Key Engineering Materials Vols. 611-612

Abstract: For a continuous feeding of sheet metals in forming press lines mechanical roll and gripper feeders are used. Typical resulting problems are the damage of the sheet surface due to the mechanical contact. The present contribution deals with the investigations of an electromagnetic material feeder for electric conductive sheet metals. The concept is based on the principle of an asynchronous linear motor. Here the sheet metal acts directly as the secondary part. The new approach was first analysed and designed by means of finite element simulation. With experimental measurements the simulations could be validated using a demonstrator of the electromagnetic feeder. The results indicate that the feeding forces of partially 1000 N can be doubled in comparison to conventional mechanical roll feeders.

Abstract: The organization of workflow and design of tools and processes in automotive manufacturing will become even more dominated by topics of energy efficiency due to increasing environmental requirements in the future. From this point of view a detailed analysis of all manufacturing processes in the body shop, taking into account the reduction of energy consumption and required area covered by equipment, is necessary. In automotive manufacturing welding and gluing processes as well as metal forming processes are commonly used for joining of single parts to an assembly group, such as doors or closures. In order to determine typical process characteristics as well as to develop more efficient hemming solutions an experimental study was performed in this paper. Using a modular hemming test, representing a conventional table-top hemming process for hang-on parts, theoretical energy consumption during flanging, pre-hemming and final-hemming was determined experimentally. The forming force characteristic shows typical process related development of each single operation. Based on these findings a first experimental parametric study was performed to determine the significance of single material and hemming parameters regarding energy consumption of the entire process workflow. The most significant hemming parameters also were quantified. In a further investigation the identified parameters were used to improve efficiency of the single forming operations (flanging, pre-hemming and final hemming). Therefore are more detailed DoE study was performed considering hemming tool and process parameters. In the final step of the investigation all process steps were combined to a high efficient hemming routine and positive and negative interactions of single steps were considered. For the evaluation of efficient hemming process the quality of the hemming rope was analyzed.

Abstract: Due to the increase of lightweight design in car bodies, there is a raise in use of tailored welded blanks (TWB). With these blanks it is possible to strengthen the car body where it is necessary. This can lead to less weight. In the case of tailored welded blanks, there is a weld line, which influences the deep drawing behavior significantly during forming. In the presented results two different high strength steels (HCT980X and HCT600X) are welded together. One forming operation is performed, in which the weld line is positioned differently. The results show the influence of the weld line on the forming behavior which is realized by the comparison of deep drawn monolithic parts with the deep drawn tailored welded blanks. While the monolithic parts could be formed without failure, the forming of tailored welded blanks was accompanied by cracks in dependency to the weld line orientation and the applied load in this region. The results also show that the failure occurs in the base material and that the weld line is not damaged by the applied load. After the characterization of the base materials and the weld material, a numerical modelling of the whole TWB could be realized in this work. Two different ways of modelling techniques of the weld line are compared and the necessity of the consideration of the weld line properties is demonstrated. Furthermore, in consideration of the weld line properties in the FE-Model, it is possible to show that the weld line resists the forming operation without failure.

Abstract: In this paper, a new light weight construction is developed. The steel hollow sphere (MHS) sheet is sandwiched between two pure aluminum plates and the mechanical properties of the construction are investigated by means of compression test, bending test and stab-resistant test. As the results, the advanced specific stab-resistant strength and the plateau compression behaviour are found. In addition the damage progress inside of the construction is observed using a CCD camera. The fracture condition of the sandwiched MHS are compared with that of a conventional foam metal sandwich construction. The formability of the plate and energy absorption property are measured and the optimal construction condition is discussed.

Abstract: Cold forging processes require high-capability tribological systems in order to ensure sound forming results. Due to a rising ecological awareness, alternatives to the established and reliable conversion coatings are necessary. Single bath systems like polymers and salt wax coatings with integrated lubrication appear to be the most promising approach to prevent galling. For an optimization and investigation of the tribological system a definition of the tribological loads is necessary. However, only insufficient values are available in literature. Especially, long sliding distances, which occur in multistage operations, can cause a breakdown of the lubricant. Therefore, approaches are necessary to enable long sliding distances. This paper presents the results obtained with a cold forging tribometer, the Sliding Compression Test, which reveal the high impact of remaining lubricant on the friction coefficient. Also, tests with prelubricated tools show the ability to reduce the friction and the results of investigations with rough tool surfaces are presented.

