Papers by Keyword: Wrinkling

Abstract: Wrinkling during diaphragm forming of engineering fabrics compromises structural integrity and surface quality. This study investigates two strategies—diaphragm pre-tensioning and fabric inter-ply lubrication—to mitigate wrinkle formation. A pre-tensioning (PT) blank holder was designed and evaluated through deep-draw experiments supported by finite element analysis (FEA). Results show that pre-tensioning (50% strain) significantly reduces wrinkle severity compared to a conventional blank holder. The PT blank-holder creates initial equi-biaxial strain consistent with analytical and FEA predictions. Resin inter-ply lubrication also decreased wrinkling and reduced forming force by approximately 70%, primarily by lowering inter-ply friction. However, pre-tensioning proved more effective overall. These findings demonstrate the potential of diaphragm pre-tensioning for improving forming quality and provide a foundation for advanced multi-step thermoforming processes.

Abstract: Reliable composite forming experiments are required to characterize composite formability, to aid material development, and to validate process simulations models. Due to practical reasons, however, typically a limited amount of forming configurations is studied. The objective of this study is, therefore, to develop a methodology for obtaining controlled forming results in a wide range of configurations. Press forming experiments using a dome geometry were used to explore the formability of two commercial unidirectional thermoplastic composite materials. A variety of forming configurations was employed by changing the blank dimensions and layup. The observation of wrinkling defects was simplified by leaving an additional 3 mm tool gap. Blank width and layup had the most influence on the wrinkling severity, followed by blank thickness and length. Quasi-isotropic layups were found to produce wrinkles in nearly all cases, confirming a difficulty in general to form double curved parts. The size and number of wrinkles in these layups were found to change with the stacking sequence. Cross-ply layups showed better formability, but significant wrinkles were still observed depending on the orientation of the blank relative to the layup. The formability experiments using a dome geometry provided a reliable methodology for controlled forming results in many configurations using a generic toolset. Additionally, a comprehensive comparison of formability for two commercial thermoplastic UD materials in a variety of scenarios was provided.

Abstract: Wrinkling, developed due to compressive instability, is one of the main failure modes in deep drawing processes. Depending on the die geometry and blank holder force, it can be observed as flange wrinkling and/or side-wall wrinkling. In this study, side-wall wrinkling in cylindrical cup drawing process is investigated by using different constitutive models that are formed by using CPB06ex2, Hill’48, BBC2008-8p and BBC2008-16p yield criteria with isotropic hardening, and von Mises yield criterion with isotropic, kinematic and combined hardening. Numerical simulations are performed by implementing CPB06ex2, BBC2008-8p and BBC2008-16p models to a commercial finite element code through user subroutines. AA5042-H2 aluminium alloy is selected as a sheet material with 0.2083 mm thickness. In order to verify the developed models, the experimental results of the previous works for wrinkling profile and punch force evolution are employed. The results are compared and presented for the considered yield criteria.

Abstract: The Fiber metal laminates (FMLs) combine the advantages of fiber-reinforced polymer properties, like stiffness and strength, with metallic alloys, like toughness and durability. These hybrid materials can unravel some problems in the industrial sector, particularly in aerospace, and advanced automotive industry. Still, there are significant challenges in the GLARE sheets forming process even for small drawing ratios, notably smaller and complex-shaped fiber metal laminate with low thickness. As a case study, a cylindrical GLARE cup was chosen. This shape with sharp bends and vertical geometrical features, still face many challenges and difficulties in the forming process. Numerical simulations have been used utilizing ABAQUS and compared with the experimental results in the Hydro-mechanical deep drawing to achieve good forming quality with higher depth. An extensive investigation of the effect of process variables has been done such as cavity pressure, blank holding force, and blank diameter. Also, their roles in wrinkles formation, tearing and thinning, and formability has been performed. Furthermore, the friction in two cases; cured, and semi-cured condition, has been considered. The results show that the application of cavity pressure within specified limits has a positive effect on the quality of the formed cup and leads to higher depths. The same conclusion for the blank holder, which has a positive impact on wrinkling elimination and friction reducing between the aluminum layers and the fiberglass. The result shows that the semi-cured condition of the GLARE has a good effect on wrinkling reduction, due to the uniform movement of the fiberglass inside the aluminum layers. Understanding these parameters and the GLARE forming behavior and have a good selection of these parameters can give the advantage to achieve smaller and more complex shapes with higher depth, particularly for mass production. Finally, this study can extend the industrial application areas of FMLs and GLARE parts.

