Double Sided Incremental Forming Research Articles

Analysis of continuous magnetic field-assisted double-sided incremental forming

This paper describes the analysis of continuous magnetic field-assisted double-sided incremental forming (M-DSIF), a derivation of magnetic field-assisted single-point incremental forming (M-SPIF). In M-DSIF, the driving magnet remains in contact with the workpiece and does not allow for relaxation between individual steps (called contours). M-DSIF enables forming of truncated cones much faster and more accurately than M-SPIF. The number of revolutions per contour of the tool greatly impacts the resulting shape. The proposed two-step M-DSIF is a viable option for distributing material from the center toward the corners of the cone base, which minimizes localized strain in the corners.

Reforming toolpath effect on deformation mechanics in double-sided incremental forming

Incremental sheet metal forming is a die-less process known for its high flexibility, making it a suitable choice for fabricating low-batch, highly customized complex parts. In this paper, the deformation mechanism of double-sided incremental forming (DSIF) with single pass or reforming toolpaths and its effect on the deformation-induced martensite transformation kinetics are investigated by experiments and finite element (FE) simulations for a truncated pyramid part geometry for the first time. An FE model accounting for tool deflection is developed, considering the change in tools' position caused by the forces applied at the contact with the blank. This is done to enhance the simulation accuracy in comparison to experimental results. A comprehensive analysis is conducted with respect to the stress state change and strain accumulation during DSIF with the single pass and reforming toolpaths. The findings reveal that material points along the pyramid wall primarily deform by a combination of plane strain tension, plane strain compression, and shear, depending on the tools’ locations on the sheet surfaces in relation to the material point of interest. The reversal of the forming direction in the reforming toolpath causes material points to experience different stress states and more strain accumulation than the single pass case. Under the same forming temperature, this phenomenon results in a higher and closer martensite transformation on both forming and supporting surfaces of the final part when employing the reforming toolpath as opposed to the single pass case.

Cluster analysis for systematic database extension to improve machine learning performance in double-sided incremental sheet forming

Incremental sheet forming is a process for the production of sheet metal parts in small batch sizes. Due to the relatively low geometrical accuracy and the lack of precise and fast finite element analysis simulations of the process, industrial use cases are rare. Recently, a vast amount of scientific approaches simulated the process by utilizing machine learning techniques. Their success is limited by the quantity and quality of the used process data. Research institutes are struggling to gather enough data without industrial cooperations. For maximizing the distribution of process data in an experimental series and therefore their applicability for machine learning, the authors present a novel cluster analysis approach to systematically extend an existing database. The whole established process database consisting of 70 forming experiments and their toolpaths and digitizations is published to be used as a foundation for similar research.

Optimal process planning for energy consumption and product quality during double-sided incremental forming

Optimal process planning for energy consumption and product quality during double-sided incremental forming

Manipulating martensite transformation of SS304L during double-sided incremental forming by varying temperature and deformation path

Double-sided incremental forming (DSIF) is a die-less sheet metal forming process capable of fabricating complex parts. The flexibility of DSIF can be used for in-situ mechanical properties alteration, e.g., by controlling deformation-induced martensite transformation of austenitic stainless steels. In this paper, SS304L is deformed using DSIF at three different cooling conditions and two different tool paths to affect the martensite transformation. Additionally, finite element analyses were used to understand the effect of tool paths on springback and plastic strain. Implementing a reforming tool path at the lowest achievable temperature resulted in a martensite volume fraction as high as 95%.

