XPS warp issue after routering

[Making chips]

I am cutting extruded polystyrene on a CNC router. The foam is warping after removing the material on one side. I have done testing and taken off equal material off of both sides, but for this project re-machining the bottom after routing the top is not an option. These are large parts 4' x 4'.

Any ideas or suggestions would be greatly appreciated.

Paul

[svenakela]

How do you hold it down?
What's the density?

[Making chips]

The foam is a 2lb density and we are holding it down with vacuum.

[svenakela]

Are you sure it doesn't compress by the vacuum?
It can happen if it's not a closed cell.

[Making chips]

I am quite confident that the vacuum is not compressing or warping the material. I have tested this and cut of 25% of the total thickness of a sheet off one side and it warps significantly, flip the part, and take the same cut off the back and it straightens back out. Similar to metal. I never would have thought this would act in this manner. I dont want to buy oversize material and machine both sides if I dont have to. Other than flipping the part to re-flatten the bottom, all of the machining is done from one side only.

[Pres]

Try "normalizing" it first by laying it on a flat surface and SLOWLY heating it to about 180-200f. Then SLOWLY let it cool down.

The high speed, typically used in extrusions, leaves a lot of built-in stress.

hth,
Pres

[Making chips]

I will have to work on that pres. Finding a heat source large enough to do that might take me some time.

Thanks for the suggestion.

Keep them rolling in.

Paul