Ceramic Electrode/Steel Diffusion Welding Residual Stress Simulation And Process Optimization

Oil well logging is the the most basic and most important part of the oil industry. Downhole environment has the characteristics of high temperature and high pressure, magnetism, electricity and other external environment also can produce larger interference, sensors that cause the common material in underground work cannot accurately measure the downhole data. Ceramic materials of high temperature resistant performance is wonderful, and it has excellent wear resistance and chemical corrosion resistance, excellent ceramic performance enough to satisfy the operation conditions of downhole complicated conditions, so the ceramic sensors in oil well logging has wide prospect of application. Although the advantages of ceramic sensors, but about the spread of ceramic and steel welding residual stress, the residual stress in the process of use, lead to ceramic electrode will appear the phenomenon of cracking, lead to inaccurate measurement data, and bring adverse effect to the production, so the ceramic and steel diffusion welding residual stress is very important.Based on the comprehensive, diffusion welding of ceramic and steel at home and abroad, on the basis of analysis to discuss two main form of ceramic and steel diffusion welding simulation, one is the simulation of the formation of joint element diffusion and reaction, is a joint simulation of deformation and stress behavior. After through research contrast, joint deformation and stress behavior of the simulation method are adopted to simulate the Al2O3 ceramics and the changes of diffusion welding residual stress of 45 steel and process optimization. This paper mainly research on without the middle tier, Al2O3 ceramics with spread of 45 steel after welding residual stress distribution rule, through comparing three direction of axial stress and shear stress under three planes, to determine the maximum axial stress and maximum shear stress, and then through the study of location, stress by ceramic electrode in the use of the cracking in the process of situation, stress mainly is the study of ceramic internal and joint stress, thus to determine the research stress for x axial stress and shear stress xy. Through without the middle layer, on the basis of study of single layer, copper, titanium, nickel and three kinds of single layer on the joint and ceramic internal residual stress change rule; And analysis of the three different layer under the condition of different thickness of the impact on the residual stress distribution rule. Determination in the middle layer thickness, and then study respectively the three different materials with 0.5 mm thickness for free combination, to explore a better way of combination, and determine the principle of configuration. In determining the proper under the condition of the middle layer, simulation studies for welding parameters.In this paper, by using the finite element software ANSYS to simulate the Al2O3 ceramics and the spread of the 45 steel welding residual stress behavior, analysis of different middle tier, the influence law of temperature and pressure on residual stress, the results show that:(1)The add of interlayer creates a significant result on relieving the residual stress in the joint surface and the inner ceramic, when adopted a single interlayer, the residual stress produced by metallic copper and the inner ceramics in the joint interface is apparently less than the metal titanium and nickel; with the increase of the thickness of the intermediate layer, the residual stress is increasing, but when it’s too thin, it not only can not play the role of barrier, but the creep will also be slow, so there should be an appropriate value of the thickness of the intermediate layer. The paper opted 1mm thickness of the interlayer; when using double intermediate layer, the placement of different materials to comply with thermal expansion coefficient and elastic modulus incremental principle; combinations of these types of intermediate layer composed of titanium and copper layered intermediate layer to reduce the effect of residual stress better than other combinations, and titanium and copper thickness ratio exists an optimal value, we use the thickness of the titanium is 0.4mm, the thickness of the copper is 0.6mm;(2) In the case of other process conditions do not change, just by changing the cooling temperature won’t have a significant influence on the residual stress, the paper simulated 830℃,930℃,1030℃,1130℃, with increasing temperature the overall distribution of the residual stress barely changes, but the residual stress increased slightly, which is somewhat different from the actual situation, theoretically the higher the temperature, the easier atom diffusing, which helps to enhance the welded rate. However, excessive temperature leads to the larger welding deformation amount, there should be an appropriate value to ensure the welded rate. By simulation, we choose 930℃ as the appropriate temperature;(3)With respect to changing the cooling temperature, the change of cooling rate for residual stress is more significant. In this paper it simulated 5℃/min、10℃/min、15℃ /min、20℃/min types of cooling rate, σx maximum possible difference 17.9MPa at most, τxy maximum can vary 10.7MPa, cooling faster, the greater the residual stress,but still change the cooling rate has little effect on the overall stress distribution;(4) In the initial cooling time, the stress change is very intense, while in the middle and later periods, the stress changes relatively little, by changing the cooling rate at different stages, both can achieve the purpose of reducing the residual stress, it can also save a lot of time and improve production efficiency. In this paper, it concluded that it should be cooling at the rate of 5℃/min in 40min, and then cooling it at the speed of 20℃/min by simulation;(5) With the increasing welding pressure, the type of welding pressure we simulated in this paper of 10MPa、20 MPa、30 MPa、40 MPa, the axial stress σx and the shear stress τxy also increased, but they just change slightly. With the welding stress increased, the maximum stress of the axial stress σx decreases, while with the stress increased, the maximum stress of ay also increased, the Add Effect of welding pressure is significantly no matter whether is tensile stress or compressive stress. By simulation it consider that the weld pressure of 15 MPa is appropriate.