Frequently Asked Question

Measurement of Flexible End Mills.
Last Updated 7 years ago

It is not trivial to measure long, slender end mills with an instrumented hammer. If you use hard steel tip, the hammer may bounce on the tool with several contacts, which leads to unacceptable Frequency Response Function (FRF). If you use soft tip, then you may not excite the natural frequency of the tool. Harder the tip is, wider the frequency range of excitation is but at the expense of bouncing. Softer the tool tip is, easier to create a single contact with the tool but at the expense of longer contact time hence lower frequency range. Therefore, you may not be measure the machine correctly.

First try some tricks:

*Put a layer of a scotch tape on the hammer tip, and see whether it reduces the bouncing.

*Try bronze or Aluminium tip.

*Use the smallest hammer you have.

If you are still unhappy with the bouncing or frequency spectrum range, do the following in MALTF:

1- Put the accelerometer at the tool tip, but hit the tool close to the chuck where it is more rigid. The bouncing will be reduced. Save the measurement as Cross FRF (i.e. xxx12.frf) using export command.

2- Move the accelerometer close to the chuck where you hit with the hammer. Hit the tool at the same location as in step 1. Save the measurement as direct FRF (xxxH22.frf) using export command.

3- Go to modal analysis module of CUTPRO. Select file -> select FRF files and click on Flexible Tool FRF option. Load both measurements collected in steps 1 and 2, and apply modal analysis, and curve fit the selected modes using any of the measurements.

4- Once you are happy about the curve fitting, click on H11 on the top right corner of Modal analysis. CUTPRO will estimate the FRF at the tool tip and display the results. You can “Save Parameters” under a file name which can be automatically used in milling/boring/turning simulations.

The program will estimate the correct FRF at the tool tip without having to hit the tool at its tip. It is not as accurate as measuring at the tool tip, but a lot better than not being able to measure it at all.

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