Papers by Keyword: Formability

Abstract: Microforming holds great importance due to the rising demand for miniaturized parts across diverse industries. It enables the efficient mass production of small-scale components using sheet metals. By exploring microforming processes, researchers can uncover the unique challenges and opportunities associated with manufacturing at the microscale. This research work investigates the impact of temperatures during the annealing on the mechanical properties, microstructural behaviour and formability of austenitic stainless steel 316 thin sheets. The thin sheet, with a thickness of 50µm was considered for the present analysis and were annealed at temperatures ranging from 400 to 1000°C for 30 minutes. Tensile tests were performed and mechanical properties were evaluated at various annealing temperatures. It was witnessed that as the temperature of annealing increases, the ultimate tensile strength reduces and ductility enhances. Erichsen cupping tests were conducted to assess the formability, measuring the dome height of the drawn cups. The results revealed that the as-received thin sheet exhibited poor formability. However, increasing the annealing temperature resulted in enhancing the formability, as evidenced by an increase in the dome height of the drawn cups. Furthermore, the annealing process led to an increase in grain size, which in turn inversely affected the material strength. Therefore, annealing not only enhanced formability but also influenced the microstructural characteristics of the stainless steel 316 foils. Fractography studies were done and the results show that higher annealing temperatures result in ductile fracture, which is favorable for practical applications. At lower temperatures, brittle fracture occurs with the presence of river markings. The present work helps in selecting appropriate annealing conditions for improved toughness and resistance to sudden failure in micro parts.

Abstract: Aluminum alloy sheets are widely considered for manufacturing lightweight thin-walled structural components in the automotive and aerospace industries. However, the poor formability of the material at room temperature is still a technical challenge. Warm forming evolved as a promising technology where the sheet metal is deformed at elevated temperatures below the recrystallization temperature. Numerical modeling is vital in the modern scenario to better understand formability and to improve the designing of tooling for complex sheet components during warm forming. Hence, it is imperative to understand the accuracy of material models on formability predictions at elevated temperatures. This work presents the effect of three yield criteria, namely, von Mises, Hill-48, and Barlat-89, on the formability predictions of AA6082-O sheet at elevated temperature, say, 200 °C. Analytical necking-based Marciniak-Kuczynski forming limit diagrams (MK-FLD) at the elevated temperature were predicted by incorporating these yield models. The accuracy of predicted MK-FLDs was validated with experimental data. Furthermore, finite element (FE) modeling of limiting dome height (LDH) tests was performed using sample sizes that developed deformation modes towards biaxial, plane strain, and uniaxial modes. The effect of different yield models on the forming behavior was studied in terms of part depths and major surface strain distributions. The compatibility of yield criteria on accuracy in prediction was assessed by overlapping with the experimental data. It was demonstrated that Barlat-89 was best suited compared to Hill48 and von Mises yield models.

Abstract: Although the Incremental Sheet Forming (ISF) technology has been studied and applied from the last decade of the previous century with more than 30 years of experiences and ameliorations of the researchers of this field, but the ability of deformation of the formed material sheet still has remained in a restrictive modest value. This sheet forming technology could be divided into 2 mains branches: Single Point Incremental Forming (SPIF) and Two Point Incremental Forming (TPIF) wherein the first one is usually applying in research and the second branch is used in production. The ISF is suitable for forming sheet for a single product or for small batch production with a great advantage of a no-need pestle and mold manufacture in advance, but the formability of formed sheet material cannot bigger than a limited formed angle of about 80^o that depends on the material and the forming parameters. There are some ameliorations for increasing the formability of the formed sheet such as heating the formed sheet in Hot SPIF or Multistage SPIF (MSPIF)… All the effort and amelioration measures are confronted with different difficulties. In this paper, we concentrate to study on the MSPIF technology on stainless steel SUS304 by simulation method with the proof of experimental method. The results were also compared to the simple SPIF to show its own pros and cons on the related field such as the technology, the productivity and the lubrication.

Abstract: This article presents an experimental research carried out on polymer sheet deformed by conventional forming, i.e. tensile and Nakajima tests, as well as by single point incremental forming (SPIF). The analysis is performed for polycarbonate (PC) polymer sheet material within the framework developed in previous recent papers of the authors, which the aim of defining a complete testing methodology for assessing formability and failure by necking and fracture of polymeric sheets. In the case of SPIF, truncated pyramid and cone test geometries are selected, enabling a variety of strain states from plane to biaxial strains. The results obtained allow an accurate evaluation and assessment of the forming limits by necking and fracture within the material forming limit diagram (FLD), and also include an analysis of the influence of the process parameters on the formability and failure modes attained in the case of incremental forming.

Abstract: The Forming Limit Curve (FLC) shows the limit combinations of principal strains on the sheet surface that can be successfully achieved before necking appears. Above the FLC, Atkins in 1996 proposed the existence of an unstable region where localized necking develops before reaching at the Fracture Forming Limit (FFL). Only the methodology for the evaluation of the FLC is covered in an international standard ISO 12004-2, where the basis of the tests consists of stretching of a previously clamped sheet blank over a Marciniak or Nakazima punch, providing an almost linear strain path in the sheet surface of the specimen. On the contrary, in single-point incremental forming (SPIF) processes, the hemispherical-shaped tools usually employed are relatively small compared to the general dimension of the specimen, producing a highly nonlinear strain path derived from both the incremental nature of the process and the severe curvature imposed by the small radii of the punches used in the forming process.Many authors have observed fracture strains in SPIFed samples well above the FFL obtained with Nakazima tests under the ISO 12004-2 standard. At the macroscopic level, the reason for this behaviour has been explained mainly based on the effect of bending and the difference in the stress triaxiality level, among others. This research analyzes the initiation of ductile fracture in Nakazima and SPIF specimens under a scanning electron microscope to elucidate the reasons of those differences at the microscopic level.

