Showing papers on "Heat-affected zone published in 1993"

Weld pool oscillation during GTA welding of mild steel

Abstract: In this paper the results are reported of a study dealing with the oscillation behavior of weld pools in the case of GTA bead-on-plate welding of mild steel, Fe 360. During welding, the weld pool was brought into oscillation by applying short current pulses, and the oscillation frequency and amplitude were measured by monitoring the arc voltage. It was found that the oscillation of the partially penetrated weld pool is dominated by one of two different oscillation modes (Mode 1 and Mode 2) depending on the welding conditions, whereas the oscillation of the fully penetrated weld pool is characterized by a third oscillation mode (Mode 3). It is possible to maintain partially penetrated weld pool oscillation in Mode 1 by choosing appropriate welding conditions. Under these conditions, an abrupt decrease in oscillation frequency occurs when the weld pool transfers from partial penetration to full penetration. Thus, weld penetration can be in-process controlled by monitoring the oscillation frequency during welding.

Calculation of weld metal composition change in high-power conduction mode carbon dioxide laser-welded stainless steels

Abstract: The use of high-power density laser beam for welding of many important alloys often leads to appreciable changes in the composition and properties of the weld metal. The main difficulties in the estimation of laser-induced vaporization rates and the resulting composition changes are the determination of the vapor condensation rates and the incorporation of the effect of the welding plasma in suppressing vaporization rates. In this article, a model is presented to predict the weld metal composition change during laser welding. The velocity and temperature fields in the weld pool are simulated through numerical solution of the Navier-Stokes equation and the equation of conservation of energy. The computed temperature fields are coupled with ve-locity distribution functions of the vapor molecules and the equations of conservation of mass, momentum, and the translational kinetic energy in the gas phase for the calculation of the evap-oration and the condensation rates. Results of carefully controlled physical modeling experi-ments are utilized to include the effect of plasma on the metal vaporization rate. The predicted area of cross section and the rates of vaporization are then used to compute the resulting com-position change. The calculated vaporization rates and the weld metal composition change for the welding of high-manganese 201 stainless steels are found to be in fair agreement with the corresponding experimental results.

Resistance welding monitor

Abstract: A welding voltage output from a power source of a resistance welder is derived on the basis of a welding current and an interelectrode voltage, and diameter of a nugget which is formed in a sheetlike work to be welded is estimated on the basis of the welding current, the welding voltage, data of material constant and a thickness of the sheetlike work, subsequently, the estimated diameter of nugget is composed with a target diameter of nugget, and thereby quality of the resistance welding is determined.

Investigation of the effect of welding parameters on weld quality of plasma arc keyhole welding of structural steels

Abstract: In the present investigation, the individual and interactive effects of the main welding parameters on weld quality of plasma arc keyhole welding of conventional structural steel, high strength microalloyed steel and strong formable microalloyed steel have been examined using welding of butt joints with a square groove in various welding positions, and welding of joint roots with a single-V-groove and the root face in the flat position. The most important welding parameters are welding current, welding speed and welding gases, especially plasma gas flow rate. Welding parameter combinations producing the best quality welds are presented. It is shown that it is possible to achieve defect-free high-quality welds with good strength and toughness properties, but the allowable range of variation of welding parameters, especially for the highest weld quality, is narrow. An argonhydrogen mixture for the plasma gas together with argon as shielding and backing gases give the best results with respect to weld quality.

Method for welding thermoplastic materials

Abstract: An improved welding rod having a solid homogeneous core of thermoplastic material and a resistance element comprised of a plurality of wires is presented with a method and apparatus for forming the welding rod. The welding rod is positioned between members of the thermoplastic material to be welded and a current and pressure is applied to the resistance element causing the thermoplastic material of the solid core and the adjacent thermoplastic members to fuse and form a unitary weld. Simultaneously the electrical resistance element is embedded in the weld, mechanically reinforcing and strengthening the connection. There is also disclosed a method for electric fusion welding of thermoplastic members wherein the welding rod is pre-attached to one of the thermoplastic members.

