Material Selection for a Fuel Tank and its FE Simulation in deep drawing

Deep drawing is a sheet metal forming process in which deformation forces are oriented in the plane of the sheet, and the surface pressures in the tool are generally lower than the yield stress of the sheet material. The present work discusses the selection of sheet material suitable for a fuel tank by experimental evaluation of tensile properties of interstitial free steel and deep draw quality steel sheets of the same thickness of 0.8mm. The tensile specimens are laser cut from a blank with a known rolling direction and are tested for tensile properties and anisotropy. These tensile properties of the sheets are used in the material model in FE simulation of the deep draw process using HyperWorks. It is observed that an optimum blank holder force is necessary to remove the wrinkling defects. It is concluded that higher ductility and normal anisotropy are the key factors for higher thinning resistance in deep drawing and hence, interstitial free steel sheet qualifies as the better material for the fuel tank.

Deep-Drawing Forming Trials on a Cross-Ply Thermoplastic Lamina for Helmet Preform Manufacture

With the evolution of modern warfare, there is a constant demand for enhanced soldier protection. The research efforts presented in this paper focus on improving the ballistic performance of composite combat helmets through the control of fiber orientations, reduction of seam density, and preservation of long fiber lengths. To accomplish these objectives, near-net-shape preforming is explored as an alternative method to the traditional cut and dart techniques used in the manufacture of combat helmets. An overview of current fabrication procedures is provided in addition to a discussion of the material selection and preform processing technique. Forming trials are conducted on Dyneema® HB80, a cross-ply thermoplastic lamina, using a laboratory deep-draw setup to explore the effects of processing parameters on the quality of the formed part. Undesirable wrinkling that manifests during deep-drawing of the material is found to be most effectively mitigated through the use of sufficient binder pressure. Furthermore, it is demonstrated that a loose ply stack up is more amenable to the production of high-quality preforms than a preconsolidated charge of material.

Development of Formability, Microstructure and Martensite Reversion during Intermediate Annealing of Metastable Austenitic Stainless Steel

Intermediate annealing is a widely used process to recover formability in multi-stage deep drawing of austenitic stainless steel sheets. A special ability of metastable austenitic stainless steel is the so called strain-induced martensite formation, which causes the TRIP-effect (TRansformation Induced Plasticity). Major issues of intermediate annealing in serial production processes are long annealing times and high costs for annealing equipment and consumed heating energy. One suggestion for optimization of this process made in this paper is to anneal austenitic material only in regions of the part where it is required and to use suitable annealing parameters. This annealing parameters need to be optimized to requirements of follow-up forming processes. Therefor, basic intermediate annealing experiments were accomplished for austenitic grade EN 1.4301 within temperature range of 100-1100°C. Measurements of mechanical properties by uniaxial tensile tests, martensite contents measured by Feritscope and micrographs are showing the development of martensite reversion as well as reconstitution of austenitic phase. Especially 400°C, 600°C and 1000°C were identified as most interesting annealing temperature levels due to formation of carbides and recrystallization. This knowledge can be used as base for further local heat treatment concepts and may enhance, simplify and save costs of intermediate annealing process of deep draw components made of stainless steel.

Forming of Automotive Aluminum Body Panels by Sheet Hydroforming

This paper discusses the application of sheet hydroforming technology to the forming of deep draw aluminum automotive body panels. Currently, the amount of aluminum in vehicle architectures is somewhat limited due to cost and also the inability to incorporate common body panel design to aluminum sheet due to lower formability. Typical aluminum sheet has approximately about 30~40% of the formability of comparative steel grades. Automotive designers have been hampered by this fact and have not been able to successfully introduce aluminum sheet for wide range of panels. Sheet hydroforming, however, has a formability advantage over many types of forming methods. This paper will discuss those advantages and show some successful applications to the automotive industry.

Effects of Draw-Bending Characteristics on Concave Wall Feature in Rectangular Deep-Drawn Parts

In recent years, the requirements on the complicated deep-drawn parts with the high dimension precision are increasingly. As the major defect, the concave wall feature which commonly encounter in the complicated deep-drawn parts of the difficult-to-deep draw material is focused. In this research, the effects of draw-bending characteristics on concave wall feature during deep-drawing process are clearly identified. The mechanism of concave wall feature related to the draw-bending characteristic was investigated and clearly identified by using the finite element method (FEM) and the experiments were also performed to validate the FEM-simulation results. On the basis of stress distribution, the effects of draw-bending characteristics on the concave wall feature could be clearly identified via the changes of stress distributions on the wall, convex feature and spring-go feature on the bottom surface, and spring-back feature on the top surface. However, comparing with U-draw bending model, the effects of draw-bending characteristics was decreased and the concave wall feature in the case of deep-drawing model was smaller than that in the case of U-draw bending model. The experiments were carried out in both cases of the deep-drawing and U-draw bending models to validate the FEM-simulation results. The FEM-simulation results showed a good agreement with the experimental results with reference to the distribution of material thickness.

Measurement & Modelling of Slip during Plug-Assisted Thermoforming

Plugs are a common feature of most deep-draw thermoforming processes and are used to ensure that the wall thickness distribution in the final product is controlled and balanced. Through contact with a moving mechanical plug, the heated sheet is locally captured and protected from excessive deformation and thinning. Previous work has clearly demonstrated that slip plays a critical role during this process and that its magnitude is determined by frictional properties that are strongly dependent on temperature. Work to discover the appropriate friction relationships has been very limited to date and this has greatly hampered the progress towards effective thermoforming process simulations. In this paper the magnitude of slip that occurs during the plugging stage of the thermoforming process was experimentally investigated. Preform shapes were created by pushing a specially designed plug into a heated sheet and then freezing it at the end of the plug displacement. A variety of processing parameters such as the plug and sheet materials, the temperature and plug displacement were evaluated. The results show that large variations in slip occur when different combinations of plug and sheet materials are employed and these are most affected by the contact temperature. A finite element based simulation of the plugging process is currently being constructed and it will be used to investigate different friction relationships and compare their performance with the experimental behaviour.

Evaluation of Stamping Lubricants in Forming Galvannealed Steels for Industrial Application

Lubrication is one of the process variables that affect the quality of stamping sheet materials. Using a good lubricant can significantly reduce scrap rate and/or improve the quality of stamping. In this study, different types of lubricants were evaluated using strip draw test (SDT) and deep draw test (DDT) for stamping of galvannealed steel sheets. Finite element (FE) simulations were carried out to determine the coefficient of friction at tool-work piece interface during deep drawing under different lubrication conditions and blank holder forces. Flow stress data of materials under biaxial load which are used in FE simulations are obtained by viscous pressure bulge tests. SDT was used as a preliminary test to evaluate the relative performance of the lubricants. Lubricants that showed good performance in this test were tested using DDT. Dimensions of the formed strips and cups and the maximum applicable blank holder force to draw parts without fracturing were the criteria used for evaluation of lubricants in both tests. In general, it was possible to form cups with higher blank holder force when synthetic/water-based lubricants were applied to the sheet. In conclusion, evaluated synthetic/water-based lubricants had better lubricity than petroleum-based lubricants.