Study On Process Technology Of Composite By Reverse Helical Milling

Carbon fiber reinforced plastics(composite)are widely used in aerospace because of their superior comprehensive mechanical properties.In aircraft assembly,a large number of holes need to be machined in composite components for bolt or rivet connections.Because of its heterogeneity and weak interlaminar bonding force,the material removal mechanism of the composite is different from that of the metal material.When conventional method is used to make holes,the hole exit of composite is easy to induce damages by axial force,such as delamination and crack.Therefore,it is of great significance to restrain the formation of damage of composite hole exit.This paper presents a reverse helical milling process,which can effectively restrain the damage of composite hole exit.The process includes hole making by forward feed and expansion hole by reverse feed helical milling.Without changing the relative position of the equipment and the workpiece,the material is removed by changing the feed direction of the cutting tool and using the back-end cutting edge of the special tool to remove the material during the return.In this paper,the process is studied as follows:Aiming at the hole making of single composite component and metal/composite layer compounds with composite material as outlet,the corresponding process scheme is put forward.The main reason for delamination at the exit of composite hole is that the axial force produced in the process of machining is greater than the critical force of delamination.Therefore,the critical force of delamination in forward hole making and reverse feed helical milling expansion hole in different process schemes is modeled.Through comparative analysis,it is proved that compared with the traditional forward hole making,reverse helical milling can reduce the axial force and improve the critical force of delamination,thus significantly improving the machining quality of the hole.The special tool with special shape is needed to realize the reverse helical milling.Compared with the flat-bottom end milling cutter and bit,the special tool grinds the back cutting edge at the connection between the helical side edge and the neck.Select the appropriate tool geometry parameters according to the machining requirements.The kinematics principle of reverse feed reaming is analyzed.The 3D model of undeformed chip is established by the motion relationship between tool and workpiece,and the geometric parameters such as thickness are simply calculated and analyzed.The feasibility of the corresponding process scheme is verified by using a single composite component and aluminum alloy/composite layer compounds.It is proved that the process can significantly improve the hole quality of the composite.According to the control experiment of forward helical milling and reaming,it is proved that the quality improvement of reverse helical milling is not due to the decrease of axial force,but to the change of cutting state of material at the exit.By designing the reverse feed reaming experiment with different process parameter combinations,it is proved that the reverse helical milling process can also obtain better exit and entrance quality when using multiple parameter combinations.The effects of spindle speed,revolution speed,axial feed speed and radial cutting depth on the machining quality of the hole are studied by experiment.the main evaluation indexes include the surface roughness,roundness and aperture difference of the hole.The results show that when the process parameters are the same,the surface roughness of aluminum alloy hole is better than that of composite material hole,the roundness of composite hole is smaller than that of aluminum alloy hole,and the diameter of composite material hole is larger than that of aluminum alloy hole.When the material is the same,the same evaluation index changes not monotonously with the increase of the parameters.