Upper bound analysis of differential velocity sideways extrusion process for curved profiles using a fan-shaped flow line model

An analytical model for predicting the shapes of rectangular bars with variable curvatures along their lengths through a novel forming method, differential velocity sideways extrusion (DVSE), previously proposed by the authors, has been developed on the basis of the upper bound method. A new flow line function was presented to describe its deformation field. The plastic deformation zone (PDZ) was assumed to be fan-shaped, where the trajectory of the material flow within the PDZ had an elliptic shape. The proposed continuous flow line function was validated using finite element simulations. The flow patterns, extrusion pressure, curvature, and effective strain predicted by the analytical solutions agreed well with modelling results. Compared to the classical discontinuous simple shear model of channel angular extrusion (CAE) with a 90° die, the new approach was shown to predict the effective strain more closely

Investigation of die designs on welding quality and billet material utilisation for multi-container extrusion of wide stiffened aluminium panels

Wide stiffened aluminium panels are extensively used in aerospace, marine, and civil industries due to their light-weight structure and high stiffness. In this paper, a wide stiffened aluminium panel was manufactured using the principle of the multi-container extrusion, and a comparative study was conducted using two different die designs at the same extrusion condition, in which metal flow behaviour, extrusion force, welding quality, and billet material utilisation have been investigated numerically. Additionally, the effect of extrusion speed on the extrusion process was evaluated with the modified design. It was shown that, compared with the initial design, better metal flow behaviour can be obtained in the modified design. Multi-container extrusion greatly reduces the extrusion force, and the modified design results in a more uniform extrusion force for each extrusion container. The total extrusion force for the modified design is slightly higher compared with the initial die design, due to the increased friction in the upper die channels and the second-step welding chamber. Besides, the modified design of the multi-container extrusion can obtain better welding quality evaluated by different welding criteria, and the extrusion speed has a minor effect on the welding quality. The most notable feature is that the modified design greatly improves the material utilisation, which could save 39.5% material compared to the initial design

Investigation of the mechanisms on the abnormal features observed in thermal-mechanical testing of AA6061 under extrusion conditions

Hot extrusion is the most common forming technology for aluminium alloy AA6061 due to its good extrudability, and thus it is important to study its high-temperature deformation characteristics. In this study, three abnormal features are observed in thermal-mechanical testing under extrusion conditions of AA6061 specimens from one billet: 1) Two types of specimens with grey-coloured surface or silver-coloured surface appear after solution heat treatment (SHT); 2) The silver-coloured specimens show orange peel surface after hot compression tests; 3) The silver-coloured specimens have lower flow stresses than the grey-coloured specimens. This paper investigates the mechanisms behind the above abnormal features. A laser scanning confocal microscope is employed to examine the surface roughening, and electron back scatter diffraction is used to characterise microstructural changes. It is found that the main causes of the above behaviour are due to different initial grain morphologies and the evolution of dislocation density after SHT. The silver-coloured specimens initially have smaller columnar grains which undergo recrystallisation and extensive growth during SHT, and the dislocation density decreases significantly, leading to orange peel defect and low flow stress during compression tests, respectively. The grey-coloured specimens have larger columnar grains. After SHT, some grains undergo recrystallisation, but others still maintain the shape of the large columnar grains, and the dislocation density does not change significantly, resulting in surface oxidation with smooth surface after thermal-mechanical testing and 10–25 MPa (30–50%) higher flow stress compared to the silver-coloured specimens in compression tests

The application of a shock wave model to some industrial bubbly fluid flows

An extended numerical model for bubbly oil/gas flows, using a more complete formulation than previously reported, is applied to five situations of industrial interest. Pressure waves propagating due to pressure differences caused by the sudden blocking of a pipeline carrying bubbly fluid, the bursting of a valve separating two regions of different pressures, and the opening and closing of a valve in a pipeline are simulated. In addition, the movement of an end plug to a bubbly flow pipeline when it fails is also modelled. In each case it is found that over-pressures, relative to the applied pressure difference, occur in the propagating pressure waves. The magnitude of the over-pressure increases with the applied pressure difference and appears close to, but not at, the boundary where the pressure difference is first applied. However, gradual application of the pressure difference reduces the maximum over-pressure. In the case of the sudden blockage of a pipeline, the over-pressure also varies with the initial flow velocity and has a greater magnitude than the predicted pressure rise calculated using only the fluid compressibility. Therefore, standard estimates for pressure rises in compressible fluids may be inappropriate for use in designing pipelines carrying bubbly fluids. Finally, the end plug simulations show that the plug accelerates quickly after the initial failure but then levels off, and that the final velocity of the end plug can be readily calculated using the numerical model

