What is the reason why the shape and size of the stamping and bending parts do not meet the requirements? How to correct it?

The shape and size of stamping and bending parts are not in conformity with the requirements, which is a quality problem often encountered in production. The reasons are various, but mainly due to the rebound of the material and the unreliable positioning. 1) Rebound caused unqualified. From the analysis of the bending deformation process, it can be known that the direction of force on both sides of the neutral layer is opposite (extended on the outside and compressed on the inside). When the bending is completed, the elastic recovery direction of the materials on both sides of the neutral layer is opposite, resulting in obvious recovery. bomb. Bending deformation is generally limited to a local area of u200bu200bthe material, other parts of the material are in a free state, and the elastic rebound is less restricted by the overall size, so the shape of the stamping part changes greatly. When the width of the workpiece is greater than 3 times the thickness of the material, there will be bow deflection along the bending line in the width direction. The following measures are taken to overcome the rebound: 1) Set reinforcement ribs on the workpiece. The reinforcement ribs are pressed out at the bending position, which makes it difficult for the bending part to rebound, which not only increases the accuracy of the size of the bending part, but also improves the rigidity of the bending part. 2) Use materials with large elastic modulus, low yield limit and stable mechanical properties. 3) Correction (correction) bending is used when bending V-shaped parts. 4) When bending U-shaped parts, the punching die adopts a smaller gap. 5) The blank is annealed before bending to increase its plasticity. 6) Under the condition of ensuring the use performance and the workpiece does not crack, use a small punch fillet radius. 7) Think of a solution to the structure and shape of the convex and concave molds: ①When bending the U-shaped parts, make a cylindrical surface with a radius of about 20t on the punch and the top plate (t is the thickness of the material). After bending, use The rebound at the bottom counteracts the rebound at the bend. Or the U-shaped bending punch is made with a two-way slope. ②When the thickness of the bending material is greater than 0.8 mm and the plasticity is good, the punch can be made into the shape shown in the figure below. 8) For curved bending parts with a large bending radius, the stretch bending process can be used. 9) In the bending process, a force much larger than the actual bending force is used to perform corrective bending. Second, the unreliable positioning of the blank causes unqualified. The unreliable positioning of the blank causes the blank to slide during the bending process, which makes the product unqualified. The measures to improve the positioning reliability are: 1) The ejector is composed of air cushion, rubber, spring, etc., through the top plate, the reverse pressing force is applied to the blank before the blank enters the bending. In this way, the friction of the blank is increased and the possible movement of the blank is prevented. It is also possible to make tooth patterns, pits, top cones, etc. on the top surface of the pressing rod, the pressing plate or the working surface of the punch to increase the reliability of positioning. 2) Choosing a reliable positioning method There are mainly two types of positioning in terms of shape and hole. The shape positioning operation is convenient, but the reliability is poor. The inner hole positioning operation is not convenient enough, the use range is narrow, but the positioning is reliable. If the inner hole is used for positioning and a material pressing device is used, the positioning will have a better effect. 3) The unbalanced shape of the workpiece caused by the asymmetry of the blank force will cause the blank to move due to the uneven force during bending. In order to make the blank bear uniform force during bending, asymmetrical workpieces can be combined into symmetrical workpieces, which can be bent at one time. Previous post: What are the characteristics of thin plate and thick plate stamping? How to punch small holes in the thick plate?