Cutting Tool Engineering
March 2012 / Volume 64 / Issue 3

Measuring machine productivity

By Michael Deren

Many large corporations are well versed in total productive maintenance, but smaller companies are probably not. To learn more about the concept, I attended a 1-day seminar about TPM at a local technical college.

The instructor indicated that a better name for TPM is total production maintenance. Either name implies the concept is more about equipment maintenance, but that’s not the case. TPM is really about the availability and use of equipment to produce parts. That involves not only equipment maintenance but production resources as well. Those resources include operator availability, proper tools at the operator’s disposal, correct tooling in the machine and raw parts availability at the machine.

The first objective is training operators to perform routine machine maintenance, such as checking and adding fluids or grease and keeping chips out of critical areas. Those areas include electronic cabinets and motors. For example, it doesn’t take long for oil-laden chips to build up on a motor cover. Eventually, the motor starts to overheat and the machine fails. Also, putting special markings on gages and reservoirs can help operators see at a glance if things are running fine during daily routines.

By setting up a team, usually including an engineer, a maintenance technician and machine operators, everyone can better understand the shop’s equipment and identify potential problem areas before a failure shuts down production. This doesn’t necessarily mean preventing a mechanical problem. It could be a problem with the flow of product to and from a piece of equipment, or perhaps the process is an issue.

There are six major equipment-related losses:

Breakdowns (unscheduled machine malfunction);

Changeover (time lost between the last good part off the current run and the first part off the next run);

Idling or minor stoppages (hidden losses when running equipment stops and needs minor operator intervention to resume operation);

Reduced speed (anomalies that keep equipment from running at optimal speed);

Startup losses (as a new job starts, several parts may get scrapped as the machine warms up and settings are adjusted); and

Quality defects.

Those six can be broken down to three main categories:

  • Nos. 1 and 2 are availability losses;
  • Nos. 3 and 4 are performance losses; and
  • Nos. 5 and 6 are rate-of-quality losses.

Another goal is to improve overall equipment effectiveness, or OEE. The formula for OEE is availability × performance efficiency × rate of quality. OEE is used to implement TPM by determining current output, identifying major losses, prioritizing what needs improvement and finding the root causes of problems.

The instructor provided examples, such as one where a 600-minute shift only produced parts for 222 minutes because of equipment stoppages. To determine OEE, a team determines the priority stoppage to target, resolves that issue and then re-evaluates, using a spreadsheet, until stoppages reach an acceptable total. OEE results, or the number of minutes of actual part production, from 85 to 90 percent are considered “world class.” The OEE for the above example is a mere 37 percent. Based on my experience, I believe many shops are in the 35 to 40 percent range.

Creating a spreadsheet for your equipment may help determine issues at your work centers, but you should start by attending a class or seminar about TPM and OEE. The cost to my employer was about $300. The return on investment should be tremendous. CTE

About the Author: Mike Deren is a manufacturing engineer/project manager and a regular CTE contributor. He can be e-mailed at mderen1@wi.rr.com.
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