Investigation On Contact System Connection With Resistance Spot Welding And Endurance Of Relay

As an electrical control component,relays play a fundamental and important role in many fields.With the continuous development of science and technology,the technology in these fields has been innovated and the higher endurance of relays are required.Historical failure statistics show that failures of the contact systems are main forms for relays failures.At present,the connection of the contact system still follows the riveting process of the last century.The nature of the connection based on the mechanical deformation will gradually deteriorate the connection relationship between the contact and the moving reed with the increasing of the working-time,which will limit the endurance of the relay.The nature of resistance spot welding is metallurgical bonding,whose connection is stable and reliable.In the paper,a systematic study is made on the connection problem for resistance spot welding and the endurance,which is significant for updating and developing relays with high endurance(electrical endurance 500,000 cycles,mechanical endurance 50 million cycles for AC and 100 million cycles for DC).First,in order to solve the connection problem for resistance spot welding between contacts and moving reeds,based on a number of literature data,the process parameters of resistance spot welding are preliminarily determined by the basis of energy estimation in this paper and resistance spot welding connection tests are carried out.The dynamic process of the resistance spot welding connection is investigated by the finite element method in detail.The test results indicate that the primary process parameters is available for realizing the resistance spot welding connection between the contact and the moving reed.Finite element results indicate that the due to the contact resistance between the contact and the moving reed,diameters of nugget increase rapidly before its thickness.The rapid increase of nugget thickness is mainly caused by the relative size between the body resistance and contact resistance of the contact and the moving reed.There is a corresponding relationship between variations of nugget dimensions and the average temperature of the contact surface,which could provide an available approach for monitoring nugget variations and controlling nugget dimensions.Second,aiming at investigating effects of the resistance spot welding connection for the contact system on the endurance of the relay.Relay samples are manufactured and tested for the electrical and mechanical endurance with meeting the requirements in IEC 61810-7:2006.The test results indicated that the requirement for the electrical endurance of the relay was satisfied but the mechanical endurance was not done.The failure specimens in tests showed that the moving reeds were broken and the fracture positions were similar.All of them were located near by the root of the contacts.Last,in order to realize the high endurance requirement of the relay,the problem of the moving reed fracture was analyzed with mechanical and thermal factors.Effects of thermal factors was analyzed based on variations of metallographic structures and hardness in the fracture position of the moving reed.Effects of mechanical factors was analyzed based on stress distributions and its variations in the relay working process obtained by finite element dynamic simulation.By analyzing and combining the macro-morphology and micro-morphology of the fracture,the main cause of the fracture is determined by thermal factors and improvement measures are put forward.It is verified through experiments and tests that the improvement measures are reasonable and effective.