Showing papers on "Welding published in 1983"

Introduction to the physical metallurgy of welding

Abstract: Providing a thorough introduction, this second edition has been updated and expanded to cover new topics such as the numerical analytical techniques now being used in industry. This book should be of use to welding professionals and those studying metallurgy and materials science.

Temperature fields produced by traveling distributed heat sources

Abstract: The solution of a traveling distributed heat source on a semi-infinite plate provides information about both the size and the shape of arc weld pools. The results indicate that both welding process variables (current, arc length and travel speed) and material parameters (thermal diffusivity) have significant effects on weld shape. The theoretical predictions are compared with experimental results on carbon steels, stainless steel, titanium and aluminum with good agreement. 25 references, 23 figures, 1 table.

Effect of solidification conditions on the solidification mode in austenitic stainless steels

Abstract: The effect of the solidification conditions on the solidification mode in the composition range in which the primary austenitic and ferritic modes compete is studied by varying the welding parameters in gas tungsten arc (GTA) welding and by comparing the results with those obtained from other laboratory experiments. A good agreement holds if the effect of the composition is described by the ratio Creq/Nieq (Creq = pct Cr + 1.37 × pct Mo + 1.5 × pct Si + 2 × pct Nb + 3 × pct Ti and Nieq = pct Ni + 0.31 × pct Mn + 22 × pct C + 14.2 × pct N + pct Cu) and the effect of the solidification conditions by the growth rate. The critical value of the ratio Creq/Nieq corresponding to the transition from primary austenitic to ferritic solidification increases from 1.43 to 1.55 with increasing growth rate. The upper limit is valid in GTA welding at high welding speeds, while the lower limit corresponds to the practical conditions which exist in ingot and shaped casting. The validity and applicability of this solidification model are discussed.

Heating and bonding mechanisms in ultrasonic welding of thermoplastics

Abstract: An experimental study of the heating and bonding mechanisms in ultrasonic welding is described. Polystyrene specimens were joined under a variety of welding conditions while the temperatures at the interface and within the interior of these specimens were measured. The power input, amplitude of vibrations, and amount of deformation during welding were measured concurrently. In general, the rate of heating at the interface is greatest at the beginning of the weld cycle, but slows markedly after the interface temperature reaches approximately 250°C. The interface temperature peaks well before the weld is completed. Temperatures within the body increase most rapidly at temperatures near the glass transition temperature. Welded specimens were broken on a special testing apparatus under combined torsional and compressional loads to determine the weld strength. The results show that weld strength is dependent on the amount of energy input and the degree to which material flows out of the interface region. Possible mechanisms for heating and bonding during ultrasonic welding are discussed in light of the observed behavior.

Arc welding method

Abstract: An arc-welding method, which comprises: arc-welding objects of welding together along the line of a groove formed between said objects of welding by continuously moving a welding electrode along the line of said groove while reciprocating said welding electrode in the width direction of said groove; characterized by: calculating at prescribed time intervals, for each one reciprocation of said welding electrode in the width direction of said groove, deviations (l-lo) of values (I) of one of arc current and arc voltage from a previously set reference value (lo), for each of left-side deviations (L) and right-side deviations (R) relative to the vertical plane which passes through the center of amplitude of said one reciprocation of said welding electrode and is parallel to the line of said groove; calculating at said time intervals, when said welding electrode moves over the left side of said groove relative to said vertical plane, differences (L-R) between said left-side deviations (L) and the immediately preceding right-side deviations (R), to controllably aligning the center of said amplitude of said one reciprocation of said welding electrode with the center of said groove In the width direction thereof at said prescribed time intervals so that said differences (L-R) become null; and, calculating at said prescribed time intervals, when said welding electrode moves over the right saide of said groove relative to said vertical plane, differences (L-R) between said right-side deviations (R) and the immediately preceding left-side deviations (L), to controllably aligning the center of said amplitude of said one reciprocation of said welding electrode with the center of said groove in the width direction thereof at said prescribed time intervals so that said differences (L-R) become null.

