Incremental Sheet Forming Processes Research Articles

Numerical Modelling for Efficient Analysis of Large Size Multi-Stage Incremental Sheet Forming

Incremental sheet forming (ISF) is an advanced flexible manufacturing process to produce complex 3D products. Unlike the conventional stamping process, ISF does not require any high cost dedicated dies. However, numerical computation for large-size ISF processes is time-consuming, and its accuracy for spring back due to unclamping tools after ISF cannot satisfy industrial demand. In this paper, an advanced numerical model considering complicated forming tool paths, trimming, and spring back was developed to efficiently simulate the multi-stage deformation phenomena of incremental sheet forming processes. Numerical modeling accuracy and efficiency are investigated considering the influence of tool path, material properties of the blank, mesh size, and boundary conditions. Through a series of case studies and comparisons with experimental results, it is observed that the numerical model with kinematics material properties and a moderate element size (5 mm) may reproduce the deformation characteristics of ISF with good accuracy and can obtain practical efficiency for a large-size ISF part.

Formability Analysis of Stretch and Shrink Flanging by Single Point Incremental Forming Based on Stresses

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.

On the effective peek application for customized cranio-maxillofacial prostheses: An experimental formability analysis

Single Point Incremental Forming (SPIF) is a dieless and flexible forming technology that allows performing complex shapes and presents a high economic payoff for low production series. In this context, this research presents an experimental investigation of Polyether ether ketone (PEEK) sheets deformed by SPIF at room temperature, determining the influence of the process parameters on the material formability. The research is performed in terms of principal strains that are evaluated within the material Forming Limit Diagram (FLD) obtained by means of Nakajima tests allowing to establish the forming limits of PEEK sheet material. On the other hand, the results of the SPIF tests performed gave rise to an analysis in terms of formability, modes of failure, temperature, forming force, and geometry accuracy. These experiments allow assessing the optimal parameters and forming methodologies/procedures for the manufacturing of cranio-maxillofacial prostheses. In this sense, it was performed a global study in terms of the formability of the manufactured prostheses, as well as the shape accuracy, temperature and roughness analysis, among others. This research showed that the maximum strains attainable by the two prostheses were still found far away from the Fracture Forming Limit (FFL) of the material, showing the feasibility to obtain extra formability within the forming safe zone. In conclusion, this work proved the high potential of manufacturing prostheses in the biomedical field using Incremental Sheet Forming (ISF) processes in combination with advanced biocompatible polymers such as PEEK.

Influence of mechanical characterization on the prediction of necking issues during sheet flow forming process

Flow forming is an incremental sheet forming (ISF) process during which a sheet metal is compressed and stretched multiple times by means of one or multiple rotating roller tools. The local tool-workpiece contact zone evolves during the entire process. The necking phenomenon, which corresponds to an uncontrolled thinning of the part wall, is introduced. This phenomenon represents a major issue for ISF processes. A review of the state-of-the-art about ISF processes shows that most studies do not consider the loading path complexity when choosing the mechanical characterization test and its associated constitutive model. Besides, the prediction of necking occurring during sheet flow forming is poorly studied in the literature. In this paper, a finite element analysis (FEA) using the FORGE® software enables a detailed understanding of the loading path (strain and stress states) prevailing during the flow forming operation. Based on the peculiarities of this loading path, different mechanical tests associated with adequate constitutive models are chosen to characterize the material behavior. The ability of each constitutive model used within the FE approach to predict necking is then assessed. Results show that the best prediction of a geometry exhibiting necking issues is obtained with the cyclic in-plane torsion test (ITT) associated with its calibrated isotropic – kinematic hardening model. These results suggest that the behavior characterization under cyclic shear loadings is relevant. Using a simple tensile test with associated power-law provides a faster and conservative necking prediction.

A Comprehensive Review on Experimental Conditions, Strategies, Performance, and Applications of Incremental Forming for Deformation Machining

Abstract The demand for product customization and flexible manufacturing techniques is growing day by day to meet the rapid changes in customer requirements. The current review presents the developments in the domains of incremental sheet forming (ISF) and deformation machining (DM) strategies to obtain thin monolithic geometries. The study focuses on the literature on room temperature single point incremental forming that can be applied to the DM. Thin structural parts are challenging to produce by machining because they have inadequate static and dynamic stiffness and low thermal stability. Significant research work on the evolution of diverse theories that emerged to address the fundamental mechanisms of ISF and DM processes has been reported in the literature. This paper presents an outline of the significant process and response parameters, experimental strategies, deformation mechanics and fracture behavior, toolpath generation techniques, and processes’ applications. The paper reports the motivation, research directions, existing gaps, and expansion in the domains of DM processes. The paper also outlines the evolution of incremental forming for deformation machining in the context of future critical applications in the domains of biomedical, aerospace, and automotive engineering.

