Causes And Elimination Strategies Of Defects In Abrasive Water Jet Machining On Polymer Matrix Composites

Polymer matrix composites have been increasingly widely used in many advanced industries,such as aerospace,military and national defense with their high specific strength and high specific modulus.However,due to the obvious anisotropy and heterogeneity,the machining damages such as burrs,tearing and delamination are produced easily.The high tool cost in the traditional processing has also become a hindrance to its large-scale application.As an emerging non-traditional cold processing technology,abrasive water jet processing is increasingly valued at home and abroad for its advantages of no thermal damage,small cutting force,flexible processing,wide range of materials to be processed,green environmental protection and low processing cost.Its material removal mechanism,which is completely different from traditional processing,makes it a more innovative technology for processing composite materials.However,for hard-to-machine materials such as polymer matrix composites with large thickness,due to the unique material removal mechanism of abrasive water jet,there are still many different kinds of defects in the process of processing,which are embodied in the taper of the kerf,the deformation at the bottom of the kerf,the striation zone of the kerf side wall,the high surface roughness at the bottom of the kerf side wall and delamination,etc.How to reduce the processing defects of hard-to-machine materials,such as polymer matrix composites with large thickness,and improve their processing accuracy and surface quality,is one of the most urgent problems to be solved in abrasive water jet machining.Based on the project funded by the National Natural Science Foundation of China and Liaoning Joint Fund(Project No.U1708256),“Research on Abrasive Water Jet Machining Technology for Aero-engine Complex Curved Surface Parts”,this paper aims at the “under-processing” and “over-processing” defects in abrasive water jet machining of difficult-to-machine materials represented by polymer matrix composites.Taking large thickness aramid fiber composites and carbon fiber composites as examples,the common defects of kerfs were characterized by experimental study,the causes of defects were analyzed,the process optimization was carried out,and the corresponding defect reduction methods were put forward.The forward and side feeding directions of abrasive water jet processing are defined,and the processing areas of abrasive water jet are defined.The single(multiple)cut-off processing(rough cutting),abrasive water jet precision cutting and abrasive water jet finish cutting are proposed.Microscopic observation and variance analysis show that the above methods can effectively eliminate the “under-processing” and “over-processing” defects in the process of abrasive water jet machining of polymer matrix composites,effectively control the processing shape and position accuracy,and achieve the consistency of surface roughness from top to bottom.The processing quality of different methods under the condition of equivalent efficiency is compared and analyzed.The results show that the abrasive water jet technology strategy of “rough-precision-finish cutting” for polymer matrix composites can be an effective method to achieve higher quality kerfs in engineering practice.Based on this strategy,the corresponding dimension accuracy control principle is put forward,and a set of relatively perfect abrasive water jet finishing method for polymer matrix composites is formed on the whole.Preliminary experimental results show that the method can also be effectively applied to the forming of convex surfaces of polymer matrix composites represented by spherical cylinders,and can obtain better machining accuracy and surface quality.