Showing papers in "Welding and cutting in 2002"

Methods of predicting the fatigue lives of laser-beam welded lap welds subjected to shear stresses

Abstract: One prerequisite for reliably predicting the fatigue lives of joined components in complex products such as a vehicle is that not only the local stresses but also the local stressability of the material are known to a sufficient extent. This contribution presents the structural-stress concept, the structural stress taking account of geometrical effects and the notch-stress concept as methods of describing the local stresses on a laser-beam weld subjected to shear loads. The stressability is obtained by assigning the stress-cycle lines to the respective local stresses. If the suitable local stresses are chosen, this results in the stressability as a pure material property. On the basis of bearable loads and bearable local stresses, laser-beam stitch welds are compared with resistance spot welds.

Welding with two wire electrodes: Status and prospects of the optimisation of gas-shielded metal-arc welding

Abstract: A variant of high-productivity metal-active gas welding is presented below. It works with two wire electrodes which are electrically insulated from each other and is designated as "Time-Twin" at Fronius. Memories of the older T.I.M.E. process relate to the increases in productivity possible with it, achieved with standard shielding gases. The information provided ranges from the objectives, the status, the application, the process itself, the appliance-technology components and the options right up to the perspectives.

Electrical effects and influencing quantities in the case of the hybrid plasma-MIG welding process

Abstract: The hybrid plasma/metal-inert gas welding process is regarded as an interesting alternative to conventional gas-shielded arc welding processes. Although it has been known for many years already, hardly any functioning systems are available. The complex thermodynamic, flow-technology and electrotechnical relationships lead to a system with many influencing quantities and boundary conditions. The electrotechnical foundations and interlinks of the two processes of plasma welding and metal-inert gas welding (MIG welding) are presented.

High-quality and economically viable coating by means of tandem gas-shielded metal-arc welding

Abstract: Tandem gas-shielded metal-arc welding in the high-productivity range (high-productivity tandem GMA welding) is suitable not only for joint welding but also for weld surfacing. Its high deposition rate, the flexible handling and a good surface quality make it economically viable to manufacture high-quality corrosion-resistant, temperature-resistant and wear-resistant components. Additional advantages are the great diversity of available filler metals as well as the very low dilution with the parent metal. Therefore, unalloyed steel plates were coated with chromium-nickel and nickel-base alloys and with other wear-resistant filler metals by means of high-productivity tandem GMA welding and were subjected to a material-science assessment [1].

Electrode force as an important process variable in the case of resistance spot welding

Abstract: For many years now resistance spot welding has assumed a dominant role in the manufacturing industry, particularly in the production of automotive parts and white goods. Its extensive use is primarily due to the simple and flexible nature of the technology, which has made successful automation of the process possible. However, it is this automation, without monitoring, which is now being addressed as a primary concern as it can lead to a high number of defective parts being produced before a problem is identified. Rectification of the fault may lead to expensive and unscheduled machine down time. The temporary use, or permanent installation, of a device to record the clamping forces generated during the weld process would minimise these problems, by early recognition of any non-optimum parameters. Two new systems designed to monitor, not only the maximum clamping force, but also the force curve produced during the welding operation are detailed below. The first allows for periodic checks to be conducted, the second for continuous on line monitoring of the weld process.

Development of a methodology for the optimisation of the welding parameters in the case of resistance welding

Abstract: In the case of resistance welding, the choice of the optimum welding parameters may be extremely dependent on the material, possibly even on the batch in question. Mathematical optimisation methods were therefore applied and assessed in order to determine the welding range and the optimum welding parameters (welding duration, welding current and electrode force). The target variable was the highest possible tensile shear force of the welded spot. It was shown that the modified simplex method was the most suitable method. Corresponding software was developed on this basis.

Application potential of gas-shielded metal-arc welding with a strip electrode

Abstract: Gas-shielded metal-arc welding (GMAW) with a strip electrode is an increasingly interesting variant of high-productivity GMAW. The particular electrode shape results not only in a high attainable deposition efficiency butalso in other process-related (e.g. good gap-bridging capacity) and metallurgical (e.g. lower susceptibility to pores) advantages. Against this background, investigations were conducted into the possibilities of using GMAW with a strip electrode for series production. For this purpose, a typical parent metal in automobile construction, S315 (QStE300), was welded together with different weld geometries and sheet thicknesses. The experiments concentrated on the welding speeds which could be achieved with a defined gap width. The effects of the modified parameters on the structure and the tensile strength were then investigated.

Ultrasonic testing on friction-stir-welded aluminium alloys

Abstract: The typical weld defects arising during the friction stir welding [1] of aluminium sheets were classified and were investigated using the ultrasonic pulse-echo method. By means of vertical incidence, it was possible to identify almost all the defect geometries above a critical size. Merely those cracks with planes in the direction of incidence (as are typical of root gaps) could not be detected. However, even these defects could be established very precisely by means of diagonal incidence.

