Introduction to stretching process

One: Concept

Stretch: Press the sheet into a hollow section (basically the same thickness)

Drawing die design process: refers to the transfer of material from the plane (flange) to the outer wall of the cylinder (box), so that the size of the plane has a larger change< /span>

Stretch index: the ratio of stretch diameter to body diameter "m" (the degree of deformation from body to workpiece)

For wide flange barrel parts, it is generally required to stretch to the required flange diameter first, and then try to choose a smaller m1, so as to have sufficient deformation ability, It is also necessary to keep the flange diameter unchanged after each deep drawing (flange unchanged principle)

Second: Important factors affecting deep drawing indicators

(1) Mechanical properties of the material (yield strength---- elastic deformation; compressive strength---- plastic deformation; elongation coefficient; area shrinkage)

2) Relative thinness of the material (T/D<1D refers to the diameter of the embryo)

3) Drawing frequency: because of cold work hardening conditions, except for the intermediate annealing process, the m value is generally increased each time (m14) Drawing method: with or without pressure plate The rate for the m value is that the m with the pressure plate can be smaller; if the die base R is too small, it is more likely to produce dangerous section cracks

5) Radius of punch and die: a large cavity R can reduce the friction of forming, but if it is too large, the reduction of the pressing area will cause wrinkles

6) The smoothness of the surface of the drawing die and its wetting standard, clearance, etc. Drawing speed: If the drawing speed is too fast, the flange material cannot be converted into the outer wall in time, and cracks will easily occur