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The use of die cast magnesium for automobile transmission cases offers promise for reducing weight and improving fuel economy. However, the inferior creep resistance of magnesium alloys at high temperature is of concern since transmission cases are typically assembled and joined by pre-loaded bolts. The stress relaxation of the material could thus adversely impact the sealing of the joint. One means of assessing the structural integrity of magnesium transmission cases is modeling the bolted joint, the topic of this paper. The commercial finite element code, ABAQUS, was used to simulate a well characterized bolt joint sample. The geometry was simulated with axi-symmetric elements with the exact geometry of a M10 screw. Frictional contact between the male and female parts is modeled by using interface elements. Material creep is described by a time hardening power law whose parameters are fit to experimental creep test data.

This paper provides a review of the fatigue properties reported in the open literature for die cast magnesium-based alloys. Recently developed fatigue data, in the form of stress versus number of cycles to failure for bending fatigue (R=-1), are presented for die cast AM60B and AZ91D alloy specimens with thicknesses between 1 and 10 mm. The effects of specimen thickness and macrostructural features, such as porosity distributions and surface features (parting line and ejection pin marks), on the fatigue data are discussed.

This paper describes the high-pressure die castability assessment of two high temperature magnesium alloys, AE42 and the AC series alloy. AE42 is a commercially available alloy. Results showed that AE42 was a castable material for use in high-pressure die casting applications, including large transmission components. AE42 was determined to have similar operating/manufacturing costs if produced in equivalent volumes to AZ91D. The AC series alloy is an experimental alloy comprised of AM50 combined with small percentages of calcium (Ca). It was found that the castability of the AC series alloy decreased with increasing calcium content. Over 0.3% calcium content yielded poor castability performance. Selected mechanical and corrosion properties of AZ91D, AE42, AM50 and the AC series alloys were also explored.

The effect of calcium on the creep and bolt load retention (BLR) behavior of AM50 alloy has been investigated. Four AM50 alloys 0, 0.25, 0.56, and 0.88% Ca have been die-cast. BLR-tests have been conducted at 125, 150, and 175°C and preloads of 14, 21, and 28kN. Tensile and compressive creep tests were also conducted at 150°C and initial stresses from 40 to 80 MPa. Both creep and BLR were significantly influenced by calcium content, with increasing calcium content resulting in improved relaxation resistance. The BLR of AM50 with 0.88% Ca was better than that of AE42 at all temperatures although the effect of calcium was temperature dependent. Calcium did not change the sensitivity of BLR to preload, while it increased the relaxation limit (Fr) of AM50 significantly. In addition, calcium improved the creep resistance of AM50 significantly.

A new heat-resistant magnesium alloy (hereafter referred to as “ACM522”) for die-casting based on the Mg-Al-Ca-RE system has been developed by Honda R&D Co. In the 150°C temperature range, the ACM522 alloy yields high creep resistant characteristics which are superior to the conventional AE42 heat-resistant magnesium alloy, and it also exhibits an excellent resistance to both heat and corrosion which can be favorably compared with the A384 general-purpose aluminum alloy. The use of magnesium for oil pans has raised a number of issues such as reduced axial force in the bolted areas and, until now, oil pans made of magnesium had not reached the stage of commercial viability for mass-produced automobiles. The authors applied the ACM522 alloy to develop light-weight oil pans which are 35% lighter than conventional aluminum oil pans.

Weigth saving is more and more recommended due to future demands for low energy consumption. Especially the automotive industry continues to search as diligently as ever for ways to build lighter vehicles. Therefore, the use of light weight metals, preferably aluminum and magnesium is on the rise. This contribution shows effective possibilities to fasten magnesium components, which require special fastening elements, if high stressed and reliable mechanical connections are necessary. Topics are fundamental mechanics of magnesium fastening as well as examples for applications with screws, rivet nut and self piercing rivet.

