Applied Mechanics and Materials Vol. 794

Abstract: A multi-material concept in sandwich design using two steel foils and continuous fiber-reinforced thermoplastics represents a promising structural approach to the production of hybrid parts. This contribution deals with the experimental and numerical analysis of a conventional sheet metal forming process using a composite material based on Polyamide 6 (PA6) with unidirectional endless glass fiber reinforcement and HC220Y+ZE steel foil. A unidirectional composite plate is positioned between two steel foils in sandwich design and formed into the hybrid part under appropriate temperature conditions. Afterwards, the forming process is analysed numerically with the software LS-DYNA and for verification of the FEA the geometry of the hybrid part is measured optically with ATOS system of the company GOM.

Abstract: Due to current ecological and economic developments there is a growing demand for functional components with complex and closely tolerated geometrical features. Conventional sheet and bulk metal forming operations leads to products which are often limited in their geometrical and functional variety. A promising approach is the process-class sheet-bulk metal forming (SBMF). SBMF is characterised by the application of bulk and sheet forming operations on sheet metals [1]. This combination leads to locally and temporally varying load conditions regarding stress as well as strain states. In order to get high quality parts, controlling the material flow is of major importance. Modified Surfaces, so-called tailored surfaces represent an innovative approach to control the material flow. The objective of the current study is the experimental investigation of the effectiveness of locally adapted tribological conditions using workpiece-and tool-sided tailored surfaces within SBMF processes. The study has shown that the local adaption of workpiece and tool surface increased the heights of functional elements. Thus, using locally adapted tribological conditions leads to an improvement of the quality of the produced gearing components. In a further step the influence of surface modifications on the surface properties of the manufactured components are analysed. Additionally, investigations regarding the wear behaviour of tool-sided surface adaptions lead to the assumption, that the effectiveness of tailored surfaces is reduced during the operating time of the tools.

Abstract: The new manufacturing technology sheet-bulk metal forming (SBMF) combines the sheet metal forming and bulk metal forming techniques. At the Institute of Forming Technology and Machines (IFUM), a new multistage SBMF process is being developed. In order to reduce the friction and improve the dimensional accuracy of the parts, superimposed oscillation is used within the new SBMF process. SBMF processes allow the manufacturing of solid metal components out of flat steel. To analyse the effect of friction on the superimposed oscillating SBMF process more precisely, superimposed oscillating and non-oscillating ring compression tests at room temperature were carried out. Like the semi-finished products for SBMF process the ring specimens were cut out of a sheet plate by water jet cutting. A new tool system with an integrated hydraulic oscillation system was developed for superimposed oscillating compression of the ring specimens. This tool system enables the absorption of the forming force and displacement stroke of the ring specimen during the ring compression test. After the practical experiments, the force profiles of superimposed oscillating and of non-oscillating process were compared. The influence of the frequency on the surface roughness of ring specimens was investigated. Furthermore, the tribological conditions of the superimposed oscillating ring compression test were analyzed.

Abstract: In order to enhance the tool life of hot forging dies, increasing the wear resistance of the forming tool surface is of great importance. In addition to thermal and thermo-chemical surface treatments, methods applying thin wear-resistant coatings gain more importance. Therefore, ceramic-based mono- or multilayer hard coatings are used in combination with a supporting nitride layer. Due to their low material-specific thermal conductivity, ceramic coatings have an increased sensitivity to abrupt temperature changes. To avoid such thermal shocks, an adjustment of the cooling behaviour is required. This paper presents the results of laboratory forging tests conducted under different cooling and lubrication conditions on nitrided dies with ceramic coatings. By means of a selective cooling of the forming tool surface and using boron nitride as lubricant the wear behaviour of the forging dies could be improved.

