Browsing by Author "Wandera, Catherine"

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    Characteristics of resistance spot welding using annular recess electrodes
    (Journal of Advanced Joining Processes, 2020) Watmon, Titus Bitek; Wandera, Catherine; Apora, James
    Resistance spot welding is widely used in manufacturing industries, such as automobile structural body manufac- ture, 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.
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    Characterization of the melt removal rate in laser cutting of thick-section stainless steel
    (Journal of Laser Applications, 2010) Wandera, Catherine; Kujanpaa, Veli
    The efficiency of the laser cutting process depends on both the rate of melting and rate of melt removal from the cut kerf. The depth of flow separation and the dross attachment on the lower cut edge relate to the efficiency of the melt removal process and can be used to characterize the rate of melt removal from the cut kerf. The melt flow velocity and melt film thickness are formulated in this study by consideration of the fundamentals of viscous incompressible fluid flow. The calculated melt flow velocity and melt film thickness are correlated with the depth of flow separation on the 10 mm stainless steel AISI 304 EN 1.4301 laser cut edge. The effects of process parameters—including assist gas pressure, nozzle diameter, nozzle standoff, focal point position, and cutting speed—on the depth of flow separation and the dross attachment on the lower cut edge are investigated. The assist gas pressure, nozzle diameter, and focal point position are found to significantly affect the efficiency of melt removal from the cut kerf.
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    Cutting of stainless steel with fiber and disk laser
    (Laser Institute of America, 2006) Wandera, Catherine; Salminen, Antti; Olsen, Flemming O.; Kujanpää, Veli
    Laser cutting is a major application of laser materials processing. The cutting is usually performed with CO2-laser due to its good beam quality and its relatively low costs of ownership. Ever since entering the market the high power solid state lasers have been expected to achieve a dominating role also in cutting applications. This has not happened mainly due to the fact that beam quality has not been sufficient. The introduction of new generation of solid state lasers has raised the interest of use of them in cutting application. This study was concentrated on use of fiber and disk lasers, the new laser types with a high beam quality, in cutting of austenitic stainless steel. The performance of these new lasers at power level of 4 kW was compared with CO2-laser in respect of cutting speed, kerf width, kerf edge roughness and perpendicularity (squarness) in order to validate the potential of both of the new lasers against traditional CO2-laser. The results showed that the new lasers offer a great potential in improving the productivity of cutting phase with an acceptable edge quality. This is emphasized in thin sheets of 1.3 and 2.3 mm thickness. In that case the width of the cut kerf is considerably narrow especially when using a fiber laser. In case of thicker sections (4.3 and 6.2 mm) the focal length was increased in order to reach an acceptable cut quality still providing a competitive cutting speed in comparison to a CO2-laser. The fiber laser was the fastest cutting laser in case of each thickness. The results were very promising and it can be stated that these new laser types have a great potential in cutting and will probably gain a considerable market share not only in 3D cutting applications but also in ordinary flat sheet cutting.
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    Inert gas cutting of thick-section stainless steel and medium-section aluminum using a high power fiber laser
    (Journal of laser applications, 2009) Wandera, Catherine; Salminen, Antti; Kujanpaa, Veli
    Inert gas assisted laser cutting of 10 mm stainless steel plate and 4 mm aluminum sheet was performed with a 5 kWfiber laser. The effects of laser power, cutting speed, focal point position, and assist gas pressure on the cutting performance and cut quality were investigated. Clean cut surfaces without or with minimal dross were achieved with some combinations of process parameters and attempts were made to define parameter windows in terms of cutting speed and laser power for good quality cutting. The maximum cutting speeds for acceptable cut quality were determined at different power levels. The range at which complete through cutting could be achieved so-called parameter window was limited upwards by insufficient power intensity to obtain through cutting at high cutting speeds and downwards by heat conduction at slow cutting speeds. The effects of focal point position and assist gas pressure on the striation pattern cut surface roughness were also examined. Low surface roughness was achieved with the focal point position inside the workpiece showing the need for a wider kerf for better melt ejection in thick-section metal cutting. There was also a reduction in surface roughness with increase in assist gas pressure, but there was no significant reduction in surface roughness above the gas pressure of 16 bar, which could be due to the gas flow dynamics inside the narrow cut kerf at high assist-gas pressures.
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    Potential Benefits of adoption of Laser Materials Processing in East Africa's Manufacturing Industry
    (DeKUT International Conference, 2018) Wandera, Catherine; Niyibizi, Alphonse
    Laser technology is applied in a wide range of applications in various sectors, including industrial manufacturing, medical, and communication, among others. The laser is a versatile tool for materials processing as it is a non-contact tool that is CNC programmable and can be utilized in various industrial production processes. One of the most important and unique features of laser radiation is that it can be focused into a microscopic spot size generating high power densities in tens MW/cm2 that are capable of melting and vaporizing metals at fast rate yielding high speed production processes. Different types of laser sources - differing in features such as operating wavelength, maximum output power, beam quality, and method of beam delivery - are now widely deployed in specific applications with realization of benefits in process performance and product quality. The laser characteristics that benefit various laser materials processing applications include kilowatt output power, high beam quality, fiber optic beam delivery, and small footprint (compact laser systems). Lasers are used in the manufacturing industry for materials processing applications such as cutting and welding of metals, surface hardening and cladding of metals, joining of plastics, marking/engraving, drilling/micromachining, etc. Equipment manufacturers often use the laser in production processes such as profile cutting and welding of metals; the laser is often utilized in profile cutting of sheet and plate metal whereby a large number of parts are nested to improve material usage and avoid wastage. The laser is also used for maintenance and repair works involving surface hardening and surface cladding of worn out machine components. Uganda and Kenya have recently started to exploit their oil deposits and there are prospects of industrial growth in the region to service the oil sector as well as other sectors that will benefit from the oil proceeds. Large multibillion-dollar infrastructure projects - such the Standard Gauge Railway, SGR, the Lamu Port, Southern Sudan-Ethiopia Transport Corridor, LAPSSET and Uganda-Tanzania oil pipeline – are also underway in the region. Consequently, East Africa’s manufacturing industries need to position themselves to meet the stringent demands for high quality equipment and machinery for the oil and gas industry as well as meet the maintenance requirements of such an ultramodern infrastructure. The process benefits that will be realized from utilization of laser technology in East Africa’s manufacturing industry include high productivity through high processing speeds, reproducibility of high product quality, and flexibility of manufacturing as the same laser source can be used for different production processes.