Showing papers on "Spot welding published in 1995"

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.

An offset finite element model and its applications in predicting sheet metal assembly variation

Abstract: Dimensional variation in sheet metal assembly affects product fit and functionality. To predict the variation of assembled products, variation simulation analysis has been gradually adopted in the early design stage. However, variation simulation based on rigid body assumptions usually results in over estimation of the assembly variation. In this paper, we propose an offset beam element model for predicting the assembly variation of deformable sheet metal parts joined by resistance spot welding. The purpose of using the offset beam element is to include the shear effect provided by resistance spot weld nuggets that cannot be captured by the conventional beam element. The offset element is then applied to predict sheet metal assembly variation for one-dimensional (1D) models extracted from industrial practice. The first example evaluates the effects of sheet metal thicknesses on assembly variation. The second example shows how the assembly sequence affects assembly variation. These models provide interesting insights into the mechanisms of variation stackup and will lead to the understanding of more complex sheet metal assemblies.

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.

Determining the constitutive properties of the heat-affected zone in a resistance spot weld

Abstract: A methodology is described for determining the mechanical properties of the heat-affected zone (HAZ) in a resistance spot weld. To perform detailed finite-element analyses of spot weld overload failures, it is necessary to have the mechanical properties of the various HAZ subzones. To this end, simulated HAZ material samples were fabricated in a process that utilized a resistance spot welding machine fitted with specially modified electrodes. Tensile tests at several loading rates were performed on miniature notched-bar specimens machined from the simulated HAZ material. These tests provided the empirical data from which the strain hardening capacities and strain rate sensitivities of the weld HAZ were determined through detailed finite-element analyses of the notched-bar tensile tests.

The role of failure mode, resistance spot weld and adhesive on the fatigue behavior of weld-bonded aluminium

Abstract: Fatigue behavior of the weld-bonded (combination of welding and adhesive bonding) aluminium joint was investigated as part of a study attempting to replace steel with aluminium in the lightweight vehicle structure. Aluminium 5754-H40 alloy and bis-phenol-A epoxy adhesive were used in specimen fabrication. Test results showed that weld-bonded aluminium has a slightly lower fatigue resistance than the adhesive-bonded aluminium (i.e., the presence of the resistance spot weld decreases the fatigue strength by 11% at 3 × 10 6 cycles) but a much higher fatigue resistance than the aluminium of weld-bonded aluminium occurred by either «nugget-through» where failure originated from the weld nugget, or «adherent-tearing» where failure started from the edge of adherend overlap. Statistical analyses of the test results of weld-bonded aluminium indicated that fatigue strength is not significantly affected by the failure modes

An intelligent control system for resistance spot welding using a neural network and fuzzy logic

Abstract: An intelligent control system based on fuzzy logic able to compensate for variations and errors during automatic resistance spot welding (RSW) and produce consistent sound welds was developed. A fuzzy logic control (FLC) scheme was employed to overcome the lack of a precise mathematical model of the process. Electrode displacement, indicative of weld nugget growth, was used as the feedback signal to create appropriate actions to adjust power delivered to welds in real time. Control action is generated from a rule-based system constructed from experimental data for welds made under a wide variety of conditions. A neural network (NN) was constructed to provide process input-output relationships and tune the fuzzy rules off line. The FLC system was evaluated using the NN to describe electrode displacement as a function of percentage maximum heat input and welding time. Results showed the suitability of applying this control scheme to deal with the uncertainties of RSW in a typical automated production environment.

Recent developments of ultrasonic welding

Abstract: New ultrasonic welding methods of metal and plastic materials have been proposed by the author and their effectiveness shown. For welding of thick and large metal specimens: (1) ultrasonic butt welding methods joining thick metal specimens end to end are proposed. Large capacity vibration sources and solid state power amplifiers of 50, 100 kW were developed; (2) a welding method using two vibration systems crossed at a right angle is effective, and 10 mm thick aluminum plates were joined successfully. For medium size metal welding specimens; (3) complex vibration welding tips were shown to be very effective, and one-dimensional complex vibration systems are developed to simplify the systems. For welding of small metal specimens; (4) higher vibration frequency and a complex vibration wire bonding system are proposed, and it is shown that they are significantly effective. The bonding systems of 60 to 780 kHz were designed and the required vibration amplitude and velocity obtained for thin aluminum wire using the 40 to 780 kHz bonding systems. For welding of plastic materials; (5) high frequency, complex vibration and two-vibration-system welding methods are effective.

