Among the methods of sheet metal forming, deep drawing is one of the most widely used manufacturing processes for the production of three-dimensional parts, such as sinks, cups, bottles, cans, and various components used in automotive and appliance industries. The geometry and size of the formed part are mainly determined by the punch and die design and the applied forces.
Deep drawing is a complicated forming process which usually involves large plastic deformation with relative low force. The plastic deformation begins with the engagement of the drawn part between the punch and die. After the contact is established, the drawn part is pulled into the die cavity and is simultaneously plastically deformed due to the uniform axial loading. During the deep drawing operation, it is essential to ensure that the blank remains in contact with the die, otherwise the part will misplace, leading to poor part quality or even cracking.
The formation of cracks or defects in deep drawing is a common occurrence, which has a significant impact on the product quality and dimensional precision. Usually, these are related to the complex strain pattern and the residual stress distribution in the parts which result from the high degree of plastic deformation. In this regard, it has been established that the cracks will initiate when the maximum principle tensile stress coincides with a quite localized strain held at the locations forming the boundaries of the cracking areas.
The most common causes of cracking in the deep drawing process are excessive internal stress resulting from the non-uniform deformation and higher blank holder force. Finite Element Analysis (FEA) is a computer-based simulation method used to assess the effect of these parameters on the developing stress and strain fields throughout the material. Some useful analysis includes the determination of forming limit diagrams, stress-strain behavior, springback and strain distribution, as well as crack propagation and stress intensities.
Apart from evaluating the effect of loadings on the nascent crack condition and propagation, FEA can also be used to study the influence of the tool design on deep drawing process. In this regard, the design of the geometry and size of the die and blank holder have been studied to optimize the process performance, such as the reduction of cracking and the improvement of forming accuracy. Finite element simulations can evaluate the development of the strain and stress field throughout the forming process and suggest the best tool design, such as the top radius as well as the draft angle.
Finally, FEA can be used to investigate the deep drawing process with variable initial blank size. In this respect, FEA can assess the size distributions and the shape deformation of the formed parts. The performance of several initial blank sizes can be studied with respect to the applied force, wrinkling and cracking, as well as die wear. The studies are aimed to identify the optimum blank size and shape, in addition to the corresponding forming force required.
In conclusion, FEA has demonstrated its usefulness in the analysis and optimization of the deep drawing process. The simulations are used to evaluate the effect of various loading conditions and tool designs on the forming behavior and product quality by predicting the strain and stress field, as well as the risk of part rejection due to cracking.
