A parametric study on the accuracy of bending in micro W-bending using Taguchi method

High dimensional accuracy of micro-bent parts, particularly the desired bent angle, is often required. In the study reported in this paper, a micro W-bending process was used for the study addressing this issue. Four main parameters affecting the bending accuracy of the micro W-bent parts were considered: foil thickness, grain size, foil orientation and punching frequency. Based on Taguchi L8 orthogonal array (OA), a micro-sheet-metal forming machine equipped with W-shaped punch and die was used to conduct the micro W-bending experiments. The experimental results were analyzed using signal-to-noise (S/N) ratio and the analysis of variance (ANOVA). It was identified that the extent of the effect by these parameters on the micro W-bending process depends on springback behaviours. The foil thickness had highest influence on the springback amount of the bent parts. However, the negative springback was influenced mostly by the grain size, closely followed by the foil thickness. Furthermore, the optimum bending conditions for different types of the springback were obtained. Confirmation experiments were then performed not only to validate the improved bending accuracy but also to verify the extent of the contribution from each parameter to the amounts of the springbacks. Finally, mathematical models for both, positive springback and negative springback, were developed using the regression analysis. It was observed that the predicted values fit well with the experimental results, indicating the adequacy of the established models

The generation of bending sequences in a CAPP system for sheet-metal components

An important process-planning task in sheet-metal manufacturing is the determination of bending sequences for individual components. Computer-aided generation of these sequences, as part of a computer-aided process-planning (CAPP) system, can relieve the workload of process-planning departments, this being especially important in small batch manufacturing environments. This paper discusses the functions that have to be performed during the determination of bending sequences, focusing on accuracy aspects. The generation of bending sequences is also put into the broader perspective of an integrated CAPP system such as PART-S, which is under development presently in the author's laboratory

Roebel cables from REBCO coated conductors: a one-century-old concept for the superconductivity of the future

Energy applications employing high-temperature superconductors (HTS), such as motors/generators, transformers, transmission lines and fault current limiters, are usually operated in the alternate current (AC) regime. In order to be efficient, the HTS devices need to have a sufficiently low value of AC loss, in addition to the necessary current-carrying capacity. Most applications are operated with currents beyond the current capacity of single conductors and consequently require cabled conductor solutions with much higher current carrying capacity, from a few kA to up to 20-30 kA for large hydro-generators. A century ago, in 1914, Ludwig Roebel invented a low-loss cable design for copper cables, which was successively named after him. The main idea behind Roebel cables is to separate the current in different strands and to provide a full transposition of the strands along the cable direction. Nowadays, these cables are commonly used in the stator of large generators. Based on the same design concept of their conventional material counterparts, HTS Roebel cables from REBCO coated conductors were first manufactured at the Karlsruhe Institute of Technology (KIT) and have been successively developed in a number of varieties that provide all the required technical features such as fully transposed strands, high transport currents and low AC losses, yet retaining enough flexibility for a specific cable design. In the past few years a large number of scientific papers have been published on the concept, manufacturing and characterization of such cables. Times are therefore mature for a review of those results. The goal is to provide an overview and a succinct and easy-to-consult guide for users, developers, and manufacturers of this kind of HTS cables

Inelastic Behaviour of Hybrid Steel/Concrete Column-to-Flat Slab Assemblages

The use of tubular columns in conjunction with reinforced concrete flat slabs provides structurally efficient solutions which avoid undesirable failure modes such as those associated with shear. This thesis is concerned with the development of a tubular column-to- flat slab connection system that enables reliable performance under seismic loading conditions. During this research a novel detail which features a gap around the column is proposed and developed; hence only the structural steel shearhead establishes the connection. The exposed parts of the shear arms (fuses) are designed to yield prior to punching shear failure, in a way that utilises the favourable features of steel in terms of the response to seismically induced loads. The proposed connection could serve as a primary lateral resisting system within all building configurations in regions of low to moderate seismicity or as a secondary system in areas of signi cant seismicity. In order to provide validation for the proposed details as well as associated numerical and design procedures, a purpose-built rig which is suitable for large scale testing of structural sub assemblages under combined gravity and uniaxial lateral loading, has been designed and constructed, and subsequently employed for a number of tests. Test results and numerical analyses are presented with respect to a conventional con guration, as well as for the proposed, partially embedded connection. The latter is shown to offer enhanced ductility compared with traditional forms. The results are used to demonstrate the favourable inelastic performance of the proposed detail in terms of ductility, low degradation effects and increased energy dissipation capabilities. Complementary small scale slab panel tests are also used to further optimise the composite behaviour of the proposed detail. Additionally, a closed form solution based on plastic limit analysis which can serve as a basis for a simplified design approach is proposed. Finally, the main findings from the experimental and analytical investigations are highlighted, and recommendations for future research are outlined