Effect of pre- and post-weld heat treatments on the mechanical properties of electron beam welded Ti-6Al-4V alloy

Abstract: This paper represents a summary of experimental work carried out to find the effect of various pre- and post-weld heat treatments on Ti-6Al-4V alloy. In the as-welded state the samples exhibit about 80% of the tensile ductility and about 90–95% of the impact/fracture toughness of the base metal. Low temperature stress relieving or ageing carried out subsequent to the welding operation improves the tensile properties but decreases the toughness at the fusion zone. Solution treatment followed by welding and ageing or the post-weld solution treatment and ageing treatment leads to only a marginal increase in tensile strength at the expense of toughness at the fusion zone. High temperature annealing of the welded samples does not increase the tensile ductility but improves the toughness at both the fusion zone and the heat affected zone. The above facts and a special burst-pressure test conducted on a gas bottle in the as-EB welded state show that Ti-6Al-4V components can be used without subjecting them to any post-weld heat treatments.

Beneficial effects of low‐frequency pulsed MIG welding on grain refinement of weld metal and improvement of solidification crack susceptibility of aluminium alloys: Study of low‐frequency pulsed MIG welding

Abstract: (1993). Beneficial effects of low‐frequency pulsed MIG welding on grain refinement of weld metal and improvement of solidification crack susceptibility of aluminium alloys: Study of low‐frequency pulsed MIG welding. Welding International: Vol. 7, No. 6, pp. 456-461.

Fracture toughness analysis of heat-affected zones in high-strength low-alloy steel welds. [Fe-0. 13C-0. 4Si-1. 43Mn-0. 01P-0. 001S-0. 065Al-0. 3Cu-0. 22Ni-0. 017Ti-0. 021Nb]

Abstract: This study is concerned with a correlation of fracture toughness with microstructural factors in heat-affected zones (HAZs) of a normalized high-strength low-alloy (HSLA) steel. In order to explain weld joint performance, tensile and plane strain fracture toughness tests were conducted for the simulated coarse-grained HAZ microstructures. The micromechanisms of fracture processes involved in void and microcrack formation are identified by in situ scanning electron microscopy (SEM) fracture observations and void initiation study. The fracture toughness results are also interpreted using simple fracture initiation models founded on the basic assumption that a crack initiates at a certain critical strain or stress developed over some microstructurally significant distance. The calculated K[sub Ic] values are found to scale roughly with the spacing of the stringer-type martensite islands associated with voids, confirming that martensite islands play an important role in reducing the toughness of the coarse-grained HAZs. These findings suggest that the formation of martensite islands should be prevented by controlling the chemical compositions and by using the proper welding conditions to enhance fracture toughness of the welded joints of the HSLA steel.

The effects of process variables on the weld deposit area in submerged arc welds

Abstract: The results of bead-on-plate submerged arc welding experiments are presented to determine the effects of process variables on the weld deposit area at a constant heat input of 2kj/mm. It is found that the deposit area is a function of the welding current, welding voltage, welding speed, electrode polarity, electrode diameter and electrode extension. In general, welds made using direct current electrode negative (DCEN) polarity, a small-diameter electrode, long electrode extension, high welding current, low welding voltage and high welding speed have large deposit areas. The weld deposit area is, however, not affected significantly by the power source or the flux type used in this investigation.

Fracture toughness analysis of heat-affected zones in high-strength low-alloy steel welds

Abstract: This study is concerned with a correlation of fracture toughness with microstructural factors in heat-affected zones (HAZs) of a normalized high-strength low-alloy (HSLA) steel. In order to explain weld joint performance, tensile and plane strain fracture toughness tests were conducted for the simulated coarse-grained HAZ microstructures. The micromechanisms of fracture processes involved in void and microcrack formation are identified byin situ scanning electron microscopy (SEM) fracture observations and void initiation study. The fracture toughness results are also interpreted using simple fracture initiation models founded on the basic assumption that a crack initiates at a certain critical strain or stress developed over some microstructurally significant distance. The calculated KIc values are found to scale roughly with the spacing of the stringer-type martensite islands associated with voids, confirming that martensite islands play an important role in reducing the toughness of the coarse-grained HAZs. These findings suggest that the formation of martensite islands should be prevented by controlling the chemical compositions and by using the proper welding conditions to enhance fracture toughness of the welded joints of the HSLA steel.

