Casting can produce blanks with complex shapes, especially complex inner cavities, and the size and weight are not limited. It can be produced in a single piece or in batches. Most of the materials used are from a wide range of sources, and the price is low. Scrap materials and waste parts can also be used, so the cost is low. The shape and size of castings and parts are close to the machining allowance.
The disadvantage of castings is that there are many procedures and the process control is difficult. Due to the internal stress generated when the metal is cooled, defects are prone to occur, so the quality is unstable; due to the coarse and uneven internal structure, its mechanical properties are not as high as forgings. At present, there are still problems of high labor intensity and poor working conditions.
Casting production methods are divided into two categories: sand casting and special casting, with sand casting as the main method.
Sand casting is mainly used for the production of cast iron, cast steel, cast copper, cast aluminum and other materials. When designing the casting structure, it is necessary to consider the requirements of the casting process and the performance of the metal to prevent shrinkage, shrinkage, insufficient pouring, cold partition, deformation and cracks, and the following issues should be paid attention to:
①The castings should have reasonable wall thickness and structural inclination, and the casting wall thickness should be as uniform as possible.
②The connection of the casting wall: the connection of the casting wall should have structural rounded corners. Avoid crossing and sharp-angle connections, and the connection between thick and thin walls should be gradually transitioned.
③ Castings should avoid excessively large horizontal surfaces.
④In order to prevent warping and deformation of castings, large flat castings and long boxes with uneven wall thickness should be designed into a symmetrical shape or ribs should be added to improve their rigidity.
2. Special casting
① Investment casting, which uses wax as the material to make molds, also called "lost wax manufacturing", can cast various non-ferrous and ferrous metal castings.
②Metal mold casting, the model can be used 40,000 times repeatedly, the casting has good accuracy (reaching IT12~IT14), the surface is smooth, it can be used with little or no processing, and it can be mechanized production.
③Pressure casting: liquid or semi-liquid metal is poured into the pressure chamber of the die-casting machine to fill the shape and form and crystallize under high pressure. The common die-casting specific pressure is 5~150MPa, and the metal flow rate is 5~100m/s. High efficiency, easy automation, good product quality, low chip and chipless processing, and low cost.
④ Low pressure casting.
⑤ Centrifugal casting: molten metal is added to the rotating mold.