Papers by Keyword: Sheet Forming

Abstract: Tribometer measurements are used to simulate and investigate friction and wear mechanisms in sliding solid state systems. In metal forming and especially in deep drawing, tribometers are used to study the friction characteristics in the area of the stamp edge and draw edge rounding of a deep drawing tool. To replicate the reality of the deep drawing process a commercially available pin-on-disc tribometer is only useable to a certain extent because only a circular path can be traversed. At the Upper Austria University of Applied Sciences in Wels a spiral tribometer has been developed that can measure the friction coefficient along the desired friction distance. During the deep drawing process the temperature on the surface of a deep drawing tool rise due to the friction and wear conditions caused by the process. In order to investigate the influence of temperature the spiral tribometer is equipped with a heating system. To verify the results, comparison tests are performed with a commercially available pin-on-disc tribometer. Comparative tests confirm that the results obtained with the developed spiral tribometer match the values of the pin-on-disc tribometer.

Abstract: In the field of materials forming processes, the use of simulation coupled with optimization is a powerful numerical tool to support design in industry and research. The finite element software Forge®, a reference in the field of the two-dimensional and three-dimensional simulation of forging processes, has been coupled to an automatic optimization engine. The optimization method is based on meta-model assisted evolutionary algorithm. It allows solving complex optimization problems quickly. This paper is dedicated to a specific application of optimization, inverse analysis. In a first stage, a range of reverse analysis applications are considered such as material rheological and tribological characterization, identification of heat transfer coefficients and, finally, the estimation of Time Temperature Transformation curves based on existing Continuous Cooling Transformation diagrams for steel quenching simulation. In a second part, a novel inverse analysis application is presented in the field of cold sheet forming, the identification of the material anisotropic constitutive parameters that allow matching with the final shape of the component after stamping. The advanced numerical methods used in this kind of complex simulations are described along with the obtained optimization results. This article shows that automatic optimization coupled with Forge® can solve many inverse analysis problems and is a valuable tool for supporting development and design of metals forming processes.

Abstract: In the present work the disc compression test used to determine the balanced biaxial strain-ratio $r_b$ is analyzed in terms of the influence of contact friction using non-linear finite element analysis (FEA). The FEA results reveal an unexpectedly strong sensitivity of the $r_b$-value on contact friction, which is discussed in detail. The most important outcome of the present work is that the FEA can reproduce the $r_b$-value imposed by the utilized yield function very well, but only when the prescribed Coulomb friction coefficient has a very small value; for increasing friction coefficients a gradual deviation from the imposed $r_b$-value can be observed. This finding implies that in experiments contact friction must be eliminated to a larger extent than commonly expected, otherwise the determined $r_b$-value using disc compression testing will considerably deviate from the actual one, particularly when $r_b$ is far from one.

Abstract: A superplastic-like forming (SPLF) process involving the use of hot drawing along with blow forming is studied here. The hot drawing stage helps in enhancing the formability and in fast forming the metal sheet into a hollow shape with desired amount of material draw-in. During the blow forming stage, gas pressure was applied onto the pre-formed part to complete the forming process at a targeted strain rate. Ti-6Al-4V sheets have been successfully formed by this process at 800 °C in 16 min. In this paper, finite element modeling (FEM) was used to demonstrate the effects of each stage (hot drawing and blow forming) during SPLF. A plasticity model based on tensile test data was adopted as a material model for simulation. The pressure cycle which was predicted from the simulation has been used in the process to maintain the sheet forming at an average strain rate (e.g. 10^-3, 5×10^-4 and 10^-4 s^-1. Experimental measurements, i.e. material draw-in and thickness distribution, were used to compare and validate the results from simulations. The validated simulations have shown the capability of the model to be used for the forming process. The influences of varying process parameters, such as drawing stroke, blank-holder force, friction coefficient and pressure cycle, were investigated by the simulations. It was found that the punch geometry and drawing stroke played significant roles on the thickness uniformity of the final part, from which an optimized hot-drawing system that could result in minimum thinning has been designed by FEM.

