Forming Of Aluminum Alloy Sheet Research Articles

Simple Contact Sensor for Material on Die in Sheet Hydroforming

A simple material contact sensor on the forming tool was devised for sheet hydroforming. The applicability was investigated for the shallow forming of aluminum alloy sheet. A flat bottom axisymmetric die or a conical one was used. An antistatic electric tape was used as contact sensor. It is flexible and attached to the die cavity in the radial direction. Electrical resistance of the tape between the center and the contact position of the material changes as the forming progresses. The change in voltage of the resistance part corresponding to the contact length was captured continuously. The strain at the center of the circular test piece was also continuously measured using a strain gage for large deformation. A short contact length was captured for the flat bottom die, since the test piece deforms into a dome shape, and the tip of the dome contacts to the center of the die cavity. On the other hand, the captured length was longer in the forming with the conical die. The repetitive separation and contact motion of the test piece to the die in impact forming due to the impulsive water pressure was successfully captured by the contact sensor. The accuracy was relatively coarse due to that the diameter of the die cavity was small. However, it was found that the simple contact sensor can be applied to evaluate the deformation behavior of the material. The measured maximum strain of the test piece was larger in impact forming, and the strain concentration occurred. This may be due to the negative strain rate sensitivity of the material.

Influence of elevated surface temperature on the formability in cold forming of aluminum alloy sheets

In recent decades, deep drawing has been widely used in the automotive industry for producing lightweight car body components of 5xxx and 6xxx aluminum alloys. Although sheets of these alloys are usually deep-drawn at room temperature, heat generated by friction and plastic deformation may locally increase the surface temperature of the drawing tools during the serial production of components. Therefore, this work investigates the influence of elevated surface temperatures of the tool on the formability of commercial hotmelt-lubricated 1.5 mm-thick EN AW-5182 and EN AW-6016-T4 sheets. Deep drawing experiments were performed at different constant surface temperatures between room temperature (RT) and 80 °C using a cross-shaped tool with open die. With increasing surface temperature, the maximum drawing depth – that was considered as indicator for the formability – decreased by about 21 % and 28 % for EN AW-6016-T4 and EN AW-5182, respectively. Tribological experiments performed using a pin-on-plate tribometer confirmed this trend. The results clearly showed that the coefficient of friction (COF) between the sheet and the tool significantly increase at elevated surface temperature; the most notable increase of the COF occurred between 40 °C and 60 °C.

Numerical Simulation and Experimental Research on Multi-Point Forming of Aluminum Alloy Sheets Based on Ultrasonic Vibration

In this study, the multi-point plastic forming of 2024-O aluminum alloy sheets is the research object, ultrasonic vibration-assisted forming is applied in the stamping process, a combination of ABAQUS/EXPLICITE numerical simulation and theory is used, and multi-point forming experiments are performed to verify the research. In the process of multi-point forming, the influence of ultrasonic vibration on the plastic deformation and springback of sheet metal has inspired a new idea and method for multi-point forming of sheet metal. This paper presents the following: the basic theory of multi-point stamping and ultrasonic vibration-assisted metal sheet plastic forming; a comparison of the material parameters of the multi-point stamping method with and without ultrasonic vibration; the influence of different times on the results; the changes in parameters such as stress and strain at different frequencies; and the effect of its springback.

A review of electrically assisted heat treatment and forming of aluminum alloy sheet

A review of electrically assisted heat treatment and forming of aluminum alloy sheet

Electromagnetic attractive forming of aluminum alloy sheets utilizing a low-frequency half-wave current

ABSTRACT The generation and optimization of attractive force between the coil and the workpiece is of significance for expanding the application of electromagnetic forming. In this work, a method using a low-frequency half-wave current is proposed to improve the attractive force, and to achieve a high-performance attractive forming. To verify the effectiveness of this method, an RLC circuit with a thyristor switch is introduced to generate the half-wave current, and the deformation behavior of an AA1060-H24 sheet is analyzed. According to both numerical and experimental investigations, it is demonstrated that the aluminum alloy sheet can be efficiently attracted toward the coil surface with a maximum deformation of more than 6 mm after a single discharge. On this basis, a series of simulations and experiments are carried out to clarify the effects of the discharge energy and current frequency on the attractive forming process. It is found that under the same forming depth, the required discharge energy and coil temperature rise for a smaller capacitance (1280 μF) can be decreased by almost 35% and 50%, respectively, compared to that for a larger capacitance (2880 μF). The obtained results are of certain value to promote the development of electromagnetic attractive forming.

