Papers by Keyword: Sheet Metal Forming

Abstract: China Steel Corporation was founded in 1971 being the largest integrate steel mill in Taiwan. After several stages of expansion projects, its crude steel production has reached 16.5 million tons annually. CSC has made consistent efforts on its technology innovation mainly carried out by two R & D departments. One of the major tasks of its R & D activities is to establish the advanced technologies for the manufacturing better steels and aluminum alloys as well as product application technology for downstream users. This presentation will mainly brief the research activities of CSC in the field of metal forming including rolling, sheet metal forming and thermal mechanical simulations carried out at Gleeble 3800. Work rolls with continuously variable crown (CVC) were applied to produce hot-rolled strips having precise profile and flatness. Lubrication rolling technology with high speed steel rolls was developed to diminish the wearing of work rolls at hot strip mills. The campaign life of rolling cycle was greatly prolonged. Computer-aided engineering (CAE) simulation technology of sheet metal forming has been established which proved to be an effective way to deal with the sever spring back and breakage of the cold forming of high strength steel automobile parts. Hot stamping has also been developed to support the technology innovation of CSC’s downstream customers. Flow stress and microstructure evolution during hot rolling for aluminum alloys were investigated using a Gleeble 3800 simulator. Both high strength AA5182 for can end and low earing AA3104 for can body aluminum sheets have been successfully developed.

Abstract: Sheet metal deep-draw die is primarily constructed with draw bead, which is then modified based on trial and error to obtain a successful forming without splitting. This work aims at a robust design of forming die using numerical analysis and the Taguchi method. A three dimensional elastoplastic finite element model of a sheet metal forming process of SPCEN steel has been successfully developed using the material flow stress obtained from the modified Erichsen cup test. The model was validated with the actual forming experiment and the results agreed well. The influence of draw bead parameters on splitting and thinning distributions were examined using the Taguchi method. Four parameters, namely the friction coefficient, draw bead height, radius and shoulder radius were investigated. The Taguchi main effect analysis and ANOVA results show that the height and shoulder radius of the draw bead are the most important factor influencing the thinning distribution. Applying the Taguchi method and using the minimum thinning percentage as the design criteria, the optimum die design was identified as height, radius, shoulder radius and the friction coefficient of 4, 8, 8 mm and 0.125 respectively. The verified finite element model using the optimum die design was conducted. The predicted Taguchi response was within 5.9% from finite element analysis prediction. The improvement in the reduction of thinning percentage was 22.35%.

Abstract: Recent years laser-assisted manufacturing techniques are increasingly the focus of the automotive and aerospace industry due to cost price, low energy efficiency and safety. Among these techniques is laser-assisted flow forming process that combines laser beam technology with conventional flow forming process. During forming the material undergoes a rapidly heating and cooling cycles with the irradiative action of the laser beam, which is quite different from the traditional process. A transient three-dimensional model was developed to investigate the influence of laser irradiation on the forming process, in which a user-defined function was created to overcome the problem of a moving Gaussian heating source. The result indicates that a ring-shaped temperature field is acquired when the heating source scans workpiece along a thread; the deformation area on the workpiece during forming is extensively and continuously heated by intense laser radiation and the thermally induced loss of material strength significantly increases the formability concerning the achievable material reduction rate and tool service life; the possibility of accuracy improvement by laser assistance has been investigated and an accuracy error decreases 10%-28.5%.

Abstract: Topographgy optimization is a special kind of size optimization and it has been widely used to enhance the stiffness of sheet metal formed component by adding beads to the geometry. In this paper we present a methodology on how this concept can be employed in order to reduce formed part geometry deviation due to springback. An automotive part from Numisheet benchmark 2008 was used in this study. Several bead patterns were first generated by topography optimization subject to load constraints. Then the effects of these bead patterns location and size were studied by numerical forming and springback simulation. Our results show that the bead patterns have a significant effect on the springback. Finally, a methodology has been developed so that springback-free design can be incorporated in the early stage of part design.

