Showing papers on "Welding published in 1995"

Physical processes in fusion welding

Abstract: In recent years, major advances have taken place in our understanding of welding processes and welded materials Because of the complexity of fusion welding processes, solution of many important contemporary problems in fusion welding requires an interdisciplinary approach Current problems and issues in fusion welding are reviewed Solution of these problems, apart from being a contribution to the advancement of science, is also necessary for science-based tailoring of composition, structure, and properties of the welded materials

Method for welding biological tissue

Abstract: A method for joining or reconstructing biological tissue comprises providing a solid filler material in the form of a preformed sheet, where the sheet comprises collagen, gelatin or a mixture thereof. The filler material is placed over tissue. Radiofrequency energy or optical energy is thereafter applied to the filler material in an amount sufficient to melt or denature the filler material.

Apparatus and method for computerized interactive control, measurement and documentation of arc welding

Abstract: An apparatus and method for computerized interactive control, measurement and documentation of are welding utilizing a single power source that facilitates continuous precision welding Operational interactivity between the welding operations and the workpiece operations, in connection with predetermined optimum welding operational parameters, provides contemporaneous feedback of critical welding operational parameters to the welding operator, producing an alarm if welding is attempted outside a first predetermined range of deviation from optimum welding operational parameters and temporarily interrupting power to the welding operation if welding is attempted outside of a second predetermined range of deviation from the optimum welding operation parameters A complete log of the welding operational parameters is stored for subsequent retrieval and display, providing training and evaluation of welding operators as well as verification of compliance with required welding practices and procedures Methods of performing continuous precision welding, facilitating temperbead welding, training and qualifying welders for such operations and verifying practice and procedure compliance are available utilizing the above-described apparatus

Welding/sealing glass-enclosed space in a vacuum

Abstract: A method of welding and sealing the edges of two juxtaposed glass sheets (12, 14) together to seal a vacuum space between the sheets comprises the steps of positioning a radiation absorbant material (110), such as FeO, VO2, or NiO, between the radiation transmissive glass sheets adjacent the edges and then irradiating the absorbant material, preferably with a laser beam, through at least one of the glass sheets (12, 14). Heat produced by the absorbed radiation in the absorbant material melts glass in the portions of both glass sheets (12, 14) that are adjacent the absorbant material, and the melted glass from both sheets flows together to create the weld (216) when the melted glass cools and hardens. The absorbant material can be dissolved and diffused into the melted glass to the extent that it no longer absorbs enough energy to keep the glass melted, thus, with appropriate proportioning of absorbant material to source energy power and welding heat needed, the process can be made self-stopping.

Sensing and Control of Weld Pool Geometry for Automated GTA Welding

Abstract: Weld pool geometry is a crucial factor in determining welding quality, especially in the case of sheet welding. Its feedback control should be a fundamental requirement for automated welding. However, the real-time precise measurement of pool geometry is a difficult procedure. It has been shown that vision sensing is a promising approach for monitoring the weld pool geometry. Quality images that can be processed in real-time to detect the pool geometry are acquired by using a high shutter speed camera assisted with nitrogen laser as an illumination source. However, during practical welding, impurities or oxides existing on the pool surface complicate image processing. The image features are analyzed and utilized for effectively processing the image. It is shown that the proposed algorithm can always detect the pool boundary with sufficient accuracy in less than 100 ms. Based on this measuring technique, a robust adaptive system has been developed to control the pool area. Experiments show that the proposed control system can overcome the influence caused by various disturbances.

Method of high speed high power welding

Abstract: A method of welding using a high energy density radiation beam such as an electron beam or preferably a laser beam to weld a pair of sheets using an oblong focused beam spot for reducing the power density of the oblong beam spot to maximize welding speed while minimizing welding defects. The high energy density radiation beam source has a power of at least one kilowatt for achieving Keyhole welding, and a beam delivery system capable of focusing the beam into an oblong spot shape, such as a generally rectangular focused beam spot shape, and directing the beam spot onto at least one of the sheets to weld the sheets. During welding, the beam is focused into an oblong focused beam spot and trained on at least one of the sheets to weld them with the longitudinal axis of the beam spot preferably oriented generally tangent to the weld line, generally parallel to the weld direction, or acutely angled relative to the tangent to the welding direction. Preferably, if a laser is used, it is a laser emitting a continuous wave beam, a pulsed laser operating at a duty cycle of at least 50% such that it substantially performs as a laser emitting a continuous wave beam, or a laser in rippled or modulated mode having a continuous beam component with an average output power of at least 80% of the peak power of the laser so that it substantially performs as a continuous wave laser beam.

