Showing papers on "Heat-affected zone published in 1988"

Vibration welding of thermoplastics. Part I: Phenomenology of the welding process

Abstract: In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters in vibration welding are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time. How these parameters affect weld quality, the conditions that result in the best welds, the weldability of dissimilar plastics, and the effect of fillers such as glass are of interest. To address these issues, a research vibration welding machine in which all the parameters can be independently and accurately controlled and monitored was designed and fabricated. The phenomenology of welding, as determined by experiments on the four thermoplastics polycarbonate, poly (butylene terephthalate), polyetherimide, and modified poly (phenylene oxide), is described.

Vibration welding of thermoplastics. Part II: Analysis of the welding process

Abstract: The vibration welding process for thermoplastics is known to consist of four phases: (1) initial heating of the interface to the melting temperature by Coulomb friction; (2) unsteady melting and flow in the lateral direction; (3) steady-state flow; and (4) unsteady flow and solidification of the film after the vibratory motion is stopped. Simple analytical models are developed for the first three phases. These models are used for estimating the molten film thickness, the size of the heat affected zone, and the weld time as functions of the weld parameters: the amplitude and frequency of the weld motion, and the weld pressure. The steady-state film thickness and the heat-affected zone are shown to be very small.

Welding parameters and the grain structure of weld metal — A thermodynamic consideration

Abstract: The grain structure of the weld metal can significantly affect its resistance to solidification cracking during welding and its mechanical properties after welding. An experimental study was conducted to investigate the effect of two basic welding parameters,i.e., the heat input and the welding speed, on the grain structure of aluminum-alloy welds. Gas-tungsten arc welding was performed under various heat inputs and welding speeds, with thermal measurements in the weld pool being carried out during welding and the amounts and nuclei of equiaxed grains in the resultant welds being examined using optical and electron microscopy. The experimentally measuredG/R ratios and the clearly revealed heterogeneous nuclei together demonstrated the thermodynamic effect of the heat input and welding speed on the weld metal grain structure.

Resistance Welding of Graphite Polyetheretherketone Composites: An Experimental Investigation

Abstract: Resistance welding of preconsolidated unidirectional graphite (AS4) rein forced polyetheretherketone (PEEK) composite laminates (I.C.I. APC-2) is investigated experimentally. An apparatus is developed to conduct experiments to identify important process variables governing the efficiency of the welding process. Experiments were con ducted under displacement control and prescribed initial consolidation pressure. Heating elements consisted of a single ply of APC-2 with adjacent layers of neat film to minimize current leakage into the laminates to be welded. Temperature at the weld interface and consolidation pressure versus time were monitored and provided insight into the welding process. A strong correlation between the extent of welded surface area and process parameters such as power, energy and time in the melt were demonstrated. The quality and extent of the welded surface is quantified using ultrasonic nondestructive evaluation techniques. Experimental results indicate that superior welds exhibiting ...

Method and apparatus for building a workpiece by deposit welding

Abstract: A method and apparatus for building an axially symmetrical workpiece of desired geometry by deposit welding which uses a translatable welding head for depositing molten weld material and a rotatable, reusable shoe which translates with the welding head. The rotatable, reusable shoe forms, supports and cools the deposited molten weld material puddle while the weld material is solidifying thereby eliminating the need for a conventional preform.

The Effect of Nitrogen on the Localized Corrosion Resistance of Duplex Stainless Steel Simulated Weldments

Abstract: The effect of nitrogen, which is one of the most important elements in duplex stainless steels (SSs), was investigated for resistance to pitting corrosion and stress corrosion cracking (SCC) in various environments. The increase in nitrogen content increases the resistance of the base metal, which results from the improvement in the resistance of the γ-phase, which has lower chromium and molybdenum contents compared to α-phase. Nitrogen is an important element in sustaining the corrosion resistance of the heat affected zone (HAZ), which is heated to 1350 C or higher, because nitrogen promotes the formation of γ-phase during the cooling process after welding and avoids the precipitation of chromium carbides or nitrides at grain boundaries. When the nitrogen content is less than 0.08% in 22%Cr, 5.5%Ni, and 3%Mo base composition, the HAZ has little -γ-phase to lead to the high susceptibility to intergranular corrosion and intergranular stress corrosion cracking (IGSCC) occurs even in a pure CO2-Cl− ...

