Aluminum alloy can be heated before forging by various heating equipment, such as resistance furnace, gas furnace, oil furnace, induction heating installation, fluid particle furnace and so on. Resistance furnace is commonly used for heating in China. In this case, it is best to install forced furnace gas circulation in the furnace to promote the average temperature of the furnace. When using gas-fired or oil-fired furnaces, it is necessary to use low-sulfur fuel, and the flame in the furnace is not allowed to directly radiate the appearance of the blank. Foreign countries think that muffle furnace is the best for aluminum alloy forging heating, and gas semi-enclosed furnace has been widely used. When the forging process of aluminum alloy is highly automated, the commonly used heating methods are induction heating, resistance heating and fluid particle heating.

The forging temperature range of aluminum alloy is narrow, and it is easy to overheat and burn, so it is necessary to measure and control the temperature accurately, and the furnace temperature deviation is preferably within 5℃.

Aluminum alloy has good thermal conductivity, so the blank with any thickness can be directly heated in a high-temperature furnace without preheating, but the heating time is longer than that of ordinary carbon steel. This is because the internal strengthening phase must be fully dissolved when aluminum alloy is heated, so as to make the alloy structure average and plastic progress. The heating time of aluminum alloy blank is calculated according to the diameter or thickness of 1.5 ~ 2 min per millimeter. The dissolution process of strengthening phase is related to the size, shape, dispersion characteristics and properties of strengthening phase. The coarser the structure, the slower the dissolution, so the upper limit of heating time should be taken for ingots, large forgings and thick bars (φ100mm or more). The heating time of billet with high content of alloying elements is longer, for example, LC4 should be longer than LD2 alloy. Under normal circumstances, the heating time of aluminum alloy is 1 ~ 2 hours. If it is necessary to extend it, the heating time can exceed 4 ~ 6 hours. If it is longer, the metal should be taken out of the furnace to prevent overheating and hydrogen absorption.

Folding process of forged aluminum alloy

The folding of forged aluminum alloy is a defect formed by the aggregation and stacking of oxidized surface metals during the deformation of metals. After the scale is cleared, the ordinary folding can be identified with the naked eye. Folds that are not easy to be detected by naked eyes can be stopped by magnetic particle inspection or immersion inspection. When the folding is shallow, the grinding workload is increased, and when it is deep, the forging is scrapped. Below, the forging manufacturer Lanxi Tongli Aluminum Co., Ltd. discusses the plan of how to deal with the folding defect of forged aluminum alloy.

1. Folding of forged aluminum alloy oil seal

Oil seal folding is a forming defect of crankshaft with oil seal flange in debugging, which has two forms: closed and incomplete closed. The main mechanism is that the local shape is formed at the initial stage of forming here, and the subsequent forming has a large axial shift, which makes the formed local shape have an obvious axial deviation. Folding defects occurred in the feeding process in the later stage of forming

The pre-forging process can change the pre-forging shape of forged aluminum alloy here and weaken the steps, which can not only coordinate the application rate of data forming at the back end, but also deal with folding defects. In the forming process without pre-forging, this kind of problem can be solved by appropriately lengthening the length of local blank at the back end. Pay attention to the positioning of the blank when consuming in batches to avoid such problems caused by leaning to one end.

Second, forging aluminum alloy connecting rod neck folding

Connecting rod neck folding is a common forming defect in the direct final forging process of die forging hammer Produced in the upper part of the parting surface on the inner side of the gear. The shape is horizontal "one" or "eight", and there are also vertical "one" or non-overlapping groove shapes. In the forming process of forging press, there are few such defects because of the pre-forging step. When the pre-forging, storage and distribution structure are unreasonable, longitudinal "one" or non-overlapping groove defects will occur in the final forging.

As for die forging hammer technology, the main reason for the folding of connecting rod neck is that there is no pre-forging step. During the initial deformation of crankshaft die forging, the protruding part of the die at the opening of connecting rod neck is formed first, and the blank will form the shape of a pit, then the pit will shift laterally, and finally the metal in its adjacent parts will reflow to fill the unfilled pit. When the pit is obvious, the folding will finally be formed at this pit. The treatment method is to control the severity of blows in different forming stages, but it requires higher operation, or to make larger rounded corners at the protruding local corners at the opening of the connecting rod neck of the die, and to increase the thickness of the skin at the opening to improve the metal activity. The latter is a common treatment method. Crankshaft consumed by forging press usually does not produce such defects because of the existence of pre-forging step, but when the pre-forging structure and parameters are unreasonable, grooves or creases will occur, usually the stored material is too thick or the thickness difference between the upper and lower skin is too large, and the blank in this part deviates too much or the blank in the upper and lower parts moves up and down in the final forging. Regarding the forging process of forging press, such defects can be easily handled by modifying the die according to the reasons.

Third, the folding of forged aluminum alloy burr press-in

The higher longitudinal burr drawn by trimming is pressed into the forging body after subsequent correction, and the crankshaft formed by twist-pin is more likely to present this kind of folding when it is calibrated. After trimming, the burr at the parting surface is turned to the position in the groove of the upper and lower dies of the correction die after twist-pin, and the longer burr after thermal correction is pressed into the forging body to form a folding. This kind of defect can be prevented by replacing or repairing the aging trimming die in time to prevent pulling out high longitudinal burr.

Fourthly, folding the parting surface of the forged aluminum alloy balance block.

As an incomplete forging, the forging body has been deeply folded at the parting surface of the balance block, and there will be local folding of the forging body after complete forming. The main reason is that the blank specification is too small. As for the easy-to-form crankshaft, although the blank size is too small, it can be fully filled and formed, but it is easy to produce balanced block parting surface folding. The subtle folding can be improved by increasing the fillet of the adjacent die in this part, and the deep folding can be handled by the tendentious material distribution design of the pre-forging structure. In the absence of the pre-forging process, it is often handled by increasing the blank size or possibly adopting a semi-closed process.

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