clamping problem on cylindrical parts

[1211978]

I joined this company recently and have to tackle this year old pb.
we machine Aluminium cylindrical parts on Mori seiki SH-403. we have this project for past 5 years. but from last year we have changed our raw material from castings(which used to be hollow) to forgings(solid), this has resulted in added mat. to be removed.

our fixture has 2 moving jaw, one side of lower jaw has a hard stop and the other side has a spring loaded mech. to prevent part from moving axially.

there is an S- shape bracket at the back that matches the bosses(circular projection, used for assembly) on either side of the part to prevent radial movement.

we do both drilling and milling on this job on three sides. 12 parts are clamped on the square pallet.

Major pb.:
1 ovality due to excess clamping forces (nonuniform clamping surface)
2 part misload
3 both radial and axial movement of part while machining.

opn seq sp. s(rpm) f(i/m)

1 0.968 drill(2 inserts) 3100 32/30

2 0.556 drill 5000 50

3 8 insert combo tool
(spring loaded stop side) 2200 35-30

4 small end combo tool
(hard stop side) 3740 39

5 reamer 1500 75

 

[jbel]

A picture is worth a thousand words. Can you post a link to a picture of the setup? I think this would go a long way toward clarifying your question.

Also, what are the diameters of the combo tools and reamer you are using??

 

[Nate101]

Is there anyway you can clamp it and rough everything in then reclamp using less pressure and finish the part?

 

[BillPSU]

I agree with jbel a picture would help.

Your problems are pretty straight forward if you think about your current results.

You are seeing distortion from your current clamping pressures. Answer reduce clamping pressure.

Can't reduce clamping pressure because of axial and radial movement of the part due to machining pressures. Reduce machining pressures, reduce feed rates, change to tools with lower cutting pressures(fast spiral drills with split drill points or increase rpm's decreasing chip load.

Misloading part. Answer, foolproof loading of part.

The real answer is to redesign the work holding and all processes required to be done or redesign the part. Why was the decision made to change the part from a casting to a forging? Was it made because the forgings were less expensive or because of part requirements? If the change was made because the forging was less expensive then someone must think the machining would not be impacted by the change. You have discovered that is not true.

If you redesign the workholder then spread the clamping force across the wider area or change the direction of the clamping so distortion is not a factor. Reduce misloading by properly loading a part into the fixture and potting some rubber around the part. The rubber will absorb and part to part variation in size but still orientate the part properly. This could also reduce part movement.

Redesign the part: go back to the previous casting or change the part completely to an investment casting with the only operation being reaming the hole.

Your management probably wants you to solve the problem without spending any money or changing the cost of the part. Try the reducing the machining forces first. Second, add the potting around the part next. Finally ask for different tooling, or change back to the original casting, or complete redesgn of part.