Sheet Metal Forming Processes Research Articles

Effects of the tool path strategies on incremental sheet metal forming process

This paper presents a numerical simulation of the incremental sheet metal forming (ISF) process, type single point incremental forming (SPIF). A finite element model (FEM) is developed by using the commercial FE code ABAQUS. An elasto-plastic constitutive model with quadratic yield criterion of Hill’48 and isotropic hardening behavior has been adopted during ISF operation. A user material subroutine (VUMAT) is used to implement this material behavior. Four strategies of tool path during the ISF of a piece having a square box final shape are presented. Results including thickness variation of sheet metal, forming force along Z -axis and the Hill’48 stress distribution for the four strategies are presented and compared at the aim to optimize the SPIF and to see which tool path strategy makes this process more effective with the consideration of the characteristics of specimen manufactured and its material properties.

成形シミュレーションを利用した板材プレス工程最適化の動向

成形シミュレーションを利用した板材プレス工程最適化の動向

Validation of the FEA of a Sheet Metal Forming Process of Composite Material and Steel Foil in Sandwich Design

A multi-material concept in sandwich design using two steel foils and continuous fiber-reinforced thermoplastics represents a promising structural approach to the production of hybrid parts. This contribution deals with the experimental and numerical analysis of a conventional sheet metal forming process using a composite material based on Polyamide 6 (PA6) with unidirectional endless glass fiber reinforcement and HC220Y+ZE steel foil. A unidirectional composite plate is positioned between two steel foils in sandwich design and formed into the hybrid part under appropriate temperature conditions. Afterwards, the forming process is analysed numerically with the software LS-DYNA and for verification of the FEA the geometry of the hybrid part is measured optically with ATOS system of the company GOM.

An investigation of the force and torque at profile sheet metal rolling-input data for the production system reengineering

The fundamental basis for implementation of reengineering is: experimental measurement of forces and torques on the rollers-tools production line for profile sheet metal forming. The paper presents the experiments of measuring forces and torques, modeling and simulation in the aim of redesigning the process of sheet metal forming, selecting of the optimal process of sheet metal forming for each forming module and totally for the production line and increasing productivity on production lines. In the experimental research forces and torques were measured on the rollers of forming modules for profile forming of sheets for different values of the input parameters of the process: material type σm, sheet thickness s and sheet width b. Based on the experimental results mathematical models were defined, which enabled the analysis and implementation of reengineering the production system.

Feasibility Analysis of Lubrication through Magneto-Rheological Fluids in Sheet Metal Forming Processes

Magneto-rheological fluids represent one of the most recent technologies introduced in many industrial applications to design fast and reliable electro-mechanical devices. Such fluids, which consist of a dispersion of metallic particles in a fluid carrier, may drastically change their rheological properties when subjected to external magnetic fields with short response times and low power consumption. Up to date, the most common applications of MR fluids regard the integration in mechatronics applications mainly in civil and mechanical fields, where they are often used as active lubricants in rotary components such as bearings. However, no investigations can be found in literature on their tribological performances when applied in metal forming processes.The paper aims at investigating the tribological behaviour of magneto-rheological fluids when applied as lubricants in sheet metal forming processes. To this aim, a new experimental apparatus has been developed to test the friction coefficient at the interface between the tools and the metal sheet when different magnetic fields are applied. The stamping of AA alloys was taken as reference case to select the process parameters in terms of contact pressure, magnetic field and sliding speed.

Experimental Test and FEA of a Sheet Metal Forming Process of Composite Material and Steel Foil in Sandwich Design Using LS-DYNA

A structural concept in multi-material design is used in the automotive industry with the aim of achieving significant weight reductions of conventional car bodies. In this respect, the specific use of steel foils and continuous fiber-reinforced thermoplastics represents an interesting material combination for the production of hybrid parts in sandwich design. This contribution deals with the experimental and numerical analysis of a conventional sheet metal forming process using a composite material based on Polyamide 6 (PA6) with unidirectional endless glass fiber reinforcement and HC220Y+ZE steel foil. A unidirectional composite plate is positioned between two steel foils in sandwich design and formed under appropriate temperature conditions. For the numerical analysis of the forming process the software LS-DYNA is used.