The effect of plasma formation on beam focusing in deep penetration welding with CO2 lasers

Abstract: This paper deals with the absorption and defocusing of a CO2 laser beam by the laser-induced plasma plume in deep penetration welding. To derive the `effective` intensity distribution in the focal plane theoretically, the laser beam propagation through the plasma plume is calculated by solving the paraxial wave equation with a finite-difference scheme. Corresponding to experimental results, documented in the literature, the properties of the plasma plume (spatial temperature distribution and shielding gas content) are pre-set within the calculation. Parametric studies demonstrate that the intensity at the focus is reduced due to the defocusing effect of the plasma plume, mainly, and only to a minor extent due to absorption within the plume. Because of refraction within the plume, the intensity distribution in the focal plane is dependent on the plasma`s size, position and temperature. On studying the dependency of the optical properties on plasma temperature and shielding gas composition, it is found that, by applying a shielding gas mixture of He and Ar in the ratio 3:1, the variation of the focal diameter with plasma temperature can be significantly reduced. This shielding gas mixture, therefore, is recommended for enhancing process stability when welding with high-power CO2 lasers.

Laser weld quality monitoring system

Abstract: A method is provided for monitoring of the progression and the quality of laser material processing. Sensors and detectors are placed in the vicinity of reaction area to capture the signatures of material processing. The signals include light, temperature, sound, gas, smoke, vapor, particles, etc. emanating from the reaction area. The intensity and the timing of certain signals indicate the stages of the processing and the processing quality. One example of this invention is the use of photodiode sensors to monitor the progression of laser spot welding of a certain electronic component. Three photodiode sensors are used to monitor the laser pulse, the reflected beam, and the transmitted beam. A computer analyzes these signals in real time to determine the progressive stages of the laser welding process and the expected weld quality.

Endoprosthesis having multiple laser welded junctions method and procedure

Abstract: An endoprosthesis is provided which presents an endoprosthesis body of a helically wound strand of generally malleable material exhibiting a repeating pattern of undulations that follow a generally helically wrapped axis. Adjacent full circle windings each have at least one weld joining together apex-like portions of adjacent full circle windings. In a preferred arrangement, a plurality of these welds define a substantially in-line helical pattern of welds along the endoprosthesis or stent. One, two, three or more of these substantially in-line helical patterns of welds can be provided. Also provided is a method for forming the endoprosthesis which includes fusion welding, typically within an inert gas atmosphere and in a manner such that the entirety of the stent lies along the same generally cylindrical three-dimensional plane. A procedure is included whereby the endoprosthesis or stent is implanted by deployment with a suitable expansion device, the deployment expanding the pattern of undulations in a uniform manner to provide an especially consistent support surface throughout the endoprosthesis.

Method for processing workpieces by ultrasonic energy

Abstract: A method of welding two thermoplastic workpieces (W) together along a predetermined weld line during a weld cycle utilizing a high frequency vibration sonic or ultrasonic welding apparatus. This welding apparatus includes an electroacoustic transducer (18) which transmits such vibrations to a horn (19) which is dimensioned to be resonant with the horn being brought into forced engagement with at least one of the workpieces to be welded. The method comprising the steps of bringing the workpieces into bearing relation against one another along the weld line. Then the electroacoustic transducer is energized so as to resonate the horn with a desired motional amplitude. Forceful contact is established between the horn and one of the workpieces. Then, the forceful contact between the horn and the one workpiece is maintained throughout the weld cycle. The motional amplitude of the horn is varied in accordance with a desired motional amplitude profile.

A robust method for vision-based seam tracking in robotic arc welding

Abstract: This paper presents a robotic seam tracking system which is aimed at achieving robustness against some welding noises such as arc glares, welding spatters, fumes etc. In particularly, a syntactic analysis is used to improve the extraction reliability of the joint features. The joint features thus obtained are used to extract the 3-dimensional information of the weld joint and then achieve the robot path correction. To show the performance of the developed system, a series of experiments on joint feature detection and robotic seam tracking are conducted for different types of weld joints. The results exhibit that the system is very robust to various welding noises as well as variations in appearance of weld joint and workpiece.