Some aspects of the fluid dynamics of laser welding

Abstract: When a laser beam is used as the energy source for welding two pieces of metal together, a hole is formed perpendicular to the plane of the workpiece. The latter is moved relative to the laser and metal is transferred from the front to the rear by fluid flow round the hole. The equations governing the process are set out and the conditions at the two boundaries in the problem (one between the hole and the molten metal, and the other between the liquid and the solid states of the metal) are considered.Approximate solutions of the problem for low welding speeds are obtained for four different models. The first is one in which the viscosity is taken to be constant. In the second, the viscosity is allowed to depend linearly on temperature. The third model divides the liquid into a region in which the cooler part is taken to be viscous and the hotter part inviscid; the fourth model is then constructed as a limit, with the liquid motion considered as wholly inviscid. It is found that the motion is not irrotational in this last model. The models all display a downstream displacement of the boundary between the solid and liquid states, in agreement with observations. An expression for the minimum power of the laser is calculated.

Robotic Arc Welding: Research in Sensory Feedback Control

Abstract: Robotic arc welding and its dependence on sensory feed-back control for successful application is discussed. Problems unique to arc weld sensing are identified and sensor requirements are categorized as a function of welding design requirements, joint imperfections, weld shape deviations, and process characteristics. The two most prevalent approaches of weld sensing, i.e., optical and through-the arc sensing, are covered.

Microprocessor controlled welding apparatus

Abstract: A microprocessor-controlled are welding power supply is disclosed. A silicon controlled rectifier ("SCR") bank is used to generate a direct current arc welding current under program control. Positive synchronization is provided by the microprocessor using a phase locked loop and a polarity detector, so that the gating signals applied to the SCRs are correctly timed. Optimum tradeoffs between hardware and software are accomplished by using look up tables to store correction factors that can be quickly accessed during execution, and by using timers as smart interface chips to fire the SCRs at the same angle during each cycle until changed or updated by the microprocessor. The arc welding power supply is capable of operating in a constant current or constant voltage mode without rewiring the circuit.

Infrared thermography for sensing the arc welding process

Abstract: This paper was presented at the Annual AWS Convention, Philadelphia, Pa., Apr. 1983. The Authors present experimental results that could aid in the development of a closed-loop feedback system capable of correcting for perturbations that arise during automatic arc-welding. Specific weld faults were intentionally introduced into an arc-welding process, and the resulting surface isotherms were observed with a scanning infra-red camera for both stationary and moving arcs, Each fault produced a recognisably different distribution of the surface temperature. The results are presented and discussed in some detail, and it is concluded that infra-red thermography appears to be a suitable sensor for incorporation into a closed-loop feedback system for continuous process and quality controlled welding.

Wear-resistant stainless steel

Abstract: A high chromium stainless steel especially suited for use as wear (galling) resisting components, for example, valve parts. A typical alloy generally contains chromium, nickel, silicon, carbon, an effective cobalt content and the balance iron plus normal impurities. The alloy may be produced in the form of castings, P/M products, hardfacing and welding materials and wrought mill products.

Welding method combining laser welding and MIG welding

Abstract: Welding of deep penetration is obtained in a sustrate by a method which comprises first melting the joint portion of the substrates by MIG welding and then focusing a laser beam in the bottom surface of a crater formed in consequence of the MIG welding thereby effecting laser welding of the crater.

Determination of necessary preheating temperature in steel welding

Abstract: This paper was presented at the AWS Annual Meeting, Kansas City, Apr. 1982. The Authors describe an investigation in which an examination was made of various tests that are used to determine the critical preheating temperatures for avoiding cold cracking when welding conventional and newly-developed steels, with carbon contents between 0.02% and 0.26%. An important finding is a proposed new carbon equivalent for use in assessing the cold-cracking susceptibility of the steel; it results in a more satisfactory assessment than either the IIW carbon equivalent or the Ito carbon equivalent .

