| The electro-mechanical equipment industry makes extensive use of powder metallurgy composite contacts in circuit interruption mechanisms and joins these contacts to conductive metals by resistance brazing. This research examines the resistance brazing process for joining these materials and presents a methodology for quantitatively investigating and modeling the process.; The objectives were to: (1) Quantify the effects of the process parameters on joint quality, (2) Optimize the process, (3) Develop an empirical model of the process, (4) Develop and substantiate a numerical model of the process. The methodology presented accomplished these objectives and provided a framework for comprehensive investigations of similar processes.; A database was developed through orthogonal, fractional factorial experiments which provided the foundation for optimizing, empirically modeling, and numerically modeling the resistance brazing process, as well as, quantitative insights into the contributions of the parameters controlling the process.; The resistance brazing process parameters investigated included: current, pulses, heating cycles, cooling cycles, electrode force, filler metal thickness and alloy, contact material, base material surface condition, and electrode degradation. Joint quality was measured by evaluating the maximum shear stress of the joint during a destructive torsional test, and by measuring the amount of molten material not retained by the joint. These quality measurements generally conflict and the work presented provides a method of interpreting and resolving this conflict.; A thermal response model of the resistance brazing process was developed to predict the effects of the process parameters. This transient one-dimensional model incorporated interfacial resistivities, Joule heating, phase change, and the temperature dependence of thermal and electrical material properties. The model was validated by comparing the predicted filler metal temperature with micrographs of the joint interface. The model was also correlated with the maximum shear strength of the joint.; The process examined was optimized and a local empirical model of the process developed. The optimized process was robust and expected to produce at a zero-defect level within the scope of the work. The quantitative observations can be extended to other geometries via the numerical model which can also be readily adapted to other resistance brazing processes and joints. |
