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Common quality problems of bending and stamping parts and improvement countermeasures

by:Fortuna     2021-03-05
Bending stamping parts have gradually been widely used in engineering machinery products. In order to meet their product quality and production needs, their quality standards have gradually improved. In the cold state, the bending machine can use the equipped general mold or special mold to bend the metal sheet into various required geometric cross-sectional shapes. The rationality of the bending process directly affects the final formed size and appearance of the product. In response to bending defects, stamping parts processing plants must use process control and prevention in normal work, and take corresponding effective process measures to improve the quality of stamping parts. 1. Fracturing: After shearing or punching, burrs or fine cracks often appear on the edge of the material, which will easily form stress concentration and be broken during bending. When shearing (surface with burrs) (when shearing), shear outwards , The cracking position occurs on the shearing and kneading belts of the stamping parts. The technical measures taken for this purpose are as follows: the workpiece after shearing or punching should be ensured that the shearing surface is inward during bending, that is, under pressure, and the forming effect is better. Before bending, the workpiece is deburred, and after bending, the bending part can be ground with a manual grinding wheel. 2. Protrusion: For the bending of medium and thick plates (thickness t≥6mm), the situation is quite special. The area near the bending line will become longer in the fibrous structure during the bending process, resulting in the formation of protrusions at the corners of the bend. According to the observation of the formed workpiece in the workshop, the size of the fillet protrusion increases with the increase of the plate thickness. For some workpieces with high quality requirements, the rounded protrusions will affect the welding or assembly dimensional accuracy, and process measures must be taken to remove them. The technological measures adopted for this are: if the thermal cutting equipment is used for blanking, when the process personnel unfold the blanking of the plate, make an inwardly concave arc on the blanking drawing with the bending line as the center, and remove the excess plate material, where R Is the arc radius. For workpieces that have not been cut with concave arcs for sheet metal, they should be manually trimmed to the required dimensional accuracy after the bending is completed. If the assembly accuracy is high, the workpiece needs to be milled. 3. Rebound: In the bending process, the plastic deformation and elastic deformation of the metal material are synchronized. When the bending ends, springback occurs due to the recovery of elastic deformation. The springback phenomenon directly affects the dimensional accuracy of stamping parts, so it must be controlled. The technical measures adopted for this are: angle compensation method. If the bending angle of the workpiece is 90°, the opening angle of the lower slot (V-shaped) of the bending machine can be 78°. The pressure duration increases the correction rate. When the bending is over, the contact time between the upper die, the workpiece and the lower groove of the bending machine is extended by pressure correction to increase the plastic deformation of the corners of the lower groove, so that the springback of the fibers in the tension and compression zone cancel each other out, thereby reducing the springback . 4. Sliding material: (1) The bending line of the stamping part to be bent is not parallel to the edge line of the workpiece, that is, one end has a fulcrum at the lower groove of the bending machine, and the other end has no fulcrum. Technicians add slits to the blanking diagram along the direction of the bending line of the workpiece, the length of which is the outward offset of the bending line of the workpiece, and the offset width is half of the width of the lower groove of the selected bending machine; increase the margin processing. (2) The bending line of the workpiece to be bent is parallel to the edge of the workpiece, but there is no fulcrum at the lower groove of the bending machine at both ends. The technicians increase the size according to the blanking drawing, so that the edge of the lower groove of the pipe bender has a fulcrum to meet the pipe bending requirements. After the bending process is completed, cut allowances and trim cuts are carried out according to the product drawings to meet the product quality requirements. 5. Indentation or slippage: In the bending process, the stamping parts are squeezed by the upper die and the lower groove of the press brake to produce different degrees of indentation or slippage. The surface roughness of ordinary carbon steel parts is not required to be high, and it will not cause slight damage. However, for some special materials, such as 430-2B, 12Cr17Mn6Ni5, etc., the appearance of the mirror surface needs to be protected by certain technological measures. The technical measures taken for this purpose include: for carbon steel materials, the bending width of the lower groove should be increased to increase the radius of the formed fillet, and the extrusion of the lower groove on the workpiece is reduced; for special stainless steel materials, the preparation before bending The work is to isolate the paper at the lower groove of the bending machine. If both sides of the workpiece need to be protected, the paper can also be separated from the workpiece along the direction of the bending line. With good production conditions, anti-indentation pads can be used. Our stamping parts processing plant proposes reasonable solutions to the common defects and process problems of bending stamping parts based on the daily production process of the workshop and combined with the usual work experience. These process measures are verified by production and will surely meet the quality requirements and improve the quality of stamping parts. . Recommended article: Discussion on the influence of punching clearance of metal stamping dies on the quality of stamping parts Previous: Several structural forms of commonly used bending dies and their respective characteristics
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