How to choose the casting method for different castings?
The most common casting method is sand casting, followed by special casting. The principles of casting methods are as follows:
1. Sand casting is the preferred method. Compared with other casting methods, sand casting has advantages such as low cost, simple production process, and short production cycle. Therefore, about 60% to 70% of the total casting output is produced by sand casting. About 70% of sand casting is produced using clay sand molds. In clay sand casting, the wet clay mold process should be the first choice (casting weight can range from a few kilograms to tens of kilograms). Only when the wet mold cannot meet the requirements should surface-dry clay sand molds, dry sand molds (casting weight can reach tens of tons), or other sand molds be considered.
Generally, for large and medium-sized castings, resin self-hardening sand molds can be used for cast iron; water glass sand molds or resin self-hardening sand molds can be used for cast steel.
When higher requirements are placed on certain properties such as casting precision, surface quality, material density, metallographic structure, and mechanical properties, special structural methods should be adopted, such as investment casting, pressure casting, low-pressure casting, and lost foam casting.
2. The casting method should be appropriate for the production volume.
2.1. The following aspects should be considered in sand casting.
2.1.1. Factories engaged in mass production should select advanced molding and core-making methods. For small castings, horizontal or vertical parting boxless high-pressure molding lines offer high productivity and a small footprint. For medium-sized castings, various boxed high-pressure molding lines and air-impact molding lines should be used to meet the requirements of fast, high-precision molding production lines. Core-making methods can include cold box, hot box, and shell core making, among other efficient methods. Older vibratory molding machine production lines have low productivity, high labor intensity for workers, and high noise levels, making them unsuitable for mass production and should be gradually upgraded.
2.1.2. For medium-volume production of large castings, resin self-hardening sand molding and core making can be used.
2.1.3. For single-piece and small-batch production of heavy castings, manual molding remains an important method. Manual molding can adapt to various complex requirements, requires minimal process equipment, and can utilize water glass sand molds, VRH process water glass sand molds, organic ester water glass self-hardening sand molds, clay dry molds, resin self-hardening sand molds, cement sand molds, etc. For important castings produced in single batches, pit molding is cost-effective and allows for rapid production. For mass production or long-term production of fixed-type products, sand box molding and split-box molding methods are more suitable. Although the initial investment in molds and sand boxes is high, this can be compensated for by saving molding time and improving product quality.
2.2. Special casting methods include low-pressure casting, pressure casting, centrifugal casting, etc. Due to the high cost of equipment and molds, they are only suitable for mass production.
3. The casting method should be suitable for the factory conditions. Different enterprises have different production conditions (equipment, site, employee skills, etc.), production habits, and production experience. Based on these conditions, a molding method suitable for the factory conditions should be selected. For example, when producing large machine tool bed castings, pit core molding is generally used, without making sand boxes and patterns, while some factories use pattern sand box molding.
4. A balance must be struck between casting precision and cost. Different casting methods yield castings with varying precision, initial investment, productivity, and ultimately, economic benefits. Therefore, to achieve "good, economical, high-volume, and fast" casting, all aspects must be considered. A preliminary cost estimate should be conducted for the selected casting method to determine the one that offers high economic efficiency and guarantees casting quality.
