Thickness Of Sheet Metal Research Articles

Modeling of flow separation of assist gas as applied to laser cutting of thick sheet metal

The present paper describes the results of mathematical modeling of supersonic flows of a viscous compressible gas, obtained by numerically solving three-dimensional full Navier–Stokes equations, and also the results of experiments with visualization of gas jet flows in channels geometrically similar to the laser cut. Separation of the gas flow from the cut front is predicted numerically and then validated by experiments on a model setup. The gas flow structure arising in a narrow channel behind a sonic (conical) or supersonic nozzle is described. Specific features of originating in the flow separation on a smooth surface in a narrow channel are examined, and mechanisms controlling the separation are proposed. Flow separation directly affects the changes in the shape and structure of striations and is the one of main reason for the worse quality of the laser cut surface. It is shown that the changes in the structures of striations over the thickness of the sheet being cut are closely related to aerodynamic features of jet flows of the assisting gas in the cut channel.

Laser cutting of large-aspect-ratio rectangular blanks in thick sheet metal: Thermal stress analysis

The laser cutting of high-aspect-ratio (length to width) rectangular blanks from a thick sheet steel is carried out and the temperature and thermal stress fields in the cut sections are examined. The temperature and stress fields are computed using the finite element model and X-ray diffraction (XRD) is used to measure the residual stress levels in the corners of the cut geometry. A scanning electron microscope equipped with an energy dispersive spectroscopy unit is used to examine the morphological and metallurgical changes in the cut section. It is found that the von Mises stress remains high in the region of the cut surfaces and the predicted values of the residual stress closely agree with experimental results. The micrographs reveal that the cut sections are free from cracks.

Laser cutting of thick sheet metals: Residual stress analysis

Laser cutting of tailored blanks from a thick mild steel sheet is considered. Temperature and stress field in the cutting sections are modeled using the finite element method. The residual stress developed in the cutting section is determined using the X-ray diffraction (XRD) technique and is compared with the predictions. The structural and morphological changes in the cut section are examined using the optical microscopy and scanning electron microscopy (SEM). It is found that temperature and von Mises stress increase sharply in the cutting section, particularly in the direction normal to the cutting direction. The residual stress remains high in the region close to the cutting section.

Modeling and analysis of compliant sheet metal assembly variation

PurposeMaterial variation is inevitable in volume production, especially the sheet metal thickness variation, which influences part stiffness characteristic. The purpose of this paper is to present a new variation model of compliant sheet metal assembly with consideration of material variation influence.Design/methodology/approachThe theory of computational solid mechanics is used to obtain the relationship between part stiffness matrix and material characteristic. The method of influence coefficients is adopted to deduce the assembly variation model.FindingsMaterial variation‐induced influence coefficients to assembly variation are obtained, and a variation model of compliant sheet metal assembly with sources of material variations, part geometric variations and fixture variations is presented. Analysis shows that material variation has an important influence to assembly variations.Originality/valueA quantitative relationship between assembly variations and material thickness variations is firstly given and a new variation model of compliant sheet metal assembly is presented to help designers to more exactly predict the assembly variation and diagnose variation sources.

Pigment layers and precious metal sheets by energy‐dispersive x‐ray fluorescence analysis

AbstractA portable energy‐dispersive x‐ray fluorescence (EDXRF) equipment was used to measure pigments and precious metal composition. From the x‐ray spectra it was also possible to assign each pigment to the correct pigment layer, and in the case of metal sheets (e.g. gildings) to identify the correct layer distribution. Several methods have also been developed to determine the thickness of pigment layers and metal sheets. They were specifically applied to measure gold thickness in Giotto's halos in the Chapel of the Scrovegni in Padua, and in gilded copper objects from the Royal Tombs of Sipán and from the Museum of Sicán. Copyright © 2008 John Wiley & Sons, Ltd.

The strain gradient approach for determination of forming limit stress and strain diagrams

The forming limit stress diagram (FLSD) has been reported as being much less path dependent and much more favourable than the forming limit diagram (FLD) in representing forming limits in the numerical simulation of sheet metal forming processes. Therefore, the purpose of this study was to develop a methodology for the prediction of the forming limits both in strain and stress forms. All simulations are based on strain gradient theory of plasticity in conjunction with the Marciniak—Kuczynski (M—K) approach. This approach introduces an internal length scale into conventional constitutive equations and takes into account the effects of deformation inhomogeneity and material softening. The non-linear second-order ordinary differential equation of the thickness of sheet metal has been solved using the collocation method. It is shown that this method overcomes the imperfection sensitivity encountered in the conventional M—K method. An evaluation of the theoretical results is carried out. The comparison between the experimental and theoretical results for FLDs and FLSDs as predicted by different methods indicates that the present approach is suitable for these problems.

