Establishment method of carbon fiber composite material cutting model with large fiber cutting angle

Abstract

The invention provides a method for establishing a large fiber cutting angle carbon fiber composite material cutting model, and relates to the technical field of carbon fiber composite material cutting processing. The establishment method comprises the following steps: firstly, establishing a large-fiber cutting angle single-fiber cutting model considering the change of the contact state of cut fibers and a cutter in the CFRP cutting process, the multidirectional constraint effect of the cut fibers and fiber fracture; then establishing a CFRP cutting model considering the extrusion effect of the cutting edge and fiber micro-buckling failure; and finally, establishing a CFRP macroscopic cutting force prediction model containing a fiber bending area and a fiber extrusion area, and verifying the accuracy of the cutting model in combination with experiments. According to the method, the fiber deformation and fracture process, resin and interface cracking and the extrusion effect of a cutting edge on the fibers can be represented, the influence of large fiber cutting angle fiber fracture on machining surface pit damage and the quantitative relation between macroscopic cutting force and machining parameters are obtained, and a basis is provided for tool design and technological parameter formulation.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber composite material cutting and processing, and in particular to a method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle. Background Art

[0002] Carbon fiber reinforced polymer (CFRP) has the advantages of light weight, high strength, and integral manufacturing, and is the preferred material for reducing weight and increasing efficiency of high-end aerospace equipment. However, CFRP is a typical difficult-to-process material, and its components are easily damaged during the cutting process, which reduces the performance of the parts. Therefore, suppressing processing damage is a prerequisite for ensuring the reliable service of CFRP components.

[0003] Carbon fiber reinforced composite materials are essentially different from homogeneous materials such as traditional metals. They are multiphase mixed states of fibers, resins and interfaces at the microscopic scale, and are stacked and anisotropic at the macroscopic scale. Therefore, the essence of cutting CFRP includes the cutting of fibers, resins and interfaces at the microscopic scale, and the formation of chips by a large number of cut fibers, resins and interfaces at the macroscopic scale. Since the fibers in CFRP have obvious directionality, the angle between the cutting speed and the fiber direction, that is, the fiber cutting angle, changes periodically in the range of 0° to 180° as the tool rotates during cutting. The fiber cutting angle is an important factor affecting the cutting removal mode and processing damage of CFRP. Especially when the fiber cutting angle is greater than 90° + the front angle, that is, the large fiber cutting angle, the cut material will first contact the front cutting surface. Under the pushing action of the front cutting surface, a large area bending deformation occurs, which is easy to cause cracking of the resin and interface. The bonding strength of the interface is about 30 to 80 MPa, which further leads to an increase in the fiber deformation depth, and finally the fiber fracture position occurs below the cutting plane, resulting in pit damage. However, pit damage can reduce the tensile strength of CFRP components by 25% to 32%, seriously reducing the mechanical properties of CFRP components. Therefore, starting from the cutting nature of CFRP with large fiber cutting angles, establishing a cutting model for carbon fiber reinforced composites with large fiber cutting angles, studying the basic theory of its material removal process and pit damage formation mechanism, and then guiding the optimization of CFRP processing tools and processes, is an effective way to inhibit pit damage.

[0004] In terms of CFRP cutting theory, Jia Zhenyuan et al. invented "A method for establishing a cutting model for carbon fiber composite materials", patent number 201610446046.5, which involves a method for establishing a cutting model for carbon fiber composite materials, which can accurately calculate fiber deformation, fracture and macro-cutting force when the fiber cutting angle is small. However, this cutting model fails to fully consider the removal process of CFRP with large fiber cutting angles and the influence of fiber deformation and fracture on the formation of pit damage. It cannot accurately analyze the removal process of CFRP with large fiber cutting angles, and it is difficult to effectively guide the formulation of pit damage suppression methods.

[0005] In summary, in order to effectively inhibit pit damage and accurately describe the destruction and fracture process of fiber, resin and interface during CFRP cutting with large fiber cutting angle, it is necessary to develop a method for establishing a cutting model of carbon fiber reinforced composite materials with large fiber cutting angle that takes into account the cutting removal characteristics during CFRP cutting with large fiber cutting angle and has high accuracy. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a method for establishing a cutting model for carbon fiber composite materials with a large fiber cutting angle, aiming to reveal the influence of processing parameters and tool structure on the formation of pit damage, and to provide guidance for the optimization of CFRP processing tools and processes.

[0007] The present invention provides a method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle, the method comprising the following steps:

[0008] Step 1: Obtain material performance parameters and cutting processing parameters of the CFRP unidirectional laminate to be cut;

[0009] Step 2: Establish a single fiber cutting model with multiple contact states to describe the fiber deformation and fracture process under large fiber cutting angles;

[0010] Step 3: Based on the microbuckling failure mechanism, an extrusion model between the cutting edge and the fiber is established to calculate the extrusion force F exerted by the microbuckling on the tool under the extrusion of the cutting edge after the fiber breaks. Q2 ;

[0011] Step 4: Establish a macro cutting force prediction model to calculate the cutting force of the CFRP unidirectional laminate to be cut;

[0012] The material performance parameters described in step 1 include: fiber elastic modulus E f , fiber axial tensile strength limit σ t , fiber diameter d f , fiber Poisson's ratio ν f , fiber volume fraction V f , fiber section moment of inertia I f , resin and interface elastic modulus Em , resin and interface Poisson's ratio ν m , resin and interface shear modulus G m , resin and interface bonding strength σ b and the equivalent homogeneous Poisson’s ratio v;

[0013] The cutting parameters in step 1 include: tool back angle α, tool rake angle γ, cutting edge radius r e , cutting speed v c and fiber cutting angle θ;

[0014] The step 2 further comprises:

[0015] Step 2.1: The constraint states of the cut fiber at different locations along the fiber axis are divided into three constraint states, and the deformation control equations of the cut fiber in each constraint state are constructed respectively;

[0016] Step 2.2: Based on the deformation control equation of the cut fiber under each constraint state, solve the general solution of fiber deformation deflection under different constraint states respectively;

[0017] Step 2.3: According to the contact state between the cut fiber and the tool and the change of the fiber state during the cutting process, the fiber deflection and single fiber cutting force during the cutting process are solved by using the general solution of fiber deformation deflection under different constraint states;

[0018] Step 2.4: Based on the fiber deflection and single fiber cutting force obtained in the cutting process in step 2.3, starting from the initial contact between the front cutting edge of the tool and the fiber end point on the cut fiber, as the tool moves, the contact state or boundary conditions between the cut fiber and the tool will switch and change in Case 1-Case 8. The tool movement distance is gradually increased, and the deflection, slope, maximum tensile stress inside the fiber, and bonding resistance of the resin and the interface of the cut fiber after the tool moves in each iteration round are calculated using an iterative algorithm and boundary conditions. The bending fracture of the cut fiber under the machining surface is used as the iteration termination condition, and the deflection of the cut fiber, the fiber fracture position, and the single fiber cutting force when the fiber fracture occurs are solved;

[0019] The three constraint states described in step 2.1 include:

[0020] The first constraint state is: when the cut fiber is subject to the normal constraint and tangential constraint of the unprocessed material above the workpiece surface, the cut fiber is in the first constraint state, and the deformation control equation of the cut fiber in the first constraint state is constructed as follows:

[0021]

[0022] where km0 k is the normal constraint effect of the unprocessed material above the workpiece surface on the cut fiber; m10 E is the tangential constraint of the unprocessed material above the workpiece surface on the cut fibers; f is the fiber elastic modulus; ω(x) is the deflection at a distance x from the top of the cut fiber;

