Vacuum rim is a safety component of the driving system of transportation machinery such as commercial vehicles and engineering vehicles. It is a typical small modulus, large contour and thin-walled part. There are annular grooves around the casting (as shown in Figure 1), and the spoke plate has multiple air holes and installation holes. The material grade of the casting is QT450-15, the casting mass is 60 kg, and the average wall thickness is 10 ~ 15 mm. Its mechanical properties and internal quality directly affect the driving safety, comfort and service life.
Because there is no annular groove around the outer circumference of ordinary rim (non vacuum) castings, the upper and lower boxes can be molded directly. Generally, z148 micro shock compaction molding, static pressure molding, resin sand molding and even manual molding are adopted. The above casting process focuses on solving the problems of internal quality, appearance quality and production efficiency of products to varying degrees and different degrees. However, for vacuum rim castings with annular grooves on the outer circumference, the method of directly pulling out the outer shape by two box molding cannot be adopted. To pull out the outer shape, the annular grooves on the outer circumference of the casting need to be realized by placing an annular integral sand filling core, This not only affects the product appearance quality, reduces the production efficiency, increases the material and labor costs, but also increases the wall thickness mismatch of the lower core, which causes the corresponding thinning and uneven wall thickness, which is a fatal defect affecting the driving safety performance of the vacuum rim. Therefore, considering the influence of product structure, safety performance, appearance quality, production efficiency, cost and other factors, the EPC forming process scheme with certain advantages is determined.
Vacuum rim castings are produced by EPC process, which has the following advantages:
(1) Due to the vacuum adsorption, the pouring filling capacity is good, which solves the problems of cold shut and insufficient pouring. At the same time, due to the vacuum adsorption and the chilling effect of the pouring cavity of thin-walled parts, the internal structure of the casting is dense.
(2) Compared with the usual process, the surface quality of vacuum rim casting is significantly improved, meets the quality requirements and is recognized by customers.
(3) It can cast the air hole system and valve hole, save and reduce the corresponding machining process and equipment investment, and reduce the machining cost.
(4) The process adopts physical condition control and binder free pearl sand. The process is easy to control, stable and reliable, recycled, green and environmental protection, improves product quality, and has remarkable comprehensive effect.