Experimental study on sheet metal bending with medium-power diode laser

In an experimental study of laser sheet bending, a 160 W diode laser is used for two-dimensional sheet bending of low-carbon steel. The variables investigated include metal sheet thickness, laser scan speed, laser power, laser beam width, and laser scan pass number. Bend surface appearances are also analysed. The laser sheet bend results demonstrate that a 940 Nm diode laser is an effective tool for laser forming of carbon steel sheets. No additional surface coating was required. The buckling mechanism may be the main source contributing to the large angle of bend found for the laser-beam-width to sheet-thickness aspect ratio close to 4; for a laser-beam-width to sheet-thickness aspect ratio of less than 2, both temperature gradient and buckling mechanisms contributed to the lower bend angles. The laser beam width study showed that, for the given material thickness range and laser beam profile, the maximum bend angle depends mainly on the material thickness, not the power intensity distribution across the bend line. However, a more evenly distributed laser beam gave the same bend angle with less material property and surface appearance changes. For obtaining the same bend angle, less laser line energy was required if a higher laser scan speed was applied, except for the extreme high-line energy level. Also, multi-path bend strategies may be preferred for maximizing the total bend angle as well as reducing bend surface morphology changes.

Production of aluminum tall container with flange by hydraulic bulging with compression of surrounding material

Bulging process is suitable to produce cups with wide flange because of keeping the contour shape of blank sheet unchanged. On the other hand, it is difficult to form tall cups by conventional bulging because, at punch shoulder, thickness of metal sheet becomes much smaller than other portions and it results in a quick breakage there. When the way to decrease the thickness of a sheet metal during the process approaches more to the uniform one, it becomes possible to form cups with both of wide flange and large height. In this study, a new bulging process combined with ironing was proposed in order to form tall cups with wide flange. In this new method, as in the conventional hydraulic bulging method, hydraulic pressure was used to deform metal sheet uniformly. In this hydraulic bulging, compression around die hole by a metal ring assisted the hydraulic pressure to put material into the die-hole. In addition to that, a counter metal punch was used to prevent the material on the head of bulged portion from locally thinning. Furthermore, following ironing makes it possible to decrease thickness of sidewall. In order to clarify the effectiveness of this method, differences of the configuration and the thickness strain distribution between products formed by conventional and new methods were investigated. Finally, it was confirmed that this method make it possible to produce a cup four times as tall as conventional one.

A smart stamping tool for punching and broaching combination

The crescent search for production time reduction is a factor that stimulates the improvement of the existent manufacturing techniques. In this work, a combined process using tools that perform punching followed by broaching in only one operation is studied in order to obtain holes with improved precision and surface finish. This researched combo process should make possible the manufacturing of pieces in less time with better use of material and equipment. This allows the use of only one process for heavy-duty jobs on thick sheet metal. In order to study this process, eighteen tools with three types of geometry with parallel and nonparallel cutting angle were made. Tool lubrication/cooling conditions were also analyzed using cutting fluids with concentrations of 100, 75 and 50% Hislip with respective 0, 25 and 50% of water. The hole final surface roughness, diameter and conical form, cutting tool angles, tool temperatures and cutting tool degradation were analyzed. The data obtained through the analysis of the variance (ANOVA), showed that this process is viable due holes obtained with overall superior quality, when compared with the ones generated in conventional stamping processes. Holes produced by tools types I, II and III presented good results in the holes overall precision. Nevertheless, in general, the best results were seen using tools type I, with punch angle of 22.5° and, lubrication/cooling conditions using 75% Hislip concentration as cutting fluid (water emulsion).

