Secondly, due to errors, the size and shape of castings will deviate from the standard, which may be larger or smaller.
Thirdly, parts are the products of casting processing, and the machining allowance of castings is usually cut off, so the size and shape of parts are smaller than those of castings.
Castings cannot be used instead of templates for modeling.
Because the role of the template is to provide standard size and shape, the casting itself has errors. If the casting is used for modeling, the errors will be superimposed, which will make the casting deviate from the design size too much and produce waste products. The picture below shows the casting of an airplane. It can be seen that the size and shape are not standard.
Extended data:
Casting is mainly divided into sand casting and special casting, of which sand casting is the most widely used. The main processes of sand casting are: drawing, mold making, core making, forming, cleaning and dressing.
Drawings: The traditional method is to obtain casting drawings and send them to foundry. This process can be completed in the quotation. Now more and more customers and foundries are turning to computer-aided design.
Making molds: In sand casting, molds are made of wood or other metal materials. In this process, we ask our engineers to make the die size slightly larger than the finished product. This difference is called shrinkage allowance. The purpose is that the molten metal acts on the mold to ensure the solidification and contraction of the molten metal, so as to prevent cavities from appearing in the casting process.
Core-making: Core-making can only be achieved by putting resin sand particles into a mold to form a casting with an inner surface. Therefore, the gap between the core and the mold eventually becomes a casting.
Molding: A pair of molds need to be prepared in the process of melt molding. Molding usually includes the supporting frame of the mold. In the casting process, the mold is pulled out to separate it, the pre-placed core in the mold is melted, and then the mold mouth is closed.
Cleaning: The purpose of cleaning is to remove sand, polishing and excess metal from castings. Welding and sand cleaning can improve the surface appearance of castings. Remove burnt sand and scale to improve the surface appearance of castings. Remove excess metal and other risers. Further welding, grinding and other steps. Finally, check its defects and comprehensive quality.
Baidu encyclopedia-sand casting