Multi-spot Welding Research Articles

Joint interface optimization of all-CFRTP composite honeycomb prepared by ultrasonic multi-spot welding

An all carbon fiber reinforced polyetheretherketone (CF/PEEK) composite honeycomb is prepared by the multi-spot ultrasonic welding in this work. The interfacial responses and flat compression failure behaviors of the honeycomb are firstly analyzed. It is found that ultrasonic welding has both positive and negative effects on honeycomb performance. High-frequency vibration results in fiber waviness, which is beneficial to elevating both the bending resistance of the joints and the compression strength of the honeycomb. However, melted EDs also lead to resin-rich areas at the interface. Based on the findings, the multiwall carbon nanotubes/PEEK (MWCNTs/PEEK) energy directors are developed, providing new insights on optimizing the properties of the interface. The experimental results indicate that the interfacial node tensile strength is enhanced by 400 % (1267 kPa) with the MWCNTs content increasing to 7.5 wt%, and the optimized CF/PEEK honeycomb shows more superior specific energy absorption and specific compressive strength than those of the commercial light-weight honeycombs. Moreover, the joint failure behaviors are investigated thoroughly. The addition of MWCNTs is found to induce fiber bridging between the cell walls and facilitate stress transfer through the joint interface. The optimized ultrasonic welding method provides a new opportunity for efficient and volume manufacturing of carbon fiber reinforced composite honeycombs without dimension limitation and large mold costs.

Selected Aspects of the FEM-Based Numerical Modelling of Current Propagation in the Resistance Multispot Cruciform Welding of Bars

The article presents selected aspects of the FEM-based analysis concerning resistance welding processes performed using multispot welding systems. The analysis was based on a three-spot welding machine used for the joining bars in the cruciform configuration. Both two and three-dimensional modelling was performed as the comparative analysis of two computing software packages, i.e. the commercial ANSYS Mechanical software package and the ARTAP software package, available on an open access basis. The research work involved the determination of current propagation in various welding process configurations as well as the identification of the percentage loss of welding current and power resulting from the bridging of current by neighbouring welds. The article discusses the effect of the method of the power supply and the earthing of the system of electrodes along with the welded material on the manner of current propagation. The analyses presented in the article were performed in relation to the DC power supply (inverter welding machine). Related calculations were performed using averaged (in terms of heat and resistance) material parameters.

Investigation of Pore Reduction in Hybrid Joints of Conventionally and Additively Manufactured AlSi10Mg Using Electron Beam Welding

Laser powder bed fusion (LPBF) is particularly well suited for the production of geometrically complex functional metal components. However, the size of the components that can be produced is limited technologically by the volume of the construction chamber, and economically by the low build‐up rates. With the provision of a reliable welding technology, size limitations can potentially be overcome to a degree by joining two additively manufactured (AM) components or by hybrid construction of components. Therefore, this study investigates the production of hybrid joints from additively and conventionally manufactured AlSi10Mg material by electron beam welding (EBW). It is known that EBW of LPBF‐processed aluminum alloys in the keyhole welding mode results in the distinctive formation of pores in the weld seams. To avoid this, two different joining strategies are pursued, namely, beam offset and multispot welding methods. It is thus determined that an adequate weld seam quality can only be achieved by means of a three‐spot welding process with adapted EB parameters. Accordingly, the investigations prove the applicability of the EB keyhole welding mode in EBW for the production of low‐porosity LPBF mixed joints.

The Reduction of Welding Current Asymmetry in Multispot Welding Machines by Differentiating the Cross-Section of Welding Machine Arms

The article discusses the analysis of the propagation of current in resistance multispot welding machines and the adjustment of the cross-section of the welding machine arms aimed to compensate the asymmetry of welding current in individual welds. The analysis involved the effect of the length of multispot welding machines where the span of the arms (distance between welds) amounted up to 2 m, the arms were characterised by various cross-sections and the structural material was characterised by various resistivity (resulting from changes in temperature). The analysis was performed in relation to welding machines using a nominal welding current of 5 kA. The tests made it possible to determine the effect of changes in the value of current on the cross-section of the weld nugget.

