Calibration of CNC Machines - Does anyone have written documentation procedures?



Does anyone have written documentation procedures on how to calibrate CNC machines to ensure that produce consistent product?


In my experience (working with a Machine Tool Manufacturer a few years ago - lots of CNC machines in this facility) when calibration of these machines came up, the manufacturer of the machine had supplied the alignment and calibration procedures and in fact for most of the machines, these procedures could be found in the Technical Manuals. I would check these two places first. These are procedures that are performed usually during the initial installation and set-up of the machines.

Even though most machines came with a 'Test' program, this facility developed their own 'test' program for each machine that related to the parts they were actually producing. This program was used in conjunction with written instructions for setting up the machine to perform the test. This procedure (written instructions and test program)was run after the initial set-up, calibration and alignment of the electronic and mechanical systems was performed. Depending on the machine, the program instructed the machine to produce a part or machine raw material to a specific size, pattern, shape or whatever, and then this was checked using standard micrometers, calipers, gages, etc. and the data recorded.

One aspect determined to be a big factor in the machine passing the 'test' program test, was the tooling currently in the machine. After many runs, it was determined that the actual cutting edge of the tool being used contributed the most error or variance in the piece being produced as opposed to the finite movement and placement control of the cutting tool.

Subsequent checks of machines were done using this test program and written procedure only. Cycles were every 3 or 6 months. This cycle was determined mostly by the production rate of the machine. If the part was produced to size/spec., the machine was considered 'in cal.' If the part was not produced properly, the full calibration/alignment procedure was performed.

Hope this helps.


I should add that some machines were tested more frequently than the 3 or 6 months stated above. This facility had 110 or so machines. Generally the smaller machines were tested more frequently - two weeks to 1 month cycles. This was due to the heavy production load and nature of the machines.

Tool life was also monitored and tooling was changed based on number of cuts or time in service as opposed to when it got dull (of course it could be changed any time sooner if warranted.) This was to prevent the tooling from getting worn to the point that the variance introduced was unacceptable.
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