Deep drawing: Process and applications
Deep drawing is used for sheet metal and various plastics. The process is equally suitable for industrial small-series and mass production. Many everyday objects consist of deep-drawn parts.
What is deep drawing?
Deep drawing is a frequently used process of forming technology, which is regulated in DIN 8584. The deep-drawing process is a tensile compression forming process in which usually an open-top metallic hollow body is created. However, the process can also be used to form a preformed hollow body into a workpiece with a smaller cross-section. Special deep-drawing presses are used for deep drawing. The flat sheet blanks used are square or round. Unalloyed thin and extra-thin sheets, aluminum, stainless steel, copper, brass and bronze are used in the conventional deep-drawing process with rigid tools. Deep drawing is possible with both small and large batch sizes. The manufacturing process is used in various industries, such as the automotive industry, packaging industry, aviation and model construction. The most commonly manufactured deep-drawn parts include automotive body parts, faucets, bathtubs, sinks, cooking pots, plastic buckets and yogurt cups.
What are the advantages and disadvantages of deep drawing?
Tensile compression forming
- is also suitable for small batch sizes and for individual production
- is flexible in terms of material thickness, shapes and sizes
- has short reaction times
- causes only low tool costs
- allows the use of various materials
- permits efficient prototyping
- is cost-effective
- requires extensive specialist and material knowledge
- requires adaptation of the production machine to the material
- is not suitable for all precision parts
What is the effect of deep drawing on the workpiece?
Production-related displacement movements within the crystal lattice cause stresses, which trigger work hardening of the material. Various errors can occur during the deep-drawing process. These errors include:
- non-compliance with production steps
- incorrect estimation of material expansion and grain
- insufficient consideration of material texture
Quality assurance is either carried out during production or by checking the forming tool before the process using optical 3D measuring systems. They measure each point of the tool without direct contact and save the result. In this way, the entire process can be reconstructed in the event of later problems without remeasuring. The scans provide full-field images, making manual corrections easier. The production is monitored by robot-guided sensors directly on the production line.
How does deep drawing of sheet metal work?
The automatically controlled deep drawing of sheet metal is performed 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. 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. The sheet metal forming process is as follows: 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.