Weld trial processed data

Results for the weld trials lead to interesting developments and outcomes. Although more than 4 weld trials were performed, it was decided to look at 4 in particular weld trials under similar conditions and steady state. Two of the weld trials for each are at 1200 and 1600 rpm respectively. Each set was performed at different times which also allowed one to see the conformity for the comparisons and how repeatable the procedure is. Although there are some discrepancies, results do show some similarity for valid conclusions to be drawn.

The initial results for the FLIR-temperature comparison for the same weld rotation for various weld trials compare fairly well, suggesting better results, whereas the last indicate a greater difference. Possible influences could be any of the following;

 Angle of camera changes further out on the weld line, therefore emissivity value might be different

 Reflective temperature has an influence on final temperature results as well

 There is also the possibility that the CNC machine has a discrepancy with input which results in the uncertainty that the rotation is set correctly, though this last may seem unlikely, it just ensures that these parameters need to be checked and ensured that they are correct.

Based on calculations performed to get the heat transfer coefficient with total heat transfer at particular temperatures, one is able to conclude whether sticking, sliding or a combination of each is occurring. Based on total heat flux transfer, one is able to conclude as to what condition the process is undergoing, it is assumed that based on the table for Total heat flux along radius for both contact conditions, values lie between the sticking and sliding condition. This conclusion is also comparable to literature and is outlined in [25]

Other notes on the temperature rate for FLIR;

 Heat flux transfer is higher at higher rotations than at lower rotations and this is due to the increase in friction generation rate between the two surfaces.

114  For higher rotations, the rate of increase in the temperature is faster than those at lower rotations. This is a valid conclusion since higher rotations cause faster heat generation since friction coefficient increases at a faster rate. With this been said it can be concluded that the friction coefficient is some way influenced by the rotation parameter of the FSW process. It should be noted however, that for weld trials of 1a and 1b for the work piece, there is some discrepancy since the lower rotation exhibits a higher increase in temperature rate. Possible reasons for this could be due to the camera handling which would lead to, data points being inconsistent when processing the temperature results.

The total heat flux calculated for the tool using equation 10, clearly depicts the heat is mostly concentrated from the middle of the tool outwards and distributed along the weld line, where the temperature would be expected highest in the middle and gradually decrease from the weld line. This type of temperature measurement is difficult to measure experimentally and is where the FEA model would contribute to determining these temperatures. This would also lead to conclusions of the condition at the centre whether sticking is occurring at this point. Together with the aforementioned, correct parameters can then be selected to account for this and also would benefit the tool design.

The convection coefficients for the work piece were first based on an initial assumption that the heat from the top surface was the highest, this was to observe the effects thereof the varying surfaces and what type of convection coefficients one could expect. Average convection coefficients were determined for the dwell period and it can be noted that at higher rotations, the convection coefficients are higher, which relates to the rate at which the heat transfer is occurring. The tools convection coefficients, especially for the clamped part of the tool are very high. Though one can note that for the tools shoulder convection coefficients, they relate very similarly to the FEA convection coefficients used for the first few model runs, after which it was changed to a lower setting for observation purposes. It is however, concluded that for the tool shoulder convection coefficients, one could possibly use 100-300 W/m2_{K when inserting this value into the FEA model.}

Factors contributing to the convection coefficients of the clamped surface could be due to the force value worked out based on the operating conditions of the CNC machine. Since this force value was not measured, there is an uncertainty that it may not be correct. This value also affects that of the other values and could outline certain errors for the calculated heat transfer and hence the convection coefficients in the weld trial samples.

115 Temperature results obtained by placing spots across the weld line (Figures 5.4-5.7) , clearly indicate that a bell shape curve can be made for each of the data points set out in the figures for the temperature plots. The steadier the camera is set, the better the temperature results will be and can observed in the figures where there are erratic lines, although still depicting the correct trend, one will not be able to use those values as reliably as those results which show smoother increases in temperature.

The weld trial did however compare well to each other and although there are many precautions and consideration to take into account when setting up the experimental procedure for the thermal camera, it was noted that a percentage difference of less than 5% for the same parameters was obtained. This then proves to be a very good method in obtaining data since with the correct precautions and set up to consider, it makes the experimental procedure fairly repeatable and therefore a good comparison to be used with the FEA model temperature results.