Study On Cutting Mechanisms And Quality Improvement Methods Of Abrasive Water Jet

Abrasive water jet(AWJ)has powerful cutting ability,which can cut almost all hard-to-cut materials.However,the workpiece cut by abrasive water jet often has quality defects such as striation and kerf taper,which seriously limits the further application and development of this technology.This paper started with the structure and the energy distribution of abrasive water jet.The mechanism of material removal by abrasive water jet was analyzed.The formation mechanism and main characteristics of cutting defects were studied.The essence and internal relation of the influences of process parameters on cutting indexes were analyzed.The models were built from multiple points of view and the strategy of rapid selection of process parameters was given.On this basis,several effective ways to improve cutting quality were put forward.Finally,the method of stacked cutting to improve cutting efficiency was explored.The main research contents of this paper are as follows:(1)The research of erosion characteristics and erosion characteristics of abrasive water jet.Based on the analysis of structure of abrasive water jet and distribution of abrasive particles,velocity of abrasive water jet,and energy of abrasive water jet,as well as the study of the material removal mechanism of abrasive water jet erosion,the erosion characteristics were summarized.Based on the analysis of erosion characteristics of abrasive water jet,an analysis model of erosion characteristics of abrasive water jet based on nozzle tilt erosion was proposed.Based on the model,the effects of abrasive impact and shear on material removal were analyzed.The research results effectively improved the understanding of the process of abrasive water jet erosion,and verified the dominant role of impact in material removal.(2)The formation mechanism and related characteristics of striation and kerf profiles.The shortcomings of the theory of striation formation based on radial distribution of jet energy were analyzed,and a new formation mechanism of striation was proposed based on the widely accepted theory of cutting step.The effective erosion boundary of abrasive water jet was analyzed,and the relationship between the effective erosion boundary and the kerf profile was studied.On this basis,the formation mechanism of the kerf profiles was proposed.The main differences and relations between jet lag and kerf taper were analyzed.The composite effect of jet lag and kerf taper on the dimensional deviation of the upper and lower surfaces of the workpiece in the jet curve cutting was studied.On this basis,the overall control idea of the total dimension deviation based on the characteristics of the consistency of the influence of process parameters on the cutting indexes was given.(3)The influence mechanism of process parameters on cutting indexes and its internal relation.The erosion and cutting experiments of abrasive water jet and plain water jet were carried out.The role of abrasive particles undertaking major material removal task in abrasive water jet machining was clarified again.The single factor experiments of cutting depth with four main process parameters were carried out.The influence law of process parameters on cutting depth was studied.The influence stage and relation of process parameters on jet cutting were clarified.On this basis,the essence of the influence of process parameters on cutting performance was further analyzed.The internal consistency of the influence of process parameters on cutting depth,cutting quality and space for improving cutting efficiency was clarified.(4)The built of simulation model,arithmetic model and mathematical model of abrasive water jet.The simulation models of formation process and erosion process of abrasive water jet were built respectively.The output of the simulation of formation process of abrasive water jet was used as the input of the simulation of erosion process of abrasive water jet.Through this way,the whole process simulation of abrasive water jet machining was realized.The BP neural network prediction model for abrasive water jet cutting was built.With the data from orthogonal experiments and single factor experiments as sample data,the BP neural network was trained by using MATLAB.Taking the material removal volume as the focus,the mathematical model of abrasive water jet cutting depth was built based on the equivalent relation between the micro-removal and macro-manifestation of material by abrasive water jet.(5)The built of process parameter back-stepping model and the realization of rapid selection of process parameters.A strategy for selecting process parameters based on cutting depth prediction models was proposed.However,it was found that the strategy is still not direct enough for selecting process parameters.In order to get rid of the trial-and-error link of process parameter selection completely,based on the high flexibility of artificial neural network,the back-stepping model of process parameters was built by adjusting the structure of the cutting depth prediction model of BP neural network.According to the prediction accuracy error of the cutting depth prediction model of BP neural network,a guarantee coefficient was introduced to modify the target cutting depth to ensure that the parameters predicted by the model can cut off the workpiece.Through these operations,the rapid selection of process parameters was realized.(6)The methods of improving cutting quality of abrasive water jet.The limit of improving cutting quality by optimizing process parameters was analyzed.Aiming at this problem,the secondary cutting methods including secondary cutting and reversed secondary cutting were put forward,the multipass cutting methods including trimming-cutting and deepening-cutting were put forward,and the 3D nozzle tilt cutting method integrating the two existing nozzle tilt cutting methods was put forward.The cutting characteristics,advantages and disadvantages of various cutting methods were studied and compared.The selection priorities of various cutting methods were given for different cutting requirements.These cutting methods provide several feasible ways to break through the limitation of process parameters and further improve the cutting quality.(7)The cutting quality control strategy of stacked cutting and the built of cutting depth prediction model.In order to multiply the cutting efficiency of abrasive water jet,a method of stacked cutting was proposed based on the powerful cutting ability of abrasive water jet.The influence of workpiece thickness on cutting quality was analyzed,and the characteristics of abrasive water jet stacked cutting were studied.On this basis,the cutting strategy of stacked cutting that can get better cutting quality was given.Referring to the modeling idea of the mathematical model of cutting depth,a prediction model of cutting depth for two-layer materials stacking was built,which was further extended to the prediction model of cutting depth for multi-layer materials stacking.