Machining Technologies Of High Performance Lightweight Materials And Composite Components

The lightweight laminated composite components made up of high performance lightweight materials have a broad application prospect in armor protection field, and the key materials of composite components are engineering ceramics and fiber reinforced plastic composites (FRP). Usually, afterprocessing is necessary for the lightweight composite components before assembling, such as drilling, cutting, slotting, etc. Remarkably, hole drilling is the main form. Engineering ceramics and FRP are all difficult-to-machine materials and their performances are distinct, so machining composite components is extremely difficult. Based on traditional machining methods, this dissertation presented an intensive and systematical study on machining technologies of lightweight composite components, thus providing technical supports for the application of lightweight composite components.Firstly, an indepth research was conducted on the machining process of the ceramic composite component. The development of the special sintering diamond thin-wall bit was detailed from such aspects as ceramic drillability, diamond parameter, bond parameter and sintering process. The copper based matrix of complex alloy and hot pressing process were introduced. The machining mode with constant feeding pressure was determined through drilling experiment, and the process equipment with compressive pre stress exerted on the drilling zone was proposed to improve the machining quality. Moreover, water was used as the cutting coolant. Also, the machining process is suitable for machining engineering ceramics, fiber reinforced plastic composites and the similar lightweight composite components.Secondly, the machining mechanisms of lightweight composite component were studied theoretically and experimentally. After the calculation expressions of mean load and cutting depth per diamond on the lip face were set up, the forming mechanisms of ceramic ground surfaces was presented, with the indentation fracture mechanics of ceramics combined. Through SEM observations of ground surfaces, the material removal modes and grinding damages of ceramics were analyzed. Also, the forming model of abrasive dust was established. The results show that most of ceramic ground surfaces are formed through brittle fracture and few through ductile deformation. There is small effect by grinding on pore area, however, grinding damages in areas of looseness and crystal boundary during grinding are evident. Microcracks are few in the ground surfaces generated by brittle fracture, but in the surfaces generated by abrasive scratching microcracks are plentiful. Theoretically, the drilling mechanism of FRP was analyzed. Through SEM observations, the fracture mechanisms of glass fiber and Kevlar fiber and the characteristics of ground surfaces of FRP were studied. The results indicate that the essential of drilling is that fibers are broken by shearing, stretching or bending under the actions of abrasive grains. There are six kinds of broken appearances for glass fiber but seven kinds for Kevlar fiber. And, the whole ground surface of FRP can be divided into two kinds of area, namely the area covered with polymer and the area dominated by broken fibers, with three kinds of fiber fracture area found, which influences the surface quality greatly. The drilling procedure of the ceramic composite component was analyzed, and the bit skidding mechanism in exit area was studied. Furthermore, the empirical formula for drilling engineering ceramics by using sintering diamond bit was built through multiple regression analysis.Thirdly, the overall analysis on bit wear was conducted from such four views as wear converting phase of the lip face, bit skidding, microscopic abrasion morphology and macroscopic wear regularity. The mechanisms of wear converting phase of the lip face and bit skidding were studied theoretically and experimentally. Through SEM observations, the abrasion appearances of abrasive diamond and bond matrix and the bit wear mechanisms were analyzed. Also, the macroscopic wear regularity of the bit was presented by experimental analysis. The results show that the wear converting phase of the lip face during drilling is inevitable, according to the distributions of pressure and working load per diamond on the lip face. The abnormal wear converting phases include severe inner trumpet shape wear and groove shape wear. When bit skidding, the majority of diamonds on the lip face are worn to planar shapes. The wear process of diamond on the lip face involves three phases, namely complete crystallographic form, mild wear and severe wear, but most of diamonds on the outer cylindrical surface are only in the mild wear phase during the bit working life. The characteristic of bond wear is the quicksand phenomenon. And, the wear mechanisms comprise mechanical wear and chemical wear, and mechanical wear includes abrasive wear and breaking wear. The wear rate of the bit is less under the conditions of smaller grit, higher concentration, less water gap, thinner wall and smaller bit load, however, the spindle speed basically has no influence on the whole wearing resistance of the bit. The regularities of the wear rate and drilling speed of the bit with the whole drilling depth are close to periodic variation but there is no relationship between them. Moreover, the bit wear loss can not be determined by the drilling speed. The whole wear process of the bit can be divided into three phases, such as, high speed wear, steady wear and rapid wear.Finally, machining experiments on both lightweight composite components and KFRP were undertaken, providing references for the practical production. By using the special sintering diamond bit and aiming at high efficiency drilling of the ceramic composite component and KFRP, these performance parameters of bit and technological parameters were optimized, respectively. The rational drilling process for the double composite component was presented, and the main factors influencing machining efficiency were discussed experimentally. By using the special diamond tools developed, step hole, through slot and blind slot in the ceramic composite component were machined successfully. After the effects of cutting processes on machining qualities of composite components and KFRP were discussed, cutting experiments were conducted by using the sintering diamond sawblade.The machining technologies presented in this dissertation have been applied successfully in the practical productions of some key bulletproof parts of a certain special type vehicle, with higher promotion value.