Welding Manufacturing Research Articles

On intelligentized technologies for modern welding manufacturing

On intelligentized technologies for modern welding manufacturing

Off-line programming of flexible welding manufacturing cells

Abstract The use of robotized welding to achieve better quality has demanded research of new technologies to integrate and test the systems. The complete control of a flexible manufacturing cell involves perfect task synchronisation among all of its robots and equipment. Off-line programming provides an essential link between CAD and CAM. The development of off-line programming systems should result in greater use of robots and accelerate the implementation of flexible manufacturing systems (FMS). It also offers an alternative for complex automated production lines and should allow rapid response to changing product/process issues. This article describes some features of graphic simulation and off-line programming focusing on its applications to robotized welding.

Mechanisms of electrode degradation when spot welding coated steels

The present work compares the behaviour of precipitation hardened and dispersion strengthened electrodes during the manufacture of resistance spot welds in coated steel sheet. The primary mechanism causing the failure of spot welding electrodes was growth of the electrode tip. Under normal welding conditions electrode tip growth was primarily dependent on local alloying morphology so that deterioration was mainly a function of the type of coating present on the steel. However, welding with high currents or use of current stepping programmes could extend electrode performance such that softening became a more dominant electrode degradation mechanism. Under these conditions, use of dispersion strengthened material could extend electrode campaign life.

Scaling issues in resistance-welded thermoplastic composite joints

Resistance welding has been demonstrated as a viable technique for joining thermoplastic composites. Extensive research has been conducted in previous studies on the processing and postprocessing evaluation of coupon-sized resistance welded specimens using this thermoplastic fusion bonding technique. This work focuses on the manufacturing and evaluation of large-scale resistance welds used to join carbon fiber (CF)/polyetheretherketone (PEEK) thermoplastic composite parts. Applications using the present resistance welding technology are assessed, and potential applications of resistance welding are discussed. The sequential resistance welding process is introduced as an approach to large-scale welding that increases joint quality and performance while maintaining modest pressure and weld power requirements. The single-step and alternate multiple-step (sequential) techniques are implemented for large-scale resistance welds of CF/PEEK adherends comolded with polyetherimide (PEI) (i.e., the Thermabond® process). Nondestructive ultrasonic evaluation, mechanical testing, fractography, and microscopy show that: (1) a higher weld uniformity was obtained with the multiple-step weld than the single-step weld; and (2) uneven heating and overheating were minimized by reducing the heating element length within the bond region through the use of the sequential resistance welding process. The different welding techniques produce a large variation in lap shear strength; direct comparison of the weld quality and lap shear strength shows that the sequential resistance welding process yields a superior bond. With the principles developed in this investigation, resistance welding can be used to join large-scale thermoplastic composite parts with consistent, high levels of performance and quality. © 1997 John Wiley & Sons, Inc. Adv in Polym Techn 16: 279–295, 1997

Simulation of microstructure and liquation cracking in 7017 aluminium alloy

Welding in a 7000 series aluminium alloy can lead to the development of a white zone microstructure and liquation cracking in the heat affected zone adjacent to the fusion boundary. A Gleeble 1500 thermomechanical system has been used to study the conditions associated with damage development. A range of simulations has been carried out covering thermal and thermomechanical conditions typically encountered during weld manufacture. Results show that both the white zone microstructure and liquation cracking can be simulated at a sufficient scale to permit full characterisation in laboratory testpieces. Data analysis has defined and mapped the stress and temperature conditions leading to crack initiation. This evaluation demonstrates that the susceptibility for cracking is minimised by increasing the cooling rate following weld manufacture.

