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11. How to measure OEE in long-run milling process?

Q: We are tool & die maker for  the automotive industry. Overall each die will take 20 to 35 days (based on size) to complete. Depending on the shape (contour) of the die, the process is done manually or auto mode. The mode depend on our CAD/CAM capability to do the programming.

How do we create a correct OEE calculation in our milling process?

Our situation

There is no handling or movement once the die is placed on the machine. Only tool change is done few times depending on the shape of the surface.

The ‘speed’ of the processing is determined by several factors namely material, shape of the die and tool bit used

Arno Koch •  In the ideal situation, the mill, where the die is mounted, would be milling 24 hrs each day non-stop, at maximum milling speed, given the material and the tool mounted that moment, and there would be no quality defects.

Steps to consider

  1. If the machine is not scheduled for a 24/7 operation, make sure to register the non-scheduled time and take it either in the OEE or at least visualize it in OOE or TEEP. (Your customer is waiting!)
  2. If the process goes in a multitude of milling stages, the registration could be setup per shift of 8 hrs. If the milling-runs are very extensive, so the machine runs multiple shifts without a stop, it could be necessary to define a (very) long ‘shift’.
  3. Now, when the machine is scheduled to run, register each instance when it is not milling. Since the throughput time is up to 35 days, there will be a substantial part of time been lost by idling of the machine. Handling like tool-change, measuring etc is all waiting time to the machine.
  4. Whenever the machine is milling, determine the theoretical maximum milling speed for the tool and the material that is being milled at that point. (ie X grams/minute)
  5. When a stage of the milling is done, determine the actual speed of the milling. This can be done by weighing the die, weighing the milled chips or calculating the milled space through the CAD software.  If this is not possible; try to make a rough estimation; that will give enough clues later on.
  6. Whenever a milling-run resulted in an out-of-spec situation, the whole milling-run has to be seen as non-quality.

What to look for

The ultimate number of your OEE/TEEP calculation is no so relevant; it will be very low anyway. The value of the measurement here would be to get an insight why it takes so long to make this die; where the losses are and thus where the potential points of improvement are.

Please let us know what your findings are?

See also:

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