Frequently Asked Question

How can we increase the productivity in low speed milling of Titanium, Inconel, and Stainless Steel alloys?
Last Updated 7 years ago

The spindle speed may be very low when you use cutters with large diameters. The useful stability lobe will depend on which natural frequency is causing the chatter vibrations.
We recommend the following:

  • 1- Tap test the cutter on the machine. If the workpiece is flexible, tap test it as well.

  • 2- Using MALDAQ, measure the vibrations during machining using an accelerometer attached to the spindle headstock or with a microphone. Take FFT, and check the frequency corresponding the highest peak. There may be some high peaks at the spindle speed (rev/sec) and tooth passing frequency (no. of teeth times spindle speed), and their integer multiples. These are forced vibrations in most cases, and you can neglect them. The chatter will occur close to one of the natural frequencies measured with the tap test.

  • 3- If you use a large diameter cutter and low speed, the chatter will cause by low frequency modes of the machine (spindle, spindle housing). If the diameter is small and speed is also low, the chatter will be caused by the higher modes of the spindle but hardly by the high frequency tool modes except at excessive depth of cuts.

  • 4- Apply curve fitting (Modal Analysis) to tap test but do not include modes which have values 1.5 times higher than the chatter frequency. Disregard the higher frequency range. Alternatively, using CUTPR milling module, you can use raw tap test data and indicate only the low frequency range to be read from the file.

  • 5- If the chatter frequency and tooth passing frequency is close, or if the chatter frequency/tooth passing frequency is less than 5, you will see a useful chatter stability pocket by following the recommendation given in step 4.

  • 6- If the chatter/tooth passing frequency is higher than 5, you can cut deeper than the lobes indicate due to process damping (ploughing between the flank and finish surface). If you want to increase the chatter free depth of cut a lot further, you need to design a variable pitch cutter using CUTPRO. If you want a slight increase in the depth of cut, you may wish to increase helix or approach angle of the cutter using CUTPRO. You can see how the change in cutter geometry affects the stability using CUTPRO simulations prior to manufacturing the cutter.

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