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In order to understand the effects of different content of copper vapor entering the arc plasma on the arc behavior, the tungsten-copper materials with copper contents of 0%, 10%, 20% and 30% were made into special tungsten electrodes, which replaced the melting electrode to generate copper vapor. The effects of different content of copper vapor on the arc morphology, arc voltage, arc pressure, current density and arc axial temperature were studied. When copper vapor was transported into the arc plasma, the arc consisted of two parts: a high brightness arc core and the surrounding green luminous area. Through the observation and measurement of the stabilized arc, the results showed that as the content of copper vapor increased, the radius of the greenish region gradually increased, the brightness and size of the core area gradually decreased, the axial temperature of the arc gradually decreased and arc voltage gradually increased with a maximum difference of 1.5 V. This is because the increase of copper vapor concentration changes the net emission coefficient, resulting in a decrease in arc temperature and electrical conductivity. The distribution of arc pressure and current density showed unimodal distribution on the anode surface, and as the content of copper vapor increased, the distribution curves were gradually flattening. A factor contributing to this is that with the increase of copper vapor concentration, the current tends to flow through the edge of the electrode, which expands the conductive path and makes the arc disperse. And the coupling mathematical model of tungsten electrode and arc were established to further explain the experimental results.
At present, conventional flame correction has shortcomings such as random heating route and low efficiency. The welding seam of the aluminum alloy ship frame skin structure is concentrated and the frame restraint is large. It is difficult to control and eliminate the local convex deformation after welding. In order to improve the conventional orthopedic technology and improve the orthopedic efficiency, the pre-elastic deformation technology is proposed. Using the method of combining numerical simulation and experiment, the orthopedic effect of conventional and pre-elastic orthopedic technology is studied, and the influence of pre-deformation variables and heating path on deformation control of the frame skin structure after welding is simulated. The simulation results show that the technical key to the control of convex deformation lies in the control of the pre-elastic deformation and the setting of the heating route. The experimental verification results show that the pre-elastic deformation technology has a better control effect than conventional orthopedics, can significantly improve the orthopedic efficiency, and provides a new method for deformation control in the shipbuilding industry.
This study has been conducted to evaluate the application of silver nanoparticles (NPs) in Electrically Conductive Adhesives (ECAs), filled with hybrid silver flakes and NPs, and silver flakes as a control sample, at a filler loading of 78 wt.%, 83 wt.% and 88 wt.% and cured at 150 ℃ and 180 ℃, respectively. The results show that the electrical and thermal conductivities of ECAs were improved with the increasing of filler loading and curing temperature. Adding silver NPs in silver flakes negatively affected the electrical and thermal conductivities of ECAs at a low filler mass fraction of 78 wt.%, because the segregation of NPs enlarged the average distance of silver flakes; while it positively influenced the electrical and thermal conductivities of ECAs at a loading ratio of 88 wt.%, probably due to NPs filling in the gaps between silver flakes or even sintering together with each other or with silver flakes, especially when curing at high temperature of 180 ℃.
In order to establish the groove model for intersecting structures of circular tubes, mathematical model of the intersecting line is established by the method of analytic geometry, and parametric equations are thus determined. The dihedral angle, groove angle and actual cutting angle for any position of the intersecting line are derived as well. In order to identify groove vectors for two pipes, a new analytical method, i.e. coplanarity of vectors, is further proposed to complete the groove model. The established model is virtually verified by programming and simulation calculation in the MATLAB environment. The results show that groove vectors of intersecting structures simulated by MATLAB are consistent with the theoretical groove model, indicating that the theoretical groove model established in this paper is accurate, and further proves that the proposed coplanarity of vectors for solving groove vectors is correct and feasible. Finally, a graphical user interface (GUI) is developed by MATLAB software to independently realize functions such as model drawing, variable calculation and data output. The research outcome provides a theoretical foundation for the actual welding of circular intersecting structures, and lays an essential basis for weld bead layout and path planning.
Dilution of a pad weld must be limited to a certain critical level to improve its wear and/or corrosion properties. To do that, a novel single wire indirect arc metal inert gas welding process operated in streaming mode was realized. A metal inert gas welding torch, arranged perpendicular to a substrate in vertical position, is fixed with an auxiliary tungsten electrode horizontally. The arc is ignited between a wire through the torch and the auxiliary electrode. The substrate is not electrically connected. The welding current is set in the range of streaming mode. 304 stainless steel was pad welded on Q235 substrates in vertical position by this process. Microstructures were analyzed with optical microscope. Dilution ratios were measured with stereo light microscope and calculated. The results show that, after eliminating interference of the massive torch setup, the dilution ratio of the pad weld with optimized parameters is 5.07%, much less than that with a metal inert gas welding process, which is 26.46%. The pad weld is bonded to the substrate without defects. Microstructures of the pad weld consist of columnar austenite and ferrite between the columns. The dilution ratio increases with increasing welding current or welding velocity, and decreases with increasing distance to the substrate.
Due to local uneven heating during the welding process, the residual stress of the structure after welding affects the reliability of it. In order to ensure the reliability, it is of great significance to test the residual stress distribution of the welded joint. It has always been the focus to find a simple and feasible method for residual stress testing to quickly and accurately obtain the residual stress distribution of welded joints. The mechanical measurement method has high measurement accuracy, convenient and easy operation, but it will cause certain damage to the components. Physical measurement method can avoid damage to components, but its test cost is usually high, and its measurement accuracy can also be affected by the material microstructure characteristics of welded components. Based on the advantages and disadvantages of these two residual stress test methods, a modal test method is proposed. This method is a non-destructive measurement method. Based on the mathematical relationship between the residual stress of the welded structure and the natural frequency (mathematical model), the natural frequency is measured through the modal test to calculate the residual stress quickly. However, it is difficult to establish a mathematical model with this method, and it is not suitable for realization.
Ceramic-copper substrate is used to achieve the combination between copper and ceramic (Al2O3 or AlN) under high temperatures by bonding or brazing process, then through dedicate lamination – etching technology to develop the designed layout in copper surface, finally parts go with plating and singulation process for surface treatment before shipping to the end-user. Ceramic-copper substrate has perfect performance in terms of insulation, thermal conductivity, solderability, and adhesion strength. Besides, the copper on surface can afford huge current due to the fact that ceramic has good reliability and thermal-cycling performance. According to technical visit and audit to suppliers’ manufacturing process and based on several years’ experience of mass production for electric vehicle power module package, this article introduces two mainstream ceramic-copper substrate processing methods currently on the market: direct bond copper (DBC) and active metal brazing (AMB) which can be widely used for the intelligent power module and electric vehicle power module, also introduces the major failure mode during application and analyzes the root cause for each failure mode, clarifies key incoming monitoring method, like crosshatch, silver plating thickness measurement and blister test. This article also clarifies the Incoming Quality Control system, which can provide guidance to process engineer during the application.