Duc-Toan Nguyen

Finite element method study of incremental sheet forming for complex shape and its improvement

Abstract In order to improve the incremental sheet forming process for the product of complex shape (e.g. human face), a combination of both computer-aided manufacturing (CAM) and finite-element modelling (FEM) simulation, is implemented and evaluated from the histories of stress and strain value by means of finite-element analysis. Here, the results, using ABAQUS/Explicit finite-element code, are compared with forming limit curve at fracture in order to predict and improve the forming conditions by changing process variables of tool radius, tool down-step, and friction coefficient according to the orthogonal array of Taguchis method. First, the CAM simulation is used to create cutter location data. This data are then calculated, modified, and exported to the input file format required by ABAQUS through using MATLAB programming. The FEM results are implemented for negative incremental sheet forming and then investigated by experiment.

Combination of isotropic and kinematic hardening to predict fracture and improve press formability of a door hinge

Abstract To predict a fracture in the concentrated stress and strain area of a door hinge, the criterion for a ductile fracture, as developed by Oyane (Journal of Mechanical Work. Technology,

A New Constitutive Model for AZ31B Magnesium Alloy Sheet Deformed at Elevated Temperatures and Various Strain Rates

Abstract In this study, a new constitutive model is established for AZ31B magnesium alloy sheet at elevated temperatures and strain rates in order to describe two competing mechanisms for deformation, i.e. both work-hardening and softening stage of AZ31B magnesium alloy sheet. Stress-strain curves obtained by conducting uni-axial tensile tests at elevated and strain rates were first separated at the maximum stress and corresponding strain values. Voces law [25] was then employed to fit separated hardening and softening stage. A MATLAB tool is used to determine material parameters by using least square fitting method at various temperatures and strain rate. The mergence of separated work-hardening and softening equations is in good agreement with experimental data. The parameters of fitting curves are utilized to determine them as a function of temperature and strain rate using a surface fitting method. The final equation is then implemented to predict stress-strain curves at various temperatures and strain rates. The proposed equation showed the good comparability between the simulation results and the corresponding experiments.

Characteristics optimization of powder mixed electric discharge machining using titanium powder for die steel materials

In the present study, four quality characteristics of the electrical discharge are simultaneously presented and optimized using titanium powder mixed electric discharge machining. The Taguchi method and the grey relational analysis are applied to the processing parameters to investigate the following: workpiece material, tool material, polarity, pulse-on time, current, pulse-off time, and powder concentration. The combination of the Taguchi method and grey relational analysis is applied to optimize simultaneously four quality characteristics of powder mixed electric discharge machining, including material removal rate, tool wear rate, surface roughness, and microhardness surface. Optimal results by the Taguchi–grey relational analysis show that both surface roughness and tool wear rate decrease, while both material removal rate and microhardness surface increase, respectively. This approach proves effective in terms of improving the processing efficiency of the study parameters. The results from both optimization calculations and experimentation demonstrate high accuracy and efficiency. Furthermore, powder mixed electric discharge machining has improved significantly. The concentration of titanium powder is the processing parameter with the strongest influence on the efficiency of powder mixed electric discharge machining.

Simulation and experimental studies to verify the effect of cutting parameters on chip shrinkage coefficient and cutting forces in machining of A6061 aluminum alloy

This article predicts the relationship between chip shrinkage coefficient and cutting parameters such as cutting speed and uncut chip thickness in a cutting process of A6061 aluminum alloy. To this end, shrinkage coefficient–based finite element method was first estimated using the Johnson–Cook (J-C) and Bao–Wierzbicki (B-W) material fracture models. After that, experimental measurements of the chip shrinkage coefficients were performed at the same cutting conditions to compare with simulation data and confirm the accuracy of material damage models. By a simultaneous evaluation of the effects of cutting parameters on the chip shrinkage coefficient, the B-W model was found to match well with the experiment. So that, the B-W model was then utilized to verify the effect of various cutting speeds and uncut chip thicknesses on the chip shrinkage coefficient and cutting force. Finally, using the least square method, the relationship between chip shrinkage coefficient and cutting force was obtained. The above-mentioned relationship is believed to be useful in determination of optimal cutting conditions in high-speed machining.

