Browsing by Author "Apora, James"

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    Characterisation of resistance spot welding Electrodes with annular recess design
    (Kyambogo University (un published work), 2018-11) Apora, James
    This study investigated the characteristics of resistance welding electrode with annular recess design for supplying an electric current to metallic workpieces for welding two workpieces together. It comprises cylindrical body of an electrically conductive material (copper) having an annular recess tip for contacting workpiece. The tip is formed with a recess which gave the tip annular workpiece contacting surface. The recess was filled with an electrical and heat resistant material containing ceramic cement known as kaolin mixed with clay. The novel idea of the tool design is to enable formation of molten material pool which forms weld nuggets with even strength around the joints. The beginning facts about the recess design tool is that the annular recess minimizes current and voltage concentration in the middle of the tool tips, thereby; causing molten materials to flow both to the centre and onto the perimeter of the spot welded joint where the welding pressure is applied. Studies have shown that conventional spot welding tools produce joints which are stronger on the edges but weaker in the centre of the nuggets which presumably experience high voltage concentration. The data collection was done through RSW welding experiments where welding of sheet metal materials with same thickness was carried out; alloy steel materials cut from a salvage vehicle were used to make the sample strips measuring 50mm by 175mm each. The design and manufacture of annular recess was carried. The welded joints were subjected to different tests to characterize the weldability and integrity of the welded joints. The tests involved destructive testing and non-destructive tests of the joints. Magnetic Particle Inspection (MPI) was used to test the weld joint integrity beside the visual inspection. In this research study, effect(s) of electrode tip geometry on the tensile-shear strength in resistance spot welded joints of metal steel sheet (body panel) cut out from an old salvage vehicle of similar thickness (1mm) was studied. The outcome of this study showed remarkable improvement on the tensile-shear strength of RSW joint with a nugget diameter about 8.1mm by approximately 11.4KN using the annular recess electrodes compared to 5.7KN at nugget diameter of 7.8mm using the conventional electrode. The annular recess electrode provided an enhanced joint strength by approximately 2 times than the conventional electrode. Therefore application of this new technique creates a new tool that can enhance RSW joints strength in metal fabrications and also improvement on the crash worthiness of the vehicle. Keywords: Current, Electrode, Nuggets, Resistance, Spot-welding,
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    Characteristics of resistance spot welding using annular recess electrodes
    (Elsevier: Journal of Advanced Joining Processes, 2020-07) Watmon, Titus Bitek; Wandera, Catherine; Apora, James
    Resistance spot welding is widely used in manufacturing industries, such as automobile structural body manufacture, rail vehicle construction, electronics manufacture, battery manufacture, etc. Resistance spot weld integrity is of paramount importance in the manufacturing industry, especially in automotive body joining to ensure that the automobile bodies can withstand the stress levels that the vehicle is subjected in operation. A number of factors - including electrode geometry, electrode force, welding current and welding time - influence the quality of the resistance spot weld. The electrode material that ensures electrical conductivity and compressive strength and electrode geometry defined by the electrode tip profile, shape, size are important factors in resistance spot welding. This paper discusses the comparative performance of resistance spot welding electrodes with annular recess design and the conventional solid design in welding of a 1 mm thick steel sheet used in construction of automobile structural bodies. The copper-based electrodes used in this study were prepared as described in the ISO 5182:2008 Standard. The annular recess electrode was designed using SolidWorks Version 2015; a hole measuring 4 mm deep and 2.50 mm in diameter was created centrally on the electrode tip and filled with heat resistant mixture of cement and kaolin ceramics. The effects of applied electrode force, current, and weld time on weld-integrity were investigated for the two designs of resistance spot welding electrodes. Linear regression analysis of data obtained established that the weld strength and nugget diameter was higher for the annular recess electrode than the conventional solid electrode. An analysis of variance established that the observed variation of the nugget diameter with weld time was statistically significant but the variations of weld strength with applied electrode force and variation of nugget diameter with current were not statistically significant which may require further study.