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Metal forming or shaping processes, such as sheet metal forming and bulk forming, are widely used in many industries including automotive industry. Before computational simulations were widely used in the field of metal forming industry, the trial-and-error based empirical approach was conventionally applied to the optimization of the metal forming process and product. The most commonly employed numerical approach in the metal forming process for robust process optimization is the finite element analysis. Friction, one of the parameters that significantly affect the accuracy of numerical analysis, depends on several variants such as surface quality, contact pressure, lubrication, deformation, and the forming environment. Despite the complexity and difficulty of identifying friction mechanisms, accurate friction models are essential and hence have been proposed by numerous researchers. In this paper, the friction models in the previous studies are reviewed by categorizing them into the boundary lubrication condition and mixed-boundary lubrication condition according to their evaluative influences on friction. Since friction models have been proposed based on the contact theories, an overview on the contact models is also included in this paper. In addition, the contribution of several parameters on the friction such as surface roughness and material properties of the tool, adhesion, contact pressure, sliding speed, bulk deformation is also discussed. This review paper aims to provide an understanding and insight into the friction modeling and simulation along with associated friction experiments. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation on the incremental sheet metal forming assisted by ultrasonic vibration (UV). With the aid of a new acoustoplasticity constitutive model which can accurately capture the deformation response to ultra-high strain rates, extensive numerical analyses on incremental sheet metal forming under UV were conducted by using the finite element method. Corresponding experimental investigations were also carried out to examine the capacity of the constitutive and numerical models. The effects of critical parameters, such as tool size, tool revolution speed, feed rate, pitch and tool vibration amplitude, on the forming force, maximum sheet thickness reduction and springback, were investigated in detail. It was found that the models can realistically predict the incremental sheet metal forming under UV. It is expected that this research can facilitate the development of ultrasonic vibration–assisted forming techniques. [ABSTRACT FROM AUTHOR]

One of the most critical tasks within the scope of Design for Manufacturing (DfM) is to define the set of Geometrical Product Specifications (GPS) in the 3D model or in the engineering drawing that ensures the functionality and the interchangeability of parts, as well as the intended functional performance of an assembly. Several methodologies have been proposed for the optimal designation of such specifications; however, the majority of them do not effectively take into account the deformations that are inevitably induced during assembly and operation for the vast majority of mechanical components. Motivated by the widely accepted tolerancing practice for sheet metal parts in the automotive industry, where the distinction between free state and constrained state is considered, the paper investigates the influence of the deformations induced during assembly and operation on GPS. The effect of part stiffness in the resultant functional GPS of the assembly/component is explored, through CAD surfacing and non-linear numerical finite element analysis tools including the contact problem. The current stage of development of a novel, performance-based methodology for the GD&T design procedure is presented. The methodology is applied on a real-world mechanical assembly that is derived from tolerance stack up-related literature. This study illustrated is that for an unpredictably wide range of mechanical components the default, free-state GPS scheme should only be assigned after rigorous analysis of their compliance behaviour. The proposed approach will lead to deduce the correlation between production cost and performance through a further development in future study. [ABSTRACT FROM AUTHOR]

This paper focuses on numerical simulation of single point incremental forming (SPIF) process. Via a user-defined material (VUMAT) subroutine is employed to implement a non-associated mixed isotropic-kinematic hardening material model. The accuracy of the proposed non-associated flow rule model to predict the material behavior and the anisotropy in sheet metal forming simulations is examined by comparing numerical results with experimental measurements. The suggested model shows good agreement with experimental results compared to the associated Hill_R and Hill_S models. The proposed non-associated flow rule demonstrates a good efficiency to simulate the springback after sheet metal forming and to predict the thickness variation during incremental sheet metal forming process. The present non-associated model can improve the prediction of both anisotropic and hardening behaviors of material used in numerically controlled sheet metal forming technology. [ABSTRACT FROM AUTHOR]

This paper presents a variant of the traditional 'mortise-and-tenon' joint, which has been used for thousands of years by carpenters and blacksmiths to connect wood or metal parts. The new proposed joint is utilized to fix longitudinally in position two metal sheets (or plates) perpendicular to one other by sheet-bulk metal forming, at room temperature. The development is performed by means of a combined finite element and experimental investigation focused on the identification of the major process parameters and on the understanding of their influence on the overall joining feasibility. Destructive testing is carried out to characterize the performance of the new proposed joint, and an analytical expression is provided to determine the maximum tensile force that the joint can safely withstand. [ABSTRACT FROM AUTHOR]

Numerical simulation is becoming one of the main methods to investigate various engineering problems with sophisticated conditions. A considerable amount of research is conducted on numerical analysis of sheet metal forming process to address different aspects of the problem. Among the numerical simulation methods for sheet metal forming process, finite difference method (FDM) and finite element method (FEM) have been the main methods. In this paper, the progresses in simulation techniques, advantage and disadvantage of numerical methods for simulating sheet metal forming process are discussed based on these numerical methods. Currently, FEM being the main simulation method for sheet metal forming, development in solution strategies and formulation, element selection are further brought into attention. Historical development of anisotropy and yield criteria, which are theoretical foundation for numerical simulation, and their application in simulation software are briefly classified. Formability of sheet metal is presented from the numerical simulation point of view. Numerical investigations on springback are reviewed in terms of simulation techniques and factors influencing springback. Simulation techniques for novel sheet metal forming techniques such as laser forming and incremental sheet forming (ISF) are presented. [ABSTRACT FROM AUTHOR]