Simulation Analysis of the Electromagnetic Force Distribution and Formability Parameters for Sheet Metal Electromagnetic Bulging Using a New Magnetic Field Shaper

While electromagnetic forming of aluminum alloy sheet has gained several advantages, the uneven radial deformation of the sheet is still one of the main drawback of this technology that calls for reliable and cost-effective solution. Aiming at this point, this paper presents an electromagnetic bulging system equipped with a new magnetic field shaper placed between the driving coil and the object sheet to modulate the distribution of the induced eddy current in the sheet, and hence regulating the distribution of the electromagnetic force to achieve more uniform deformation. A finite element electromagnetic-structure 2D coupling model simulating this process is developed and the effects of workpiece geometry and deformation speed on the circuit, magnetic field and structure field are considered. The coupling between the electric circuit and magnetic field; magnetic field and workpiece deformation is realized to simulate the actual system of thin plate electromagnetic bulging. The performance of the proposed system is compared with that of the traditional system through investigating the profiles of the induced eddy current, electromagnetic force and forming effect. Simulation results show that the uniformity of sheet metal forming is improved by using the proposed magnetic field shaper, and the maximum uniform deformation area is increasing from 32.1 mm to 73.8 mm, which stimulates more industrial applications of sheet metal electromagnetic forming.

Forming of aluminum alloy sheet to non-axisymmetric double-skin structure

Forming of aluminum alloy sheet to non-axisymmetric double-skin structure

Parametric Optimization of Robot-based Single Point Incremental Forming Using Taguchi Method

Sheet metals forming process is widely used in consumer and industrial products. However, the conventional sheet metal forming has low flexibility and product quality. It also prolongs the time-to-market in producing prototype products that required low costs. Single point incremental forming (SPIF) is one of relatively new sheet metal forming process. The increase interest in new techniques for forming processes and the usage of robotics in the industry has created more researches on the SPIF. Robot-based SPIF is a method of deforming a sheet metal to create designed workpieces by utilising a forming tool that attached to an industrial robot. In this present work, an optimization study for combination of process parameters in robot-based single point incremental forming of aluminum alloy sheet was experimentally investigated using Taguchi method to achieve an excellent surface roughness. A number of forming experiments were conducted using the L18 orthogonal array. Analysis of Variance (ANOVA) was used to identify the most significant process parameters affecting the surface roughness. The results analysis indicates that the optimum process parameters for surface roughness are obtained as 0.3 mm of step size, 150 mm/s of robot speed and 45 degree of wall angle. The most significant process parameter is step size and followed by robot speed. The study revealed the surface quality could be improved by proper selection of process parameters.

A Springback Prediction Model for Warm Forming of Aluminum Alloy Sheets Using Tangential Stresses on a Cross-Section of Sheet

Warm U-draw bending tests were performed on a 5182 aluminum alloy under isothermal and non-isothermal conditions, and the amounts of springback under the corresponding conditions were measured. Finite element method analyses were then conducted to calculate the tangential stress distribution on the cross-section of the sheet during the warm forming process. It was found that the experimentally measured springback values were proportionally related to the differences in the amounts of tangential stresses at the top and bottom layers of the sheet section. A functional model that can account for the correlation between the amount of springback and the difference in tangential stresses at the top and bottom layers of the sheet section was derived based on an Euler beam and a nonlinear flow stress model with temperature and strain rate dependencies. The developed model, which can predict springback behavior using only results of forming analyses of warm formed aluminum alloy sheets, is anticipated to provide for advancements in the understanding of springback behavior at warm temperatures and improve the efficiency of design and analysis processes used to fabricate parts with complicated shapes by saving considerable time and costs for the analysis of springback.

