Forming-based geometric correction methods for thin-walled metallic components:a selective review

Geometric correction processes contribute to zero-defect manufacturing for improved product quality. Thin-walled metallic components are widely used in numerous applications such as electric vehicles and aircraft due to the lightweight feature, facilitating to achieve zero-emission goals. However, many components suffer geometric imperfections and inaccuracies such as undesired curvatures and twists, seriously affecting subsequent manufacturing operations, for example, automatic welding and assembly. Geometric correction techniques have been established to address these issues, but they have drawn little attention in the scientific community despite their wide applications and urgent demands in the industry. Due to the strict geometric tolerances demanded in high-volume automated production, it is urgent to increase the knowledge needed to develop new techniques to address future industrial challenges. This review paper presents an overview of typical geometric defects in thin-walled components and clarifies the associated underlying generation mechanisms. Attempts have also been made to discuss and categorize geometric correction techniques based on different forming mechanisms. The challenges in correcting complex thin-walled products are discussed. This review paper also provides researchers and engineers with directions to find and select appropriate geometric correction methods to achieve high geometric accuracy for thin-walled metallic components.</p

ICHSF2014

Since the first ICHSF, which was held in 2004 at the Technische Universität Dortmund, Germany, this biannual conference has grown into one of the major events for high speed forming technologies and its applications. This meeting series is now being organized with the support of the International Impulse Forming Group (I2FG) that was formed in October 2008 through the vision of Professor Erman Tekkaya. His goal was to model this in many ways after the International Cold Forging Research Group which has been instrumental in applying cold forging to wide manufacturing practice. The public face of this site can be found at http://www.i2fg.org with useful information as well as the proceedings of all the ICHSF meetings. This 6th conference is organized as a joint event of the Department of Mechanical Engineering of KAIST (Korea Advanced Institute of Science and Technology) and the Institute of Forming Technology and Lightweight Construction of Technische Universität Dortmund

Analysis and Modeling of the Forces Exerted on the Cookware in Induction Heating Applications

We present a semianalytical model for calculating the forces exerted on cookware in domestic induction heating applications. The developed model is based on the Maxwell''s stress tensor and is also based on the existing semianalytic expressions of the electromagnetic fields in planar induction heating systems, which are expressed in terms of Fourier-Bessel series. Taking advantage of the axial symmetry of usual domestic induction heating systems, the flux of the vertical component of the Maxwell''s stress tensor is analytically integrated and the vertical force is obtained. The proposed model captures both eddy currents and magnetization that occurs in typical ferromagnetic cookware. The model is verified by means of two-dimensional Finite Element simulations and also is tested by means of measurements of the change of the weight experimented by cookware due to the forces during the heating process

Self-adaptive overtemperature protection materials for safety-centric domestic induction heating applications

Security aspects in the household sphere have become a major concern in modern societies. In particular, regardless of the technology used, users increasingly appreciate a protection system to prevent material damage in the case of human errors or distractions during the cooking process. This paper presents a sensorless method for detecting and limiting overtemperature, unique to induction cooktops, based on their specific features, such as automatic pot detection and load power factor estimation. The protection system exploits the change in the load material properties at certain temperatures, the effect of which may be enhanced by arranging a multilayer structure comprising a low Curie temperature alloy and an aluminum layer. The proposed multilayer load exhibits two differentiated states: a normal state, where the cookware is efficiently heated, and a protection state, above the safety temperature, where the power factor abruptly decreases, limiting the overheating and making the state easily detectable by the cooktop. This method of overtemperature self-protection uses the electronics of conventional induction cooktops; therefore, no other sensors or systems are required, reducing its complexity and costs. Simulation and experimental results are provided for several cookware designs, thereby proving the feasibility of this proposal

Latest Hydroforming Technology of Metallic Tubes and Sheets

This Special Issue and Book, ‘Latest Hydroforming Technology of Metallic Tubes and Sheets’, includes 16 papers, which cover the state of the art of forming technologies in the relevant topics in the field. The technologies and methodologies presented in these papers will be very helpful for scientists, engineers, and technicians in product development or forming technology innovation related to tube hydroforming processes

Metal Micro-forming

The miniaturization of industrial products is a global trend. Metal forming technology is not only suitable for mass production and excellent in productivity and cost reduction, but it is also a key processing method that is essential for products that utilize advantage of the mechanical and functional properties of metals. However, it is not easy to realize the processing even if the conventional metal forming technology is directly scaled down. This is because the characteristics of materials, processing methods, die and tools, etc., vary greatly with miniaturization. In metal micro forming technology, the size effect of major issues for micro forming have also been clarified academically. New processing methods for metal micro forming have also been developed by introducing new special processing techniques, and it is a new wave of innovation toward high precision, high degree of processing, and high flexibility. To date, several special issues and books have been published on micro-forming technology. This book contains 11 of the latest research results on metal micro forming technology. The editor believes that it will be very useful for understanding the state-of-the-art of metal micro forming technology and for understanding future trends

