PMMA (polymethyl methacrylate) is widely used in model making, signage, lightboxes, and various display props due to its high transparency, excellent weather resistance, and good processability. Achieving the desired high surface finish and clarity in PMMA products relies heavily on CNC machining and subsequent polishing.
Machining Complex Parts: For structurally complex or thin-walled PMMA parts, a “Multiple Light Cuts” strategy can be employed. This involves a roughing cut that leaves excess material, followed by a finishing cut to achieve the final dimensions, which effectively controls deformation and stress.
Combined Process Applications: After CNC machining, other PMMA processing techniques like thermoforming or bonding can be combined based on product requirements to create more complex products. For example, individual components can be first CNC milled, then shaped through thermoforming, and finally assembled using specialized adhesive.
PMMA offers very high transparency, with a light transmittance of up to 92%, superior to glass. It is lightweight, has good weather resistance, but its surface hardness is lower than glass, making it susceptible to scratching.
After CNC machining is completed, tool marks remain on the edges or surfaces of PMMA, giving them a frosted, white appearance that affects clarity. Subsequent polishing is a critical step to restore its “crystal-like” transparency.
| Polishing Method | Best Application Scenario | Advantages | Disadvantages |
|---|---|---|---|
| Flame Polishing | Flat or regular edges | Fast, Excellent results, Low cost | Requires experience, Safety risks, Only suitable for edges |
| Diamond Polishing | High-precision requirements, Complex 3D shapes | High precision, Uniform results, Automatable | High equipment cost, Material removal process |
| Buff Polishing | Flat surfaces, Simple curves | Low cost, Relatively simple operation | Unsuitable for complex shapes, May introduce scratches |
| Chemical Polishing | Complex 3D structures, Tiny internal features | Stress-free, Can handle any complex shape | Softer finish effect, Uses strong acids, High environmental/safety requirements |
| Vibratory Polishing | Small parts, Deburring | Suitable for batch processing, Good consistency | Cannot target specific areas, Rounds off sharp edges |