Laser machining system.

Abstract: A laser machining system with x, y and z-axis beam manipulating mechanisms to perform welding, cutting and localized heat treating operations on a workpiece with the operation of the system for each operation and the changeover between operations being under the control of an automatic control system. A computer numerical control (CNC) system provides control of the laser functions and movement of the laser beam using a sampled-data following error servo system.

Light pattern projector especially for welding

Abstract: Structured light patterns are introduced into the arc vicinity within the field of view of the integral optical sensor on a gas tungsten arc welding torch. Processing the image yields data needed to guide the torch and control and assess the weld process. The optical welding torch has a projector system with a remote light source and flexible fiber optic bundle over which the light pattern passes to an exit projection and relay assembly mounted on the torch. A programmable laser pattern projector, useful for other applications, has a beam deflection device that traces a two-dimensional pattern on the entrance of a coherent fiber optic bundle; no moving parts or electrical connections are needed at the terminal end. An optional modulator changes the pattern intensity spatially or temporally.

The stress intensity factor for a crack perpendicular to the welding bead

Abstract: An analysis of the stress intensity factor due to the residual stress is made for a crack perpendicular to the welding joint in a large plate. The residual stress distribution is represented by a simple function which is chosen to satisfy the physical requirements for the residual stress and to simulate the commonly observed distribution. The stress intensity factor is obtained using customary method based on the superposition principle. The function chosen for the residual stress distribution leads to an exact expression of the stress intensity factor in a simple closed form. The solution yields somewhat conservative values of the stress intensity factor for large cracks and it may be conveniently used for practical applications.

Three-dimensional heat flow and solidification during the autogenous GTA welding of aluminum plates

Abstract: A theoretical and experimental study of heat flow and solidification during the autogenous GTA welding of aluminum plates was carried out. The theoretical part of the study involves the development of a computer model which describes three-dimensional heat flow during welding. The model, though valid for any plate thickness, is particularly useful for moderately thick plates since both full- and partial-penetration welds can be considered. The experimental part of the study, on the other hand, involves the measurement of the thermal response of the workpiece during welding, and the examination of the configuration, grain structure, and subgrain structure of the fusion zone. The experimental results were compared with the calculated ones and the agreement was very good. With the help of the computer model, the effects of welding parameters on weld penetration in moderately thick plates were discussed. These parameters are the heat input per unit length of the weld, the thickness of the workpiece, the preheating of the workpiece, and the power-density distribution of the heat source.

Method and apparatus for manipulator welding apparatus with improved weld path definition

Abstract: Control apparatus for manipulator welding apparatus is provided that includes a vision correction system for workpiece sensing. During an initial teach mode, the manipulator is taught the desired welding path on a workpiece and data is recorded representing the welding path relative to a frame of reference defined by the workpiece. In addition to the data representing the taught welding path and the frame of reference, data representing one or more reference images or templates are also recorded in the teach mode. As successive workpieces are presented to the manipulator for performing the desired welding path, the control apparatus in a repeat work cycle mode is first controlled to measure and define the new location and orientation of the frame of reference in accordance with the workpiece. The new frame of reference data is utilized to modify the path data. In a preferred arrangement, a first repeat pass is performed by controlling the manipulator to move over the weld path in accordance with modified weld path data as determined from the new frame of reference data. The vision system utilizing an image processor detects the deviation between the first repeat pass welding path and the actual welding path of the workpiece. The control apparatus in response to the deviation data provided by the image processor in the first repeat pass modifies the first repeat pass weld path data to provide corrected welding path data for the welding of the actual workpiece during a second repeat pass with the weld being initiated at a predetermined point relative to the frame of reference.

Foil welding device

Abstract: The foil welding device for welding thermoplastic foil bags in its upright position enables the hanging of the bags onto the suction nozzle whereat the bag can be filled with food and thereafter air can be sucked therefrom and it can be welded, while in lying position the device is provided for welding bags from which air need not be sucked.