Static and dynamic characteristics of spot welded sheet metal beams

Abstract: Although widely employed as structural components in the auto industry, spot welded sheet metal beams manifest static and dynamic behavior that is not well characterized. For the present study, sample beams of three representative cross-sections-hat, box and box with partition-were fabricated of sheet steel. The spacing between the spot welds that hold these sections together was varied from 25.4 mm (1 in.) to 203.2 mm (8 in.) using a 25.4 mm (1 in.) increment. The beams were subjected to static bending and static torsion tests, and bending and torsional stiffnesses were determined as functions of spot weld spacing. The beams were then vibrated, and significant lower natural frequencies were determined as functions of spot weld spacing. Mode shapes were also observed for these frequencies. Pains were taken throughout the testing to ensure that the results obtained were of good statistical quality. Work was also done to distinguish the effect on results of beam length and end conditions from that of spot weld spacing. As part of the study finite element models of the beams were constructed. The results of finite element analysis (FEA) and experiment are compared and insights are offered concerning the appropriate modeling of such structures.

Flexible jumper and method of making

Abstract: A flexible laminated jumper is formed from a stack of half hard tempered copper sheets. Contact plates are clamped to opposite sides of one end of the stack, such plates being provided with short stress relief sections away from the end of the stack. The clamped end is positioned properly in a press welder so that the fiat portion of the contact plates are gripped by graphite electrodes of a press welder. The gripped end of the stack is then press welded while the balance of the stack is cooled so that the heat from the press welding does not affect the temper of the sheets of the stack. This is preferably done by immersion in chilled water with the water level being in close proximity to the electrode. After the press welding, the entire stack is cooled and the still tempered stack is formed to the desired configuration. The application of the contact plates and press welding of the opposite end of the stacks is repeated, again with the balance of the stack isolated from the heat of the press weld to protect the temper. After cooling and final trimming, machining, cleaning and silver plating, the jumper is completed. Such jumpers form, for example, improved spot welding gun shunts which have lower resistance levels which improve the efficiency of the spot welding process and cooler shunt operating temperatures which not only provide longer shunt life, but more consistent quality, since the shunt resistance does not change over time.

Building tomorrow`s automobiles

Abstract: Detroit is awhirl these days with speculation about the next generation of automobile. Pressures are clamping down on the industry to produce cars that are free from emissions, much more fuel efficient, and, through it all, salable. Right now, a great deal of attention is being paid to the body-in-white or that part of the automobile represented by the frame and the body parts. Will it be high-strength steel, aluminum, plastic, composite, or a combination of different materials? Will resistance spot welding and gas metal arc welding still be used? What role will the laser play in all of this activity? Can welding expect severe competition from other joining processes, like adhesive bonding and riveting? The best answers to the above questions are yes, maybe, and no. Whatever happens, it seems the jury is still out. Nevertheless, the verdicts will be critical to the welding industry because the automotive industry is the largest single market for welding. Competitively, welding technology has its hands full. A number of Fortune 500 companies are developing improved adhesives. There is also a quasi-riveting process popular in Europe that is being introduced here in the States. And there is a rivet bonding version of thatmore » process. Also, weld bonding or the technique of making resistance spot welds through adhesives is gaining ground among the designers of the next generation of automobile. Over the years, the number one market for arc welding and resistance welding has been the automotive industry. Changes in the designs of automobiles have required adjustments on the part of welding technologies, but there has not been anything unusual in that respect. For the most part, the requirements have been met.« less

Method for weld repairing of structures in nuclear reactors

Abstract: Disclosed is a highly reliable weld repairing method to repair a crack defect in structures and apparatus inside pressure vessels of nuclear reactors, while preventing generation of new crack defects in the structures and apparatus during the repairing. These structures and apparatus are made of any of stainless steel and Ni-base alloys, and are irradiated with high energy corpuscular ray during operating period of the reactor. The repairing method includes the steps of eliminating a region of the structure or the apparatus including a portion having the crack defect, and executing spot welding at a surface of the region continuously or interruptedly in a manner so as to form a first welded layer in a manner that each of the spot welded spots is half-overlapped with adjacent welded spots. Additionally, welding for forming at least a second layer, on the first welded layer, so that the at least a second layer is not deeper than a weld penetration thickness of the first welded layer can be performed.

