Numerical Study of Tube Hydroforming Process Using Conical Dies

In this paper the effect of die angle, fluid pressure and axial force on loading paths were studied. In order to reduce the cost and time for the experimental work, ANSYS program is used for implementing the Finite Element Method (FEM), to get optimized loading paths to form a tube using double – cones shape die. Three double die angles θ (116˚ 126˚, 136˚), with three different values of tube outer diametres (40, 45, 50) mm were used. The tube length L_o and thickness t_o for all samples were 80 mm and 2 mm respectively. The most important results and conclusions that have been reached that had the highest wall thinning percentage of 26.8% with less corner filling is at tube diameter 40 mm and cone angle of (116^°) at forming pressure of 43 MPa with axial feeding 10 mm. However, the lowest wall thinning percentage was 6.9% with best corner filling at diameter 50 mm and cone were angle of (136^°) and forming pressure of 30 MPa with axial feeding 4.5 mm. Two wrinkles constituted during the initial stages of forming the tube with initial diameter of 40 mm where the ratio d⁄(t=20) (thick-walled tubes) for all die angles, while only one wrinkle is formed at the center for tubes diameter 45 and 50 mm (thin-walled tubes) . The difference in the location and number of wrinkles at the first stage of formation depends on the loading paths that has been chosen for each process, which was at the diameter 45 and 50 mm towards thin-wall cylinder deformation mode was uniaxial tension. The maximum wall thinning percentage was at the bulge apex for tube diameter 40 mm. But, the maximum wall thinning for tubes of diameters 45 and 50 mm was found at the two sides of the bulge apex .

Investigation on wrinkling behaviors of metal thin-walled tube in pulsating hydroforming with axial feeding

Pulsating tube hydroforming with axial feeding is an effective method to improve the forming performance of thin-walled tube. A beneficial wrinkle can make the tube wall thickness more uniform and create a greater bulging height during forming process. The method of expressing the degree of wrinkle with geometrical and mechanical criteria is applied to distinguish the wrinkle types, and thus, the wrinkles can be divided into beneficial ones and harmful ones based on the deformation wrinkle features with different forming parameters. The wrinkling behavior in tube pulsating hydroforming with axial feeding was investigated in this article by experimental study, numerical simulation and theoretical analysis. The results showed that loading parameters had great influence on formability and wrinkling behaviors and that the beneficial wrinkles could be identified and used effectively by controlling the relation of wrinkling degree and forming parameters. Furthermore, the evolution processes of wrinkling behaviors in tube-bulging experiment were observed, the characteristics of wrinkling in every stage were analyzed and the relationship between wrinkling degree and forming parameters was established in the experiment.

Hot Gas Forming of Aluminum Alloy Tubes Using Flame Heating

Hot metal gas forming (HMGF) is a desirable way for the automotive industry to produce complex metallic parts with poor formability, such as aluminum alloys. A simple hot gas forming method was developed to form aluminum alloy tubes using flame heating. An aluminum alloy tube was heated by a flame torch while the tube was rotated and compressed using a lathe machine and simultaneously pressurized with a constant air pressure. The effects of the internal pressure and axial feeding on expansion and wall thickness distribution were examined. The results showed that the proposed gas forming method was effective for forming aluminum alloy tubes. It was also indicated that axial feeding is a vital parameter to prevent reductions in wall thickness by supplying the material flow during the forming process.

Prediction of wrinkle types in tube hydroforming under pulsating hydraulic pressure with axial feeding

Wrinkling frequently occurs in tube hydroforming, resulting in an undesirable loss of quality and precision of the formed workpiece, and is generally regarded as a defect. However, wrinkling can also be utilised to improve the formability of tubular materials if it can be gradually reduced or even flattened in the follow-up tube hydroforming. For this reason, wrinkling is classified into two types—harmful wrinkle and useful wrinkle. In this paper, two prediction methods, geometry-based prediction method and mechanics-based prediction method, are proposed to predict the wrinkle type occurring in tube hydroforming under pulsating hydraulic pressure with axial feeding. Then, the corresponding tube hydroforming experiments are presented, which were carried out to validate the two proposed prediction methods by comparing the deformation and wrinkling behaviours. Finally, the characteristics of the two approaches are compared and discussed. The results indicate that the wrinkle type occurring in the present tube hydroforming experiments under pulsating hydraulic pressure with axial feeding could be predicted by both prediction methods, with the geometry-based prediction method providing more accuracy than the mechanics-based prediction method.