Melt pool dynamics during laser welding

Abstract: The dynamics of the melt pool and keyhole was investigated during CO2 laser welding using high-speed video photography and the laser reflectometer technique. A low-power argon laser beam, focused on the weld pool, provided illumination to obtain a direct image of the weld pool surface. The near-surface plasma emission background was decreased by using a narrow-bandwidth interference filter centred at the argon laser wavelength (514 nm). A variation in the shape of the keyhole opening with a characteristic frequency higher than 1 kHz was observed both during spot welding and during welding with a moving beam. For the case of spot welding with a 20 ms laser pulse, long-wavelength (about 1 mm) oscillations of the weld pool were observed with a frequency during the laser pulse and the first 5 ms after the laser pulse in the range 200-500 Hz. In the time interval starting at 25 ms and ending at approximately 40 ms from the beginning of the laser pulse, the long-wave oscillation frequency increased up to 1.3 kHz. The solidification time was determined to be approximately equal to the pulse duration for the spot welding. Surface deformation during cooling was also observed. This information is used to develop a model illustrating the dynamics of the post-pulse weld pool.

Method and apparatus for controlling and simultaneously displaying arc welding process parameters

Abstract: A system (and method) of controlling and simultaneously displaying arc welding torch parameters includes a power supply for supplying weld voltage and current to the torch in accordance with demand signals from a computer. The computer also supplies a demand motor speed to a motor for controlling the travel speed of the torch electrode relative to a workpiece or the fed rate of a filler wire to the weld area. The actual values of the weld voltage/current and the motor speed are fed back to the computer and displayed on a video color display in separate colors and in real time to enable on operator to readily correlate the actual with the demand parameter values. The position of the electrode relative to the workpiece is also fed back to the computer for presentation on the video display. In addition, deviations of the individual actual parameter values from acceptable tolerance limits are highlighted on the display.

Determination of near surface residual stresses on welded joints using ultrasonic methods

Abstract: Ultrasonic velocity measurements are used to determine residual stresses induced by welding processes. A welded stainless steel pipe and aluminium alloy plate are analysed in their near surface residual stress distribution by using subsurface longitudinal waves and Rayleigh waves. The experimental procedure is presented: measurement of time of flight, calibration of the acoustoelastic effect, methods for residual stress measurements. The effects of a slightly orthotropic symmetry on wave velocities are investigated in the case of the aluminium alloy plate, which exhibits a texture due to rolling processes. Special calibration, performed on two test specimens, allows the effect of this texture to be taken into account. The acoustic birefringence technique is also used in the case of the aluminium plate to verify the stress distribution in the thickness. The results of surface residual stress distribution are compared with those obtained with an X-ray diffraction technique.

Method for teaching welding torch orientation

Abstract: First, an operator sequentially teaches the start point A, the end point F and junction points B, C, D, E on the welding path by moving the torch head by jog feed without paying attention to the torch orientation. Next, a reference plane to define the orientation of the torch is specified, and an inclination angle and a forward angle representing the torch orientation be inputted into a robot controller. On the basis of these inputted angle data and the taught data, a basic welding orientation is automatically calculated. Further auxiliary points are set around the junction points B through E each forming corner parts connecting straight lines; tool vectors which may give a smooth torch orientation change through the corner parts are automatically calculated for the auxiliary points and the junction points; and on the basis of the results, a welding program is produced. Among elements which determine the torch orientation, an element relating to the rotation around the torch axis reflects the state at the time of teaching of points A to E.

Method of production of workpieces by welding equipment

Abstract: Starting on the surface of a foundation body (2) weld material is applied in runs to form layers by an equipment for profiling building-up welding and hence a workpiece (1) is manufactured, where the foundation body (2) may be a component of the workpiece (1). The course of runs to form layers as well as the approximate rate of application of weld material are calculated by a computer system (11), starting from a two- or three-dimensional data model of the workpiece (1) in the form of software, and given over to the system control (10) which positions the welding torch (7) by means of the robot (5) and the workpiece (1) located on a turntable (4) by a clamping mechanism (3) with respect to one another, and regulates the rate of application of weld material applied by the welding apparatus (8) in such a way that the liquid weld material adheres to the layer lying underneath without running down and irregularities in the runs to form layers are levelled out. Hence metal workpieces having manifold bodily shapes and theoretically of any size and having any thickness of wall, even consisting of different metallic materials, may be manufactured by profiling building-up welding without auxiliary cores or other devices supporting the liquid weld material.

Semiconductor leadframe and its production method and plastic encapsulated semiconductor device

Abstract: A method of producing a leadframe for use in semiconductor devices, comprises the steps of forming a space between leads 1a and 1b which are to be overlapped and welded each other, and welding the leads at a region including the space and melting and cutting off one of the leads. In one of the leads which is melted, cohesion and separation of molten metal occur in the region around the space. As a result, unnecessary portions such as an outer frame used for positioning can be cut off at the same time when the leads are connected by welding. Thus, high precision positioning of a plurality of element leadframes as well as high assembling productivity are achieved.