Formability Enhancement of AA5182-O During Electro-Hydraulic Forming

In this research, formability improvement of AA5182-O aluminium sheet during electrohydraulic forming (EHF) was investigated by means of experimental and finite element analysis. Free and conical die formed EHF was carried out on grid sheet blanks and formability improvement was measured by comparing grid analysis results at each EHF condition with different forming limit curves (FLCs). It is found that AA5182-O shows minor improvement in formability when formed freely into EHF. But a significant rise in effective strain in safe grids is observed when EHF into 34, 40 and 45-degree conical dies provided a critical threshold of input energy has been used. In order to understand the mechanical aspects of formability improvement, related factors such as strain rate, stress triaxiality, and compressive through-thickness stress were studied using finite element simulation with an accurate description of the hardening behaviour of AA5182-O. Another advantage of the numerical simulation carried out in this work is that unlike previously published works, the driving force for EHF deformation was not simplified as uniform pressure and it resembles the actual process of EHF. Ignition and growth model was used in conjunction with Coupled Eulerian-Lagrangian (CEL) approach to simulate the EHF pulse formation. Moreover, 3D solid elements were used instead of shell elements and this facilitated measurement of stress in elements located in the bulk of sheet material. The tensile flow behaviour of AA5182-O sheet was investigated in the strain rate range of 0.001 to 1000s−1 and at different material directions (RD, DD, and TD) by means of both phenomenological models and neural networks (NNs). Genetic algorithm (GA) and linear regression analysis methods were used to calculate the constants in Johnson-Cook (JC), Khan-Huang-Liang (KHL) and modified Voce hardening functions, and user-material subroutines were developed and used in FE software. Moreover, in order to predict the rheological behaviour of AA5182-O without the limitations of a mathematical function, two types of feed-forward back-propagation neural networks were trained and used in the FE model. Simulation results were compared with experimental tensile flow curves and the most accurate method is used to predict the mechanical response of AA5182-O in FE simulations of the EHF process. FE results suggested that a combination of EHF process related parameters including compressive through-thickness stress (negative stress triaxiality) generated during the deformation could postpone the failure, when specimens are formed into a die cavity (EHDF). Also, the increased velocity and significant impact pressure at the final stage of deformation not only prevent strain localization but also help in further suppressing the damage. It is found that very high peak strain rates develop in the sheet as it contacts the die surface which further postpone the failure since AA5182-O exhibits positive strain rate sensitivity at such high-strain rates. Moreover, damage mechanisms of AA5182-O sheets were investigated during EHF tests and are compared with those occur during quasi-static (QS) deformation. The results confirm that void nucleation, growth and coalescence are the main damage mechanisms of AA5182-O at both high and low strain rates. It is found that Mg2Si particles do not significantly influence void formation and the main source of void nucleation is cracking of Al3(Fe-Mn) intermetallic particles. More importantly, it is found that specimens deformed under QS conditions contained more voids in areas away from the sub-fracture surface but EHF specimens exhibit higher rate of void growth close to sub-fracture areas. Optical microscopy results confirmed that void formation is suppressed by increasing the applied energy in EHF. And more importantly, the growth of voids is suppressed due to the high-velocity impact of the sheet against the die which plays an important role in increasing formability of AA5182-O aluminium sheet in EHF. Optical microscopy showed that AA5182-O grains experience significant shearing strain during the EHF deformation in the apex area of conical EHDF specimens. The results of transmission electron microscopy showed that dislocation density increases when specimens are formed using EHF process but the magnitude of this increase is not significantly greater than in quasi-static deformations. Finally, it is concluded that the combination of high strain rate deformation and compressive through-thickness stress during the deformation, leads to formability improvement of AA5182-O in EHDF

Electrohydraulic Forming of Near-Net Shape Automotive Panels

The objective of this project was to develop the electrohydraulic forming (EHF) process as a near-net shape automotive panel manufacturing technology that simultaneously reduces the energy embedded in vehicles and the energy consumed while producing automotive structures. Pulsed pressure is created via a shockwave generated by the discharge of high voltage capacitors through a pair of electrodes in a liquid-filled chamber. The shockwave in the liquid initiated by the expansion of the plasma channel formed between two electrodes propagates towards the blank and causes the blank to be deformed into a one-sided die cavity. The numerical model of the EHF process was validated experimentally and was successfully applied to the design of the electrode system and to a multi-electrode EHF chamber for full scale validation of the process. The numerical model was able to predict stresses in the dies during pulsed forming and was validated by the experimental study of the die insert failure mode for corner filling operations. The electrohydraulic forming process and its major subsystems, including durable electrodes, an EHF chamber, a water/air management system, a pulse generator and integrated process controls, were validated to be capable to operate in a fully automated, computer controlled mode for forming of a portion of a full-scale sheet metal component in laboratory conditions. Additionally, the novel processes of electrohydraulic trimming and electrohydraulic calibration were demonstrated at a reduced-scale component level. Furthermore, a hybrid process combining conventional stamping with EHF was demonstrated as a laboratory process for a full-scale automotive panel formed out of AHSS material. The economic feasibility of the developed EHF processes was defined by developing a cost model of the EHF process in comparison to the conventional stamping process