Gas metal arc welding method

Abstract: A gas-metal-arc welding method is provided for high speed, high melting rate, substantially spatter-free, all-position welding. The method is particularly useful for out-of-position welding, that is, to produce vertical, inclined and overhead welds. A consumable wire electrode is held within and fed through the tubular contact tip of a continuous feed type welding gun having a tubular nozzle surrounding and extending beyond the tip. A shielding gas, formed of unique ratios of a minor proportion of a carbon dioxide and oxygen mixture combined with a major proportion of an argon and helium mixture, is flowed in a substantially longitudinally laminar pattern between the nozzle and contact tip and along the electrode extension from the tip. The contact tip is cooled, and sufficiently high power electrical current is passed through the contact tip and electrode extension to produce the arc and to melt the end of the electrode into molten drops for short-circuiting (e.g., low current) or for spray (e.g., higher current) transfer of the drops to the weld deposit. The electrode extension is pre-heated by maintaining a long electrode extension or stick-out beyond the contact tip end, with a substantial portion of the extension recessed within the nozzle.

Mechanics of Explosive Welding

Abstract: The explosive welding process is one of the most useful and widely employed applications of the high energy rate methods to the fabrication of materials. Its major advantage lies in that it does not suffer from the limitations imposed on other welding processes by their specific characteristics. For example, in fusion welding melting of the two metals to be welded is essential at the interface, and in pressure welding large plastic deformation is required. Both processes are therefore limited to metals which have comparable melting points and plastic flow stresses respectively. Practical problems are also encountered in the case of metals and alloys with high melting points (e.g. tungsten) or with high mechanical strengths. Neither melting nor excessive plastic flow are essential for explosive welding to succeed though they may be observed under certain conditions, and hence no serious limitation is imposed by large differences in the corresponding metal properties. The use of explosives imposes nevertheless a limitation from the view point of safety regulations (see Chapter 5).

Adaptive welder with laser tv-scanner

Abstract: The invention pertains to a welding system having automatic groove tracking and adaptive groove filling capabilities. Data produced by a coordinated laser spot projector (10) and TV-scanner (12) combination is determined to an Intel 8085 computer (28) to provide a substantially continuous analysis of groove locations in a three-axis coordinate system as well as groove depth and area. Location information is fed to an LSI-11 computer (38) to control the tracking function through coordinate axis servo-type drives (46) and to control a fourth-axis or "swing" function which provides freedom between the welding torch (14) and the optical system (10, 12) which leads the torch by several inches. The groove depth and area information is also fed to the LSI-11 to control the welding parameters, i.e.; deposition rate and voltage and produce the desired weld along the groove.

A method of joining prefabricated heat insulated pipes and a welding fitting therefor

Abstract: For mounting a protective sleeve (14) of plastic over a joint between prefabricated heat insulated pipes (2, 4), typically subterranean district heating pipes, an axially split plastic sleeve (16) is inserted laterally over the joint so as to bridge the opposed ends of outer protective plastic tubes (10) of the joined pipes. A plastic welding strip (20) as provided with a number of embedded parallel heating wires (34) is placed along and over the relevant annular joint (46) with its opposed ends located spaced from each other adjacent the axial split (18) of the sleeve. The ends of the strip (20) are provided with terminals (22) for parallel connection of the embedded wires, and the wires are electrically heated to weld together the welding strip and the two plastic tube ends. The axial split (18) is then sealed by means of a similar welding strip (54).

Fibrogenic potential of welding fumes.

