Thick Metal Plate Research Articles

Numerical Simulation and Experiment Research on Surface Defects for Thick Plate Multi-Point Forming Process

Multi-point forming (MPF) is an advanced flexible manufacturing technology for three-dimensional sheet metal forming. The substance of MPF is replacing the conventional solid dies by a set of discrete punches called punch group. Due to the discrete contacts between the workpiece and punches, the dimple defects occurred, which are inevitable and particular for MPF. In this study, the analysis of the deformation features of the dimple defects was implemented. The dynamic explicit finite element method was chosen to implement the simulation of MPF process. The influencing factors of the surface defects were researched. The relevant experiment was implemented, and it verified that the forming defects decreased with the increasing of the thickness of metal plate and the objective surface curvature radius.

Keyhole welding with CF-TIG (cathode focussed GTA)

In this paper, the results for keyhole welding of stainless steel 1.4301 and mild steel 1.0117 with a cathode focussed gas tungsten arc process are presented. These tests were carried out in preparation for welding the root faces of Y- or double V-groove weld preparations of thick metal plates. Welded plate thicknesses range from 6 to 10 mm for stainless steels and 6 to 12 mm for mild steels. Welding speeds are in the range of 20 to 115 cm/min at currents from 400 to 800 A. Especially for stainless steel, a big range of applicable and stable process parameters could be found. The process also works fine for mild steel even though the achievable parameter range is smaller.

Numerical and Experiment Study of Residual Stress and Strain in Multi-Pass GMA Welding

There must selection an optimal of welding parameter and condition that reduces the risk of mechanical failures on weld structures.The residual stress and welding deformation have the large impact on the failure of welded structures.To achieve the required precision for welded structures, it is required to predict the welding distortions at the early stages.Therefore, this study uses 2DFinite Element Method (FEM) to predict residual stress and strain on thick SS400 steel metal plate. A birth and death technique is employed to control the each weld pass welding. Gas Metal Arc (GMA) welding experiment is also performed with similar welding condition to validate the FE results.The simulated and experiment results provide good evidence that heat input is main dependent on the welding parameter and residual stress and distortions are mainly affected by amount on heat input during each weld-pass.

Application of Wavelet Threshold De-Noising Method in Electromagnetic Ultrasonic Signal Processing

In order to solve the problem of containing noise in echo signal detected by electromagnetic ultrasonic metal plate thickness, wavelet threshold method was used for de-noising. First to choose the wavelet function and decomposition scale to decompose the echo signal, then structure threshold rules by the weighted average method and dispose the wavelet coefficient obtained by decomposition, reconstruction signal. De-noising signal acquired by MATLAB simulation had obvious effect and SNR was 9.4441, RMSE was 0.2. Experimental results show that wavelet threshold value method can effectively inhibit noise doped echo signal and improve electromagnetic ultrasonic detection accuracy.

Analysis of Ultrasonic Signals Generated by Pulsed Laser Action on a Metal Plate

An approach of detecting ultrasonic signals generated by pulsed laser is studied. The influence factors are analyzed on the received signals. Based on pulsed laser generating ultrasonic, a metal plate is used as a detected target. The ultrasonic is induced by way of combining high-power pulsed laser with optical attenuation unit, and then received by a piezoelectric ultrasonic transducer. The difference between ablation regime and thermo elasticity with different pulsed laser input parameters are compared. Moreover the ultrasonic propagation under different thickness of metal plate and the impacts of relative position of stimulating point and detection point on ultrasonic signal is researched. The validity of this method is demonstrated through these experiments and the laser input parameters are determined when in thermo elasticity.

