Overview of Deep drawing process and types (R)

WHAT IS DEEP DRAWING?

Deep drawing is usually related to the manufacture of cups, cans and comparable containers. The operation is generally divided into essential groups: first-degree drawing, wherein a flat round steel clean is made right into a cup; and a redrawing degree (or stages) wherein the cup reaches its very last size.

The latter operation is usually necessary because the first stage drawing has a blank-to-die neck diameter ratio (drawing ratio) of approximately 2.2 or a cup height/diameter ratio of 2.2. This is because it is not possible to produce a higher deformation than there is. The operating procedure is as follows. First, the sample held in place by a sheet metal holder is partially in contact with the die, partially in contact with either the die or the punch, and sometimes only with the punch. Pulling begins when you move the stamp downwards.

he outer rim of the clean is then subjected to natural radial drawing (i.e. drawing toward the vertical axis of the system) among the die and clean holder. A part of the metal bends and slides over the die and is in addition stretched among the punch and the die, while the fabric begins inside the place of the punch head and in fact in touch with it bends and slides over the radiused a part of the punch and stretches over the punch head.

A commonly used redrawing system is shown in Figure 16.56. In the figure, (a) and (b) show the direct redraw method with and without a blank holder, respectively, and (c) show the reverse method. In (a), the wall of the cup undergoes two bending and unbending times, but its strength is expected to be high because the directions of each deformation are perpendicular to each other. system

In (b), despite being a double bend, the gravity is lower due to the support of the tapered wall. This system can only be used when the ratio of pot diameter to wall thickness is relatively small and no holddown is required. Compared to the direct method, the system (c) The use of well-rounded die profiles tends to reduce (or completely eliminate for semicircular profiles) the extent of bending and bending effects.

Whether the use of the system provides significant benefits depends on the balance between redundancy reduction and practical production considerations. Defining "redundancy" in deep drawing is not easy. Because redundancy is not necessarily related to macro-shear effects. It is in the nature of the process that a part of the blank undergoes several deformation stages, which in itself creates redundant effects, but is physically unavoidable to complete the process.

It is consequently the diploma of severity imposed as opposed to the avoidance of a sure section of the operation that matters. In this respect, the procedure differs substantially from the bulk-forming operations mentioned previously. The 3 essential re-assets of pointless pressure in and/or distortion of the clean or cup cloth are flange wrinkling, the already mentioned bending and unbending, and, partly, ironing.

The latter is used to eliminate the increase in cup wall thickness, which can be up to 30% during the first stage of drawing. If there is a further significant increase in successive processing steps, resulting in wrinkles, an additional stretching process will be required. As far as redundancy is concerned, ironing is the only process that restores the "standard" functionality of shearing.

Since the formability of the material depends on the blank holder pressure, the deep drawing ratio R = Q/d can be limited by flange wrinkles, cup bottom tears, or wear. Figure 16.57 schematically illustrates the limits of these conditions and indicates the existence of a ``safety window'' in which deep drawing is likely to be successful. When determining drawability, criteria regarding the first occurrence of the defect must be applied.

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