Loop Stiffness of Grinding Machine Developed for 450 mm Silicon Wafers

Increasing the wafer diameter from φ300 mm to φ450 mm is required to enhance semiconductor devices productivity. A high-stiffness rotary grinding machine equipped with water hydrostatic bearings was developed for a φ450 mm silicon wafer. The grinding machine has an upper structure consisting of a wheel spindle system and a lower structure consisting of a rotary worktable system. The spindle shaft creates both rotary and axial feeding motion. The upper and lower structures are clamped together rigidly by three kinematic couplings. A higher loop stiffness is required for the grinding machine because grinding the larger wafer requires a higher grinding force. This paper investigates the loop stiffness of the developed wafer grinding machine.

Research on Wrinkling Behavior in Tube Hydroforming with Axial Feeding

Tube hydroforming (THF) is one of metal forming technologies which has been widely used to manufacture complex hollow workpeices. In THF, a variety of failures may occur and one of them is wrinkling. But recent researches show that wrinkling may be used as a preforming process to improve the formability of tubes. In this paper, a new geometry-based wrinkling indicator is proposed to evaluate the wrinkling level in THF and the wrinkle evolution diagram (WED) based on the shape change of the wrinkles is presented to display the four-stage evolution of the useful wrinkles. The wrinkling levels in THF with axial feeding under various loading paths are predicted respectively via finite element simulation, the influence of loading paths on the wrinkling behavior is investigated, and the evolving stages of the useful wrinkles is revealed via the proposed WED. The results indicate that the proposed wrinkle indicator can distinctly evaluate the wrinkling level, the wrinkling level under pulsating loading path is higher than that under polygonal linear one and four-stage evolution of the useful wrinkles could be evidently demonstrated via the WED. Notation

Experimental Research and Numerical Simulation Analysis for Hydroforming of an Instrument Panel Beam

Due to the apparent advantages of tube hydroforming technology in reducing weight and energy consumption, and saving material and cost, it has been applied in the production of instrument panel beam. By constructing the FEM models of instrument panel beam, three numerical simulation schemes are designed according to the matching relationship between internal pressure load and axial feeding. Then the simulation results are given and compared with the experimental data. The simulation and experimental analysis indicate that the optimal matching relationship between internal pressure load and axial feeding influences hydroforming result of parts. It provides a theoretical reference for the design of hydroforming process and its die, and the setting of critical process parameters.

Determination of Forming Limit Curves of Steel Pipes for Hydroformability Evaluation

The aims of this research are to establish the forming limit curve (FLC) of tubular material low carbon steels commonly used in Thai industry, verify these FLCs with real part forming experiments and compare these experimentally obtained FLCs against analytical ones available in FEA software database. A self-designed bulge forming apparatus of fixed bulge length and a hydraulic test machine with axial feeding are used to carry out the bulge tests. Loading paths resulting to linear strain paths at the apex of the bulging tube are determined by FE simulations in conjunction with a self-compiled subroutine. These loading paths are used to control the internal pressure and axial feeding punch of the test machine. In this work a common low carbon steel tubing grade STKM 11A, with 28.6 mm outer diameter and 1.2 mm thick is studied. Circular grids are electro chemically etched onto the surface of tube samples. Subsequently, the tube samples are bulge-formed. The forming process is stopped when a burst is observed on the forming sample. After conducting the bulge tests, major and minor strains of the grids located beside the bursting line on the tube surface are measured to construct the forming limit curve (FLC) of the tubes. The forming limit curves determined for these tubular materials are put to test in formability evaluations of test parts forming in real experiment. It was found that the tool geometry can keep the strain ratio constant is not dependent on the thickness but only on OD of the tube, as in equations L=OD and rd=(15xOD)/25.4. The experimen-tal FLDs have predicted failures in forming process consistently with the real experiments. The ex-perimentally obtained forming limit curves (determined following STKM 11A) differ from empiri-cal one (from FEA software) and analytical one by about 0.02339 and 0.15736 true strain respec-tively at FLD0, the corresponding plane strain values.