A method for determining an ultrasonic milling amplitude parameter of a ceramic matrix composite

Abstract

The application discloses a kind of ceramic matrix composite ultrasonic milling amplitude parameter determination method, belongs to composite material processing technical field, it is characterized in that, including the following steps: a, according to the fracture mode of fiber in macroscopic brittle fracture domain, fiber orientation angle is divided into three intervals;B, three fiber orientation angle intervals are proposed micro-macro brittle fracture transition critical criterion;C, the critical depth of three fiber orientation angle intervals is calculated respectively by selecting corresponding critical depth model;D, according to the critical depth of all fiber orientation angles, select minimum value as the amplitude value of ceramic matrix composite ultrasonic vibration assisted face milling.The minimum value of the calculated all fiber orientation angle micro-macro brittle fracture transition critical depth is used as the amplitude value of ceramic matrix composite ultrasonic vibration assisted face milling, and is used for ceramic matrix composite ultrasonic vibration assisted processing, which greatly reduces the machined surface roughness of ceramic matrix composite.

Description

Technical Field

[0001] This invention relates to the field of composite material processing technology, and in particular to a method for determining the amplitude parameters of ultrasonic milling of ceramic matrix composite materials. Background Technology

[0002] Ceramic matrix composites possess excellent comprehensive properties, including lightweight, high strength, high temperature resistance, oxidation resistance, corrosion resistance, wear resistance, and high damage tolerance. As a highly promising high-temperature resistant material, ceramic matrix composites have found numerous applications in the aerospace field. During the material preparation process, the dimensions of parts made of ceramic matrix composites can change, and the surface quality can be poor. Therefore, after the parts are manufactured, machining is required to obtain high-precision and high-quality assembly surfaces and to improve the appearance by finishing the existing surface. Milling is essential to achieve large-area, large-scale material removal and high-precision, high-quality surfaces.

[0003] Compared to most single-phase materials, ceramic matrix composites are composed of phases with different properties. The synergistic effect between the high-hardness matrix, the anisotropic fiber-reinforced phase, and the weak interface phase is beneficial to improving the material's performance, but at the same time, it significantly reduces the material's machinability. Chen et al. (Transformation of Fracture Mechanism and Damage Behavior of Ceramic-matrix Composites during Nano-scratching) pointed out that, based on the differences in fiber fracture mechanisms, the brittle domain of ceramic matrix composites can be further subdivided into micro-brittle fracture domains and macro-brittle fracture domains. During machining, removing material in the micro-brittle fracture domain can yield a high-quality machined surface, while removing material in the macro-brittle fracture domain, due to the randomness of fiber fracture location and the micro-pits caused by fiber tilting fracture, will significantly reduce the quality of the machined surface. For ceramic matrix composites, defects and damage caused by machining will permanently exist in the parts, directly affecting the thermo-mechanical properties, reliability, and service life of the parts. Components with high costs and extremely harsh service environments require reliable service performance and sufficient service life. Therefore, in the finishing process of ceramic matrix composite parts, it is necessary to suppress processing damage and improve the quality of the machined surface through process optimization.

[0004] Ultrasonic vibration-assisted machining (UVM) technology is widely used in the cutting of hard and brittle materials. It utilizes changes in the kinematic characteristics of the cutting edge to alter machining properties, thereby improving the machinability of difficult-to-machine materials. As a typical material combining the characteristics of both hard and brittle materials and composite materials, UVM technology holds great promise for improving the machining quality of ceramic matrix composites. Currently, UVM technology has been tested in the fabrication of planes, grooves, holes, and cavities in ceramic matrix composite parts.

[0005] Current research on ultrasonic vibration-assisted milling of ceramic matrix composites focuses primarily on analyzing the material removal mechanism and conducting parameter experiments, followed by parameter optimization to obtain suitable ultrasonic vibration-assisted milling parameters for ceramic matrix composites. Fundamental research on the material removal mechanism reveals that the amplitude of ultrasonic vibration has a significant impact on material removal. Setting an appropriate ultrasonic amplitude in ultrasonic vibration-assisted milling of ceramic matrix composites is crucial for obtaining high-quality machined surfaces.

[0006] Chinese patent document CN111755083A, published on October 9, 2020, discloses an analytical method for characterizing fiber fracture in rotary ultrasonic milling of ceramic matrix composites, characterized by the following steps:

[0007] Step 1: Define two cutting modes: “fiber forward cutting” and “fiber reverse cutting”. First, simplify the rotating milling process into two-dimensional orthogonal cutting, retaining the main cutting edge, rake face and flank face of the milling cutter. Then, divide the fiber cutting angle range into forward and reverse parts, with the fiber layup direction being orthogonal to the rake face of the tool as the boundary.

[0008] Step 2: Establish a single fiber cutting deflection curve model for composite materials: First, take a single fiber as the unit of mechanical analysis and treat it as an elastic cylindrical beam structure. The remaining fiber matrix is ​​regarded as a homogeneous material. Then, take a micro-element on the fiber for stress analysis. Obtain the fiber deflection differential equation according to the stress balance equation. Finally, substitute the boundary conditions of fiber deformation to obtain the fiber deflection equation under cutting force.

