The sand casting process plan typically includes the following aspects: the selection of molding and core-making methods and the type of mold, determination of the pouring position and parting surface, and the number and arrangement of castings in the flask. A reasonable casting process plan can only be developed based on the casting material, production batch, casting quality requirements, and production costs, with an analysis of the casting process feasibility of the part structure, combined with production process conditions.
1. Priority to Clay Green Sand Molding
Clay green sand molding offers advantages such as strong adaptability, simple production processes, short production cycles, and low molding material costs. It is the most widely used casting method in industrial assembly line production and should be the first choice when formulating a sand casting process plan. When clay green sand molding cannot meet the quality requirements of castings in terms of dimensional accuracy and surface roughness, other sand molds should be considered. However, clay sand dry molds/cores, oil sand core-making, and Qili sand molds/cores are generally not used.
For medium and large iron castings, resin self-hardening sand molds are typically used, while sodium silicate sand molds are generally used for steel castings. For tall castings, castings with large horizontal walls in the pouring position, large and complex castings, or molds that require a long waiting time before pouring and have many chillers placed inside, resin self-hardening sand molds and sodium silicate sand molds should be considered.
2. Suitability for Casting Production Batch
For mass production of castings, advanced molding and core-making processes should be adopted to improve production efficiency, ensure casting quality, reduce labor intensity, and improve the working environment. For mass production of small parts, horizontal or vertical parting flaskless high-pressure molding machine production lines can be used. For medium-sized parts, automated molding production lines such as high-pressure molding, static pressure molding, or air impact molding can be adopted. For core-making, efficient methods such as cold box, hot box, and shell core processes can be selected. For large castings in medium batches, resin self-hardening sand or sodium silicate sand molding and core-making can be considered.
For single-piece or small-batch production of heavy castings, such as large machine tools and mining equipment, manual molding and core-making remain the primary methods due to their simplicity in tooling and adaptability to various complex requirements. Sodium silicate self-hardening sand or resin self-hardening sand can be used. For single-piece production of heavy castings, pit molding is cost-effective. For batch production or long-term production of standardized products, multi-part molding or split molding is more suitable. Although the investment in patterns and flasks is high, the savings in molding man-hours and improvements in product quality can offset the costs.
3. Adaptation to Enterprise Production Conditions
An enterprise typically has only a few fixed molding and core-making methods, and production conditions (including equipment, workspace, workforce skills, etc.), production habits, and accumulated experience vary among enterprises. For example, in producing large machine tool bed castings, some enterprises use flask molding with patterns, while others adopt core assembly molding, focusing on the design and standardization of core boxes without making patterns and flasks. They assemble cores in pits and still ensure casting quality. Therefore, the selection of molding and core-making methods should align with the actual on-site conditions and production experience of the enterprise.
4. Balancing Casting Quality and Cost
Casting quality varies with different casting methods, particularly in terms of precision. The initial investment and productivity of different casting methods also differ, ultimately affecting economic efficiency. To achieve high output, speed, quality, and cost-effectiveness in casting production, a comprehensive consideration of casting quality and cost is necessary when selecting molding and core-making methods. Costs should be preliminarily estimated based on production batch, and while ensuring casting quality requirements, production costs should be minimized as much as possible to enhance economic efficiency.