Manufacturing SiC cermet coatings by means of high-velocity oxy-fuel flame spraying

Abstract: Composite powders with silicon carbides (SiC) were developed for the manufacture of wear-resistant and corrosion-resistant protective coats by means of high-velocity oxy-fuel flame spraying. It was possible to embed the SiC particles in ductile matrix alloys in order to prevent their disintegration. The matrices used were nickel, nickel-base, cobalt-base and stellite alloys. Tests relating to high-velocity oxy-fuel flame spraying with different systems were performed after the manufacture of agglomerated, sintered and mechanically mixed composite powders. The porosities, SiC contents and structures of the coatings were analysed and their wear and corrosion resistances were examined in cyclic wear tests and in ageing tests. In this respect, the main influencing quantity was the SiC content which proved to be dependent on the spraying parameters.

Thermal coating of components for biomass power stations

Abstract: Components in biomass power stations are frequently exposed to extreme corrosion attacks and erosive wear. Special coating processes based on the thermal spraying of gas-tight coatings which consist of NiCrMoSiB alloys and are applied according to the molten-composite method were developed in order to tackle this problem. In practical tests, their high density and good adhesion proved to be superior to those of refractory linings, hardfacing coatings and other composite materials.

Utilisation of the finite-element method in order to optimise shaping plasma-arc powder weld surfacing for the manufacture of forming tools suitable for high stresses

Abstract: The welding deformations and residual welding stresses caused on flat components by the intensive heat input during shaping weld surfacing exert a negative influence on the component properties, particularly in the case of multi-pass weld surfacing. Investigations were conducted not only into the resulting molten-pool geometry, the welding-induced deformations and the residual stresses in the case of single-pass and multi-pass surfacing welds consisting of nickel-base and cobalt-base alloys on flat components but also into possibilities of optimising them. The dependence of the resulting welding deformations and residual welding stresses on the number of passes, on the weld width and on the buffer layers was analysed by means of numerical calculations and experimental investigations. In this respect, it was possible to achieve very good coincidence between the calculations and the experiments.

Up-to-date synopsis of thermal spraying technology

Abstract: This contribution reports on the current status of the research and development with regard to thermal spraying. Emphasis is placed on improving the installation technology and optimising high-productivity and hybrid processes. Diagnostic methods for quality assurance are presented as well. Another field of interest is the development of coating removal processes. All in all, thermal spraying proves to be a very promising surface coating process with a great potential for development.

Extending the electrode life in the spot welding of aluminium alloys by using composite electrodes

Abstract: In order to extend the electrode life in the spot welding of aluminium alloys composite electrodes which consisted of a copper-chromium-zirconium alloy with an insert made of tungsten at the electrode tip were manufactured. Electrode-life investigations were conducted on one three-phase direct-current welding machine and on one medium-frequency direct-current welding machine. In this case, the tensile shear strengths were determined depending on the number of welded spots and the appearance of the spots was assessed. It was shown that, by using composite electrodes, the electrode life can be extended by 1.5 to 2 times in comparison with conventional electrodes. The most favourable solution proved to be a somewhat thicker tungsten insert with a diameter of 4 mm in a three-phase rectifier welding machine and preceding cathodic arc cleaning of the aluminium surface.

Brazing of high-strength steel sheets

Abstract: New brazing alloys on a copper basis which are suitable for the joining of sheets made of high-strength steel were developed. The processes used were metal-inert gas brazing (MIG brazing), plasma brazing with cold wire and the hybrid plasma/MIG brazing process. When the process parameters had been optimised, test brazed joints were manufactured and were tested in tensile and/or fatigue tests. It was shown that the brazing alloys lead to good results, particularly in connection with combined plasma/MIG brazing.

Electromagnetic compatibility of resistance welding machines. Part 2: Influencing factors and noise-reducing measures

Abstract: In the first part of the article [1], it was explained that consideration must be given to a few particular features in the case of measurements relating to the electromagnetic compatibility (EMC) of resistance welding machines. Investigations into influencing factors and noise-reducing measures are presented below. While those influences on the noise emission which originate from the welding process proved to be insignificant, the power sections of the machines with the power semi-conductors used there constituted major sources of the electromagnetic disturbances.

Electromagnetic compatibility of resistance welding machines. Part 1: Initial situation and measuring methodology

Abstract: The power parameters and mostly intermittent operating mode of resistance welding machines result in certain particular characteristics with regard to the metrological evaluation of the electromagnetic compatibility (EMC)of these machines. The special aspects of the measuring methodology which are explained in the article primarily relate to the decoupling of the interference voltages, to the coordination of the measuring sequence between the resistance welding machine and the radio-interference measuring receiver as well as to the type of noise evaluation to be made by the measuring receiver.