[0023] The second constraint state is: when the cut fiber is subject to the normal constraint and tangential constraint of the unprocessed material, the cut fiber is in the second constraint state, and the deformation control equation of the cut fiber in the second constraint state is constructed as follows:

[0024]

[0025] where k m k is the first parameter of the unprocessed material, which is used to characterize the normal constraint effect of the unprocessed material on the cut fiber; m1 It is the second parameter of the unprocessed material, used to characterize the tangential constraint effect of the unprocessed material on the cut fiber;

[0026] The third constraint state is: when the cut fiber is simultaneously subject to the normal constraint of the unprocessed material, the tangential constraint, and the bonding effect of the resin and the interface, the cut fiber is in the third constraint state, and the deformation control equation of the cut fiber in the third constraint state is constructed as follows:

[0027]

[0028] where k b It is the tensile stiffness of the resin and the interface, and is used to characterize the bonding effect of the resin and the interface on the fiber;

[0029] The general solution of fiber deformation deflection under different constraint states described in step 2.2 includes:

[0030] The general solution of fiber deformation deflection ω1(x) under the first constraint state is:

[0031]

[0032] Among them, A1, A2, A3, and A4 are all integral constants;

[0033] The general solution of fiber deformation deflection ω2(x) under the second constraint state is:

[0034]

[0035] Among them, B1, B2, B3, and B4 are all integral constants;

[0036] The general solution of fiber deformation deflection ω3(x) under the third constraint state is:

[0037] ω3(x)=e -α3x (C1cosβ3x+C2sinβ3x) (6)

[0038] Where C1, C2 are integral constants; e is a natural constant;

[0039] In addition to the above three constraint states, since the deflection of the fiber end point is related to the tool movement and the tool rake angle, the deflection ω of the fiber end point in the cut fiber O It is expressed as:

[0040]

[0041] Where t is the tool movement time;

[0042] During the bending process of the cut fiber, when the slope of a certain point on the cut fiber is less than or equal to cot(γ-θ), the cut fiber is in line contact with the rake face, and the fiber deflection of the line contact part is generally solved as follows:

[0043]

[0044] Where ω0(x) is the general solution of the fiber deflection in the part of the cut fiber that is in line contact with the rake face;

[0045] The solution method for the fiber deflection and single fiber cutting force in the cutting process described in step 2.3 is as follows: for the cut fiber, the fiber end point is recorded as point O, the point where the fiber and the workpiece plane coincide is recorded as point A, the fiber breakage points generated by the fiber one by one are recorded as point F, the contact end point where the fiber and the front cutting edge produce line contact is recorded as point E, the cracking end point after the resin and the interface crack is recorded as point C, and the infinite end of the fiber is recorded as point D. The cut fiber is divided into several sections according to the different contact states between the fiber and the tool, and the general solution of the fiber deformation deflection under different constraint states is used to describe the deflection of each section of the fiber, thereby obtaining the single fiber cutting force of the cut fiber during the cutting process; the specific process is as follows:

[0046] For the node at a distance x from the top of the cut fiber in the cut fiber, the deflection of the node under different constraint states is ω i (x), where i represents the i-th constraint state, and i = 1, 2, 3; the slope is k i =dω i (x) / dx, bending moment is M i =-E f I fd 2 ω i (x) / dx 2 , the shear force is Q i =-E f I f d 3 ω i (x) / dx 3 +k m dω i (x) / dx, and when i=1, Q1=-E f I f d 3 ω1(x) / dx 3 +k m0 dω1(x) / dx;

[0047] The first contact state Case 1: When the fiber and the tool make initial contact, the initial contact between the fiber end point and the tool rake face is called point contact. The fiber is divided into OA segment, AC segment and CD segment, where the position coordinates of point O, point A and point C along the fiber direction are expressed as: O 、x A and x C , where x O =0,x A =-v c tcosθ,x C =h+(a c -δ) / sinθ; a c is the cutting depth; h is the cracking depth; δ is the springback height of the cut material;

[0048] Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integration constants A1, A2, A3, A4, B1, B2, B3, B4, C1, and C2:

[0049]

[0050] Then, the fiber deflection solutions ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OA, AC and CD segments. At this time, the single fiber cutting force f of the cut fiber is y for:

[0051]

[0052] where p m0 is the support resistance on the unprocessed workpiece surface; p m is the support resistance below the fiber breaking point; q b is the bonding resistance; p m0 (ω1), p m (ω2) and pm (ω3) is the support resistance of the fiber microelement length of the OA segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment;

[0053] The second contact state Case 2: before the fiber breaks for the first time, when the fiber is in line contact with the tool rake face and the contact end point is above the workpiece plane, the fiber is divided into OE segment, EA segment, AC segment and CD segment, where the position coordinates of point O, point A and point C along the fiber direction are: x O =0;x A =-v c tcosθ;x C =h+(a c -δ) / sinθ;

[0054] Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integration constants A1, A2, A3, A4, B1, B2, B3, B4, C1, and C2:

[0055]

[0056] Then, the fiber deflection solutions ω0(x), ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OE segment, EA segment, AC segment and CD segment. At this time, the single fiber cutting force f of the cut fiber is y for:

[0057]

[0058] where p m0 (ω0), p m0 (ω1), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length in the OE segment, EA segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment;

[0059] The third contact state Case 3: before the fiber breaks for the first time, when the fiber is in line contact with the rake face of the tool and the contact end point is below the plane of the workpiece, the fiber is divided into OE segment, EC segment and CD segment, where the position coordinates of point O, point A and point C along the fiber direction are: x O =0;x A =-v c tcosθ;x C =h+(a c -δ) / sinθ;

[0060] Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integral constants B1, B2, B3, B4, C1, and C2:

[0061]

[0062] Then, the fiber deflection solutions ω0(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OE, EC and CD segments. At this time, the single fiber cutting force f of the cut fiber is y for:

[0063]

[0064] where p m0 (ω0), p m (ω0), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length of the OA segment, AE segment, EC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment;

[0065] The fourth contact state Case 4: After the fiber breaks, when the fiber and the tool rake face are in point contact, that is, only the fiber break point F is in contact with the tool rake face, and the fiber break point F is located above point A, the fiber is divided into OF segment, FA segment, AC segment and CD segment, and the position coordinate of the fiber break point is marked as x F , and the position coordinates of point O, point A, and point C along the fiber direction are: x O =0;x A =-v c tcosθ;x C =h+(a c -δ) / sinθ;

[0066] Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integration constants A1, A2, A3, A4, B1, B2, B3, B4, C1, and C2:

[0067]

[0068] Then, the fiber deflection solutions ω0(x), ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OF segment, FA segment, AC segment and CD segment. At this time, the single fiber cutting force f of the cut fiber is y for:

[0069]

[0070] where p m0 (ω0), pm0 (ω1), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length in OF segment, FA segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment;

[0071] The fifth contact state Case 5: After the fiber breaks, when the fiber makes point contact with the tool rake face and the fiber break point F is below point A, the fiber is divided into OF segment, FC segment and CD segment, and the boundary conditions are used to solve the unknown integral constants B1, B2, B3, B4, C1 and C2:

[0072]

[0073] Then, the fiber deflection solutions ω0(x), ω2(x) and ω3(x) under different constraint states are used to describe the OF, FC and CD segments of the fiber. At this time, the single fiber cutting force f of the cut fiber is y for:

[0074]

[0075] where p mF is the support resistance above the fiber breaking point; p m0 (ω0), p mF (ω0), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length of the OA segment, AF segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment;