Analytical heat conduction modelling for shaped laser beams

Conduction mode laser spot welding and laser spot hardening usually employ Gaussian or top-hat-like beam modes. One main requirement of these techniques is the avoidance of overheating in the centre of the laser-material interaction zone. Process flexibility can be improved by spatially and/or temporally shaping the beam, which can enable higher process quality, robustness or speed. A desired spatial beam shape can be achieved by a suitably designed diffractive optical element. However, the prediction of a suitable beam shape for a particular process can be complex. A simplified analytical heat conduction model has been developed that can rapidly calculate the temperature field and cooling behaviour for almost any spatial and temporal beam shape. The potential and limits of the model are demonstrated and discussed by calculating and analysing temperature profiles for several cases of multi-spot welding.

A Study on Friction Stir Multi Spot Welding Techniques to Join Commercial Pure Aluminum and Mild Steel Sheets

To achieve significant improvement in the shear strength of dissimilar joints between aluminum and mild steel sheets, four methods of friction stir multi-spot welding processes, were investigated. Initially, in all these methods, plasticized aluminum layer was deposited on the steel side by friction surfacing. Subsequently, the deposited aluminum was compacted by friction forming. After dressing, spot welding with different tool configurations was performed. Tool rotational speeds of 900, 1120, 1400 and 1800 rpm were used to analyze their effects on the weld nugget. Different mechanical and metallurgical characterizations were done on the welds thus made. The process with aluminum layer on grooved mild steel followed by friction stir multi-spot welding using concave tipped welding tool resulted in welds. These welds had better metallurgical bonding characteristics and higher shear strength, which at a rotational speed of 1120 rpm was more than twice that of the welds made with conventional friction stir spot welding.

Mechanical Properties of Resistance Spot Welded Components of High Strength Austenitic Stainless Steel

Resistance multi-spot welding (MSW) in column, triangle and tetragonal symmetry arrangements was prepared using cold-rolled 301L high-strength sheets, and their static and fatigue properties were investigated. The effects of spot welds on the fracture strengths and fatigue limits were discussed. The results show that the static strengths can be estimated using an inherent linear relationship formula of the load versus the welding area. It was based on the 28%–33% volume fraction of α′ martensite induced at the interfacial spot weld fracture because of the failure deformation. The fatigue limits of the MSW nonlinearly increase with the number of spot welds. The arrangement of spot welds in the MSW significantly affects the average fatigue limit of each spot weld; its 26% maximum reduction occurred in the triangle, and the interaction stress between spot welds led to its 18% reduction in the tetragonal symmetry. The calculated fatigue stress of all MSW loadings with their mean fatigue limits was 230–270 MPa.

Joining of multiple sheets in a butt-joint configuration using single pass laser welding with multiple spots

The introduction of high-power single mode fiber lasers has given deeper and narrower welds than previously seen using lasers. In some cases, the weld becomes too narrow and must be expanded to fit the geometrical shape of a given welding task. Instead of using only one beam, it was suggested to split the beam into multiple spots placed in a prespecified pattern. In this way, the dimensions of the weld pool could be controlled. In this work, the spots are placed on a row perpendicular to the welding direction. This provided the ability to control the final weld face by controlling the width and depth of penetration independent of each other with minimum heat input. An examination was conducted on how the weld cross section is influenced by spot distance, number of spots, power, and focus. It is shown that a weld seam can be widened in steps by using multiple spots, and the depth can be controlled independently from the width by adjusting the laser power. It is possible to produce a rectangular like cross section of the weld by choosing correct design parameters. For a pattern with multiple spots on a row, equal depth of penetration in the weld bead is reached if the edge spots have 5%–10% more power than the center spots. Basic rules for design of spot patterns are given for a configuration with a single mode laser and spot diameter of Ø85 μm. The ability to bridge gaps is increased in multispot welding compared to multiple single passes. The technique shows promising results in welding parts which resembles the conditions of a real production regarding robustness and tolerances.

