Narrow Results

A simplified one-step inverse analysis of sheet metal forming is a suitable tool to simulate the bending forming since the deformation path of bending forming is an approximately proportion one. A fast spring-back simulation method based on one-step analysis is proposed. First, the one-step inverse analysis is applied to obtain the stress distribution at the final stage of bending. Then, the unloading to get a spring back is simulated by LS-DYNA implicit solver. These processes are applied to the unconstrained cylindrical bending and the truck member rail. The spring-back and member rail widths at the several key sections are compared with experimental ones. It is well demonstrated that the proposed method is an effective way to predict the spring-back by unloading after bending process.

Springback is a problem in the manufacture of a variety of automotive components. To determine springback, it is necessary to know the strength of the material after plastic deformation and the slope of the unloading curve (i.e. the unloading modulus). Prior investigations have shown that the unloading modulus for steels after plastic deformation has a slope that is lower than the normally accepted value for Young's modulus. Previous studies on the slope of the unloading curve were after uniaxial tensile plastic deformation. In the present study, the unloading modulus for an aluminum killed drawing quality (AKDQ) steel was evaluated after both uniaxial and near plane strain deformation. A tube hydroforming system was used for near plane-strain deformation. The average unloading modulus following uniaxial deformation for the AKDQ steel is approximately 168 GPa. The average unloading modulus for the circumferential stress component after near plane-strain deformation is lower than after uniaxial deformation. For a given amount of overall plastic deformation, the axial component of the unloading modulus is greater than the circumferential component, and with increased plastic strain, the unloading modulus for both components decreases. These results demonstrate that the components of the unloading modulus are dependent on the strain path of the prior plastic deformation.

A new incremental sheet forming technology with local heating is proposed to form lightweight hard-to-form sheet metals such as aluminum-magnesium alloy (JIS A5083) sheet or magnesium alloy (JIS AZ31) sheet. The newly designed forming tool has a built-in heater to heat the sheet metal locally and increase the material ductility around the tool-contact point. Incremental forming experiments of A5083 and AZ31 sheets are carried out at several tool-heater temperatures ranging from room temperature to 873K using the new forming method. The experimental results show that the formability of A5083 and AZ31 sheets increases remarkably with increasing local-heating temperature. In addition, springback of formed products decreases with increasing local-heating temperature. The developed incremental sheet forming method with local heating has great advantages in not only formability but also shape fixability. It is an effective forming method for lightweight hard-to-form sheet metal for small scale productions.

High-strength galvanized steel has the advantages of high strength, lightweight and high reliability. However, there are many defects in the forming process, especially the springback, which seriously affects the forming quality. To improve the forming quality of high-strength galvanized steel in rolling forming, a three-dimensional finite element analysis model of a hat-shaped section roll forming process was built by software ABAQUS. The hat-shaped section with a single-layer flange was simulated with three different base-level roll forming methods. The base-level roll forming method was used to simulate and experiment the hat-shaped section with double-layer flanges. This paper provided a method to precisely control the springback angle of high-strength galvanized steel and improved its forming quality.

Precision guided projectiles (PGPs) experience severe shock loads during launch emanating from the propellant gases inside the barrel and the surrounding air. The complex flow environment that exists within the confined space of the barrel and at muzzle exit is greatly influenced by the supersonic speed of the projectile, the compressibility of the air, and the rapid state transition of the projectile from the confined volume of the barrel to the surrounding free-space. In our earlier efforts (X. W. Yin, P. Verberne and S. A. Meguid, Multiphysics modelling of the coupled behaviour of precision-guided projectiles subjected to intense shock loads, Int. J. Mech. Mater. Des.10 (2014) 439–450; P. Verberne and S. A. Meguid, The coupled behaviour of precision-guided projectiles subject to propellant induced shock loads using multiphysics analysis, in 8th Int. Conf. Mech. Mater. Des. (2019); P. Verberne and S. A. Meguid, Dynamics of precision guided projectile launch: Fluid-structure interaction, Acta Mech. (2020)) examined the fluid–solid interaction problem. In this paper, we expand our earlier effort by examining the underlying mechanisms associated with the solid–solid interaction between the projectile and the barrel walls that severely govern the survivability of the embedded electronic systems (EES). This was achieved by conducting comprehensive finite element (FE) simulations of the dynamics of the entire launch process of a projectile accounting for the intense combustion pressures of the propellant, the large accelerations experienced during the launch and the induced shock waves. Our FE simulations successfully capture the interaction of the projectile with the barrel. Our work reveals that frictional forces due to contact inside the barrel significantly affect the projectile’s acceleration response at muzzle exit. Immediately following muzzle exit, the rapid reduction of the frictional forces inside the barrel results in a rapid increase of the projectile acceleration followed by a rapid reduction due to the free expansion of the propellant gases and air drag, leading to large acceleration fluctuations.