[0076] The sixth contact state Case 6: After the fiber breaks, when the fiber makes linear contact with the front cutting edge of the tool, and the fiber break point F is above point A, and the contact end point E where the fiber makes linear contact with the front cutting edge is above point A, the fiber is divided into OE segment, EA segment, AC segment and CD segment, and the unknown integral constants A1, A2, A3, A4, B1, B2, B3, B4, C1 and C2 are solved by formula (11), and then the general solutions of fiber deflection under different constraint states ω0(x), ω1(x), ω2(x) and ω3(x) are used to describe the OE segment, EA segment, AC segment and CD segment fibers, respectively, and the single fiber cutting force of the cut fiber is calculated according to formula (12);

[0077] The seventh contact state Case 7: After the fiber breaks, when the fiber makes line contact with the front cutting edge of the tool, and the fiber break point F is above point A, but the line contact end point E is below point A, the fiber is divided into OE segment, EC segment and CD segment, and the unknown integral constants B1, B2, B3, B4, C1 and C2 are solved using formula (13); then, the general solutions of fiber deflection ω0(x), ω2(x) and ω3(x) under different constraint states are used to describe the OE segment, EC segment and CD segment fibers, and the single fiber cutting force of the cut fiber is calculated according to formula (14);

[0078] The eighth contact state Case 8: After the fiber breaks, when the fiber is in line contact with the front cutting edge of the tool, and the fiber breaking point F is below point A, the solution method for the fiber deflection and the single fiber cutting force of the cut fiber is the same as that of the seventh contact state Case 7;

[0079] The fiber breakage and resin and interface cracking are judged based on the maximum tensile stress inside the fiber and the resin and interface bonding resistance. When the maximum tensile stress inside the fiber reaches the fiber tensile strength, the fiber breaks:

[0080]

[0081] where σ max is the maximum tensile stress inside the fiber; r f is the fiber radius; σ t is the fiber tensile strength;

[0082] When the bonding resistance between the resin and the interface is greater than the tensile strength limit of the resin and the interface, the resin and the interface will crack:

[0083] q b =k b ω(x)≥σ b (20)

[0084] where q b is the bonding resistance between resin and interface; b is the ultimate tensile strength of the resin and interface;

[0085] The specific method of step 3 is: after the fiber breaks, under the extrusion of the cutting edge, the cut fiber will fail again, and the failure mechanism is micro-buckling. At this time, considering the compressive strength σ of the CFRP unidirectional laminate mb for:

[0086]

[0087] Where η is the bonding property of the resin and the interface; ξ represents the slip parameters of the resin and the interface in microbuckling;

[0088] The force required for fiber extrusion failure is calculated by multiplying the compressive strength by the projected area of ​​the tool cutting edge on the workpiece. Assuming that the axial force increases linearly and the fiber breaks within a certain distance from the cutting edge, the extrusion force F acting on the tool by microbuckling is Q2 for:

[0089] F Q2 =0.5t w σ mb (r e sinθ-r e cosθ) (22)

[0090] where t w is the thickness of CFRP unidirectional laminate;

[0091] The macro cutting force prediction model includes two parts: the bending effect of the cutting tool rake face on the fiber in the fiber bending and breaking area and the squeezing effect of the cutting edge on the fiber in the fiber squeezing area;

[0092] For the bending effect of the cutting tool rake face on the fiber in the fiber bending zone, the total cutting force F required to bend all the fibers is Q1 Cutting force as fiber bending and breaking zone:

[0093]

[0094] where d f is the fiber diameter;

[0095] The cutting force in the fiber bending zone is decomposed along the cutting speed direction and perpendicular to the cutting speed direction to obtain the theoretical cutting force component F in the fiber bending zone. Q1X and F Q1Y , expressed as:

[0096]

[0097] Where μ is the friction coefficient;

[0098] For the fiber compression effect of the cutting edge in the fiber compression zone, the average force F acting on the tool due to microbuckling is Q2 The cutting force in the fiber extrusion zone is decomposed along the cutting speed direction and perpendicular to the cutting speed direction to obtain the theoretical cutting force component F in the fiber extrusion zone. Q2X and F Q2Y , expressed as:

[0099]

[0100] The theoretical cutting force component F in the fiber bending zone is used Q1X and F Q1Y The theoretical cutting force component F in the fiber extrusion zoneQ2X and F Q2Y Calculate the cutting force F of the CFRP unidirectional laminate to be cut X and F Y , expressed as:

[0101]

[0102] The beneficial effects of adopting the above technical solution are:

[0103] The method of the present invention establishes a single fiber cutting model with a large fiber cutting angle that takes into account the contact state change between the tool rake face and the cut fiber and the multi-directional constraints on the cut fiber, and proposes an analytical method for the fiber deformation and fracture process, resin and interface cracking, and single fiber cutting force during cutting with a large fiber cutting angle. By introducing the microbuckling failure theory to consider the extrusion effect of the cutting edge on the fiber, a CFRP macro-cutting force prediction model including the fiber bending and breaking zone and the fiber extrusion zone is established, and the quantitative relationship between the cutting force and cutting parameters of CFRP cutting processing is analyzed. BRIEF DESCRIPTION OF THE DRAWINGS

[0104] Figure 1 This is a flow chart of a method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle in this embodiment;

[0105] Figure 2 This is a schematic diagram of the forces acting on the cut fibers in this embodiment;

[0106] Figure 3 Schematic diagram of fiber deformation curve when fiber breaks under tool rake angle in this embodiment; wherein Figure (a) is a schematic diagram of fiber deformation curve when fiber breaks under small tool rake angle; Figure (b) is a schematic diagram of fiber deformation curve when fiber breaks under large tool rake angle;

[0107] Figure 4 This is a schematic diagram of the comparison between theoretical prediction and experimental results of cutting force in this embodiment;

[0108] In the figure: 1-CFRP, 2-fiber, 3-tool, 4-fiber direction, 5-deformation curve when fiber breaks, 6-cutting force F obtained by theoretical analysis X , 7- Experimentally obtained cutting force F X , 8- Cutting force F obtained by theoretical analysis Y , 9- Experimentally obtained cutting force F Y . DETAILED DESCRIPTION

[0109] In order to facilitate the understanding of the present application, the specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thoroughly understood.

[0110] The present invention firstly establishes a single fiber cutting model which takes into account various contact states between the fiber and the tool, multi-directional constraints on the cut fiber and fiber fracture forms, and then establishes a CFRP cutting model which takes into account the fiber extrusion effect of the cutting edge. Finally, a CFRP macro-cutting force prediction model including the fiber bending and breaking zone and the fiber extrusion zone is established.

[0111] A method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle in this embodiment is as follows: Figure 1 As shown, the method comprises the following steps:

[0112] Step 1: Obtain the material properties and cutting parameters of the CFRP unidirectional laminate to be cut.

[0113] The material performance parameters include: fiber elastic modulus E f , fiber axial tensile strength limit σ t , fiber diameter d f , fiber Poisson's ratio ν f , fiber volume fraction V f , fiber section moment of inertia I f , resin and interface elastic modulus E m , resin and interface Poisson's ratio ν m , resin and interface shear modulus G m , resin and interface bonding strength σ b and the equivalent homogeneous Poisson's ratio v.

[0114] The cutting parameters include: tool back angle α, tool rake angle γ, cutting edge radius r e , cutting speed v c and the fiber cutting angle θ.

