Before assembly, cleaning the surface of molded metal parts to remove oil and impurities is crucial, as it affects not only assembly accuracy but also the mold's lifespan and molding quality. Oil stains may originate from cutting fluid and lubricating oil used in processing, or dust, metal shavings, and other impurities from the storage environment. If not thoroughly removed, they can lead to abnormal clearances between parts, jamming, and even mold cracking under high pressure. Therefore, a systematic cleaning process, combining physical and chemical methods, is necessary to ensure the part surfaces meet assembly requirements.
Preliminary mechanical cleaning is the first step, primarily targeting large particles and loose oil. Operators can use a soft brush or compressed air to thoroughly clean the part surface, focusing on removing dust and metal shavings from grooves, holes, and threaded areas. For stubborn deposits, such as metal burrs left from processing, gently polish with a fiber wheel or sandpaper to avoid excessive cutting that could damage the part's dimensional accuracy. Careful tool selection is essential at this stage; hard bristles or sandpaper may scratch the surface, making subsequent cleaning more difficult. Therefore, tools must be matched to the part's material and surface roughness.
Chemical cleaning is the core step in removing oil stains, and the appropriate cleaning agent must be selected according to the type of oil stain. For mineral oil or synthetic cutting fluid, alkaline cleaning agents can decompose the oil stains through saponification. They have strong penetrating power and can reach even the smallest crevices to remove residue. During operation, immerse the parts in the cleaning solution or spray it evenly with a spray gun, allowing sufficient time for the cleaning agent to fully react. For precision parts or complex cavities, ultrasonic cleaning equipment can be used. High-frequency vibration accelerates the separation of the cleaning agent and oil stains, while avoiding mechanical friction damage to the surface. After chemical cleaning, rinse thoroughly with clean water to prevent cleaning agent residue from corroding the metal.
Soluble cleaning is suitable for alkaline-sensitive metal materials, such as aluminum alloys or plated parts. Organic solvents such as trichloroethylene, acetone, or specialized metal cleaners can quickly dissolve oil stains without leaving residue. Operation should be carried out in a well-ventilated environment, with protective gloves and masks worn to avoid harm from solvent evaporation. Solvent cleaning can be done by wiping or immersion. For parts with complex cavities, a soft cloth dampened with solvent can be used for repeated wiping, or a spray gun can be used to atomize the solvent and spray it on, ensuring that even hidden areas are covered. After cleaning, parts should be dried with compressed air to prevent moisture residue from causing rust.
Steam cleaning is a highly efficient and environmentally friendly cleaning method, especially suitable for the rapid processing of large batches of parts. High-temperature steam softens oil stains and removes adhering substances through pressure impact, leaving the parts dry and residue-free after cleaning. During operation, steam temperature and pressure must be controlled to avoid deformation or plating peeling due to high temperatures. For precision parts, a pure water rinsing step can be added after steam cleaning to further remove any remaining impurities. Steam cleaning equipment requires regular maintenance to ensure the steam generator and nozzles are not clogged, guaranteeing stable cleaning results.
Surface passivation treatment can improve the corrosion resistance of cleaned parts. Cleaned metal surfaces are highly reactive and easily react with moisture or oxygen in the air to form an oxide layer. By spraying rust-preventive oil or immersing in passivating solution, a protective film can be formed on the surface, isolating it from environmental corrosion. The choice of rust-preventive oil depends on the material of the parts and the storage period. A thin layer of oil can be used for short-term storage, while a thicker layer or vapor phase rust inhibitor is required for long-term storage. After passivation, parts should be suspended or laid flat in a dry environment to prevent damage to the oil film.
Final inspection is the final step in the cleaning process, requiring visual inspection and tactile assessment to confirm the cleaning effect. Under bright light, the surface of the parts should be free of oil, water stains, or impurities, especially on mating surfaces and sealing areas. Touching the surface should feel smooth and non-sticky; if there is a grainy feel or oil residue, the parts must be returned to the previous step for reprocessing. For high-precision parts, the surface can be wiped with a white cloth to check for cleanliness, quantifying the degree of cleanliness.
The cleaning of mold metal parts before assembly must balance efficiency and quality. Through the coordinated use of mechanical cleaning, chemical cleaning, solvent cleaning, steam cleaning, passivation, and final inspection, surface oil and impurities can be thoroughly removed, providing a reliable guarantee for subsequent assembly and use. Standardizing the cleaning process is just as important as training operators' skills. Only by strictly following the process requirements can we ensure that every part meets the assembly standards.