In this paper, an iterative learning control (ILC) model is constructed with the state function, forming quality function, and learning updating law to optimize the sheet forming process. The state function, which is hardly calculated explicitly, is replaced by finite element simulation to predict the workpiece state with a specific drawbead geometry scheme. Then, the forming quality function is defined by accumulating the elements' thinning strain deviation with different weights. Afterwards, the learning updating law is designed to provide a new scheme of drawbead geometry based on the forming quality function multiplied by a learning gain. The ILC model guarantees a quick convergence and greatly improves the optimization efficiency for industrial application. To apply the ILC model to optimizing the drawbead geometry automatically, schemes of seamless integration of computer-aided engineering system into the CATIA platform and the drawbead geometry parameterization are adopted. Lastly, the rapidity and practicability of the optimization method for drawbead geometry are verified by the numerical experiment of the engine hood inner panel. [ABSTRACT FROM AUTHOR]

In this paper, finite element prediction of sheet metal forming process is investigated using solid elements. A three-dimensional rigidviscoplastic finite element method with linear tetrahedral MINI-elements is employed. This technique has traditionally been used for bulk metal forming simulations. The solid element approach with remeshing capability is applied to simulating a plate metal forming process to reveal its possible problems. The similar approach is also applied to a typical sheet forming process. Both single- and double-layer finite element mesh systems are studied, with particular attention to their effect on the deformed shape of the workpiece and thickness variation of a cold sheet forming process. The procedure is applied to the well-known problem of the NUMISHEET93 international benchmark. The resulting predictions are compared with experimental observations found in the literature, and good agreement is noted. [ABSTRACT FROM AUTHOR]

Currently, more and more tailor-welded blanks (TWBs) are used in the automobile industry. It is very important to locate the weld line and predict its movement during the forming process. The initial weld line can be predicted by one-step finite-element analysis according to the desired weld line in the final workpiece. Meanwhile, weld line movement during the deformation process can be evaluated in advance. In this paper, the procedures of finite-element analysis of one-step FEM with TWBs are established. The contact between tool and blank and the effect of restraining forces under the blankholder due to drawbead and blankholder pressure are considered as well. Forming limit diagram (FLD) is used to show not only the tendency of reduction in thickness and fracture but also of increase in thickness and wrinkle. Hydraulic controlled pads used to clamp the weld line during the deep drawing process are simplified as static external force to eliminate the movement of the weld line. In order to speed up and ensure the convergence of Newton-Raphson iterations, energy-based 3D mesh mapping algorithm is introduced to obtain the initial solution. The above-mentioned methods have been implemented in the authors’ in-house one-step FEM code InverStamp. A rectangular cup drawing case demonstrates that this approach can be easily implemented to evaluate weld line movement and develop initial blank in sheet metal stamping with tailor-welded blanks. [ABSTRACT FROM AUTHOR]

This paper presents a more accurate predictor-corrector scheme that combines the stream line method (SLM) and feasible sequential quadratic programming (FSQP) using the explicit dynamic finite element method (FEM) to design the optimum blank in the deep drawing process of square cup with flange. It is clear that faster convergence and better results of calculating optimum blank shape are guaranteed when FSQP uses a better initial guess. But it is not easy to guess the initial blank shape due to the variation of blank thickness, material anisotropy, and friction on the flange area at the beginning in the deep drawing process. SLM can obtain a preliminary prediction of the optimum blank shape with a little computational effort, so with SLM it is feasible to predict the initial guess of optimum blank with the assumption of fixed height of square cup with flange. FSQP can continue to adopt the predictor obtained by SLM to correct the optimum blank efficiently and accurately. Then the optimum blank is used in the final simulation and experiment. From comparison of the target shape between the simulated and experimental results, a good correspondence is confirmed. Other comparisons of the punch load, punch stroke, and wall thickness of the target square cup also show good agreement. [ABSTRACT FROM AUTHOR]

Blank holder force (BHF) is one of the key parameters affecting the process of sheet metal stamping. Numerous researchers have demonstrated two primary failures (wrinkling and tearing) could be avoided if appropriate variable BHF profile was implemented during punch stroke. Several approaches are proposed to determinate optimal BHF by experiment or FEM simulation. In this study, new control objective was adopted based on the definition and analysis of BHF formability window. The PID controller was integrated into FEM code to conduct closed-loop forming simulation of step rectangle box, through which the optimal BHF trajectories were determined for each separated binder. The trajectories were verified on a multipoint variable BHF hydraulic press and showed good effect to avoid wrinkling and tearing. The proposed BHF determination approach in this paper can be applied to stamping parts of different geometry due to the application of new objective, which makes it a robust strategy. [ABSTRACT FROM AUTHOR]

Prediction of the influence of tool wear influence in sheet metal blanking/punching processes is investigated in this paper using the finite element method. In order to simulate accurately sheet metal-cutting processes by a material shearing mechanism, a finite element model valid for the numerical description of such processes has been developed. Damage and crack propagation has been taken into account by means of an elastoplastic constitutive law to study the effects of the variation of process parameters on the geometry of the sheared edges and the evolution of the force-punch penetration. Furthermore, a numerical investigation has been carried out to study the effect of tool wear on burr formation. During analysis, the initiation of a crack is assumed to occur, at any point in the sheet metal where the damage reaches a critical value. Crack propagation is simulated by the propagation of a completely damaged area. This is taken into account in the finite element model by a decrease of the stiffness of the broken elements. [ABSTRACT FROM AUTHOR]