Study On Metal Rapid Prototyping Based On Arc Welding Robot

In recent years, the technology of metal rapid prototyping based on arc welding, which has the advantages of lower cost and higher efficiency, has become the research hotspot in the fields of material processing and advanced manufacturing. However, this technology has the deficiency of shaping precision and property because of more adjustable parameters, less controllability of weld pool shape and the complexity of thermal cycling in arc welding process. In this thesis, system composition, process control and shaping process are studied. The study has important theoretical significance and practical value for the application of metal rapid prototyping based on arc welding.A system of welding rapid prototyping is established, in which the MOTOMAN HP6 arc welding robot serves as a main body. Combined with the Al-alloy MIG rapid prototyping, the main research contents in this thesis are listed as follows.First, the system of metal rapid prototyping based on arc welding is studied. The hardware and software of system are designed with an emphasis on system composition, process control and off-line programming. The system hardware is composed of arc welding robot, MIG welding machine and infrared sensing and monitoring system of point temperature scan measurement. The path planning scheme of interlayer and bead is proposed according to the characteristics of metal rapid prototyping based on arc welding. The metal rapid prototyping off-line programming is implemented primarily, which solve the transformation problem between off-line planning data and job file of MOTOMAN robot.Second, the analysis and research of temperature monitoring in metal rapid prototyping process are carried on. Because metal rapid prototyping based on arc welding is realized by welding layer by layer, the thermal cycling of rapid prototyping is more complex. In order to improve shaping precision, the infrared sensing and monitoring system of point temperature scan measurement is set up by using infrared radiation thermometers (Optris CT20). The initial temperature variation of workpiece in air cooling condition is on-line predicted using regression prediction.Third, fitting analysis of characteristic shaping dimensions is carried on by using radial basis function neural network with heat input and initial temperature of workpiece as main variables. From the E-T0 fitting surfaces of bead width (B), bead penetration depth (H) and bead height (h), B, H and h increase with the increasing of E; however, B and H increase with the increasing of the workpiece preheating temperature T0, and h decreases with the increasing of T0. Heat input and preheating temperature of workpiece are the important factors for the characteristic shaping dimensions of metal rapid prototyping based on arc welding.Forth, the influence law of the droplet transfer form, heat input and initial temperature of workpiece to shaping precision is studied, and the shaping process of droplet transfer with the combination of short circuit transfer and spray transfer is proposed. This process has the advantages of short circuit transfer and spray transfer. Compared with spray transfer, this process can improve stability of shaping dimensions and reduce average heat input of bead.At last, vickers hardness and surface stress of formed parts are measured, and microstructure analysis of formed parts is made. The results show that the average hardness of weld center is larger than the hardness of fusion zone, and under the condition of same heat input, short circuit transfer shaping leads higher Mg wt%; for short circuit transfer shaping and spray transfer shaping both, Mg wt% decreases with heat input increases. Combination transfer shaping compromises low Mg loss and high deposit rate, which is favor of grain refinement and improving strength of Al-alloy bead.