Wireless Temperature Sensor for Condition Monitoring of Bearings Operating Through Thick Metal Plates

This research presents the first wireless temperature sensor for bearing condition monitoring, capable of operating through thick metal (greater than 18-mm thick) plates. The sensor is a combination of a ring-shaped permanent neodymium magnet and a Hall Effect sensor. Based on the temperature-induced change in the magnetic field, the sensor is able to detect bearing temperature remotely from a distance of 40.5 mm. Additionally, temperature-induced change in magnetic field is detected at a distance of 26 mm through two 9.5-mm-thick copper, stainless steel, and aluminum plates. Furthermore, the sensor concept is experimentally demonstrated by mounting it on a commercially-available bearing and performing dynamic tests at 1500 rpm with 100-150 lb load. Maximum temperature readings for dynamic tests are in the order of 80°C -90°C, and are presently limited by the bearing test rig. However, the presented magnets are rated for operating up to 150 °C with an estimated lifetime of greater than 10000 hours in operation.

Nonlinear Finite Element Analysis of Spring-Back Characteristics in the Cold-Forming Process of Three-Dimensionally Curved Thick Metal Plates

The present paper is part of the study to develop the advanced computer aided manufacture (CAM) system called the changeable die system (CDS) that applies the cold-forming technique to produce curved thick metal plates with complex, three-dimensional geometry [Paik et al., 2009, “Development of the Changeable Die System for the Cold-Forming of Three-Dimensionally Curved Metal Plates,” The Lloyd's Register Educational Trust Research Centre of Excellence, Pusan National University, Korea]. This paper focuses on the procedure of predicting the spring-back characteristics using elastic-plastic large deflection finite element method, which is a key technical element within the framework of the CDS process. The validity of the procedure is confirmed by comparison with experimental results obtained by the CDS machine in the cold-forming process of curved steel plates.

Circuit Model for Extraordinary Transmission Through Periodic Array of Subwavelength Stepped Slits

In this paper, two circuit models are proposed for analytical investigation of extraordinary transmission through periodic array of subwavelength stepped slits in a thick metallic plate. A cascade model is first developed and then a stub model is suggested for cases that the cascade model is not accurate. The parameters of the proposed circuits are given by closed-form expressions. Both symmetric and asymmetric stepped slits are considered.

Numerical Methodology for Predicting the Nonlinear Elastic Deflection of Curved Beams and Plates Using Nonlinear Integral Equations

Ships, ship-shaped offshore structures, land-based structures and aerospace structures typically consist of various curved beam and plate components. An important issue is how to manufacture and construct systems correctly and accurately when their variously shaped curved beams and plates display structural nonlinear behaviour. Multi-point forming is a general process that can be used to form variously shaped curved plates and beams. It has been difficult to apply the integrated systems to thin and/or thick metal plates and beams that have the characteristic of non-linear structural mechanics, such as nonlinear behaviour when loading is applied to the plates. The aim of this study was to derive a simplified numerical calculation based on the formulation of a nonlinear integral equation and a mathematical solution, to predict the nonlinear elastic deflection, load profile and elastic foundation of curved plates or/and beams during the early stages of the advanced manufacturing process of plate and beam formation. The validity of the method is demonstrated through simulations of the proposed numerical approach with experimental results.

Deformation Behavior of Doubly Curved SS400 Thick Metal Plates by High Frequency Induction-Based Line Heating

Line heating-induced deformation behavior of an SS400 thick plate was investigated through both numerical analysis and experimental counterpart by applying induction heating (IH) as a heat source. The drastic increase of temperature gradient upon increasing input power could mainly be predicted by numerical analysis, which attributes to the amount of permanent bending deformation of the thick plate. After plotting the amount of vertical deformation as a function of various positions from top surface of the plate, we found that the higher input power, the more thermomechanical deformation can be generated, regardless of the purposed doubly curved shapes such as concave and saddle-type plates. Also there is good agreement between the numerical analysis and experimental measurement in terms of the transverse curvature.