Finite element simulation of the inertia welding of two similar parts

Abstract: A complete thermo‐mechanical model for the simulation of the inertia welding process of two similar parts is described. The material behaviour is represented by an incompressible viscoplastic Norton—Hoff law in which the rheological parameters are dependent on temperature. The friction law was determined experimentally and depends on the prescribed pressure and the relative rotating velocity between the two parts. The mechanical problem is solved considering the virtual work principle including inertia terms. The computation of the three components of the velocity field such as radial, longitudinal and rotational velocity, in an axisymmetric approximation allows to take into account the torsional effects. The domain is updated based on a Lagrangian formulation. The non‐linear heat transfer equation with boundary conditions (convection, radiation and friction flux) is solved separately for each time step. Error estimators on mechanical and thermal computation are devised to adapt the mesh in an automatic w...

Recent Development in Controlling the Microstructure and Properties of Low Alloy Steel Weld Metals

Abstract: As advanced steels are developed and used in welded structures, performance of weldments is one of prime issues as well as cost performance of welding. Demands for high-performance steel welds have been increasing in various application areas, not only in shipbuiding and offshore sructures but also in building construction and engineering works. Improvement in low-temperature toughness and stress-corrosion-cracking resistance of welds is critical to recent oil and gas exploitation and gathering in severe environments. Large heat-input welding and higher-strength welds are required with increasing the size of welded structures, while fire-resisting properties of steels and their welds are important for high-rise buildings.The present paper reviews a recent progress of welding technology for low alloy steels in light of the above trend. Effect of alloying elements and microstructures on weld performances are outlined, and significance of controlling alloy and phase chemistries in the welds is discussed in order to meet the increasing demands for improved weld performances.

Modeling of casting, welding and advanced solidification processes, 7

Abstract: The seventh international conference in the series of Modeling of Casting, Welding and Advanced Solidification Processes was held in London, England from 10--15 September, 1995. This conference series, sponsored by the Engineering Foundation, began in 1980 and has charted the progress of research in both the modeling and software technology of the physical processes associated with liquid-solid phase change behavior in metals. The enduring interest in this research area and the continuing development of the associated software technology has witnessed a dramatic leap in the understanding of the physics of casting/welding family of processes and the ability to design products that are fit for purpose and fit for manufacture first time. In order to serve the needs of the community with respect to high quality data for model validation a benchmark experiment was carried out. Data was provided by Professor John Campbell of the University of Birmingham on the filling and subsequent solidification behavior of aluminum in a mould. A number of research groups ran their models without knowledge of the key results. The entries received were, by and large, of good quality. Topics included fluid flow and heat transfer in casting and welding, magnetohydrodynamics and integrated modeling, thermomechanical stressmore » in casting and welding, novel techniques and technologies, structure, and applications. One hundred and nine papers have been processed separately for inclusion on the data base.« less

The prospects for joining titanium aluminides

Abstract: This paper reviews relevant published data and presents some new data on the joining of titanium aluminides. Some of the problems encountered in the development of suitable joining procedures for both α 2 and γ titanium aluminides are described, together with current progress in resolving these problems. The difficulties highlighted include the lack of data on transformation kinetics (particularly for γ alloys), the potential for hydrogen embrittlement, the low ductility of the material and the lack of suitable welding consumables. However, there is no evidence for any susceptibility to hot cracking. The alloys have been welded successfully by several methods, including fusion processes, such as gastangsten arc (GTA), laser and electron beam welding, and solid state processes, such as friction welding and diffusion bonding. However, there is little information on the mechanical properties of the welds, in particular at high temperatures. The importance of thorough metallographic studies of welded joints is emphasized, as this is considered to be a vital step in understanding the complex relationships between the welding procedure, microstructure and mechanical properties. Such an understanding is an essential prerequisite to the development of optimized joining procedures.

Technique for welding dissimilar metals

Abstract: For an implantable medical devices, a system is provided for welding electrically conductive ribbon, typically stainless steel, to electrically conductive wire, typically platinum, the melting point of steel being substantially lower than that of platinum. An aperture is formed in the ribbon having an opening smaller than that of the wire. The ribbon is engaged with the wire such that the aperture is generally coextensive with the wire. Thereupon, a pulse laser beam is directed transversely of the ribbon through the aperture and onto the wire to simultaneously melt the wire and the ribbon and to create a homogeneous mix of the molten steel and platinum in the region surrounding the aperture. Thereafter, operation of the laser beam is discontinued to allow solidification and thereby achieve a welded connection between the ribbon and the wire.