The effect of strain rate on tensile properties of cold chamber die cast AZ91D, AM60B and AM50A test bars is reported. The strain rate was varied from 15 s1- to 130 s-1, a range typical of deformation and crash. All tests were done at room temperature. The properties measured include fracture elongation and ultimate tensile strength values. The results are discussed in terms of the work hardening characteristics and strain rate sensitivities of the materials, and parameters in a material model suggested by Johnson-Cook have been determined. It has been found that flowstress increases and that elongation is not affected by strain rates from 15 s-1 to 130 s-1. The energy absorption during deformation increases therefore with the speed of deformation, emphasizing the positive properties of magnesium die cast alloys for safety related applications.

To achieve a mass goal and minimize the bell mouthing phenomenon of Passenger Air Bag Housing which takes place when the air bag is in explosive action and detrimental to the safety of passenger side because excessive canister bell mouthing may distort and crash the top surface of instrument panel, a study on the replacing process of a PAB housing to a different material and process was performed. The explosive action of current steel PAB housing was firstly analized to evaluate the reaction forces transferred through the PAB and find out the adaptable material for replacing process. Due to the properties among the die casting alloys, the AM60B alloy was chosen for our new material for PAB housing. Then, stress analysis by the finite element method was performed for a design modification of magnesium one piece housing.

A Draw Bead Simulator (DBS), with modified draw beads, was employed in this study to understand the springback behavior of sheet metal subjected to multiple bending-unbending cycles. The investigations were carried out in both the rolling and the transverse rolling directions on four types of materials: Electro-Galvanized DQ steel, light and heavy gauge Hot-Dip Galvanealed High Strength Steels, and Aluminum alloy AL6111. The sheet geometries, thickness strains, pulling forces and clamping forces were measured and analyzed for the purpose of establishing a benchmark database for numerical predictions of springback. The results indicate that the springback curvature changes dramatically with the die holding force. The conditions at which the springback is minimized was observed and found to depend on the material properties and the sheet thickness. Analysis with an implicit FEM showed that the predicted and the experimental results are in very good agreement.

Tubular bending and hydroforming expansion processes are studied experimentally and numerically in this paper. The experimental results show that the hydroforming process is sensitive to material grades and process variables, and the axial feeding used in this case causes more material deformation near the inner bending surface. Finite element analysis (FEA) was carried out on an S-shape bending and expansion process using the incremental code LS_DYNA. The simulation results successfully explain the phenomena occurring in the experiments. A methodology of analyzing tubular bending process using a One Step FEA code is proposed to improve simulation efficiency. This approach is validated by comparisons with both the incremental FEA predictions and the experimental results. One Step FEA is not only highly efficient but also reasonably accurate in predicting the deformation mode and thickness distributions during the bending operation.

The use of commercial finite element analysis (FEA) software to perform stamping feasibility studies of automotive components has grown extensively over the last decade. Although product and process engineers have now come to rely heavily on results from FEA simulation for manufacturability of components, the prediction of springback has still not been perfected. Springback prediction for simple geometries is found to be quite accurate while springback prediction in complex components fails to compare with experimental results. Since most forming simulation FEA software uses a dynamic explicit solution method, the choice of various input parameters greatly affects the prediction of post formed stresses in the final component. Accurate stress prediction is critical for determination of springback, therefore this study focuses on the effects of some of the simulation parameters such as, element size, tool/loading speed and loading profile.

Present models and methods for simulations of sheet metal forming processes are reviewed in this paper. Because of rapid progress of computer hardware, complex computations, formerly impossible to perform due to high computational cost, are now feasible. Therefore, more realistic and computational intensive models are suggested for finite elements, materials, and frictional forces. Also, simulation methods suitable for sheet metal forming processes are recommended. Four numerical examples at the end of the paper are presented to support the recommendations.

The springback behavior might be different due to different gap clearances between die and punch. A study using FEA simulation is done to investigate the die gap effect. A 3D brick element and an explicit-implicit method are employed to investigate a few simple problems. A draw form, a crash form with an upper pad and a flange form are investigated separately. Numisheet’93 2D draw bending springback problem is also investigated using an explicit dynamic code. Comparisons between springback simulation results on several different die gaps are illustrated. The Kirchhoff assumption of C° shell element and the Mindlin/Love assumption of thin shell element are also examined on different cases. A case study then is performed on a rail type panel. Conclusions and recommendations for future studies are summarized.

