Unveiling the Principle of Precision Sheet Metal Forming: Key Technologies for Stamping, Bending, and Stretching

Precision sheet metal forming is a processing process that causes plastic deformation of metal sheets through external forces to obtain specific shapes. Stamping, bending, and stretching are the three core processes, and although their technical principles are based on the plastic deformation characteristics of materials, they form the technical key due to differences in the force mode and deformation logic.

The core of stamping technology is the separation of materials and local shaping. By using the cutting edge of the die and the concave die to match, the sheet metal is separated by instantaneous impact force when the stress exceeds the strength limit, forming material falling or punching. The key to its technology lies in the precision of the cutting edge and the control of the punching gap: the cutting edge needs to be kept sharp to reduce the tearing of the sheet, and the gap value needs to match the thickness of the sheet - if the gap is too large, it will cause edge burrs, and if it is too small, it will exacerbate mold wear. For stamping parts with shallow stretching (such as shallow cup-shaped structures), it is also necessary to control the stamping depth and mold fillet to avoid material cracking due to excessive stretching. At this time, the plastic flow of the sheet should be evenly distributed to prevent local thinning beyond the allowable range.

The essence of bending technology is the plastic deformation of materials through bending. By applying a bending moment to the plate through a mold, the surface of the material is subjected to tension and the inner layer is subjected to compression, forming a specific angle of bending. The key to its technology lies in stress control in the deformation zone: the bending radius needs to be greater than 1.5 times the thickness of the material (brittle materials need to be larger) to prevent cracks in the outer material due to excessive stretching; At the same time, the compensation angle design of the mold is used to counteract rebound - the material will experience angle deviation due to elastic recovery after unloading, and the reverse compensation amount needs to be pre-set according to the material characteristics. In addition, the pressing force during bending should be uniform to avoid dimensional deviation caused by slip of the sheet metal. For long workpieces, it is necessary to ensure the synchronization of the contact between the mold and the sheet metal to prevent distortion and deformation.

The stretching process focuses on the flow and thickness reshaping of materials, using the combination of convex and concave molds to draw flat billets into open hollow parts (such as cylindrical or box shaped). The key to its technology lies in controlling the radial flow and thickness changes of the material: the rounded corners of the concave die need to have a smooth transition to reduce material flow resistance; The clearance between the convex and concave molds should be slightly greater than the thickness of the sheet, leaving space for material thickening. During the stretching process, appropriate pressure should be applied through the edge pressing ring to prevent wrinkling of the billet edge and ensure sufficient material flow into the concave mold. For complex shaped stretching parts, a multi pass stretching process is often used to gradually increase the forming depth and avoid local cracking caused by excessive deformation in a single pass. Annealing treatment is also required between each pass to eliminate the decrease in plasticity caused by material work hardening.

Although each of the three processes has its own emphasis, they all rely on the synergy of material plasticity, mold accuracy, and process parameters. Understanding the separation logic of stamping, the stress balance of bending, and the material flow law of stretching is the core of mastering precision sheet metal forming technology.