Abstract: It is proposed to use actual computer software systems, providing a visualization and automation of the wrinkling and visualization and automation of the results of the numerical finite-element modeling of stretch forming a convex-concave shape in view of the fact that the saddle-backed surface of the shell has two families of asymptotic real straight lines. Along these lines, the saddle-backed surface of the shell with convex-concave shape is easy to break up or riffles are formed along them. The objectives of computer simulation are to predict unwanted distortion geometric form of the shell because of wrinkling and to find a ways to minimize the deviations of its surface deviations from the required shape.

Abstract: This article examines the prediction of wrinkling initiation in self-reinforced thermoplastic composite materials for potential application in rapid forming of this class of materials. Whilst most of recent researches concentrate on examining metallic wrinkling behavior, this article aims to introduce a wrinkling indicator for composite sheet. The material system involved in the study is a self-reinforced polypropylene woven composite with a fiber orientation of 0°/90° along the warp and weft directions. Square specimens were stretched uniaxially along diagonal direction until the onset of wrinkling. It is observed that when the wrinkling occurs, strain increment ratio exhibits an abrupt change. This fundamental observation leads to the prediction of onset of wrinkling by using abrupt changes in strain increment ratio as a metric.

Abstract: In this work, experiments were conducted to examine the impact of fiber orientation of self-reinforced polypropylene on wrinkling phenomenon. Defects due to wrinkling are major quality issues in rapid forming of sheet materials. This article examines the influence of two fiber orientations [0°/90° and 45°/-45°] on wrinkling initiation of a self-reinforced polypropylene composite (Curv®) material system. It was found that 45°/-45° specimen wrinkles at smaller axial displacement compared to 0°/90° specimen. In both specimens, there was an abrupt change in strain increment ratio that corresponded to the onset of wrinkling. This phenomenon validates the robustness of the wrinkling indictor based on strain increment ratio concept.

Abstract: Micro hydro deep drawing is a promising technology to fabricate micro metal products with complex 3D shapes. However, the size effects in the micro hydro deep drawing become considerable and significantly influence shape accuracy of drawn cups. In this study, a Voronoi micro scale simulation model was developed to consider the size effects of SUS304 foils. A surface layer model was additionally applied in the simulation to further explain the size effects. The micro hydro deep drawing experiments were conducted with annealed SUS304 foils and the drawn cups were examined. The wrinkling phenomenon was generally aggravated with the hydraulic pressure. Simulation results also show that the high hydraulic pressure does not improve the shape accuracy of the drawn cups as that in the normal scale hydro deep dawning process does. The simulation results are in accordance with the experimental results.

Abstract: This paper presents the theoretical foundations and methodology of the modeling process of forming a half ring alloy blank AMg5M in software product Pam-Stamp. At the following technological sizes of a half-tore: the blank radius 516.5 mm; hole’s radius R₀=480.74 mm, distance from the generating circle center to the axis of rotation R₁=714 mm, the generating circle radius R_p=93 mm, curvature radius of die R_d=16 mm, the process is stable. The results of numerical analysis of the drawing half-tore from the ring blank directed to determining the optimal process parameters are revealed. Modeling shows that the size of the holes in the blank has a significant influence on the distribution of strain along the generatrix of the stamped parts. Using the ring blank reduces the probability of wrinkling in the free areas.

Abstract: This paper presents the roller hemming operation of FEE220BH sheet metal with convex edge-convex surface geometry. The investigation is focused on process parameters of bending angle and roller geometry whose effects have not been investigated in previous studies. A set of numerical simulations is designed to observe the multi response of the process parameters. The objective of the study is to determine the influences of these parameters on deformation, undesired wrinkling formation and hemming force which are directly related to the material reliability and the visual quality in the operation. The results are discussed to improve the outputs of the operation.