There’s nothing more frustrating and costly than an unmanned production batch gone wrong half way through. Your tool grinder should have a number of features to help you monitor and control your process from the first tool in the pallet to the very last.
If you’ve optimised your process properly, machine and tool accuracy should be very stable throughout an entire batch. However, due to wheel wear and possibly machine accuracy changes due to temperature shifts, you might experience slight inaccuracies creeping into your process during the grinding of a batch, which, if unmonitored, might result in part of your batch being ground out of spec.
Statistical Process Control (SPC) is a statistical technique for monitoring and controlling a process to ensure it remains within desired boundaries.
If your CNC includes in-built SPC software, then you can switch this on and it will use the touch probe to monitor small samples of tools, usually by measuring the OD size or flute depth and will then feed adjustments back to the CNC to ensure the process stays within spec for the whole batch. Your SPC software will also chart the progress of your batch and report on your capability index so you have immediate feedback on the quality of the tools you are producing.
Although modern Tool Grinders are built to minimise the effects that changes in temperature can have on tool accuracy, today’s tight tolerance requirements mean that in some cases, you’ll need to make adjustments to the process as the ambient temperature of the process changes.
If you have a coolant chiller and good ambient air conditioning, this effect will be minimal, but not everyone has the luxury of a tightly controlled thermal environment and some people run to such tight tolerances that even slight changes in temperature can adversely affect tool quality.
This is where Coolant Temperature Variation (CTV) Compensation can help. If your tool grinder is equipped with CTV, then at periodic intervals during a large batch of tools, the machine can use the touch probe to reference a known surface, re-calibrating the machine axes on the fly.
The sample frequency can be increased at the start of the batch while the machine temperature stabilises. The compensation can be scheduled at any point in the operating sequence to ensure the compensation occurs as near as possible to the most critical grinding operation. CTV can help you achieve very tight tolerances throughout an entire production run.
So make sure you utilise good process monitoring and control techniques and take full advantages of your tool grinder’s automatic measurement and compensation features.