Bulk forming of sheet metal

Ever increasing demands on functional integration of high strength light weight products leads to the development of a new class of manufacturing processes. The application of bulk forming processes to sheet or plate semi-finished products, sometimes in combination with conventional sheet forming processes creates new products with the requested properties. The paper defines this new class of sheet-bulk metal forming processes, gives an overview of the existing processes belonging to this class, highlights the tooling aspects as well as the resulting product properties and presents a short summary of the relevant work that has been done towards modeling and simulation. © 2012 CIRP.

A Videogrammetric As-Built Data Collection Method for Digital Fabrication of Sheet Metal Roof Panels

A roofing contractor typically needs to acquire as-built dimensions of a roof structure several times over the course of its build to be able to digitally fabricate sheet metal roof panels. Obtaining these measurements using the exiting roof surveying methods could be costly in terms of equipment, labor, and/or worker exposure to safety hazards. This paper presents a video-based surveying technology as an alternative method which is simple to use, automated, less expensive, and safe. When using this method, the contractor collects video streams with a calibrated stereo camera set. Unique visual characteristics of scenes from a roof structure are then used in the processing step to automatically extract as-built dimensions of roof planes. These dimensions are finally represented in a XML format to be loaded into sheet metal folding and cutting machines. The proposed method has been tested for a roofing project and the preliminary results indicate its capabilities.

A novel process for transforming sheet metal blanks: Ridged die forming

Up to 20% of all sheet metal produced is scrapped as blanking skeletons. A novel process is therefore designed and examined, aiming to transform tessellating 'pre-blanks' in-plane into the real blanks required for stamping. Prior to blanking, the sheet is formed with a set of ridged dies, from which pre-blanks are cut and then flattened into true blanks. Several different approaches to designing ridged dies are evaluated by simulation and experiment, and the best results demonstrate a potential reduction in blanking yield losses for can-making from 9.3% to 6.9%. © 2013 CIRP.

Characterizing the class of local metal sheet thickening processes

The need to create high-value products for specialist applications, and the search for efficient forming routes that obviate the need for some machining steps, is driving Interest In a novel class of forming processes aiming to create locally thickened features within sheet work- pieces. A number of novel forming processes have been proposed to meet this need, but it is as yet unclear which processes will be most effective in creating local thickening of various geometries, and many process configurations have yet to be tried. This paper aims to provide some basic principles for designing and characterising process behaviour. A simplified generic description of sheet thickening processes is provided, with two tools of variable operating on a sheet workpiece in plane strain, with different tool separations and motions parameterised. A comprehensive numerical study of the behaviour of this class of processes is conducted in Abaqus to predict the main characteristics of the material flow in each configuration. The results are used to classify the different basic behaviours that can be achieved by the sheet-bulk thickening processes and to give guidance on future process development, capability and applicability. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA. Weinheim.

Thermal quenching of luminescence from buried and surface InGaAs self-assembled quantum dots with high sheet density

Variable-temperature photoluminescence (PL) spectra of Si-doped self-assembled InGaAs quantum dots (QDs) with and without GaAs cap layers were measured. Narrow and strong emission peak at 1075 nm and broad and weak peak at 1310 nm were observed for the buried and surface QDs at low temperature, respectively. As large as 210 meV redshift of the PL peak of the surface QDs with respect to that of the buried QDs is mainly due to the change of the strain around QDs before and after growth of the GaAs cap layer. Using the developed localized-state luminescence model, we quantitatively calculate the temperature dependence of PL peaks and integrated intensities of the two samples. The results reveal that there exists a large difference in microscopic mechanisms of PL thermal quenching between two samples. (c) 2005 American Institute of Physics.

The structure and current-voltage characteristics of multi-sheet InGaN quantum dots grown by a new multi-step method

Multi-sheet InGaN/GaN quantum dots (QDs) were grown successfully by surface passivation processing and low-temperature growth in metalorganic chemical vapor deposition. This method based on the principle of increasing the energy barrier of adatom hopping by surface passivation and low-temperature growth, is quite different from present methods. The InGaN quantum dots in the first layer of about 40-nm-wide and 15-nm-high grown by this method were revealed by atomic force microscopy. The InGaN QDs in upper layer grew bigger. To our knowledge, the current-voltage characteristics of multi-sheet InGaN/GaN QDs were measured for the fist time. Two kinds of resonance-tunneling-current features were observed which were attributed to the low-dimensional localization effect. Some current peaks only appeared in positive voltage for sample due to the non-uniformity of the QDs in the structure. (C) 2002 Elsevier Science B.V. All rights reserved.