Abstract: The influence of local inner die cooling on the heat balance in hot aluminum extrusion was investigated. For the manufacturing of the die with cooling channels close to the forming zone, the layer-laminated manufacturing method was applied. The new tooling technology was applied in order to decrease the profiles exit temperature and to avoid thermally induced surface defects with the aim to raise the productivity in hot aluminum extrusion processes. Numerical and experimental investigations revealed that, while maintaining the exit temperature of the extrudate, a distinct increase of the production speed up to 300% can be realized, while the extrusion force increases only slightly. An effect on the profiles microstructure was also detected. By applying die cooling, grain coarsening can be significantly limited or even be avoided.

Abstract: These days, the call for more efficient cars, e.g. EURO 6, to reduce substantial the emissions of carbon dioxide and nitrous oxide raises the demand and development for Battery Electric Vehicles (BEV) or Plug-in Hybrid Electric Vehicles (PHEV). Thus, the German Government in cooperation with the industry has the goal to get at least 6 million electric vehicles on German streets by the year 2030. Until today battery systems increase the cars weight significantly, therefore weight reduction and utilization of the required space are two of the most important strategies. Because of its low density and high formability aluminum is preferred as cell housing material. Besides a light material it is necessary to use the required space of the battery pack in the car as efficient as possible. Thus a prismatic shape is favored compared to a cylindrical one. Unfortunately a prismatic cell causes an asymmetric material flow and an asymmetric tool loading during the production via bulk metal forming as the material tends to flow into the direction of the larger edges of the housing walls. That is why new forming tools for bulk forming have to be developed. To do this economically the development will be done by using design of experiments (DoE) and the finite element method (FEM). On the one hand DoE shortens time-consuming FE-simulations by stating exactly which simulations need to be done to identify main determining factors for the personal command variable(s) e.g. tool lifetime. On the other hand FEM can be used to achieve simulation results, e.g. tool loading, which are comparable to real life experiments. By using DoE, 2D FE-simulations show that the geometry of the punchs extrusion shoulder can decrease the required forming force precisely. In addition the geometry of so called deceleration seams can affect the forming force in minor degree. In combination of all significant geometric parameters and the number and position of deceleration seams the tool loading of a cold extrusion punch could be reduced significantly.

Abstract: In order to investigate the multi-variable friction phenomenon during aluminium and magnesium extrusion, tribological experiments with the alloys AA6060 and AZ31 against hot working steel 1.2344 were carried out. Using a new axial friction test, the effects of the normalized normal stress (1.5-6), the temperature (300 °C - 500 °C) and the relative sliding speed (0.1 - 50 mm/s) were investigated. The influence of each parameter on the friction behavior is analyzed, the friction results are depicted and a modified Tresca friction model is developed.

Abstract: Finite element analysis (FEA) is applied to study metal flow in an asymmetric porthole die with two ports where one port is bigger than the other. It is shown how FEA predicts the velocity differences between the two ports to depend on applied extrusion velocity, i.e., the ram speed, and in addition, how increasing size difference between the ports changes the flow balance between the ports. Two of the simulations have been validated by experiments in previous work, so the trends shown by FEA have also been confirmed experimentally. In long billet extrusion metal flow through the two die channels is predicted stable throughout the major part of the extrusion stroke. However, in the end stage of the process, there is predicted a shift in metal flow. Now the velocity in the small channel is speeded up on the expense of that in the big channel. In short billet extrusion the same shift in metal flow is also confirmed towards end of extrusion. An explanation is given why the metal flow in the small channel speeds up towards end of extrusion. In the article it is also quantified (in a diagram) how big the shift in flow balance between the two ports is as the size difference between the ports increases.

Abstract: The velocity and strain rate fields in the primary deformation zone ahead of the extrusion die opening are investigated by theory and FE-simulation for direct and indirect Al extrusion. The metal flow obtained in the FEM-models of extrusion is compared with the flow recorded in previous experiments and it is shown that the FE-analysis mimics real metal flow with good accuracy. The velocity and the strain rate fields computed by FEA (using DEFORM^® 2D) are described and comparison is made with the idealized spherical velocity field of Avitzur, to see if there is good agreement between the results from theory and FEA, and the correlation between the results from the two is discussed. Moreover, a clear difference in metal flow is confirmed between the two processes direct (FwE) and indirect extrusion (BwE).