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Tin can Deep drawing process analysis（1）
Deep drawing is a cold stamping process in which flat blank or semi-finished blank is deep drawn into an open hollow part by means of a mould.Drawing process can be made into the shape of products: cylindrical, gateway, spherical, conical, rectangular and other irregular open hollow parts.Drawing process combined with other stamping process, can produce complex shape parts, such as blanking process and drawing process combined with blanking compound die.
1. Deformation process of deep drawing
In deep drawing, the blank of the middle plate is first compressed by the blank holder, and the punch goes down, forcing the material (flange part) under the blank holder to generate plastic deformation and flow into the gap between the convex and concave dies to form the side wall of the cylinder.
2. Various drawing phenomena
When drawing deep, the tangential compressive stress of the flange part is large enough to exceed the anti-instability ability of the material, and the flange part of the material will become unstable and swell, which is called wrinkling.Wrinkling is one of the main causes of waste products in deep drawing process. Normal deep drawing process is not allowed.The pressure of the common pressure ring holds down some materials of the flange to prevent wrinkling.
2) cutting margin
Due to uneven die clearance, thickness change, unequal friction resistance, inaccurate positioning and materials, mechanical properties of directivity, etc., resulting in the drawing part of the high and low, for the high requirements of the drawing part, need to add a cutting process.
3) calculation of blank size
It is mainly based on the principle of volume invariance and the variation of wall thickness in drawing.The principle of equal surface area between workpiece and blank before and after drawing is called equal area method.
4) factors affecting the drawing coefficient
A. mechanical properties of materials
B. Relative thickness of blank T/D
C. Drawing method: when there is a pressure ring, the drawing coefficient M can be smaller.
D. Die structure: the drawing coefficient is greatly affected by the size of the round corner of the concave punch of the drawing die and the clearance between the concave punch.
E. Friction and lubrication conditions: the contact surface between the die, pressure ring and the blank shall be smooth.But punch and blank contact surface to rough some good, not lubrication, in order to increase the friction, reduce the possibility of cracking.
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