PC Sheet Cold Bending and Cold Folding: Minimum Radius, Parameters and Spring-Back
The short version
- PC (polycarbonate) sheet can be cold bent, but the minimum bending radius is 150 times the sheet thickness — hard-coated (AR) sheet is the exception. For smaller radii, switch to thermoforming.
- Cold folding is for thin sheet only. The folding radius and angle have hard upper limits; do not exceed the table values.
- Cold folding requires about 25° of over-folding to compensate spring-back, and the part only assumes its final shape after several days of stress balancing — the day it is folded is not the final state.
- Cold-folded and cold-bent parts must never come into contact with aggressive chemicals.
1. Cold bending: minimum radius = 150 × sheet thickness
All PC sheets — except hard-coated (AR) sheet — can be cold bent as long as the bending radius is not less than 150 times the sheet thickness:
Minimum radius = 150 × sheet thickness
For a few common thicknesses:
| Sheet thickness | Minimum bending radius |
|---|---|
| 2 mm | 300 mm |
| 3 mm | 450 mm |
| 5 mm | 750 mm |
| 10 mm | 1500 mm |
In other words, cold bending produces large radii — the sweeping curve of an equipment guard, an arc-shaped shield, a curved observation window. Do not expect a small corner radius from cold bending. If the designed radius is smaller than 150 × thickness, the part should be thermoformed instead; where integral forming is impractical, that feature can be split into joined pieces or machined flat (see our guide to PC sheet machining parameters).
For curved panels mounted in metal frames, thermal expansion clearance must be planned as well — see our article on PC and acrylic sheet distortion control.
2. Cold folding: the parameter table (do not exceed)
Cold folding presses a thin sheet along a fold line at room temperature — no heating, high efficiency. The guide values below, which should not be exceeded:
| Sheet thickness (mm) | Bending radius (mm) | Maximum folding angle |
|---|---|---|
| 1 to 2.5 | 2 | 90° |
| 3 and 4 | 3 | 90° |
| 5 and 6 | 4 | 60° |
Three points of practice:
- Thin sheet only. Cold folding is explicitly restricted to thin sheets. There is no table entry above 6 mm — do not extrapolate.
- Parameters vary from machine to machine. Pressure, bending-knife angle and similar settings differ, so some trial and error on each machine may be needed to find the correct settings.
- High stress at the edges. Cold folding creates high stress in areas at the edge of the material — which is exactly why the chemicals rule below exists.
3. Spring-back compensation: over-fold by about 25°, then wait
Relaxation occurs immediately after cold folding, so the sheet must be over-folded by approximately 25° relative to the target angle.
Another easy trap: the part is not in its final shape when it leaves the machine. The internal and external stress levels take a few days to become balanced, and only then does the part assume its final shape. In production terms:
- Set the fold to “target angle + about 25°”.
- Final inspection, hole matching and frame assembly should wait until the part has stabilized — do not fit against it on the same day.
4. The chemicals rule
The practice rule is explicit: avoid the use of aggressive chemicals, particularly with cold folded and cold bent parts. Stress levels in the fold zone are high, and exposure to aggressive media sharply raises the cracking risk. Build this into incoming inspection and cleaning procedures: neutral detergent only, no solvent wiping — see our PC sheet cleaning guide.
FAQ
Q: Can a 3 mm sheet be cold folded to 120°?
No. The table caps 3–4 mm sheet at a 90° folding angle with a 3 mm radius, and the values should not be exceeded. For larger angles, use hot line bending or thermoforming.
Q: Why did the folded angle change after a few days?
That is expected: after the ~25° over-fold compensates spring-back, internal and external stresses need several days to balance before the part reaches its final shape. Schedule final inspection and assembly after stabilization.
Q: Can hard-coated (AR) sheet be cold bent?
Hard-coated (AR) sheet is the exception to cold bending. If a hard-coated sheet must be formed, confirm the feasible process with the sheet supplier first — do not apply the standard-sheet parameters.
What Cremage can do for you
Wuxi Cremage Technology operates line bending and cold folding equipment alongside precision PC/acrylic machining. Working from your drawings we produce large-radius cold bends, thin-sheet cold folds and the follow-up machining for equipment guards, observation windows and door panels. Before committing to production we review minimum radius, folding angle and spring-back compensation for feasibility, then run trial folds and inspect after stabilization.
References
- [1] Exolon® Technical Manual Solid (Makrolon® sheet, now Exolon®), chapter 5 Forming: https://www.exolongroup.com/index.php/fuseaction/download/lrn_file/mf0261_e_210502.pdf