A study of combined finite element method simulation/experiment to predict forming limit curves of steel DP350 sheets

In this study, to estimate the forming limit curves of a steel DP350 sheet, a combination of the finite element method simulation and experimental methods was adopted using the fracture height of experimental specimens and the corresponding in-plane major/minor strains of the finite element method simulation. Hecker’s punch stretching tests were first performed to measure the fracture height for forming limit curve testing specimens with a different notch radius. The finite element method process was then performed to get in-plane major/minor strains (ε1 and ε2) at various points on specimens with different dimensions and the same fracture height of each corresponding experimental data point. An interpolated curve from the tip of the strain paths was derived using the limit curve (FLC1) of a DP350 steel sheet. The resultant FLC1 will be the input data for a finite element method simulation, in order to predict the formability of the steel DP350 sheet. Finally, experiments for difference specimens of Hecker’s punch stretching tests were performed as a comparison and showed a good agreement between the simulation and experimental results.

A study on spring-back in U-draw bending of DP350 high-strength steel sheets based on combined isotropic and kinematic hardening laws

In this article, a numerical model for predicting spring-back in U-draw bending of DP350 high-strength steel sheet was presented. First, the hardening models were formulated based on combined isotropic–kinematic hardening laws, along with the traditional pure isotropic and kinematic hardening laws. A simplified method was proposed for determining the material parameters. Comparison of stress–strain curves of uniaxial tests at various pre-strains predicted by the numerical models and experiment showed that the combined isotropic–kinematic hardening model could accurately describe the Bauschinger effect and transient behavior subjected to cyclic loading conditions. Then, a finite element model was created to simulate the U-draw bending process using ABAQUS. Simulations were then conducted to predict the spring-back of DP350 high-strength steel in U-draw bending with geometry provided in the NUMISHEET’2011 benchmark problems. It was shown that the predictions of spring-back using the proposed model were in good agreement with the experimental results available in the literature. Finally, the effects of various tool and process parameters such as punch profile radius, die profile radius, blank holding force, and punch-to-die clearance on the spring-back were investigated. The simulation results suggested the significance of tool and process parameters on the final shape of the formed parts influenced by the spring-back.

Formability Predictions of Deep Drawing Process for Aluminum Alloy A1100-O Sheets by Using Combination FEM with ANN

The FEM simulation results of deep drawing process are carried out to create training cases for the artificial neural network (ANN), and then the well-trained ANN(s) is used to predict the formability of aluminum alloy A1100-O sheets. The OYANE’ s ductile fracture criterion equation [J. Mech. Work. Technol. 4 (1980), pp. 65-81] was implemented to predict the formability of deep drawing process. This ductile fracture criterion is introduced and evaluated from the histories of stress and strain calculated by means of finite element analysis in order to get the ductile fracture value (I). The resolution of the results of ductile fracture criterion equations is carried out via a VUMAT user material, using ABAQUS/Explicit finite element code. From the calculative results of FEM simulation with the changing of various parameters, the formability predictions using ANN methodology was investigated by comparing with random case studies of FEM results and shown good agreements

A Study on Developing Robustness Engineering by Using Stochastic Analysis Method

The purpose of this study is to evaluate the influence of the scatter in mechanical properties and stamping process parameters on an industrial sheet metal forming process. Based on a previously optimized forming process, a robustness analysis has been performed. The robustness analysis clearly showed production problems for the part not initially revealed by the analysis of the process that was trimmed for “optimality”. The sensitivity of the results on the variation of the parameters was evaluated. It was shown that all parts of the sheet do not react equally sensitively to the variation of the input. Zones of critical response could be identified in accordance with the zones on the actual part that showed failure in mass production. The results reveal that the common practice of performing evaluations with fixed safety margins is non-effective and hence very dangerous, or is extremely conservative and thus costly. The application of stochastic simulation methods reduces the need for wide safety margins while simultaneously increasing the reliability of the process by incorporating uncertainty into the simulation

A Development of Lancing Engineering Method for Lamp-CAN Stamping Process by Using Forming Analysis

The products manufactured by the Sheet metal process are widely used in automobile and aircraft industries due to their high strength and superior surface characteristics. In this study, to improve the formability of the lamp-can, forming process was conducted using the Lancing engineering method. Lancing process is a press operation in which the work-piece is sheared and cut with one strike of the die to be a single-line cut or split, without removing any metal. Finite element method (FEM) was used to predict and investigate the improvement of formability of a lam-can with lancing process. As a result, it is believed that the Lancing process used in lamp-can forming would be helpful in the development of high-quality forming products because it can make material flow run well.