bending of steel after milling

[dhiruj]

hi

we are machining mild steel plates of thickness 3 inches. the size of the job vaires from 300x400mm to 800x800mm.. we are doing it in a vertical cnc machine.

the parameters are...:

• 0.65mm depth of cut
  32mm dia of the tool
  8000mm/min feed rate
  1800 rpm

I am getting a tool life of around 2 hours per cutting edge and the tool has 3 cutting edges..

my problem is that my job bends... some times it even bends by 3-4mm. the job is clamped with a magnet.

we do only dry machining as when we tried wet machining the tool life reduced a lot.

we are using tools from a european company called SECO.

Dhiruj

[ViperTX]

Carbide, HSS, coated or uncoated?

[dertsap]

mild steel will normally relieve itself if enough material is being removed at one time ,generally hogging out the rough stock in one op then going with finishing ops later is necessary

[dhiruj]

its carbide tool..

from Seco... www.secotools.com

dhiruj

[One of Many]

That is the nature of steel plate stress relieving in its raw state when removing material from only one face.

You could have it stress relieved in a heat treat process prior to milling, or cut half the amount off each face to balance the relief.

I've sent plates like this out for Blanchard grinding after heat treat stress relief and they came out very flat and parallel.

Cutting through the mill scale is probably what is killing the cutting edge.

DC

[dhiruj]

Originally Posted by dertsap mild steel will normally relieve itself if enough material is being removed at one time ,generally hogging out the rough stock in one op then going with finishing ops later is necessary

does that mean i put the job once on the machine for roughing and then again for finishing.. what we observed is that, for example our initial job side is 500x400x70mm. we machine a pocket in the centre of the job removing 400x300x52mm of steel.. hence only a wall of 25mm on each side an a bottom portion of 18mm is left.. this is our actual requirement.. how do you propose we do this... because once i put the job then again take it out reload will lead to a lot of wasteful time...

[dhiruj]

Originally Posted by One of Many That is the nature of steel plate stress relieving in its raw state when removing material from only one face. You could have it stress relieved in a heat treat process prior to milling, or cut half the amount off each face to balance the relief. I've sent plates like this out for Blanchard grinding after heat treat stress relief and they came out very flat and parallel. Cutting through the mill scale is probably what is killing the cutting edge. DC

Hi

the tool life is reducing if I use coolant,.... When I am doing dry machining the tool life is very good,..

Do you think giving cool air to the tool instead of only air will help in reducing the stress in the job????

Dhiruj

[dertsap]

Originally Posted by dhiruj once i put the job then again take it out reload will lead to a lot of wasteful time...

nature of the beast

stress releaving is the only other alternative

also,i highly doubt the part is getting hot enough to bend because your dry running the tool

[widgitmaster]

What grade carbide are you using, C2, C5, or C6?
C6 is the toughest of these three grades!

[Geof]

It is practically impossible to machine plate and have it finish up not warped. You can try taking the same amount of each side but this will often result in it being wavy rather than just a smooth curve.

I think your only solution is stress relieving before machining and hope that this will be enough. You may find the only solution is to rough machine to within a few mm, stress relieve and then finish.

[WA Toolman]

If it is Hot Roll steel, a coated insert will probably be best. Also, (assuming Hot Roll) you will need to take a rough cut DEEP ENOUGH TO GET UNDER THE SCALE, then go back with finish cut after mat'l is stable. If it is Cold Roll, it will probably keep moving on you no matter what.
Another alternative: Ask Engineering to open tolerances

[One of Many]

1800rpm sounds rather high for a 32mm cutter. Which could be an issue as far as tool life in the skin of hot rolled plate. As the FPM is near 600, this could generate a lot of heat in the tools cutting edge to which adding coolant can induce thermal shock, whick leads to edge breakdown.

Look into the PDF troubleshooting section for tool failure conditions.

The concensus here is leaning toward roughing, stress relieving with heat treat(AKA Normalizing), then finishing to size. Although stress relieving first may reduce part handling. It may also help the materials cutting properties.

DC