Fast simulation of incremental sheet metal forming by multi-tooling

Fast and precise numerical analyses are necessary for virtual process design in the incremental sheet forming (ISF) process to extend its utilization effectively to industrial applications. Reliable process simulation ensures the short lead-time process advantage by ensuring the right products in the first attempt. Previous studies illustrate that explicit finite elements with mass or time scaling can reduce the simulation time without compromising the results. Still, the simulation time is much higher than the time consumed during real production. Keeping this in view, an approach of multi-tooling, which is rarely investigated, is focused on in this work to minimize the simulation time by utilizing the Abaqus software. The complete toolpath was split into equal segments, and one pair of tools was assigned to each segment. Instead of continuous movement in a single direction, as occurs in the case of single pair of tools, the tool was moving back and forth in the consecutive contours while moving simultaneously in the negative Z-direction in its designated segment. This concept was first trialed on the pyramid shape for sheet thickness variation, geometric precision, Mises stresses, equivalent strain, and forces. After verifying the model with the experimental results for some key quality attributes and simulation results based on single pair of tools (which was used as a reference computation as it represents the actual experiment), it was extended to a large industrial component with five pairs of tools in a double-sided incremental forming (DSIF) process and was compared with the reference computation. The results acquired with multi-tools were in good agreement with experimental and reference computation while reducing the simulation time by more than 200 %. The concept of multi-tooling, which is extensively studied in this work, can be easily implemented without adding a complex algorithm to the finite element model.

A toolpath strategy for double-sided incremental forming of corrugated structures

This study focuses on developing a new toolpath strategy for manufacturing near-net shape corrugated structures using rectangular sheets whose two opposite edges are clamped based on the mechanics of Double-sided incremental forming (DSIF) process. The newly suggested strategy, Regional Plastic Incremental Bending (RPIB), is designed to capitalize on the effect of regional plastic bending in a way that a local geometric feature is incrementally formed without causing global elastic springback. The performance of the RPIB toolpath strategy is compared to the previously developed linear toolpath strategy that does not consider any anticipated springback errors in its design stage. It has been experimentally proven that the RPIB strategy results in significant improvements in the geometric accuracy of formed corrugated profiles. • A new toolpath strategy for manufacturing corrugated structures with Double-sided Incremental Forming (DSIF) technology. • Investigation of DSIF process characteristics under the condition of two opposing edges of the sheet are clamped. • Analysis of possible process failure modes in DSIF of corrugated structures.

Effect of support force on quality during double-sided incremental forming: an experimental and numerical study

Effect of support force on quality during double-sided incremental forming: an experimental and numerical study

Multipass double-sided incremental forming method for improving geometric accuracy and forming quality

Double-sided incremental forming (DSIF) has been extensively researched due to its high flexibility, good formability, and low cost when performed in small batches, and it enables the production of personalized sheet parts. However, the influences of process parameters on the geometric accuracy, thickness distribution, and forming quality are not well understood. In this paper, a multipass DSIF method is proposed. Based on the law of sines, the distance between the closest surface of the hemispherical forming tool and the supporting hemispherical tool is given, and a series of experiments are conducted. The influences of process parameters such as the toolpath strategy, incremental depth, and squeeze factor on the quality metrics in multipass DSIF, such as the geometric error, thickness distribution, and forming quality are investigated and compared to those formed by DSIF, accumulative double-sided incremental forming, and mixed double-sided incremental forming. The results show that multipass DSIF can effectively improve the geometric accuracy, thickness distribution, and surface quality. The thinning of the material increases slightly with the squeeze factor of the first D-pass decreases, and the different incremental depths have little effect on the thickness distribution. The multipass DSIF method provides some significant engineering advancements for improving geometric accuracy and forming quality.

Prediction of forming temperature in electrically-assisted double-sided incremental forming using a neural network

Electrically-assisted double-sided incremental forming (EA-DSIF) is a flexible forming method suitable for processing hard-to-form materials and complex-shaped parts. A challenge in EA-DSIF experiments is temperature measurement. Since the localized forming zone is blocked by the tools, it is not possible to measure the actual forming temperature distribution in the forming zone. To address this issue, we propose an artificial neural network (ANN) framework for predicting the forming temperature using measurements of the surrounding temperature and toolpath features. The ANN model was trained using the temperature outputs of finite element models. A simplified EA-DSIF simulation model was developed for computational efficiency needed for synthetic data generation. Model simplifications were justified in multiple cases and validated with experimental data by comparing the temperatures from positions that is visible to an infrared camera. The feasibility of applying the developed ANN model to untrained geometries and in practical applications was demonstrated. The findings generated from this study are crucial for selecting optimum process parameters, estimating the forming force, and predicting microstructure evolution during EA-DSIF.