[0009] Step 3: Construct a stress model for a single fiber in fiber-reinforced ceramic matrix composite material during fiber-forward rotating ultrasonic milling: During fiber-forward cutting, the axial ultrasonic vibration of the tool changes the force direction between the cutting edge and the fiber, thereby changing the stress condition of the fiber. First, the reaction force of the homogeneous material at each point of the fiber is calculated according to the fiber deflection curve equation, and the compressive stress of the tool tip on the fiber is obtained by integrating and summing the reaction forces. Then, the ultrasonic milling friction force is solved according to Coulomb's friction law and the rotational ultrasonic milling motion equation. Finally, the fiber-tool contact stress under the action of compressive force and friction force is calculated according to Hertz contact theory.

[0010] Step 4: Construct a stress model of a single fiber in fiber-reinforced ceramic matrix composite material by reverse ultrasonic milling: During the reverse cutting process, the rake face of the tool compresses the fiber, and the ultrasonic vibration of the tool changes the deformation boundary conditions of the fiber deflection model. First, according to the motion equation of rotary ultrasonic milling, the boundary conditions of the fiber deflection differential equation are solved, and then the deflection equation is obtained. Finally, the maximum shear force and the maximum bending moment on the fiber are calculated.

[0011] Step 5: Characterize the fiber fracture mechanism of rotary ultrasonic milling fiber-reinforced ceramic matrix composites: According to the fiber stress model established in Steps 3 and 4, the fiber bending strength and shear strength are checked respectively. When a certain stress value exceeds its strength value, the fiber will break. Correspondingly, the fiber fracture mode is identified, and the interface debonding length damage at the time of fracture is calculated.

[0012] The analytical method disclosed in this patent document for characterizing fiber fracture in rotary ultrasonic milling of ceramic matrix composites analyzes the stress-induced fiber fracture process during milling and clarifies the mechanism of ultrasonic vibration in fiber removal. However, because it only divides the process into two intervals—forward and reverse fiber cutting—it cannot obtain suitable amplitude values ​​and therefore cannot effectively reduce the surface roughness of the machined ceramic matrix composite. Summary of the Invention

[0013] In order to overcome the defects of the prior art, the present invention provides a method for determining the amplitude parameters of ultrasonic milling of ceramic matrix composites. The present invention uses the minimum value of the critical depth of cut for the micro-to-macro brittle fracture transition of the full fiber orientation angle as the amplitude value of ultrasonic vibration-assisted face milling of ceramic matrix composites, and uses it for ultrasonic vibration-assisted machining of ceramic matrix composites, which greatly reduces the surface roughness of the machined ceramic matrix composites.

[0014] This invention is achieved through the following technical solution:

[0015] A method for determining the amplitude parameters of ultrasonic milling of ceramic matrix composites, characterized by comprising the following steps:

[0016] a. Based on the fracture mode of fibers in the macroscopic brittle fracture domain, the fiber orientation angle is divided into 0°≤θ<γ. n γ n ≤θ<90°+γ n and 90°+γ n The three intervals are ≤θ<180°, where θ is the fiber orientation angle and γ is the fiber orientation angle. n The rake angle of the cutting tool;

[0017] b. Propose a critical criterion for the micro-macro brittle fracture transition in three fiber orientation angle ranges;

[0018] c. Calculate the critical cutting depth by selecting the corresponding critical cutting depth model for each of the three fiber orientation angle intervals;

[0019] d. Based on the calculated critical cutting depth of the 0°-180° full fiber orientation angle, select the minimum value as the amplitude value of ultrasonic vibration-assisted face milling of ceramic matrix composites.

[0020] In step b, the critical criteria for the micro-to-macro brittle fracture transition include critical criterion one, critical criterion two, and critical criterion three.

[0021] In step b, when the fiber orientation angle is 0°≤θ<γ n At that time, the critical criterion one is adopted: under the driving force of cutting force, interfacial slippage occurs between the fiber and the matrix, resulting in interfacial debonding, and the maximum shear stress at the fiber-matrix interface reaches the interfacial shear strength, expressed as:

[0022] τ t，max =τ s，interphase Formula 1

[0023] Where, τ t，max τ is the maximum shear stress at the fiber-matrix interface. s，interphase The interfacial shear strength.

[0024] In step b, when the fiber orientation angle is γ n ≤θ<90°+γ n At that time, the second critical criterion is adopted: during cutting, the cutting edge of the tool first contacts the fiber, forming a contact area between the cutting edge and the fiber. The local high stress in the contact area causes the fiber to break. Based on the maximum tensile stress criterion, the maximum tensile stress in the fiber-cutting edge contact area reaches the fiber tensile strength, and the expression is:

[0025] σ t，max，c =σ T，fiber Formula 2

[0026] Where, σ t，max，c The maximum tensile stress in the fiber-edge contact area is σ. T，fiber This represents the tensile strength of the fiber.