[0115] In this embodiment, a T800 grade CFRP unidirectional laminate is used as the experimental piece, and the specific material performance parameters are shown in Table 1. The processing parameters are set as follows: tool back angle α = 5°, tool rake angle γ = 15°, cutting edge radius r e =5μm, cutting speed v c =50mm / s, fiber cutting angle θ=135°.

[0116] Table 1 Material performance parameters

[0117]

[0118]

[0119] Step 2: Establish a single fiber cutting model with multiple contact states to describe the fiber deformation and fracture process under large fiber cutting angles.

[0120] In this embodiment, if Figure 2 As shown in the figure, the x-axis is the coordinate axis along the fiber direction, and the y-axis is the coordinate axis perpendicular to the fiber direction. Point O is defined as the fiber endpoint, and a coordinate system is established with point O as the coordinate origin to represent the position coordinates of each point. Point A is the point where the fiber coincides with the unprocessed workpiece surface, point F is the fiber break point, point E is the end point of contact between the fiber and the front cutting edge of the tool, point C is the end point of cracking, and point D is the infinite end of the fiber. According to the constraint state of different parts of the cut fiber along the fiber axis, it is divided into three constraint states for research.

[0121] Step 2.1: The constraint states of the cut fiber at different locations along the fiber axis are divided into three constraint states, and the deformation control equations of the cut fiber in each constraint state are constructed respectively;

[0122] In this embodiment, the cut fiber is divided into three constraint states according to the constraint states of different parts along the fiber axis. The first is that the cut fiber is subject to the normal constraint and tangential constraint of the unprocessed material above the workpiece surface, and the fiber deformation control equation is established by formula (1); the second is that the cut fiber is subject to the normal constraint and tangential constraint of the unprocessed material, and the fiber deformation control equation is established by formula (2); the third is that the cut fiber is subject to the normal constraint, tangential constraint and the bonding effect of the resin and the interface of the unprocessed material at the same time, and the fiber deformation control equation is established by formula (3).

[0123] The three constraint states include:

[0124] The first constraint state is: when the cut fiber is subject to the normal constraint and tangential constraint of the unprocessed material above the workpiece surface, the cut fiber is in the first constraint state, and the deformation control equation of the cut fiber in the first constraint state is constructed as follows:

[0125]

[0126] where k m0 k is the normal constraint effect of the unprocessed material above the workpiece surface on the cut fiber; m10 E is the tangential constraint of the unprocessed material above the workpiece surface on the cut fibers; f is the elastic modulus of the fiber; ω(x) is the deflection at a distance x from the top of the cut fiber.

[0127] The second constraint state is: when the cut fiber is subject to the normal constraint and tangential constraint of the unprocessed material, the cut fiber is in the second constraint state, and the deformation control equation of the cut fiber in the second constraint state is constructed as follows:

[0128]

[0129] where k m k is the first parameter of the unprocessed material, which is used to characterize the normal constraint effect of the unprocessed material on the cut fiber; m1 It is the second parameter of the unprocessed material, which is used to characterize the tangential constraint effect of the unprocessed material on the cut fiber.

[0130] The third constraint state is: when the cut fiber is simultaneously subject to the normal constraint of the unprocessed material, the tangential constraint, and the bonding effect of the resin and the interface, the cut fiber is in the third constraint state, and the deformation control equation of the cut fiber in the third constraint state is constructed as follows:

[0131]

[0132] where k b It is the tensile stiffness of the resin and the interface, and is used to characterize the bonding effect of the resin and the interface on the fiber.

[0133] Step 2.2: Based on the deformation control equation of the cut fiber under each constraint state, solve the general solution of fiber deformation deflection under different constraint states respectively.

[0134] The general solution of fiber deformation deflection under different constraint states includes:

[0135] The general solution of fiber deformation deflection ω1(x) under the first constraint state is:

[0136]

[0137] Among them, A1, A2, A3, and A4 are all integral constants;

[0138] The general solution of fiber deformation deflection ω2(x) under the second constraint state is:

[0139]

[0140] Among them, B1, B2, B3, and B4 are all integral constants;

[0141] The general solution of fiber deformation deflection ω3(x) under the third constraint state is:

[0142]

[0143] Where C1, C2 are integral constants; e is a natural constant;

[0144] In addition to the above three constraint states, since the deflection of the fiber end point is related to the tool movement and the tool rake angle, the deflection ω of the fiber end point in the cut fiber O It is expressed as:

[0145]

[0146] Where t is the tool movement time.

[0147] During the bending process of the cut fiber, when the slope of a certain point on the cut fiber is less than or equal to cot(γ-θ), the cut fiber is in line contact with the rake face, and the fiber deflection of the line contact part is generally solved as follows:

[0148]

[0149] Where ω0(x) is the general solution of the fiber deflection in the portion of the cut fiber that is in line contact with the rake face.

[0150] In this embodiment, the general solution of fiber deformation deflection under different constraint conditions is then solved. The general solution of fiber deformation deflection under the first constraint state ω1(x) is solved by formula (4); the general solution of fiber deformation deflection under the second constraint state ω2(x) is solved by formula (5); the general solution of fiber deformation deflection under the second constraint state ω3(x) is solved by formula (6); the deflection ω of the fiber endpoint is O It is related to tool movement and tool rake angle and is solved by formula (7). During the fiber bending process, the deflection of the part where the fiber and the front tool face are in line contact is solved by formula (8).

[0151] Step 2.3: According to the contact state between the cut fiber and the tool and the change of the fiber state during the cutting process, the fiber deflection and single fiber cutting force during the cutting process are solved by using the general solution of fiber deformation deflection under different constraint states.

[0152] The method for solving the fiber deflection and single fiber cutting force in the cutting process is as follows: for the cut fiber, the fiber end point is recorded as point O, the overlap between the fiber and the workpiece plane is recorded as point A, the fiber breakage points generated by the fiber one by one are recorded as point F, the contact end point where the fiber and the front cutting surface produce line contact is recorded as point E, the cracking end point after the resin and the interface are cracked is recorded as point C, and the infinite end of the fiber is recorded as point D. The cut fiber is divided into several sections according to the different contact states between the fiber and the tool, and the deflection of each section of the fiber is described by the general solution of the fiber deformation deflection under different constraint states, so as to obtain the single fiber cutting force of the cut fiber in the cutting process; the specific process is as follows:

[0153] For the node at a distance x from the top of the cut fiber in the cut fiber, the deflection of the node under different constraint states is ω i (x), where i represents the i-th constraint state, and i = 1, 2, 3; the slope is k i =dω i (x) / dx, bending moment is M i =-E f I f d 2 ω i (x) / dx 2 , the shear force is Q i =-E f I f d 3 ω i (x) / dx 3 +k m dω i (x) / dx, and when i=1, Q1=-E f I f d 3 ω1(x) / dx 3 +k m0 dω1(x) / dx.

[0154] In this embodiment, in order to obtain the deflection caused by fiber deformation under the action of the tool rake face, the boundary conditions of each segment in the cut fiber are used to solve and calculate the deflection, slope, bending moment and shear force at each node.

[0155] The first contact state Case 1: When the fiber and the tool make initial contact, the initial contact between the fiber end point and the tool rake face is called point contact. The fiber is divided into OA segment, AC segment and CD segment, where the position coordinates of point O, point A and point C along the fiber direction are expressed as: O 、x A and x C , where x O =0,x A =-v c tcosθ,xC =h+(a c -δ) / sinθ; a c is the cutting depth; h is the cracking depth; δ is the springback height of the cut material.

