Yingyot Aue-u-lan

Optimizing tube hydroforming using process simulation and experimental verification

Abstract The success of a tube hydroforming (THF) process is highly dependent on the loading paths (axial feed versus pressure) used. Finite element (FE)-based simulation was used to determine optimum loading paths for hydroforming of structural parts with different tubular materials. Experimental and simulation results have demonstrated that FE-based loading paths can significantly reduce trial and error, enhance productivity and expand the THF capability in forming complex parts. The test results also demonstrated that the reliability of the FE-based loading paths is highly dependent on the accuracy of the material properties of the blank, interface friction, and how close the properties of the welding zone are to the base material of the tubular blank.

On the characteristics of tubular materials for hydroforming—experimentation and analysis

Abstract Increasing acceptance and use of hydroforming technology within the automotive industry demands a comprehensive understanding of related issues such as material characteristics, tribology, part and tooling design. Among these issues, characterization and specification of tubular material properties under hydroforming conditions is the main concern of this paper. Analytical improvements and their comparison with experimental findings on measurement of material properties of tubes under hydraulic bulging conditions are explained. With these improvements, ‘on-line’ and continuous measurement of flow stress for tubular materials become possible, and are proven to be in good agreement with previous ‘off-line’ measurements presented by the authors.

Feasible pressure and axial feed path determination for fuel filler tube hydroforming by genetic algorithm

Successful fuel filler tube hydroforming largely depends on proper loading paths, that is, application of internal pressure and axial feeding during the forming time duration. Generally, two part quality criteria are considered in selecting the feasible loading paths: (a) minimum part wall thinning and (b) part wrinkle free. Due to the highly nonlinear nature of the tube hydroforming process, iterative finite element analyses with adjustments based on forming experience are typically conducted to design the loading paths. In this research, genetic algorithm was integrated into the finite element analysis–based optimization, resulting in enhanced determination of the feasible loading paths. Genetic algorithm is a heuristic search based on mechanics of natural selection. A pair of pressure and axial feeding profiles was represented by connecting genes making up to be a chromosome. In each search, mutation and crossover operations generated a new generation of chromosomes. Fitness functions were formulated to assess performance of the chromosomes reflecting the part quality. Generations after generations, the optimal chromosomes are found only when the evaluated fitness function value falls within a user-defined tolerance. Unlike the typical iterative finite element analysis approach, it was shown that the iterative finite element analysis augmented with genetic algorithm was able to determine feasible pressure and axial feeding paths autonomously. The current approach still requires a lot of simulation runs, which must be offset by high-performance computing resources.

Influence of Process Parameters on Electric Upsetting Process by Using Finite Element Modeling

Electric Upsetting Process (EUP) is a process combining the forming process with the electric heating system. It is commonly used to manufacture a preform of a bar with high upsetting ratio, such as an axial shaft. The reliable forming process requires the understanding the effect of process and electrical parameters. Currently, the designer develops this process by trail-and-error. To successfully develop this process, the relationship between the electric heating and the forming parameters needs to be clearly understood. In this study, three parameters are investigated; namely anvil speed, upsetting load and heating voltage. Finite Element Modeling (FEM) is used as a tool for evaluating these parameters. The FEM results indicate that those parameters play significant roles on the material flow as well as the heating characteristics (i.e. temperature distributions and heat flow).

Improving the Sensitivity of T-Shape Test to Friction Conditions for the Evaluation of Friction Behaviour in Microforming

In this paper, the sensitivity of T-Shape test to friction conditions was evaluated by observing the extrusion height and load curves throughout the normalized stroke (relative to workpiece diameter). Using the finite element code Deform 2D and assuming plane strain approximation, the effects of changing die geometry to the T-Shape test results were investigated. The sensitivity of the T-Shape test was also improved by introducing the double-sloped T-Shape design. The double-sloped T-Shape test was able to separate the extrusion height curves for shear coefficient of friction 0.0 to 0.4 which was unable to distinguish using the original T-Shape setup.