Investigations on the forming characteristics of a novel flexible incremental sheet forming method for low-ductility metals at room temperature

• Proposed a novel flexible ISF method without edge constraint on target blank for low-ductility materials at room temperature. • Proposed analytical model of sheet thickness for undesired severe thinning region. • Investigated deformation characteristics and advantages by comparison with other ISF processes. • Fabricated several freeform panels with typical low-ductility materials to evaluate formability and geometric deviation. As important structural freeform panels (FFPs) for medical implants and aerospace system, lightweight thin wall panels with lower ductility are conventionally produced by hot forming process by utilizing the die on the press, which is not efficient or cost-effective for small batch or customized manufacturing. The dieless incremental sheet forming (ISF) provides a promising solution with increased formability, but making sheet metal panels with low-ductility at room temperature is still a challenging work. Targeting to solve this puzzle, a novel ISF without edge constraint on the target blank between the two edge-fixed supporting layers is developed to get flexible and free plastic deformation for the target blank. To reveal the deformation mechanism of this new method, an analytical prediction model of sheet thickness in ISF process is developed to calculate the deformed thickness in severe thinning region, which indicates that the undesired severe thinning region of conventional ISF process is caused by different stress states near the constrained edge, and can be completely eliminated by this proposed method to obtain uniform plastic deformation and improved formability. Different FFPs of magnesium alloy AZ31 and titanium alloy TC4 are fabricated by the novel flexible free ISF (FFISF) to validate the improved formability, and compared with conventional ISF and three-sheet incremental forming. Experimental studies demonstrate that the proposed method provides potentials for flexible fabrication of FFPs with low ductility at room temperature. More importantly, the promising geometric accuracy without trimming can be obtained by this new method, and multiple axisymmetric parts can also be formed within a cycle time.

Recent Developments and Future Challenges in Incremental Sheet Forming of Aluminium and Aluminium Alloy Sheets

Due to a favourable strength-to-density ratio, aluminium and its alloys are increasingly used in the automotive, aviation and space industries for the fabrication of skins and other structural elements. This article explores the opportunities for and limitations of using Single- and Two Point Incremental Sheet Forming techniques to form sheets from aluminium and its alloys. Incremental Sheet Forming (ISF) methods are designed to increase the efficiency of processing in low- and medium-batch production because (i) it does not require the production of a matrix and (ii) the forming time is much higher than in conventional methods of sheet metal forming. The tool in the form of a rotating mandrel gradually sinks into the sheet, thus leading to an increase in the degree of deformation of the material. This article provides an overview of the published results of research on the influence of the parameters of the ISF process (feed rate, tool rotational speed, step size), tool path strategy, friction conditions and process temperature on the formability and surface quality of the workpieces. This study summarises the latest development trends in experimental research on, and computer simulation using, the finite element method of ISF processes conducted in cold forming conditions and at elevated temperature. Possible directions for further research are also identified.

A review article on process parameters affecting Incremental Sheet Forming (ISF)

The design and fabrication processes involved in traditional sheet metal forming processes are typically expensive. Whereas Incremental Sheet Forming (ISF) is extremely adaptable towards traditional milling kind of machinery and involves minimal utilization of complex tooling, forming presses, and dies along with lowering the cost of the process. In addition to that, it is very convenient to automate the process for the wide scope of application. In the last two decades, comprehensive ISF research has led to substantial progress in basic understanding and the creation of new processing and tooling solutions. The current review article seeks to present a thorough assessment of ISF processes' current state-of-the-art along with the considerations on process parameters of the ISF and their effect on the ISF process, in terms of their technical capability and limitations. ISF process parameters on forming forces, formability, Springback, surface roughness, and accuracy, have been given specific attention. The article initially explains the fundamental of the ISF process along with its attraction and limitation point-of-view. Moreover, a brief classification of the ISF process is described following it. In addition, the critical aspects such as forming forces, formability, Springback, accuracy, and surface roughness are explained considering the influence of process parameters over them.