[0156] Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integration constants A1, A2, A3, A4, B1, B2, B3, B4, C1, and C2:

[0157]

[0158] Where ω1(x O ) is the deflection of point O in the first constraint state; M1(x O ) is the bending moment at point O in the first constraint state; ω1(x A ) is the deflection of point A in the first constraint state; ω2(x A ) is the deflection of point A in the second constraint state; k1(x A ) is the slope of point A in the first constraint state; k2(x A ) is the slope of point A in the second constraint state; M1(x A ) is the bending moment at point A in the first constraint state; M2(x A ) is the bending moment at point A in the second constraint state; Q1(x A ) is the shear force at point A in the first constraint state; Q2(x A ) is the shear force at point A in the second constraint state; ω2(x C ) is the deflection of point C in the second constraint state; ω3(x C ) is the deflection of point C under the third constraint state; k2(x C ) is the slope of point C in the second constraint state; k3(x C ) is the slope of point C under the third constraint state; M2(x C ) is the bending moment at point C in the second constraint state; M3(x C ) is the bending moment at point C in the third constraint state; Q2(x C ) is the shear force at point C in the second constraint state; Q3(x C ) is the shear force at point C under the third constraint state.

[0159] Then, the fiber deflection solutions ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OA, AC and CD segments. At this time, the single fiber cutting force f of the cut fiber is y for:

[0160]

[0161] where p m0 is the support resistance on the unprocessed workpiece surface; p m is the support resistance below the fiber breaking point; q b is the bonding resistance; p m0 (ω1), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length of the OA segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance exerted on the fiber microelement length of the CD segment.

[0162] The second contact state Case 2: before the fiber breaks for the first time, when the fiber is in line contact with the tool rake face and the contact end point is above the workpiece plane, the fiber is divided into OE segment, EA segment, AC segment and CD segment, where the position coordinates of point O, point A and point C along the fiber direction are: x O =0;x A =-v c tcosθ;x C =h+(a c -δ) / sinθ.

[0163] Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integration constants A1, A2, A3, A4, B1, B2, B3, B4, C1, and C2:

[0164]

[0165] Where ω1(x E ) is the deflection of point E in the first constraint state; ω0(x E ) is the deflection of point E when line contact occurs; x E is the position coordinate of point E along the fiber direction; k0(x E ) is the slope of point E when line contact occurs; k1(x E ) is the slope of point E in the first constraint state.

[0166] Then, the fiber deflection solutions ω0(x), ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OE segment, EA segment, AC segment and CD segment. At this time, the single fiber cutting force f of the cut fiber is y for:

[0167]

[0168] where p m0 (ω0), p m0 (ω1), p m (ω2) and p m(ω3) is the support resistance of the fiber microelement length in the OE segment, EA segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance exerted on the fiber microelement length of the CD segment.

[0169] The third contact state Case 3: before the fiber breaks for the first time, when the fiber is in line contact with the rake face of the tool and the contact end point is below the plane of the workpiece, the fiber is divided into OE segment, EC segment and CD segment, where the position coordinates of point O, point A and point C along the fiber direction are: x O =0;x A =-v c tcosθ;x C =h+(a c -δ) / sinθ.

[0170] Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integral constants B1, B2, B3, B4, C1, and C2:

[0171]

[0172] Where ω2(x E ) is the deflection of point E in the second constraint state; k2(x E ) is the slope of point E in the second constraint state.

[0173] Then, the fiber deflection solutions ω0(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OE, EC and CD segments. At this time, the single fiber cutting force f of the cut fiber is y for:

[0174]

[0175] where p m0 (ω0), p m (ω0), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length of the OA segment, AE segment, EC segment and CD segment respectively; q b (ω3) is the bonding resistance exerted on the fiber microelement length of the CD segment.

[0176] The fourth contact state Case 4: After the fiber breaks, when the fiber and the tool rake face are in point contact, that is, only the fiber break point F is in contact with the tool rake face, and the fiber break point F is located above point A, the fiber is divided into OF segment, FA segment, AC segment and CD segment, and the position coordinate of the fiber break point is marked as x F , and the position coordinates of point O, point A, and point C along the fiber direction are: x O=0;x A =-v c tcosθ;x C =h+(a c -δ) / sinθ.

[0177] Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integration constants A1, A2, A3, A4, B1, B2, B3, B4, C1, and C2:

[0178]

[0179] Where ω1(x F ) is the deflection of point F in the first constraint state; ω0(x F ) is the deflection of point F when line contact occurs; M1(x F ) is the bending moment at point F in the first constraint state.

[0180] Then, the fiber deflection solutions ω0(x), ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OF segment, FA segment, AC segment and CD segment. At this time, the single fiber cutting force f of the cut fiber is y for:

[0181]

[0182] where p m0 (ω0), p m0 (ω1), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length in OF segment, FA segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance exerted on the fiber microelement length of the CD segment.

[0183] The fifth contact state Case 5: After the fiber breaks, when the fiber makes point contact with the tool rake face and the fiber break point F is below point A, the fiber is divided into OF segment, FC segment and CD segment, and the boundary conditions are used to solve the unknown integral constants B1, B2, B3, B4, C1 and C2:

[0184]

[0185] Where ω2(x F ) is the deflection of point F in the second constraint state; M2(x F ) is the bending moment at point F in the second constraint state.

[0186] Then, the fiber deflection solutions ω0(x), ω2(x) and ω3(x) under different constraint states are used to describe the OF, FC and CD segments of the fiber. At this time, the single fiber cutting force f of the cut fiber is y for:

[0187]

[0188] where p mF is the support resistance above the fiber breaking point; p m0 (ω0), p mF (ω0), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length of the OA segment, AF segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance exerted on the fiber microelement length of the CD segment.

[0189] The sixth contact state Case 6: After the fiber breaks, when the fiber makes linear contact with the front cutting edge of the tool, and the fiber breakage point F is above point A, and the contact end point E where the fiber makes linear contact with the front cutting edge is above point A, the fiber is divided into OE segment, EA segment, AC segment and CD segment, and the unknown integral constants A1, A2, A3, A4, B1, B2, B3, B4, C1 and C2 are solved by formula (11), and then the general solutions of fiber deflection ω0(x), ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the OE segment, EA segment, AC segment and CD segment fibers, respectively, and the single fiber cutting force of the cut fiber is calculated according to formula (12).

[0190] The seventh contact state Case 7: After the fiber breaks, when the fiber is in line contact with the front cutting edge of the tool, and the fiber breakage point F is above point A, but the line contact end point E is below point A, the fiber is divided into OE segment, EC segment and CD segment, and the unknown integral constants B1, B2, B3, B4, C1 and C2 are solved using formula (13); then, the general solutions of fiber deflection ω0(x), ω2(x) and ω3(x) under different constraint states are used to describe the OE segment, EC segment and CD segment fibers, respectively, and the single fiber cutting force of the cut fiber is calculated according to formula (14).

[0191] The eighth contact state Case 8: After the fiber breaks, when the fiber is in line contact with the front cutting edge of the tool and the fiber breakage point F is below point A, the solution method for the fiber deflection and the single fiber cutting force of the cut fiber is the same as that for the seventh contact state Case 7.

[0192] The fiber breakage and resin and interface cracking are judged based on the maximum tensile stress inside the fiber and the resin and interface bonding resistance. When the maximum tensile stress inside the fiber reaches the fiber tensile strength, the fiber breaks:

[0193]

[0194] where σ max is the maximum tensile stress inside the fiber; r f is the fiber radius; σ t is the fiber tensile strength.

[0195] When the bonding resistance between the resin and the interface is greater than the tensile strength limit of the resin and the interface, the resin and the interface will crack:

[0196] q b =k b ω(x)≥σ b (20)

[0197] where q b is the bonding resistance between resin and interface; b It is the ultimate tensile strength of the resin and the interface.

