The Key Technology Research Of Laser Thermo-repairing On Grey Cast Iron Equipment Surface

Now, in field of heavy mechanized equipments, castings made of grey cast iron are beingwidely used. Under the bad working conditions, the cracks are very common to generate atthe surface of equipments. It is becoming an urgent problem that must be solved at present torepair failure parts quickly and realize recycling manufacture of machinery, and which hasbecome an important research project in the field related. Because of the advantages of highpower laser technology in areas of material process, a method of laser thermo-repairing is putforward. The research works in this paper are mainly based on the following content:Study the heat transfer law through analysing the interaction of the laser, the substrateand the repair powders. The dynamically simulation of repair powders feeding is conductedthrough birth-death element technology. Meanwhile, the mathematical expression of a newcombined body heat source is presented and the constraints of the workpiece on theworkbench are simulated by the contact connections. The numerical simulation of the laserthermo-repairing overall process on surface of the gray cast iron is established. All the workscan provide reliable research method and means for the quantitative analysis of the heattransfer and mechanical behavior during the process of the laser thermo-repairing process ofthe material surface.For achiving the repairing process, laser thermo-repairing project is designed for thecrack defect on grey cast iron surface to comfirm the category of alloy powders that can beused to repair. Through the research of metallurgical combination states of repaired zone andmatrix, the character of microscopic organization and the transform disciplines are definite.According to the research,with the continuous laser energy function, the differentcombinational states form between the different alloy powder materials with matrix; so thatthe thermal repairing technology can be flexibly adjusted according to the actual workingcondition requirements and the performances can be improved.According to the epaired layer features, three-point turn-off tests are adopted to analyzethe fracture performance and bond strength. The influence laws of laser repairing on matrix fracture toughness and combining strength are compared. It is found that the anti-crackingability is improved. By further analysis of the crack from repaired zone and its propagation,the anti-cracking model is founded which reveals the crack resistance mechanism of repairedlayer, identify that the laser thermal repair system can keep the original strength of the graycast iron, the fracture toughness of the material can also be strengthened.Through numerical simulation and experimental study, substrate size, laser processingparameters and medium environment as well as its model of action are the importantinfluencing factors on laser thermo-repairing. Substrate size and medium environmentinfluence the internal heat conduction of substrate and its heat exchange with the outsideworld, thus immersion type fluid environment can help to reach the performance requirements,such as the special hardness and wear-resisting, etc. Additionally, laser parameters collocation,based on experimental results, can obtain the better parameter combination between the highanti-cracking toughness and the moderate hardness.A strategy of laser partial self-preheating is designed in order to improve the repairingqulity, and the influence of different preheating processes on repairing effectiveness isanalyzed through numerical method and experiment study which determines the appropriatepreheating process parameters. The laser partial self-preheating can effectively reduce thelevel of thermal tensile stress and make the distribution of residual stress more reasonable.Through this strategy, the Crispy hard phase and white iron texture are reduced whichhomogenizes the texture and decreases cracked initiation rate at the end of graphite. Thismethod has a better preheating effect compared with the other existing methods whichprovides theory support, and a flexible and efficient technology to perfect the laser thermalreparation system and improve the repairing quality.The powder conveying and workpiece feeding are important effect factor on repairingperformances. Therefore, the structure parameters of laser coaxial powder spray nozzle areinvestigated in order to clarify their effects on the powder focus and concentration distribution.So, a vertical coaxial powder nozzles and its sending device are designed, which can beapplied to the carrying and gravity feeding style; meanwhile, the focus of the powder flow canbe adjusted. Then, a new type laser repairing work table is designed by using the linear motordrive with characteristics of high precision and fast responding, and the motion parameters aredetermined. The digital prototype of repairing work table is set up, and by the motionsimulations, the table movement is smooth and can fulfill the repairing demand.