Introduction

Detailed Explanation of Plastic Material Machining Characteristics

ABS
Internal Angle Limitations: When CNC machining, the recommended minimum internal corner radius (R) is R ≥ 0.5 mm. Maintaining a sufficient R helps avoid stress concentration and ensures the structural strength of the part.

Surface Finishing: ABS is highly suitable for surface treatment and is widely used, including painting, PVD coating, screen printing, water transfer printing, hot stamping, and laser engraving. Surface activation and priming are often required before any treatment to ensure optimal coating adhesion.

PC (Polycarbonate)

Internal Angle Limitations: The recommended minimum internal corner radius is R ≥ 0.4 mm. PC is sensitive to notch stress, so a sufficient R angle is particularly important.

Surface Treatment: PC is also suitable for a variety of surface treatments, such as painting and PVD coating. However, special care should be taken to avoid contact with chlorine-containing chemicals or strong solvents during the treatment process to prevent stress cracking.

PA6 / PA66 (Nylon)

Inside Angle Limitation: The recommended minimum inside corner radius is R ≥ 0.5 mm.

Surface Treatment: Nylon can be painted, screen-printed, water transfer printed, and laser engraved. Because nylon absorbs water easily, it must be thoroughly dried before any surface treatment, and a nylon-specific primer must be used to ensure adhesion.

POM (Plastic-on-Metal)

Inside Angle Limitation: Due to its excellent material stability, it can be processed to a minimum R ≥ 0.3 mm.

Surface Treatment: POM has low surface energy and poor adhesion, making it one of the most difficult plastics to paint. While it can be painted or laser engraved after complex pre-treatments such as plasma activation, it is generally not recommended for applications requiring a high surface finish.

PMMA (Acrylic)

Inner Corner Restrictions: To avoid corner cracking or cracking during processing, a minimum inner corner radius of R ≥ 0.5 mm is recommended.

Appearance Finishing: PMMA inherently has high gloss and transparency, and can generally be directly polished with a diamond knife to achieve an excellent appearance. Painting or laser engraving are also acceptable, but care must be taken to avoid using solvents that may cause whitening or cracking.

Glass Fiber Reinforced Plastic (e.g., PA+GF, PC+GF)

Inner Corner Restrictions: The minimum inner corner radius of R ≥ 0.5 mm is recommended. The addition of glass fiber makes the material brittle, making a sufficient R angle even more necessary to avoid stress concentration.

Appearance Finishing: Painting, PVD coating, and other methods are acceptable. However, since the fibers float on the surface, direct spraying may not achieve a smooth, mirror-like finish. A thicker primer or putty is usually required to smooth the surface.

PEEK

Inner Corner Restrictions: Processing to a smaller R ≥ 0.3 mm is possible.

Appearance Finishing: PEEK has a stable surface, similar to POM, and is not easily painted. However, it is well-suited for laser engraving and PVD coating.

Key Glossary

• Minimum Inner Corner Radius: Also known as the R-angle. Because CNC machining uses a cylindrical milling cutter to cut the material, the inside corners of a part cannot be machined to a perfect 90° angle. Instead, a circular arc corresponding to the cutter’s radius is left. The minimum radius of this arc is the inner corner limit. Designing for a larger R-angle than the limit not only reduces machining difficulty and cost, but also effectively distributes stress and prevents cracking at the corners.

Conclusion

When designing plastic parts for CNC machining, considering the minimum R-angle limit and understanding the surface finishing processes the material can support will make your design more manufacturable and ensure the desired final product appearance is achieved. Different processing methods have different temperature and solvent requirements. Choosing a process that matches the material properties is the only way to ensure appearance quality and part stability.