[0198] Step 2.4: Based on the fiber deflection and single fiber cutting force obtained in the cutting process in step 2.3, starting from the initial contact between the front cutting edge of the tool and the fiber end point on the cut fiber, as the tool moves, the contact state or boundary conditions between the cut fiber and the tool will switch and change in Case 1-Case 8. The tool movement distance is gradually increased, and the deflection, slope, maximum tensile stress inside the fiber, and bonding resistance of the resin and interface of the cut fiber after the tool moves in each iteration round are calculated using an iterative algorithm and boundary conditions. The bending fracture of the cut fiber under the machining surface is used as the iteration termination condition, and the deflection of the cut fiber, fiber fracture position, and single fiber cutting force when the fiber fracture occurs are then solved.

[0199] In this embodiment, the fiber deflection and single fiber cutting force in the cutting process are solved according to the contact state between the fiber and the tool and the change of the fiber state. When the front face of the tool just contacts the fiber, it is a point contact, that is, the first contact state. The tool is subjected to an initial displacement. At this time, the unknown constants A1~A4, B1~B4, C1, and C2 are solved by formula (9), and then the general solution of the fiber deflection and the single fiber cutting force are obtained, as well as the fiber slope, maximum tensile stress, resin and interface bonding resistance; based on the fiber breakage judgment condition, the resin and interface cracking judgment condition, and the line contact judgment condition, the contact state between the fiber and the tool after the tool applies the initial displacement is determined; as the tool moves, the contact state or boundary conditions between the fiber and the tool will switch and change in eight situations. The boundary conditions under the contact state are selected in formulas (9), (11), (13), (15), and (17), and the unknown constants are solved to obtain the general solution of the fiber deflection. Therefore, the method of gradually increasing the tool movement distance is adopted, and the deflection, slope, maximum tensile stress, and bonding resistance of the resin and interface of the fiber after the tool moves are calculated through an iterative algorithm. The bending and fracture of the fiber under the machining surface is taken as the iteration termination condition. The fiber deformation deflection, fiber fracture position, single fiber cutting force and other results when the fiber breaks can be solved.

[0200] In this embodiment, the fiber deformation curve when the fiber breaks when the tool rake angle γ is 5° and 35° is calculated using a single fiber cutting model with multiple contact states. The material parameters of CFRP1, fiber 2, resin and interface used are shown in Table 1. The cutting depth a c =30μm, cutting speed v c =50mm / s, fiber cutting angle θ = 135°, the fiber deformation curve results are as follows Figure 3 As shown in the figure, by comparing the fiber direction 4 and the deformation curve 5 when the fiber breaks, it can be seen that when the small tool rake angle is 5°, the fiber 2 undergoes a large fiber deformation under the action of the rake face of the tool 3. In this way, in the actual cutting process, the number of fibers 2 that cause bending deformation on a macro scale increases, which will increase the number of fibers 2 pulled out, forming relatively serious pit damage; when the large tool rake angle is 35°, the fiber 2 will break directly below the cutting plane after deformation, and will not break above the cutting plane, indicating that increasing the tool rake angle is beneficial to the fracture of the fiber 2. This means that increasing the tool rake angle can reduce fiber deformation, thereby reducing pit damage on the machined surface.

[0201] Step 3: Based on the microbuckling failure mechanism, an extrusion model between the cutting edge and the fiber is established to calculate the extrusion force F exerted by the microbuckling on the tool under the extrusion of the cutting edge after the fiber breaks. Q2 .

[0202] The specific method of step 3 is: after the fiber breaks, under the extrusion of the cutting edge, the cut fiber will fail again, and the failure mechanism is micro-buckling. At this time, considering the compressive strength σ of the CFRP unidirectional laminate mb for:

[0203]

[0204] Where η is the bonding property of the resin and the interface; ξ represents the slip parameters of the resin and the interface in microbuckling.

[0205] The force required for fiber extrusion failure is calculated by multiplying the compressive strength by the projected area of ​​the tool cutting edge on the workpiece. Assuming that the axial force increases linearly and the fiber breaks within a certain distance from the cutting edge, the extrusion force F acting on the tool by microbuckling is Q2 for:

[0206] F Q2 =0.5t w σ mb (r e sinθ-r e cosθ) (22)

[0207] where t w is the thickness of CFRP unidirectional laminate.

[0208] In this embodiment, after the fiber breaks, it will fail again under the extrusion of the cutting edge, and the failure mechanism is micro-buckling. At this time, considering the compressive strength σ of the CFRP one-way plate of a specific material, mb The force required for fiber extrusion failure is calculated by multiplying the compressive strength by the projected area of ​​the tool cutting edge on the workpiece, i.e., the CFRP unidirectional laminate. Assuming that the axial force increases linearly and the fiber breaks within a certain distance from the cutting edge, the extrusion force F acting on the tool due to microbuckling is Q2 Calculated by formula (22).

[0209] Step 4: Establish a macro cutting force prediction model to calculate the cutting force of the CFRP unidirectional laminate to be cut.

[0210] The macro-cutting force prediction model includes two parts: the bending effect of the front cutting surface of the tool on the fiber in the fiber bending and breaking area and the squeezing effect of the cutting edge on the fiber in the fiber squeezing area.

[0211] For the bending effect of the cutting tool rake face on the fiber in the fiber bending zone, the total cutting force F required to bend all the fibers is Q1 Cutting force as fiber bending and breaking zone:

[0212]

[0213] where d f is the fiber diameter.

[0214] In this embodiment, the cutting force theoretical value is decomposed according to the direction of the experimental coordinate system, that is, along the cutting speed direction and perpendicular to the cutting speed direction.

[0215] The cutting force in the fiber bending zone is decomposed along the cutting speed direction and perpendicular to the cutting speed direction to obtain the theoretical cutting force component F in the fiber bending zone. Q1X and F Q1Y , expressed as:

[0216]

[0217] Where μ is the friction coefficient.

[0218] For the fiber compression effect of the cutting edge in the fiber compression zone, the average force F acting on the tool due to microbuckling is Q2 The cutting force in the fiber extrusion zone is decomposed along the cutting speed direction and perpendicular to the cutting speed direction to obtain the theoretical cutting force component F in the fiber extrusion zone. Q2X and F Q2Y , expressed as:

[0219]

[0220] The theoretical cutting force component F in the fiber bending zone is used Q1X and F Q1Y The theoretical cutting force component F in the fiber extrusion zone Q2X and F Q2Y Calculate the cutting force F of the CFRP unidirectional laminate to be cut X and F Y , expressed as:

[0221]

[0222] In this embodiment, the cutting force in the fiber bending zone is the total cutting force required for a series of bending fibers, as shown in formula (23). Then, the theoretical value of the cutting force is decomposed according to the direction of the experimental coordinate system, that is, along the cutting speed direction and perpendicular to the cutting speed direction, to obtain the theoretical cutting force component F Q1X and F Q1Y As shown in formula (24). Then, based on formula (22), the theoretical cutting force component F in the fiber extrusion zone is Q2X and F Q2Y It is calculated by formula (25). Finally, considering the cutting forces in the above two cutting zones, the CFRP macro-cutting force in the experimental coordinate system is shown in formula (26).

