Solution to the problem of dragging during injection molding of electroplated molds
Electroplated molds, with their smooth surface, high hardness, and excellent wear resistance, are often used in injection molding for high-performance parts, such as exterior and transparent components. However, in actual production, electroplated molds sometimes exhibit a phenomenon called “scratching.” This occurs when the mold surface scrapes the part during demolding, resulting in defects such as scratches and bruises, seriously affecting the part’s appearance. This phenomenon not only increases scrap rates but also shortens the mold’s lifespan, necessitating effective solutions to eliminate this problem.
To solve the problem of scratching on electroplated mold products, we first need to identify the cause of the scratching. The scratching phenomenon is mainly caused by excessive friction between the plastic part and the mold electroplating layer, or defects in the mold electroplating layer surface, which causes the plastic part surface to be scratched during the demolding process. Specifically, possible reasons include: the surface roughness of the mold electroplating layer does not meet the requirements, and there are defects such as burrs and pinholes; the compatibility between the plastic part material and the mold electroplating layer is poor, and the friction coefficient is too large; the demolding angle is insufficient, resulting in excessive contact pressure between the plastic part and the mold surface during demolding; the presence of pollutants such as oil, impurities, etc. on the mold surface increases friction; the injection molding process parameters are unreasonable, such as the mold temperature is too low, the holding pressure is too high, etc., which leads to increased adhesion between the plastic part and the mold surface.
To address issues with the mold’s electroplating layer itself, the electroplating process requires strict control to ensure the quality of the coating. First, the mold surface should be thoroughly pretreated before electroplating to remove impurities such as oil, rust, and scale, ensuring a smooth and even surface. Scratches, dents, and other surface defects should be removed and polished to ensure a surface roughness of Ra 0.02-0.05μm. During the electroplating process, parameters such as the plating solution concentration, temperature, and current density should be carefully controlled to ensure a uniform and dense coating with a thickness of 5-10μm. After electroplating, the coating should undergo post-treatment, such as passivation and sealing, to improve its wear resistance and smoothness and minimize surface defects. Furthermore, the mold’s electroplating layer should be regularly inspected and maintained. Any burrs or scratches should be promptly polished and repaired to prevent scratches.
Optimizing plastic part material selection and mold release design is a key measure to address the problem of smearing. For electroplated molds, select materials with good compatibility with the plating layer and a low coefficient of friction. For example, polyolefin plastics (such as polyethylene and polypropylene) have a low coefficient of friction and are more compatible with plating layers such as chrome and nickel, making them less likely to cause smearing. In contrast, materials such as polyvinyl chloride and polyoxymethylene have a higher coefficient of friction and are prone to adhesion to the plating layer, resulting in smearing. If a material with a higher coefficient of friction is necessary, an appropriate amount of lubricant, such as zinc stearate or silicone oil, can be added to reduce friction between the part and the mold surface. Furthermore, the draft angle of the plastic part should be appropriately designed. For parts with high aesthetic requirements, the draft angle should be no less than 1°-2° to ensure smooth release from the mold and reduce contact pressure and friction time with the mold surface. For parts with deep cavities or complex structures, the draft angle should be increased or demolding ribs should be installed to further reduce demolding resistance.
Adjusting injection molding process parameters is also key to eliminating the “drag” phenomenon. Mold temperature significantly affects the adhesion between the plastic part and the mold surface. Excessively low mold temperature causes the part to cool too quickly, increasing shrinkage and adhesion to the mold surface, which in turn increases friction during demolding. Excessively high mold temperature prolongs cooling time, reduces production efficiency, and may cause part deformation. Therefore, the mold temperature should be controlled within a reasonable range based on the material and structural characteristics of the part. For example, for ABS material, the mold temperature is typically set between 50-70°C. The holding pressure and holding time also need to be adjusted appropriately. Excessively high holding pressure or prolonged holding time can increase internal stress in the part, strengthen adhesion to the mold surface, and easily cause “drag.” While maintaining part dimensional accuracy, the holding pressure and holding time should be appropriately reduced. Furthermore, the ejection speed can be increased before demolding to reduce the contact time between the part and the mold surface. However, the ejection speed should be kept within a reasonable range to avoid deformation or damage to the part.
Doing a good job of daily cleaning and maintenance of the mold can effectively prevent the occurrence of dragging. Before each production, the mold cavity, core and other surfaces should be thoroughly cleaned to remove surface oil, plastic debris, dust and other pollutants. You can use a special mold cleaner or alcohol to wipe to ensure a smooth and clean surface. During the production process, the mold should be inspected regularly and any surface contaminants should be cleaned in time. At the same time, attention should be paid to the lubrication of the mold. For moving parts such as ejectors and guide pins, special lubricants should be added regularly to ensure smooth movement and avoid increased demolding force due to component jamming, which in turn causes dragging. In addition, when storing the mold, the mold surface should be avoided from contact with other hard objects to prevent the electroplating layer from being scratched; molds that are not used for a long time should be coated with anti-rust oil to prevent oxidation and corrosion of the electroplating layer.
