Showing papers on "Heat-affected zone published in 1986"

Industrial Applications of Lasers

Abstract: The unique non-contact nature of laser welding and the ability to join both similar and dissimilar metals with a minimal heat affected zone is proving very popular in many assembly operations. Laser welding has enabled one company, Fischer Porter Co, of Warminster, PA, to simplify product designs and to salvage previously unrepairable expensive subassemblies for their line of process control systems. The cost savings are such that this numerically controlled laser welding system will pay for itself in 15 months.

Thermoplastic fitting electric heat welding method and apparatus

Abstract: A method and apparatus for electrically heat welding a thermoplastic fitting having an electric resistance heating element disposed therein whereby a regulated quantity of electric power is supplied to the heating element during the welding process and the making of a high quality weld is insured. In accordance with the method, a controlled electric power is supplied to the resistance heating element of the fitting. The initial magnitude of the current flowing through the heating element is sensed and compared with predetermined current levels for various sizes of fittings whereby the size of the fitting as well as the total time the controlled electric power should be supplied to the heating element of the fitting for the making of a high quality weld are determined. The magnitude of the current flowing through the heating element over the time the controlled electric power is supplied thereto is sensed at predetermined time intervals and compared with predetermined current levels for the size of fitting being welded to thereby determine if the welding process is proceeding abnormally at such time intervals. The electric power supplied to the heating element is terminated when it is determined that the welding process is proceeding abnormally or otherwise at the end of the total time determined to be required for the making of a high quality weld.

Resistance spot welding of galvanized steel: Part II. Mechanisms of spot weld nugget formation

Abstract: Dynamic inspection monitoring of the weld current, voltage, resistance, electrode displacement, and force was performed in conjunction with a detailed study of the effects of material variations and weld process parameter modifications on resistance spot welding of coated and uncoated steels. In order to determine the mechanisms of weld nugget formation and growth, scanning electron microscopy photos were taken of the developing nugget. These physical changes were then related to the dynamic inspection curves and the welding current lobe. The effects of material variations and weld process modifications, the results of which were presented in Part I, can be explained through an understanding of these mechanisms.

Method for repairing a steam turbine or generator rotor

Abstract: This is a method for repairing low alloy steel steam turbine (both high pressure and low pressure sections) or generator rotors. The defective section of the original rotor is removed and a replacement end is used, with mating attachments machined on the replacement end and the original rotor. The inner portion of the weld joining the replacement end to the original rotor is provided by a narrow gap weld, either by gas metal or by submerged arc welding. The outer 1/2-2 inches of the weld is provided by gas tungsten arc welding. The mating attachment and at least the inside 1/4 inch of the weld is bored out to remove possible crack initiation sites and to provide a smooth inspectable bore. In this manner, a fast and reliable technique is provided which provides accurate alignment, fast, essentially distortion free welding, and the superior mechanical properties of gas tungsten arc welding in the outer, more highly stressed zones.

Interaction between Impurities and Welding Variables in Determining GTA Weld Shape Depending on the trace elements in the base materials, identical changes in welding variables can have an opposite effect on weld shape

Abstract: Variations in GTA weld shape, or penetration, have been shown in many cases to arise from small changes in trace element content of the base metal. Heiple and Roper have proposed that CTA weld shape is generally deter­ mined by fluid flow patterns in the weld pool, and that certain trace elements can alter the fluid flow patterns by changing surface tension gradients on the weld pool. The surface tension gradients will also be altered by changes in tempera­ ture gradients on the weld pool surface since the surface tension is temperature dependent. We propose that the primary mechanism by which welding parameter variations affect GTA weld shape is by changing the temperature gradient on the weld pool surface through changes in the input power density. A welding vari­ able change which increases the input power density will magnify the tempera­ ture gradient, and thus the surface ten­ sion gradient, thereby driving the existing fluid flow pattern more strongly. Identical changes in welding variables can there­ fore produce opposite changes in weld shape in materials with different trace element content. The effects of current, travel speed, arc length, electrode tip angle, and torch gas composition on GTA weld shape are reported for high purity and sulfur or selenium doped 304 stain­ less steel. All weld bead geometry changes caused by changing welding variables were found to be consistent with the surface tension driven fluid flow model.