[0223] In this embodiment, the macroscopic cutting force of CFRP is calculated using formulas (23) to (26) based on the single fiber cutting force and extrusion force calculated in steps 2 and 3. c =10μm / 30μm / 50μm / 70μm, cutting speed v c =50mm / s, fiber cutting angle θ =135°, the theoretical analytical value and experimental value were obtained and compared, such as Figure 4 As shown, by comparing the cutting force 6 obtained by theoretical analysis and the cutting force 7 obtained by experiment, as well as the cutting force 8 obtained by theoretical analysis and the cutting force 9 obtained by experiment, it can be seen from the figure that the model not only accurately describes the mesoscopic failure mechanism but also has a high prediction accuracy for the cutting force amplitude.

[0224] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for establishing a cutting model for carbon fiber composite materials with a large fiber cutting angle, characterized in that: The method comprises the following steps: Step 1: Obtain material performance parameters and cutting processing parameters of the CFRP unidirectional laminate to be cut; Step 2: Establish a single fiber cutting model with multiple contact states to describe the fiber deformation and fracture process under large fiber cutting angles; Step 3: Based on the microbuckling failure mechanism, an extrusion model between the cutting edge and the fiber is established to calculate the extrusion force of the microbuckling on the tool under the extrusion of the cutting edge after the fiber breaks; Step 4: Establish a macro cutting force prediction model to calculate the cutting force of the CFRP unidirectional laminate to be cut.

2. The method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle according to claim 1, characterized in that: The material performance parameters described in step 1 include: fiber elastic modulus E f , fiber axial tensile strength limit σ t , fiber diameter d f , fiber Poisson's ratio ν f , fiber volume fraction V f , fiber section moment of inertia I f , resin and interface elastic modulus E m , resin and interface Poisson's ratio ν m , resin and interface shear modulus G m , resin and interface bonding strength σ b and the equivalent homogeneous Poisson's ratio v.

3. The method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle according to claim 2, characterized in that: The cutting parameters in step 1 include: tool back angle α, tool rake angle γ, cutting edge radius r e , cutting speed v c and the fiber cutting angle θ.

4. The method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle according to claim 3, characterized in that: The step 2 further comprises: Step 2.1: The constraint states of the cut fiber at different locations along the fiber axis are divided into three constraint states, and the deformation control equations of the cut fiber in each constraint state are constructed respectively; Step 2.2: Based on the deformation control equation of the cut fiber under each constraint state, solve the general solution of fiber deformation deflection under different constraint states respectively; Step 2.3: According to the contact state between the cut fiber and the tool and the change of the fiber state during the cutting process, the fiber deflection and single fiber cutting force during the cutting process are solved by using the general solution of fiber deformation deflection under different constraint states; Step 2.4: Based on the fiber deflection and single fiber cutting force obtained in the cutting process in step 2.3, starting from the initial contact between the front cutting edge of the tool and the fiber end point on the cut fiber, as the tool moves, the contact state or boundary conditions between the cut fiber and the tool will switch and change in Case 1-Case 8. The tool movement distance is gradually increased, and the deflection, slope, maximum tensile stress inside the fiber, and bonding resistance of the resin and interface of the cut fiber after the tool moves in each iteration round are calculated using an iterative algorithm and boundary conditions. The bending fracture of the cut fiber under the machining surface is used as the iteration termination condition, and the deflection of the cut fiber, fiber fracture position, and single fiber cutting force when the fiber fracture occurs are then solved.

5. The method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle according to claim 4, characterized in that: The three constraint states described in step 2.1 include: The first constraint state is: when the cut fiber is subject to the normal constraint and tangential constraint of the unprocessed material above the workpiece surface, the cut fiber is in the first constraint state, and the deformation control equation of the cut fiber in the first constraint state is constructed as follows: where k m0 k is the normal constraint effect of the unprocessed material above the workpiece surface on the cut fiber; m10 E is the tangential constraint of the unprocessed material above the workpiece surface on the cut fibers; f is the fiber elastic modulus; ω(x) is the deflection at a distance x from the top of the cut fiber; The second constraint state is: when the cut fiber is subject to the normal constraint and tangential constraint of the unprocessed material, the cut fiber is in the second constraint state, and the deformation control equation of the cut fiber in the second constraint state is constructed as follows: where k m k is the first parameter of the unprocessed material, which is used to characterize the normal constraint effect of the unprocessed material on the cut fiber; m1 It is the second parameter of the unprocessed material, used to characterize the tangential constraint effect of the unprocessed material on the cut fiber; The third constraint state is: when the cut fiber is simultaneously subject to the normal constraint of the unprocessed material, the tangential constraint, and the bonding effect of the resin and the interface, the cut fiber is in the third constraint state, and the deformation control equation of the cut fiber in the third constraint state is constructed as follows: where k b It is the tensile stiffness of the resin and the interface, and is used to characterize the bonding effect of the resin and the interface on the fiber.

6. The method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle according to claim 5, characterized in that: The general solution of fiber deformation deflection under different constraint states described in step 2.2 includes: The general solution of fiber deformation deflection ω1(x) under the first constraint state is: Among them, A1, A2, A3, and A4 are all integral constants; The general solution of fiber deformation deflection ω2(x) under the second constraint state is: Among them, B1, B2, B3, and B4 are all integral constants; The general solution of fiber deformation deflection ω3(x) under the third constraint state is: Where C1, C2 are integral constants; e is a natural constant; In addition to the above three constraint states, since the deflection of the fiber end point is related to the tool movement and the tool rake angle, the deflection ω of the fiber end point in the cut fiber O It is expressed as: Where t is the tool movement time; During the bending process of the cut fiber, when the slope of a certain point on the cut fiber is less than or equal to cot(γ-θ), the cut fiber is in line contact with the rake face, and the fiber deflection of the line contact part is generally solved as follows: Where ω0(x) is the general solution of the fiber deflection in the portion of the cut fiber that is in line contact with the rake face.

