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Defects in stamping parts and preventive measures

February 4, 2024





The mechanism of fuzzing problem:

During the stamping process of cold-rolled steel plates, when the sheet metal is in sliding motion, adhesive wear occurs due to the forced contact between the sheet metal and the mold, resulting in severe surface damage to the stamped parts.


The main reasons for the problem of burrs are: the hardness of the stretching part of the mold is not enough, and the hardness of the stretching part of the mold should be greater than the surface hardness of the mold; The hardness of the stretching part of the mold is uneven. The material of the stretching mold is generally alloy cast iron and high-strength cast iron, which are manually quenched. Due to the technical level of the operator and the quenching process, the surface hardness of each point after quenching is uneven, and the mold lacks lubrication during the stamping process.


Brushing defects not only reduce the performance of vehicle body coverings, such as collision safety, pitting corrosion, and fatigue resistance, but also reduce the lifespan of the mold.


The phenomenon of roughening reduces the stability of stamping processes, leading to an increase in scrap rates and becoming one of the main reasons for cost waste in manufacturing enterprises.

Prevention and countermeasures of hair pulling problems

1. Product development stage

In the development stage of products, some products have a "several" shape, with relatively deep drawing depth and high strength requirements. Due to the shape of the parts, in mold manufacturing, the side walls of the parts are basically designed to be vertically drawn. During the drawing process, due to the small stamping angle, the side walls of the parts will produce serious burrs due to shear force.

Prevention plan:

(1) In the initial stage of product design, it is necessary to fully consider the stress situation on both sides of such parts, adjust the angle between the two arms of the "Ji" shaped part and the stamping direction to be greater than 3, reduce the vertical shear force between the formed insert and the sheet metal, and avoid the occurrence of burrs.

(2) Using other materials instead of high-strength plate materials while meeting the strength requirements of the components.


2. Process analysis and design stage

The problem of burrs occurs when there is severe local contact between the mold and the sheet metal. In the process design stage, software tools should be carefully used for analysis. Necessary corrective measures should be taken for areas where burrs may occur, such as rotating the stamping direction of the workpiece, improving the hardness of local formed inserts, etc. The occurrence of burrs should be reduced as much as possible in the early stage of process design. Figure 4 shows a method of eliminating burrs by changing the stamping direction.

Process design directly affects the production quality of the mold in the later stage, and is also one of the fastest and most effective methods to control the occurrence of burrs on the workpiece, which can fundamentally reduce the occurrence of burrs.

The preventive measures for controlling the occurrence of fuzzing can be basically divided into:

(1) Correct selection of stamping direction

The process stage should avoid situations where the side walls are deep and straight.

(2) To avoid local contact, as shown in Figure 4, the part is shaped, and a sharp point is formed at the bottom of the shaping blade, causing the plate to be subjected to a concentrated force at one point, resulting in burrs.

(3) Through software analysis, predict in advance the approximate location of burrs, and adopt the method of improving the local hardness of the mold (local inlay blocks) to avoid burrs.


3. Structural design stage

Following the results of process analysis, try to design insert block structures in areas with severe local forming contact, improve the hardness and production continuity of vulnerable areas, and ensure service life. Principle of splicing and tiling: Generally, for sheet materials with t>1.2mm, a segmented structure is adopted for forming and trimming; The depth of the forming part is deep, the material flow is large, and high hardness of the insert block is required; To avoid the alignment of the joint between the two inserts and the direction of material flow, it is advisable to make the joint and the direction of material flow 5-10.


4. Mold manufacturing stage

The mold manufacturing stage is the last process of mold manufacturing and also the last technical barrier to eliminate burrs. Therefore, the measures to control burrs are concentrated here, with many methods, which are reflected in:

(1) Improve the roughness of the mold surface, reduce the friction between the mold and the workpiece, and make the material flow smoother.

(2) Generally, quenching treatment is used to improve the hardness of the mold. Taking Cr12MoV as an example, overall quenching is basically used, which can make the hardness of the insert reach 58-62HRC. However, due to the use of manual operation, there are too many unstable factors, resulting in uneven hardness of the mold surface and the formation of soft spots. Soft spots cause uneven feeding speed of the sheet metal and result in burrs. In addition to quenching, there are several good surface treatment methods, such as chrome plating, nitriding, solution injection, and TD treatment, but the price is relatively high.

(3) The adjustment of mold forming clearance, with small mold clearance, is also one of the factors that cause burrs. Reasonably adjust the mold clearance on site to avoid burrs.

(4) Adjust the size of the R angle at the forming part.