Technical Requirements for Precision Casting

For example, in the case of sand mold precision casting, factories engaged in mass production should create conditions to adopt technologically advanced molding and core-making methods. The production lines equipped with old-fashioned jolting or jolt-squeezing molding machines have low productivity, high labor intensity for workers, and excessive noise, which fail to meet the requirements of mass production and should be gradually renovated.

• For small-sized castings: Production lines with flaskless high-pressure molding machines (either with horizontal or vertical parting) or full-mold molding can be used. These methods offer high production efficiency and require less floor space.

• For medium-sized castings: Various production lines with flask high-pressure molding machines or air-impact molding lines are suitable, as they meet the demands of fast and high-precision molding lines. For core-making, high-efficiency methods such as cold box, hot box, and shell core processes can be adopted.

• For medium-batch production of large castings, resin self-hardening sand can be considered for molding and core-making.

In the case of single-piece or small-batch production of heavy castings, hand molding remains an important method. Hand molding is flexible enough to adapt to various complex requirements and does not require extensive process equipment. The following sand mold types can be used:

• Sodium silicate sand molds

• VRH (Vacuum Replacement Hardening) sodium silicate sand molds

• Organic ester-cured sodium silicate self-hardening sand molds

• Clay dry sand molds

• Resin self-hardening sand molds

• Cement sand molds

For single-piece production of heavy castings, the pit molding method is cost-effective and enables quick production launch.

For batch production or long-term production of standardized products, multi-flask molding or split-flask molding is more appropriate. Although the initial investment in molds, sand flasks, etc., is high, this cost can be offset by saving molding time and improving product quality.

Casting methods such as low-pressure casting, die casting, and centrifugal casting involve expensive equipment and molds, so they are only suitable for mass production. The selection of methods should align with specific conditions. For instance, when producing large castings like machine tool beds:

• Some factories generally use the core assembly molding method (no patterns or sand flasks are made, and cores are assembled in pits).

• Other factories adopt the sand flask molding method (patterns are made).

Different enterprises vary in production conditions (including equipment, workshop space, and employee competence), production habits, and accumulated experience. Enterprises should determine which products they are suitable for manufacturing and which they are not (or cannot) based on these factors.

Precision Requirements and Costs

Different casting methods yield castings of varying precision, and they also differ in initial investment, productivity, and final economic benefits. Therefore, to achieve the goals of "high output, speed, quality, and cost-effectiveness," all factors must be balanced. A preliminary cost estimation should be conducted for the selected casting method to ensure that the method is both economically efficient and capable of meeting the casting’s requirements.