Tig or mig arc augmented laser welding of thick mild steel plate

Abstract: Effects of various operating parameters on penetration depth were investigated in laser +TIG and laser +MIG welding of steel plate. In laser +TIG welding (of C-Mn-Nb-V steel), DCEN TIG welding at 100-300A was closely followed by laser welding with 1-5kW beam power. Effects of welding speed, distance between TIG electrode and laser beam, focal position of laser and TIG welding current were determined. In laser +MIG welding (of C-Mn-Ni-Mo steel), DCEP helium-MIG welding at 400A was followed by laser welding at up to 5kW. Effects of arc-beam distance, focal position, joint preparation and laser beam power were determined.

Experimentally determined transient and residual stresses in a butt-welded pipe

Abstract: Single pass butt-welding of a pipe is studied. Low heat input has been used to obtain high cooling rate with adherent martensite in the final phase transformation in the heat affected zone. Strains and stresses have been measured during and after welding on the pipe outer surface. Deviations from rotationally symmetric strain and stress fields in the pipe are studied. Two different analytical solutions for the residual stress field from the literature are discussed. The experimentally obtained residual stresses are compared with those analytical solutions. Qualitatively good agreement between experiments and analytical solutions was obtained, although the analytical solutions do not consider effects of phase transformations.

Microstructural transformations in austenitic-ferritic transition joints

Abstract: The relatively complex microstructures developed at the interface between ferritic steel and weld metal on austenitic-ferritic transition joints have been examined by metallographic observation and by hardness tests in the as-welded condition and in the as-welded-and-tempered condition. Both austenitic stainless steel and nickel-based filler metals were used in welds. On as-welded specimens a sharp change of hardness in low-alloy steel has been measured, with increasing distance from weld metal; the hardness values have been related to the observed metallographic constituents. On post-weld heat treated specimens, the behaviour is different according to the composition of filler material, either austenitic steel or nickel-based alloy. In the case of austenitic filler material, a dark-etching narrow diffusion region of carbon toward weld metal is formed, with an adjacent markedly decarburized zone, exhibiting the minimum microhardness values in a narrow band of about 60 micrometres. Since this sharp structural variation is recorded just in the zone where often failures occur, the final post-weld heat treatment appears to be proposed with due caution. In the case of nickel-based filler material, carbon diffusion is inhibited by the precipitation of alloy carbides at the weld interface. This determines a more homogeneous heat affected zone (HAZ) in the ferritic steel and a reduced decarburization near the fusion line after a post-weld heat treatment, confirming the reasons of the preference recognized to this filler material, especially when service temperature is elevated and submitted to frequent changes, or whenever a post-welded heat treatment is required.

Microfissuring of Alloy 718 in the Weld Heat-Affected Zone

Abstract: Alloy 718 suffers from microfissuring in the weld heat-affected zone, and compositional, structural and mechanistic causes of this defect have been examined. Both bulk sulfur and bulk carbon increase microfissuring, and heat treatments typical ofhomogenization, solution annealing and age hardening reveal that microfissuring is sensitive to the microstructural and chemical distributions established during heat treatment. Increased grain size increases microfissuring more than heat treatment or bulk chemistry. The mechanistic cause of microfissuring, constitutional liquation of niobium carbide and Laves phases, produces intergranular liquid films with wetting angles that are dependent on the chemical composition of the grain boundary region prior to welding. Microfissuring also correlates with the temperature dependence of the intergranular liquid wetting angle in the heat-affected zone.

