Microstructure and Mechanical Properties of Narrow Gap Laser-Arc Hybrid Welded 40 mm Thick Mild Steel
Both laser-arc hybrid welding and narrow gap welding have potential for the fabrication of thick sections, but their combination has been seldom studied. In this research, 40 mm thick mild steel was welded by narrow gap laser-arc hybrid welding. A weld with smooth layer transition, free of visible defects, was obtained by nine passes at a 6 mm width narrow gap. The lower part of the weld has the lowest mechanical properties because of the lowest amount of acicular ferrite, but its ultimate tensile strength and impact absorbing energy is still 49% and 60% higher than those of base metal, respectively. The microhardness deviation of all filler layers along weld thickness direction is no more than 15 HV0.2, indicating that no temper softening appeared during multiple heat cycles. The results provide an alternative technique for improving the efficiency and quality of welding thick sections.
Formation and suppression mechanism of lack of fusion in narrow gap laser-arc hybrid welding
In this study, the main defect, i.e., lack of fusion (LOF), occurring at the sidewalls in narrow gap laser-arc hybrid welding (NGHW) was confirmed to depend on the cross-sectional shape of previous pass, which was classified into four types, namely concave, convex, middle convex, and inclined shapes. Only the concave shape was effective in suppressing the LOF because the sharp corner between the weld and sidewalls could not be completely filled by next pass in the other three types. The effects of the welding parameters on the concave degree of weld cross-sectional shape were obtained from the dimensionless analysis related to the driving forces in the molten pool. It was found that the welding parameters, namely the arc current, welding speed, and groove width had a significant effect on the concave degree, whereas the laser power and laser-arc distance had no direct effect. A semi-quantitative criterion was proposed to predict the occurrence of the LOF. The LOF was suppressed when the ratio of the electromagnetic force to the liquid viscosity force was larger than 3.21 × 105, and the ratio of the surface tension gradient to the liquid viscosity force was larger than 1.28 × 104. The suppression mechanism of the LOF in NGHW was discussed in terms of the forces and melt flow in the molten pool.
Fault Diagnosis and CAN Bus/Ethernet Redundancy Design of a Monitoring and Control System
The ship monitoring system is used to monitor and control the working status of various equipment on the ship. The navigational safety of the ship is affected directly by the stable working of the monitoring system. In this paper, a ship monitoring system with fault-type judgment function and bus redundancy is designed to improve system reliability and reduce fault checking cost. A redundant Ethernet/CAN bus communication network is constructed in the system, which connects multiple simulation nodes. The simulation node can simulate the faults that may occur during the communication process and feeds back the fault information to the host computer. The host computer will analyze and display the corresponding fault type on the user interface with the feedback information is received. The system reconfigures the network route autonomously when the simulation node has a communication fault. Routing of fault nodes can be switched to redundant routing, and the load balancing of the communication network can be maintained. Through experimental tests, the system can accurately locate faults and achieve fast switching of redundant routes between buses. Hence, the reliability of data transmission is improved.