Chun-feng Li

Numerical Modeling and Deformation Analysis for Electromagnetically Assisted Deep Drawing of AA5052 Sheet

Electromagnetic forming (EMF) is a high-velocity manufacturing technique which uses electromagnetic (Lorentz) body forces to shape sheet metal parts. One of the several advantages of EMF is the considerable ductility increase observed in several metals, with aluminum featuring prominently among them. Electromagnetically assisted sheet metal stamping (EMAS) is an innovative hybrid sheet metal processing technique that combines EMF into traditional stamping. To evaluate the efficiency of this technique, an experimental scheme of EMAS was established according to the conventional stamping of cylindrical parts from aluminum and the formability encountered was discussed. Furthermore, a ”multi-step, loose coupling” numerical scheme was proposed to investigate the deformation behaviors based on the ANSYS Multiphysics/LS-DYNA platform through establishing user-defined subroutines. The results show that electromagnetically assisted deep drawing can remarkably improve the formability of aluminum cylindrical parts. The proposed numerical scheme can successfully simulate the related Stamping-EMF process, and the deformation characteristics of sheet metal reflect experimental results. The predicted results are also validated with the profiles of the deformed sheets in experiments.

Multi-pass spinning of thin-walled tubular part with longitudinal inner ribs

Based on the process experiments, micrography analysis was dedicated to advancing the understanding of plastic flow of the metal in backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Micrography analysis reveals that severe plastic deformation leads to grain refinement, grain orientation and grain flow line of the spun part. Based on rigid-plastic finite element method, DEFORME3D finite element code was used to simulate and analyze multi-pass backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Finite element simulation results involve the distributions of the strain, the shape variation of the inner ribs as well as the prediction of the spinning loading.

Effects of coil length on tube compression in electromagnetic forming

The effects of the length of solenoid coil on tube compression in electromagnetic forming were investigated either by theory analysis or through sequential coupling numerical simulation. The details of the electromagnetic and the mechanical models in the simulation were described. The results show that the amplitude of coil current waveform and the current frequency decrease with the increase of the coil length. And the peak value of magnetic pressure is inversely proportional to the coil length. The distribution of the magnetic force acting on the tube is inhomogeneous while the tube is longer than the coil. The shortened coil length causes the increases of the maximum deformation and energy efficiency. The numerically calculated result and the experimental one of the final tube profile are in good agreement.

Magnetic pulse joining of aluminum alloy–carbon steel tubes

Abstract The magnetic pulse joining (MPJ) between 3A21 aluminum alloy and steel 20 tubes was experimentally investigated with a solenoid coil assisted by a field shaper. The mechanical properties and microstructure of MPJ joints were tested and observed. The results show that the metallurgical joints can be obtained at a voltage of 15 kV, a radial gap of 1.2–1.4 mm, and a slope angle of 3°–7° in the lapping area. The joint comprises a transition zone with different widths, two matrix metals and two interfaces between the zone and the two metals. The interface presents a typical wavy pattern and mutual diffusion of Fe and Al elements happens in the zone. The transition zone is composed of Fe–Al intermetallics, micro cracks and micro pores. The microhardness of the transition zone is much higher than that of the matrix metals.

Microstructure and mechanical properties of Ti6Al4V powder compacts prepared by magnetic pulse compaction

Abstract Ti6Al4V powder compaction was performed by using magnetic pulse compaction in air at 200 °C. Effects of process parameters such as voltage, capacitance, discharge times on the microstructure, compressive strength, hardness and relative density of compacts were investigated. The experimental results show that the relative density, hardness and compressive strength of compacted specimens increase with increasing voltage. In addition, the relative density and compressive strength of compacted specimens increase with the augmentation of capacitance in the range investigated. The relative density increases, the hardness firstly increases and then tends to be a fixed value; and the compressive strength firstly increases and then decreases from one to five times compaction. Both values of the hardness and compressive strength reach the maxima of HRA 69.1 and 1 062.31 MPa, at three times compaction, respectively. There are pores in and between particles.