Automatic arc-welding method

Abstract: An automatic arc-welding method, which comprises, when welding two objects to be welded together by means of a welding wire along a first groove formed between the objects to be welded on a first side thereof, continuously determining by calculation a target welding current, with which a depth of penetration agrees with a target value thereof, on the basis of the root gap, the material of the welding wire and the like; continuously determining by calculation a target feeding rate of the welding wire, at which an extension length of the welding wire agrees with a target value thereof, on the basis of the welding current, the material of the welding wire and the like; continuously determining by calculation a target welding speed, at which a height of the weld bead agrees with a target value thereof, on the basis of the feeding rate of the welding wire, the material of the welding wire, the root gap and the like; and on the other hand, when welding the objects to be welded together by means of the welding wire along a second groove formed on a second side of the objects to be welded, opposite to the first groove, continuously determining by calculation a target welding current and a target welding speed while taking into consideration the depth of penetration and the weld bead in the first groove; thereby automatically controlling the welding current, the feeding rate of the welding wire and the welding speed on the basis of the respective target values thus determined.

Resistance welding of galvanized steel

Abstract: A coating for improved resistance welding of galvanized steel parts or sheets comprises a binder, and a metal phosphide pigment, preferably a ferrophosphorus pigment, having a particle size of from about 0.1 to about 30 microns. The pigment can also include up to about 40% by weight of an additional metal such as tin, aluminum or lead, which can be combined with the metal phosphide in pigment form or deposited onto the surface of the particles. The coating can be applied to either the faying or non-faying surfaces of the galvanized steel, or to the resistance welding electrode, and may be removed, if desired, after the welding operation. The advantages of the present invention include a significant reduction in welding current and an increase in the weldability lobe width, a restoration of the dynamic resistance beta peak, and an increase in electrode life.

Apparatus for welding tubular components of thermoplastic material

Abstract: An apparatus for welding tubular components of thermoplastic material. The apparatus includes a heating device for heating the ends of the tubular components to be welded together until the melting range of the thermoplastic material is reached. Two outer support rings which are slid toward each other after the thermoplastic material has melted and an expandable inner support member ensure that welding pressure is built up, so that a welded connection can be obtained which is strong and free of welding beads.

Gas tungsten arc welding machine with infinite rotating welding head and torch tilt

Abstract: This invention relates to a machine for practicing the gas tungsten arc welding process which includes means (5) for rotating the welding torch (28) continuously while welding. Means are provided for feeding the shielding gases, feed wire and electric current to the rotating torch while welding. Means (23) and (24) are also provided for tilting the torch about the point of welding. This invention makes it possible to weld continuously along a spiral path about a cylindrical object or on a flat or irregular surface.

Method for bonding and/or repairing component parts made of an oxide dispersion-hardened nickel-based superalloy in the zone-annealed state of coarse-grained, longitudinally oriented column crystals

Abstract: Component parts made of an oxide dispersion-hardened nickel-based superalloy in the state of coarse-grained, longitudinally oriented column crystals are renovated by fusion welding according to the argonarc, electron-beam, laser-beam or plasma-burner method by build-up welding (deposition welding, overlay welding) and/or joined together by junction welding, by first being subjected to a heat treatment in order to increase their ductility. Said heat treatment comprises solutionisation in the temperature range between 1160@C and 1280@C, followed by slow cooling at a rate of from 0.1@C/min to 5@C/min, to a temperature in the range between 500@C and 700@C, followed by cooling in air down to room temperature. Particularly advantageous economical method for in situ repairs on guide vanes (diffuser blades) and rotor blades of gas turbines.

Process for automatic fusion welding of rails

Abstract: A process for automatic fusion welding of rails by a combination of submerged arc welding and electroslag welding, comprising a root run for welding a rail base by submerged arc welding and, without interruption of the welding, subsequent runs for welding the rail base and welding a region from a rail web to a rail head by electroslag welding; wherein, during all of the runs, a metal mold is mounted on an upper surface of the rail base and a metal shoe is mounted on the metal mold to prevent an outflow of molten slag and molten metal and, during all of the runs, welding is performed by using a DC welding transformer having constant potential characterisitcs, a filler-wire having a diameter of from 1.2 to 2.0 mm, and a fused-type flux. The inventive process avoids the use of different fluxes and an alteration of welding machine conditions during the whole sequence of welding from the rail base through to the rail head.