Hole flanging with ironing process of two-ply thick sheet metal

An incremental updated Lagrangian elasto-plastic finite element method(FEM) was employed to analyze the hole-flanging with the ironing of circulate plates using a pre-determined smaller hole at the center of the two-ply sheet metals. An extended r min technique was employed such that each incremental step size can be determined not only by the yielding of an element Gaussian point, but also by the change under the boundary conditions of penetration, separation, and the alternation of the sliding-sticking state of friction along the tool-sheet interface. Two-ply sheet metals are generally composed of metals that have different mechanical properties. Thus, the forming process of these materials is complicated. A number of experiments and simulations were performed using a conical punch with a cone angle of 45°. The experimental results were compared with FEM-simulated results. It is found that using the elasto-plastic FEM can effectively predict the generation process of the deformed shape until unloading. The calculated sheet geometries and the relationship between punch load and punch travel are in good agreement with the experimental data.

Study on multi-stage sheet metal forming for automobile structure-pieces

Abstract Automobile structure-pieces are usually stamped by multi-stage sheet metal forming. The stage number and the content of every stage decide if the structure-pieces can be formed successfully and the final forming quality. In this paper, the forming characteristics of left-rear hanger are analyzed firstly and two-stage drawing pattern is adopted. Then four kinds of schemes are used to research the influence of different drawn patterns and deformed amount on the forming quality of subsequent drawing. By means of FLD, changes of sheet metal thickness, distribution of maximum major strain and the drawing safe deformability, the multi-stage forming process design of automobile structure-piece is researched finally.

Design and applications of a pneumatic accelerator for high speed punching

High speed forming is an important production method that requires specially designed HERF (high energy rate forming) machines. Most of the HERF machines are devices that consist of a system in which energy is stored and a differential piston mechanism is used to release the energy at high rate. In order to eliminate the usage of specially designed HERF machines and to obtain the high speed forming benefits, the accelerator which can be adapted easily onto conventional presses has been designed and manufactured in this study. The designed energy accelerator can be incorporated into mechanical press to convert the low speed operation into high-speed operation of a hammer. Expectations from this work are reduced distortion rates, increased surface quality and precise dimensions in metal forming operations. From the performance test, the accelerator is able to achieve high speed and energy which require for high speed blanking of thick sheet metals.

Investigation on the Mechanisms of Flexible Sheet Metal Forming Using Plasma Arc

An investigation on the mechanism of flexible sheet metal forming using plasma arc have been performed in this paper. The experimental results show that temperature gradient mechanism (TGM) is caused by a steep temperature gradient across the sheet metal thickness, which will generates bending towards the plasma arc, while buckling mechanism (BM) usually causes sheet metals to bend away from the plasma arc on the condition that the plasma arc diameter is large compared to the sheet metal thickness and the scanning speed is low. The strain-hardening effects and phase transformation effects were also conducted in the investigation, which can be of great significance for the micro hardness and deformation of sheet metal in the heated area. The investigation reveals the mechanisms of sheet metal forming using plasma arc, and provides theoretical foundation for its industry application.

Effect of heat treatment on developmental stages of Callosobruchus maculatus (Coleoptera: Bruchidae) in stored adzuki bean Vigna angularis

Effect of heating on Callosobruchus maculatus (Fabricius) in Vigna angularis (Willd.), Ohwi & Ohashi, seed was assessed using an 118° obtuse base angle solar box heater. The box heater was constructed with 1.2 mm thick sheet metal, glued inside with aluminium foil and insulated on the outside by fixing 1 cm thick polystyrene and glazed with 0.15 mm thick clear plastic sheet. Electric energy from a solar simulator panel adjusted to simulate heat trapped from natural solar energy was used. Exposure of the various developmental stages of C. maculatus infesting adzuki bean seed to heat for 45 min and more raised the temperature between and within the seeds well in excess of the lethal level (>60 °C) and resulted in complete control. Heating at 60°C of up to 3 cm adzuki bean seed (seven to eight seed layers) took about 1 h and resulted in complete control of the pest. This would enable this heater to treat large amounts of seed at a time compared with solar heaters demonstrated so far in which only a single layer of seed can be treated. Therefore, solar heating of infested adzuki bean seeds using the aforementioned box heater around noon, for 1 h, gives effective control of C. maculatus . Results of the effect of heat treatment on seed viability and moisture content showed that adzuki bean seed germination is affected by heating; hence seed meant for planting should not be heat treated to control storage insect pests. Heat treatment also did not affect seed moisture content.