Laser welding metal sheets with associated trapped gases

Abstract: A method is disclosed for laser welding two sheets of metal, the metal being of the type having associated gases tending to be trapped and expand in the weld zone during welding due to heat from the laser. These expanded gases tend to separate the upper and lower portions of the weld zone and/or expand through the weld zone toward the laser beam to create porosity in the final weld. Such metal may be coated, such as galvanized steel, in which case the zinc vaporizes into a gas in the weld zone between the adjacent sheets, or it may be poorly fitting sheets, in which case air is trapped in surface irregularities between the sheets. In either case, the method adds to the standard laser beam a surrounding stream of pressurized shield gas effective to create a pressure at the surface of the weld zone sufficient to force the molten metal of the two sheets together and force the expanded associated gases out of the weld zone in a direction away from the laser beam, whereby a non-porous weld may be created. The pressure is higher than that of shield gas in the prior art used for protection from oxygen or dispersal of plasma. Specific pressure ranges are disclosed for argon and helium.

Improvement of Residual Stresses of Circumferential Joint of Pipe by Heat-Sink Welding

Abstract: Intergranular stress corrosion cracking may occur in some specific conditions on the inner surface of the welded joints of stainless steel pipes which are furnished in nuclear plants. One of the remedies for this cracking is to convert welding residual stress on this surface into compression. In this research, in order to improve welding residual stress, the authors investigated the effectiveness of the heat-sink welding (water cooling) by conducting theoretical analyses and experiments on SUS 304 pipes of different sizes in comparison with the conventional welding. The mechanisms of production of residual stresses by both methods are clarified and conditions for effective application of the heat-sink welding such as limitation of heat input, procedure of welding are indicated.

Resistance spot welding of galvanized steel: Part I. Material variations and process modifications

Abstract: Material variations and process modifications have been studied to determine their effects on the acceptable range of resistance spot welding conditions for galvanized steel sheet. The material variations studied include zinc coating integrity, structure, composition, thickness, roughness, oil, and the amount and type of Fe-Zn intermetallics. Process modifications studied include upsloping and downsloping of the weld current, preheat current, postheat current, electrode tip geometry, and applied force. It was found that hot-dipped galvanized materials with coatings which have a very thin Fe-Zn alloy layer have a wider range of acceptable welding conditions than the commercial galvannealed products, which have a fully alloyed Fe-Zn coating. The decreased lobe width of the galvannealed material is due to the discontinuous Fe-Zn coating structure and morphology. Small variations in the thickness of the coatings studied have no significant effect on the welding current range. Surface roughness of the coating has no effect on lobe width. Upsloping and downsloping of the weld current increase the welding range of hot-dipped products when using truncated cone electrodes, whereas sloped current has no advantage for galvannealed or uncoated materials. Radiused electrodes can increase the lobe width of hot-dipped products but are not beneficial when using sloped current or when welding galvannealed or uncoated materials.

Method of welding aluminum alloys

Abstract: A method of welding together aluminum alloy workpieces of the same aluminum alloy, and comprises disposing a selected alloying metal on the workpiece in the desired weld area, locally heating the workpieces in the weld area to form a localized liquid solution, and solidifying the localized liquid solution to form the weld between the like aluminum alloy workpieces. The selected alloying metal is silicon for aluminum alloys of interest, and a laser is the preferred heating means for effecting the welding.

CO/sub 2/ laser beam weldability of Zircaloy 2

Abstract: BWR (boiling water reactor) fuel rods are manufactured by stacking pellets into a zirconium alloy, cladding tube-zircaloy 2(Zr2). A fuel rod is designed as a pressure vessel in order to prevent failure of the cladding and release of radioactive fission products. As a result, there are very strict requirements from the welding methods employed. The usual welding methods for Zr2 are based on the tungsten inert gas (GTAW) resistance welding (RW) and electron beam welding (EBW) processes. There is very little information about laser beam welding (LBW) of Zr2. The recent development of multikilowatt laser systems has led to dramatic improvements in their welding performance. In the present work, laser beam welding of Zr2 was investigated. A comparison with GTA welding was carried out. The use of a high-power laser beam to weld nuclear fuel containers made of zircaloy has many advantages: (1) The high-power density of the focused laser beam enables very high welding speeds in comparison with arc welding. As a result, a narrow heat-affected zone is produced and the distortion of the parts is reduced to a minimum. (2) The beam can be transmitted to different stations alternatively, even to ones located far from one another. Itmore » also transmits to hot cells, glove boxes or any inert gas pressure chamber through suitable windows. (3) The process can easily be automated to enhance mass production. It is very simple, does not require skilled welders, and does not need the use of different electrodes, collets, etc. (4) The laser beam does not contaminate the weld metal with tungsten or other elements.« less

