Deep drawing in focus
Deep drawing is a manufacturing process in which sheet metal is progressively formed into a threedimensional shape through the mechanical action of a die forming the metal around a punch . The deep drawn metal stamping process work hardens the metal , resulting in a seamless finished part that is stronger than the base material . When the length of a stamped part is equal to or greater than ½ of its diameter , it is generally termed as being “ deep drawn .”
Deep drawing uses radial tension-tangential compression to shape the metal . This deep drawn process transforms flat sheet metal , or a blank , into a hollow vessel that may be cylindrical or box-shaped , with straight or tapered sides or a combination of straight , tapered and curved sides . The vessel is then redrawn through a series of dies , reducing its diameter and increasing its length with minimal change to the wall thickness . A flat sheet metal blank can be formed into a hollow body open on one side or a hollow body can be formed into a hollow body with a smaller crosssection [ DIN 8584 ]. In pure deep drawing , there is no reduction of sheet metal thickness .
Deep drawing sheet metal
Deep drawing creates seamless , sheetmetal parts that are closed at one end and have a depth greater than their radius .
Deep drawn parts achieve their shape by drawing metal into a cavity rather than by stretching or thinning over a die , so the original sheet thickness remains essentially the same from start to finish . A deep drawn part can be recognized by its depth and smooth , radiused corners .
“ The automatically controlled deep drawing
Image : Albert Jagger Engineering .
Deep drawn parts . of sheet metal is done on a forming press , which consists of an upper and a lower tool . The forming press consists of an insertable die ( drawing ring , on the bottom ) and a punch surrounded by a blank holder ( on the top ). This blank holder is positioned just far enough from the edge of the die so that the punch does not cause wrinkles or creases ,” explained measurement specialist , ZEISS .
“ To ensure that the sheet blank slides smoothly over the edge of the die , the drawing ring and punch are rounded at their edges . The middle area of the drawing ring incorporates the negative of the later deep drawn workpiece ,” it continued .
The sheet blank is placed on the die so that it is fixed by the sheet metal holders . The blank-holder moves downwards . The punch is then pressed onto the die basement using pressing force . The punch pulls the sheet blank along with it . After forming , the top tool moves upwards so that the deep drawn part can be removed .
“ From a technical point of view , the forming is carried out by radial tensile stress and the resulting tangential compressive stress . The tensile stress prevents the sheet from thickening . When machining round metal sheets , the compressive stress reduces the diameter in the edge area . If the desired drawing depth cannot be achieved in a single pass , the forming is carried out in several iterations . If the sheet is deep drawn using a pressure-regulated water cushion , higher drawing ratios occur ,” added ZEISS .
FOCUS ON DEEP DRAWING
A deep drawn drawer .
A stamped tyre rim using the deep draw process .
Depending upon the shape being produced , tooling and set-up costs can vary widely . For simple shapes , costs can be lower than other processes but with increased complexity comes increased cost . In some cases , that cost may be offset by deep drawing ’ s minimal downtime , low maintenance and reduced technical labour requirements over the lifetime of the product .
Deep drawing benefits
■ No seams : Deep drawing produces shapes that are uniform and seamless , reducing potential weak points in the finished part . There are no seams , parting lines or microholes .
■ Strength : In some cases , material hardening during deformation can increase the strength of parts .
■ Uniformity : Deep drawn parts have a high degree of consistency , and
Image : D & H Industries . Image : Fellows Manufacturing .
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