Research On Cutting Mechanism And Tool Design Technology Of CFRP Ultrasonic Assisted Bidirectional Progressive Hole Milling

Carbon fiber Reinforced Plastics(CFRP)has rapidly become the main material in the aerospace manufacturing industry instead of metal.It has been widely used in the main bearing components such as fuselage and wing due to its lightweight weight,large modulus and high strength.The quality of the connecting holes directly affects the fatigue performance of the assembled members.However,due to the influence of interlayer anisotropy and anisotropy of CFRP,the hole making damage such as fiber pulling out and lamination tearing occurs frequently,which makes the high-quality hole making technology of CFRP have to face new challenges.By changing the cutting trajectory,the ultrasonic assisted technology makes the cutting edge and the processed part produce periodic contact separation,changes the mechanical behavior of the material in the process of cutting,and then improves the quality of the parts.It is recognized as one of the most effective processing technologies for high-quality hole making of CFRP.However,the anisotropy and low interlaminar shear strength of carbon fiber reinforced composites lead to large differences in manufacturing performance,frequent hole damage such as material delamination and fiber pull-out,so that the cutting field must face new challenges.By changing the motion path of the milling cutter,ultrasonic assisted vibration makes the tool and the workpiece have periodic contact-separation,which has significant advantages in reducing the cutting force and improving the surface quality of the workpiece.It is considered to be an effective method to realize the efficient and high-quality hole making of carbon fiber composite materials.However,until now,the problems such as delamination and tearing defects of CFRP holes have not been effectively suppressed and solved.In this paper,based on the principle of ultrasonic assisted cutting,the material removal mechanism of high-quality cutting technology is studied by reducing and restraining CFRP outlet damage,combined with finite element simulation technology,and the tool fit design and manufacturing method is proposed,and the experimental mixture method is applied.The new cutting technology,its optimization scheme and adaptive tool technology are systematically studied and discussed in the aspects of tool structure,cutting parameters to cutting efficiency and product quality control.The research contents mainly include the following aspects:Firstly,carry out the progressive spiral milling material removal performance and inhibition mechanism of layered double order milling research,reveal the ultrasonic assisted double order gradual milling technology with ultrasonic micro milling steps separation properties,ultrasonic gradual wedge filter effect,significantly improve the patent of CFRP cutting front,and to promote fiber cutting Angle to 90 °,and the suitability of the technology as a tool design and manufacturing standards.At the same time,based on the milling spiral bevel cutting principle and application of the finite element simulation software ABAQUS,establish three-dimensional oblique cutting CFRP microscopic simulation model of the parallel cutting and vertical cutting relations,arrange fiber cutting relation,the inverse relationship between fiber cutting four direction under the condition of fracture mechanism of CFRP material,reveal the material into constructing the mechanism of cutting surface It is proposed that the material removal mechanism of ultrasonic assisted double-step progressive milling is brittle fracture with ductility mode,which provides a research basis for cutting process optimization scheme of hole damage control and tool fit design.Secondly,based on the principle of CFRP exit layer suppression,the cut-off layer critical model of tool-workpiece exit boundary cutting and the second-order reverse cutting layer regeneration model were established.The structure design concept of two-order progressive spiral milling cutter fit was proposed,and the tool structure design for ultrasonic assisted cutting was optimized by finite element simulation.The geometric shape of the undeformed chip is established by the kinematic theory,which lays a good model foundation for correctly describing the mechanical characteristics of milling cutter.The tool structure design and modeling optimization were carried out with the theory of differential geometry.The transverse parallel grinding method,slow feed peristaltic grinding method and triple adaptive oblique axis grinding method were proposed to study the adaptive tool manufacturing technology.Thirdly,using the micro-element cutting theory,equivalent plane and twodimensional orthogonal cutting theory,the exponential prediction model of milling force for ultrasonic assisted dual-order progressive milling CFRP was established.The cutting force coefficients of the first-order forward and second-order reverse stages were identified by the average cutting force method.The effects of prediction error of milling force model and tool structure with cutting parameters on cutting specific energy were analyzed by hybrid test verification method.The cutting specific energy consumption law of first-order forward cutting at the entrance,hole wall area and exit and the optimization scheme of second-order reverse cutting mechanical properties were revealed.It is helpful to establish the mapping between the quality control of parts and the mechanical law of cutting parts under the ultrasonic assisted double step cutting technology.Finally,in order to reveal the influence of the new ultrasonic assisted bidirectional progressive milling technology in the process of surface creation and damage,the three-dimensional surface topography detection method of "low reverse rate,table feedback,fixed range and re-leveling" was used to evaluate the quality of the parts.The aperture accuracy met the requirements of IT7-IT10,and there were no obvious burr,delamination and tearing defects.The damage process of bidirectional wedge progressive milling cutter was studied.The characteristics of the wear band of the edge of bidirectional progressive milling cutter were "wedge","strip" and "arc" distribution,the trend of "linear" wear of the reverse cutting edge and the law of "scoop" wear of the bottom edge were revealed.The optimization scheme of ultrasonic assisted bidirectional progressive milling is A1B3C2 by grey correlation analysis.