Abstract: A search of 3600 indexed pathology cases has disclosed pulmonary fibrosis in 29 welders. Scanning electron microscopy of biopsy material revealed macrophages laden with inorganic particulates which have characteristics compatible with welding aerosols. In order to establish a possible relationship between fibrotic reaction and welding-fume exposure, the fibrogenic potential fo some 11 different welding fumes and metallic aerosols, considered to be reference standard surrogates for the commonly used welding technologies and applications responsible for 70% of welders exposure, were screened using the Rat Peritoneal Macrophage in vitro bioassay. Only one class of fumes, that from the manual metal arc welding of stainless steel, showed distinct fibrogenic potential. This fume is, however, not common to more than four or five of the heretofore 90 cases of pulmonary fibrosis reported among welders. Thus, although insoluble Cr(VI) is probably the active fibrogen in stainless steel fumes, an etiological factor common to all fibrogenic welding exposures must be sought. It is tentatively proposed to be NO2, a potential experimental in vivo fibrogen copiously produced by certain welding processes and ubiquitous at low concentrations in the welding environment.

Power dissipation in the column of a TIG welding arc

Abstract: The characteristics and structure of power dissipation in Tungsten Inert Gas (TIG) welding arcs is investigated for argon atmospheres at pressures of up to 135 bar. Electrical characteristics are reported and probe measurements of local electric field strength and total radiated power have been made. These have been combined to obtain the radially averaged axial dependence of arc properties (e.g. temperature, mass flow rate, plasma velocity and arc radius). It is found that both anode and cathode fall voltages are substantially independent of pressure P while the column electric field strength increases in accordance with P0.5. This is associated with an increase in convective and radiative dissipation from the column such that temperature is little affected by pressure and plasma flow velocity falls. The total energy balance of a 100 A, 10 mm argon arc indicates that convective dissipation accounts for about 70% of column power at all pressures investigated. Radiation consists of 18% at 1 bar increasing to 26% at 20 bar with conduction decreasing in significance with pressure.

Progressive ultrasonic welding system

Abstract: A method of progressively ultrasonically welding together workpieces is provided wherein the spot welds effected are initiated as small points and then progressively grow to full size. The method employs an ultrasonic welding apparatus of the type having a welding tip and a complimentary anvil between which the workpieces to be welded may be inserted. The workpieces are first clamped together and the workpieces "presqueezed" to disperse any adhesives which may be used between the workpieces. Initial pressure and energy levels are then introduced to "scrub" the workpieces. Pressure and energy are then synchronously ramped in phase to maximum levels to effect a weld between the workpieces. The welding operation is controlled by control means which permit automatic synchronization of the operation.

Urine chromium as an estimator of air exposure to stainless steel welding fumes

Abstract: Welding stainless steel with covered electrodes, also called manual metal arc welding, generates hexavalent airborne chromium. Chromium concentrations in air and post-shift urine samples, collected the same arbitrarily chosen working day, showed a linear relationship. Since post-shift urine samples reflect chromium concentrations of both current and previous stainless steel welding fume exposure, individual urine measurements are suggested as approximate although not exact estimators of current exposure. This study evaluates the practical importance of such measurements by means of confidence limits and tests of validity.

Hot gas sealing device

Abstract: A device for hot air welding, comprising a nozzle for activation of a sealing area around an opening at the inside of a hollow body. The nozzle has a slot device for directing a flow of air out through the opening for activating the sealing area when the nozzle is in the operative position thereof. Means are arranged for cooling the hollow body externally around the sealing area. There are also provided means for recirculation of the gas.

Automatic system for assembly and welding of motor vehicle bodies

Abstract: An automatic assembly and welding system is provided for carrying out the building of various shaped sheet metal members, particularly motor vehicle bodies. The system comprises a single welding station, horizontal conveyor means for conveying vehicle frames to the welding station, and a pair of endless vertical conveyor mechanisms located on opposite sides of the welding station. The vertical conveyor mechanisms are capable of selectively bringing to a vertically oriented position adjacent the welding station and removing from the welding station various different automotive frames or body members to enable a continuous circulation of the body members along a path established by the vertical conveyor mechanism operating to repeatedly deliver new body members to the welding station.