Abstract: Short cycle stretch forming (SCS) is an innovative stretch forming technology, developed by the Institute for Metal Forming Technology (IFU) at the University of Stuttgart. The SCS technology combines plane pre-stretching and deep drawing operations within the same stroke of the press ram. The sheet metal thickness is reduced, and the denting resistance as well as the yield stress are increased due to hardening effects.In this study, the SCS technology is applied to rotational-symmetric bodies. A process simulation of an SCS cupping process was carried out for producing tinplate cans. Based on these results, a tool was produced. First results showed that the metal thickness of cups for two-piece drawn and ironed (D&I) steel can bottoms can be reduced. With this technological goal, it is possible to save the material cost in series production.This paper analyses how batch fluctuations affect the thinning of cup bottoms in SCS cupping. Therefore, preliminary experiments have been conducted, using their results to improve the previously used FE process model. With the aid of this model, an FEA-based parametric study on the variation of material properties is conducted. To examine batch fluctuations, tensile tests have been taken into account, and initial material parameters for simulation, such as friction coefficient, initial blank thickness, Lankford parameter and hardening behaviour, have been varied.The results of this paper show that SCS cupping offers a promising potential for material savings and demonstrate the main effects of batch fluctuations.

Abstract: In metal forming a trend is observed towards increasing the performance of products by means of functional integration. One approach being pursued is the integration of electronic components. Multifunctional profiles with electrical conductors can transmit data and energy in addition to the mechanical function. They can be produced efficiently by roll forming. During the roll forming of multifunctional profiles wrinkles and cracks in the conductors may occur in the area of the contact of the rollers due to the contact normal stresses. In this paper, a design approach for multifunctional profiles preventing these failures in the tool contact area is presented and discussed on the basis of experimental and numerical investigations.

Abstract: Hybrid structures made of aluminium and steel are used in an increasing amount to produce lightweight optimised parts, e.g. for the automotive industry. One option to produce these optimised components is a combination of a steel sheet with a reinforcing aluminium rib structure by high pressure die casting. Achieving a reliable junction between the different materials during the short casting time is a major challenge in creating these hybrid components. Improving this junction is the topic of an ongoing research study in which a form closure connection is enabled by structuring the steel surface prior to the casting process. In order to meet the demands of the later application, the surface structure has to ensure the filling during the casting as well as a stable form closure connection. Thus, deep groove structures with a perpendicular wall angel straight to the casting direction were identified, since a deeper structure increases the clamping area and a perpendicular wall angle improves the form closure connection. However, the production of this structure in a large scale and a short time becomes difficult using conventional structuring processes. In this work the capability of an adapted rolling process which consists of stacked discs with varying thickness and diameter was studied in order to manufacture these grooves. Several experiments were performed to determine the influence of the height reduction and rolling force on the resulting structure. First results obtained with the presented experiments show the good predictability of the resulting size of the structure depending on the thickness reduction and the rolling force normalised to one millimetre structured width.

Abstract: Micro lubrication pockets decrease the frictional losses and improve the wear resistance of lubricated machine elements. Depending on the application, the pocket dimension and the area density (ratio of the projected pocket area to the non-textured area) must be optimized. Otherwise, the lubrication pockets might increase friction and wear. Besides the determination of the optimized texture, the production process needs to manufacture the pockets with high reproducibility and accuracy, since each deviation of the texture might reduce the improvement of the tribological properties. The goal of this work is to develop a new forming setup capable of decreasing the influence of deviations in the material, of the tool or due to a process inaccuracy ́s. Therefore, a roller-coining process based on a pneumatic system was developed to keep the forming force and thus the pocket dimension constant. This setup was as well used to texture the roller, since the manufacturing of a prominent micro texture on a curved surface with high tolerances is a difficult task for other texturing methods. The experimental verification of the setup showed that by using the pneumatic setup the standard deviation of the pocket depth was reduced by an average factor of 1.9.

Abstract: Seamless rings are used in several industrial sectors and are mainly produced by radial-axial ring rolling. To be able to detect process or form errors, which nowadays cannot be detected reliably by the conventional sensor technology of a radial-axial rolling machine, an image pro­cessing device has been mounted above the table of the ring rolling machine. This paper introduces the possibilities for measurements via image processing during and after radial-axial rolling of rings.

Abstract: The application of bulk forming operations on sheet metal enables the manufacture of functional components with local wall thickness variations. Using process adapted semi-finished parts with a local material pre-distribution and strain hardening in these processes leads to an increased forming of the functional components. In addition material efficiency is improved. Transferring the positive results acquired with mild deep-drawing steel to high-strength steel tailored blanks enables new possibilities for lightweight design. Given challenges in the manufacture of tailored blanks out of DP600 that reach the same geometry as the ones made of mild deep-drawing steel will be presented in this paper. Furthermore possible ways to overcome them by means of adjusted orbital forming will be presented.