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Analysis of Some Basic Knowledge about Hot Forging Process

Analysis of Some Basic Knowledge about Hot Forging Process
Forging can be divided into hot forging, warm forging, and cold forging according to the deformation temperature. Hot forging and warm forging require heating, while cold forging does not. Whether to heat, the heating temperature and holding time, the initial forging temperature and the final forging temperature all have a great relationship with the quality of the forgings and cost reduction. At present, most of the forgings used in various industries are hot forgings, while warm forging and cold forging are mostly used in the mass production of parts in automobiles, general machinery, etc.
Why heat?

Heating can reorganize and recrystallize the metal lattice, improve metal plasticity, reduce deformation resistance, facilitate metal deformation, and obtain good post-forging structure and mechanical properties. Heating contributes greatly to improving the forging production rate, ensuring the quality of forgings, and saving energy consumption. Direct forging without heating requires larger tonnage equipment and is likely to cause lattice distortion of the material, generate internal stress, and easily cause cracks or fractures in the forgings.

What are the heating methods?
According to the different heat sources used, the commonly used heating methods in forging production are divided into flame heating and electric heating.
Flame heating:
Method: The method of burning fuel (solid such as coal, coke, liquid such as heavy oil, diesel, or gas such as coal gas, natural gas) in a flame heating furnace to produce high-temperature gas (flame) containing a large amount of heat energy, and transferring the heat energy to the blank through convection and radiation. When the heating temperature is below 600~700℃, the blank is mainly heated by convection; after the heating temperature reaches 700~800℃, the blank is mainly heated by radiation.
Advantages: The furnace structure is simple, the fuel source is wide, the cost is low, and the adaptability to the blank is wide, which is easy to be widely adopted;
Disadvantages: Poor working conditions, slow heating speed, difficult to control the furnace atmosphere, furnace temperature and heating quality, low thermal efficiency;
Application: The flame heating method is widely used for heating various large, medium, and small blanks.
Flame heating classification: intermittent loading, continuous loading
Electric heating
Method: The method of converting electrical energy into heat energy to heat the blank.
Advantages: Fast heating speed, easy to control furnace temperature, less oxidation and decarburization, good working conditions, easy to achieve mechanization and automated production, etc.;
Disadvantages: There are certain restrictions and requirements on the shape and size of the blank, the equipment structure is complex, the investment cost is relatively large, and the operation and use technology requirements are high.
Application: It is mainly used for heating high-demand die forging and precision die forging, non-ferrous metal alloys, and some high-temperature alloys.
Electric heating classification: According to the heat transfer method, it can be divided into resistance furnace heating, contact electric heating, salt bath furnace heating, and induction electric heating, etc.
Choice of heating method:
Determined based on various factors such as forging requirements, local energy conditions, investment benefits, and environmental protection.
Large forgings are generally mainly flame heated; medium and small forgings can choose flame heating or electric heating; precision die forging is recommended to choose induction electric heating or other non-oxidizing heating methods.
Heating precautions:
1. Heat to the predetermined temperature at the fastest speed under the conditions of the allowable thermal conductivity and internal stress of the metal material, to improve efficiency and save energy;
2. Try to reduce the absorption of gases such as oxygen, hydrogen, and nitrogen by the metal material, and reduce heating defects, such as oxidation, decarburization, or hydrogen brittleness, etc.;
3. Prevent material rupture caused by improper heating, leading to a large temperature difference between the metal surface and the core;
4. Heat according to heating specifications, pay attention to heating temperature, speed, time, and insulation conditions, and strictly prevent overheating and overburning.

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