A Review on Part Geometric Precision Improvement Strategies in Double-Sided Incremental Forming

Low geometric accuracy is one of the main limitations in double-sided incremental forming (DSIF) with a rough surface finish, long forming time, and excessive sheet thinning. The lost contact between the support tool and the sheet is considered the main reason for the geometric error. Researchers presented different solutions for geometric accuracy improvement, such as toolpath compensation, adaptation, material redistribution, and heat-assisted processes. Toolpath compensations strategies improve geometric precision without adding extra tooling to the setup. It relies on formulas, simulation, and algorithm-based studies to enhance the part accuracy. Toolpath adaptation improves the part accuracy by adding additional equipment such as pneumatically or spring-loaded support tools or changing the conventional toolpath sequence such as accumulative-DSIF (ADSIF) and its variants. It also includes forming multi-region parts with various arrangements. Toolpath adaptation mostly requires experimental trial-and-error experiments to adjust parameters to obtain the desired shape with precision. Material redistribution strategies are effective for high-wall-angle parts. It is the less studied area in the geometric precision context in the DSIF. The heat-assisted process mainly concentrates on hard-to-form material. It can align itself to any toolpath compensation or adaptation strategy. This work aims to provide DSIF variants and studies, which focus on improving geometric accuracy using various methodologies. It includes a brief survey of tool force requirements for different strategies, sheet thickness variation in DSIF, and support tool role on deformation and fracture mechanism. Finally, a brief discussion and future work are suggested based on the insights from several articles.

A toolpath strategy for improving geometric accuracy in double-sided incremental sheet forming

The double-sided incremental forming (DSIF) improved the process flexibility compared to other incremental sheet forming (ISF) processes. Despite the flexible nature, it faces the challenge of low geometric precision like ISF variants. In this work, two strategies are used to overcome this. First, a novel method is employed to determine the optimal support tool location for improving geometric precision. In this method, the toolpath oriented the tools to each other systematically in the circumferential direction. Besides, it squeezed the sheet by the same amount at the point of interest. The impacts of various support tool positions in the circumferential direction are evaluated for geometric precision. The results demonstrate that the support tool should support the master tool within 10° to its local normal in the circumferential direction to improve the geometric accuracy. Second, a two-stage process reduced the geometric error of the part by incrementally accommodating the springback error by artificially increasing the step size for the second stage. With the optimal support tool position and two-stage DSIF, the geometric precision of the part has improved significantly. The proposed method is compared to the best DSIF toolpath strategies for geometric accuracy, surface roughness, forming time, and sheet thickness fluctuations using grey relational analysis (GRA). It outperforms the other toolpath strategies including single-stage DSIF, accumulative double-sided incremental forming (ADSIF), and two-stage mixed double sided incremental forming (MDSIF). Our approach can improve geometric precision in complex parts by successfully employing the support tool and managing the springback incrementally.

Influence of the Different Combination of Diameters of Two Tool Heads on Forming Quality in Double Sided Incremental Forming

The existing double sided incremental forming (DSIF) mostly uses two tools with the same diameter as the upper/lower tools, which is not conducive to improve the forming quality and forming efficiency. In this paper, the influence of the different combination of the upper and lower tool head diameters on the thickness distribution and the contour dimension accuracy of the formed part is studied by using ANSYS / LS-DYNA software and by taking the model with bidirectional convex features as the research object. It is found that the reasonable combination of different diameters of the upper/lower tools based on the characteristics of the parts to be formed can improve the forming quality and forming efficiency.