Method and apparatus for measuring weld penetration in an arc welding process

Abstract: The penetration in an arc welding process is measured in real time by monitoring the natural frequency of oscillation of the weld pool. Spatial oscillations are induced in the weld pool by modulating either the shielding gas or the welding current at a plurality of different frequencies, and the light reflected from the pool at a non-specular angle is sensed and processed to determine the natural frequency of oscillation. Both pulse and swept frequency modulations are employed for excitation of the weld pool.

Laser-weld heat-affected zone liquation and cracking in a high-strength Mg-based alloy

Abstract: Alliage pour applications aerospatiales, de composition nominale 5,25%Y; 3-5% lanthanides riches en Nd; 0,5%Zr (en poids), presentant une liquefaction aux joints de grains au cours du cycle thermique de soudage, engendrant des tensions au refroidissement

Process for the control of the welding time of an electrical welded union

Abstract: Two tubes of thermo-plastic material are joined by a sleeve in an inner portion of which there is an electrical resistance coil, the ends of which are connected to terminals projecting from the outer surface of the sleeve. An electrical circuit supplies electric current to the coil to heat an inner weld zone to welding temperature, while leaving enveloping outer portions at lower temperature. In the sleeve there is provided a radial hole or recess into which the heated material expands upon reaching welding temperature. The material expanding into the hole or recess when welding temperature is reached is sensed by a pressure responsive micro-switch or electro-optically by an optical transmitter and receiver and through a control circuit, shuts off the power to the resistance coil. The parts being thereby fused together, are allowed to cool to complete the weld.

Baked flux for submerged arc welding

Abstract: A baked flux of high basicity for submerged arc welding which has a chemical composition suitable for use in universal combination with various types of welding wires in welding low alloying steels. The baked flux reduces the oxygen content and diffusible hydrogen content of the weld metal to form a weld metal having a high toughness, enables forming regular beads without causing weld defects such as lack of fusion and slag inclusion, and facilitates welding work. The performance of baked fluxes is described in comparison with that of the conventional baked fluxes.

Method for overlap welding clad steels by means of an energy beam

Abstract: Welding of clad steels using laser emission. Method for overlap welding at least two clad-steel plates using a laser-emission energy beam and in which a molten weld crater is formed in the metal, the said plates being held applied against each other, characterised in that it consists in leaving a gap 6 between the contact faces of the plates 1-2.

Gas-shielded arc welding apparatus

Abstract: A gas-shielded arc welding apparatus automatically welds materials to be welded, such as rails or shape steel. The apparatus includes a gas-shielded chamber and a pair of side backing plates arranged within the chamber whereby the whole weld zone of the materials is gas shielded and a welding nozzle and shielding gas outlets are separated from each other. The apparatus also includes a welding apparatus proper and a control unit thereby performing the welding in a fully automatic manner.

Manufacturing method and apparatus for a cylindrical sheet metal package by laser beam welding

Abstract: 1. A process for manufacturing by laser beam welding a cylindrical sheet metal package, of the kind for containing preserved foods, which consists in overlapping two zones (30, 30' and 50, 62 and 50', 63) of the parts to be welded, these parts having been previously out and/or shaped, and in assembling and welding these two zones by focussing a laser beam and by causing relative movement between the said beam and the said zones along a predetermined welding line, characterized in that it consists in thinning (30, 50) at least one of the said zones by a forming operation, prior to welding, and in focussing the said laser beam (40) on the thinned zone.

Influence of process variables in flux cored arc welding of hardfacing deposits

Abstract: A lack of knowledge and objective data on the effects of welding process variables in the application and performance of weld deposited hardfacings has led to many past failures and a subsequent mistrust of the technology. This paper sets out, first, to review both the influence of welding process variables in hardfacing and the important characteristics and properties which determine the effective performance of a hardfacing deposit. Second, the results are presented of a full factorial experiment, which was performed in an effort to evaluate and interpret the effects of arc current, voltage, and polarity, as well as of travel speed, torch stand-off distance, and preheat, on the nature and properties of a commercial flux cored arc welded hardfacing deposit. In this programme, the effects of the welding parameters were evaluated with the aid of a number of computer analyses, with arc current, voltage, and polarity being shown to have the greatest effect: a high arc current (360 A) gives the most s...

