The difference between casting process and forging process

Casting process

Casting is the process of melting metal into a liquid that meets certain requirements and pouring it into a mold. After cooling, solidification and cleaning, a casting (part or blank) with a predetermined shape, size and performance is obtained.

The cost of the blank produced by casting is low, and it can show its economic efficiency for parts with complex shapes, especially those with complex inner cavities; at the same time, it has wide adaptability and good comprehensive mechanical properties. Casting is a metal heat treatment technology that humans have mastered earlier, with a history of about 6,000 years.

There are many types of castings, which are divided into: ordinary sand castings, including three types of raw sand, dry sand and chemically hardened sand; special castings, according to different modeling materials, can be divided into special castings with natural mineral sand and gravel as the main modeling materials (such as precision castings, clay castings, shell castings in foundries, negative pressure castings, solid castings, ceramic castings, etc.) and special castings with metal as the main mold material (such as metal mold casting, pressure casting, continuous casting, low pressure casting, centrifugal casting, etc.).

The casting process generally includes:

① Preparation of molds (containers for making liquid metal into solid castings). Molds can be divided into sand, metal, ceramic, clay, graphite, etc. according to the materials used, and can be divided into one time according to the number of uses. The main factors affecting the quality of castings are the quality of castings, semi-permanent and permanent.

② Melting and pouring of casting metal. Casting metals (casting alloys) mainly include cast iron, cast steel and non-ferrous alloys.

③ Casting processing inspection, casting processing includes removing foreign matter from the core and casting surface, removing protrusions such as pouring risers, shovel burrs and overhanging seams, as well as heat treatment, shaping, rust prevention and rough processing.

Forging process

Forging is a processing method that uses a forging machine to apply pressure to a metal blank to produce plastic deformation to obtain forgings with certain mechanical properties, certain shapes and sizes.

Through forging, the as-cast looseness of the metal and welding holes can be eliminated, and the mechanical properties of forgings are generally better than those of castings of the same material. For important parts of machinery with high load and harsh working conditions, in addition to simple shapes, profiles or welded parts that can be rolled, forgings are mostly used.

According to the forming method, forging can be divided into:

① Open forging (free forging). The metal between the upper and lower anvils (anvils) is deformed by impact or pressure to obtain the required forgings, mainly manual forging and mechanical forging.

② Closed forging. The metal blank is compressed and deformed in a forging die with a certain shape to obtain forgings. Forgings can be divided into die forging, cold heading, rotary forging and extrusion. According to the deformation temperature, forging can be divided into hot forging (processing temperature is higher than the recrystallization temperature of the blank), warm forging (lower than the recrystallization temperature) and cold forging (normal temperature).

The forging materials are mainly carbon steel and alloy steels of various compositions, followed by aluminum, magnesium, titanium, copper, etc. and their alloys. The original state of the material includes bars, ingots, metal powders and liquid metals. The ratio of the cross-sectional area of the metal before deformation to the cross-sectional area of the die after deformation is called the forging ratio. The correct choice of forging ratio has a lot to do with improving product quality and reducing costs.

Regardless of the process, using X-ray technology for non-destructive testing during or after the workpiece is manufactured can keep a good check on quality issues.