Numerical Analysis of the Effect of Spot Superposition on Laser Peen Forming of Aluminum Alloy Sheet

In order to study the effect of laser spot superposition on aluminum alloy sheet forming by laser peening, the finite element analysis method was introduced to simulating the forming of 7075 aluminum alloy with different spot superposition case. The results showed that the forming effect and stress distribution of the metal sheet was effected by the laser spot superposition modes. The forming effect of transverse spot superposition mode was better than the other three spot superposition modes.

Identification of two aluminum alloys and springback behaviors in cold bending

Aluminum alloys have drawn more and more attention in automobile and electronics industry. However, springback is a big challenge in cold forming of aluminum alloy sheets. In order to identify two aluminum alloys and their heat treatment condition, chemical composition detections, microstructure observation by OM (Optical Microscope), SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscope) were carried out. With additional hardness tests, the results indicate that the two aluminum alloys should be 6xxx aluminum alloy. They went through solution heat treatment after hot rolling and then underwent different time of natural aging. For the purpose of investigating springback behaviors of the two aluminum alloys sheets in cold forming, strain hardening exponents (n), strength coefficient (K) and plastic strain ratios (r) in three directions were calculated by tensile tests. Then cold bending experiments and finite element (FE) simulations with the implementation of the calculated n and r were carried out. The tensile results show that the formability of the two aluminum alloy sheets in cold forming is poor for the small values of n and anisotropy was found based on the r values. The cold bending results indicate that the springback decreased with the increasing bending angle and thicker sheets had smaller springback. Besides, the simulation and experiments agreed well with each other, indicating that the springback prediction using the calculated values of n and r were suitable. It will provide significant guide in in springback prediction of aluminum alloys in cold forming and help to design the tools.

Combined process of hydroforming and electro hydraulic precision reshaping for aluminium alloy

Hydroforming has become an important process for aluminum alloy sheet forming. The advantages of this process include that it conserves mold material, energy and man power etc. However, at room temperature, due to aluminum alloy’s low plasticity and large springback after forming, the shape of the aluminum alloy parts will not meet the precision requirements, and therefore, reshaping the aluminum alloy parts to meet the precision requirements becomes a challenge. The plasticity of aluminum alloy can be improved at high speed deforming at room temperature [1]. Therefore, electromagnetic forming and electro hydraulic-forming become options. For the parts with simple shapes, it is possible to perform precise reforming with electromagnetic shaping. For the parts with complex shapes, electro hydraulic-forming becomes a better choice. Hence, combined process of hydroforming and electro hydraulic precision reshaping is a new leading process used for the precise forming of aluminum alloy sheet. This paper discusses the details of this combined process by introducing this process, analyzing the details of the parts formed, as well as providing evidence to support the superiority of this process.

503 工具-被加工材熱電対法による摩擦撹拌インクリメンタルフォーミングにおける加工部温度の測定

Temperature at the forming point in friction stir incremental forming of aluminum alloy sheets was measured directly by tool-workpiece thermocouple method. A5052-H34 aluminum alloy sheet with a thickness of 0.5mm was formed. The tool feed rate was fixed to 2000mm / mm and formability and temperature at the forming point were measured by changing the tool rotation rate and the wall angle When the tool rotation rate was 9000 rpm, the wall angle was 20°, the formability became maximum. The temperature at the forming point with conditions obtained maximum formability was 580℃ When the wall angle was 35°, temperatures at forming point at the tool rotation rate of 5800 and 5900 rpm were almost equal to 420℃, however, formability at those conditions were different significantly.

Damage percolation during stretch flange forming of aluminum alloy sheet

A multi-scale finite element (FE)-damage percolation model was employed to simulate stretch flange forming of aluminum alloys AA5182 and AA5754. Material softening and strain gradients were captured using a Gurson-based FE model. FE results were then fed into the so-called damage percolation code, from which the damage development was modelled within measured microstructures. The formability of the stretch flange samples was predicted based upon the onset of catastrophic failure triggered by profuse void coalescence within the measured second-phase particle field. Damage development is quantified in terms of crack and void areal fractions, and compared to metallographic results obtained from interrupted stretch flange specimens. Parametric study is conducted on the effect of void nucleation strain in the prediction of formability of stretch flanges to “calibrate” proper nucleation strains for both alloys.

