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Feasibility Evaluation of Sheet Metal Hydroformed Components through Shape Factors Application

Sheet hydroforming has gained increasing interest in the automotive and aerospace industries because of its many advantages such as higher forming potentiality, good quality of the formed parts which may have complex geometry. The main advantage is that the uniform pressure can be transferred to any part of the formed blank at the same time [1]. In this paper, a “shape factors” set has been defined with the proper goal to understand if it can be used to help engineers to define “process rules” for the studied non conventional technology [2]. A specific prediction model, obtained thanks to a numerical factorial fractional plane, has been used in order to preview the process responses vs each defined shape factor. These shape factors have been used to track the process performances through their variation thanks to the usage of the numerical simulation that has been validated with an appropriate experimental campaign executed thanks to the usage of a specific equipment properly designed.

Lattice structures integration with conventional topology optimization

Additive manufacturing (AM) processes enable the production of functional parts with complex geometries, multi-materials as well as individualized mass production. Another significant benefit of AM is the ability to produce optimized geometries with near perfect strength to weight ratios. For several years now, the topology optimization techniques assist the designers in order to develop components that have a good material distribution in order to reduce the weight ensuring the request stiffness. Therefore, the topology optimization generates concepts based on the subtractive approach and usually these geometries require a further post processing in order to obtain a geometry “ready to produce” that represents a compromise between the topologic result and the manufacturing constraints. The advent of the AM opens new scenarios in terms of definition of innovative geometries that are not feasible with the conventional processes (such as lattice structures). In order to exploit the AM capabilities, new topo...

Shape Factors and Feasibility of Sheet Metal Hydroformed Components

The authors have investigated, in other paper, the problem related to the definition of a “set of shape factors” in order to declare the feasibility of a product through sheet hydroforming. In particular the defined shape factors are three different a-dimensional coefficients by which it is possible to declare the feasibility of a product through the calculation, in different sections, of the three previous shape factors. The robustness of this methodology is related to the correct calculation of the “limit value” of each shape factor. In fact the feasibility is reached if, in any section, the calculated shape factors are higher than their respective limit values. In this paper the authors have performed an extensive numerical and experimental campaign, taking into account a different geometry respect to that of the first paper, in order to: re-calculate the limit value for each shape factor and, then, verify the correctness of the limit values exposed in the previous first paper. The numerical campaign has been used, after the evaluation of the accuracy of the numerical model, in order to study the feasibility of the product without engaging the hydroforming machine. Finite Element Analysis (FEA) has been extensively used in order to investigate and define each shape factor with a proper comparison to the macro feasibility of the chosen component geometry. The limit values that have been calculated by the authors in this paper are slightly different from those calculated in the first paper. From this point of view it is possible that, although the shape factors are a-dimensional coefficients, they are affected by different choices of the users as, for example, the dimensions of the initial blank. Anyway, the small differences in the shape factors limit values do not adversely affect the use of the shape factors in order to predict the feasibility of the product.

Numerical – Experimental Correlation of Sheet Hydroformed Component

Sheet hydroforming has gained increasing interest in the automotive and aerospace industries because of its many advantages such as higher forming potentiality, good quality of the formed parts which may have complex geometry. The main advantage is that the uniform pressure can be transferred to any part of the formed blank at the same time. This paper reports numerical and experimental correlation for symmetrical hydroformed component. Experimental tests have been carried out through the hydroforming cell tooling, designed by the authors thanks to a research project, characterized by a variable upper blankholder load of eight different hydraulic actuators. The experimental tests have been carried out following a factorial plane of two factors, with two different levels for each factor and three replicates for each test with a total of 12 tests. In particular two process parameters have been considered: blank holder force, die fluid pressure. Each factor has been varied between an High (H) and Low level (L). The order in which have been conducted the tests has been established through the use of the Minitab software, in order to ensure the data normality and the absence of auto-correlation between the tests. An ANOVA analysis has been performed, in addition, with the aim of evaluating the influence of process parameters on the thickness distribution of the component, its formability and feasibility. Finally, finite element analysis (FEA) was used to understand the formability of a material during the hydroforming process. In this paper, the commercial finite element code LS-Dyna was used to run the simulations. A good numerical – experimental correlation has been obtained.

The Use of FEA in the Simulation of a Metal Cutting Operations in the Presence of Random Uncertainty

Forces and temperatures in specific orthogonal cutting conditions and calculated by finite element analysis, have been evaluated taking into account the uncertainty of some process conditions. A traditional deterministic approach, in machining simulations, is not able to explain the uncertain physical variations related to material characteristics (yield and tensile strenght, hardness, etc.) and tool/chip/workpiece interface conditions (friction and tool wear). During machining operations many different sources of non-controllable process variations usually display their effect leading to a degree of uncertainty in the final parts quality. Statistical tools and methods are increasingly being used in combination with FE numerical simulation, in order to take in account of the variability of the process. Then, if one of the purposes of process design is to study and model robustness or reliability of a given process in aleatory conditions, a CAE study might become a feasible way to do it. Today, the evaluation of the performances of a metal cutting process is possible using several commercial FEA packages. These software tools automatically allow the preventive evaluation of the robustness of technological decisions. In this work the authors, by means the integration between stochastic simulation tools and machining FE codes, have evaluated the process sensitivity to a random variation of uncontrollable parameters or conditions. Furthermore, a specific experimental and numerical activity has been performed in order to better understand the technical capabilities in terms of process simulation in stochastic conditions.