A prototype fuzzy resistance spot welding system

Abstract: In assembly automation, the need to perform on-line quality monitoring and to provide near real-lime inspection of resistance spot welds, has attained unsurpassed importance in industries. This paper describes the development of a prototype fuzzy control system for a two-stage resistance spot welding machine with potential of being incorporated into an automation line. It encompasses a new approach aimed at providing simultaneous control of more than two major welding parameters for achieving consistent quality spot welds by assessing the condition of the heat affected zone created. The prototype system, developed in C language, comes with a decision making mechanism and a quick search mechanism. Its rule-base contains a total of 125 heuristic control rules derived from literature reviews and interviews with experts and through experiments. The various factors affecting the quality of spot welds are outlined in the paper. The correlation between spot weld quality and welding parameters were examined using...

Automatic assembling system of galvanized steel sheet by spot welding

Abstract: A method and apparatus for continuously spot-welding galvanized steel sheets overlapped to be bonded by way of a spot welding machine having a pair of electrodes. The galvanized steel sheets clamp a resistance increasing material including a spacer to ensure a gap between the sheets. Bonding surfaces of the galvanized steel sheets partly contact each other when the pair of electrodes pressurize the galvanized steel sheets such that a part of the gap is retained around the spacer between the bonding surfaces. The retained gap has a size in which zinc melted or vapored when a weld current flows between the electrodes can escape through a weld section of the galvanized steel sheets to outside. The method comprises the step of recording an inter-electrode resistance for each spot when the continuous spot welding is executed by the pair of electrodes. The method estimates an electrode lifetime defined by one of the number of spots and a duration of the spot welding until a sufficient nugget will not be formed by way of the electrodes according to the record of the inter-electrode resistance. The method automatically changes weld conditions to enable the continuous spot welding when the electrode lifetime reaches a predetermined electrode lifetime.

Resistance projection welding system and method for welding a projection weld nut to a workpiece

Abstract: A system and method is disclosed for monitoring and controlling a resistance projection welder for welding a projection weld nut to a workpiece. A displacement sensor measures the displacement of a welding electrode of a weld gun in real time during the welding procedure. A computer is coupled to the displacement sensor and determines whether the projection weld nut is correctly loaded between the workpiece and the welding electrode. The computer instructs a programmable logic controller (PLC) to trigger a weld controller to apply power to the welding electrode if the projection weld nut is correctly loaded onto the workpiece. The computer instructs the PLC to inhibit power if it determines the projection weld nut to be inverted, missing, or misaligned in order to allow for the removal and replacement of the projection weld nut. The computer further instructs the PLC to control and terminate the power to the welding electrode in real time in order to form a projection weld between the projection weld nut and the workpiece that is substantially similar to a predetermined projection weld. The computer processes the displacement data and provides a fault signal when the projection weld is unacceptable. A marker marks the unacceptable workpieces in response to the fault signal.

Cold-welding recovery method for thin wall of cast iron cylinder

Abstract: The repairing process mainly consists of repairing and maintaining the crevice, then taking crevice as kernel to heat partially, two kinds of thin welding rod are selected to accomplish double layer welding with the method of suitable small current and scattered and crossed circling spot welding. The adrantages of said invention are capable of operating in a narrow space, high quality of welded seam, not limited by the length of crevice, capable of making the welded seam have good fatigue resistance and reliability by double layer welding, meanwhile the circling spot welding method can make each welded point feature throughly welded, high strength and small stress, thus the welding quality is ensured.

