Blank Geometry Research Articles

Blank geometry design for preforming of woven composites based on numerical modeling

Blank geometry design for preforming of woven composites based on numerical modeling

A numerical and experimental analysis of noncircular blank spinning

The process of conventional spinning has been widely used in the production of sheet metal parts, but nearly in all cases, the initial blank of the process has a circular shape. In this article, the novel idea of spinning non-circular blanks is studied. To do so, an octagonal blank made of AL-1050 was chosen and the experimental works as well as numerical simulations, taking the effects of anisotropy into account, were performed. Shape deviation from the ideal form in terms of springback and strain distribution was studied for the deformed component. The numerical simulations revealed that uneven compressive strains at the edges as well as bending moment effects at the edges are responsible for the specific shape deviation in the final geometry. The comparison between the anisotropic and isotropic behavior of shell and solid elements with experimental results in three different thicknesses showed the shell element predicts the springback phenomena better than the solid element. On the other hand, solid element gives better results in the prediction of major and minor strains. The results of the numerical simulations and the experimental works show that more variety of geometries that would otherwise need an extra cutting process can be produced by deviating the initial blank geometry from circular form.

Process-based surface flattening method for laser peen forming of complex geometry

Laser peen forming (LPF) is a novel flexible forming process with several advantages, such as noncontact and high controllability, but it lacks a method to obtain the initial blank geometry based on its specific deformation behavior, limiting the application of the process. This study proposes a process-based surface flattening method to determine an optimal initial blank of complex geometry to accommodate the precise forming requirement. The process-based surface flattening method is developed based on the deformation behaviors of the laser-peened (LPed) and non-LPed zones with equal-strain and equal-area criteria, respectively. The objective surface is first flattened with the equal-area criterion, then the in-plane strain in LPed zones is loaded into the equal-area flattened blank. Because the in-plane strain is unknown before flattening, an optimization model is conceived to solve the in-plane strain in LPed zones based on the proposed equal-strain flattening method. Experiments are designed to validate the surface flattening methods regarding the LP-formed saddle surface as the objective with a known initial blank. The flattening blanks are quantitatively compared with the initial blank. The process-based flattening method presents the blank geometry with a mean absolute error (MAE) of 0.027 mm, while the geometry-based flattening method presents the result with a MAE of 0.398 mm, illustrating the process-based method can provide a more effective initial blank shape.

Multi-operation blank localization with hybrid point cloud and feature-based representation

Sustainability objectives, including the endeavor to reduce waste, energy consumption and machining effort gave rise to the near net shape (NNS) machining concept, which requires the initial rough blank to be as close to the final machined product as possible. Nevertheless, the opportunity of savings in material, energy and effort come with a risk of manufacturing scrap even in case of a very small geometrical error of the blank. This issue is addressed by blank localization, i.e., the act of placing the final machined product in the geometry of the rough blank. Multi-operation blank localization was proposed recently to exploit tolerances in the product design to compensate potential geometrical errors of the blank. It places each feature group, machined together in the same operation, separately in the blank. When tolerances connecting different feature groups allow, these feature groups can be moved slightly according to the measured actual blank geometry. This paper proposes a novel multi-operation blank localization approach that models the rough blank as a free-form geometry, capturing all possible geometrical errors, whereas represents the final product using a feature-based model. The problem of blank localization for minimizing tolerance errors while leaving sufficient allowance is formulated and solved as a convex quadratically constrained quadratic program (QCQP). In a case study from the automotive industry, it is shown that the proposed multi-operation approach outperforms earlier methods that handle the product as a single solid geometry.

Dimensional optimization of variable thickness tube in T-shaped tube hydroforming using response surface methodology

In this work, a variable thickness tube blank geometry is proposed to be used in T-shaped tube hydroforming. The dimensions of the tube blank are optimized by the response surface method (RSM) linked with finite element simulation during T-shaped tube hydroforming. The influence of the wall thickness, angle and length of the tube blank are discussed on the thinning ratio and branch height. Multi-objective functions that relate objectives and design variables are formulated. Furthermore, the design variables having greatest impact on the objectives are obtained by sensitivity analysis. The optimal the geometric dimensions are determined within the given criterion by RSW and desirability approach. The optimized results have good agreement with the obtained results by finite element simulation and experiment.

