Plastic Fabrication & CAM
Acrylic Line Bending & PMMA Prepress Engineering Guide
Line bending (strip heating) is the premier manufacturing technique for creating seamless, crystal-clear 3D enclosures, retail displays, sneeze guards, and machine shields from flat plastic sheets. This guide details heating zone sizing, temperature control, and flat blank DXF unrolling.
1. Cast vs Extruded Acrylic Bending Dynamics
- Cast Acrylic (GS / PMMA): Higher molecular weight. Wider softening temperature window ($150^\circ ext{C} - 165^\circ ext{C}$). Outstanding optical clarity with minimal risk of boiling bubbles. Requires flame or diamond polishing along cut edges before bending.
- Extruded Acrylic (XT): Lower melting point ($140^\circ ext{C} - 150^\circ ext{C}$). More susceptible to overheating blisters and skin crazing. Heats roughly 15% faster but requires strictly monitored power output.
- Polycarbonate (Lexan / Makrolon): High impact resistance. Must be pre-dried in an air circulating oven at $120^\circ ext{C}$ to purge absorbed water vapor before heating, otherwise internal steam produces milky white bubbling along the bend line.
2. Strip Heater Zone Width Formula
If the heated strip zone is too narrow, the outer plastic radius stretches beyond its tensile yield point, resulting in optical distortion and micro-crazing. The required radiant band opening is:
W_heat = (π × θ / 180) × (R_i + 0.5 × T) + 2 × T
Where $ heta$ is the bend angle in degrees, $R_i$ is inside bend radius, and $T$ is sheet thickness.
3. Laser Cutting Edge Preparation for Bending
Laser cut acrylic edges contain microscopic recast notches and thermal micro-stresses. When subjected to subsequent heat line bending, these edge notches can propagate into catastrophic full-thickness cracks. Best practices:
- Use smooth tangential lead-ins to avoid pierce blowouts near the bend line.
- Anneal or flame-polish the cut perimeter if severe optical clarity is required.
- Offset the laser pierce point at least $3 imes T$ away from the heated zone boundary.
Need Laser-Ready DXF Files for Plastic Fabrication?
SpotItLive provides precision 2D vector conversion with calculated outside setbacks and bend allowances for laser cutting and CNC router fabrication.
Order Vector Fabrication Pack (29 DKK)