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What percentage of time are your machines in production?

I’ve done quite a bit of in-plant consulting and training over the years. While walking shop floors, and as you can imagine, I’m always very interested in the CNC processes taking place. As long as it doesn’t bother the people running the machines, I’m always looking over someone’s shoulder to see what’s going on and peering into machines to see the cutting operations being performed.

I’ve noticed something pretty consistent from one company to the next. CNC machines never seem to be in production for as much of the time as management and engineering staff seem to think they are. At some point during my visit, I’ll always ask for some general percentages of setup time compared to production run time. And during production run time, how much time the machines are actually running (as opposed to being down for part loading, tool maintenance, adjustments, etc.).

I hear some pretty conflicting things from management and engineering people. According to management in one company I recently visited (data taken from computer printouts), setup time was about 12 percent and production run time (machines actually running) was about 78 percent. I was quite impressed with the efficiency they had achieved. Yet the next time I toured the facility, over half the machines were sitting idle! During the week of my visit I kept making my way through the shop at various times (and over the course of two shifts), and never were more than half the machines actually running.

This didn’t sound right to me so I questioned whether something special was happening during my visit. Maybe more people than normal had called in sick. Maybe there were a lot of people taking vacation days. Maybe there wasn’t enough work for the machines while I was there. Whatever. But I was assured that things around the plant were quite normal.

Admittedly, my stay was relatively short – surely I was getting just a snapshot of what was probably happening in the company over the long haul. But as I said, I’ve found the estimated production running time to be consistently high in many of the companies I’ve visited.

One of the first tasks to undertake when considering making any improvement, of course, is objectively assessing the current state of affairs. Machine downtime should be an obvious target for improvement, but if you are not getting a true picture of what is happening on the shop floor – for whatever reason – you may not even recognize the need to improve.

My suggestion is to question and test your production run-time numbers. Simply do what I did. After determining what the accepted run-time percentages are, go out into the shop and determine what percentage of machines are sitting idle at any given time. If you find discrepancies, it should be taken as a signal that there may be some errors in your data collection and reporting system. They shouldn’t be too difficult to spot.

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