Thermal Analysis for Resistance Welding of Large-Scale Thermoplastic Composite Joints:

Abstract: The need for effective and reliable joining methods continues to grow as the use of thermoplastic composites becomes widespread. It is now possible to join large-scale components with the development of an automated sequential resistance welding process. The thermal history generated by the heating element placed at the interface between adherends determines the quality and performance of the welded joint. This article presents a thermal analysis for the resistance welding of large-scale components that overcomes the limitations of previous models. To simulate welding of the interface, a heat generation term was incorporated that accounts for the Joule heating of graphite fibers in the heating element. A parametric study was conducted to investigate the influence of welding parameters and assess the uniformity of interface temperatures. Components were joined by the resistance welding process to obtain experimental verification. Regions of localized overheating where potential current leakage may occur were identified as a function of process parameters. Insights on promoting more uniform heating for the resistance welding process are discussed. 11 refs.

System for welding pipes

Abstract: An automatic welding system uses an anti-gravitational welding controller to minimize or eliminate the undercutting and concavity of the roots of the welds caused by gravitational effects. The pressure within the pipes to be welded is continually changed as the welder orbits the pipes. At the upper section of the weld, positive pressure is applied to the pipes to eliminate undercutting at the upper surface of the weld and negative pressure (vacuum) is applied to the lower section of the weld to eliminate concavity of the root of the weld. In one mode, the internal pressure within the pipes is varied as a function of the position of the orbital welder. In another mode, the arc voltage at the tip of the weld, i.e., the distance between the tip of the weld and the surface of the weld, is maintained constant by varying the pressure within the pipes. The system allows for the completion of high quality welds with less weld material, less passes, and less time. It also allows the welding to be performed by welders who are less experienced and skilled as the present welders.

Process and apparatus for welding or heat treating by laser

Abstract: Method and apparatus for welding, cutting, surface machining or heat treating workpieces by a laser beam which includes providing an optical element in the path of the laser beam to modify the pattern of the laser beam such that different geometric patterns can be projected on the focal plane, and this beam pattern spans at least the width of the heat treatment, cutting, surface machining or welding zone on the workpieces.

Intermetallic alloy welding wires and method for fabricating the same

Abstract: Welding wires for welding together intermetallic alloys of nickel aluminides, nickel-iron aluminides, iron aluminides, or titanium aluminides, and preferably including additional alloying constituents are fabricated as two-component, clad structures in which one component contains the primary alloying constituent(s) except for aluminum and the other component contains the aluminum constituent. This two-component approach for fabricating the welding wire overcomes the difficulties associated with mechanically forming welding wires from intermetallic alloys which possess high strength and limited ductilities at elevated temperatures normally employed in conventional metal working processes. The composition of the clad welding wires is readily tailored so that the welding wire composition when melted will form an alloy defined by the weld deposit which substantially corresponds to the composition of the intermetallic alloy being joined.

Process for the electric welding of two weld parts

Abstract: The invention relates to a process for the electric welding of two weld parts by the flow of electric current through a welding point and the use of fluid such as an inert or protective gas to inhibit or prevent or eliminate oxidation at the welding point. The fluid is supplied through a continuous bore in one weld part and is directed toward the welding point, so that the fluid sweeps over the welding point radially from the bore. The fluid may be an inert gas such as argon or nitrogen, optionally mixed with carbon dioxide; alternatively the fluid may be aqueous liquid, the water being vaporized in the region of the welding point.

Penetration sensor/controller arc welder

Abstract: An arc welding device apparatus for controlling an arc welder through use of a neural network in real-time. The invention can also record output from an arc welding apparatus, indicating whether penetration has occurred during the welding process, and can also activate an alarm when penetration occurs during the arc welding process.

