Cold Drawing: Metal Flow in Deep Drawing Dies ~ MECHTECH GURU

Cold Drawing: Metal Flow in Deep Drawing Dies

Cold Drawing

Like hot drawing, it also involves the forcing of a metal through by means of a tensile force applied to the exit side of the drawing die. Most of the plastic flow is accomplished by the compressive force which arises from the reaction of metal with die. It is the operation in which the metal is made to flow plastically by applying tensile stresses to the metal. The blank of calculated diameter is placed on a die and held of it by a blank holder and bottom is pressed into the die by a punch and the walls are pulled in as shown in Fig. The efficiency of operation depends upon blank size, reduction factor, drawing pressure, blank holding pressure, punch and die diameters, type of lubricant, die material etc. Therefore, this process is generally used for making cup shaped parts from the sheet blanks, without excessive wrinkling, thinning and fracturing. It can undertake jobs of nearly any size. It is a process   of managing a flat precut metal blank into a hollow vessel. Utensils of stainless steel are generally made by this process.

Cold drawing
Cold drawing

Metal Flow in Deep Drawing Dies

When the punch of a deep drawing press forces a portion of metal blank through the bore of the drawing, different forces came into action to cause a rather complicated plastic flow of the material. The volume and thickness of the metal remain essentially constant, and the final shape of the cup will be similar to the contour of the punch. The flow of metal is summarized as follows.

(i)  There is no metal deformation takes place in the blank area which forms the bottom of the cup.

(i)  The metal flow of the volume elements at the periphery of the blank is extensive and involves an increase in metal thickness caused by severe circumferential compression. The increase is usually slight because it is restricted by the clearance between the punch and bore wall of the die ring.

(ii)   The metal flow taking place during the forming of the cup will uniformly increases with cup height.

Metal flow in deep drawing
Metal flow in deep drawing

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