Effects of gripper location and blank geometry on the thermoforming of a carbon-fiber woven-fabric/polyphenylene sulfide composite sheet

The effects of gripper location and blank geometry on the thermoforming of a pre-consolidated carbon-fiber woven-fabric/polyphenylene sulfide (PPS) thermoplastic composite sheet (deformed into a U-beam geometry) are investigated both experimentally and numerically. The thermoforming experiments and simulations are performed at constant tool (160oC) and sheet (315oC) temperatures by using four thermoplastic composite blanks, which are different in geometry and inserted into the blank holder using gripping springs. Thermocouples are inserted on the composite sheet and forming molds in order to monitor the temperature variations during thermoforming. Thermoforming process is simulated in Ls-Dyna; the composite sheet is modeled using the Anisotropic Hyperelastic Material Model (MAT_249). An optimum punch speed and a spring constant are initially determined through numerical simulations. Afterward, the numerical thermoforming processes of four different blanks are implemented separately. Results reveal that the simulations show good agreements with the experiments in terms of defects formation and the maximum shear angles between the fiber directions on the final thermoformed U-beam geometry. When the blank is attached with eight springs from the lugs to the blank holder, the deformation and distortion of the net edge of the sheet are avoided, resulting in significant reductions in the extent of defect formation.

Influence of the Initial Blank Geometry on the Final Thickness Distribution of the Hemispheres in Superplastic AZ31 Alloy

This work deals with the design of the thickness of an AZ31 alloy blank, which is a superplastic magnesium material, to manufacture a hemisphere with a uniform final thickness. The finite element technique was used for the design process. The superplastic free-forming manufacturing was simulated for a part whose initial thicknesses were made to vary through two independent design parameters to obtain a linear thickness decrease from the pole to the end of the blank to form. This is because a linear thickness decrease is easily obtained through a machining process. The optimized blank, that is, the blank with a non-constant thickness that leads to the most uniform thickness distribution of the formed product, allows the manufacturing of a hemisphere with more uniform thickness values with a reduction in forming times and in weight in comparison with that formed by a constant initial thickness blank. At the same time, experimental tests confirmed the results highlighted by the finite element technique.

Blank Shape Optimization Considering 3D Space Targets for External and Internal Boundaries in Sheet Metal Forming Processes

Optimum design of the shape of the initial blank is an important task before sheet metal forming processes. It reduces production costs, material waste and improves the quality of the product significantly. In the present work, the blank shape optimization problem is considered based on the 3D space target contours and moreover the sheet metal can have an internal boundary. In other words, the shape optimization process can be applied on the internal boundary, external boundary or both. To the best knowledge of the authors, there are no published works in this subject. Using the iterative simulation-based optimization process, a special shape error index and also updating algorithm were proposed to modify the blank geometry in each iteration until capturing the optimum shape. The sheet forming process is highly nonlinear in nature due to plastic behaviors, large deformations and frictional contact surfaces. Therefore, the updating formula should be robust enough to have less sensitivity with respect to the initial guess. To evaluate the proposed updating formula and its robustness, some numerical examples were considered and the effects of different tools geometries, 2D and 3D target contours, internal and external boundaries and different initial guesses were examined.

Blank shape optimization in the deep drawing process by sun method

Deep drawing is one of the most important and widely used processes in industry for the production of various parts. In this process, the optimal design of the blank has many advantages such as reducing the cost of production and waste and improving the quality of the process and thickness distribution. In this study, blank optimization involves finding an initial blank geometry in which the edge contours of the final product approach a target contour, taking the required shape after deep drawing. A new iteration based method is proposing for optimizing the shape of a blank in the deep drawing process. The behavior in such problems is severely nonlinear as a result of major plastic deformations and contact phenomena. The general solution to such problems has been to use numerical simulation iterative based methods. The present study implements a similar approach and presents a new algorithm to make geometrical corrections to the external boundaries of a blank in several iterations. A computer program was developed to automatically run these iterations to study the features of the proposed method. Next, two numerical example was solved, and the results are compared with other studies. The proposed method is robust against the initial guess as it manages to optimize the blank regardless of it.

Analytical and numerical investigation of wrinkling limit diagram in deep drawing of two-layer sheets with experimental verification

Wrinkling, which is primarily caused by insufficient blank holder force, is a significant issue that induces inconsistencies in forming parts, particularly in the deep drawing process. In this article, an investigation of the wrinkling in the deep drawing process of two-layer sheets is performed through an analytical approach, numerical method, and experimental tests. Increasing in the blank holder force, the process is under control by the proposed algorithm. Consequently, it aims to find the minimum required blank holder force to avoid wrinkling. The energy technique is utilized to predict the wrinkling in the analytical approach. Similarly, finite element simulations are implemented to investigate the effect of forming parameters on wrinkling. The experimental tests are performed to verify the analytical and numerical results. The impact of the material properties and stacking sequences (lay-up) on blank holder force and forming force are studied. Results show that the optimum blank holder force is dependent on the material properties, blank geometry, and layer stacking sequences. Also, a good agreement between analytical, numerical, and experimental results is achieved.

