Double Sided Incremental Forming Research Articles

A Mixed Double-Sided Incremental Forming Toolpath Strategy for Improved Geometric Accuracy

Double-sided incremental forming (DSIF) is a relatively new dieless forming process which uses two hemispherical ended tools, one on each side of the sheet, moving along a predefined trajectory to locally deform a peripherally clamped sheet of metal. DSIF provides greater process flexibility, higher formability, and eliminates the tooling cost when compared to conventional sheet forming processes. While DSIF provides much improved geometric accuracy compared to other incremental forming processes, current toolpath planning strategies suffer from long forming times. A novel mixed double-sided incremental forming (MDSIF) toolpath strategy is proposed in the present study. It simultaneously reduces the total forming time by half while preserving the best currently achievable geometric accuracy. The effect of the forming parameters, i.e., of the incremental depth and of tool positioning on the geometric accuracy of the parts formed with MDSIF was investigated and compared to those formed by traditional DSIF strategies.

Effects of Tool Positions in Accumulated Double-Sided Incremental Forming on Part Geometry

In accumulated double-sided incremental forming (ADSIF), two hemispherical tools impart the local deformation to the sheet via their programed in-plane spiral motion and the depth of the part is achieved via rigid body motion of the already formed part. Unlike single point incremental forming (SPIF) and double-sided incremental forming (DSIF), ADSIF does not impose forces on the already-formed part and, therefore, has the potential of achieving higher geometric accuracy. A systematic method is proposed in this work to study the influences of the relative tool positions on the local formed shape and the final geometry, which is essentially the accumulation of all previously formed local deformations. Meanwhile, the concepts of the stable angle and the peak angle are introduced to better describe the cross-sectional geometry of a formed part with a constant wall angle at that particular cross section. It is recommended that, while multiple combinations of the relative positions of two forming tools may achieve the same stable angle that the positioning parameters should be chosen such that the resultant forming force or the wall angle variation between the stable and peak angles is minimized.

Challenges and Process Strategies Concerning Multi-Pass Double Sided Incremental Forming

The design domain of Double Sided Incremental Forming (DSIF) can be enhanced through the use of multipass strategies. The chosen tool gap in multipass DSIF, or multi-DSIF, is dependent on the estimated thickness of the sheet being formed, which is traditionally done through the Sine Law. In this work, a simple modification to the Sine Law is performed so as to prevent the tool gap from approaching zero at regions where the part contains a near vertical wall. Additionally, various multipass strategies regarding the design of the intermediate stages were trialed in an effort to increase geometric accuracy. Increasing the depth between subsequent stages of DSIF was found to provide the best results due to the accommodation of rigid body motion.

Investigation of material deformation mechanism in double side incremental sheet forming

Double side incremental forming (DSIF) is an emerging technology in incremental sheet forming (ISF) in recent years. By employing two forming tools at each side of the sheet, the DSIF process can provide additional process flexibility, comparing to the conventional single point incremental forming (SPIF) process, therefore to produce complex geometries without the need of using a backing plate or supporting die. Although this process has been proposed for years, there is only limited research on this process and there are still many unanswered open questions about this process. Using a newly developed ISF machine, the DSIF process is investigated in this work. Focusing on the fundamental aspects of material deformation and fracture mechanism, this paper aims to improve the understanding of the DSIF process. Two key process parameters considered in this study include the supporting force and relative position between master and slave tools. The material deformation, the final thickness distribution as well as the formability under varying conditions of these two process variables are investigated. To obtain a better understanding from the experimental results, an analytical model has been developed to evaluate the stress state in the deformation zone. Using the developed model, an explicit relationship between the stress state and key process parameters can be established and a drop of stress triaxiality can be observed in the double contact zone, which explains the enhanced formability in the DSIF process. Based on the analytical and experimental investigation, the advancements and challenges of the DSIF process are discussed with a few conclusions drawn for future research.

Optimization of relative tool position in accumulative double sided incremental forming using finite element analysis and model bias correction

Double-Sided Incremental Forming (DSIF) uses two small, independently moving, hemispherical tools on either side of the sheet to form a desired shape by following a predefined tool path. This study was motivated by the observation that the relative tool position of the tools, specified in the tool path generation algorithm, affects the formed geometric accuracy. A methodology for defining the relative tool positioning in the tool path generation algorithm based on local part geometry is proposed using simplified Finite Element Analysis (FEA) and sample physical experiments combined with Gaussian Process modeling techniques. This approach can take into account the mechanics of deformation in DSIF explicitly and physical compliance of the DSIF machine implicitly. Physical experiments were performed to demonstrate the effectiveness of the proposed framework.