Development of Accurate Numerical Models for Bending of Aluminum Tailored Blanks

Nowadays the main target in the automotive field is the realization of lightweight and safe components. In this way it is possible to reduce costs and improve fuel consumption and, at the same time, enhance passenger safety. The use of tailored blanks has increased considerably in the automotive industry. Tailored blanks are a combination of different thicknesses or different materials, obtained by welding together two or more blanks, used in particular in car body panels. A new requirement in the automotive sector is the application of aluminum tailored blanks. The main target of this paper is the development of accurate numerical models for bending tailored blanks made from thin aluminum sheets, joined by laser welding, without filler metal. The FE bending simulations have been carried out using an explicit solver. The accuracy of the numerical models has been estimated and improved through a comparison with the results from an experimental study. The experimental tests have been performed using bending testing equipment, designed and developed by the authors. Three different bending radii have been tested. Tailored blanks, used as specimens, have been made by laser welding of thin Al6061 sheets. The considered outputs, used for the numerical-experimental comparison, are the punch force and the bending angle. The experimental results have been compared with the numerical ones in order to verify the accuracy of the FE model related to thickness and radius variations.

Numerical Modeling of Ductile Plastic Damage in Tensile Test

Material behaviour description frequently used in commercial codes may not be adequate to simulate real forming processes. One of the reasons is the fact that they rarely include the modeling of internal damage of material. This is a decisive feature in order to be able to predict defective parts in processes like forging or to describe processes in which fracture is a part of the process itself as in sheet blanking or metal cutting. In large deformation of metals, when plastic deformation reaches a threshold level, which may depend on the loading, the fatigue limit and the ultimate stress, a ductile damage process may occur concomitantly with the plastic deformation due to the nucleation, growth and coalescence of micro-voids. Although damage and plastic deformation are two distinct dissipative processes, they influence each other. In this paper a numerical benchmark of the uniaxial tensile tests, for aluminium alloy, has been performed using Ls-Dyna and Deform 2D without damage. Then, a numerical uniaxial tensile tests has been studied using a coupled model of elasto-plasticity and ductile damage implemented in LS-DYNA. Experimental material property present in literature has been used.

Modelling of Damage in Blanking Processes

Fracturing by ductile damage occurs quite naturally in metal forming process due to the development of microcracks associated with large straining or due to plastic instabilities associated with material behavior and boundary conditions. Metal forming processes generally introduce a certain amount of damage in the material being formed. Predictions of the damage formation and growth in a series of forming steps may assist in optimizing the individual operations and their order. This is particularly true for operations such as cutting and blanking, which rely on the nucleation of damage and cracks in order to separate material. In this work numerical simulation of the blanking process, using Deform 2D, taking in account the damage, has been performed. In order to evaluate the accuracy of the numerical solution, experimental test have been performed. Furthermore a numerical – experimental correlation has been carried out.

Blank Shape Optimization in Sheet Hydroforming Process

Blank shape is one of the most important parameters of sheet metal stamping. In fact it can directly affect the forming quality of parts and it has to be taken in account in sheet hydroforming design. Reasonable blank shape not only can reduce materials and production cost but, also, it can improve the strain distribution of the material and product quality in the hydroforming process. However, it is not easy to find an optimal blank shape because of complexity of deformation behavior and presence of many process parameters like die radius, punch radius, punch speed, blank holder force and friction. In fact, they affect the result of the process i.e. tearing, wrinkling, springback and surface conditions such as earing. Even a slight variation in one of these parameters can result in defects. This paper reports numerical and experimental correlation for axis symmetrical hydroformed component using initial blank with different shape and size. Experimental tests have been carried out through the hydroforming cell tooling, designed by the authors thanks to a research project, characterized by a variable upper blankholder load of eight different hydraulic actuators. Two different initial blank shapes, square and circular, of same material and thickness have been used.

Bending Testing Rig Development through CAE Tools Application

Bending can be considered one of easier sheet metal forming processes. In fact, it represents one of the basic variants of applied deformations to metal blanks. However, the numerous research contributions dedicated to sheet metal bending that have been published over the past decade and the constant stream of announcements by R&D departments of machine constructors are strong indications that not all research challenges related to sheet metal bending have been done. This paper reports the developed activity carried out to design a bending testing rig characterized by: a working horizontal axis, a maximum bending length equal to 200 mm, a maximum applicable force equal to 80 kN. A partitioned blankholder has also been designed to allow bending operations on tailored blanks. Moreover, a Graphical User Interface hollows to set up the process parameters and the acquisition of testing data (Temperature and/or Force as function of the process time or punch stroke). CAE tools application had a strategic role to develop the best layout and to find the optimum solutions for the process variables tuning. CAE techniques have allowed to investigate and verify different layout solutions both for the bending process and the structural components of the tooling.