PLEXIGLAS® cannot be cold line-bent.
PLEXIGLAS® Resist 75 or 100 can be “bent” cold at a radius exceeding twice the sheet thickness, but this is not advisable because it leads to deterioration of the mechanical and optical properties.
For this, PLEXIGLAS® sheets are heated linearly, then bent and held in place in the desired shape until the parts have cooled down. Bending is performed with the aid of a jig or over an edge. When bending over an edge, the material must be clamped on one side only in order to avoid stretching and thus a pronounced thickness reduction in the bend area. Moreover, the edge of the clamping device must be rounded in such a way that it does not touch the heated sheet area so as to avoid unwanted mark-off.
The bending radius should be at least twice the sheet thickness. Smaller radii cause excessive stress or even creasing on the inside. The required bending angle determines the width of the heated area.
Normally it should be at least three to five times the sheet thickness. If the heated area is too narrow, the material may be overexpanded or stretched.
A smooth transition in the blank between the heated and cold areas avoids “expansion thresholds.” To achieve this, it is necessary to install a screen between the heat source and the sheet. Tight bends can be obtained by strictly limiting the width of the heating zone, where the clamping bars are cooled.
If the line-bent parts are to be subsequently bonded, the clamping bars should be heated instead to between 60 and 75 degrees Celsius (°C) to avoid stress cracking.
Heated parts formed into angles with short legs tend to warp in the bending axis while cooling down. This is due to thermal expansion, shrinkage and flexural stress in the bending area. The deviation from the straight line can be offset by curving in the opposite direction on the bending jig and/or pre-heating the blank briefly in the oven at approx. 70 to 80°C.
The minimum cold-curving radius of PLEXIGLAS® depends on the product grade. The following values apply:
Sheet thickness x 330
Sheet thickness x 300
Sheet thickness x 250
Sheet thickness x 210
Sheet thickness x 170
Sheet thickness x 150