Koen Faes

Joining of Copper to Brass Using Magnetic Pulse Welding

In magnetic pulse welding, electromagnetic pressure is used to deform, accelerate and weld workpieces. The process is mostly used for tubular specimens. In this study, experiments were performed in order to investigate the weldability of copper tubes to brass solid workpieces. The tubes had an outer diameter and wall thickness of 25,0 mm and 1,5 mm respectively. A multi-turn coil with 5 windings in combination with a field shaper was used to focus the electromagnetic flux and thus realize the high pressures needed for welding. The process parameters for joining these materials were optimised for maximum weld length. The parameters taken into account were the position of the field shaper relative to the workpieces, the width of the air gap between the tube and the internal workpiece and the energy level. The weld quality was verified based on metallographic examinations, scanning electron microscopy and hardness measurements.

Electromagnetic pulse crimping of axial form fit joints

Electromagnetic pulse crimping of form fit joints was investigated using tubes in the aluminium alloy EN AW-6060, with a diameter of 50 mm and a wall thickness of 1,5 mm. First the influence of the charging voltage and the geometrical groove parameters on the deformation behaviour and localised thickness reduction of the tube wall was investigated. The experimental results provided data for optimising the groove design. The Design of Experiments method was used to optimise the shape and dimensions of the internal workpieces with a double groove design. Results of tensile tests on the crimp joints allowed determining the most important parameters for the groove design. Based on these observations an optimal double groove joint design was proposed. The deformation and failure behaviour of the crimp joints during tensile testing were experimentally studied using the digital image correlation technique. This technique was used to measure the local and global deformation of the joint. Failure mechanisms include pull-out, local shearing and fracture of the tube. Three main failure modes were observed.

Design of Electromagnetic Pulse Crimp Torque Joints

Electromagnetic pulse crimping of form fit joints was investigated using tubes with a diameter of 50 mm and a wall thickness of 1,5 mm, in the aluminium alloy EN AW-6060. The tubes were crimped onto steel internal parts, which were designed to bear torsional loads. Grooved, knurl rolled and knurl cut internal workpieces were used. To assess the torque strength of the connections, a torque test set-up was designed and built. In a first test series, grooved internal parts were used. The influence of the internal workpiece design and the energy level on the torque resistance was investigated. Related to the geometry of the internal workpiece, the following parameters were varied: the groove depth, the groove width, the edge radius and the number of grooves. In a second test series, knurl rolled and knurl cut internal workpieces were used. For the joints with a knurl rolled internal part, the influence of the knurl pattern, defined by the pitch, was investigated. For the connections with a knurl cut internal part, the influence of the energy level was studied. The different joint failure mechanisms were determined.

Investigation of the weldability of copper to steel tubes using the electromagnetic welding process

Magnetic pulse welding is an innovative joining method which allows joining of dissimilar metal combinations. However, much remains unknown about the process and its parameters. In this paper, the weldability of copper tubes to steel rods and tubes is discussed, with the goal of examining the influence of the wall thickness of the supporting steel tube on the weld and the deformation of the components. Large deformations were observed, causing an undesirable decrease in diameter of the tubes. The quality of the obtained welds was shown to decrease with decreasing inner tube thickness as well, most likely due to the deformation of the workpieces in radial direction. Because of this, it is advisable to use an internal support to prevent deformation of the support tubes. To gain more insight in the precise mechanisms of weld formation and failure, numerical simulations are advised.

Feasibility study of the friction surfacing process

Friction surfacing is a solid state cladding process based on the plastic deformation of a translating and rotating metallic consumable rod pressed against a stationary substrate. It is mostly used on mild and stainless steel and on aluminium. Thanks to the solid state nature of the process, it allows to join dissimilar metal combinations, e.g. aluminium to steel or to ceramics or several combinations of non-ferrous metals. Moreover, a continuous and fine-grained deposition is formed. Most research has been focussed on the feasibility of certain material combinations and on correlating the deposited layer quality to input parameters. In this work, a methodical approach to evaluate clad layers and to assess their properties is discussed. This approach consists of a visual assessment, a macrographic examination and a performance analysis and has shown to be apt to compare the clad layer quality.