Weldability studies in Cr-Mo-V turbine rotor steel

Abstract: This study was undertaken to establish the weldability of a high pressure steam turbine rotor (1.0Cr-1.0Mo-0.25V steel). Characterization of the as-received material and subsequent evaluation of a de-embrittlement procedure suggests that such heat treatment should be carried out prior to welding. But the improvement in toughness experienced by the heat affected zone (HAZ) of welds produced on both as-received and de-embrittled steel coupons suggests that a preweld de-embrittlement treatment is unnecessary. Further, a postweld heat treatment (PWHT) at the optimum temperature was found to improve the impact properties of both the HAZ and the base metal. The welds were automatically made on steel coupons with the welding parameters held constant, controlled by a microprocessor. In terms of short-term mechanical properties, the turbine rotor can be weld repaired. Studies are presently being conducted under simulated service conditions for long-term testing.

A high-power-density beam welding method in combination with upset welding and apparatus therefor

Abstract: The method comprises forming along abutting edges of metal materials to be welded a continuous weld line for high-power-density beam welding by using an upset welding, and welding the metal materials by irradiation of a high-power-density beam along the weld line with an output of the high-power-density beam determined on the basis of an input heat produced by resistance exothermal reaction in the metal materials during the upset welding as well as a welding pressure given to the metal materials.

Metal transfer mechanisms

Abstract: This article describes the basic mechanisms involved in the transfer of metal from the electrode to the weld pool in consumable electrode arc welding processes. The transfer modes observed in practice are explained and an indication of the resultant process characteristics is given. A brief introduction to the theoretical background of the subject is also provided.

Automatic stepper for resistance welding

Abstract: A method is disclosed for controlling the magnitude of current delivered through welding electrodes to a workpiece to be welded using resistance welding techniques, in order to prevent weld expulsion and concomitant diminishment of weld quality. Weld expulsion is detected by determining changes in resistance during formation of the weld, by periodically determining the power factor, and the primary circuit of the welding transformer. The power factor is determined by determining the relative timing between the commencement of the applied voltage, the zero crossover point of the applied voltage, and the ensuing zero point of the applied current.

Method for heat-treating straight bead welded pipes

Abstract: A method for welding and heat treating straight bead welded pipes made of austenitic, ferritic or austenitic-ferritic rust-resistant steel includes welding a straight bead on a pipe forming a welding seam region, a heat affected zone and a remaining region, and annealing the pipe after welding the straight bead by only partially solution-annealing in the welding seam region and the heat affected zone, while heat treating the remaining region at a reduced temperature. An apparatus is also provided for carrying out the method.

Microstructure effects on dynamic welding of Ag/W contacts

Abstract: A computer-controlled device was used to simulate contact bounce on closing to evaluate the dynamic weld strength of some silver-tungsten contact materials. The effects of composition, microstructure modifications (such as different tungsten particle sizes), and the thickness of the silver-rich surface layer on the tendency to weld were evaluated. Probability analysis showed that silver has the highest tendency to weld. The addition of tungsten lowers the weld strength, with a minimum in the range of 35-62 vol.% of tungsten. The weld probability is lower than that predicted by a volume-mixing-rule calculation. The tungsten particle size was found to be a very important parameter in determining weld tendency. The optimum tungsten particle size for lowest weld tendency was dependent on the volume percent of tungsten. In general, an increase in tungsten particle size increased welding tendency. Silver enrichment of the contact surface by electrochemical etching also increased weld tendency. The welding tendencies were found to be related to the metallurgical properties of the contacts and the welding process. >

