Generally speaking, the hidden cracks in the inspection of automobile stamping parts (also called hidden cracks, professionally called necking), cracking problems are still based on visual inspection and perception and prevention. This requires a certain amount of experience accumulation:
Needless to say, PTJ automobile stamping parts show cracking. It is obvious that necking is more difficult to detect. First, understand the mechanism of material deformation. The process of material stretching and plastic deformation is mainly from the uniform elongation stage to the local elongation stage. , The cracking stage consists of these three stages. The uniform elongation stage is the ideal stage while the material is in the length direction. The thickness is uniformly thinned, the surface quality is good, smooth and the original roughness of the material has no obvious change, which is almost invisible to the naked eye. In the local elongation stage, the material is basically close to the limit of elongation. At this time, the purpose of elongation is mainly achieved through local severe and rapid deformation. In this way, the length direction is extended while the thickness direction is sharply thinned. Due to insufficient material flow, The surface is rough and the grain is obvious. It looks like orange peel to the naked eye. The closer it is to the cracking, the rougher the surface, and as the degree of necking increases, the surface will appear off-white. These two are more obvious features. Of course, the relationship between it and the thickness of the material needs to be summarized in actual experience. The method is to do a cut test, cut parts of different phenomena, and then measure the degree of thinning. Focus on and manage areas prone to cracking.
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