A model for heat and mass input control in GMAW

Abstract: This work describes derivation of a control model for electrode melting and heat and mass transfer from the electrode to the work piece in gas metal arc welding (GMAW). Specifically, a model is developed which allows electrode speed and welding speed to be calculated for given values of voltage and torch-to-base metal distance, as a function of the desired heat and mass input to the weldment. Heat input is given on a per unit weld length basis, and mass input is given in terms of transverse cross-sectional area added to the weld bead (termed reinforcement). The relationship to prior work is discussed. The model was demonstrated using a computer-controlled welding machine and a proportional-integral (PI) controller receiving input from a digital filter. The difference between model-calculated welding current and measured current is used as controller feedback. The model is calibrated for use with carbon steel welding wire and base plate with Ar-CO[sub 2] shielding gas. Although the system is intended for application during spray transfer of molten metal from the electrode to the weld pool, satisfactory performance is also achieved during globular and streaming transfer. Data are presented showing steady-state and transient performance, as well as resistance to external disturbances.

A theoretical lower limit for laser power in laser-enhanced arc welding

Abstract: A physical mechanism for the enhancement effect in laser-enhanced arc welding (LEAW) is proposed. The minimum laser power for a CO2 and a Nd:YAG laser is calculated in the case of Fe-, Al- and Cu-based welding materials. The results are compatible with the pertinent welding experiments.

Three-dimensional analytical temperature field around the welding cavity produced by a moving distributed high-intensity beam

Abstract: An analytical solution for the three-dimensional temperature field in the liquid and heat-affected zones around a welding cavity produced by a moving distributed low- or high-power-density-beam is provided. The incident energy rate distribution is assumed to the Gaussian and the cavity is idealized by a paraboloid of revolution in workpieces of infinite, semi-infinite, or finite thickness. The present study finds that temperature fields can be described by the Laguerre and confluent hypergeometric functions

Corrosion resistant welding of stainless steel

Abstract: A process for welding stainless steel tubing in the presence of an inert gas comprising a silicon base gas, in particular silane SiH₄. During the welding operation, a suitable quantity of silicon is deposited by chemical vapor deposition at the weld joint to significantly improve the corrosion resistance of the weld.

Electric fusion welding of thermoplastic materials

Abstract: An improved welding rod having a solid homogeneous core of thermoplastic material and a resistance element comprised of a plurality of wires is presented with a method and apparatus for forming the welding rod. The welding rod is positioned between members of the thermoplastic material to be welded and a current and pressure is applied to the resistance element causing the thermoplastic material of the solid core and the adjacent thermoplastic members to fuse and form a unitary weld. Simultaneously the electrical resistance element is embedded in the weld, mechanically reinforcing and strengthening the connection. There is also disclosed a method for electric fusion welding of thermoplastic members wherein the welding rod is pre-attached to one of the thermoplastic members.

Toward understanding alloying element vaporization during laser beam welding of stainless steel

Abstract: During laser beam welding of many important engineering alloys, appreciable changes in the composition and properties of the weld metal can occur due to pronounced vaporization of alloying elements from the weld pool. Currently there is no comprehensive theoretical model to predict, from fundamental principles, laser-induced metal vaporization rates and the resulting weld pool composition changes. The velocity distribution functions of the gas molecules at various locations above the weld pool surface and the heat transfer and fluid flow phenomena in the pool have been coupled to model the rates of the vaporization of various alloying elements during laser beam welding of stainless steels. The procedure allows for computation of both the evaporation and condensation fluxes based on the equations of conservation of mass, momentum and energy applied to the vapor and the liquid phases. Computed values of the rates of vaporization of various alloying elements and the vapor composition were found to be in good agreement with the corresponding experimental values. Synthesis of the principles of gas dynamics and weld pool transport phenomena can serve as a basis for the calculation of alloying element vaporization rates during laser beam welding of alloys.

Prediction of welding thermal history by a comprehensive solution

Abstract: A comprehensive solution has been developed to examine heat conduction in three different welding cases. Case 1 is a quasi-steady-state model to predict the shape of the heat-affected zone (HAZ), and the thermal histories and cooling times between 800 and 500 C (t[sub 8/5]) in wide plates. Case 2 is an instantaneous heat source model to predict cooling time from solidification to 100 C (t[sub 100]) in small test pieces. Case 3 is an unsteady heat model to predict t[sub 100]s in locally preheated plates. Rosenthal's and Tanaka's formulas can be derived from a solution of Case 1. These three cases were applied to the predictions of thermal histories, cooling times and HAZ shapes. The calculated results have been compared with the experimental results of several different cases of arc welding and good agreement has resulted.