Micro bulging of thin T2 copper sheet by electromagnetic forming

Electromagnetic micro bulging experiments on T2 copper were achieved in order to find the effects that different voltages and depths of mold work on deformation characters. Laser scanning confocal microscope and contourgraph were used to study the effects of electromagnetic forming parameters such as voltage and die depth on material. Results show that width and depth of micro channel increase with the increases of voltage with a certain die depth, moreover, forming depth reaches the maximum at 7 500 V. And then rebound emerges and forming depth decreases. Forming depth and width of channel increase with the decease of die depth at a certain voltage; and forming depth reaches maximum at 0.5 mm of die depth. Therefore, rebound is weakened and the traces caused by bad exhaust disappears gradually, and surface roughness decreases simultaneously in electromagnetic bulging experiments.

Effect of hydrogen content and stress state on room-temperature mechanical properties of Ti-6Al-4V alloy

Abstract This work aims to investigate the effects of hydrogen content (in the range of 0%–0.5%, mass fraction) and stress state (tension and compression) on the room-temperature mechanical properties of Ti-6Al-4V alloy through mechanical properties tests. The effects of hydrogen content on microstructure evolution of Ti-6Al-4V alloy is also examined by optical microscopy, X-ray diffractometry, transmission electron microscopy and scanning electron microscopy. The results show that hydrogen content and stress state have important effects on the room-temperature mechanical properties of Ti-6Al-4V alloy. Tensile strength and ultimate elongation decrease with increasing the hydrogen content, while compressive strength and ultimate reduction are improved after hydrogenation. The reason is that the intergranular deformation dominates at the state of tension. Hydrogen atoms in solid solution and hydrides at grain boundaries increase with increasing the hydrogen content and they can promote the initiation and propagation of cracks along grain boundaries. While the intragranular deformation dominates at the state of compression. The plastic beta phase and hydrides increase with increasing the hydrogen content and they improve the ultimate reduction and compressive strength.

Equal channel angular extrusion of NiTi shape memory alloy tube

Abstract As a new attempt, equal channel angular extrusion (ECAE) of nickel–titanium shape memory alloy (NiTi SMA) tube was investigated by means of process experiment, finite element method (FEM) and microscopy. NiTi SMA tube with the steel core in it was inserted into the steel can during ECAE of NiTi SMA tube. Based on rigid-viscoplastic FEM, multiple coupled boundary conditions and multiple constitutive models were used for finite element simulation of ECAE of NiTi SMA tube, where the effective stress field, the effective strain field and the velocity field were obtained. Finite element simulation results are in good accordance with the experimental ones. Finite element simulation results reveal that the velocity field shows the minimum value in the corner of NiTi SMA tube, where severe shear deformation occurs. Microstructural observation results reveal that severe plastic deformation leads to a certain grain orientation as well as occurrence of substructures in the grain interior and dynamic recovery occurs during ECAE of NiTi SMA tube. ECAE of NiTi SMA tube provides a new approach to manufacturing ultrafine-grained NiTi SMA tube.

Effect of tube size on electromagnetic tube bulging

The commercial finite code ANSYS was employed for the simulation of the electromagnetic tube bulging process. The finite element model and boundary conditions were thoroughly discussed. ANSYS/EMAG was used to model the time varying electromagnetic field in order to obtain the radial and axial magnetic pressure acting on the tube. The magnetic pressure was then used as boundary conditions to model the high velocity deformation of various length tube with ANSYS/LSDYNA. The time space distribution of magnetic pressure on various length tubes was presented. Effect of tube size on the distribution of radial magnetic pressure and axial magnetic pressure and high velocity deformation were discussed. According to the radial magnetic pressure ratio of tube end to tube center and corresponding dimensionless length ratio of tube to coil, the free electromagnetic tube bulging was studied in classification. The calculated results show good agreements with practice.

Influence of hydrogen content on room temperature compressive properties of Ti-6Al-4V alloy at high strain rate

Abstract Electromagnetic forming tests were done at room temperature to reveal the influence of hydrogen content on the compressive properties of Ti–6Al–4V alloy at high strain rate. Microstructure was observed to reveal the mechanism of hydrogen-enhanced compressive properties. The experimental results indicate that hydrogen has favorable effects on the compressive properties of Ti–6Al–4V alloy at high strain rate. Compression of Ti–6Al–4V alloy first increases up to a maximum and then decreases with the increase of hydrogen content at the same discharge energy under EMF tests. The compression increases by 47.0% when 0.2% (mass fraction) hydrogen is introduced into Ti–6Al–4V alloy. The optimal hydrogen content for cold formation of Ti–6Al–4V alloy under EMF was determined. The reasons for the hydrogen-induced compressive properties were discussed.