Abstract: This study aims to find a solution to improve the formability in a deep drawing process. For this purpose drawbeads were used to avoid wrinkles and ruptures. The finite element method was applied to simulate the 3D metal forming process using a die and drawbead. The drawbead amount, position, size and form were studied for their affects on the formability. 3 drawbead patterns with 3 different heights were examined. The simulation was performed for each drawbead pattern and each drawbead geometrical parameter and the failure elements were counted. The best pattern chosen was the pattern that resulted in the least failure elements.

Abstract: This paper deals with the formability of AA 6061 sheet metal. The forming limit diagram of precipitation hardenable Al–Mg–Si alloy namely AA 6061 was evaluated for sheets rolled at two different temperature media namely room temperature and cryogenic temperature. The sheets were subjected to solutionising, rolling either in room temperature or cryogenic temperature with 50% or 75% reduction and short annealing before forming operation. The forming limit diagrams of the rolled sheets were plotted together to obtain a clear idea about their comparative formability.

Abstract: Off-line testing of new tribo-systems for sheet metal forming production is an important issue, when new, environmentally benign lubricants are to be introduced. To obtain useful results it is, however, vital to ensure similar conditions as in the production process regarding the main tribo-parameters, which are tool/workpiece normal pressure, sliding length, sliding speed and interface contact temperature. The paper describes a generic methodology for such tests exemplified on an industrial, multistage deep drawing example, where deep drawing is followed by two successive re-drawing operations leading to very high tool/workpiece interface pressure and temperature in the second re-draw. Under such conditions only the best lubricant systems work satisfactory, and the paper shows how the performance of different tribo-systems in production may be predicted by off-line testing combined with numerical modelling in order to ensure proper test conditions.

Abstract: Knowing the flow curve of a sheet metal, strain distribution on a sheet strip may be used to roughly but quickly evaluate the Coulomb friction coefficient. Strain distribution on the strip being stretched on a cylindrical surface of interest may be measured by an optical strain measurement system. This could be used to estimate the stresses on the specimen. The capstan equation is then used to roughly evaluate the coefficient of friction acting between the sheet strip and the cylindrical surface. Validation of the approach is done using the simulation of the process. The corresponding experiments can be performed easily on a sheet metal testing device equipped with an optical strain measurement system, which is commonly used for the experimental evaluation of FLCs.

Abstract: Conventionally manufactured cold work tool steel is often used in sheet metal forming as die material. Due to the forging process, the as-cast network structure of carbides is broken into elongated particles. Depending on the tool cross-section, the orientation and shape of carbides in the active tool surface is different. In the present research, the influence of tool steel hard phase orientation and shape on galling was investigated. D2 type tool steel was cut in three different orientations and tested in lubricated sliding conditions against AISI 304 austenitic stainless steel. Tests were performed using a Slider-On-Flat-Surface and galling was detected by changes in friction and post-test microscopy. The lubricant was Castrol FST8 using 5 g/m² sheet material. Results showed a strong correlation between sliding distance to galling and tool steel hard phase orientation and shape at low loads, whereas high load contact resulted in early galling in all cases. Material transfer was observed mainly to the tool steel matrix. The worst performance was observed for specimens cut so that the tool steel hard phase, M₇C₃ carbides in the D2 steel, were oriented along the sliding direction, which resulted in longer open tool matrix areas contacting the sheet material.

Abstract: In present time the FE-simulation of body parts in sheet metal drawing processes has to be continuously improved to increase the prediction accuracy. The objective of this paper is to describe a methodology to improve the simulation by mapping the complex tribological conditions of the process in the simulation. This methodology focuses on the dependency of influencing parameters on the friction coefficient. The influence respectively the dependency of these factors has been investigated, both in an experiment of a plane strip drawing test and in a FE-simulation of this test. With the sensitivity analysis in the numerical simulation it is possible to compare the implemented Coulomb-friction-model against the experimental results. The results of the experimental and numerical investigation show the need of further investigations on a more geometrical complex test to prove if it is possible to transfer the knowledge and dependencies that has been found in the experiment with the strip drawing test to a more geometrical complex test.