Experimentation and Design of Prototype Device for Three Point Incremental Forming

Based on the principle of Single Point Incremental Forming (SPIF) and Double Side Incremental Forming (DSIF), A new Three Point Incremental Forming (TPIF) prototype device was developed to improve the forming accuracy. The mechanical structural components and the control system were designed and the TPIF prototype device was assembled. A TPIF trial example proved that this TPIF device can realize more forming accuracy than SPIF and DSIF. This TPIF prototype device provides a good platform for further study of the three point incremental forming.

Comparison of the Geometric Accuracy by DSIF Toolpath with SPIF Toolpath

As there is no sufficient support between the single moving tool and fixture, the formed metal sheet is easy to bend in single point incremental forming (SPIF). Double sided incremental forming (DSIF) is proposed in which two tools are used on each side of the sheet to improve the components forming accuracy. Element finite method is introduced to simulate the forming process with both DSIF and SPIF toolpaths and the component geometric accuracies are compared. The simulation result shows the DSIF toolpaths can obtain better geometric accuracy than SPIF.

Deformation mechanics in single-point and accumulative double-sided incremental forming

Single-point incremental forming (SPIF) uses one small hemispherically ended tool moving along a predefined toolpath to locally deform a completely peripherally clamped sheet of metal such that the sum total of the local deformations yields the final desired shape of the sheet. While SPIF is characterized by greater formability than conventional forming processes, it suffers from significant geometric inaccuracy. Accumulative double-sided incremental forming (ADSIF) is a substantial improvement over SPIF in which one hemispherically ended tool is used on each side of the sheet metal. The supporting tool moves synchronously with the forming tool, therefore acting as a local but mobile die. ADSIF results in considerably enhanced geometric accuracy and increased formability of the formed part as compared to SPIF. In light of the aforementioned advantages of ADSIF as compared with SPIF, an investigation of the mechanics associated with the ADSIF process, which has yet to be presented in the literature, is warranted. The present study sheds light on the differences in deformation mechanisms between SPIF and ADSIF. Finite element analyses are performed to simulate deformation in the two processes, and a detailed analysis of the deformation history is presented. It is shown that the presence of the supporting tool in ADSIF elicits substantial differences in the plastic strain, hydrostatic pressure, and shear strains as compared to SPIF. The implications of these trends on the prevalent modes of deformation in ADSIF along with possible explanations for increased formability observed in the process arediscussed.

Accumulative-DSIF strategy for enhancing process capabilities in incremental forming

This work proposes a novel Accumulative Double Sided Incremental Forming (ADSIF) strategy in which the forming begins at the location of the deepest feature and gradually shapes up the features by taking advantage of rigid-body motions. Compared to the conventional toolpath used in DSIF and SPIF, this strategy can dramatically improve geometric accuracy, increase formability, form components with desired thickness and create complex components. Furthermore, an examination of the forming forces shows that the dominant forces using this strategy are in the plane of the sheet resulting in a significant improvement in geometric accuracy.

Improvement of Geometric Accuracy in Incremental Forming by Using a Squeezing Toolpath Strategy With Two Forming Tools

Single point incremental forming (SPIF) is plagued by an unavoidable and unintended bending in the region of the sheet between the current tool position and the fixture. The effect is a deformation of the region of the sheet in between the formed area and the fixture as well as deformation of the already formed portion of the wall, leading to significant geometric inaccuracy in SPIF. Double sided incremental forming (DSIF) uses two tools, one on each side of the sheet to form the sheet into the desired shape. This work explores the capabilities of DSIF in terms of improving the geometric accuracy as compared to SPIF by using a novel toolpath strategy in which the sheet is locally squeezed between the two tools. Experiments and simulations are performed to show that this strategy can improve the geometric accuracy of the component significantly by causing the deformation to be stabilized into a local region around the contact point of the forming tool. At the same time an examination of the forming forces indicates that after a certain amount of deformation by using this strategy a loss of contact occurs between the bottom tool and the sheet. The effects of this loss of contact of the bottom tool on the geometric accuracy and potential strategies, in order to avoid this loss of contact, are also discussed.