Electromagnetic forming of aluminum alloy sheet: Free-form and cavity fill experiments and model

A series of high-rate electromagnetic-forming experiments are presented that consider free-forming and two configurations of cavity fill operations, one with a flat-bottomed die and the other with a hemispherical protrusion on the bottom of the die cavity. The experiments are performed on 1 and 1.6 mm AA5754 and 1 mm AA5182 aluminum alloy sheet; all of which are candidates for lightweight automotive structural applications. Increasing energy levels of discharge resulted in increased cavity fill and strain level in the formed parts. The effect of die geometry on formability, strain state and location of failure is examined. Numerical simulations of the high-rate deformation and structural impact that occur during electromagnetic forming are presented, and provide insight into the physics of the problem and the transient nature of this high-rate deformation process. A transient electromagnetic finite-element code is used to model the time-varying currents that are discharged through the coil in order to obtain the transient magnetic forces that are imparted to the workpiece. The body forces generated by electromagnetic induction are then used as the loading condition to model the high-rate deformation of the workpiece using an explicit dynamic finite-element code. A “two-way, loose coupling” of the electromagnetic analysis with the elastic-plastic structural analysis is utilized to account for the effect of changing workpiece geometry on the transient body forces. Validation of the numerical model is performed through comparison between predicted and measured strain distributions within the formed parts.

The Effect of Tool–Sheet Interaction on Damage Evolution in Electromagnetic Forming of Aluminum Alloy Sheet

A study of the effect of tool–sheet interaction on damage evolution in electromagnetic forming is presented. Free form and conical die experiments were carried out on 1 mm AA5754 sheet. Safe strains beyond the conventional forming limit diagram (FLD) were observed in a narrow region in the free form experiments, and over a significant region of the part in the conical die experiments. A parametric numerical study was undertaken, that showed that tool–sheet interaction had a significant effect on damage evolution. Metallographic analysis was carried out to quantify damage in the parts and to confirm the numerical results.

Effects of temperature on yield locus for 5083 aluminum alloy sheet

Warm press forming of aluminum alloy sheets is quite attractive, since undesirable stretcher strain marks, which often appear on the surface of the sheets during cold press forming, will disappear at high temperature, and furthermore, some aluminum alloys exhibit high-temperature superplasticity at a certain forming speed. In order to determine the optimum condition of press forming for an aluminum alloy sheet, the effect of forming temperature on the yield locus was experimentally investigated. The yield locus for a fine-grain Al–Mg alloy (5083-O) sheet was obtained by performing biaxial tensile tests, using cruciform specimens, at temperatures of 30, 100, 170, 250 and 300°C at strain rate of 10s−1. The size of yield locus drastically decreased with increasing temperature. Neither von Mises’ criterion or Hill’s can well predict the shape of the yield locus of this sheet metal. Instead of these quadratic yield functions, the yield criterion of Logan–Hosford or Barlat is a better choice for the accurate description of biaxial stress–strain responses at a high temperature.

Performance of a new dry lubricant in the forming of aluminum alloy sheets

In metal forming processes, lubricants are necessary to prevent adhesion, scratching, galling and material transfer. With increasing concerns about environment and health, development and application of green lubricants became very important. In this paper, the usefulness and lubricity of boric acid dry films for cold forming of aluminum alloy sheets has been investigated. Drawing and stretching test results revealed that, regardless of types of alloys, the lubricity of boric acid films is comparable with that of some commonly used commercial solid and liquid lubricants over a wide range of forming speeds. Since boric acid is non-toxic and water soluble, the post-cleaning process is relatively simple and safe. Thus, it can be expected that the type of lubrication adopted in this study is not only cost-effective and highly efficient for aluminum forming, but also is environmentally safe.

Superplastic Forming of Aluminum Alloy Sheet Processed by Mechanical Alloying

Superplastic Forming of Aluminum Alloy Sheet Processed by Mechanical Alloying