The galling wear resistance of new iron-base hardfacing alloys: a comparison with established cobalt- and nickel-base alloys

Abstract: Iron-base wear-resistant alloys, designated NOREM™, were developed to address concerns unique to the nuclear power industry. Laboratory evaluations of the galling wear resistance of candidate NOREM compositions and other iron- and nickel-base alloys were performed using a pin-on-plate specimen geometry, and these results were compared with those obtained from the long-established cobalt-base Stellite™ alloys. The hardfacing alloy was typically deposited as powder using gas tungsten arc welding or as wire using automatic gas tungsten are welding. Attempts were made to correlate the results from the galling wear tests to factors such as alloy compositions, microstructure and deposited hardness. The galling wear resistance of NOREM and other iron-base alloys matched or exceeded that of the cobalt-base standard, but the factors responsible for good resistance to galling wear could not be identified. Nickel-base alloys typically showed much higher values of surface damage in these tests.

Method and apparatus for vision control of welding robots

Abstract: A vision system for controlling welding robots and a method of controlling a welding robot using a vision system are disclosed. The vision system includes an ordinary unoriented light source, such as a fluorescent light source, to illuminate a part to be welded so that a light intensity gradient is created along a seam to be welded. An image of the light intensity gradient is captured by one or more fixed solid-state video cameras. The image is compared with a stored image of a reference part so that a deviation of the seam to be welded with respect to the seam of the reference part can be computed for each of a plurality of predefined reference points. The deviation at each reference point is translated by a microprocessor into a coordinate adjustment which is downloaded to a controller for the robot. The controller converts the learned coordinates of the reference part into the actual coordinates of the seam to be welded using the coordinate adjustments provided by the microprocessor, permitting the robot to weld the seam without vision sensing or weld path adjustments during the welding process. The advantage is a cost effective vision system which can be shared among robots, simpler equipment, simpler control software, and increased efficiency because real time weld path correction maneuvers are eliminated.

Computer simulation of resistance spot welding in aluminum: Part 1

Abstract: A computer-based model of resistance spot welding with hemispherical electrode tips has been developed to include simulation of elastic-plastic mechanical deformation as well as ohmic heating and thermal conduction. The primary effect of the mechanical deformation is in its influence on the contact read and current density developed at the faying surface. The model was used to simulate spot welding in aluminum alloys. Preliminary results show the effects of variations in input current, contact resistance, applied force and position of the cooling water with respect to the electrode tip. It is shown that the value of the contact resistance has a large effect on nugget formation in the spot welding of aluminum alloys and that the applied force has a significant effect arising from its effect on the area of contact at the faying surface. The formation of a resistance spot weld in aluminum is also sensitive to the position of the cooling water-electrode interface because of the high thermal conductivity of aluminum alloys.

Automated butt weld inspection system

Abstract: An automated system for non-destructive inspection of a weld through the use of ultrasonic waves produced by an electromagnetic acoustic transducer (EMAT) The system includes: a computer control unit (31); a transport apparatus (32) having a first EMAT (24) for producing an ultrasonic SH shear wave and a second EMAT (26) for receiving an ultrasonic SH shear wave reflected from a butt weld (22); a data acquisition unit (33) and a calibration means (38) The computer control unit, which is in electrical communication with a welding apparatus, the transport apparatus and the data acquisition unit, coordinates the weld test with completion of the weld An edge detection sensor, which is affixed to the transport apparatus is used to automatically position the transport apparatus for a weld scan and to signal completion of the scan The system includes an electrostatic shield to protect the second EMAT from electromagnetic and radio frequency interference Other new and improved electronic features permit certain system components to be remotely located from the transport apparatus and the welding apparatus

The particle size distribution, density, and specific surface area of welding fumes from SMAW and GMAW mild and stainless steel consumables

Abstract: Particle size distributions were measured for fumes from mild steel (MS) and stainless steel (SS); shielded metal arc welding (SMAW)and gas metal arc welding (GMAW) consumables. Up to six samples of each type of fume were collected in a test chamber using a micro-orifice uniform deposit (cascade) impactor. Bulk samples were collected for bulk fume density and specific surface area analysis. Additional impactor samples were collected using polycarbonate substrates and analyzed for elemental content. The parameters of the underlying mass distributions were estimated using a nonlinear least squares analysis method that fits a smooth curve to the mass fraction distribution histograms of all samples for each type of fume. The mass distributions for all four consumables were unimodal and well described by a lognormal distribution; with the exception of the GMAW-MS and GMAW-SS comparison, they were statistically different. The estimated mass distribution geometric means for the SMAW-MS and SMAW-SS consumables we...