PMMA Annealing
PMMA Annealing
(OP)
Hi everyone,
I have made some laser cut parts (4 mm thick) from PMMA which have bent significantly after the cutting process.Sadly, I do have a flatness tolerance for these parts so I need to find a way to correct them. I checked about annealing processes and found this:
http://www.plexiglas.com/acrylicresin/technicaldat...
So, what I did is, I put the part between 2 thick aluminum flat surfaces to make it flat and then I inserted the assembly in a heat press. I applied a small load (the part was already straight from the weight of the aluminum plate anyway) and I followed the annealing procedure. I wasn't sure which type of PMMA I had so I used the highest temperature procedure on the list. The results were disappointing. The bending was not removed at all. I tried higher and higher soaking temperatures, at some point a couple of thinner features melted. Even then, the bending was still present. At first I thought it had something to do with the cooling rates, maybe one side of the part was hotter than the other or it was cooling faster than the other, but then I noticed that I had put 2 parts upside down and they both retained their original bending. So I am not sure how to correct this..
Does anyone have any ideas?
Best,
George
I have made some laser cut parts (4 mm thick) from PMMA which have bent significantly after the cutting process.Sadly, I do have a flatness tolerance for these parts so I need to find a way to correct them. I checked about annealing processes and found this:
http://www.plexiglas.com/acrylicresin/technicaldat...
So, what I did is, I put the part between 2 thick aluminum flat surfaces to make it flat and then I inserted the assembly in a heat press. I applied a small load (the part was already straight from the weight of the aluminum plate anyway) and I followed the annealing procedure. I wasn't sure which type of PMMA I had so I used the highest temperature procedure on the list. The results were disappointing. The bending was not removed at all. I tried higher and higher soaking temperatures, at some point a couple of thinner features melted. Even then, the bending was still present. At first I thought it had something to do with the cooling rates, maybe one side of the part was hotter than the other or it was cooling faster than the other, but then I noticed that I had put 2 parts upside down and they both retained their original bending. So I am not sure how to correct this..
Does anyone have any ideas?
Best,
George






RE: PMMA Annealing
For 1/4" thick acrylic, with lapped flat platens, to get a few hours at the recommended annealing temperature, we had to use an oven with a fancy control, lock the door, and ramp up and down very slowly, so the whole cycle took ~40 hours. All attempts to speed the process resulted in warped parts.
Mike Halloran
Pembroke Pines, FL, USA
RE: PMMA Annealing
RE: PMMA Annealing
Since the laser cutting introduces significant heat at the cutting lines(surfaces) that leads to a new energy equilibrium of the polymer causing warpage, you may want to consider less intrusive cutting methods like CNC with low feed rates or water jet cutting.
George
G. Markus
www.robustmolding.com