A Comparative Investigation of Conventional and Hammering-Assisted Incremental Sheet Forming Processes for AA1050 H14 Sheets

Incremental Sheet Forming (ISF) is emerging as one of the popular dieless forming processes for the small-sized batch production of sheet metal components. However, the parts formed by the ISF process suffer from poor surface finish, geometric inaccuracy, and non-uniform thinning, which leads to poor part characteristics. Hammering, on the other hand, plays an important role in relieving residual stresses, and thus enhances the material properties through a change in grain structure. A few studies based on shot peening, one of the types of hammering operation, revealed that shot peening can produce nanostructure surfaces with different characteristics. This paper introduces a novel process, named the Incremental Sheet Hammering (ISH) process, i.e., integration of incremental sheet forming (ISF) process and hammering to improve the efficacy of the ISF process. Controlled hammering in the ISF process causes an alternating motion at the tool-sheet interface in the local deformation zone. This motion leads to enhanced material flow and subsequent improvement in the surface finish. Typical toolpath strategies are incorporated to impart the tool movement. The mechanics of the process is further explored through explicit-dynamic numerical models and experimental investigations on 1 mm thick AA1050 sheets. The varying wall angle truncated cone (VWATC) and constant wall angle truncated cone (CWATC) test geometries are identified to compare the ISF and ISH processes. The results indicate that the formability is improved in terms of wall angle, forming depth and forming limits. Further, ISF and ISH processes are compared based on the numerical and experimental results. The indicative statistical analysis is performed which shows that the ISH process would lead to an overall 10.99% improvement in the quality of the parts primarily in the surface finish and forming forces.

Studying Formability Limits By Combining Conventional and Incremental Sheet Forming Process

In this work it is assessed the potential of combining conventional and incremental sheet forming processes in a same sheet of metal. This so-called hybrid forming approach is performed through the manufacture of a pre-forming by conventional forming, followed by incremental sheet forming. The main objective is analyzing strain evolution. The pre-forming induced in the conventional forming stage will determine the strain paths, directly influencing the strains produced by the incremental process. To conduct the study, in the conventional processes, strains were imposed in three different ways with distinct true strains. At the incremental stage, the pyramid strategy was adopted with different wall slopes. From the experiments, the true strains and the final geometries were analyzed. Numerical simulation was also employed for the sake of comparison and correlation with the measured data. It could be observed that single-stretch pre-strain was directly proportional to the maximum incremental strains achieved, whereas samples subjected to biaxial pre-strain influenced the formability according to the degree of pre-strain applied. Pre-strain driven by the prior deep-drawing operation did not result, in this particular geometry, in increased formability.

Studying parameters affecting the thinning rate during heat-assisted incremental sheet forming of the lightweight material

ABSTRACT Incremental sheet forming (ISF) is a promising sheet forming process and becomes a worthy alternative to the traditional sheet forming processes. ISF has used in manufacturing small batch or customised sheet components in various industrial sectors. One of the main challenges in this process is how to deals with hard to form materials like lightweight materials. Heat-assisted ISF processes have suggested improving the formability at warm or hot conditions. Among all heat-assisted ISF processes, frictional stir-assisted Single Point Incremental Forming (SPIF) recommended to deform AA6061-T6 sheets. The aim is to investigate the impact of the process parameters on the thinning rate of the final components. A Taguchi technique and varying wall angle conical frustum (VWACF) test have employed to conduct the experiments. Furthermore, analysis of variance (ANOVA) utilised to find the influence of these parameters on the thinning rate. The results show that spindle speed is the main parameter affected the formability of AA6061-T6 sheets in terms of thinning rate. The percentage contribution of this parameter was 90.53%. The maximum thinning is 59.56 % at a rotation speed, feed rate, step size, and tool diameter of 1200 rpm, 500 mm/min., 0.2 mm, and 10 mm, respectively.