Abstract: Based on Pam-Stamp software platform, standardization procedure of finite element analysis for sheet metal forming was customized by set up module such as model building, meshing, setting of boundary conditions, calculation submitting, viewing of results and report generating. Standardization procedure has been successfully applied in the development of new products, which shortens the preparation cycle of procedure, improves the forming quality of the parts and enhances the capability for rapidly researching and developing.

Abstract: In the sheet metal CNC incremental forming, the forming is realized by its tool's step by step and point by point extrusion movements along the pre-programmed contour tool path in the outline of the sheet part. Therefore, the correctness of the forming path used to control the tool's movement has a magnificent impact on the forming quality. And a NC incremental forming process simulation method which is used to verify the correctness is showed in this paper. Meanwhile the simulation software system is developed by using VC++ and OpenGL. The case study shows that the software system can be used in the verification of NC incremental forming path and the motion analysis of forming tool, and the software system runs steadily and reliably.

Abstract: Simulation of multiple-step incremental roll-bending forming and springback of large-scale sheet metal with U shape was implemented in this paper using ABAQUS. In view of the semi-ellipse shape of work piece, a geometric plan using fives arcs with different radius to approach the original shape in piecewise is proposed. On the basis of the programming, reasonable arrange the rolling steps, adjust the parameters in ABAQUS. The largest error of curvature radius of different arcs is less than 5% after simulation of the sheet metal forming according to optimized process fitting with Origin8.0. The results show that the incremental roll-bending method forming the semi-ellipse shape work piece is feasible.

Abstract: A combined experimental-numerical approach using digital image correlation (DIC) and finite element simulation in order to get the temperature dependent mechanical behaviour is presented. Results from a series of experiments on a Ti6Al4V titanium alloy sheet are shown. Tensile tests were carried out on specimens along 3 different orientations in order to characterise the material anisotropy. The strain-rates are varied from 10-1 to 10-2 s-1 while observations are made at temperatures from 903 to 1003 K. The samples are heated by Joule effect, which allows to use the image correlation in order to obtain the deformation fields and thus the coefficients of Lankford [1]. Differences in the responses of this alloy are observed in terms of work hardening, strain rate and temperature sensitivities. The Norton-Hoff model and the Hill [2] criterion are used to effectively simulate the observed responses obtained from these experiments. An inverse analysis model using kriging meta-model [3] is applied to determine each parameter of the mechanical behaviour law. The model, with the constants determined from these experiments, is then used to predict the mechanical behaviour of Ti6Al4V. Thus, the model is implemented into the implicit finite element code Forge® to model forming of thin-walled structures. The predictions are found to be very close to the observations.

Abstract: The recently developed SSH3D solid-shell element [1], which is based on the Enhanced Assumed Strain (EAS) and the Assumed Natural Strain (ANS) techniques, is utilized for the modeling of a severe bending sheet forming process. To improve the element's ability to capture the through thickness gradients, a specific integration scheme was developed. In this paper, the performances of this element for the modeling of the T-bent process were assessed thanks to comparison between experimental and numerical results in terms of the strain field at the outer surface of the sheet. The experimental results were obtained by Digital Image Correlation. It is shown that a qualitative agreement between experimental and numerical results is obtained but some numerical parameters should be optimized to improve the accuracy of the simulation predictions. In this respect, the influence of the penalty coefficient of the contact modeling was analyzed.

Abstract: This study investigated the twisting phenomenon in curved hat channel products made of dual-phase 980-MPa-class high-tensile-strength steel sheets. The stroke returning deep drawing (SRDD) method was proposed to deal with twisting. In this new method, after the punch reaches the bottom dead point, it returns to a certain drawing height without the blank holder being removed. With the application of the SRDD method, twisting hardly occurred, but sidewall curl increased. A two-step SRDD was then proposed to reduce the sidewall curl of SRDD products. In the two-step SRDD method, a stroke returning process is carried out in two steps under different conditions. The results showed that the two-step SRDD method reduced the sidewall curl and twist simultaneously.