Basic Research On Ultra-low Temperature Milling Hole Of Aramid Fiber Reinforced Composites

Aramid fiber reinforced composite(AFRP)has superior physical properties,such as high strength and good impact resistance,and is widely used in aerospace,armor protection,weapon equipment and other fields.Especially in the aerospace field,rivets or bolts are usually used in the assembly of equipment parts.In order to achieve the assembly precision and meet the requirements of the use of components,the precision of connecting holes must reach a higher standard.Due to the high orientation of aramid fiber,its composite material has complex multiphase structure and presents anisotropy,which is usually accompanied by burr,stratification,ablation and other defects in mechanical processing.Therefore,it is difficult to obtain ideal processing surface,which affects the processing quality and the performance and safety of components,and also becomes the bottleneck restricting its application.Therefore,it is particularly important to improve AFRP hole processing technology.In this paper,the machining mechanism and the causes of machining defects during dry cutting of AFRP were firstly analyzed.Based on the low-temperature mechanical properties of AFRP,fiber reinforcement and resin matrix,the method of spiraling hole milling for AFRP by liquid nitrogen medium cooling was proposed.An AFRP spiral milling hole force model considering the temperature of the cutting microzone is established,and the influence law of the material property change caused by various process parameters and temperature change on the milling force is predicted.At last,the spiral hole milling test of AFRP was carried out under dry cutting and liquid nitrogen cooling conditions by using single factor analysis method,and the low-temperature machining performance of AFRP was studied.The influence law of various processing parameters and low-temperature conditions on milling hole force and hole machining quality was obtained,and the cutting mechanism of ultra-low-temperature cooling AFRP was revealed.The results show that the milling force is mainly related to spindle speed,cutter feed and AFRP mechanical properties at different temperatures,and spindle speed has less influence on milling force than feed.In addition,high cutting temperature and lack of chip are the main causes of machining defects.After the intervention of low-temperature medium,the temperature rise of the cutting area decreases rapidly,the mechanical properties of AFRP are changed,the shear strength is increased,the bonding ability between layers is improved,and the ability to resist external load is enhanced.Therefore,the milling force is increased by 20%-30% compared with that of dry cutting,while the processing defects such as fiber edging and lamination are inhibited,the surface roughness of hole wall is reduced by about 30% compared with that of dry cutting,and the processing quality is obviously improved.Therefore,the change of mechanical properties of AFRP at low temperature is the root cause of inhibiting machining defects.In summary,liquid nitrogen cooling and milling hole can effectively inhibit the machining defects of AFRP dry milling hole,improve the machining quality of the hole,and provide a new field of view for the high-quality and low-damage machining of the material.