Microstructural characterization of CO2 laser welds in the Al-Li based alloy 8090

Abstract: The microstructural development of the Al-Li-Cu-Mg-Zr alloy 8090 has been studied after autogenous CO2 laser welding. Sheets ranging in thickness from 1–4 mm were welded at speeds of between 20–120 mm s−1 and powers from 1.5–3.8 kW. Optical microscopy, scanning and transmission electron microscopy were used to study the as-received base metal, the heat-affected zone and the solidified fusion zone. The base metal was supplied in a superplastically formable condition and thus had an unrecrystallized grain structure containing 1–2 μm sized sub-grains with sub-micrometre δ′ and β′ precipitates in the matrix. In the fusion zone, the as-solidified grain structure was columnar at the interface with the base metal but became equiaxed in the central region of the weld pool. The weld depth and top bead width both increased with decreasing welding speed and increasing beam power within the limits investigated. The fusion zone microstructure was cellular-dendritic. Intermetallic precipitates, which are rich in copper, magnesium, silicon (and presumably lithium), formed in the cell/dendrite boundaries. Very fine-scale δ′ precipitates were present in the as-solidified α-Al matrix but there was no evidence for the β′, S′ and T1 phases. The heat-affected zone was only 100 μm wide and was characterized by regions of partial melting. Radiographs of welds reveal that porosity occurred predominantly along the weld centre-line. In partial penetration welds, two types of pores were observed: near spherical and irregular. However, in fully penetrating welds, only the spherical type of porosity was present. Overall volume fractions of porosity were measured from metallographic sections and were found to vary with welding speed and weld type, i.e. partial or full penetration.

Space charge in plasma arc welding and cutting

Abstract: In transferred arc plasma arc welding, the plasma is not electrically neutral. Some simple mathematical models are constructed to demonstrate this fact and orders of magnitude are obtained. The relevance of these models to plasma arc welding and cutting is considered; quite long arcs can be achieved if the flow rate is sufficiently high, and an arc from a consumed tubular field emitting cathode of 75 mm length is described. In keyhole welding it is found that the current earths at the surface of the workpiece, or close to the top of the keyhole.

Method of controlling welding current in direct-current resistance welding machine

Abstract: A workpiece is welded successively at a plurality of welding points by a direct-current resistance welding machine with a constant current in a welding current supply period at each of the welding points, and the constant current is varied depending on whether expulsions are produced on the workpiece when it is welded, to determine an expulsion-producing limit current value as a maximum current beyond which expulsions will be produced. The workpiece is welded with a first stepped welding current having a first current value that is smaller than the expulsion-producing limit current value by a predetermined value and a second current value that is greater than the expulsion-producing limit current value, and an average current value higher than the expulsion-producing limit current value, and also with a second stepped welding current having a variation of the second current value based on whether expulsions are produced or not on the workpiece when it is welded with the first stepped welding current.

Hot ductility and hot cracking behavior of modified 316 stainless steels designed for high-temperature service

Abstract: The weldability of the modified 316 stainless steel was evaluated by the Gleeble hot ductility test and two hot cracking test methods (Varestraint and Sigmajig). The fusion zone and weld metal heat-affected zone (HAZ) hot cracking susceptibilities of the modified 316 stainless steel are similar to conventional fully austenitic 316 stainless steels and greater than the conventional 316 materials that have a primary ferritic solidification mode. The Gleeble hot ductility test results correlate with the base metal HAZ hot cracking results from the Varestraint test and indicate that the modified 316 materials show a considerably higher base metal HAZ hot cracking susceptibility as contrasted to nuclear grade 316 stainless steels. Varestraint test results and Sigmajig test results and Sigmajig test results for the tested materials showed good correlations. The sensitivity of the base metal to HAZ liquation cracking has been successfully predicted by using a newly developed hot ductility criterion, the ratio of ductility recovery (RDR). An excellent correlation between the Gleeble Test criterion RDR and the Varestraint Test criteria (TCL, MCL and CHL) has been found.