FOCUS ON DEEP DRAWING
Seamless sheet metal parts
Deep drawing creates seamless , sheetmetal parts that can be 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 . Examples range from cans , pots , kegs and compressed gas cylinders to eyelets , sinks and automotive body panels .
“ Simple parts can be drawn to their finished shape in a single step while complex shapes , including parts that are especially deep , may require multiple steps . Deep drawing typically is used in combination with other techniques , such as blanking and piercing , to create a finished product . In some cases , all steps can be completed using a single press ,” commented press manufacturer , Macrodyne . “ Deep drawing works best with ductile metals . In general , any metal that can be coldrolled into sheet should have sufficient ductility to be deep drawn , but material properties like work hardening or anisotropy may also need to be considered . Appropriate materials include aluminium alloys ; brass , copper and copper alloys ; titanium ; cold-rolled low carbon sheet steel and some stainless steels . Ideal shapes for deep drawing include rectangles and axi-symmetric structures such as cylinders or hemispheres , but the process can also handle more complex shapes ,” it continued .
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 .
Stamping characteristics
The deep-drawing process contains many components and steps . All of these deep-drawn processes combine to influence the metal- stamping industry . There are various characteristics of deep drawn stampings / pressings , which can be summarised as follows : -
■ Wall thickness variation : Deep-drawn metal stampings typically exhibit some wall thickness variation . Consistent thickness may require additional or secondary processing .
A deep-drawn part for a high-end blender ( image : Boehm Pressed Steel , Inc .)
■ Work hardening : As raw material is formed into shapes through the deep drawing process , the grain structure is stretched and cold-worked generating improved material strength properties . This work hardening results in a finished part exhibiting more strength than the base material used to produce it .
■ Radii : In some cases , the deep-draw metal stamping process does not allow sharp corner radii that can be achieved by other processes . A good general rule of thumb is that inside corner radii should not be less than 1 / 2X the starting stock thickness .
■ Part tolerances : The deep drawing process can produce precise parts . However , it is not always possible to generate tolerances that can be achieved by machining , grinding or lapping . Near machining tolerances can be achieved on certain part features while other features require greater tolerance .
Left : A stamped tyre rim using the deepdraw process ( image : D & H Industries ).
Below : Deep-drawn parts ( image : Albert Jagger Engineering ).
Benefits of deep drawing
■ No Seams : Deep drawing produces shapes that are uniform and seamless , reducing potential weak points in the finished part .
■ Strength : In some cases , material hardening during deformation can increase the strength of parts .
■ Uniformity : Deep-drawn parts have a high degree of consistency from the start of a production run to the end .
■ Rapid Cycle Time : Presses set up for deep drawing can be cycled quickly , making this a very efficient way to produce large quantities of parts .
■ Reduced Technical Labour : Deep drawing can be automated , reducing labour costs significantly .
■ Low Maintenance : Deep draw set-ups require less ongoing maintenance than competing processes .
■ Faster Assembly : Deep drawing can create shapes with a closed end , reducing or eliminating the need for fabrication or welding as secondary processes .
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