Abstract: Aluminium 8011 cast plates subjected to cold rolling to reduce thickness from 12 mm to 3.5 sheets. As rolled aluminium sheet was subjected to annealing treatment after rolling. This work deals with the study of planar and normal anisotropy parameters of as rolled aluminium and rolled with annealed aluminium sheets. The tensile test samples were cut at 0°, 30°, 45°, 60° and 90° with respect to the rolling direction of as rolled Al sheet and rolled with annealed Al sheet. Tensile properties were measured at different orientations to the rolling directions. The wide variation in tensile strength was found in case of as rolled Al samples at different orientation to rolling direction of sheet (208 to 243 MPa). On the other hand nearly uniform tensile strength (128 MPa to 132 MPa) was measured for rolled and annealed Al samples at different orientations. As rolled Al samples shows anisotropic tensile properties where as isotropic tensile properties were measured for rolled with annealed Al samples. Al grains are more elongated along the rolling directions where as rolled and annealed Al sample shows more equiaxed grains which is attributed to isotropic behaviour of Al sheets. The normal anisotropy parameter or average r_m value is higher (1.24) in case of rolled and annealed sheet sample as compared to as rolled Al sheet r_m value (1.06). This is attributed to isotropic behaviour of rolled and annealed samples. Toughness and ductility properties are improved more than 3 times in case of rolled and annealed Al sheet samples. Annealing treatment of rolled Al sheet samples shows elongated grain morphology changes to equiaxed grains of aluminum which tends to improved formability and isotropic mechanical properties Al sheet. For determination of normal anisotropy (r_m) value, tensile results R values are required at angles of 0 degrees, 45 degrees, and 90 degrees. However in this study additional R values are estimated at 30 degree and 60 degree in order to understand trend of R value at every 30 degree from 0 to 90 degree.

Abstract: Flanges are commonly used in aircrafts to provide stiffness and support for the assembly Incremental Sheet Forming (ISF) processes have been approached to produce both stretch and shrink flanges as a low-cost alternative in the fabrication of a small number of parts and prototypes. This work analyzes stretch and shrink flanges of AA2024-T3 sheet with different geometries manufactured by Single Point Incremental Forming (SPIF). The numerical simulation using Finite Elements of the flanges allows evaluating the stress in successful and failed flanges. On the one hand, the formability of stretch flanges is usually evaluated in terms of principal strains within the Forming Limit Diagram (FLD). However, this approach does not seem to capture all the physics to explain the enhancement in formability observed in SPIF over the conventional forming. A formability analysis is performed in the field of stress triaxiality versus equivalent plastic strain, discussing the differences between successful and fractured specimens. On the other hand, for shrink flanging, the appearance of wrinkles is analyzed in terms of the compressive stresses along the flange during the incremental forming. This allows to determine a critical limit stress of winkling to predict the failure in practice for a given geometry and forming condition.

Abstract: Single-Point Incremental Forming (SPIF) is a flexible technology that can form a wide range of sheet metal products without the need for using punch and die sets. As a relatively cheap and dieless process, this technology is preferable for small and medium customised production. However, the SPIF technology has drawbacks, such as the geometrical inaccuracy and the thickness uniformity of the shaped part. For the purpose of determining the optimal value for the technological parameters from the experimental results when evaluating the forming ability through the strain angle α during the processing of SUS 304 sheet material by SPIF technology. The article has conducted experiments to collect parameters; and experimental planning to establish a mathematical model, determine the optimal value for the parameters of the machining process such as tool diameter, tool feed and tool running speed.

Abstract: The composite materials are high on demand in various applications, because of the wide range of properties that they offer, for that, they need to adapt into complex shapes to serve as a functional part. So, the forming process must be mastered and studied to benefit from what composites offer. The most used manufacturing process for composite materials are the resin transfer molding (RTM), which require a preforming of the dry fabric into the desired shape. During the pre-forming process yarns networks orientation change and different defects can be generated due to a variety of factors that have a role in their appearance, such as the process settings, type of the reinforcement, the characteristics of the shapes’ geometry. In this study, we concentrate on the effect of the geometries’ characteristics on the appearance of the different defects and the induced shear on the fabric. Different geometries have been selected based on a benchmark of the shapes studied in the literature [1–3]. The pre-forming was conducted on 3 types of dry fabrics. Woven and non-woven, balanced, and unbalanced fabrics have been intentionally selected as fabrics with completely different structures (type of material, weaves, balance...) to observe the change in the fabric’s behavior and he induceddefects, in terms of profil, location and amplitude.

Abstract: This study presents a numerical analysis of the tube expansion process by conventional tube-end forming versus single point incremental forming (SPIF) using DEFORM. The work includes the assessment of the strain paths within the principal strain space of these processes with respect to the formability limits as well as their evaluation within the equivalent strain versus stress triaxiality space. The results obtained demonstrated that the mechanics of tube flaring process in conventional and incremental forming are substantially different. This analysis of formability in the light of the accumulated equivalent strain and the average stress triaxiality allowed a better understanding of the differences between both processes in terms of the fracture limit strains.