How to choose casting method for different castings
The common casting method is sand casting, followed by special casting. The principles of casting method are as follows:
1.Sand casting is preferred.
Compared with other casting methods, sand casting has the advantages of low cost, simple production process and short production cycle. Therefore, about 60%~70% of the total output of castings is produced by sand casting. About 70% of sand castings are produced by clay sand mold. In the clay sand mold, the clay wet mold process should be selected first (the casting weight can range from thousands of grams to tens of kilograms). When the wet mold cannot meet the requirements, the clay sand surface dry sand mold, dry sand mold (the casting weight can reach tens of tons) or other sand mold should be considered.
Generally, for large and medium castings, resin self-hardening sand mold can be used for cast iron; Water glass sand mold or resin self-hardening sand mold can be used for steel castings.
When the casting precision, surface quality, material density, metallographic structure, mechanical properties and other properties are required to be higher, special structural methods such as investment casting, pressure casting, low pressure casting, full mold casting, etc. shall be adopted.
2. The casting method shall be suitable for the production batch.
Sand casting shall consider the following aspects:
For mass production plants, advanced modeling and core making methods should be selected. For small castings, horizontal parting or vertical parting boxless high pressure molding line is adopted, with high productivity and small floor area. For medium castings, various high pressure molding lines and air impact molding lines are used to meet the requirements of fast and high-precision molding production lines. Core making methods can be selected: cold core box, hot core box, shell core and other efficient core making methods. However, the production line of the old shock molding machine has low productivity, high labor intensity and high noise, which is not suitable for the requirements of mass production, and should be gradually transformed.
For large castings of medium batch, resin self-hardening sand molding and core making can be selected.
Manual molding is still an important method for producing heavy castings in small batches. Manual molding can adapt to various complex requirements without much process equipment. You can choose sodium silicate sand mold, VRH sodium silicate sand mold, organic ester sodium silicate self-hardening sand mold, clay dry mold, resin self-hardening sand mold, cement sand mold, etc. For important castings produced by single piece, pit molding has low cost and rapid production. For the finalized products produced in batch or for a long time, it is more appropriate to adopt sand box modeling and split box modeling. Although the investment in mold and sand box is high at the beginning, compensation can be obtained from saving molding time and improving product quality.
Special casting includes low pressure casting, pressure casting, centrifugal casting and other casting methods. Due to the high price of equipment and molds, it is only suitable for mass production.
3. The casting method shall be suitable for the factory conditions.
The production conditions (equipment, site, staff quality, etc.), production habits, and production experience of different enterprises are different. According to these conditions, the modeling method suitable for the factory conditions should be considered. For example, for the same production of large machine tool bed castings, pit core assembly modeling is generally adopted, and sand box and pattern are not produced. Some factories use pattern sand box modeling.
4. The precision and cost of castings should be considered.
The casting precision obtained by various casting methods is different, the initial investment and productivity fluid are different, and the final economic benefit fluid is different. Therefore, in order to achieve "good, economical, multiple and fast", we should take into account all aspects. A preliminary cost estimate should be made for the selected casting method to determine the casting method with high economic benefits and can ensure the casting quality.