One-Step Ionic Liquid-Assisted Electrochemical Synthesis of Ionic Liquid-Functionalized Graphene Sheet Directly from Graphite

Graphite, inexpensive and available in large quantities, unfortunately does not readily exfoliate to yield individual graphene sheets. Here a mild, one-step electrochemical approach for the preparation of ionic-liquid-functionalized graphite sheets with the assistance of an ionic liquid and water is presented. These ionic-liquid-treated graphite sheets can be exfoliated into functionalized graphene nanosheets that can not only be individuated and homogeneously distributed into polar aprotic solvents, but also need not be further deoxidized. Different types of ionic liquids and different ratios of the ionic liquid to water can influence the properties of the graphene nanosheets. Graphene nanosheet/polystyrene composites synthesized by a liquid-phase blend route exhibit a percolation threshold of 0.1 vol % for room temperature electrical conductivity, and, at only 4.19 vol %, this composite has a conductivity of 13.84 S m(-1), which is 3-15 times that of polystyrene composites filled with single-walled carbon nanotubes.

Structure and mechanical properties of extruded Mg-Gd based alloy sheet

The Mg-8Gd-2Y-1Nd-0.3Zn-0.6Zr (wt.%) alloy sheet was prepared by hot extrusion technique, and the structure and mechanical properties of the extruded alloy were investigated. The results show that the alloy in different states is mainly composed of alpha-Mg solid solution and secondary phases of Mg5RE and Mg24RE5 (RE = Gd, Y and Nd). At aging temperatures from 200 degrees C to 300 degrees C the alloy exhibits obvious age-hardening response. Great improvement of mechanical properties is observed in the peak-aged state alloy (aged at 200 degrees C for 60 h), the ultimate tensile strength (sigma(b)), tensile yield strength (sigma(0.2)) and elongation (epsilon) are 376 MPa, 270 MPa and 14.2% at room temperature (RT), and 206 MPa. 153 MPa and 25.4% at 300 degrees C, respectively, the alloy exhibits high thermal stability.

Surprising arching sheet-like dendrites growing from BaF2 nanocubes

BaF2 nanocubes were prepared from quaternary reverse micelles of cetyl trimethyl ammonium bromide (CTAB), n-butanol, n-octane, and water. Interestingly, there are arching sheet-like dendrites growing between two neighbouring sides of these cubes. X-ray powder diffraction (XRD) analysis showed that the products were BaF2 single phase. Scanning electron microscopy (SEM) or transition electron microscopy (TEM) was used to estimate the size of the final products. The results showed that the shape and size of particles were strongly dependent on the reaction conditions, such as the temperature and reaction time. When the reaction temperature was 25 degreesC, we obtained cuboid-like particles with 'clean' surfaces (no dendrites growing on them), and when the temperature was 35 degreesC, we obtained nanocubes with dendrites growing from them between the neighbouring sides. The influence of reaction time at a temperature of 35 degreesC is also discussed.

Dependence of performance of organic light-emitting devices on sheet resistance of indium-tin-oxide anodes

The dependence of the performance of organic light-emitting devices(OLEDs) on the sheet resistance of indium-tin-oxide(ITO) anodes was investigated by measuring the steady state current density brightness voltage characteristics and the electroluminescent spectra. The device with a higher sheet resistance anode shows a lower current density, a lower brightness level, and a higher operation voltage. The electroluminescence(EL) efficiencies of the devices with the same structure but different ITO anodes show more complicated differences. Furthermore, the shift of the light-emitting zone toward the anode was found when an anode with a higher sheet resistance was used. These performance differences are discussed and attributed to the reduction of hole injection and the increase in voltage drop over ITO anode with the increase in sheet resistance.

Electric field-induced conformational transition of bovine serum albumin from alpha-helix to beta-sheet

The irreversible conformational transition of bovine serum albumin (BSA) from alpha-helix to beta-sheet, induced by electric field near the electrode surface, was monitored by circular dichroism (CD) with a long optical path thin layer cell (LOPTLC).

A unified criterion for initiation of sediment motion and inception of sheet flow under water waves

A unified criterion is developed for initiation of non-cohesive sediment motion and inception of sheet flow under water waves over a horizontal bed of sediment based on presently available experimental data. The unified threshold criterion is of the single form, U-o = 2 pi C[1 + 5(T-R/T)(2)](-1/4), where U-o is the onset velocity of sediment motion or sheet flow, T is wave period, and C and T-R are the coefficients. It is found that for a given sediment, U-o initially increases sharply with wave period, then gradually approaches the maximum onset velocity U-o = 2 pi C and becomes independent of T when T is larger. The unified criterion can also be extended to define sediment initial motion and sheet flow under irregular waves provided the significant wave orbital velocity and period of irregular waves are introduced in this unified criterion.