Supply of welding parts and spot welding system therefor

Abstract: PROBLEM TO BE SOLVED: To shorten a cycle time of a work assembling work by lapping (synchronizing) each operation of work carry-in/carry-out, supplying of a welding parts and welding. SOLUTION: In a supporting device 6 for parts supplied to the welding position between electrodes by holding welding parts at the tip part of a spindle from a supplying position for parts intersected with a reciprocating way of the spindle by advancing the spindle from a driving source 14, to join both parts by supplying the electric power under pressurizing, an electric motor is used as the driving source 14 and the rotating movement of the electric motor is converted into a straight line movement and a stroke and a moving speed of the spindle are made to be changable in stepless. By this system, the movements by each device of a work carrying robot 1, supplying device 6 for the parts and spot welder 4 are lapped and the shortening of the work assembling tact is realized and the supplying miss of the parts can be detected and the detective welding is prevented and the noise of exhaust gas from the driving source caused by the supplying of the parts is eliminated and the maintenance of working environment is established.

Spot welding apparatus and its power supplying method

Abstract: A spot welder apparatus includes: a single welding power source (5); a welding current distributor (7) connected to the single welding power source; and a plurality of spot welders (1A, 1B, 1C) connected to the welding current distributor. Each of a plurality of the spot welders is activated alternately by welding current distributed by the welding current distributor. When two start signals are generated almost simultaneously, a first spot welder which generates the start signal earlier is activated, and a second spot welder which generates the start signal later is kept under pressurized condition. Immediately after the first spot welder is deactivated, the second spot welder is then activated. The spot welder apparatus is low in cost and small in installation space, without increasing the user' current capacity.

Resistance spot weld quality in Al‐Mg alloy sheet

Abstract: The investigation results on the resistance spot weld quality of Al-Mg alloy sheet are summarized as follows;(1) Comparison of continuous spot weldability with mild steel sheet Compared with mild steel, the Al-Mg alloy exhibits degradation and variation of tensile shear strength associated with continuous resistance spot welding, and causes excessively serious wear in electrodes.(2) A study for variation of tensile shear strength in continuous resistance spot welding Variation of tensile shear strength in continuous resistace spot welding is due to nonuniform corona bond formation and nonuniform nugget size and profile.(3) Effects of oxide film and heat condition, (1) The oxide film causes localized wear in electrodes, and in addition, even prevents the formation of corona bond. (2) If the heat input after saturation of nugget growth is regaded as extra heat, it promotes wear in electrodes and causes corona bond formation. (3) Variation of tensile shear strength is improved mainly by removing oxide film. In addition by reducing the heat input, it causes degradation of tensile shear strength and makes the failure mode sparse, the formation of corona bond is suppressed and then tensile shear strength become stable and electrode life is extended.

Electrode drive device of spot welding machine

Abstract: PURPOSE: To provide an electrode drive device of spot welding machine which sufficiently alleviates shock between a moving electrode and work, further shortens cycle time as well. CONSTITUTION: A pressing device of spot welding consists of a fixed electrode 2, moving electrode 3, welding gun 30, pressing controller 71, etc. When the operating switch of pressing controller 70 is switched on, the moving electrode 3 of a welding gun 30 is descended in high speed, subsequently, after high speed descending time TD has elapsed, the moving electrode 3 is descended in decelerated speed and then in low speed. Further, by discriminating a whether grounding detected signal is inputted or not from a grounding detecting device 71, as inputted, the time TR from staring of decelerated descending to inputting of grounding detected signal is temporarily stored. After this spot welding treatment is completed one cycle, based on the time TR temporarily stored, the next high speed descending time TD is obtained. COPYRIGHT: (C)1996,JPO

Method and equipment for spot welding

Abstract: PURPOSE: To improve the precision of the welding by reading the control data corresponding to the applied pressure during the spot welding from the memory to operate a robot. CONSTITUTION: In a 6-axis robot 1, a lower arm 5 is tumable around the first axis J1 and angular-displaceable around the second axis J2 on a base 4 to be fixed to a floor 2. An upper arm 6 is angular-displaceable around the third axis J3 and a wrist 7 are angular-displaceable around the fourth, fifth and sixth axes J 4 , J 5 , J 6 . A gun 8 for the spot welding is mounted on the wrist 7. The control data are stored in the memory so that the position of the tip part may not be changed according to the applied pressure to a work 10 at the tip part of the welding tip of the gun 8. The applied pressure is detected during the spot welding, the data corresponding to the applied pressure are read from the memory, the robot 1 is activated, and the position of the tip part is kept stationary thereby. The service life of the welding tip can be improved thereby. COPYRIGHT: (C)1996,JPO

Process monitoring and control for robotic resistive welding

Abstract: Spot welding is a commonly used process for joining metals. Under nominal operating conditions, existing weld controllers can produce high quality welds. In practice, however, the process can significantly deviate from the nominal condition, and thus compromise the quality of the weld. This paper presents an overview of the main contributing factors to the process variation and suggest methods to detect and ameliorate them.

