Special casting is a special casting technology, which is compared with traditional sand casting. Special casting has significant difference from common sand casting in moulding material, moulding method, filling form of liquid metal and solidification condition of casting mould.
Common special casting methods include investment casting, metal mould casting, pressure casting, low pressure casting and differential pressure casting, squeeze casting, centrifugal casting and continuous casting, ceramic casting, lost foam casting, etc.
Among many special casting methods, investment casting and metal mould casting have the longest history in modern industrial history. Special casting really appeared at the end of the 19th century and the first half of the 20th century. Practical and perfect special casting technology developed rapidly in the second half of the 20th century after the 1980s. With the gradual integration of the world economy and the rapid development of the global economy, modern industry can not be compared with traditional industrial technology. As the pillar of industry, one-dimensional foundry industry should also invest in the tremendous wave of technological renewal, and constantly improve the production process in the wave, constantly weeding out the old and bringing forth the new. Only by continuously optimizing production conditions and modes can we find our position quickly and accurately under the background of global economic integration, and realize long-term development limited by constraints. This paper focuses on two casting methods, investment casting and metal casting.
1. Investment casting
Investment casting, also known as wax loss method, is a special casting technology developed on the basis of ancient wax loss casting. The concrete operation method is: using fusible material to make casting model, then wrapping the model with plastic material, after condensation and hardening, then heating, melting and discharging the model, so as to obtain the casting without parting surface. After casting, the casting process can be described as: wax mould manufacturing, crusting. Dewaxing, roasting and pouring. Because the main component of fusible material is paraffin, investment casting, also known as wax-loss investment casting, has the greatest advantage of high quality and dimensional accuracy and good surface finish. The castings that are manufactured and moulded do not need to be cut again. They can be directly used in mechanical parts, reduce other unnecessary processes, and greatly save production materials.
2. Metal mold casting
Metal mould casting is a process in which liquid metal is poured into the metal mould to obtain the casting. The characteristics of the metal mould are as follows: firstly, the vertical parting method is widely used in the casting mould; secondly, the core is usually made into a combined form so as to extract the metal mould from the casting mould. First, the casting mould has the following advantages: firstly, because the casting mould is made by the vertical parting method. Metal manufacturing has the characteristics of not easy to deform and reuse, so the mould can be cast many times, thus improving the productivity of the castings. Secondly, the cooling speed of the metal mould is fast, the instant surface of the castings crystallizes very fine, and the mechanical properties of the castings can never be greatly improved. Thirdly, no sand is used in the casting moulding, which greatly improves the productivity of the castings. Finally, the worker's working conditions are improved. The size of the castings has high precision and the surface finish is high. However, there are some shortcomings in the metal mould casting method. For example, the manufacturing process of the metal mould is complex and the cost is high, which results in insufficient production cycle. Moreover, the casting process requirements are more stringent, metal casting is prone to defects such as insufficient pouring, cold insulation, cracks, blowhole and so on, and the castings are prone to self-hole.
