Surface treatment of injection molds is a key link in mold manufacturing, directly affecting product surface quality, mold service life and production efficiency. Scientific and standardized process standards can ensure consistent treatment effects, meet the molding needs of products made of different materials, and reduce production costs. Combining industry practice and technical trends, this paper clarifies the core process requirements, testing standards and application points of surface treatment of injection molds, providing reference for production practice.
Applicable to injection molds requiring high product surface gloss, such as household appliance shells and food packaging molds. The process shall use gradually refined abrasives, progressing from rough grinding to fine polishing to avoid surface scratches. The standard requires that the mold cavity surface has no obvious processing marks after polishing, the roughness reaches Ra≤0.02μm, the mirror effect is uniform, and there is no fog or orange peel phenomenon. During polishing, the grinding pressure and speed shall be controlled to prevent overheating and deformation of the mold base material. For complex cavities, special polishing tools shall be used to ensure that the corner parts are properly treated.
Focuses on improving corrosion resistance and wear resistance, suitable for molding molds of products with strong corrosion such as PVC and flame-retardant plastics. The chrome plating layer shall evenly cover the mold cavity and key molding surfaces, with a thickness of 0.01-0.03 mm, no pinholes, bubbles or peeling. The process shall strictly control the plating solution composition and temperature to ensure the coating hardness reaches HRC≥60 and the adhesion meets relevant industry standards. Under current environmental protection requirements, low-chromium or chromium-free plating solutions shall be adopted to reduce wastewater discharge and meet green production needs.
Applicable to steel injection molds, especially precision molds that need to improve surface hardness while avoiding deformation. The treatment temperature is controlled at 500-550℃, and the holding time is adjusted according to the mold size. The nitrided layer formed after nitriding has a thickness of 0.1-0.3 mm, and the surface hardness can reach HV≥850. The standard requires that the nitrided layer is uniform and continuous, without defects such as delamination and cracks. The dimensional change of the mold cavity after treatment shall be controlled within the allowable range, and it can be put into use without secondary processing.
A new type of surface strengthening process, suitable for high-wear and high-precision injection molds, such as engineering plastics and glass fiber reinforced material molding molds. Common coating materials include titanium nitride and chromium nitride. The coating thickness is controlled at 2-5 microns, with hardness up to HV≥2000, and excellent wear resistance and mold release performance. The process standard requires that the coating is firmly combined with the base material, the adhesion meets the first-class standard specified in GB/T 13913, the surface has no particles, scratches and other defects, and the stability of the coating in the high-temperature molding environment shall be guaranteed.
Visual inspection or 5-10 times magnifying glass inspection shall be adopted. After surface treatment, the injection mold shall have no cracks, pits, peeling, color difference and other defects. The cavity surface shall be flat and smooth, with rounded corner transitions, meeting the requirements of the mold design drawings. For mirror-polished molds, observation under natural light shall show no obvious uneven reflection.
A coating thickness gauge shall be used to detect the thickness of the plating layer or coating, with an error controlled within ±10%. A roughness meter shall be used to measure the surface roughness, with no less than 3 detection points, and the average value shall be taken as the final result, which shall meet the roughness standard of the corresponding process. The key dimensions of the mold cavity shall be verified by a coordinate measuring machine to ensure that the dimensional accuracy after treatment meets the molding requirements.
The wear resistance shall be verified by simulated molding tests. After thousands of consecutive moldings, the mold surface shall have no obvious wear marks. The corrosion resistance shall be tested by salt spray test, and no rust shall appear on the surface after tens of hours of testing in a neutral salt spray environment. The adhesion test shall adopt the cross-cut method. After cross-cutting, the coating shall be peeled off with adhesive tape, and no peeling of the coating is qualified.
With the tightening of environmental protection policies, traditional high-pollution treatment processes are gradually being replaced. Environmentally friendly materials such as chromium-free coatings and water-based polishes have been widely used. Processes such as gas nitriding and PVD coating have become mainstream choices in the industry due to low pollution and energy consumption. In the future, process parameters will be further optimized to improve treatment efficiency and environmental performance.
To meet the needs of complex working conditions, composite treatment technology is increasingly popular, such as nitriding + PVD coating composite, polishing + chrome plating composite, etc. Through the combination of multiple processes, the surface hardness, wear resistance and mold release performance of the mold can be improved simultaneously, and the service life of the mold can be prolonged. It is especially suitable for the molding of high-demand engineering plastic products.
The surface treatment of injection molds shall select appropriate treatment processes according to product materials, molding processes and service life requirements. The mold base material shall be quenched and tempered in advance to ensure uniform hardness and lay a foundation for subsequent surface treatment. During the treatment process, process parameters shall be strictly controlled and process records shall be made to ensure traceability of treatment effects. At the same time, the treated mold shall be properly maintained to avoid damp storage environment or collision, which may affect the treatment effect.
The process standard for surface treatment of injection molds is the core to ensure mold quality and production stability, and needs to be continuously optimized in combination with technological development and production practice. In practice, it is necessary to strictly follow the process requirements and testing standards, select appropriate treatment schemes, so as to give full play to the mold performance and improve product quality and production efficiency.