Mathematical modeling of single action pressing of powder materials under dry friction conditions

The paper presents a theoretical analysis of the single action pressing of powder materials featuring plasticity and compressibility. It takes into account dry external friction between the die material and side walls, which determines the strong nonlinearity of the problem considered. This problem has a number of features that complicate its numerical solution: the presence of external friction, the elastic-plastic law of material behavior description, as well as the calculation of large displacements and, as a consequence, strong geometric nonlinearity. To consider these features, a combination of Fleck–Kuhn–McMeeking and Gurson– Tvergaard–Needleman models was used to consider a wide range of changes in the porosity of materials. The numerical solution of the problem was carried out using finite element analysis with isoparametric elements. The increment of plastic deformations at each step was determined from nonlinear equations of plastic flow. Stresses at the Gaussian points were updated according to the specified increments of deformations to calculate the material behavior during deformation. Unknown density and strain values as functions of coordinate and time were calculated. The influence of the different height-to-diameter ratio of the blank and the value of external friction of the material stress-strain state and compaction kinetics were considered. The distribution of equivalent stresses and the value of volumetric plastic deformations in the material, as well as the nonuniformity of relative density at the end of the pressing period were studied. The theoretical analysis made it possible to study the basic compaction kinetics laws for powder materials with nonuniform density under conditions of dry friction on side walls. The results obtained are relevant for predicting possible negative changes in the blank geometry when implementing the single action pressing scheme for powder materials.

Some improvements on the one-step inverse isogeometric analysis by proposing a multi-step inverse isogeometric methodology in sheet metal stamping processes

Recently, isogeometric methodology has been successfully implemented in one-step inverse analysis of sheet metal stamping processes. However, these models are not capable of analyzing forming processes which require severe deformation and/or several forming stages. This paper presents a multi-step inverse isogeometric methodology to enhance the precision of one-step models in predictions of the initial blank, strain distributions, and drawability of the formed parts. This methodology deals with the minimization of potential energy, deformation theory of plasticity, and considering membrane elements. The presented methodology utilizes the NURBS basis functions to create the final, middle, and blank geometries, and also to analyze sheet metal deformation. The characteristics of the applied formulations make it possible to simultaneously observe the effects of changing part parameters on its formability. One advantage of this approach is that the linear system of governing equations is solved without concerning about the convergence. In addition, the presented methodology is able to successfully generate the middle geometry and to restrict the movements of physical nodes along the middle surface, by presenting a new NURBS-based mapping and sliding constraint technique. The performance of the presented model is evaluated under two classical problems including forming of a rectangular box and a two-step drawing of a circular cup. In forming of the rectangular box, the results of the presented model are compared with those of experiment and forward FEM simulation. Also, in the second problem, the presented approach is only compared with forward FEM simulation. Results comparisons indicate the credibility of the presented model in prediction of forming parameters at a low computation time.

Accuracy analysis of earing compensation procedures

In the present work, the analytical model proposed by Van Houtte et al. (1993) is applied to predict geometric earing in cup drawing using a non-circular blank geometry. In order to validate the theoretical results, non-linear finite element simulations were carried out. It is observed that the predictions of the theoretical model are in close agreement with the results of the finite element simulations, even for unusual blank contours. Based on this confidence, the analytical earing model is paired with a simple iterative earing compensation procedure in order to calculate the blank contour which is required to obtain an earing-free cup. These results, in turn, are confronted with those obtained by means of the analytical earing compensation approach proposed by Engler et al. (2011). Very good agreement between both approaches is found. Practical applications of the analytical earing compensation approach involving anisotropic materials demonstrate its very good performance.

Blank geometry design for carbon fiber reinforced plastic (CFRP) preforming using finite element analysis (FEA)

Carbon fiber reinforced plastics (CFRPs) have attracted growing attention from transportation industry because of their superior performance over metal counterparts. The thermoforming process has been invented for mass-production of CFRP parts. This thermoforming process involves multiple steps and numerous parameters, and one of the most important process parameters is the initial blank geometry. To optimize blank geometry in thermoforming and minimize trimming work for the final part, an innovative approach integrating automatic mesh adjustment and FEA modeling method for preforming is developed as foundation of design and reported in this paper. Preliminary trial-and-error optimization algorithm demonstrates that this newly-developed approach can accurately design blank geometry under various typical process conditions.

Methodology for the design of recursively axially formed rotor shafts made of two or more combined segments

Abstract Electric drives are used in all industrial fields in a growing number. Whereas the rotor shafts used in the area of machinery and plant engineering are designed as solids, the shafts mainly used in the field of automotive industry are hollow shafts focusing on the lightweight potential and the improvement of motor characteristics. This paper describes a shaft design consisting of two or more segments manufactured by a new combination of certain cold forming processes before joining. This design enables higher flexibility of variants as well as optimization of production efficiency and logistic chains. Thus, the joint zone design is a special serration with a helix angle in order to reach a high robustness of the shaft. A detailed FEM simulation of the elastoplastic behavior of the joint zone and the mechanical characteristics of the complete shaft leads to an evaluation of possible applications of this joint geometry and the corresponding manufacturing process. Based on experimental investigations, the simulations have been validated successfully. An empirical model designed by regression analysis of further simulation results is used to propose a design methodology for the identification of design parameters of the assembled shaft and the joint zone as well. These parameters can be used for planning the forming processes and the blank geometry.