Switched model predictive path control of incremental sheet forming for parts with varying wall angles

As a promising rapid manufacturing technology, incremental sheet forming (ISF) has been tentatively applied in forming prototype parts in many industries, such as aerospace, automobile etc. One of the problems facing scientists and engineers is that geometric accuracies of the parts formed by typical open-loop ISF processes cannot meet dimensional requirements in industries. To address this problem, linear model predictive control (MPC) approaches have been developed that optimize the ISF tool paths to reduce geometric errors. However, in the ISF process, the geometric response of the formed part relative to the tool perturbation is highly non-linear. Due to model mismatch, existing linear MPC path control approaches have been successfully applied to simple geometries only. In contrast, this paper proposes a generic and systematic tool path control approach for forming parts with varying wall angles which have more complex geometric features. In particular, a Switched MPC framework based on linearizing the non-linear ISF geometry response with linear parameter-varying (LPV) state-space models is developed. Then, optimized tool paths to compensate geometric errors were determined by solving convex optimization problems. Experiments were conducted to validate the performance of the developed control approach. The results show that the developed Switched MPC was able to reduce the maximum geometric error by 72 %, 49 % and 80 % in the wall, conjunction and base zones of the formed “funnel”-shaped part respectively. Compared to the Conventional MPC, the Switched MPC improved the maximum geometric error in the wall zone by 0.21 mm. The Switched MPC control algorithm is then shown to be robust on two other complex shapes with varying wall angles.

Deformation Feature of Sheet Metals During Inclined Hole-Flanging by Two-Point Incremental Forming

Incremental hole-flanging is an applicable extension of incremental sheet forming (ISF), but the knowledge on the deformation of metallic sheets during the course is lack, especially when the axes of the flanged necks are not perpendicular to the sheet plane. The current study used Al 6061 and SUS 304 stainless steel sheets with the thickness of 1 mm and 0.3 mm to examine the inclined hole-flanging processes on the flat plates by two-point ISF processes. It was found that, although as a whole the thickness variation is thinning, the decreasing degrees within upper and lower domain are not equal, and the difference increases with the inclination angle. Crack, buckling and local deformity are typical defects found in the experiments. The maximum springback increases with tool diameter, inclination angle and feeding pitch. Due to the material properties and a thinner thickness, local deformity is easier to take place on SUS 304 sheets during forming. Utilizing the tool feeding path along the oblique plane can obtain even force and consequently, more uniform deformation. Moreover, the equations for preliminarily determining the dimension of precut holes were derived according to the radial developed length of the flanged neck.

Double-Sided Incremental Forming: A Review

Incremental sheet-forming (ISF) processes have been developed rapidly in the past two decades. Its high flexibility and easy operability have a significant appeal for industrial applications, and substantial progress has been made in fundamental understanding and demonstration of practical implementation. However, there are a number of obstacles including achievable accuracy and instability in material deformation, which are considered as a main contributing factor for preventing the ISF process to be widely used in industry. As a variant of the general ISF process, double-sided incremental forming (DSIF) uses an additional supporting tool in the opposite side of the workpiece, maintains the flexibility, and at the same time improves the material deformation stability and reduces material thinning. In recent years, there has been increased research interest in looking into DSIF-specific material deformation mechanisms and investigation. This paper aims to provide a technical review of the DSIF process as benchmarked with single-point incremental forming (SPIF). It starts with a brief overview of the current state of the art of both SPIF and DSIF. This is followed by a comparative study between SPIF and DSIF with the key research challenges identified. This leads to a recommendation of future directions for DSIF focused research.

Investigation of the Effect of Process Parameters on Energy Consumption in Incremental Sheet forming

The selection of machine tool and process parameters plays a crucial role in the energy consumption in manufacturing processes such as incremental sheet forming (ISF) process. The analysis of how the process parameters influence the energy required during ISF processes will not only provide opportunity to reduce the environmental consequences, but also reduce economic cost. To this end, an empirical power model is presented with the aim of understanding energy consumption composition during ISF performed on a milling machine. The effects of process variables (e.g., material strength, step down, sheet thickness, tool diameter, and feed rate) on the power, forming time, and energy required for ISF processes are experimentally investigated. In particular, experimental results are in-depth analyzed to understand energy required breakdown by a machine tool during the ISF. Further, the mechanism on how the process parameters affect the energy required for the sheet plastic deformation is revealed. Based on the analysis above, useful energy-saving suggestions on selecting process parameters are provided.

Experimental and numerical study of a new hybrid process: multi-point incremental forming (MPIF)

Multi-Point Incremental Forming (MPIF) process is a new hybrid process that combines two common manufacturing methods. These are Multipoint Forming (MPF) and Incremental Sheet Forming (ISF) processes. In this study, an experimental set-up, based on a MP reconfigurable die, was designed and manufactured to explore the flexibility of this innovative process and its potentialities to produce complex parts using the same tools. The obtained results have indicated that this novel technique, that doesn’t require costly equipments, is an effective approach to manufacture multitude of parts with different shapes. Moreover, it has been shown that the parts geometrical accuracy as well as thickness distribution are enhanced compared to the conventional ISF process and that the geometrical defects, called ‘dimples’ and caused by the pins’ ends, are significantly reduced and almost eliminated after the insertion of a rubber piece between the reconfigurable die and the blank sheet. On the other hand, the effect of the size and geometry of the rectangular pins on the geometrical accuracy and the dimpling defect has been studied using a finite element analysis.

