In precision mold manufacturing, high-precision polishing of the mold cavity is a core step in ensuring mold performance and product quality. Polishing directly affects not only the surface finish and release properties of the mold, but also its corrosion resistance, wear resistance, and service life. Achieving high-precision polishing requires a comprehensive approach encompassing process flow, tool selection, operational techniques, and environmental control.
High-precision polishing typically follows a graded polishing principle from coarse to fine, progressively reducing surface roughness through three stages: rough polishing, semi-fine polishing, and fine polishing. The rough polishing stage primarily removes macroscopic defects such as machining marks and EDM layers. Common tools include oilstones and ultrasonic grinders, eliminating protrusions through cutting or plastic deformation. The semi-fine polishing stage uses sandpaper to further refine the surface, gradually eliminating traces left by rough polishing and laying the foundation for fine polishing. The fine polishing stage is crucial in determining surface quality, requiring high-precision tools such as diamond polishing paste and polishing wheels. Through the synergistic effect of micro-cutting and plastic flow, a mirror-like finish is achieved.
Tool selection and matching are another core element of high-precision polishing. During rough polishing, the grit size of the oilstone must be appropriately selected based on the initial surface roughness; too coarse a grit easily leads to scratches, while too fine a grit results in low efficiency. In the semi-finish polishing stage, the sandpaper grit should be increased gradually to avoid fluctuations in surface quality caused by skipping grits. In the finish polishing stage, the grit size of the diamond polishing paste and the material of the polishing wheel must be strictly matched. For example, 9μm polishing paste paired with a wool wheel can effectively remove sandpaper marks, while polishing paste smaller than 1μm requires the use of soft tools such as felt to avoid scratches. Furthermore, auxiliary tools such as cork sticks, bamboo strips, and copper sheets must be customized according to the shape and size of the mold cavity to ensure uniform polishing pressure and controllable direction.
Operating techniques have a significant impact on polishing quality. When sanding, the polishing direction should be changed (usually 45°~90°) to cross-remove marks from the previous process and avoid forming directional scratches. Simultaneously, each time sandpaper or polishing paste is changed, the surface must be thoroughly cleaned with a pure cotton cloth soaked in alcohol to prevent residual particles from causing secondary damage. Pressure control is particularly crucial in the fine polishing stage; excessive pressure can easily cause "orange peel" defects, while insufficient pressure leads to low efficiency. In practice, thin copper sheets or shavings can be added to the tools to reduce localized pressure and ensure uniform polishing. Furthermore, polishing time must be strictly controlled to avoid surface heating due to prolonged friction, which could lead to material phase transformation or burning.
Environmental control is an implicit guarantee for high-precision polishing. The polishing workshop must maintain a constant temperature and humidity to reduce the impact of temperature fluctuations on the thermal expansion and contraction of the material, preventing a decrease in polishing precision due to dimensional changes. At the same time, the workshop must have an efficient dust removal system to ensure that there are no suspended particles such as dust and smoke in the air, preventing them from adhering to the mold surface and forming defects. For polishing processes requiring precision of 1μm or higher, it must be carried out in a cleanroom. Operators must wear dust-proof clothing and gloves, and regularly clean their hands and tools to prevent contaminants such as body oils and sweat from coming into contact with the mold surface.
Material properties and pretreatment conditions are also crucial factors affecting polishing quality. High-quality steel is a prerequisite for good polishing results. Inclusions, porosity, or uneven hardness in the steel can easily lead to defects such as scratches and edge collapse during polishing. Furthermore, a hardened thin layer forms on the mold surface after EDM (Electrical Discharge Machining), which needs to be removed through rough grinding or precision EDM; otherwise, polishing will be significantly more difficult. For pre-hardened steel molds, high-grit sandpaper (e.g., #1500 and above) should be avoided to prevent surface burns.
High-precision polishing also requires advanced testing technology for process monitoring. Equipment such as optical projectors and surface roughness meters can be used to monitor polishing progress and surface quality in real time, allowing for timely adjustments to process parameters. For example, in the fine polishing stage, an interferometer can be used to detect surface waviness to ensure it meets design requirements. In addition, experienced polishing technicians are key to ensuring quality. They can accurately judge the polishing status by observing surface reflection and tactile feel, and flexibly adjust operating strategies accordingly.
High-precision polishing in precision mold manufacturing is a systematic project that requires coordinated efforts from multiple aspects, including process design, tool selection, operating procedures, environmental control, material pretreatment, and inspection and monitoring. Only by strictly adhering to the principle of graded polishing, rationally matching tools and materials, precisely controlling operating parameters, and creating a clean processing environment can a mirror-like finish be achieved in the mold cavity, meeting the stringent performance requirements of high-end products.