7. The method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle according to claim 6, characterized in that: The solution method for the fiber deflection and single fiber cutting force in the cutting process described in step 2.3 is as follows: for the cut fiber, the fiber end point is recorded as point O, the point where the fiber and the workpiece plane coincide is recorded as point A, the fiber break points generated by the fiber one by one are recorded as point F, the contact end point where the fiber and the front cutting edge produce line contact is recorded as point E, the cracking end point after the resin and the interface crack is recorded as point C, and the infinite end of the fiber is recorded as point D. The cut fiber is divided into several sections according to the different contact states between the fiber and the tool, and the general solution of the fiber deformation deflection under different constraint states is used to describe the deflection of each section of the fiber, thereby obtaining the single fiber cutting force of the cut fiber in the cutting process; The specific process is as follows: For the node in the cut fiber at a distance x from the top of the cut fiber, the deflection of the node under different constraint states is ω i (x), where i represents the i-th constraint state, and i = 1, 2, 3; the slope is k i =dω i (x) / dx, bending moment is M i =-E f I f d 2 ω i (x) / dx 2 , the shear force is Q i =-E f I f d 3 ω i (x) / dx 3 +k m dω i (x) / dx, and when i=1, Q1=-E f I f d 3 ω1(x) / dx 3 +k m0 dω1(x) / dx; The first contact state Case 1: When the fiber and the tool make initial contact, the initial contact between the fiber end point and the tool rake face is called point contact. The fiber is divided into OA segment, AC segment and CD segment, where the position coordinates of point O, point A and point C along the fiber direction are expressed as: O 、x A and x C , where x O =0,x A =-v c tcosθ,x C =h+(a c -δ) / sinθ; a c is the cutting depth; h is the cracking depth; δ is the springback height of the cut material; Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integration constants A1, A2, A3, A4, B1, B2, B3, B4, C1, and C2: Then, the fiber deflection solutions ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OA, AC and CD segments. At this time, the single fiber cutting force f of the cut fiber is y for: where p m0 is the support resistance on the unprocessed workpiece surface; p m is the support resistance below the fiber breaking point; q b is the bonding resistance; p m0 (ω1), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length of the OA segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment; The second contact state Case 2: before the fiber breaks for the first time, when the fiber is in line contact with the tool rake face and the contact end point is above the workpiece plane, the fiber is divided into OE segment, EA segment, AC segment and CD segment, where the position coordinates of point O, point A and point C along the fiber direction are: x O =0;x A =-v c tcosθ;x C =h+(a c -δ) / sinθ; Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integration constants A1, A2, A3, A4, B1, B2, B3, B4, C1, and C2: Then, the fiber deflection solutions ω0(x), ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OE segment, EA segment, AC segment and CD segment. At this time, the single fiber cutting force f of the cut fiber is y for: where p m0 (ω0), p m0 (ω1), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length in the OE segment, EA segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment; The third contact state Case 3: before the fiber breaks for the first time, when the fiber is in line contact with the tool rake face and the contact end point is below the workpiece plane, the fiber is divided into OE segment, EC segment and CD segment, where the position coordinates of point O, point A and point C along the fiber direction are: x O =0;x A =-v c tcosθ;x C =h+(a c -δ) / sinθ; Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integral constants B1, B2, B3, B4, C1, and C2: Then, the fiber deflection solutions ω0(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OE, EC and CD segments. At this time, the single fiber cutting force f of the cut fiber is y for: where p m0 (ω0), p m (ω0), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length of the OA segment, AE segment, EC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment; The fourth contact state Case 4: After the fiber breaks, when the fiber and the tool rake face are in point contact, that is, only the fiber break point F is in contact with the tool rake face, and the fiber break point F is located above point A, the fiber is divided into OF segment, FA segment, AC segment and CD segment, and the position coordinate of the fiber break point is marked as x F , and the position coordinates of point O, point A, and point C along the fiber direction are: x O =0;x A =-v c tcosθ;x C =h+(a c -δ) / sinθ; Based on the continuity assumption of the beam, the boundary conditions are used to solve the unknown integration constants A1, A2, A3, A4, B1, B2, B3, B4, C1, and C2: Then, the fiber deflection solutions ω0(x), ω1(x), ω2(x) and ω3(x) under different constraint states are used to describe the fibers in the OF segment, FA segment, AC segment and CD segment. At this time, the single fiber cutting force f of the cut fiber is y for: where p m0 (ω0), p m0 (ω1), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length in OF segment, FA segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment; The fifth contact state Case 5: After the fiber breaks, when the fiber makes point contact with the tool rake face and the fiber break point F is below point A, the fiber is divided into OF segment, FC segment and CD segment, and the boundary conditions are used to solve the unknown integral constants B1, B2, B3, B4, C1 and C2: Then, the fiber deflection solutions ω0(x), ω2(x) and ω3(x) under different constraint states are used to describe the OF, FC and CD segments of the fiber. At this time, the single fiber cutting force f of the cut fiber is y for: where p mF is the support resistance above the fiber breaking point; p m0 (ω0), p mF (ω0), p m (ω2) and p m (ω3) is the support resistance of the fiber microelement length of the OA segment, AF segment, AC segment and CD segment respectively; q b (ω3) is the bonding resistance of the fiber microelement length in the CD segment; The sixth contact state Case 6: After the fiber breaks, when the fiber makes linear contact with the front cutting edge of the tool, and the fiber break point F is above point A, and the contact end point E where the fiber makes linear contact with the front cutting edge is above point A, the fiber is divided into OE segment, EA segment, AC segment and CD segment, and the unknown integral constants A1, A2, A3, A4, B1, B2, B3, B4, C1 and C2 are solved by formula (11), and then the general solutions of fiber deflection under different constraint states ω0(x), ω1(x), ω2(x) and ω3(x) are used to describe the OE segment, EA segment, AC segment and CD segment fibers, respectively, and the single fiber cutting force of the cut fiber is calculated according to formula (12); The seventh contact state Case 7: After the fiber breaks, when the fiber makes line contact with the front cutting edge of the tool, and the fiber break point F is above point A, but the line contact end point E is below point A, the fiber is divided into OE segment, EC segment and CD segment, and the unknown integral constants B1, B2, B3, B4, C1 and C2 are solved using formula (13); then, the general solutions of fiber deflection ω0(x), ω2(x) and ω3(x) under different constraint states are used to describe the OE segment, EC segment and CD segment fibers, and the single fiber cutting force of the cut fiber is calculated according to formula (14); The eighth contact state Case 8: After the fiber breaks, when the fiber is in line contact with the front cutting edge of the tool, and the fiber breaking point F is below point A, the solution method for the fiber deflection and the single fiber cutting force of the cut fiber is the same as that of the seventh contact state Case 7; The fiber breakage and resin and interface cracking are judged based on the maximum tensile stress inside the fiber and the resin and interface bonding resistance. When the maximum tensile stress inside the fiber reaches the fiber tensile strength, the fiber breaks: where σ max is the maximum tensile stress inside the fiber; r f is the fiber radius; σ t is the fiber tensile strength; When the bonding resistance between the resin and the interface is greater than the tensile strength limit of the resin and the interface, the resin and the interface will crack: q b =k b ω(x)≥σ b (20) where q b is the bonding resistance between resin and interface; b It is the ultimate tensile strength of the resin and the interface.

8. The method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle according to claim 7, characterized in that: The specific method of step 3 is: after the fiber breaks, under the extrusion of the cutting edge, the cut fiber will fail again, and the failure mechanism is micro-buckling. At this time, considering the compressive strength σ of the CFRP unidirectional laminate mb for: Where η is the bonding property of the resin and the interface; ξ represents the slip parameters of the resin and the interface in microbuckling; The force required for fiber extrusion failure is calculated by multiplying the compressive strength by the projected area of ​​the tool cutting edge on the workpiece. Assuming that the axial force increases linearly and the fiber breaks within a certain distance from the cutting edge, the extrusion force F acting on the tool by microbuckling is Q2 for: F Q2 =0.5t w s mb (r e sinθ-r e cosθ) (22) where t w is the thickness of CFRP unidirectional laminate.

9. The method for establishing a cutting model of a carbon fiber composite material with a large fiber cutting angle according to claim 8, characterized in that: The macro cutting force prediction model includes two parts: the bending effect of the cutting tool rake face on the fiber in the fiber bending and breaking area and the squeezing effect of the cutting edge on the fiber in the fiber squeezing area; For the bending effect of the cutting tool front face on the fiber in the fiber bending zone, the total cutting force F required to bend all the fibers is Q1 Cutting force as fiber bending and breaking zone: where d f is the fiber diameter; The cutting force in the fiber bending zone is decomposed along the cutting speed direction and perpendicular to the cutting speed direction to obtain the theoretical cutting force component F in the fiber bending zone. Q1X and F Q1Y , expressed as: Where μ is the friction coefficient; For the fiber compression effect of the cutting edge in the fiber compression zone, the average force F acting on the tool due to microbuckling is Q2 The cutting force in the fiber extrusion zone is decomposed along the cutting speed direction and perpendicular to the cutting speed direction to obtain the theoretical cutting force component F in the fiber extrusion zone. Q2X and F Q2Y , expressed as: The theoretical cutting force component F in the fiber bending zone is used Q1X and F Q1Y The theoretical cutting force component F in the fiber extrusion zone Q2X and F Q2Y Calculate the cutting force F of the CFRP unidirectional laminate to be cut X and F Y , expressed as:

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