Application of solid casting in the manufacture of car interior parts mould
1 Introduction
In many cases, molds have laid a good foundation for the development of the foundry industry. Such as: casting models, die-casting molds, etc., they are necessary tools for the production of high-quality products. With the booming development of the automotive industry in China and the development of some new products, casting has also created a precedent for the manufacture of some special molds. Such as: automotive interior parts molds, inspection tools, and so on. Among them, real casting has the most direct impact on mold manufacturing.
Although China's car industry started late, it has developed rapidly. Now the fierce competition has made the domestic car gradually evolve from simple CKD assembly to localization of parts. This year, most of the new car parts development is carried out in China, so the mold The manufacturing industry has put forward higher requirements and accelerated the application of solid casting technology in mold manufacturing.
2 real casting process characteristics
Solid casting was invented by Americans in 1956. From the first small-volume production to large-volume small-scale production, it is most representative of industrial production in the United States, Italy, Germany, Russia, and Japan. It was applied to the production of auto parts in the mid-1980s, which stimulated the further improvement and development of the process.
China's research on real casting technology began in the mid-1960s, starting with the production of parts blanks, mainly cast iron and cast steel. Nearly a hundred factories have produced solid castings, most of which are small. In recent years, as Chinese cars have entered the family of the people and the automobile industry has developed rapidly, a number of solid casting production lines for auto parts have been built. It has also begun to be used in mold manufacturing.
The traditional sand casting method is: firstly, the wood mold and the core box are manufactured according to the drawings, and then the box shape is molded and the mold is cast. The real casting is: firstly, the original shape of the expanded polystyrene plastic is the same as that of the casting. When the shape is formed, the original sample is placed in the sand box. After the molding, the foam molding is not taken out to form a mold having a solid cavity. The metal gasification pattern is cast, the molten metal replaces the pattern space, and is cooled and solidified to form a non-slit casting having the same shape as the pattern.
Compared with the traditional sand casting process, the real casting process has the advantages that the cost of making the casting model is lower than that of the wood mold; the shape and the shape of the casting are exactly the same, and the dimensional inspection is easy; no core is used, no classification is used. The casting time is greatly reduced; the complex parts can be cast, and the inserts and cooling water pipes can be easily embedded; the raw material cost, labor cost and production cost are generally lower than ordinary sand casting.
3 Car interior parts mold requirements
Car interior parts are the most critical part of automotive interiors, such as the main carpet, trunk side panels, trunk rugs, coat racks, doors and ceilings. The car interior parts are made up of two parts: fabric and skeleton. Most of the fabrics are needle-punched carpets, tufted carpets, fabrics, etc.; the skeleton is mostly made of hemp fiber + polypropylene (PP), cotton fiber + polypropylene (PP), waste fiber + resin, wood powder board and so on. In the manufacturing process, the fabric does not need to be heated, and the skeleton needs to be heated and softened beforehand, and then bonded to the fabric to form a cooling. Moreover, the shape of these interior parts is a free-form surface, the profile is undulating, the height difference is large, and the outer shape is large. Therefore, this type of mold has its uniqueness. The molding die cannot use conventional steel materials. At the same time, the mold material is required to have good thermal conductivity and no rust, in addition to the basic hardness.
According to the characteristics of the above products, due to the large size of the interior parts, considering the factors of the mold's own weight, we choose aluminum alloy as the material of the mold. In addition, the cooling effect of the mold directly affects the formation of the skeleton and the production efficiency, so the water pipe must be embedded in the mold. Therefore, it is necessary to use a casting method to obtain a blank of a mold that meets the requirements for use.
4 Manufacturing process
According to the requirements of the car interior parts mold, the traditional mold design and manufacturing process can not meet the requirements of product molding and customer production cycle. We use 3D modeling or reverse engineering to build product models and mold design, and use solid casting process to cast dynamic and fixed mold blanks of aluminum alloy molds.
4.1 Model making
4.1.1 Material selection
According to the conditions of aluminum alloy casting, polystyrene plastic with low density, high strength, rapid gasification, less residue and convenient molding process is used as the raw material of gasification mold. The characteristics of the original beads are shown in the attached table.
Relative molecular weight water content bulk density particle size
180000 - 270000~ 0.3%600 ~ 650 Kg/m30.3 ~ 0.5mm
4.1.2 Forming Process
The model is processed using CAD/CAM technology that is currently mature in mold manufacturing. Manually repair and assemble the pattern and casting system. At the same time, the cooling water pipes are arranged at the same distance below the forming surface.
4.2 Coating
Coatings are one of the key factors in the success of a solid casting process. Solid casting coatings should have good strength, gas permeability, refractoriness, thermal insulation, chilling resistance, coating, dripping, suspension and moisture absorption. It is generally composed of refractory materials, entanglement agents, solvents, suspending agents, thixotropic agents and other additives.
The coating is applied by a brushing method, and a uniform, comprehensive, and non-exposed exposed portion of the model is required.
After the coating is finished, it needs to be dried. Dry at 8 ° C for about 8 – 10 hours. In addition, the humidity of the drying equipment should be controlled during the drying process, and the general humidity is not more than 30%. And pay attention to the reasonable placement and support of the model to prevent deformation of the model.
4.3 modeling
Choose a reasonable sand box and use a resin self-hardening sand molding process to establish a reasonable exhaust passage. The resin content is controlled to be 0.8% or less. The casting time is controlled more than 8 hours after the molding is completed.
4.4 casting
Pyrolysis of styrofoam is a complex physical-chemical process that often absorbs heat. Therefore, the casting temperature of aluminum alloy is generally higher than that of ordinary sand casting. Recommended control is in the range of 700 - 750 °C.
5 Conclusion
(1) The application of solid casting in the manufacture of car interior parts moulds is very reasonable. It can not only gain valuable time in the competition of new car development and old car change, but also reduce costs, obtain complex and special Required castings. Economic and social benefits are obvious.
(2) The use of real casting technology, CAD/CAM technology and reverse engineering technology to manufacture automotive interior parts and moulds has reached the international advanced level in the same industry, which is of great significance for promoting the rapid development of domestic car industry and localization of parts.
(3) Due to the difference in casting temperature and alloy composition, solid casting of large aluminum alloy castings is much more difficult than cast iron and cast steel. However, it has been proved by practice that reasonable process design and casting methods can improve the quality of castings.
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