We can rebuild it: Turning Performance

My machining career began at the machine shop that I started with my father. Our first machine tools were old manual machines from the 1940s and 1950s. As our shop grew, we found ourselves buying CNC machine tools because order quantities increased and machinists were becoming hard to find. As the CNC machines became troublesome, we discussed rebuilding some of them. But the cost of a good rebuild was almost as much as a new machine, so we looked at machines as disposable.

My career path changed in 2005 when I accepted a job as a manufacturing engineer with an automotive manufacturer. It had 1,200 machine tools at the plant where I worked. We ran three shifts per day for seven days a week and shipped 2.5 million units in my first year. Machine tools constantly operated at the facility.

Surprisingly to the new guy, many of these machines were old. Most of the CNC turning centers were over 20 years old, which meant they had processed more than 6.5 million parts in their lifetimes. Amazingly, the centers still were able to hold 0.01 mm (0.0004″) tolerances and produce very fine surface finishes while running 24 hours a day.

I learned that the company operated a machine rebuild shop not far from the main plant. At this shop, workers would tear down and rebuild key pieces of equipment. It seemed odd that a plant that was part of the largest automotive company in the world would continue to use old machines. Why not buy new?

Most of our CNC lathes were designed specifically for automotive manufacturing. They were about the size of a residential refrigerator and had tiny working envelopes to improve efficiency at the factory. These lathes were no longer being manufactured, so purchasing new ones was not an option. Buying new machines that were much larger would have required changing the cell layout from a proven design, which was undesirable. Rebuilding was the only option.

These compact lathes were so valued that we began buying used ones from other manufacturers and started a rotation program. Used lathes would be purchased, brought to our shop and rebuilt. After rebuilding a machine, we would pull a worn-out one from the line and drop in the rebuilt machine. Then we initiated the process again. Machine rotation was part of our total productive maintenance program.

Standardization also drove our decision to rebuild rather than buy. Having different machines necessitates retraining operators and maintenance personnel. Because the machines, tooling and controls remained the same throughout the plant, we easily could shift workers from one line to another so we could better utilize operators.

Our rebuild shop was a teaching location too. New maintenance technicians would spend time at the rebuild shop, where they could learn the machines and controls. Training them in this way allowed them to literally learn a machine inside and out. When machines malfunctioned, which was rare, troubleshooting time was shortened.

Purchasing new machines also would have hurt our inventory of spare parts. We kept a lot of critical parts in our inventory, which translated to a significant amount of dollars stored on the shelves of the toolroom. Buying new machines would have required additional inventory for spares. By rebuilding machines, we were able to maintain levels of inventory. And on the scarce occasion when we needed a part that wasn’t in the toolroom, the rebuild shop usually had a spare that could be used.