Fabrication method and compressive properties of CFRP isogrid cylindrical shells

Since isogrid structures are composed of triangular grid stiffeners and a surface skin, they have a high specific strength and stiffness. These structures are now being mainly used for aerospace applications. In order to produce a metal isogrid cylindrical shell, most of the thick metal plates must be cut off while the remaining thin surface skins with the stiffeners and both ends of the skins are welded to each other. This process needs a long lead time and a high cost, and unstable behaviors are observed in the joint parts. On the other hand, carbon fiber reinforced plastics (CFRP) isogrid cylindrical shells can be fabricated with an integral method by using a filament winding apparatus. In this study, a fabrication method of the CFRP isogrid cylindrical shells is proposed and their compressive tests are carried out to investigate the reinforcement effect of the grids on the CFRP isogrid cylindrical shells. Furthermore, the results of the static compressive tests are compared with numerical ones obtained by finite element method (FEM).

Numerical Simulation of Double-Sided Double Arc Welding without Back Chipping Based on MSC.MARC

Numerical simulation based on MSC.MARC was applied to predict the residual stress in double-sided double arc welding (DSDAW). The distribution of residual stress field in the welding seam was simulated and the actual situation in experiment of the residual stress was also measured. It shows that the calculated results are in good agreement with the experimental ones. The residual stress of conventional welding (CW) or a single arc welding (SAW) is calculated too. Moreover, the welding residual stress field of thick metal plates welded by DSDAW was carried out and compared with that of the CW method with back chipping. The result shows that the DSDAW technology had some excellent characteristics of smaller angular deformation, lower residual peak tensile stress, and well-proportioned stress distribution, which testifies that the welding procedures in DSDAW are reduced and the welding efficiency and quality of the welding joint are improved in great margin.

FDTD Numerical Analysis of Transmission Enhancement on Two-Dimensional Hole Array

Numerical simulation about transmission enhancement phenomenon on metal film hole array has been finished in the paper by East FDTD commercial software. In some wavelengths, relative transmission rate is more than 1 and we also study that the thickness of metal plate, the size of the hole and period on influence of the transmission rate. Transmission enhancement peak lowers with the increasing of silver film thickness, enlarger along with the increasing of the aperture, And when period of hole gets larger, transmission peak will shift.

Experimental demonstration of plasmonic Brewster angle extraordinary transmission through extreme subwavelength slit arrays in the microwave

We experimentally demonstrate the existence of a Brewster-like broadband extraordinary optical transmission band, in a very thick metal plate with an array of slits as narrow as $\ensuremath{\lambda}$/750 in the 8- to 40-GHz regime, by measuring the transmission from normal incidence to near grazing angles and mapping out the entire angular transmission spectrum. In the case of very narrow slits, an order of magnitude larger transmission is obtained at the Brewster angle when compared to the normal-incidence Fabry-P\'erot resonance transmission peaks. Full-wave numerical simulations are in excellent agreement with the measurements, paving the way for the observation of this phenomenon in the optical regime.

Liftoff insensitive thickness measurement of aluminum plates using harmonic eddy current excitation and a GMR sensor

This paper describes the implementation of a device that measures the thickness of metallic plates. A pancake coil for magnetic field sinusoidal excitation is used and detection is performed with a bridge giant magneto-resistor sensor. The paper uses the theory of the linear transformer to explain the liftoff effect with a special attention to the point of interception phenomenon. The transformer model shows that to attain the interception points with instantaneous measured voltages independent of the liftoff gap the excitation coil must be driven with imposed current. This effect was explored to show that a simultaneous process of thickness and conductivity measurement is feasible.

Study on Electrolyte Jet Cutting

This paper describes the development of an electrochemical machining method for cutting of metal sheets using an electrolyte jet. In this process the workpiece is machined locally in the area contacted by an electrolyte jet through which an electric current is applied. When holes and grooves are created by electrolyte jet machining, the electrolyte flow on the workpiece is influenced by changes in the configuration of the workpiece surface being machined, thereby broadening the current density distribution under the jet. Thus, in previous studies, depth of the slots was shallow, and perforation of holes or slots has never been investigated intensively. Hence, this study aims to perforate thick metal plates using electrolyte jet machining. Influences of the nozzle scanning speed and electrolysis current on the machining speed and hole shape quality were investigated. A stainless sheet of 3mm in thickness was cut successfully with a kerf width of between 220 to 230μm using a cylindrical electrolyte jet which was 210μm in diameter.