A method of determining the welding current in multispot contact welding

A method of measuring the welding current on each electrode in bilateral multispot contact welding and of determining its actual values, taking bridging into account, is proposed.

Suppressing Cracking in Resistance Welding AA5754 by Mechanical Means

In this paper mechanical aspects of cracking during single- and multi-spot welding of AA5754 was investigated by both experimental and analytical approaches. The impact of mechanical loading on crack initiation and propagation was studied with the consideration of various process parameters including the loading imposed by electrodes, the formation of liquid nugget, and constraining factors during and after welding. Tensile properties of AA5754 and their dependence on the temperature were tested at room and up to solidus temperatures, in order to provide a reference of cracking stress. Thermal-mechanical analysis was conducted based on the temperature field around the nugget and the state of stress encountered during welding. This analysis revealed that tensile stress might build up in the vicinity of the nugget during cooling, as explained in the experimental observation. General guidelines for suppressing cracking were proposed, i.e., to provide sufficient constraint around the weld spot during and after welding.

Analysis and optimisation of electrode life for conventional and compound tip electrodes during resistance spot welding of electrogalvanised steels

Rapid electrode wear is the major concern in resistance spot welding of galvanised steels. The electrode life in such instances is tremendously influenced by the continuous alloying reactions that occur between the molten free zinc and the copper electrodes. It is shown in the present work that the use of compound electrodes can considerably enhance the effective electrode life. The compound electrodes are fabricated by introducing a tungsten insert at the tip of conventional circular face electrodes. The performance of these new electrodes has been investigated under laboratory conditions during multispot welding. It is observed that the compound tip electrodes can offer superior electrode life only for a small insert size. A finite element method based numerical simulation has simultaneously been carried out. The results of the numerical calculation also indicate that the optimum design of the compound tip electrode depends on the insert size.

Ultrasonic multi-spot continuous welding of metal plate specimens using a two-vibration-system welding equipment

Vibration characteristics of metal plate specimens of ultrasonic multi-spot welding using two vibration systems of 15 kHz and 27 kHz crossed at a right angle are studied. These vibration systems are driven by 4 and 5 kW power amplifiers. Welding specimens vibrate in various modes and weld strength is altered by the vibration modes at the welding positions. Using two vibration systems, the welding position at a vibration node at one frequency can be driven because the vibration mode may be changed at a different frequency and different direction. Welding-plate specimens of aluminum, aluminum alloy, copper and steel plate specimens of 0.5 to 2.0 mm in thickness and 100 mm to 200 mm in width were welded successfully with a uniform welding strength along the specimen width by multi-spot lapped welding using the two-vibration-system ultrasonic welding equipment and by controlling the vibration modes of the plate specimens by clamping the specimen with metal vices.

Optimization of the availability of complex manufacturing systems—methods and examples

Abstract Highly automated manufacturing systems operate economically only if a high rate of availability of the system is reached. Therefore it is very important to integrate the analysis of system's reliability and availability into the process of planning and designing the structure of the manufacturing system. In this paper planning methods for all kinds of automated manufacturing systems are explained and an example for the availability analysis of a multi-spot welding line is given

Laser Welding in Automatic Assembly Line for Color-CRT Electron Gun

YAG laser welding technology has been applied to an automatic assembly line for newly designed color-CRT electron gun. In the laser welding line, optical fiber delivery systems are used. This fiber is made from pure fused quartz. It has a 400 μm core diameter and a ten meter length. In using the optical fiber system, experiments are made to determine laser damage threshold in the fiber material versus high laser power density. transmission characteristics, life test and mechanical strength test. The develpment of this technique enables the laser optical system to be simplified, with higher flexibility, compared with coventional laser welding system using mirrors. In addition, simultaneous multi-spot laser welding and laser marking optical systems were developed. This welding line has markedly raised the productivity with higher product quality and reliability level.