Milling forces

Hello there

Hope this is the right section to ask this. I'm currently doing some cutting force analysis for the milling of Inconel. The type of milling done is 1/8 immersion and an end mill cutter is used.

This is what the forces in the X axis looks like this. As you can see, some of the forces are in the negative. What are the possible explanations for this? If I were to do a comparison for the average forces when machining parameters are varied, is it reasonable to simply use the mean of the peak forces values?

http://i.imgur.com/pH5ph.jpg

No idea what instrument you are using to measure the force. No idea what formulas you are using either. Possible you are seeing machine vibration. Possible you are seeing tool vibration. Possible you are seeing rotational force being transferred into linear force if the cutting edge of the tool "grabs" material and pulls itself deeper into the cut.

I'm using dynamometers and the forces i posted is the raw data collected.

Unfortunately I don't see the data, or your set up where the sensors are. I have used load cells to detect cutting force as well, but in very soft material. If the machine is small, and your peak forces low, you will see negative tool loads on the axis if you climb mill in certain instances. Spindle load will usually increase slightly in this condition. I placed load cells between the spindle and head casting, and found similar results. The most consistent results was in drilling, since your only single axis loading. Your end data only means as much as what you plan to do with that data. Are you trying to control feed using load data, like the fanuc version? Is it for tool life analysts etc..

A few things that play havoc I found are direction of cut changes, and mechanical backlash when climb milling, as would be expected.