Tri-axial deformation of a plastic-rigid solid

The paper deals with the deformation of an ideal plastic solid that is initially rigid, i.e., elastic deformations are neglected. In addition, the solid flows by means of the mechanism of extended slip, for which the rotation-rate vector field remains continuous and the strain-rate tensor is solenoidal. The Tresca yield criterion applies to such a solid and with an associated flow-rule is represented in a manner that includes both bi-axial and tri-axial states of strain. Two new theorems are proved, and a second-order partial differential equation is derived for the first invariant of the stress tensor (hydrostatic pressure); the analogue of a similar published equation for the bi-axial strain case. To illustrate the methodology, the above theory is applied to the tri-axial problem of a thick metal plate clamped round a circle and deflected by means of pressure. It is shown, from the exact solution, that the errors due to the use of the approximate membrane formula for a clamped thin plate are small, even for a 6mm thick plate clamped on a circle 100mm in diameter. Surprisingly, there is an initial thickening of the plate and it is shown that, regardless of the plate thickness, the pressure passes through a maximum at a deflection equal to \({1/\sqrt{3}}\) of the radius of the clamping circle.

Multi-modal transmission of microwaves through hole arrays

The microwave transmission through hole arrays in thick metal plates for both large holes (cut-off below onset of diffraction) and small holes (cut-off above onset of diffraction) have been compared through both experiment and modelling. Enhanced transmission is in part mediated by the excitation of diffractively coupled surface waves. Large holes, with cut-off below the onset of diffraction (due to the hole periodicity), are able to support multiple modes in transmission when the depth of the holes is sufficient to support quantisation in the propagation direction. Small holes, with cut-off above the onset of diffraction however only support two coupled surface modes (symmetric and anti-symmetric) below diffraction.

Prediction of Heat Distribution Shape and Nozzle Diameter of Plasma Arc Cutter

Theoretical three-dimensional Gaussian heat distribution model of the complex heat flow and plasma properties of cutting plasma torches have been developed. For cutting metallic plates, plasma torches must produce a narrow supersonic plasma jet with enough energy and momentum densities to melt, vaporize, and remove the metal from the impingement region. Our model allows us to study the details of the heat distribution and to make predictions on pick temperature development on metal surface, heat transfer to the work piece, force i.e. the forces acting on the melt (aerodynamic drag, gravity, viscosity and surface tension) during plasma arc cutting, the main forces acting on the melt is believed to be the aerodynamic drag force and the gravity is significant only for thick metal plates. With the help of these assumptions and diameter of Gaussian heat source’s volume, diameter of nozzle has been calculated for thin work piece. A good agreement is found between the model results and the available experimental data.

Effect of Activated TIG Flux on Performance of Dissimilar Welds between Mild Steel and Stainless Steel

The purpose of the present work was to investigate the effect of oxide fluxes on surface appearance, weld morphology, angular distortion, and weld defect obtained with activated tungsten inert gas (TIG) process applied to the welding of 6 mm thick dissimilar metal plates between JIS G3131mild steel and SUS 316L stainless steel. The CaO, Fe2O3, Cr2O3, and SiO2 fluxes used were packed in powdered form. The results indicated that the surface appearance of TIG welds produced with oxide flux formed residual slag. TIG welding with SiO2 powder can increase joint penetration and weld depth-to-width ratio, and therefore the angular distortion of the dissimilar weldment can be reduced. Furthermore, the defects susceptibility of the as-welded can also be reduced.