Numerical Investigation of Dry and Lubricated Sheet Metal Forming Processes

The current global development towards efficient and sustainable usage of resources as well as a stronger environmental awareness motivates lubrication abandonment in metal forming. Dry forming processes accomplish besides a green production technology also a shortage in production steps and time. However, the change of the tribological conditions influences the material flow during the forming operations and has therefore to be taken into account for the design of complex sheet metal forming operations. The aim of this study is a comparison of dry and lubricated processes by numerical as well as experimental investigations. To ensure reliable results a test setup is necessary which provides a discrete control of the process parameters. Furthermore, an analysis of the local material flow by an optical strain measurement system during the whole test procedure should be possible. These requirements are well fulfilled by the so called Nakajima test, which is typically used for the characterisation of the formability of sheet metals. The influence of varying friction coefficients on the material behaviour is discussed based on the numerical model built up in the Finite Element Software LS-Dyna. The numerical results show a good conformity with the experimental outcomes by identifying the strain localisation. Based on the gained knowledge of the investigations an increase of process understanding for dry forming operations will be derived.

The Theoretical Principles of Sheet Metal Forming Processes Intensification Based on Anisotropy

Anisotropy of properties is known to be a fundamental material characteristic, which stems from its crystal structure and texturing under plastic deformation. The influence of an anisotropy on the processing and service characteristics of products can be not only negative, but also positive. In this article in order to efficiently use anisotropy of properties in metal forming processes it is described a variation of anisotropic medium plasticity theory with reference to material deformation characteristic and it is analyzed the effect, produced by anisotropy on material behavior in different technological operations (drawing, bending, stretch-forming, etc.). As a result, intensification of deformation processes, increase of production efficiency and improvement of product quality and serviceability become possible.

Wrinkling Prediction and Optimization of Sheet Metal Forming Process by Numerical Simulation

The paper deals with optimization of forming process for AISI 430 stainless steel with nominal thickness 0.4 mm. During forming of sidewall for washing machine drum, some wrinkles remain at the end of forming process in some places. This problem was solved by optimization the geometry of the drawpiece using numerical simulation. During optimization a series of modifications of the part geometry to absolute elimination of wrinkling was performed. On the basis of mechanical tests, the material model was created and imported into the material database of Autoform simulation software.

알루미늄 판재의 다단계 드로잉에 있어서 원통컵의 치수 정밀도 비교

Deep drawing of cylindrical cups is one of the most fundamental and important processes in sheet metal forming. Circular cups are widely used in industrial fields such as automobile and electronic appliances. Some of these cups are formed by a one-stage process, others such as battery cases and beverage cans are made by a multi-stage process. In the current study the multi-stage deep drawing of aluminum sheet metal is examined. The process consists of two deep drawing operations followed by two ironing operations. The press die, which can be used for the four-stage forming process, was manufactured allowing punch and die components to be easily changed for various experiments. The rolling direction of both the sheet and the drawn cups was always positioned toward the horizontal x-direction on the die face to minimize experimental errors during the progressive forming. The dimensional accuracy of the cylindrical cups formed at each stage and the earing defect due to the anisotropy of sheet were investigated. The influence of anisotropy on the thickness distribution was also examined. Both the thickness and the outer diameter of the cups were measured and compared for each set of experimental conditions. It was found that the dimensional accuracy of cups rapidly improves by employing the ironing process and also by increasing the amount of ironing.

Optical 3D Metrology for Optimization of Sheet Metal Forming Processes

3D optical metrology methods are increasingly used in the research of sheet metal materials and in sheet metal production processes. Optical measuring systems are implemented in different process stages, including design, sheet metal material research and component development, tool making and production as well as series accompanying quality control.Today’s development processes are initially driven from computational methods. Especially for the development of sheet metal components the numerical forming simulation is an important tool. However, performing a reliable forming simulation requires accurate input parameters like 3D geometry data for meshing, material parameters and boundary conditions which can be obtained with optical measuring systems. Further on the validation of these numerical simulations is supported with optical full-field sheet metal forming analysis.In the tool manufacturing phase 3D measurement data contributes in reducing the time frame for CNC machining processes, for the try-out phase, future tool reproduction as well as for repair and maintenance.With automated 3D measuring solutions series accompanying quality control is performed to determine tool wear and to shorten the response time if problems in the production occur.This paper is extending past work [1] and discusses today’s contribution of optical 3D measuring techniques in sheet metal component development and production, covering the areas of determining input parameters for sheet metal forming simulations and its validation, tool manufacturing, including the try-out, and production quality control using automated optical measurement machines.