Method and device for executing gas seal welding of nuclear fuel rod

Abstract: PURPOSE:To realize the high precision of welding by making use of the projection welding to eliminate the slip when an electrode is pressed. CONSTITUTION:An end plug W1 to be welded by a movable side electrode 2 and a fixed side electrode 3 and a coated tube W2 are held in a butted, manner, the end part held in a butted manner is surrounded in an air-tight manner, the air sucked from the surrounded butt end part, the prescribed vacuum condition is held in the coated tube, and gaseous He is filled in the vacuum coated tube, and then, the end plug is pressure welded to the coated tube by giving the pressure and the welding current required for the welding to the butt end part to seal gaseous He in the coated tube. When the slip is generated between the electrode and the work during the pressure welding, the displacement by pressure is detected and the charge-starting work is stopped to preliminarily prevent the defective welding.

Spot welding gun

Abstract: PURPOSE:To provide a spot welding gun capable of shortening the cycle time while maintaining the high pressurizing force at the time of welding and besides, capable of maniaturizing a device CONSTITUTION:The spot welding gun is provided with a cam mechanism part 22 which converts rotational operation provided with a bearing 9 provided on a rod 7 and a cam part 6 on which a cam groove 24 to be inserted and engaged with this bearing is formed into advancing and retreating motion in the axial direction The cam groove 24 of the cam part 6 has a first abutment part 24a in which advancing and retreating movement displacement of the rod 7 for an angle of rotation of the cam part 6 is large and a second abutment part 24b in which advancing and retreating movement displacement of the rod 7 for the angle of rotation of the cam part 6 to abut when a movable welding tip 32 and a fixed welding tip approach each other is small

Method for joining al member and steel member

Abstract: PURPOSE:To provide a joining method which can obtain high strength of a joined joint at the time of joining an Al member and a steel member. CONSTITUTION:At the time of joining an Al member 11 and a steel member 12, resistance spot welding is executed by using a clad material 13 of Al 13a and steel 13f, arranging an alloy or a mixture 14 of Al and Si on the surface of the Al 13a side of the clad material 13, and interposing the clad material 13 in the direction in which each Al and each steel come into contact with each other between the Al member 11 and the steel member 12.

Braided cable having a solidified end portion

Abstract: A flexible current carrying cable is provided having a cable and an end portion of the cable being solidified wherein the end portion is compressed into a unitary member having reduced voids and enabling brazing of the end portion to a current carrying apparatus. A method of forming a current carrying cable has the steps of inserting an end of a cable into a spot welding machine, solidifying the end of the cable within the spot welding machine at 1100°F-2000°F at 60-100 psi.

Spot welding gun

Abstract: PURPOSE:To improve the efficiency of welding operation owing to a highly speedy movement of a gun body and to easily and surely teach a robot by restricting the rotation of a screw shaft by acting an electromagnetic brake in the case of moving a spot welding gun with a robot or of teaching the robot, etc. CONSTITUTION:At the time of spot welding, energization of an electromagnetic brake 24 of an equalizing mechanism 13 is interrupted, and a ball screw 22 is set in a freely rotable state. Then, a ball screw 11 is rotated by actuating a servo motor 9, a spindle 6 is moved downward with a nut 8, an upper side electrode 3 is lowered, a work is clamped between the upper side electrode 3 and a lower side electrode 2, and the work is subjected to spot-welding by applying voltage to the upper side electrode 3 and the lower side electrode 2. Further, at the time of teaching a robot 12 spot welding positions for the work, the rotation of the ball screw 22 is restricted to put it in a locked state by energizing the electromagnetic brake 24 of the equalizing mechanism 24, and oscillation of the gun body 1 is restricted.