The folding of forged aluminum alloy is a defect formed by the confluence and overlapping of oxidized surface metals during the deformation and flow of metals. After scale cleaning, folding can be recognized by naked eyes. Folds that are difficult to detect with naked eyes can be inspected by magnetic particle inspection or penetrant inspection. When the folding is shallow, it increases the grinding workload, and when it is deep, it causes the forging to be scrapped.

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 formation mechanism is mainly that some shapes were formed at the initial stage of forming here, and the subsequent forming caused obvious axial deviation due to large axial movement. Folding defects occurred in the feeding process in the later stage of forming.

The forming process with pre-forging can change the pre-forging shape of forged aluminum alloy here and weaken the steps, which can not only take into account the material forming utilization rate at the back end, but also solve the folding defect. In the forming process without pre-forging, this kind of problem can be solved by appropriately lengthening the blank length at the rear end. In mass production, we should also pay attention to the positioning of blanks to prevent such problems from being biased 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 structure of pre-forging storage and distribution is unreasonable, longitudinal "one" or non-overlapping groove defects will occur in the final forging.

For the die forging hammer process, the main reason for the folding of the 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 the connecting rod neck is formed first, and the blank will form a pit shape, and then the pit will shift laterally. Finally, the metal in the adjacent part will reflow to fill the unfilled pit, and when the pit is obvious, the folding will finally be formed at this pit. The solution is to control the severity of the blow in different forming stages, but it requires higher operation, or to make a larger fillet at the corner of the protruding part at the opening of the connecting rod neck of the die and increase the thickness of the connecting skin at the opening to improve the metal flow. The latter is a common solution. Crankshaft produced 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 thickness of the joint is too thick or the thickness difference between the upper and lower joints is too large, which is formed when 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. For the forging process of forging press, such defects can be easily solved by modifying the die according to the reasons.

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

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

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

As an incomplete forging, the parting surface of the balance weight has been folded deeply into the forging body, and some parts of the forging body will be folded after being fully formed. The main reason is that the blank specification is too small. For easy-to-form crankshaft, although the blank size is too small, it can be fully formed, but it is easy to fold the parting surface of the balance block. The slight folding can be improved by increasing the fillet of the adjacent die in this part, and the deep folding can be solved by the tendentious material distribution design of the pre-forging structure. In the absence of the pre-forging process, it is often solved by increasing the blank size or possibly adopting the semi-closed process.

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