[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]

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]

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]

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

[dertsap]

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.

DC

1800 rpm is quite slow for that dia cutter in mild steel
adding coolant will cause thermal break down of the tool , because as the insert scrapes thru the steel it gets hot (friction)when it comes out of the cut coolant cools it ,so the temperature of the tool is not constant ,it is hot then cold ,thus thermal breakdown
if you look at the concepts of high speed and high performance machining the tool doesn t get very hot nor does the part to any kind of extent , the chips are hot ,very hot

[eject_21]

You could try roughing the pocket, unclamp and re-torque the part lightly, then finish.Watch for chip impressions and dont let the roughers get too dull. A sharp rougher will end in a much better result.

[ImanCarrot]

Use cast stock instead of rolled, I make optical mirrors from L111 aluminium and can only get an opticaly correct surface profile from cast stock... never from rolled- it just like warps.

The only other alternative as stated above is to Heat Treat the stock. Depending to what tolerances your working to this is viable. I work to < 2um form error over 17mm surface and rolled stock always "springs" too much for me to use.

[Bent]

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

You have to take to care to shims it op becurse the magnet wil pull the slab down. Then it wil be parallel but not stright

Bent

[dhiruj]

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

You have to take to care to shims it op becurse the magnet wil pull the slab down. Then it wil be parallel but not stright

Bent

thanx bent....

we put the shims but the probolem is that the job even bends and the shims become loose... infact once we increased the power of the magnet and the bend became so intense it actually lifted the magnet....

I tried a new thing today.. the total depth of my pocket is 50mm.. so after 25mm, i cooled the job with coolent then again finished the remaining 25mm... i found that the bendness was now much lower and within our tolerance of 1mm.

Do you think this process of cooling the job midway would be same as normalizing the steel.

Dhiruj

[Bent]

To normalize steel you have to heat it to at least 600 celcius and hold it for a couple of hours.


Bent