Process-induced defects in an L-shape profile ring rolling process

The ring rolling is a process of gradually forming the cross section of the ring material according to the outer shape of the working roll. In this study, process-induced defects in L-shaped cross section ring rolling process have been analyzed. Major defects in the L-shaped ring rolling process include folding, unfilling and groove on the bottom surface of the material. In order to understand the formation mechanisms of process-induced defects, finite element analysis and physical modeling have been performed at various processing conditions. For the process analysis, the effects of process variables such as blank geometry, dimension and rotation speed of working roll, mandrel feed speed and working temperature on the generation of defects have been investigated. From the analysis results, methodologies to prevent process-induced defects are proposed and validated by shop-floor ring rolling operations.

An advanced CAD/CAE integration method for the generative design of face gears

The conventional generative design of face gears involves CAD modeling and stress analysis by finite element analysis (FEA), which is usually performed repeatedly by optimizing design parameters until acceptable stress result is obtained. An integration of computer-aided design (CAD) and computer-aided engineering (CAE) can significantly reduce both time and labor costs to this generative design. However, this idea has not been adopted by any commercial software in designing face gears due to the complicated tooth surface geometry. The main problem is that the isoparametric discretization points of the tooth surface are non-equidistant. In this work, we derive an advanced method, based on the geometry characteristic of the tooth surface, to calculate the points as an even distribution on the tooth surface. In this method, sample points are discretized according to gear blank geometry and then a mapping between sample point and tooth surface point is established; according to which a comprehensive algorithm is proposed to recalculate the tooth surface points. Subsequently, the calculated tooth surface model is input to the proposed CAD/CAE integration method to implement the finite element analysis (FEA). The proposed method is validated by a series of face gear drives with varying shaft angles.

Development of novel forming limit curve testing method

A new concept of the forming limit curve testing method has been developed for evaluating sheet metal formability. This new method complies with the current ISO 12004-2 standard, and has been verified by the numerical analysis in terms of specimen deformation, strain path characterization and lubrication effect. It combines the advantages from both the standardized Marciniak and Nakajima tests, deforming the sheet metal materials under a complicated deformation mode following the linear strain path without using a carry blank. By comparing the simulation results with the experimental measurements, it is proven that this testing method works with the thinner and thicker sheet metals for a variety of blank geometries.

Data-driven modelling in the era of Industry 4.0: A case study of friction modelling in sheet metal forming simulations

With growing demands on quality of produced parts, concepts like zero-defect manufacturing are gaining increasing importance. As one of the means to achieve this, industries strive to attain the ability to control product/process parameters through connected manufacturing technologies and model-based control systems that utilize process/machine data for predicting optimum system conditions without human intervention. Present work demonstrates an automated approach to process in-line measured data of tribology conditions and incorporate it within sheet metal forming (SMF) simulations to enhance the prediction accuracy while reducing overall modelling effort. The automated procedure is realized using a client-server model with an in-house developed application as the server and numerical computing platform/commercial CAD software as clients. Firstly, the server launches the computing platform for processing measured data from the production line. Based on this analysis, the client then executes CAD software for modifying the blank model thereby enabling assignment of localized friction conditions. Finally, the modified blank geometry and accompanied friction values is incorporated into SMF simulations. The presented procedure reduces time required for setting up SMF simulations as well as improves the prediction accuracy. In addition to outlining suggestions for future work, paper concludes by discussing the importance of the presented procedure and its significance in the context of Industry 4.0.

Orbital forming of tailored blanks with two-sided local material thickening

Economic and ecological demands like saving resources and improved material efficiency can be achieved by the application of process adapted semi-finished parts, so-called tailored blanks, for the manufacturing of for example gearings or synchronizer rings. Functional components require the locally restricted distribution of an adequate amount of material at defined positions in order to properly form functional elements like gearings or carriers. As these elements can be formed on one or both sides of the component, an appropriate material provision on one or both sides of the sheet metal is necessary. Having material thickenings on two sides lead to the interaction between both sides for example with regard to the maximum die filling. One process to produce tailored blanks is orbital forming. While manufacturing these tailored blanks with a local material thickening on one side of the sheet metal is state-of-the-art, the realization of these tailored blanks on both sides has not been investigated yet. In this paper, the results regarding the manufacturing of tailored blanks with a two-sided local material thickening will be presented for the first time. By analyzing three different tailored blank geometries, the influence of the interactions of two-sided material thickenings will be investigated. The results will be evaluated in terms of the resulting geometrical and mechanical properties.