Large aerospace die forgings cannot use ingots directly. Usually, the ingots are forged to form uniformly structured round blanks.
The main reasons are
Firstly, the shape and size of the blank can maximize the requirements of the die forgings, while the ingots cannot meet these requirements; Secondly, the metal of the ingot does not have the performance required for the quality of the die forgings.
The forging process for die forgings using blanks includes the following steps: cutting the ingot and cutting the macroscopic organization sample (using a saw); Peeling the ingot (using a lathe); Milling the end (using a special end milling machine); Heating and forging (using an electric furnace for heating, and the electric furnace needs to be equipped with a forced air circulation device).
The process of producing large aerospace die forgings is complicated, which requires not only high equipment requirements, but also high requirements for material properties, heating control, forging and die design, etc. The following discusses the production process of large aluminum alloy die forgings.
The aluminum alloy forging process consists of the following key points: billet preparation, heating, deformation speed and degree, forging design, lubrication, cleaning, and repair.
Before the furnace is loaded, check the surface of the blank (the surface of the blank should be clean to avoid cutting chips, sand, etc. being forged into it, accelerating the wear of the mold, and causing defects on the surface of the die forgings).
Aluminum alloy is susceptible to oxidation, and the forging temperature range is very narrow. Therefore, it is best to use a resistance furnace for heating. When loading the furnace, aluminum alloy billets should avoid being heated together with steel. Mixing aluminum chips and iron oxide chips can easily cause explosions.
Deformation speed and degree
Deformation speed has no significant effect on the plasticity of aluminum alloy process, and it can be forged at low or high speed. The critical deformation degree of aluminum alloy is generally 12% to 15%. To avoid forming coarse grains during recrystallization, the deformation amount of aluminum alloy should be greater than 12% to 15% each time.
Die forging design and process operation characteristics
When selecting the parting surface, not only the metal filling capacity of the mold cavity should be considered, but also the uniformity of deformation and the distribution of flow lines. For complex shaped forgings, multiple sets of molds and multiple forging processes should be used to gradually transition from simple blanks to complex shapes. When designing the forging die, the difficult-to-form parts of the forging are usually located on the lower mold.
To increase the metal fluidity and ensure the final forging temperature, the mold must be preheated for more than 12 hours before working, and the preheating temperature is 250-420℃.
Mold lubrication is an important part of the aluminum alloy forging process. Good process lubricants can effectively improve metal flow, reduce the adhesion force between metal and mold surface, and improve mold life. An 86.7% industrial stearic acid + 13.3% industrial caustic soda lubricant can be used. This lubricant does not burn below 450℃ and does not produce harmful precipitates.
Cleaning and repair
Aluminum alloy has a soft texture and a strong adhesion force to the forging die, so the die forgings are prone to folding, cracking, peeling and other defects. If these defects are not cleaned up in time, they will continue to develop during the next forging process, causing the die forgings to be scrapped.
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