{Metal forming process is characterized by large deformation that poses a great challenge for the implementation of contact algorithm. Based on the meshless representation of the geometry, a new contact detection algorithm is presented in this paper. The advantage of this algorithm is that it can handle a wide variety of complicated geometry involved in the forming process. Because only a simple scalar criterion is used, the algorithm is applicable to parallel computing and detection of self-contact. Although the algorithm is derived based on the framework of meshless method, it can be implemented in both finite element and meshless methods.}

An automotive part formed by 10-step drawing has been simulated by finite element method aiming to reduce forming steps. The reduction of forming steps can be achieved by optimum design of tooling shapes and other process parameters per each step. The ultimate goal will be to apply the derivative based optimization scheme or any knowledge-based system to these kinds of multi-step forming problems. However, as an initial step, we determined the minimum forming steps and optimum tooling shapes using heuristic manner, insight, design rules and testing with finite element analysis incorporated with a damage model. As a result, the 10-step drawing is reduced to 6-step drawing as a practical optimum solution.

This paper examines a history of numerical methods for evaluating drawbeads in sheet metal forming, from early work with Dr. Sing Tang at the Ford Scientific Research Laboratory on special purpose drawbead simulation software, to modern general purpose software simulations incorporating analytic drawbeads in full 3D sheet forming analyses. Future directions in the field are explored through an example utilizing nonlinear optimization for drawbead design.

Metal forming is complex; hence conducting computer simulations with reasonable turn around time requires a number of assumptions and simplifications of the physical reality. Since a number of commercial software codes are now available for metal forming simulation, it is very important that the underlying assumptions are well understood. It is not a simple case of one code being “better” than another; rather it is to understand the results and to apply them effectively. The goal of this investigation was to compare the simulation results between a full bending formulation (FBF) code and a modified membrane formulation (MMF) code, with particular emphasis on how friction should be “treated”. The strategy followed was to simulate the stamping of a simple U-channel FEA first in the FBF code and then to adjust the MMF results to be comparable by changing the friction coefficient. (The full bending code has been previously quantitatively correlated to many soft and hard tool stampings.)

WRAPFORM is a mathematical model and computer program for calculating binder wrap surface shape. It employs punch-opening line of the die as a geometric input and does not use the complete binder surface. This paper presents WRAPFORM-II, an improvement of the WRAPFORM model by including the binder surface geometry in the simulation. The new model has been applied to several dies and results are compared to those of the base WRAPFORM model. For a decklid die reported in the literature, whose simulated binder wrap showed bifurcation possibilities, straightforward application of WRAPFORM-II predicts a more plausible result which is consistent with the original design intent. In another case, WRAPFORM-II predicted the feasibility of a design to put more material into the die cavity. Other applications show slightly improved simulation results by using WRAPFORM-II.

With the advent of low evaporative emission requirements there has been the rapid adoption of multilayer extrusion technology into the production of Fuel and Vapour tubing used on Fuel systems on automobiles. Multilayer extrusion technology enables a manufacturer of Fuel and Vapour tubing to simultaneously co-extrude dissimilar thermoplastic materials in tubular form. This allows the manufacturer to combine expensive and brittle high performance evaporative emission ‘barrier’ polymers with lower cost engineering polymers. However, it is a well-known characteristic of these multilayer tube constructions that the joints between them and connector ‘barbs’ have lower joint integrity. Joint integrity is most often quantified by ‘Pull-off’ and leakage tests. Recent developments in LEV-II requirements for 2004 and beyond indicate that joint integrity will become a focus area for study and improvement.

The slope discontinuity in C° contact formulation is known as the cause of iteration convergence difficulty in sliding contact. In this paper, a smooth contact surface representation is introduced to remove the slope discontinuity in a C° contact formulation. The non-uniqueness in the solution of closest point projection near the junction of C° surfaces is eliminated by this new approach. The smooth surface representation is incorporated into meshfree formulation to yield a consistent tangent operator for frictional contact problems. The proposed method is successfully applied to a sheet metal deep drawing problem involving large sliding contact and a sheet metal stamping problem.