DNC system adds flexibility and functionality at automaker's machine shop

Modern Machine Shop, June, 1993

The Experimental Machine Shop at General Motors Powertrain V6 Engineering Center, Flint, Michigan, is one of the automaker's busiest. They run a minimum of six of their 13 NC machines 24 hours a day, seven days a week at peak periods to produce prototype engine parts. Prototype parts machined include crankshafts, camshafts, engine blocks, cylinder heads, intake manifolds, and engine front covers. In all, over 450 prototype engines are produced annually. In addition, the machine shop is frequently asked to turn around special brackets and other one-of-a-kind orders within a few days that would take much longer by an outside third party vendor. Under these conditions, Powertrain can't stop to deal with computer and networking problems.

But recently it was forced to. Powertrain's existing distributed numerical control (DNC) system, installed 12 years ago, was no longer adequately handling the needs of the expanding machine shop. When operational, the antiquated DNC system was slow. When non-operational, the whole machine shop was down. Nothing could be downloaded. The only job operators could work on was the program in their machine controller.

Problems were taking too long to correct. OEM vendors no longer supported the hardware and software. Instead, it was being supported by a local third party vendor. Unfortunately, they had the bad habit of taking a couple of days to initiate repairs.

But the system's worst problem was its inability to link all of the shop's machine tools. The system had reached its capacity by linking only six of the 13 NC machines.

"We were land-locked," says Terry Bennett, Powertrain general supervisor. "We had outgrown the old system because there was no room for growth."

Concerned with this limitation, plus mounting system problems, and considering future expansion needs, Mr. Bennett assigned a management team to find a replacement system. The team consisted of GM Powertrain's Jim Schlee, N/C CAM coordinator and EDS' Mike Ruhanen, business relations analyst. They visited four or five DNC vendors to witness their equipment in operation. In one case, they even visited the Naval shipyards in Norfolk, Virginia, to discover first hand advantages and disadvantages from a users' perspective. It was important for them to see an example in operation before making a purchase decision.

As a result of these efforts, the vendor list was narrowed to one: the EDS-DNC System. "That system had all of the flexibility and expandability that we needed," says Mr. Schlee. "Plus, they had all the bells and whistles that everybody else did without some of the limitations."

"And they have a pricing structure that we found very competitive," adds Mr. Bennett. "That helped us to conservatively project a less-than two-year return on investment. Combined, these factors meant a lot to us, so we went with the EDS-DNC system."

The system includes an HP 730 workstation which serves as the DNC host. The HP730 communicates with 13 personal computers and NC machine tool controllers over an Ethernet communications system. User interfacing is through personal computers. A local area network enables communications between eight Unigraphics workstations and the machine shop.

With all this different equipment, there was concern that installation would be a time-consuming task. "We allotted two weeks for each machine and we had 13 machines to hook up," says Mr. Schlee. "But to our surprise, we had all 13 machines hooked up in just two weeks! Everything worked the first time. It scared us. It went too smooth."

"That's just the kind of flexibility we were looking for," adds Mr. Ruhanen. He goes on, "Connectivity was simple and fast because the software runs on just about any computer platform. In our open systems environment, we're running the DNC on different vendors personal computers, workstations, and machine tool controllers. It's truly a multi-vendor environment."

The new installation is compliant with General Motors' C4 program (Computer-Aided Design/Computer-Aided Manufacturing/Computer-Aided Engineering & Computer-Integrated Manufacturing). This permits Powertrain 100 percent electronic data capability and establishes a data-sharing network for interactive product development. So if Powertrain Flint's machine shop work load prohibited handling an incoming rush job, it can be sent by modem or via the EDS network to another Powertrain machine shop for completion. The setup brings products faster-to-market.

The new environment is increasing machine up-time. That's because when the old system went down, the entire shop was down. But now, if any one or all of the workstations go down, the machines can continue running. Plus, they have all their tape files stored locally on the machines at those personal computers so they can still pull up any other job they want and keep right on running. That was unheard of before."

Bi-directional transfer capabilities between the personal computer and the machine controller are another benefit that machine operators are taking advantage of for the first time. Before, tape files could only be uploaded to the controller. Today, when a machine operator writes a quick manual program on the controller, it can be extracted from the controller and stored on the personal computer.