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Principles of casting process selection

2023-12-28 15:06:59

Principles of casting process selection

1. Sand casting is preferred

(1) According to statistics, 60~70% of all castings in China or internationally are produced by sand mold, and about 70% of them are produced by clay sand mold. The main reason is that sand casting has lower cost, simpler production process and shorter production cycle than other casting methods. Therefore, castings such as engine cylinder block, cylinder head and crankshaft of automobiles are all produced by clay green sand process. When the wet mold cannot meet the requirements, the clay sand surface dry sand mold, dry sand mold or other sand molds shall be considered. The casting weight of clay green sand casting can be from several kilograms to tens of kilograms, while the casting weight of clay dry mold production can be up to tens of tons.

(2) Generally speaking, for medium and large castings, iron castings can be produced by resin self hardening sand mold, and steel castings can be produced by water glass sand mold. Castings with accurate dimensions and smooth surface can be obtained, but the cost is high. Of course, the precision, surface finish, material density, metallographic structure, mechanical properties and other aspects of castings produced by sand casting are often poor. Therefore, when these properties of castings are required to be higher, other casting methods should be used, such as investment casting (wax loss), die casting, low pressure casting, etc.

2. The casting process should adapt to the production batch
(1) For example, sand casting, mass production plants should create conditions to adopt advanced molding and core making methods. The production line of the old shock molding machine or shock compression molding machine is not productive enough, the labor intensity of workers is high, the noise is large, and it does not meet the requirements of mass production, so it should be gradually transformed. For small castings, the production line of box less high-pressure molding machine with horizontal parting or vertical parting can be used. The production efficiency of full mold molding is high and the floor area is small; For medium parts, various high-pressure molding machine production lines with boxes and air impact molding lines can be selected to meet the requirements of fast and high-precision molding production lines. The core making method can be selected as: cold core box, hot core box, shell core and other efficient core making methods. Resin self hardening sand can be used for molding and core making of large castings in medium batch.

(2) For heavy castings produced in a single small batch, manual molding is still an important method. Manual molding is flexible and can adapt to various complex requirements without requiring many process equipment. Water glass sand mold, VRH water glass sand mold, organic ester water glass self hardening sand mold, clay dry mold, resin self hardening sand mold and cement sand mold can be used; For heavy castings produced by single piece, the pit molding method is low in cost and fast in production. It is appropriate to adopt multi box modeling and split box modeling for finalized products in batch production or long-term production. Although the initial investment in mold and sand box is high, it can be compensated in terms of saving molding hours and improving product quality.

(3) Low pressure casting, die casting, centrifugal casting and other casting methods are only suitable for batch production because of the high price of equipment and molds.

3. The casting process shall be suitable for the factory conditions

For example, for the same production of castings such as large machine tool bed, the core assembly molding method is generally adopted, instead of making patterns and sand boxes, the core assembly is conducted in the pit; In other factories, the sand box molding method is used to make patterns. Different enterprises have different production conditions (including equipment, site, staff quality, etc.), production habits, and accumulated experience. We should consider what products are suitable for doing and what products are not suitable (or not) for doing according to these conditions.

4. The precision requirements and cost of castings should be considered

The casting accuracy obtained by various casting processes is different, the initial investment and productivity are also different, and the final economic benefits are also different. Therefore, in order to achieve more, faster, better and less, we should give consideration to all aspects. A preliminary cost estimate shall be made for the selected casting method to determine the casting method with high economic benefits and meeting the casting requirements.

There are many kinds of casting processes, each of which has its own advantages and is suitable for processing in different fields. Therefore, everyone must be careful when selecting the casting process, and select the most appropriate casting process according to their own needs, so that it can play its role. Due to the improvement of the requirements for casting quality, casting precision, casting cost and casting automation, the casting technology is developing towards the direction of precision, large-scale, high-quality, automation and cleaning. For example, China has developed rapidly in precision casting technology, continuous casting technology, special casting technology, casting automation and casting simulation technology in recent years.

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