Development of a Testing Method for the Identification of Friction Coefficients for Numerical Modeling of the Shear-Clinching Process

Abstract

Global competition as well as social and scientific megatrends strongly influence the modern car manufacturing industry. One of the most important approaches is the implementation of lightweight constructions. Therefore, the usage of high performance materials with tailored properties gains importance. For safety-relevant components such as automotive passenger cells it is necessary to minimize deformation to reduce the risk of injury for the vehicle occupants during a car accident. Thus, hot stamped high-strength steels have been established. High-strength and low formability of this kind of materials represent new challenges for joining technologies. One possibility to join high-strength steels is the newly developed shear-clinching technology. Due to the use of a combined cutting and joining process, the connection of dissimilar materials with high difference in strength and formability can be achieved. Further research to ensure process reliability and to improve the strength of the joint is required. One possible approach for this is the numerical investigation of the material flow during the joining process. Therefore, the definition of process parameters for the finite element model is necessary. A big impact on the quality of the results has the accuracy of the used friction values. As established testing methods are not suitable for modeling the rather complex tribological system between the joining partners of the shear-clinching process, an innovative testing method is needed. Studies in the field of sheet-bulk metal forming already demonstrated the applicability of the ring compression test for sheet metals. This paper presents a concept for the adaption of the ring compression test to the specific needs of the investigated shear-clinching process. The numerical identification of the friction coefficients is validated by experimental data and first results are qualified by experimental and simulative shear-clinching joints.

Investigation of the joinability of the high-strength aluminum alloy AA7075 in shear-clinching processes

“…Different threshold values were set and the value with the best agreement to the experimental data has been chosen. According to Müller et al 26 friction is modeled with the Coulomb friction law and a coefficient of 0.5 for the contact of aluminum and coated steel. Having changed the flow curves and set the threshold value, the accuracy of the model has been confirmed by the comparison of the process forces and the joint geometry to experimental data.…”

Development of a Method for the Identification of Friction Coefficients in Sheet Metal Materials for the Numerical Simulation of Clinching Processes

“…The ring compression test does not develop a stationary state, so that the test conditions cannot be considered independently. In [5] the ring compression test has already been adapted for mechanical joining. However, the process conditions here cannot be considered decoupled, so that the characteristics must be determined inversely.…”

Numerical Investigation of the Tool Load in Joining by Forming of Dissimilar Materials Using Shear-Clinching Technology

“…Friction is described by the Coulomb model with a global friction coefficient of µ = 0.5. This value was determined with an adapted ring-compression test for the contact between AA6016 T4 and 22MnB5 [12]. The realistic simulation of the separation of the die-sided sheet and the occurring tool loads requires a fine mesh for the sheets and the tools, which is achieved by using local refinement.…”