Introduction
PMMA (acrylic) is a transparent thermoplastic and one of the world's most widely used plastics thanks to its processability and ease of coloration. Acrylic is also chemically stable with good mechanical properties and resistance to the elements.
Applications: Lenses, light shades, light pipes, optical fibers, signage.
Behavior: Acrylic has poor chemical resistance, and can be brittle and vulnerable to stress cracks. If this poses problems, PC can be substituted in. Extra draft is required during tooling.
| Properties | Metric | |
|---|---|---|
| Density | 1.01 – 1.20 g/cc | 0.0365 – 0.0434 lb/in³ |
| Hardness | 68 – 113 | 68 – 113 |
| Tensile Strength (Yield) | 13.0 – 65.0 MPa | 1890 – 9430 psi |
| Tensile Strength (Ultimate) | 22.1 – 49.0 MPa | 3210 – 7110 psi |
| Elongation at Yield | 0.62 – 30 % | 0.62 – 30 % |
| Elongation at Break | 3.0 – 150 % | 3.0 – 150 % |
| Dielectric Strength | 18.0 – 50.0 kV/mm | 457 – 1270 kV/in |
| Melt Temperature | 180 – 274 °C | 356 – 525 °F |
Surface Finish
Painting
Painting the surface of a part improves its aesthetic appearance and can provide brand recognition to consumers. In addition, painting can have a protective effect on parts.
Screen Printing
Screen printing is a printing technique where a mesh is used to transfer ink onto a substrate, except in areas made impermeable to the ink by a blocking stencil.
Design Guideline
Wall Thickness
Between 1 mm and 3 mm
Keeping walls as thin and constant as possible will reduce warping and sinking
Thickness gradient
Wall thickness should increase by no more than three times
Transition between thicknesses can be made smoother with fillets
Internal edges
Rounded, more than half wall thickness
Add fillet with largest possible radius
External edges
Rounded, full wall thickness plus internal fillet
Add fillet with largest possible radius
Draft angle
Increase draft by 1° for every 25 mm (for parts taller than 50 mm)
Add draft to ease ejection and avoid drag marks
Textured finish
Increase draft angle by 1-2°
Increase draft to ease ejection and avoid drag marks
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