Monitoring the wear of tools

[pietro82]

Hi all,

Today I helped a coworker in doing some tests of a system he designed that is able to measure the size of big objects. For example, the tickness of walls. This brought me to think if there is anything similar which cam be used to monitor the wear of tools of cutting machines, so that an alert when the tool is worn out can be deployed to the user. Probably, something with that purpose already exists which relies on load cells or a torque applied by the motor (I'm not sure). But which other approaches could be used?

 

[MikeHalloran]

I think some CNC machines can monitor spindle motor current or vibration. I'm not sure how well they work; I'd guess it depends on what you're doing with the tool.

Many CNC machines have a Renishaw touch probe that's used for setting the zero/offset of the tools. Basically the machine creeps up on the probe until the probe signals that the tool is touching it. You could conjecturally re-check the tools' position when they're being changed, or in between workpieces. The touch cycle adds to the cycle time without making money, so again you might or might not add the touch test to the regular cycle; again it depends on what you're doing...

I think some outfits measure each workpiece right after producing it, using a touch probe as a tool. The machine should then be able to flag a produced surface that's not in the correct location. Again, the inspection time is not making money, but it's probably faster and cheaper than adding a process step involving a separate CMM machine.



Mike Halloran
Pembroke Pines, FL, USA

 

[JNieman]

Renishaw toolsetter probes are the bees knees but only measure geometric size changes. This is a great function but does not cover all wear situations. As @MikeHalloran notes, there are spindle sensors that can detect common symptoms. Typically spindle load is used to detect tool condition. Tools in good condition will only require 'x' horsepower to continue material removal. If that trend line starts to creep upward, a boundary can be set whereby the machine automatically switches to a backup tool, or throws and alarm or whatever one deems necessary. This method is probably the most common.

There's also the old fashioned, manual way. If you're running a part for a long time, using a fairly controlled process and material, you'll develop a memory of how parts a certain tool/insert is good for, and can preventatively change it out.

Skipping past in-machine inspection: There are also semi-recent advances where separate CMM or measuring machines can communicate back to the machine controller with particular dimension results, and adjust cutter compensation offsets or provide the data necessary for the tool wear monitor to switch to a backup tool. I'm still undecided on that method, mostly because of lack of experience with it. I'm not sure I'm keen on relying on dimensional results to dictate tooling action - it seems to measure something too far removed from the actual root cause, and does not account, on its own, for all possible conditions.