated from the CAD system. Some part programs can exceed 1 MB.

Mr. Rice says, "I recommended MachineMate control, since I had experience with it, and I knew it would do the job."

MachineMate's (Fond du Lac, Wis.) solution has an open, PC-based CNC architecture with integrated software PLC. The operator interface is straightforward, with most operator actions available in one or two keystrokes. Its PLC uses standard ladder-diagram programming, as well as structured text. The PLC can perform conversion between IEC61131 languages as needed, and different modules can be done in different programming languages within the same application.

The control can run its part programs directly from the PC hard disk, so part program storage is large. The control's performance is more than sufficient to handle the machine's keller cutting profiles. Memory also has space reserved for PLC-retentive variables, machine set up parameters, etc.

Achieving accuracy

During the course of the retrofit, everything would be replaced or refurbished except the machine frame and spindle head. The control, drives and motors were new. Axis ways were reground. New hydraulic components were provided.

Mr. Rice designed a new operator station for the machine, including a custom enclosure. The switch panel below MachineMate had just nine buttons, including several with more than one action. The PLC program can send the operator messages for each step of an operation (like a tool change), which means, if there is a mechanical hang-up, the operator can quickly determine the cause.

After the rebuild was finished and the machine was ready to run, a test cut of a 6-in. diameter circle was made. The first circle was within 0.0015-in. of round. With a few gain changes to the axis drive tuning, subsequent cuts were less than 0.001-in. out of round on the first day of operation.

HM Dunn also successfully ran large part programs directly from the MachineMate hard disk. Though the part program often exceeded 40 blocks per second, surface finish wasn't affected. The refurbished machine cut parts for HM Dunn in December 2000, less than eight months after rebuild began. In fact, one person handled the entire electrical and mechanical retrofit, design and rework process.

Two months after getting it into production, Mr. Rice adds, "The Matsuura with MachineMate control is putting out almost four times the work that Red Fultz thought he would get from of it. The limiting factor is the cutting tool. If he can find better cutters and get more spindle speed, he could increase throughput."

Gary A. Mintchell, senior editor gmintchell@cahners.com





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