In the injection molding industry, surface treatment of injection molds is a key factor determining mold durability, demolding performance, production efficiency, and part appearance. Appropriate surface treatment can significantly extend mold life, reduce sticking, lower scrap rates, and make part surfaces smoother or with specific textures.
- Polishing (Polishing) — The most basic and common choice Polishing is a surface treatment performed on almost all injection molds, directly affecting the gloss and appearance of molded parts. According to SPI (Society of Plastics Industry) standards, common levels include:
- SPI A grade (diamond polishing): Mirror high gloss, Ra 0.012–0.1μm, commonly used for transparent parts, optical lenses, cosmetic housings.
- SPI B grade (sandpaper polishing): Semi-gloss, suitable for consumer electronics, daily necessities.
- SPI C/D grade (stone/sandblasting): Matte or rough texture, suitable for hiding defects or increasing friction on structural parts.
Polishing has relatively low cost and is the most widely used in combination with other treatments.
- Chrome Plating (Chrome Plating / Hard Chrome) — Classic solution for wear resistance + corrosion resistance Hard chrome plating is one of the most common surface strengthening treatments for injection molds, especially suitable for glass fiber filled materials and corrosive plastics (such as PVC, halogen-containing flame retardants).
- Hardness up to 70-72 HRC, low friction coefficient (≈0.2).
- Improves demolding, reduces sticking and wear.
- Commonly used in high-wear areas such as sliders and cores.
The disadvantage is uneven thickness (prone to occur in complex geometries); for strongly corrosive materials like PVC, electroless nickel is more recommended.
- Electroless Nickel (Electroless Nickel) — Preferred for uniform coverage + corrosion resistance Uniform thickness (consistent even in complex cavities), hardness 50-62 HRC, particularly suitable for:
- Corrosive resins (such as PVC, halogen-containing materials).
- Molds requiring high precision and chemical corrosion resistance.
- Often used as an alternative to chrome plating or as an underlayer.
- PVD/CVD Coating (Physical/Chemical Vapor Deposition) — High-end wear-resistant black technology Modern injection molds increasingly favor PVD (such as TiN, CrN, AlCrN) and CVD coatings:
- Extremely high hardness (2000-3500 HV), ultra-low friction coefficient.
- Anti-adhesion, high temperature resistance, abrasion resistance.
- Suitable for engineering plastics, high-filled materials, long-term mass production.
- Common types: TiN (golden), CrN (silver-gray), DLC (diamond-like, black).
Although PVD/CVD has high initial investment, it can increase mold life by 2-5 times, especially suitable for automotive parts and medical device molds.
- Nitriding / Nitriding Treatment (Nitriding) — Economical wear-resistant entry-level strengthening Gas nitriding or ion nitriding forms a hardened layer on the surface (hardness up to 900-1200 HV), low cost and minimal deformation.
- Improves wear resistance and fatigue resistance.
- Commonly used for mid-to-low-end molds or as pre-treatment for other coatings.
- Better results when combined with PVD.
6.Mold surface texturing
Selection suggestions: Quick matching based on needs
- Pursuing high-gloss appearance → SPI A/B polishing + chrome plating/PVD.
- Corrosion resistance / high-filled materials → Electroless nickel or CrN PVD.
- Large volume, durability priority → PVD/CVD or hard chrome plating + nitriding.