Welded joint efficiency lowering preventing method

Abstract: PURPOSE:To prevent lowering of welded joint efficiency excellent in the lightweight property by inserting insert material for increasing thickness with the same material as base metals into a weld zone groove and welding the base metals and the insert material mutually by an electron beam or a laser beam. CONSTITUTION:The insert material 4 for increasing thickness with the same material as members 1 to be welded and having the size of cross section to compensate for lowering of joint efficiency is inserted into the groove part 2 which is the central part of a joint efficiency lowering range by welding heat of the members 1 to be welded. The members 1 to be welded and the insert material 4 are then welded mutually by one-pass welding of the electron beam or laser beam welding. Since the insert material 4 is provided with a cone angle, a bead after welding is smoothed and the need for cutting work of excessive thickness is eliminated. By this method, even if welded joint efficiency per unit area is lowered, the essential joint strength of a welded zone, etc., is made 100% in light weight.

High rate deposition gas-metal-arc welding process

Abstract: A gas-metal-arc welding process, utilizing a four-gas mixture and relatively high voltage, produces a high rate of weld metal deposition. The process involves continuously advancing the end of a meltable, thin wire electrode towards a weld metal deposit surface, while maintaining a predetermined length arc gap therebetween. A flow of shielding gas, which is formed of major proportions of argon and helium and minor proportions of carbon dioxide and oxygen, coaxially surrounds and flows along the electrode end portion and arc gap towards the deposit surface. A relatively high electrical voltage and current density are applied to the electrode. A roughly conically-shaped, hot plasma field is formed within the arc gap between the electrode end and the metal deposit surface. The length of the arc gap and the voltage are adjusted to provide a plasma field base diameter which corresponds to and substantially overlaps the width of the weld bead and the narrow band of the metal deposit surface upon which the weld bead is deposited. Drops melted from the electrode are deposited by globular, free-flight transfer across the arc gap upon the deposit surface substantially within the field base diameter. To form the elongated, narrow weld bead, the electrode, with its concentric arc gap band plasma field, is moved sideways in parallel alignment with the axis of the weld bead. Thus, the process may be used for high deposition rate welding within relatively deep, narrow gaps, as well as upon more exposed metal deposit surfaces.

Insert material for solid phase diffusion welding for nickel base superalloy and method therefor

Abstract: In solid phase diffusion welding of a nickel base superalloy having nickel as a main component, an insert material for solid phase diffusion welding and method thereof are disclosed which can improve the welding strength, the insert material consists of an alloy containing 5-25% by atomic % of total atomic amount of at least one selected from aluminum, titanium, tantalum and niobium, [100-(total atomic % of aluminum, titanium, tantalum and niobium)×4] % or less by atomic % of total atomic amount of at least one selected from chromium, cobalt, tungsten, molybdenum and zirconium and the balance being substantially nickel. After this insert material is previously subjected to heat treatment at between 700° C. and melting point or plastic working, it is interposed between the welded surfaces and heated up to a temperature of the melting point or less of base metal in vacuum or inactive gas solid phase diffusion welding.

Process for controlling the welding operation in the production of a spigot joint

Abstract: In a process for controlling the welding operation in the production of a spigot joint for heat-insulated conduits, in which the temperature of a heating wire provided for generating the welding heat is monitored, the temperature of the heating wire is determined by measuring the wire resistance.

Welded joint between plastic parts

Abstract: The invention relates to a welded joint between plastic parts, the welding quality of which can be checked in a non-destructive way. In particular, a coating of an X-ray contrast medium, of sharply set-off contour and of specific outline shape, is introduced, before welding, in the region of the welding gap. The coating is narrower or smaller than the zone to be welded. It can be a strip of specific width or a pattern comprising recurring contour parts. The coating can be printed on or take the form of an inserted auxiliary film. Coloring pigments based on heavy metal, metal powder, rock dust, powdered glass or ceramic powder come under consideration as X-ray contrast media.