Effects of Ultrasonic Vibration on Diffusion Welding of Aluminum(Materials, Metallurgy & Weldability)

Abstract: The ultrasonic vibration has been applied in the diffusion welding of aluminum in an attempt to break up the superficial oxide film of the bond interface. The ultrasonic vibration and subsequent welding have been carried out in a vacuum of 10-2 Pa at 875 K to 893 K under a welding pressure of 1 to 3 MPa. The bond strength increased with the increase in the input power to the transducer and working time of ultrasonic vibration. The increase in pressure to the bond interface during the vibration, however, lowered the bond strength. TEM observation and electric resistance measurement of the bond interface revealed that the application of ultrasonic vibration had the effect of breaking up and dispersing the oxide film, which was closely related to the increase in bond strength. On the fractured surface of joint, dimple patterns, increased with the rise of bond strength. These portions may be regarded as places where the application of ultrasonic vibration promotes breaking up and dispersing the oxide film.

Study on behaviour of molten pool in arc welding. (4th report) A nonlinear model of molten pool in arc welding.

Abstract: A mathematical model of the weld pool, where the heat input from arc is situated on the molten pool surface, has been developed to discuss the influence of weld pool configuration on the heat flow in arc welding.The numerical model, based on the heat flow equation in the quasi-stationary state and the surface tensional balance equation for the molten pool, makes it possible to assess the effect of process parameters such as arc pressure and wire deposition rate on the weld penetration.In the first part of this paper, the finite difference molten pool models have been proposed and the numerical method has been discussed.In the second part of this paper, the effect of thermal property of material on the weld pool shape has been discussed and the influence of weld pool configuration on the penetration has been made clear.

Modelling the fluid flow in laser beam welding

Abstract: The literature is briefly reviewed, and analytical and numerical results of two-dimensional models of the flow of molten metal around the keyhole in laser beam welding are discussed. The work illustrates the connection between the absorbed laser beam power, the weld width, the weld speed, and the size of the keyhole for different metals. An insight is gained into fluid dynamical flows of molten metal in the process of laser beam welding.

A welding apparatus and method for depositing wear surfacing material on a substrate

Abstract: @ The welding method may be used to lay down weld beads on metallic substrates with a narrow width of 0.125 inch and less. The process employs a plasma transferred arc and pulses the current delivered to the arc such that a wave form having at least a main amplitude and a lower auxiliary amplitude is provided. The powdered metal which is delivered is laid down in a series of overlapping weld deposits which solidify very rapidly and produce a fine grain structure.

Development of High Speed Submerged Arc Welding in Spiral Pipe Mill

Abstract: The studies were carried out to increase welding speed in the spiral pipe mill. The problems which prevent the increase of the welding speed are the occurrence of undercut, concave bead, convex bead.Investigations were carried out to solve these problems. Main results obtained are as follows;(1) The optimum welding conditions for the high speed welding were found.(2) The good bead appearance could be obtained by the use of the new flux bearing optimum amount of titanium dioxide.

Apparatus for laser beam welding the longitudinal edges of a can

Abstract: The invention involves the use of laser beam welding for the mass production of welded shells for sheet metal cans. The high requirements as to the precision of the welded seam are obtained through a guide system for exactly guiding pieces to the welding machine and consisting of an X-rail, a guide bar and the spring loaded jaws of a caterpillar tractor. A smooth welded seam is produced on the inner side of the can shell by having the seam welded from the inside of the can shell as well as from the outside by means of a laser beam.

Effects of weaving on temperature distribution in fusion welding

Abstract: A theoretical model has been developed to quantify the specific effects of weaving on the temperature distribution in fusion welding. Satisfactory agreement is obtained between predicted and measured fusion line, Ac3, and Ac1 contours, both in the case of high heat input strip electrode surfacing and tungsten inert gas welding at large amplitudes of weaving. Indications are that the present model also can be adapted to normal stringer bead deposition (through proper adjustments of the theoretical amplitude of weaving) to account for the influence of directed metal currents in the weld pool on the resulting bead morphology.MST/431