Infiltration, shaping and repair of die castings
Die-casting impregnation, shaping, and repair are crucial processes for repairing and correcting internal and external defects, effectively improving the yield rate and reducing production costs. These processes primarily address defects such as porosity, shrinkage, deformation, cracks, and missing material that arise during the die-casting process, restoring previously substandard die-castings to acceptable serviceability. For example, impregnation can fill small internal pores in aluminum alloy die-castings, improving their sealing properties. Shaping corrects the shape and size of die-castings deformed by uneven cooling. Repair can restore the appearance and performance of die-castings with minor missing material or cracks.
Impregnation treatment is primarily used to seal defects such as pores and shrinkage within die-cast parts, improving their compactness and sealing properties. It is suitable for die-cast parts requiring pressure resistance and sealing, such as hydraulic and pneumatic components, and engine blocks. The impregnation process involves placing the die-cast part in an impregnant and applying pressure or vacuum to allow the impregnant to penetrate the pores within the part. The impregnant is then hardened by heating or curing, sealing the pores. Commonly used penetrants include epoxy resin, phenolic resin, and anaerobic adhesives. Epoxy resin penetrants are the most widely used due to their excellent sealing, corrosion resistance, and heat resistance. The impregnation process typically includes pretreatment (cleaning and drying), impregnation, curing, and post-treatment (removal of excess penetrant). For example, for aluminum alloy die-castings that need to withstand water pressure, they must first be thoroughly cleaned and dried, then placed in a vacuum impregnation tank, vacuumed, and injected with epoxy resin penetrant. A pressure of 0.5-1.0MPa is then applied to allow the penetrant to fully penetrate the pores and shrinkage. Afterwards, they are cured in an oven at 120-150°C for 2-3 hours. Finally, excess penetrant on the surface is removed, and the parts can be used after passing the inspection.
The shaping process primarily corrects deformation in die-casting parts, bringing their shape and dimensions into line with design requirements. It is suitable for die-castings deformed due to factors such as improper die-casting processes, uneven cooling, and excessive ejection forces. There are two main shaping methods: mechanical shaping and thermal shaping. Mechanical shaping utilizes specialized shaping dies or fixtures to plastically deform the die-casting by applying external force, thereby correcting its shape and dimensions. This method is suitable for die-castings with minimal deformation. For example, to correct warped flat die-castings, the part can be placed in a shaping die, and pressure applied by a press is maintained for a period of time before being released to restore the flatness. Thermal shaping involves heating the die-casting to a specific temperature (usually below the alloy’s recrystallization temperature) and then applying external force within the shaping die to correct the deformation. This method is suitable for die-castings with larger deformation and higher rigidity. For example, deformation of large aluminum alloy frame die-castings can be corrected by heating them to 200-300°C and then using a specialized shaping fixture. This utilizes the metal’s excellent plasticity at high temperatures to achieve the desired shaping effect. The shaped die-castings then undergo dimensional inspection to ensure they meet tolerance requirements and to avoid cracks in the die-casting due to over-shaping.
The repair process primarily repairs surface defects such as missing material, cracks, dents, and scratches on die-cast parts, restoring their appearance and performance. It is suitable for die-cast parts with relatively minor defects. Repair methods include welding, filling, and electroplating. Welding is suitable for die-cast parts made of metal materials (such as aluminum alloys and zinc alloys). For small surface cracks and missing material, argon arc welding or gas welding can be used. After welding, polishing and finishing are required to achieve a smooth surface. For example, small cracks on the surface of aluminum alloy die-cast parts can be repaired using argon arc welding. Welding is performed under inert gas shielding using a wire of similar material to the base material. After welding, sandpaper is used to level the surface with the surrounding surface. Filling is suitable for surface defects in non-stressed areas. Filling materials such as putty and resin can be used to fill the defective area, followed by polishing and painting. This is suitable for repairing exterior parts. For example, small depressions on the surface of zinc alloy toy die-castings can be filled with special putty, sanded smooth after drying, and then painted to restore the appearance to normal. Electroplating repair deposits a layer of metal on the defective area through electroplating to fill the defect and is suitable for die-castings that require electroplating.
Quality control during the impregnation, shaping, and repair processes is crucial, directly impacting the repair outcome and safety of die-casting parts. Before these processes begin, die-casting defects must be thoroughly inspected and evaluated to determine their type, location, size, and severity, allowing the selection of appropriate repair methods and process parameters. For example, for internal pores, X-ray inspection or airtightness testing is required to determine their distribution and size, enabling the selection of an appropriate impregnation agent and process. For deformation defects, a coordinate measuring machine (CMM) is required to measure the amount and location of deformation, enabling the design of an appropriate shaping mold and process. During the repair process, process parameters (such as impregnation pressure, temperature, and time; shaping force and temperature; welding current and voltage) must be strictly controlled to ensure repair quality. After repair, die-castings must undergo comprehensive quality inspections, including visual inspection, dimensional measurement, and performance testing (such as sealing and mechanical properties) to ensure they meet design requirements and service standards. Unsatisfactory die-castings should be reworked or scrapped to prevent them from reaching subsequent processes or reaching end users. Through scientific and reasonable infiltration, shaping and repairing, the qualification rate of die castings can be effectively improved, production costs can be reduced and resource utilization can be improved.