두 개의 성형공구를 이용한 무금형 6축 양면점진성형기 개발

Incremental sheet forming (ISF) does not use a partial or full die at the bottom of the die; rather, a hemispherical forming tool presses the sheet layer by layer along the numerically controlled movement path to cause plastic deformation. The ISF is somewhat limited in manufacturing freeform surfaces because the die is installed at the bottom of the sheet material. To compensate for these shortcomings, a double side incremental forming (DSIF) method, which can form both sides of the sheet simultaneously, is required with two independently controlled tools. This machine is composed of a forming part and support part, Equipped with a motion controller capable of 6-axis control, the developed DSIF machine can freely and smoothly form surfaces. To verify its performance, prototype forming was performed, and the 3D contact measurement and shape data were superimposed to compare and analyze the forming accuracy and verify the usefulness of incremental forming.

A high-fidelity simulation of double-sided incremental forming: Improving the accuracy by incorporating the effects of machine compliance.

Double-Sided Incremental Forming (DSIF) is a technology for the rapid, flexible manufacturing of sheet metal parts. DSIF is highly nonlinear, requiring the use of complex finite element (FE) models to optimize and control the process in order to meet geometric accuracy and sheet thinning design criteria. Current FE models do not properly take into account the effects of machine compliance, which reduces their accuracy and hinders their use for optimization and control. The aim of this work is to create a greatly improved FE model of DSIF by taking a novel approach of modeling the aggregate effects of machine and tool compliance. The accuracy of the new model was extensively validated using the local geometry, thickness distribution, principal strains, and forming forces from a funnel experiment. The validated model was used to accurately predict the spatial distribution and time-histories of the equivalent plastic strain, von Mises equivalent stress, stress triaxiality, and Lode angle parameter across and along the sheet metal. The stress state was found to rapidly change through the sheet thickness, from highly compressive between the tools and the sheet, to a mixture of generalized shear and plane strain elsewhere. Moreover, the compressive regions between the two DSIF tools created a constrained deformation zone, which likely aids in prolonging the onset of excessive thinning. This improved FE model can now be used to quantitatively characterize the nonlinear local deformation mechanisms inherent to the DSIF process, thereby providing a solid foundation for future advances in process control.

Enhancement of accuracy in double sided incremental forming by compensating tool path for machine tool errors

Incremental Sheet Forming (ISF) is a dieless forming process and has capability to form complex 3D geometries. Double Sided Incremental Forming (DSIF) is the most flexible variant of ISF as it uses two tools, one on either side of the sheet (one tool forms the sheet and other acts as support). However, forming the components with acceptable accuracy is one of the challenges as it depends on many factors such as sheet and tool(s) deflections as well as machine tool errors. If these deflections/deviations are not compensated in tool path, accuracy of the component gets affected and support tool may lose contact or squeeze the sheet while forming components. In the present work, grid-based method is used to measure the machine tool error at discrete points of the work envelope. To enhance the accuracy and support tool contact condition, machine tool errors are compensated in tool path along with tool and sheet deflection compensations developed earlier. To demonstrate the effectiveness of developed methodology on the accuracy, components having different geometric characteristics as well as opening sizes are formed with and without compensating for machine tool errors in tool path. Results indicate that deviation in symmetry within the same contour reduced from 850 μm to less than 40 μm. In addition, support tool has maintained contact throughout support surface with maximum force of 50 N when machine tool errors are compensated.