Investigation of process parameters in superplastic forming of mechanical pre-formed sheet by FEM

Conventional superplastic forming has been applied in automotive and aerospace industries for a few decades. Recently, superplastic forming combined with mechanical pre-forming process has been reported to be capable of forming non-superplastic AA5083 at 400 °C to a surface expansion of 200 % [1]. In this paper, finite element modeling (FEM) was used to develop the combined forming process by using the non-superplastic material AA5083-O. The simulation follows the experimental sequence and was divided into two phases (mechanical pre-forming and superplastic forming). A conventional creep equation based on tensile test data was adopted as a material model for the simulation. The pressure cycle and forming time was simulated according to the actual process route. The thickness distributions obtained from simulation validated the capability of the model to be used for this case. The influence of different parameters, such as holder force, friction, and punch depth was investigated by comparing the final sheet thickness and level of material draw-in. It was found that the punch depth played a significant effect on the uniformity of thickness distribution, from which a more uniform formed part can be obtained by using the punch with higher depth during mechanical pre-forming phase.

Investigation of Thermal Effect on Hot Forging Process of Yoke Flange by Finite Element Modeling

Finite Element Modeling (FEM) has been employed widely to analyze material flow behavior and identify potential defects in a hot forging process before try-out. Normally, the isothermal assumption should be used to simulate this process because the forming time was extremely shot around 0. 5 s – 1 s due to a high velocity of a press machine. However, in some cases when the contact pressure and contact area are extremely high, the heat could significantly dissipate to the forming dies. In case of Yoke flange simulation the isothermal condition could not be used to identify the defect as occurring in the real process. The forging defect (i.e. insufficient gap) was found at the apex of a workpiece in the rough or preform step. In this study, the non-isothermal assumption was used for investigating the defects. The forming process was divided in 3 steps; namely the transportation step when the billet was transferred from an induction furnace to the forging dies by conveyer, the rough forging and the finish forging steps. Temperatures, loads and gaps between workpiece and die at each step of the forming processes were measured and compared with the simulation results. For developing the reliable simulation model, the suitable heat transfer coefficients for each step would be determined. The heat transfer during the forming steps had an effect on the material flow and, the non-isothermal simulation model and could identify the insufficient gap in the rough step.

Investigation of a Geometrical Base Parameter Affecting on Bending Quality in a Thin Sheet Metal

A geometrical base parameter is investigated to determine the effect on a bending quality of a thin sheet metal for a roll forming process. This parameter is usually used as a criterion for the quality control of incoming materials for the bending process. This study was conducted by using a FEM simulation. The determination of the geometrical base parameter is considered as an appropriate and unique characteristic for each type of materials. To find this geometrical base parameter the dimensions of the workpiece must be measured while loading. The sensitivity of the bend allowance of a sheet metal is dependent on this geometrical base parameter. The high geometrical base parameter is led to indicate the elongation and the strength of the material. The principles of the geometrical base parameter are dependent on several factors, such as the bending angle, bending radius, material thickness, bend allowance, bending types and mechanical properties of materials. The outcomes of this study could provide the information used to enhance the bend quality of the sheet metal.

Finite Element Modeling of a Non‐Isothermal Superplastic‐Like Forming Process

Conventional superplastic forming (SPF) has been modified to increase the productivity and reduce some of the drawbacks, such as high forming temperature and high percentage thinning, to suit the automotive industries. One of the modifications was to combine between the conventional SPF and the use of a mechanical preformed blank to form the non‐superplastic grade aluminum alloy (AA5083‐O). The requirement of high temperature usually results in microstructural defects during forming process. In this paper, finite element modeling was adopted to investigate the superplastic‐like forming process using the non‐isothermal heating system. In the simulation, two phases (mechanical pre‐forming and gas blow for ming) of the process were conducted under different temperatures, where the material was mechanically drawn into the die cavity at 200° C in the first phase, and it formed with gas pressure applied at a global temperature increasing from 400° C to 500° C. Because of the non‐isothermal heating of material, ...

Process and Material Property Effects in the Progressive Forming of Micro-Pins

A progressive forming process for micro-components was developed to circumvent the issue of handling of small micro-parts while keeping in mind the need for high manufacturing through-put. The mechanical properties and microstructure of the material have been found to play a significant role in the forming of micro-components. In this work, the effect of mechanical property on the forming of copper micro-pins by the progressive forming process is highlighted. Empirical results show that the forming load decreases for forming micro-pin with 0.3mm diameter after annealing but the pin height obtainable decreases as well compared to that prior to the heat treatment.