Double-curved panels produced in a flexible mould with self-compacting fibre-reinforced concrete

The number of applications with thin flat, curved or double-curved elements often produced as architectural elements for façades is rising fast. If the repetition factor of the elements is limited, which is often the case in free-form architecture, the high number of unique moulds makes this type of architecture economically less viable. Furthermore, a large volume of waste is produced through milling as a consequence of the production of unique elements. The reinforcement of thin panels poses specific demands on the material selection and production process, which directly affects their structural performance. This paper discusses a flexible mould technique, which has been developed in order to produce thin double-curved elements with concrete. Fibres are added to provide strength and ductility, the degree to what was determined by flexural testing of prisms and point loading of thin plates

Desktop microforming and welding system powered by a flextensional Terfenol-D transducer

Magnetostrictive Terfenol-D was examined as a prime-mover for bulk motion in a microforming system. Careful design and analysis led to the creation of a Terfenol-D transducer capable of 3.8 kN of blocked force and 212 µm of displacement. A linear model of the Terfenol-D transducer to simulate its output as a function of displacement under saturation magnetic field was created that matched both force and displacement within 10%. Thermal drift occurred at a rate of 2 µm/ºC. A flextensional lever system was designed to amplify the displacement of the Terfenol-D transducer to levels sufficient for microforming. Sub-micron displacement resolution was observed, with no perceivable effects from friction or backlash. The full system provided 365 N of blocked force and 1.6 mm of displacement. A linear model of the full system was also created that used the linear model of the transducer\u27s output which matched experimental results for displacement with a 2% error and force with an 11% error, which was found to be useful for selection of design parameters. In ultrasonic-assisted punching, a circular punch of 3.2 mm diameter that vibrates transversely at 9.6 kHz was used to punch samples of 1100-O at several punching speeds and vibration intensities. Higher speed punching tests showed up to a 30% reduction in punching force accompanied by an apparent elimination of adiabatic strain rate effects. Lower speed punching showed a smaller degree of softening, but an increased burnished-to-fractured area ratio. A study on the effects of vibration waveform on a polymer vibration welding process on 0.25 and 0.5 mm ABS sheet was conducted using sine, square, and triangle waves at differing penetration depths. A preliminary study was first used to determine control levels of basic welding parameters that compared the effects of clamping load and penetration depth on the two sheet thicknesses. It was found that square waves provided slightly higher penetration rates than sine waves, and triangle waves significantly lower penetration rates than sine waves. Penetration rates and achievable penetration depths varied with sheet thickness. A minimum penetration rate threshold was found below which it was not possible to achieve adequate penetration; beyond this lower penetration rates generally resulted in higher strength

Investigation on a new hole-flanging approach by incremental sheet forming through a featured tool

One of the major challenges in conventional incremental sheet forming (ISF) is the extreme sheet thinning resulted in an uneven thickness distribution of formed part. This is also the case for incrementally formed parts with hole-flanging features. To overcome this problem, a new ISF based hole-flanging processing method is proposed by developing a new ISF flanging tool. Comparative studies are conducted by performing hole-flanging tests using both ISF conventional ball-nose tool and the new flanging tool to evaluate the sheet deformation behavior and the quality of the final part. Stress distribution and strain variation are investigated by analytical approach and numerical simulation. Experiments have been conducted to validate the analytical model and simulation results, and to further study the fracture behavior. Results show that the new flanging tool generates greater meridional bending than stretching deformation in conventional ISF. The combination of bending-dominated deformation mode with localized deformation of ISF ensures more uniform thickness distribution on hole-flanging part with better resistance to fracture

Transmission of natural scene images through a multimode fibre

The optical transport of images through a multimode fibre remains an outstanding challenge with applications ranging from optical communications to neuro-imaging. State of the art approaches either involve measurement and control of the full complex field transmitted through the fibre or, more recently, training of artificial neural networks that however, are typically limited to image classes belong to the same class as the training data set. Here we implement a method that statistically reconstructs the inverse transformation matrix for the fibre. We demonstrate imaging at high frame rates, high resolutions and in full colour of natural scenes, thus demonstrating general-purpose imaging capability. Real-time imaging over long fibre lengths opens alternative routes to exploitation for example for secure communication systems, novel remote imaging devices, quantum state control processing and endoscopy