There is no fixed rule on how many tons of marine castings to start with. It depends on the size of marine castings.

General marine castings below 10mm can be considered as thin-walled parts. However, the casting is too large, for example, a few tons, maybe 20mm can be considered as a thin-walled part. Generally, thick wall parts, less than 1 ton, more than 100 mm, more than 1 ton, more than 200 mm. Moreover, it is also related to the products mainly produced by the factory.

The smaller wall thickness of the casting refers to the smaller thickness that can be achieved by the casting. The smaller thickness is not a fixed value, but changes according to the shape, material and process of the casting.

Forged parts cannot be called castings. Forging with special dies is called die forging, and forging without special dies is called free forging. Large forgings are generally small in batch, and the cost of making large molds is too high. In addition, die forging requires too large a press. Even if there is a huge die, there is no such large press. At present, the domestic large tonnage hydraulic press seems to be only 50000 tons. The main reason is that the die forging hammer in China is only 16 tons, and the equipment standard for forging large forgings is too low.

Generally, China's large die forgings mainly rely on imports. In other countries, there is a 50 ton air hammer that can forge a 5-meter-long marine crankshaft at one time. However, due to its relatively old equipment, the forging accuracy is not high!

There is also a method of die forging with clamp hammer, which can be more accurate. Therefore, free forging is generally used for large forgings.

Free forging is a simple and flexible basic forming method for metal plastic processing. It uses the upper and lower anvil blocks of forging equipment and some simple general tools to make the billet plastically deform under pressure. Free forging can be divided into manual forging and machine forging. With the rapid development of machine manufacturing industry, machine forging is mainly used in production. According to different types of forging equipment, machine forging can be divided into hammer free forging and hydraulic press free forging.

The former is used to forge medium and small forgings, while the latter is mainly used to forge large forgings. Because the tools used for free forging are simple, versatile and flexible, they are suitable for the production of single piece and small batch forgings. The free forging is formed by the gradual deformation of the blank, and the tool only contacts the blank, so the required equipment power is much smaller than that of die forging, so the free forging is also suitable for forging large forgings.

For example, the 10000 ton die forging hydraulic press can only forge forgings weighing several hundred kilograms, while the 10000 ton free forging hydraulic press can forge large forgings weighing more than 100 tons. It can be seen that the free forging technology can only be adopted for the forging of large forgings. However, free forging relies on the operation of workers to control the shape and size of forgings, so the accuracy of forgings is poor, the forging productivity is low, and the labor intensity is large. In view of the above shortcomings, in recent years, the free forging production of marine casting manufacturers has been continuously improved and developed in improving forging accuracy and realizing mechanization.