Search

Limited geometric accuracy in incremental sheet forming is a major obstacle for its wide adoption in industry. This paper develops a generic methodology, suitable for arbitrary part geometries and various ISF processes, for addressing one of the main causes of geometric inaccuracy, i.e., in-process springback. The methodology consists of three main elements: determination of key control points to treat geometric complexity, simplified simulation models to predict springback offline, and in-situ toolpath modification during forming. It is shown experimentally that the method provides an efficient and robust solution for various geometries with negligible setup cost.

Incremental sheet metal flanging is efficient and cost-effective in prototyping and low-volume production. However, how the sheet metal fails and how the overall formability is enhanced during incremental sheet flanging are still not well understood. This study attempts to provide an updated level of understanding for the deformation mechanics in fabricating a clover hole-flange with complex in-plane curvatures by double-sided incremental forming. Compared with traditional flanging methods, higher formability has been achieved for both stretch flanging and shrink flanging on a single part. Additionally, numerical simulation is conducted complementarily to reveal the strain evolution, based on which failure modes and reasons are analyzed. Moreover, DMV (Donell–Mushtari–Vlasov) equations are employed to analytically study the shrink flanging process. The investigations lead to the conclusions that meridional tension has positive effect in improving the formability during shrink flanging, while an adverse effect is found in the formability during stretch flanging.

The utilization of a supporting tool in Double-Sided Incremental Forming (DSIF) imposes a stabilizing compressive stress through the sheet’s thickness, increasing, thereby, the material’s formability and fatigue life. However, these favorable effects strongly depend on a steady tool-metal contact condition. This work presents a general DSIF control scheme, which augments the conventional position servo-loop with explicit force feedback control. The algorithm is examined for its robustness and effectiveness using complex geometries with varying curvatures and wall angles. The resulting parts have demonstrated enhanced material formability and geometric accuracy.

Woven composites are considered as a promising material choice for lightweight applications. An improved non-orthogonal material model that can decouple the strong tension and weak shear behavior of the woven composite under large shear deformation is proposed for simulating the preforming of woven composites. The tension, shear and compression moduli in the model are calibrated using the tension, bias-extension and bending experiments, respectively. The interaction between the composite layers is characterized by a sliding test. The newly developed material model is implemented in the commercial finite element software LS-DYNA® and validated by a double dome study.

Cyber-physical systems (CPS) enable unprecedented communication between product designers and manufacturers. Effective use of these technologies both enables and requires a new paradigm of methods and models to identify the most profitable and environmentally friendly production plans for a manufacturing network. The operating system for cyber-physical manufacturing (OSCM) and the paired network operations administration and monitoring (NOAM) software are introduced. These technologies guide our development of a mixed integer bilevel programming (BP) model that models the hierarchy between designers and manufacturers as a Stackelberg game while considering multiple objectives for each of them. Designers select and pay manufacturers, while manufacturers decide how to execute the order with the payment provided by the designer. To solve the model, a tailored solution method combining a decomposition-based approach with approximation of the lower level Pareto-optimal solution set is proposed. The model is applied to a case study based on a network of manufacturers in Wisconsin and Illinois. With the proposed model, designers and manufacturers alike can take full advantage of CPS to increase profits and decrease environmental impacts.

The success of a toolpath in double-sided incremental forming (DSIF) is strongly related to the specified tool gap. It is hypothesized in this work that maintained contact between tools and the sheet can improve the distribution of sheet thickness and hence, improve material formability and prevent premature fracture. Simulation and experimental studies reveal that thickness prediction models solely dependent on the local wall angle are inadequate for general part geometries. A ‘Shamrock’ geometry is proposed leading to the development of a novel improved thickness correction model that incorporates wall angle, in-plane curvature, and tool direction.

In this paper, dynamic spherical cavity expansion model is developed for rate-dependent concrete material described by modified Drucker-Prager Cap plasticity model incorporated with size effect. Penetration resistance components are computed accordingly with static resistance dependent on projectile diameter scale. Saturated region is introduced to investigate the response of concrete target under high impacting velocity. The validation of the proposed model is conducted by modelling a rigid projectile with full-scale and 1/10-scale diameter penetrating a semi-infinite concrete target. Depth of penetration numerically obtained is also compared with some widely recognized empirical penetration formulae, and better agreement is achieved by the proposed model for penetration tests with various striking velocities.

Double-sided incremental forming (DSIF) is a subcategory of general incremental sheet forming (ISF), and uses tools above and below a sheet of metal to squeeze and bend the material into freeform geometries. Due to the relatively slow nature of the DSIF process and the necessity to capture through-thickness mechanics, typical finite element simulations require weeks or even months to finish. In this study, an explicit finite element simulation framework was developed in LS-DYNA using fully integrated shell elements in an effort to lower the typical simulation time while still capturing the mechanics of DSIF. The tool speed, mesh size, element type, and amount of mass scaling were each varied in order to achieve a fast simulation with minimal sacrifice regarding accuracy. Using 8 CPUs, the finalized DSIF model simulated a funnel toolpath in just one day. Experimental strains, forces, and overall geometry were used to verify the simulation. While the simulation forces tended to be high, the trends were still well captured by the simulation model. The thickness and in-plane strains were found to be in good agreement with the experiments.

In Accumulated Double-Sided Incremental Forming (ADSIF), two hemispherical tools impart the local deformation to the sheet via their programmed 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, 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.Copyright © 2015 by ASME

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.

Incremental sheet forming has attracted considerable attention in the recent past due to advantages that include high process flexibility and higher formability as compared to conventional forming processes. However, attaining required geometric accuracy of the formed part is one of the major issues plaguing this process. The Double-Sided Incremental Forming process has emerged as a potential process variant which can preserve the process flexibility while maintaining required geometric accuracy. This paper investigates a mixed toolpath for Double-Sided Incremental Forming which is able to simultaneously achieve good geometric accuracy and higher throughput than is currently possible. The geometries of parts formed using the mixed toolpath strategy are compared to the desired geometry. Furthermore, an examination of the forming forces is used to uncover the reasons for experimentally observed trends. Future work in this area is also discussed.Copyright © 2014 by ASME

Incremental sheet forming (ISF) has gained much attention in the low volume production and rapid prototyping fields due to its inherent flexibility, low-overhead cost, and die-less nature. However, the geometric inaccuracy of the final achievable parts hinders this process from becoming commercially viable. One of the major sources of geometric inaccuracy is springback, which predominately occurs when the formed sheet metal is unloaded by the forming tools and released from the clamps. This paper focuses on the latter case. A practical annealing method that does not rely on complicated setups and geometry-specific compensation algorithms is proposed to reduce the springback that occurs after the unclamping process. Two clamping devices were developed, which have been demonstrated to significantly reduce the amount of springback. The capability of reducing springback by the proposed method and its potential of integrating it with other geometric accuracy improvement methods will enhance the ISF process towards future industrial applications.