Newell Moser

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.

An efficient and general finite element model for double-sided incremental forming

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.

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.

An investigation into the mechanics of double-sided incremental forming using finite element methods

Double-Sided Incremental Forming (DSIF) is a developing sheet metal manufacturing process that has gained a lot of attention in recent years due to its inherent flexibility, low-overhead cost, and die-less nature. However, it can be challenging to define the tool gap so as to achieve a desired pressure through the sheet thickness since one must first predict sheet thinning. In this investigation, a novel part design is proposed which varies in-plane curvature as a function of depth. A finite element model for DSIF is developed and the strain histories in various regions are extracted. It was concluded that if the supporting tool loses contact with the sheet, localized necking can occur prior to part failure. Additionally, part geometry can have significant effects on the tool contact area which, consequently, affects the evolution of strain.

Experimental and Analytical Study of Micro-Serrations on Surgical Blades

This paper reports on a study and application of laser ablation for machining of micro-serrations on surgical blades. The proposed concept is inspired by nature and mimics a mosquito’s maxilla, which is characterized by a number of serrations along its edge in order to painlessly penetrate human skin and tissue. The focus of this study is to investigate the maxilla’s penetration mechanisms and its application to commercial surgical blades. The fundamental objective is to understand the friction and cutting behavior between a serrated hard surface and soft materials, as well as to identify serration patterns that would minimize the cutting force and the friction of the blade during tissue cutting. Micro-serrations characterized by different patterns and sizes ranging from 200 μm to 400 μm were designed and manufactured on surgical blades. As supported by finite element methods (FEM), a reduction of 20∼30% in the force during blade cutting has been achieved, which encourages further studies and their applications to biomedical devices.Copyright

Quantifying Discretization Errors in Electrophoretically-Guided Micro Additive Manufacturing

This paper presents process models for a new micro additive manufacturing process termed Electrophoretically-guided Micro Additive Manufacturing (EPμAM). In EPμAM, a planar microelectrode array generates the electric potential distributions which cause colloidal particles to agglomerate and deposit in desired regions. The discrete microelectrode array nature and the used pulse width modulation (PWM) technique for microelectrode actuation create unavoidable process errors—space and time discretization errors—that distort particle trajectories. To combat this, we developed finite element method (FEM) models to study trajectory deviations due to these errors. Mean square displacement (MSD) analysis of the computed particle trajectories is used to compare these deviations for several electrode geometries. The two top-performing electrode geometries evaluated by MSD were additionally investigated through separate case studies via geometry variation and MSD recomputation. Furthermore, separate time-discretization error simulations are also studied where electrode actuating waveforms were simulated. The mechanical impulse of the electromechanical force, generated from these waveforms is used as the basis for comparison. The obtained results show a moderate MSDs variability and significant differences in the computed mechanical impulses for the actuating waveforms. The observed limitations of the developed process model and of the error comparison technique are briefly discussed and future steps are recommended.