Tool path design system to enhance accuracy during double sided incremental forming: An analytical model to predict compensations for small/large components

Abstract Double sided incremental forming (DSIF) has potential to form complex three-dimensional sheet metal components without using component specific tooling. Forming tool deflection and sheet spring-back are significant factors contributing to the geometrical inaccuracy of DSIF components. Numerical prediction and experimental measurement of sheet spring-back is time consuming. In addition, available analytical methods to predict and compensate sheet spring-back uses theory of small deflections by neglecting the membrane effects. With increase in sheet deflection beyond its thickness, membrane forces experienced by the middle plane of sheet due to stretching significantly resists the applied transverse load. In the present work, combination of small deflection and membrane theories are used to predict and compensate sheet deflections, so that a single methodology can be used for small as well as large components. Proposed methodology is validated using experimental and numerical predictions and they are in very good agreement. Two geometries (axisymmetric, free form components) with different component openings are formed to validate the proposed predictive methodology. Results indicate there is significant improvement (maximum error is less than 800 μ m) in accuracy of components formed using compensated tool paths developed using proposed model. In addition, support tool maintained contact with component throughout forming (maximum force on the support tool is less than 60 N).

Elucidating the deformation modes in incremental sheet forming process: Insights from crystallographic texture, microstructure and mechanical properties

This study investigates the exact state of deformation in single point incremental forming (SPIF) and double-sided incremental forming (DSIF) techniques using experimental observations of texture evolution coupled with a multiscale simulation of the processes. The texture evolution was investigated for different sets of forming parameters such as vertical displacement, wall angle and tool diameter. It was observed that difference in crystallographic texture due to change in tool diameter and vertical displacement was marginal. However, significant difference in texture evolution was observed upon changing the wall angle. Further analysis of crystallographic texture revealed that role of through thickness shear (TTS) is limited in case of DSIF process compared to SPIF process. Numerical simulation of SPIF process via finite element method was successful in capturing the contribution from TTS in SPIF process. Based on insights obtained from finite element calculations, Visco-Plastic Self-Consistent simulations were carried out which were successful in predicting the experimental texture. Finally, the effect of different incremental forming techniques on the mechanical properties of the formed components was studied. The observed anisotropy in yield strength was explained based on the inverse of average Schmid factor. Lankford parameter and yield locus were also estimated from the experimental textures to understand the feasibility of incremental forming at different wall angles.

Experimental and Numerical Investigation of Residual Stresses in Incremental Forming

Double Sided Incremental Forming (DSIF) is gaining importance over Single Point Incremental Forming (SPIF) due to its ability to form complex geometries and the capability to obtain better accuracies. In the present work, residual stresses are measured in pyramidal components formed using SPIF, DSIF using X-ray diffraction technique. Residual stress development mechanism during SPIF and DSIF is studied using Finite Element Analysis (FEA). Stress development along circumferential and meridional directions are explained using bending and unbending of sheet material taking place around forming tool. It is observed that the residual stresses are compressive on the outer surface and tensile on the inner surface of sheet in both circumferential and meridional directions. In DSIF, supporting tool restricts the unbending of sheet causing the residual stresses to be less compressive on the outer surface and less tensile on the inner surface compared to SPIF. It is also observed that with an increase in tool diameter, spring back increased, hence, meridional residual stress on the outer surface became more compressive and circumferential residual stress on the inner surface became more tensile. Residual stresses in ISF are compared with FEA predictions of conventional stamping process.

Research on point-pressing based double-sided CNC incremental forming

For the problem of the sheet distortion caused by the force of the two extrusion forming tools on the sheet in the double-sided CNC incremental forming, a point-pressing based double-sided CNC incremental forming was proposed in which the consecutive-extrusion of the extrusion forming tool on the sheet was replaced by the point-pressing. A point-pressing based double-sided CNC incremental forming toolpath generation algorithm based on the consecutive-extrusion based double-sided CNC incremental forming toolpath was presented. The double-sided CNC incremental forming processes based on the point-pressing and consecutive-extrusion was simulated by using the ANSYS/LS-DYNA software and the actual forming experiment. The numerical simulation results show that the double-sided CNC incremental forming based on the point-pressing compared with the process based on the consecutive-extrusion can acquire less circumferential displacement, less distortion, more evenly distributed average equivalent strain and less mutagenicity. It can be seen from the actual forming experiment that the sheet metal part formed by the point-pressing method has better geometric anastomosis with the design model than that formed by the consecutive-extrusion method.