Application of Adaptive Neuro-Fuzzy Inference System for Prediction of Surface Roughness in Incremental Sheet Metal Forming Process

In manufacturing processes, surface finish of a product is very crucial in determining the quality. Therefore, the surface quality including the surface roughness is still the most important obstacles against the incremental sheet metal forming (ISMF) process. As a consequence, the possibility to predict the surface roughness values in incremental forming and to correlate these values with the forming parameters can be useful in order to control this important target. Accordingly, an adaptive neuro-fuzzy inference system (ANFIS) is used to predict the surface roughness of parts produced by single-point incremental forming (SPIF) process. The hybrid learning algorithm is applied in ANFIS to determine the most suitable membership functions (MFs) and to simultaneously find the optimal premise and consequent parameters by directly minimizing the root mean squared error (RMSE) as a performance criterion. In order to achieve this target, five forming parameters, namely (tool diameter, incremental step size, tool shape, rotational speed and slope angle) are studied to form pyramid like shapes for the purpose of roughness measurement. Experimental results show that the difference sigmoidal MF gives the minimum RMSE. The predicted surface roughness values using ANFIS are compared with actual data. The comparison indicates that the utilization of difference sigmoidal MF in ANFIS could achieve a satisfactory prediction accuracy using both training and testing data when this MF is adopted. The training and testing prediction accuracy are 95.972% and 85.799% respectively.

Numerical and Experimental Analysis and Optimization of Process Parameters of AA1050 Incremental Sheet Forming

The incremental sheet metal forming (ISMF) process is a new and flexible method that is well suited for small batch production or prototyping. This paper studies the use of the finite element method in the incremental forming process of AA1050 sheets to investigate the influence of tool diameter, vertical step size, and friction coefficient on forming force, spring-back, and thickness distribution. A comparison between numerical and experimental results is made to assess the suitability of the model. An approach for the optimal process factors in the incremental sheet metal forming was proposed, which integrates a finite element simulation technique, artificial neural network, and genetic algorithm. This approach is incorporated to suggest a model for process factors in terms of friction coefficient (μ), vertical step size (S) and tool diameter (D). It is found that the friction coefficient decreases spring-back value whereas vertical step size results vertical force increase and minimum thickness decrease. Tool diameter increases forming force and spring-back values.

Experimental Cases in Aluminium Foils by Dieless Process and His Comparison with Others Conventional Sheet Metal Forming Process

Incremental sheet forming by the method of single point incremental forming Dieless, is a widely studied process, experimented and developed in countries with high manufacturing technologies, with friendly costs when the productive configuration in a productivity system is based in small production batches. Previously mentioned, this work pretends to develop experimental cases in aluminum foils with 1 mm- thickness, and some specific process parameters, the analysis of forming limit curve (FLC), with the objective to emphasizes in this innovative method based in CAD-CAM technologies, compare with other analogous process of deformation sheet metal like embossing, deep drawing, stamping, spinning, superforming, take correct decisions about the viability and applicability of this process (Dieless) in a particular industrial piece, which responses to the necessities of productive configurations mentioned and be highly taken like a manufacturing alternative to the others conventional process of forming sheet metal , for systems with slow batches production.

Simplified numerical approach for incremental sheet metal forming process

The current work presents a finite element approach for numerical simulation of the incremental sheet metal forming (ISF) process, called here “ISF-SAM” (for ISF-Simplified Analysis Modelling). The main goal of the study is to develop a simplified FE model sufficiently accurate to simulate the ISF process and quite efficient in terms of CPU time. Some assumptions have been adopted regarding the constitutive strains/stresses equations and the tool/sheet contact conditions. A simplified contact procedure was proposed to predict nodes in contact with the tool and to estimate their imposed displacements. A Discrete Kirchhoff Triangle shell element called DKT12, taking into account membrane and bending effects, has been used to mesh the sheet. An elasto-plastic constitutive model with isotropic hardening behaviour and a static scheme have been adopted to solve the nonlinear equilibrium equations. Satisfactory results have been obtained on two applications and a good correlation has been shown compared to experimental and numerical results, and at the same time a reduction of CPU time more than 60% has been observed. The bending phenomenon studied through the second application and the obtained results show the reliability of the DKT12 element.

Frictional Conditions of AA5251 Aluminium Alloy Sheets Using Drawbead Simulator Tests and Numerical Methods

This article presents research results on the effect of sheet metal surface roughness, lubricant conditions and sample orientation on the value of friction coefficient in the drawbead region of sheet metal-forming processes. Aluminium alloys with different temper conditions were used as test materials. The experimental results have ascertained several relationships showing the effect of surface profile and lubrication on the value of the friction coefficient. Based on experimental measurements, it may be concluded that the sample orientation and the lubrication conditions are crucial variables influencing the value of the coefficient of friction. Furthermore, a numerical model of the drawbead has been created in Msc.MARC Mentat software, and several simulations have been performed to study the stress/strain state in stretched sample during drawbead simulator tests. Both isotropic and anisotropic material models were used in the simulations taking into account the sample orientation with respect to the rolling direction of the sheet.

