[show abstract][hide abstract] ABSTRACT: The purpose of this study is to estimate temperature distribution in the vicinity of weld interface during a friction welding process involving an upset process. On the base of a simple model of friction heat input, a non-steady heat conduction analysis was carried out by finite element method. As a result from a comparison of the estimated temperature distribution with the experimental data, it turned out that the friction heat input model that allowed for the effects of temperature and linear velocity on the friction coefficient was appropriate. This heat input model could simulate adequately the change in friction heat input and temperature distribution in a friction welding process. As a result, the relationship between burn-off length and temperature distribution in upset process has been explained and also the relationship between temperature distribution and width of heat-affected zone has been obtained. This heat input model allows us to estimate temperature distribution in friction welding, from friction pressure, rotation speed and the thermal property of base metal, even where a friction-welding machine does not have a function of torque measurement.
Journal of High Temperature Society. 01/2007; 31(4).
[show abstract][hide abstract] ABSTRACT: The effect of heat input on joint strength in the brake type friction welding has become clear, but the effect in the inertia type friction welding is not clear even at present. Then in this report, inertia type friction welding of 6061 aluminum alloy was carried out in order to examine the effect of unit heat input, burn-off length and burr shape on the joint strength. The heat input (mechanical work) was calculated by burn-off speed and welding pressure in the final stage. The joint strength was examined by tensile test. The final stage (welding time) of inertia type friction welding corresponding to the upset stage of brake type friction welding was searched using the relationship between heat input and joint strength. Using the most proper-final stage obtained, the relationships between unit final deformation heat input and joint strength, final burn-off length and joint strength, and burr shape and final deformation heat input were examined. Also the minimum unit final deformation heat input and minimum final burn-off length required for making a sound joint were also examined. The results showed that within this experiment the most proper-final stage (welding time) was 0.1s, and the limit unit final deformation heat input and limit final burn-off length were 19J/s and 0.3mm, respectively.
Journal of High Temperature Society. 01/2007; 32(2).
[show abstract][hide abstract] ABSTRACT: An approach to combine a friction heat input model with a non-steady heat conduction analysis has enabled a numerical simulation of a heat input and a transient temperature distribution in friction welding processes. This report describes the result obtained by applying this approach to the friction welding process of two similar materials of S25C carbon steel or SUS304 stainless steel. When base metals are different, the friction heat input model and the thermophysical property data are changed depending on a quality of base metal. Comparison between a calculated result and an experimental result was carried out, and appropriateness of this approach was examined. Furthermore, a difference of temperature distribution in friction welding region with the difference of thermophysical property of base metal was examined, and also the heat-affected zone was investigated. As a result, it was verified that this approach could simulate a characteristic of a welding process in brake-type friction welding. And the calculated results agreed with the experimental results on a difference of quantity of heat input to be caused by a difference of a friction welding condition. A difference of a temperature history caused in a different base metal appeared to be estimated from a calculated result, and it was confirmed that this approach was appropriate. The width of heat-affected zone was estimated by an calculated result of the maximum temperature distribution in the vicinity of friction surface by using this approach combining a friction heat input model with a non-steady heat conduction analysis.
Journal of High Temperature Society. 01/2007; 32(4).
[show abstract][hide abstract] ABSTRACT: Due to the collimator aperture, the spatial resolution of SPECT data varies with source-to-detector distance. Since radius of detector rotation is bigger when scanning larger patients, the spatial resolution is degraded in these cases. Emitted gamma rays travel not only along the central axis of the collimator hole but also off-axis due to collimator aperture. However, an off-axis ray at one angle would be a central-axis ray at another angle; therefore, raw projection data at one angle can be thought of as an ensemble of central-axis rays collected from a small arc equal to collimator aperture. Thus, fine angular sampling can compensate for collimator blurring. By using sampling pitch of less than half the collimator aperture angle, compensation was performed by subtracting the weighted sum of the projection data from the raw projection data. Collimator geometry and detector rotation radius determined the weighting function. A cylindrical phantom with four different-sized rods and torso phantom for Tl-201 cardiac SPECT simulation were used for evaluation. Aperture angle of the collimator was 7 degrees. Projection sampling pitch was 2 degrees. In both phantom studies, the proposed method showed improvement in contrast and reduction of partial volume effect, thereby indicating that the proposed method can compensate adequately for image blurring caused by collimator aperture