The effect of process parameters on keyhole welding with a 400 W Nd : YAG pulsed laser

A low average power pulsed Nd : YAG laser is used for bead-on-plate welding of low carbon steel plate. The criterion for welding in the conduction and keyhole regime together with the effect of laser process parameters on weld quality is studied. It is established that for a weld with full penetration and velocities viable for industrial applications, welding in the conduction mode would not be suitable. The formation of a keyhole is found to be highly dependent on laser pulse parameters. With an average power in the range 220–240 W and a peak power of 1.8 kW, full penetration through keyhole generation of a 0.7 mm thick st14 sheet metal is achieved.

Punching and broaching combos - a newstamping tool

The crescent searches for the reduction in time production are a factor that stimulates the improvement of the existent manufacturing techniques (Von Steeg 2002 and Waurzyniak 2002). Nowadays, the new researched processes should make possible the fabrication of pieces in a smaller time with a better use of the material resources and equipments (Klein 2002). The present work has for objective to show the viability of a combined tool that makes possible to perform a punching followed by a broaching in only one operation. This combo allies the advantages of the forming processes production and machining in only one process for heavy duty jobs on thick metal sheets. In this work were tested different configurations of combined punches. The objective was to analyze which are the main parameters that can have influence on the useful life of the tool in this new process, i.e., diameter of the punches and geometric form of the teeth for broaching. The precision overall depth of the holes, the roughness and the level of metal chip generation were measured. The analysis of the obtained data showed that the process is viable once were obtained holes with superior quality to the conventional stamping processes.

張出・しごき複合加工によるフランジ付き深い容器の作製

In the bulging, the material existing at the flange portion is not drawn into the die opening, and so the periphery of a metal sheet blank does not change. This feature of the bulging is advantageous to producing cups with wide flange. On the other hand, there is a weak point that it is difficult to make cups with large height by the bulging. This is because the thickness of metal sheet at punch shoulder decreases locally and it results in a quick breakage at this portion. At this point, the thickness of the sheet at the other portions, e.g. punch head and sidewall, has been little decreased. Therefore, if the thickness of the sheet metal could be decreased more uniformly in the bulging, producing shells with wide flange and large height becomes possible. In this study, in order to get higher cups with wide flange, a new process of bulging combined with ironing was tried. In the new process, a hemispherical rubber punch and metal counter punch were used for thinning material at punch head. And the material at sidewall of the stretched cup was thinned by a following ironing process. Variations of thickness strain distribution by each process were measured and the effectiveness of the process was clarified. Finally, it was possible to make a stretched cup twice as high as that made by conventional bulging.

Development of Combined Forming of Cold Forging and Thick Sheet Metal Forming

Development of Combined Forming of Cold Forging and Thick Sheet Metal Forming

Enhanced Semi-Analytical Process Simulation of Air Bending

The air bending process is one of the most widely used process for the manufacturing of sheet metal bending parts made of thin as well as of thick sheet metal. Although the air bending process offers a very high production potential due to its great flexibility, it is associated with certain problems which can negatively influence the shape and dimensional accuracy of the bending parts. Examples for such negative influences are the springback of the material, the batch variations, or the deflections of the bending machine and tools. These differences have to be considered either in the determination of the process parameters or they have to be compensated later on in the manufacturing process itself. A well established approach to calculate process data for forming processes is the use of a process simulation. At the Institute of Forming Technology and Lightweight Construction (IUL) a simulation software called Sheet Metal Bending Simulation (SMBS) has been developed and successfully been tested for the field of sheet metal bending, based on semi-analytical approaches. Although it already provides very satisfactory results in general, disturbances such as material and batch variations as well as the deflections of C-frame, machine table, and press brake ram can still negatively affect the prediction of the punch displacement necessary to achieve a certain bend angle. While material and batch variations cannot properly be considered in a process simulation at present, the afore mentioned influences offer a promising potential for improvements. Therefore, in order to further improve the accuracy of predicted quantities such as punch displacement and bending angle, a new module describing the elastic machine behaviour of press brakes has been developed and successfully been integrated in the process simulation SMBS. Experimental investigations have been carried out on a conventional CNC press brake to verify the efficiency of the newly implemented approach.

Developments and Trends in Laser Welding of Sheet Metal

There is some remarkable progress in laser beam welding of sheet metal which is driven by the advent of improved laser systems and process technologies. Here, potentials for reducing distortion and avoiding hot cracking are highlighted, and examples of current developments are given in the field of thin and thick sheet metal welding including spot welding of difficult-to-weld materials and material combinations.