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.
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| 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.
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| Metal flow in deep drawing |
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