Papers by Keyword: Incremental Forming

Abstract: Incremental forming represents a versatile and cost-effective alternative to conventional sheet forming processes. In recent years, its application has been extended to polymers and composite materials. Among these, natural fiber-reinforced thermoplastics offer several advantages, as natural fibers are widely available, contribute to the semi-biodegradability of the composites, and serve as effective reinforcements for polymer matrices. This experimental study examines the mechanical properties of flax woven fabric-reinforced polypropylene composites, fabricated via compression molding, and their suitability for producing spherical caps through cold incremental forming. A range of features was investigated to assess the effectiveness of incremental forming on these biobased composites and to compare the mechanical performance of undeformed and deformed laminates.

Abstract: Thick-walled longitudinally arc-welded tubes are indispensable in modern infrastructure owing to their exceptional load-bearing capacity and structural integrity. Nevertheless, their fabrication remains highly challenging, as the conventional forming forces demand the use of large-scale industrial presses. To address this limitation, this research introduces a novel process architecture that integrates agile tube roll forming process for tube manufacturing, thereby enabling the production of such tubes using significantly smaller and more flexible manufacturing systems. To this end, three tube support configurations—namely, support-less, dynamic roller support, and static support—were systematically investigated in this study on 7, 9, 11, and 15 mm thick 304 stainless steel. While the supportless condition represents the most economical option, the incorporation of dynamic or static support significantly improves geometric accuracy, yielding near-net cross-sections combined with reductions in tube ovality of approximately 75 and 79 %, respectively, compared to support-less configuration. Considering the straightness of the weld line as a quality indice, the dynamic support provides the highest quality. Using the static/dynamic support strategies, the deformation forces arise between 2 and 3 times compared to support-less strategy.

Abstract: Tailor welded blanks (TWB) are commonly used in the automotive industry to achieve heterogeneous components, particularly for creating high strength, lightweight parts. Laser welding is one method for joining TWB. Laser welding was used to create TWB composed of stainless steel 304L, with varied thicknesses, in a “patchwork quilt” pattern forming quadrants within the sample. The mechanical properties and quality of the weld were evaluated via tensile testing and microscopy. Truncated pyramids were then formed with weld seams along the faces, and springback and mechanical properties after forming were analyzed. Optical microscopy revealed that the weld seams remained intact after forming. The weld seam location in the center of the pyramid walls did not have a significant impact on the geometrical accuracy of the formed parts. The results of this study show promise for the use of SPIF with quilted TWB to achieve optimal formed part properties for the intended part application.

Abstract: The human skull can become fractured or injured through impact and often requires repair through a craniectomy and subsequent cranioplasty, surgery performed to repair defects or damage to the cranium. Challenges related to material choice, which must be biocompatible, and customization for each patient’s anatomy remain. One possible solution is fabrication of patient-specific cranial implants, out of biocompatible polymers, using single point incremental forming (SPIF). In this paper, polyetheretherketone (PEEK) and ultra-high molecular weight polyethylene (UHMWPE) are formed using SPIF at room temperature to manufacture a cranial implant. The SPIF process is used to produce formed parts from which test specimens were extracted to evaluate the tensile performance and thermal properties. Formed cranial implants were impacted using a drop weight to evaluate their suitability under relevant conditions. The geometric conformance of the SPIF process was studied to compare the material behavior for the specified polymers after forming. The results validate that SPIF can be conducted at room temperature with PEEK and UHMWPE biocompatible polymers to enable custom implant manufacturing. However, PEEK exhibited superior performance in terms of tensile strength, geometric conformance, energy absorption, and melting temperature, and is recommended over UHMWPE for future implant applications.

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: The incremental sheet forming process (ISF) is the emerging forming process in the small size product manufacturing industries where as embossing, stamping, coining operations can be used to produce a product in large quantity. Therefore, ISF is one of the best solution to decrease the cost of production when a small quantity of product is demanded. In present study Efforts are devoted to study the effect of wall angle on sheet thinning, reaction forces, reaction moments, etc. for truncated cone of aluminium alloy (AA1050) using Finite Element simulation. Initially, A MATLAB code was written for spiral tool path. Modeling and simulation was done in ABAQUS software. Thereafter, a theoretical sheet thickness was computed using sine law and it was found out to be in close agreement with simulated sheet thickness.

Abstract: Forming a metallic sheet along with the consideration of computer simulation and experiment had benefited the milling industry for a long time. The ideal forming, without an error, is a concerning topic. So, the computer simulation had the advantage then direct forming. To observe the results before doing the real experiments simulation comes handy. Which helped to set the parameters for the milling process for the single point incremental forming (SPIF) process. For milling, a CAD design was converted into a 3D model. For this, a conical shape of 3D modeling was made in fusion 360. After onwards, it was simulated for finding the maximum depth for the cracking point. Next for the experimental part, the maximum forming depth was considered, and used lubricant grease for reducing friction. While forming with the grease, the impact of parameters was also changed. Throughout the process, an optimization approach was set to reduce the cracking areas for the G-code. Along with the lubricant use, smooth milling finished surface was observed. To reducing the depth forming errors, an optimization approach was introduced in this research.

Abstract: As incremental forming is a relatively new sheet metal forming process, very limited analytical and finite element prediction models are available in literature to study the process mechanics and improve its performance. Thus, most studies involve many trial-and-error iterations to optimize the processing conditions in order to take advantage of high process flexibility and material formability. However, reducing efforts of trial-and-error iterations is of utmost importance to make a process financially viable. Therefore, an FE model is developed and experimentally validated to predict the forming forces involved in incremental micro-forming process. Different mass scaling factors and element-types are used to optimize and develop the model for accurate prediction in the least possible computation time.

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.

Abstract: Friction-spinning as an innovative incremental forming process enables large degrees of deformation in the field of tube and sheet metal forming due to a self-induced heat generation in the forming zone. This paper presents a new tool and process design with a driven tool for the targeted adjustment of residual stress distributions in the friction-spinning process. Locally adapted residual stress depth distributions are intended to improve the functionality of the friction-spinning workpieces, e.g. by delaying failure or triggering it in a defined way. The new process designs with the driven tool and a subsequent flow-forming operation are investigated regarding the influence on the residual stress depth distributions compared to those of standard friction-spinning process. Residual stress depth distributions are measured with the incremental hole-drilling method. The workpieces (tubular part with a flange) are manufactured using heat-treatable 3.3206 (EN-AW 6060 T6) tubular profiles. It is shown that the residual stress depth distributions change significantly due to the new process designs, which offers new potentials for the targeted adjustment of residual stresses that serve to improve the workpiece properties.