In order to clarify the contact welding failure mechanism of DC electromagnetic relay, a series of electrical endurance tests are carried out with the use of silver tin oxide material under resistive and capacitive load conditions. The typical waveforms of contact voltage and contact current during making and breaking resistive load and capacitive load (load capacitance of 1mF, 1.5mF, 2mF and 2.5mF) are obtained by the designed model switch. Further, the variations of sensitive electrical parameters such as bounce energy, contact resistance, static contact force and break arc energy during electrical endurance test are analyzed explicitly. It is found that the variations in sensitive electrical parameters is closely related to the electrical load type. In particular, under the capacitive load conditions, the sharp increase of each sensitive electrical parameter in the end of lifetime prognosticates the dynamic welding failure of silver tin oxide contact material. Finally, with the help of SEM (Scanning Electron Microscope) pictures of failed contacts, the surface erosion features of contact materials are mainly determined by the competition between the cathode arc and the anode arc. And the material transfer and distribution are the root reason for the contact welding failure of DC electromechanical relays.

Contact dynamic welding failure problems seriously limit the electrical lifetime of electromechanical relay. However, the welding behavior occurred in contact making and breaking process and relevant influencing factors are still unknown. In this article, a series of experiments are carried out in make only, break only, and make & break (M&B) operation modes individually to differentiate the effects of making and breaking processes on contact dynamic welding. The typical dynamic force and electrical waveforms of contact making and breaking processes are obtained and the statistical results of welding force are presented. The roles of bounce arc and molten bridge in welding force are interpreted explicitly by using the variations in electrical parameters such as bounce energy, contact resistance, molten bridge energy, break arc energy, and surface substructure morphologies. It is determined that the bounce arc plays a crucial role in the formation of weld nugget and strength, and the strongest welding occurs in the M&B operation mode.

Using an electrodynamic-shaker-based test setup, experiments were performed on gold-plated contacts under a variety of fretting conditions, including different vibration frequencies, vibration amplitudes, and different environment temperatures. The variations in contact resistance with fretting cycles are recorded explicitly. The fretted surface is examined using a scanning electron microscope, energy-dispersive X-ray spectroscopy, and a con-focal laser scanning microscope to assess the surface morphology, extent of oxidation, and elemental distribution across the fretted zone. It was found that fretting damage is a complex phenomenon for electrical contact applications. Different fretting regimes, including the robust electrical contact performance, the oxidation-dominated failure, and the transient unstable conductivity failure are determined. Finally, the degradation mechanisms of gold-plated contacts are proposed.

Electrical lifetime and relative dynamic welding failure mechanisms of electromechanical relay for capacitive load are interesting topics in the area of switching devices and contact materials. In this work, silver tin oxide contact material has been tested with a capacitive load by using our designed novel model switch. The typical waveforms of contact current and contact voltage at making and breaking are presented. Further, the variations in bounce energy, static contact force, dynamic contact force, arc energy and contact resistance as a function of operation cycles are plotted and analyzed explicitly. Particularly, the intermittent long-duration arcing phenomena during breaking is observed and explained with the variations in local contact asperities. Based on the collected sensitive parameters, an associated physical degradation mechanism of contact materials under capacitive load is proposed.

Material welding failure considerably influences the electrical lifetime and reliability of low current switching devices. However, relevant studies on methods for calculating the threshold welding current and welding area under milli-Newton scale load forces are very limited. In this paper, the welding characteristics of metal material, including the threshold welding current, welding area and welding force are studied by using theoretical calculations and experiments. The comparison between the theoretical calculation and experimental results shows the accuracy of the built model. Further, the effects of mechanical load force and load current on welding force and welding area of representative metal materials are investigated. It is found that the anti-welding ability of metal materials depends not only on the exerted load force and current, but also the electrical resistivity, the thermal conductivity, the tensile strength, and the melting temperature of the materials.

Dynamic welding failure mechanisms of silver metal oxide composite contact are hot topics in the area of low current switching devices and electrical contact materials. What is the root reason for contact dynamic welding in electrical endurance tests? Is it the degradation of the physical properties of the material or the variations of mechanical operation characteristics or the changes in contact surface morphology? In this paper, a series of electrical endurance tests (including resistive load and capacitive load) are conducted by using our designed model switch. The typical waveforms of dynamic force during contact break are recorded, and then the extraction method for occurred welding force value is presented. Further, the variations in contact gap, arc energy, bounce arc energy, and static contact force as a function of operation cycles are analyzed explicitly. Particularly, the distribution of welding force are counted and explained with the change of collected parameters. Finally, the possible dynamic welding failure mechanisms of contact materials is proposed.