Laser Welding Analysis and Experiments

A "seamless engineering" approach for mechanical design and laser welding manufacturing combines a method for welding analysis with a method for stress analysis through the development of radiant heating models for use in a nonlinear finite-element computer program. Experiments were performed welding steel plates, using a five-axis computer numerical controlled (CNC) workstation to translate welding specimens under a 5-kW CO2 (carbon dioxide) laser. Thermocouples installed near the weld seam were used to measure the transient temperature field during welding. The measured temperatures were compared with the analytical predictions, and the welds were sectioned so that predictions of properties in the heat-affected zone could be compared with experimental data. This paper presents analytical results using classical methods of analysis and includes solutions for temperature fields, heating and cooling rates, and metallurgical properties in heat-affected zones.

Creep behaviour of low alloy steel weldments

Multipass, low-alloy steel weldments contain heterogeneous microstructures. The range of these structures present in a particular weld is critically dependent on composition and the thermal cycles developed during weld manufacture. For given operating conditions, the long-term, high temperature behaviour of thick-section weldments loaded by internal pressure is a function of the creep strength and ductility of the specific constituents. Variations in service performance have been experienced between seam welds and girth welds manufactured from similar creep resistant low alloy steels. The observed differences in behaviour can be explained in terms of redistribution of the stresses present.

From the industrial robot welding cell to the industrial robot welding system

The past few years have witnessed a vigorous upsurge in the use of industrial robots for welded parts manufacturing, particularly in small- and medium-size companies. Notable reasons for the sharp increase in flexible automation with industrial robots are the shorter product cycles, shrinking batch sizes and a steadily rising level of wage costs. Whereas up to now single industrial robots for automated welding manufacturing have been generally used in closed working areas, manually loaded and unloaded by an operator, today a trend towards more complex systems can be recognised. A linking of several single stations by means of material and information flow makes it possible to concentrate manual operations in a central station for loading and unloading, and moreover to have integrated storage facilities.

Experience in the replacement of safety related piping in German boiling water reactors

In the German boiling water reactors (BWR) of the 69 series and their forerunner plant, high-strength low-alloy ferritic materials were used for a large number of pipings both inside and outside the pressure boundary (PB). The choice of this type of material led to comparatively thin-walled piping which, at that time, had been designed and manufactured in accordance with the codes and standards applying in the Federal Republic of Germany. Due to material properties resulting from production in a conventional manner, design features which did not sufficiently meet the requirements for nondestructive testability, and defects caused during processing, mainly in the area of circumferential welds, the ferritic pipings inside the PB were replaced in the course of a plant upgrading by new piping designed and manufactured according to the basis safety concept. The improvements and experience gained during backfitting of five German BWR plants are part of the German safety strategy and can be summarized as follows: 1. (1) Exclusion of large fractures on the basis of an optimized quality level for the piping. 2. (2) Elimination of need for the pipe whip restraints which existed in the former piping. 3. (3) Limited reduction of the former scope of inservice inspections, mainly as a consequence of improved weld quality and optimized weld performance. 4. (4) Reduction of personnel radiation exposure, e.g. by reduced number of welds and by manufacture of welds using automatic equipment, as well as by improved nondestructive testing. 5. (5) Availability values for backfitted BWR comparable to German PWR values. The pipings made of stabilized austenitic materials, which are arranged inside and outside the containment of the BWR plants, were not replaced since their quality level has been proved to be sufficient even on the basis of the present standards.

Electroslag welding in manufacture of heavy forgings

This work presents the results of a study on the application of electroslag welding (ESW) to the assembly of heavy preforms for forgings. The technique uses ESW to join two or more blocks or ingots to form a large piece for open-die forging. Results are presented describing a development programme to manufacture and test such forgings in SAE 1045 steel in relation to commercial qualification specifications for machinery shaft application. The finished forgings are found to pass all such quality standards by a good margin. The general applicability of the technique in the field of open-die forgings is also discussed.

Elevated temperature flow strength, creep resistance and diffusion welding characteristics of Ti-6Al-2Nb-1Ta-0.8Mo

A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo has been conducted. Two mill-processed forms of this alloy were examined. The forged material had been essentially processed above the beta transus (∼1275 K) while the rolled form had been subjected to work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A “soft” interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.