SPC Fulfills Its Potential at Caterpillar

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“The best SPC data in the world isn’t worth anything if the operator doesn’t use it.”

Tom Kapraun, manufacturing specialist at the Caterpillar plant in Pontiac, Illinois, has seen paper-based and custom “black-box” implementations of SPC (Statistical Process Control) systems at the plant miss the mark because they complicated the work of the operator.

But after switching to an automated SPC solution from Factory Systems (Columbia, SC), the Pontiac plant has been able to significantly cut scrap, reduce part variation, and move closer to the quality goal of 1.33 CPK. Additionally, the long-term SPC data accumulation has helped Caterpillar make engineering changes to better match machine capability with production requirements. As a result, the plant is committed to incorporating SPC equipment with every applicable new equipment purchase.

The 800,000 square foot plant manufactures fuel systems for all Caterpillar engines, used in vehicles ranging from highway trucks to road-building machinery. Production involves both high volume and extremely rigorous specifications, with some tolerances as low as plus-or-minus .00004 inches. To help maintain continuous quality, the plant depends on SPC for electrical discharge machines (EDM), internal and external grinders, screw machines, lathes, test stands, rotary dial machines, abrasive flow machines and other equipment.

The Caterpillar plant began using SPC in the late 1970’s the same way most companies commit to SPC: Expecting operators to plot production quality with paper-based charts and graphs. In most cases, this was collected by the quality control staff, not the operator.

“All it produced for us was a lot of paper that never really was used”, remembers Kapraun. “It was a cumbersome, ineffective method of gathering data that didn’t really tell us much”.

Recognizing the shortcomings of paper-based SPC, Caterpillar began looking for ways to automate the system and to provide feedback that was more immediately useful to the operators. At that time in the mid-1980’s, there was nothing on the marketplace suitable for high-cost, high-volume production, so Caterpillar contracted with a consultant to develop a custom solution.

This “black-box” SPC solution, which was linked to a DEC VAX mid-range computer, had two failings, according to Kapraun. First, it lacked real-time capabilities. “It took 20-30 minutes for the operator to receive reports back from the VAX,” says Kapraun. “By that time, another hundred to a thousand pieces had run. The data gave us a good historical record, but it didn’t let us fix problems as quickly as we needed to.”

Another problem was the lack of upgradeability. Every time the company changed products, specifications or procedures, it had to commission programming to upgrade the system, handicapping the firm’s ability to keep up with advancing technology. Plus, there was often inter-vendor “finger-pointing” whenever there were problems interfacing with different gauges.

In 1990, the in-house quality committee decided there had to be a better way. The committee picked a search team comprised of shop-floor personnel and charged them with finding a “world-class” SPC system. After studying the industry, the search team selected eight vendors with SPC products that seemed capable of meeting the plant’s requirements.

“All the requirements were based on the needs of the operators,” says Kapraun. “If it’s too burdensome, then the best SPC system in the world is not going to make a difference.”

After demonstrations from the eight vendors, Caterpillar narrowed the list down to two and dropped the requirement concerning a PC-based SPC solution. “The demonstrations helped educate us about what a PC could and couldn’t do,” says Kapraun. “A PC solution wouldn’t work here because our plant is too big and we produce too much data. It would have been too much work to keep each PC up to date and to integrate all the information. It’s more efficient to process SPC data on our VAX.”

For the next three months, Caterpillar conducted a head-to-head “shoot-out” between the competing vendors. Equipment from the vendors was hooked to the two toughest applications – internal grinders that require tolerances of plus-or-minus .0001 and external form grinders with tolerances of plus-or-minus .00004. Each vendor’s equipment was also interfaced to multiple gauges to test compatibility. Prime criteria for the test included the ability to provide real-time SPC data to operators; upward VAX compatibility; user-friendliness; and support of internal quality goals.

“There was no question Factory Systems had the superior system,” says Kapraun. “All the operators commented that it was much easier to work with and interfaced well with all gauges. We even had to leave the trial units in because the operators didn’t want them taken away.”

Caterpillar then ordered 35 METRSTAT’ workstations which were placed on grinders, screw machines and other equipment manufacturing a new product. The METRSTAT workstations, which provide local SPC processing capabilities, were connected to the plant VAX via an Ethernet network. The VAX produces reports and stores historical data, which is used by the plant planners to fine-tune machine utilization. Later, 18 additional METRSTAT workstations were installed in a different area.

A team of dedicated and committed employees helped during the selection and installation process. These team members included Tom Garland, planning processor; Gene Denick, hardware support manager; Tom Halloran, operations training consultant; Mike Selvaggio, systems administrator; Jim Streicher, planning processor, and Larry Johnson, purchasing analyst.

Since installation, Caterpillar has concentrated heavily on training. More than 400 operators, supervisors, process planners and others have had at least two days training on how SPC and the Factory Systems workstations can be used to improve quality.

“One of the first steps was a six-hour class on SPC for machine operators, supervisors and anyone else that was interested,” says Halloran, operations training consultant, adding that processing planners received 20 hours of training. “Once the basic principles of SPC were understood, then we introduced everybody to the workstation. The operators could then understand the terminology better and see how the workstation put SPC principles to work.”

But the training just didn’t involve how to take the appropriate measurements at the right time. “We tried to teach operators more than how to put the data in,” Halloran continues. “We wanted to teach them why they are putting the data in. We focused on changing the way operators evaluated quality. They shouldn’t just consider blueprint specs but they should also be concerned with whether a part is within SPC limits.”

According to Chuck Jordan, an operations training consultant who also assisted with training, operators discovered that the METRSTAT workstations made their jobs easier, enabling them to run more pieces with less effort and with higher quality. In fact, Jordan believes the SPC training and workstation helped the Caterpillar plant pass an important quality inspection by an important customer.

The Factory Systems machines have also paid for themselves with a significant reduction in scrap, reduced part variation within good parts, and higher first test pass on the nozzle test stand. In some cases, armed with a year or more of SPC data, process controllers have been able to ask the engineering department to loosen tolerances without degrading performance or quality. “Processors have the empirical data to evaluate current machinery over the long-term and make better decisions concerning future capital equipment purchases,” says Kapraun. “When we have to rebuild gauges or machines, we have the information that tells us exactly what is wrong.

There have been other, less measurable, benefits as well. “The operators feel more in control of their jobs because they are responsible for making the necessary adjustments in response to the real-time SPC data they receive. They also have less paperwork to worry about,” says Kapraun. As a result of these and other benefits, the Pontiac plant is working toward bundling SPC equipment with each piece of new equipment purchased. “It puts the costs of SPC monitoring right where it belongs, in the capital equipment purchase,” believes Kapraun. “Operators also get to work with SPC from day one, and it becomes a part of their job.”

Caterpillar has been committed to SPC for more than a decade, but it was important to find an improvement that could both operate cost-effectively in high-volume environment and be accepted by the operators. “The METRSTAT workstations provide the real-time data, connectivity and multiple gauge interfaces we need to turn the theory of SPC benefits into reality for Caterpillar,” concludes Kapraun.