Feasibility Study on Flexibly Reconfigurable Roll Forming Process for Sheet Metal and Its Implementation

A multicurved sheet metal surface for a skin structure has usually been manufactured using a conventional die forming process involving the use of both a die and a press machine in accordance with the product shape. However, such processes are economically inefficient because additional production costs are incurred for the development and management of forming tools. To overcome this drawback, many alternative processes have been developed; however, these still suffer from problems due to defects such as dimples and wrinkles occurring in the sheet. In this study, a new sheet metal forming process called the flexibly reconfigurable roll forming (FRRF) process is proposed as an alternative to existing processes. Unlike existing processes, FRRF can reduce additional production costs resulting from material loss and significantly reduce forming errors. Furthermore, it involves the use of a smaller apparatus. The methodology and applicable procedure of the FRRF process are described. Numerical forming simulations of representative multicurved sheet surfaces are conducted using FEM. In addition, a simple apparatus is developed for verifying the feasibility of this process, and a doubly curved metal is formed to verify the applicability of the reconfigurable roller, a critical component in this forming process.

Laser Welding of High-strength Aluminium Alloys for the Sheet Metal Forming Process

Laser beam welding of similar and dissimilar joints made of 7075-T6 and 5182-O sheets is conducted. A new approach of the Helmholtz-Zentrum Geesthacht is used to solve the problems of weldability and softening. The microstructural characteristics and the mechanical properties of the joints are evaluated. With this information it is possible to initially assess the formability of the tailored blanks. Finally the formability of the welds will be validated via a sheet metal forming process. Owing to the good formability of the base materials, the results obtained for the welded joints are compared with base material properties.

Numerical analysis of fluid structure interaction in water jet incremental sheet forming process using coupled Eulerian–Lagrangian approach

A coupled Eulerian–Lagrangian approach was used to simulate the whole deformation process of a water jet incremental sheet metal forming of a conical part by three dimensional finite element method. The Eulerian elements were used to model the water jet whereas the sheet and tools were simulated by the Lagrangian elements. The geometry of the work piece, thickness distribution,and surface pressure distribution, volume fraction of water in the Eulerian elements and the vectors of the water jet flow were studied by the finite element method. In addition, the relationship between bulging height, pump pressure and inclination angle of a deformed conical copper part by water jet incremental forming was approximated by an analytical method proposed by other researchers with a plane strain formulation and momentum theory of hydrodynamics. To verify the accuracy of the calculated results, the experiment of a water jet incremental sheet metal forming of an annealed copper sheet was carried out. It was shown that the numerical and also analytical results are generally in good agreement with experimental ones. In addition, It was found that the most of the thinning occurs in the former stage of water jet incremental forming and near the first path of the defined water jet trajectory, furthermore surface pressure is higher in the stagnation point whereas it is smaller than water pressure before injection from the nozzle of water jet.

Multi-scale friction modelling for rough contacts under sliding conditions

In Finite Element (FE) simulations of sheet metal forming (SMF), the coefficient of friction is generally expressed as a constant Coulomb friction. However in reality, the coefficient of friction at the local contact spot varies with the varying operational, deformation and contact conditions. Therefore, it is important to calculate the coefficient of friction under local contact conditions to better evaluate the formability of the sheet metal product. Friction at the local contact spot is largely influenced by the micro-mechanisms occurring at asperity level like shearing in the boundary layer, ploughing, surface deformation of the sheet metal surface and hydrodynamic lubrication. In this paper, a multi-scale contact model is developed for predicting the friction occurring in the SMF processes. The model describes the asperity flattening and ploughing phenomenon between the sheet metal and the tool which is predominant amongst the other friction mechanisms. The change occurring in the surface topography of the sheet metal during the deep drawing processes influences the ploughing process. An asperity flattening model for pure plastic conditions is used to describe this phenomenon. The developed model is analyzed with various sheet metal and tool surfaces. The result shows that the coefficient of friction is very much dependent on the surface topography of the interacting surfaces at low nominal contact pressures. At high nominal contact pressures, the surface topography influences less the friction. The coefficient of friction is also compared with tool surfaces of different roughness, bandwidth and surface lay. The coefficient of friction is found to be high for rough, low bandwidth and transversal anisotropic tool surfaces.