Casting and forging have always been common metal processing techniques. Due to the inherent differences in the processes of casting and forging, there are also many differences in the final products produced by these two processing methods.
A casting is a material that is cast as a whole in a mold, with uniform stress distribution and no restrictions on the direction of compression; And forgings are pressed by forces in the same direction, so their internal stress has directionality and can only withstand directional pressure.
Regarding casting:
1. Casting: It is the process of melting metal into a liquid that meets certain requirements and pouring it into a mold, followed by cooling, solidification, and cleaning treatment to obtain castings (parts or blanks) with predetermined shapes, sizes, and properties. The basic process of modern mechanical manufacturing industry.
2. The cost of raw materials produced by casting is low, which can better demonstrate its economy for parts with complex shapes, especially those with complex internal cavities; At the same time, it has a wide adaptability and good comprehensive mechanical performance.
3. Casting production requires a large amount of materials (such as metal, wood, fuel, molding materials, etc.) and equipment (such as metallurgical furnaces, sand mixers, molding machines, core making machines, sand dropping machines, shot blasting machines, cast iron plates, etc.), and can generate dust, harmful gases, and noise that pollute the environment.
Casting is one of the earliest metal hot working processes mastered by humans, with a history of about 6000 years. In 3200 BC, copper frog castings appeared in Mesopotamia.
Between the 13th and 10th centuries BC, China had entered the heyday of bronze casting, with a considerable level of craftsmanship. Representative products of ancient casting include the 875kg Simuwu Fang Ding from the Shang Dynasty, the Yizun Pan from the Warring States period, and the translucent mirror from the Western Han Dynasty.
There are many types of subdivisions in casting technology, which can be habitually divided into the following categories according to the molding method:
① Ordinary sand casting
Including three types: wet sand mold, dry sand mold, and chemically hardened sand mold;
② Sand and stone special casting
Special casting using natural mineral sand and gravel as the main molding material (such as investment casting, mud casting, casting workshop shell casting, negative pressure casting, solid casting, ceramic casting, etc.);
③ Metal special casting
Special casting using metal as the main casting material (such as metal mold casting, pressure casting, continuous casting, low-pressure casting, centrifugal casting, etc.).
Regarding forging:
1. Forging: A processing method that uses forging machinery to apply pressure to metal billets, causing them to undergo plastic deformation to obtain forgings with certain mechanical properties, shapes, and sizes.
2. Forging can eliminate the casting porosity and welding holes of metals, and the mechanical properties of forgings are generally better than castings of the same material. For important parts with high loads and severe working conditions in machinery, forgings are often used, except for simple shaped plates, profiles, or welded parts that can be rolled.
3. Forging can be divided into:
① Open forging (free forging)
Including three types: wet sand mold, dry sand mold, and chemically hardened sand mold;
② Closed mode forging
Special casting using natural mineral sand and gravel as the main molding material (such as investment casting, mud casting, casting workshop shell casting, negative pressure casting, solid casting, ceramic casting, etc.);
③ Other casting classification methods
According to the deformation temperature, forging can be divided into hot forging (processing temperature higher than the recrystallization temperature of the billet metal), warm forging (below the recrystallization temperature), and cold forging (at room temperature).
4. The forging materials are mainly carbon steel and alloy steel with various compositions, followed by aluminum, magnesium, titanium, copper and their alloys. The original states of materials include bars, ingots, metal powders, and liquid metals.
The ratio of the cross-sectional area of a metal before deformation to the die cross-sectional area after deformation is called the forging ratio. The correct selection of forging ratio is closely related to improving product quality and reducing costs.
Identification between Casting and Forging:
Touch - The surface of the casting should be thicker, while the surface of the forging should be brighter
Look - the cast iron section appears gray and dark, while the forged steel section appears silver and bright
Listen - Listen to the sound, the forging is dense, the sound is crisp after striking, and the casting sound is dull
Grinding - Use a grinding machine to polish and see if the sparks between the two are different (usually forgings are brighter), etc