Introduction of defective products in the processing of metal stamping parts

The metal stamping process of the middle armor support is: blanking punching punching flanging forming cutting cutting flanging. There are various forms of tear and skew in the forming process of intermediate armor bracket. The tearing parts are mainly distributed at the pass of the workpiece, the junction of R arc and wall neck at the corner of side wall. Due to the difference of stamping forming and production process conditions, the proportion of each fracture part is different. Tear can be one-time forming tear, or it can be caused by the development of fatigue crack, i.e. invisible crack
Cause analysis

According to the actual situation of the site, through the inspection of the parts’ tearing position, fracture morphology and extrusion damage degree, it is considered that the tearing and skewing behaviors of the parts are mainly reflected in the flanging forming process, and the causes of this process phenomenon are as follows:

1. The execution of forming process parameters is not in place

In the process of forming parts, the process requires that the parts of the die, the core and the two must be closely connected together, and the forming can be realized by pressing the sheet metal plastic deformation when the slide of the machine tool slides down. However, due to the quality instability of the parts, it shows that the pressure of the machine tool is in the unbalanced state of pressure jump in the production process. The main reason is that the processing technicians did not adjust the machine pressure in time according to the process requirements, or did not communicate the machine pressure stability information with each other during the handover of each shift, which led to the instability of the product quality.

2. Design defects of flanging die
Since the first mock exam is a double cavity left / right part, the process is not only flanging but also with shape forming content, and the parts are very complicated, and the bending surface is narrow. Forming requires the die to match the forming face, which results in the large forming stroke and small pressing area. In the initial mold design, the designer only considered the small blank surface, but ignored the guide slip stroke of the core

There are the following design defects:
(1) The guiding length of the pressing core is designed to be 125mm, and the actual guiding length is 115mm. Although it is within the design range, the movement of the lifting part 115mm exceeds the effective guiding length by 10mm, which leads to the defects of unstable lifting of the pressure core and inaccurate positioning of the parts.
(2) For the forming height of 115mm, a special guide plate should be designed, which can not be guided by the clearance between the processing surface and the side wall of the female die. The friction force increases due to the side slope, the self-lubricating effect is very poor, and the strong lateral force cannot be effectively eliminated. After mass production, the guiding gap will increase due to long-term wear, and the normal guiding effect of the die will be lost in advance, which will lead to malignant quality problems So.

3. There are errors between the parts processed by the mould and the drawing design
If the area to be machined is clearly marked. However, due to the complex surface of the die, the guide surface was machined after casting forming, resulting in the gap error between the machining surface and the guide surface of the female die, and the die core swayed left / right during the normal operation of the die.

Before the part is formed, the positioning is carried out by the locating pin and hole on the upper plane of the pressing core. In this way, the pressing core must ensure stable, reliable and correct sliding in the forming process, otherwise, the part will lose stability in the forming process, which will cause the collision and extrusion between the core and the die wall, resulting in tensile stress of the part. When the strength limit of the material is exceeded, the part will not be torn or skewed Yes. In addition, if other factors are considered in the die structure, and the special guide plate is ignored, there is a risk that the guiding gap will be destroyed instantly and the guide can not be correctly guided after the extrusion friction is strong.

As the guiding clearance of this structure is the sliding clearance of debugging, once damaged, there will be no more effective adjustment means, which will affect the forming quality of the parts for a long time, and bring about safety risks. In addition, the special guide plate is not used in the guiding part, but the processing surface mutual guiding structure is adopted. There is a defect that the gap can not be adjusted after the gap is too large, which leads to the tearing and skew of the parts.