Creep age forming applications of 2xxx series aluminum alloys are much less than 7xxx series, which is due to the difficult control of material property and microstructure at the end of forming. Based on a four-point-bend forming tools, effects of pre-stretching on the springback, mechanical property and microstructure of 2124 aluminum alloy in creep age forming were investigated. The springback appears a ‘V’ type variation feature owing to the competition between the creep-acceleration effect of pre-stretching and the diminishing sheet thickness. And the strength property curves of the 2124 aluminum alloy present a bimodal variation characteristic with increasing pre-stretching. The first peak is related to the finer and denser intragranular precipitates caused by the introduce of pre-deformation, and the second peak is attributed to the obvious elongated grains along the tensile direction by the excessive deformation. The results of the verification test indicated that choosing a proper pre-deformation can achieve coupling control of the forming target and the material property in creep age forming process, and the recommendatory pre-stretching range for the creep age forming of 2124 aluminum alloy is 1.5%∼2.5%.

In this paper, the springback of the aluminum alloy AA7075 under hot stamping conditions was characterized under V-bending conditions. And the influence of the initial blank temperature and the radius of the punch fillet on springback of V-shape parts was studied. The results show that the springback angle of V-shaped parts decreases rapidly with the increase of initial temperature of the sheet, the minimum springback angle at 400 °C is 0.15°, which is reduced by 96.61 % compared with that at room temperature. The springback angle increases with the radius of the punch. The results of which were used to verify finite elements simulations of the processes in order to analyze the reason of springback. And finite element simulation results and experimental results have a good agreement.

Commercial aluminium alloys, AA6082 and AA7075, offer high stiffness to density as well as strength to density ratios, and are suitable for structural sheet-metal fabrication. The automotive industry tends to favour these aluminium alloys over steel for a reduction in the weight of components. However, the application of these alloys has been impeded by their poor formability at ambient temperatures. Therefore, a traditional hot stamping technique was employed to form AA6082 and AA7075, to study the springback of a U-Shape workpiece by conducting experiments at varying forming temperatures and forming speeds. It was found that springback was reduced at elevated temperatures compared to that at ambient temperatures, particularly a 16° (90%) reduction for AA7075 component. Increasing forming speed can reduce the level of springback as well, with an observed 15% reduction when comparing slow and fast forming.

A simplified one-step inverse analysis of sheet metal forming is a suitable tool to simulate the bending forming since the deformation path of bending forming is an approximately proportion one. A fast spring-back simulation method based on one-step analysis is proposed. First, the one-step inverse analysis is applied to obtain the stress distribution at the final stage of bending. Then, the unloading to get a spring back is simulated by LS-DYNA implicit solver. These processes are applied to the unconstrained cylindrical bending and the truck member rail. The spring-back and member rail widths at the several key sections are compared with experimental ones. It is well demonstrated that the proposed method is an effective way to predict the spring-back by unloading after bending process.

Springback is a problem in the manufacture of a variety of automotive components. To determine springback, it is necessary to know the strength of the material after plastic deformation and the slope of the unloading curve (i.e. the unloading modulus). Prior investigations have shown that the unloading modulus for steels after plastic deformation has a slope that is lower than the normally accepted value for Young's modulus. Previous studies on the slope of the unloading curve were after uniaxial tensile plastic deformation. In the present study, the unloading modulus for an aluminum killed drawing quality (AKDQ) steel was evaluated after both uniaxial and near plane strain deformation. A tube hydroforming system was used for near plane-strain deformation. The average unloading modulus following uniaxial deformation for the AKDQ steel is approximately 168 GPa. The average unloading modulus for the circumferential stress component after near plane-strain deformation is lower than after uniaxial deformation. For a given amount of overall plastic deformation, the axial component of the unloading modulus is greater than the circumferential component, and with increased plastic strain, the unloading modulus for both components decreases. These results demonstrate that the components of the unloading modulus are dependent on the strain path of the prior plastic deformation.

