Acrylic bending temperature is the number every workshop quotes and the one that decides least on its own. Sixty curved acrylic canopy sections, 8 mm cast, 1,800 mm radius, arrived at a hotel in Doha with a haze along every bend. The workshop had formed them at the right temperature and then cooled them against a steel jig with a fan. The bends were geometrically perfect and optically wrong, and the client rejected the lot on appearance rather than dimension.
Acrylic bending temperature is the first number in a thermoforming job and the least useful on its own. What the sheet needs is a temperature it can be shaped at, a time at that temperature, and a cooling rate that does not lock stress into the bend. Each of the three can ruin the part independently.
What acrylic bending temperature actually controls
For a straight bend on 3 to 10 mm sheet, a line heater with two elements facing each other across a 20 to 40 mm band is the standard tool. Bring the band to 150 to 160 °C, hold for roughly one minute per millimetre of thickness after the surface reaches temperature, and form while the band is still soft. Below 140 °C the bend whitens; above 175 °C the sheet blisters and the molecular weight drops.
The bend radius should be at least three times the thickness for a decorative part and five times for anything structural. A 6 mm sheet bent to a 12 mm radius will craze on the outside of the curve within weeks, because the outer surface is strained past its elongation limit. If a sharp radius is needed, it is a machined and bonded corner rather than a bend.
Drape and vacuum forming: uniform heat across the part
Drape forming over a male mould needs the whole panel at 165 to 175 °C, which for 8 mm sheet means 25 to 35 minutes in a circulating air oven, not a bank of infrared lamps. Infrared heats the surface and leaves the core cold, so the part forms on the surface and springs back at the edges. Measure with a contact probe on both faces before forming.
A simple sag test beats a pyrometer in most workshops. Clamp a 300 mm strip of the same sheet in the oven and watch it. When the free end drops 25 to 30 mm under its own weight, the sheet is ready. That test reflects the core temperature, which is what the forming depends on.
Cooling and annealing decide clarity
Cool under a felt or a heated blanket at 60 to 70 °C for the first ten minutes, then let the part come down to room temperature in still air. Forced air on a cold steel jig quenches the surface and leaves a haze band and a spring-back that shows up as a rocking panel on the frame.
For any formed part that will see sunlight or cleaning chemicals, anneal at 70 to 80 °C for one hour per 3 mm of thickness, then ramp down at 5 to 10 °C per hour. Annealing removes the forming stress and the bend stays clear. The temperature and dwell data on the sheet certificate, described in our note on reading an acrylic sheet TDS, give the grade-specific limits to work inside.
Thickness tolerance matters here too: a nominal 8 mm sheet that arrives at 7.6 mm heats faster and sags sooner than the trial piece, so form settings validated on one delivery need re-checking on the next.
For curved panels, send the radius, thickness, chord length and finish to oversales@rpplexiglass.com and we will quote formed cast acrylic with a sample bend in the production thickness for approval.
Frequently Asked Questions
At what temperature does acrylic soften for bending?
Cast acrylic becomes formable around 150 °C and is comfortably workable between 150 and 165 °C for line bending, and 165 to 175 °C for drape forming. Above about 180 °C the sheet blisters and degrades, so a controller that overshoots is worse than one that runs slightly cool.
Can I bend acrylic with a heat gun?
Only for small, non-critical parts. A heat gun heats one face and leaves the other cold, which produces an uneven bend and a high stress line. For anything longer than 300 mm or thicker than 3 mm, a line heater or an oven gives a controlled result.
Why does my bent acrylic turn white or hazy?
Usually forming too cold, or cooling too fast against a cold jig. Forming below 140 °C whitens the outside of the bend, and quenching leaves a haze band. Reheating a hazy bend above 120 °C and cooling it slowly sometimes recovers it; a cracked bend cannot be recovered and must be re-made.