Review of common hydrogen storage tanks and current manufacturing methods for aluminium alloy tank liners

With the growing concern about climate issues and the urgent need to reduce carbon emissions, hydrogen has attracted increasing attention as a clean and renewable vehicle energy source. However, the storage of flammable hydrogen gas is a major challenge, and it restricts the commercialisation of fuel cell electric vehicles (FCEVs). This paper provides a comprehensive review of common on-board hydrogen storage tanks, possible failure mechanisms and typical manufacturing methods as well as their future development trends. There are generally five types of hydrogen tanks according to different materials used, with only Type III (metallic liner wrapped with composite) and Type IV (polymeric liner wrapped with composite) tanks being used for vehicles. The metallic liner of Type III tank is generally made from aluminium alloys and the associated common manufacturing methods such as roll forming, deep drawing and ironing, and backward extrusion are reviewed and compared. In particular, backward extrusion is a method that can produce near net-shape cylindrical liners without the requirement of welding, and its tool designs and the microstructural evolution of aluminium alloys during the process are analysed. With the improvement and innovation on extrusion tool designs, the extrusion force, which is one of the most demanding issues in the process, can be reduced significantly. As a result, larger liners can be produced using currently available equipment at a lower cost

Review and Analysis of Manufacturing Curved Extrusion Components

Curved aluminium alloy extrusion profiles have been widely used in many engineering applications due to their high-strength and high-stiffness to weight ratios. The curved extrusion profiles could be formed in several forming processes, such as roll-bending, stretch-bending and extrusion bending. This paper presents the review and analysis of their manufacturing processes and includes two parts. The first part is the review of manufacturing methods for producing curved extrusion components. The current cold bending processes can be grouped into three typical operations according to their characteristics, i.e., 2-point bending (cantilever bending), 3-point bending and stretch-bending. Key features of the operations, the main advantages, disadvantages and typical defects in the bending processes are summarised and analysed. The second part is the stress and strain analysis for the cold stretch-bending and pure bending of extrusion profiles. Particularly, the stress-strain distributions through the thickness of extrusion profiles, together with the neutral axis changes, are graphically illustrated and analysed. Further stress-strain analysis has been carried out on the “inner most” and “outer most” bending profile surfaces against the bending angle. Lastly, suggestions have been given on the future research directions, and the selection of the current existing processes for manufacturing defect free components.</p

A data-informed review of scientific and technological developments and future trends in hot stamping

As a promising solution to the growing demand for lightweighting, hot stamping has gained considerable applications in the automotive industry. Over the past few decades, the market for hot stamping has experienced explosive growth, with ongoing advancements offering potential for further expansion of its applications. This paper provides a historical overview of hot stamping alongside an in-depth analysis of future trends. Scientific publications, patents and industrial applications of hot stamping are systematically reviewed, with major developments in materials, processes, tools, and other relevant aspects being highlighted. Through data analysis, the current state of hot stamping is comprehensively depicted, and the trends in the development of hot stamping are revealed. Additionally, the future of extending hot stamping technologies to a broader range of materials is discussed, with suggestions furnished from both academic and industrial perspectives

Experimental studies of the efficient use of flexible tool in creep age forming

Application of a newly developed flexible forming tool to creep age forming (CAF) process has been investigated in this study. The flexible tool mainly consists of sparsely distributed forming pins, splines and elastomeric sheet. The effect of key factors related to the forming tool on the shape of the formed parts has been studied through various CAF experiments. The key factors investigated in this study include: the interval between forming pins, the arrangement of pins, the accuracy requirement of pin height and the material of splines. It has been found that reducing the interval between pins can efficiently smooth the shape of CAFed plates. The feasibility of asymmetric arrangement of pins has been proven, which can decrease the number of used pins, reduce tool weight, and increase efficiency. The forming results are very sensitive to the pin height, thus the experimental set-up error should be carefully controlled. Additionally, compared with mild steel, spring steel is more suitable as the spline material