A new incremental sheet forming technology with local heating is proposed to form lightweight hard-to-form sheet metals such as aluminum-magnesium alloy (JIS A5083) sheet or magnesium alloy (JIS AZ31) sheet. The newly designed forming tool has a built-in heater to heat the sheet metal locally and increase the material ductility around the tool-contact point. Incremental forming experiments of A5083 and AZ31 sheets are carried out at several tool-heater temperatures ranging from room temperature to 873K using the new forming method. The experimental results show that the formability of A5083 and AZ31 sheets increases remarkably with increasing local-heating temperature. In addition, springback of formed products decreases with increasing local-heating temperature. The developed incremental sheet forming method with local heating has great advantages in not only formability but also shape fixability. It is an effective forming method for lightweight hard-to-form sheet metal for small scale productions.

Springback is one of the main defects affecting the forming precision of 3A21 thin-walled rectangular tube in rotary-draw bending process. The material hardening mode and Young's modulus influence the springback prediction greatly, while the Young's modulus changes versus plastic strain rather than a constant. Hence, the variation of the Young's modulus has been taken into account in the springback analysis to improve the springback prediction precision. Based on Von-Mises yield function and Swift isotropic hardening model, a new material constitutive model is developed considering the variation of Young's modulus. Then, a springback prediction model is established using this new constitutive law. Furthermore, the reliability of the model is validated experimentally. Comparisons between simulation results and experimental data show that the prediction model with the new constitutive law is able to predict the springback significantly more accurately.

This paper deals with the optimization of process parameters in high strength sheet metal forming in order to reduce the springback effects after forming. The optimum parameters including holder force, friction coefficient and die radius which influence springback are studied through numerical simulation and orthogonal experiment. For predicting the springback accurately, the uniform experiment was used and BP neural network model was built up. The results show that springback of the front side rail is seriously influenced by these parameters, and the springback under the case of giving a group of process parameters can be predicted by the BP neural network model.

Weld line motion is one of the difficulties in High Strength Steel Tailor Welded Blanks (HSSTWBs) forming. Studies show that an appropriate process design can reduce weld line movement and improve the HSSTWB formability. In this paper, three process schemes based on different binders were studied using Dynaform software in order to produce a qualified B-pillar. The first method employed a common binder with a constant blank holder force. The second method used a segmented binder with different constant blank holder forces applied at each part. The third method applied a stepped binder with a constant gap between die and binder. Different binders lead to different stress-strain state and metal flow. Simulations demonstrated that the last two methods can effectively improve weld-line movement, and a stepped binder is better at reducing material thinning and springback. Finally, the third process scheme was carried out to obtain a good quality B-pillar.

A springback is become a significant factor inhibition in precision part forming of magnesium alloy sheet material. There are many factors that affect springback such as blank holding force, punch speed, material thickness, material strength, die roughness and clearance during the hot forming of magnesium alloy sheet. The factors which effect on springback have been not systematized until now. Almost researcher and company have been depended on trial and error or experimental until now. Therefore, investigation of factors that affect springback is needs to optimize and systemize. In this study, we conduct a study on the effect of punch radius, die radius and material anisotropy on the springback for AZ31 Mg alloy sheet.

To solve these problems such as easily springback and hardly controlling the loading direction when arched aircraft skin is formed, stretch forming of steel plate with aluminium alloy 2024 was simulated by the finite element software Abaqus, and the shape of the stretch forming die was the arc with radius 350mm. The influence of process parameters, such as stretch forming track and dangling length on forming of arched aircraft skin was researched, and the reasonable range of stretch forming length track and dangling length was given. The results have significance for research the forming law of arched aircraft skin.