Contribution to a biomedical component production using incremental sheet forming

Incremental sheet forming (ISF) is a relatively recent technology that allows producing highly custom-made components at a reasonable manufacturing cost. Single-point incremental sheet forming (SPIF) is one of the easiest ISF processes. In this sense, recent published results have revealed an increasing interest in shaping components for biomedical uses. This paper focuses on the establishment of a platform dedicated to produce biomedical complex geometry component. The main issue to be carried out is to improve the quality and the precision of manufactured products. The study shows the feasibility of socket fittings, applied to the femoral amputees, aimed at slowing wear between friction surfaces. The thinning has been analyzed as a formability indicator; also, the surface roughness has been addressed. The experimental results show a significant effect of the spindle speed in the ISF process of the increment on the surface roughness swept by the tool/sheet contact and the forming force. The analysis carried out on the deformed sheet shows a slight offset between the programmed surface, representing the real model, and the deformed surface obtained at the end of the process.

Experimental Investigation of Forming Forces in Frictional Stir Incremental Forming of Aluminum Alloy AA6061-T6

The incremental sheet forming (ISF) process is an emerging flexible sheet-forming process, which is adequate for the manufacturing of unique or small-volume batches. Single-point incremental forming (SPIF) is the original technology of incremental sheet-forming processes. In this article, frictional stir-assisted SPIF was used to deform AA6061-T6 aluminum alloy. Experimental tests were conducted to measure the forming forces during this process for the concerned lightweight material. The influence of process parameters was investigated, which included tool rotation speed, feed rate, step size and tool diameter on the produced forming forces. A Taguchi technique for the design of experiment (DOE) and the varying wall angle conical frustum (VWACF) test was employed in this study. The results show that the rotation spindle speed was the most dominant parameter that affects the forming forces, followed by the step size, feed rate and tool diameter. In addition, the interaction between the feed rate and step size has a notable impact on the values of the forming forces.

Integration of design rules and process modelling within SPIF technology-a review on the industrial dissemination of single point incremental forming

Incremental sheet forming (ISF) processes like single-point incremental forming (SPIF) have been majorly studied since the beginning of the 2000s. Besides the applications in the prototyping field, ISF processes can also be used in the manufacture of unique parts and small batches. This capability led to new business possibilities, enabling the development of exclusive or custom products. Despite being a free-form manufacture process, ISF has some geometric limitations, mainly due to the forming mechanics and formability limit of the materials. Thus, it is important to establish well-defined guidelines to grant a feasible design. This paper presents a knowledge basis to design and manufacture ISF parts, mainly by SPIF. The possible part configurations and the design orientation are settled, allowing for a suitable part development. The hardware to perform incremental forming operations is outlined and the forming process is described, presenting alternative solutions. The process modelling is completed with a brief description of methods to improve part quality.

Capability of iterative learning control and influence of the material properties on the improvement of the geometrical accuracy in incremental sheet forming process

Incremental Sheet Forming (ISF) is a flexible technology that allows the deformation of blank sheets without the need of complex and high cost tools or equipments. One of the main lacks of ISF is the geometrical accuracy which is not comparable with the one achieved by using traditional sheet stamping processes. There are several approaches proposed to enhance this aspect and among them the Authors have developed a method based on an Iterative Learning Control (ILC). ILC consists of a cyclic and progressive error compensation method that improves the quality of the manufactured parts. ILC has been proved to be capable for optimising the production of parts with tight tolerances when dealing with ductile materials (aluminium and steel alloys) and small deformations. In this paper, the method was tested to investigate its capability in a virtual environment. The suggested compensations were checked with Finite Element Method (FEM) so to reduce the number of parts to be manufactured saving time and costs. Moreover, the algorithm was tested considering both a difficult to form material (titanium alloy) and high deformation conditions. The results demonstrated how the precision of ISF processes depends on the blank material properties. Moreover, the capabilities of ILC are shown and discussed.