[0027] In step b, when the fiber orientation angle is 90°+γ n When ≤θ<180°, the third critical criterion is adopted: the fiber undergoes bending deformation under the action of the tool's rake face. Based on the maximum tensile stress criterion, the maximum tensile stress on the fiber reaches the fiber's tensile strength, and the expression is:

[0028] σ t，max =σ T，fiber Formula 3

[0029] Where, σ t，maxσ is the maximum tensile stress on the fiber. T，fiber This represents the tensile strength of the fiber.

[0030] In step c, when the fiber orientation angle range is 0°≤θ<γ n At that time, the critical cutting depth model one is adopted;

[0031] When subjected to cutting force, the maximum shear stress τ at the fiber-matrix interface is... t，max for:

[0032]

[0033] Among them, c fiber n represents the relative fiber content in ceramic matrix composites. composite σ represents the porosity of the ceramic matrix composite material. T，matrix For the strength of the matrix, u c，micro The tangential cutting energy is the tangential cutting energy of the micro-brittle fracture domain, w is the cutting width, and a is the cutting width. p N represents the depth of cut. fiber r is the number of fibers that come into contact with the cutting edge across the cutting width. fiber The radius of the fiber;

[0034] Substituting Equation 4 into the critical criterion 1, we obtain the fiber orientation angle range as 0°≤θ<γ. n The critical depth of cut at that time.

[0035] In step c, when the fiber orientation angle range is γ n ≤θ<90°+γ n At that time, the critical cutting depth model two is adopted;

[0036] The maximum tensile stress in the fiber-edge contact area is calculated using Equation 5;

[0037]

[0038] Among them, F r E is the radial component of the force acting on a single fiber. * For the equivalent contact modulus, r tool Let {F1(e)} be the radius of the cutting edge blunt circle of the tool. -2 v is the eccentricity correction factor for the ellipse. fiber Let be the Poisson's ratio of the fiber, and e be the eccentricity of the ellipse. It is the ratio of the minor axis radius to the major axis radius of the elliptical contact region;

[0039] Substituting Equation 5 into the critical criterion 2, we obtain the fiber orientation angle range as γ. n ≤θ<90°+γ n The critical depth of cut at that time.

[0040] In step c, when the fiber orientation angle range is 90°+γ n When ≤θ<180°, the critical cutting depth model three is adopted;

[0041] The maximum tensile stress on the fiber is calculated using Equation 6;

[0042]

[0043] Among them, M max I is the maximum bending moment of the fiber. fiber Let x be the moment of inertia of the fiber cross section. f For the horizontal displacement of the fiber, z f This refers to the vertical displacement of the fiber.

[0044] Substituting Equation 6 into the critical criterion 3, we obtain the fiber orientation angle range as 90° + γ. n Critical depth of cut when ≤θ<180°.

[0045] The basic principle of this invention is as follows:

[0046] We propose critical criteria for the micro-macro brittle fracture transition in three intervals of fiber orientation angle, and establish a critical depth of cut model based on the critical criteria. The minimum critical depth of cut for the micro-macro brittle fracture transition of the full fiber orientation angle is used as the amplitude value of ultrasonic vibration-assisted milling of ceramic matrix composites, thereby realizing the milling of high-quality, low-damage surfaces of ceramic matrix composites.

[0047] During machining, the workpiece is fixed on the CNC machining center worktable. A polycrystalline diamond end mill is used with an ultrasonic vibrating tool holder. The bottom edge of the tool participates in the cutting, and profile milling is performed according to the toolpath specified in the CNC program. During profile milling, the bottom edge vibrates at a high frequency under ultrasonic excitation, repeatedly applying a cutting depth of one amplitude to the machined surface. This secondary cutting effect induced by the longitudinal ultrasonic vibration of the bottom edge can further smooth out the height difference of the machined surface and improve the quality of the machined surface.

[0048] The beneficial effects of this invention are mainly reflected in the following aspects:

[0049] 1. In this invention, the minimum value of the critical depth of cut for the micro-to-macro brittle fracture transition of the full fiber orientation angle is calculated and used as the amplitude value of ultrasonic vibration-assisted surface milling of ceramic matrix composites, which is then used for ultrasonic vibration-assisted machining of ceramic matrix composites, greatly reducing the surface roughness of the machined ceramic matrix composites.

[0050] 2. Compared with the Chinese patent document with publication number CN111755083A and publication date of October 9, 2020, which only analyzes the macroscopic brittle fracture domain, this invention, through previous theoretical and experimental research, has found that there are two material removal mechanisms in the machining of ceramic matrix composites: microscopic brittle fracture and macroscopic brittle fracture. Moreover, the quality is best when cutting in the microscopic brittle fracture domain. The minimum value of the critical depth of cut for the transition from microscopic to macroscopic brittle fracture at the full fiber orientation angle is determined as the amplitude value of ultrasonic vibration-assisted face milling of ceramic matrix composites, which greatly reduces the surface roughness of the machined ceramic matrix composites.

[0051] 3. This invention, for different grades of ceramic matrix composites, allows for the rapid determination of the amplitude of ultrasonic vibration-assisted surface milling before processing, and then the ultrasonic vibration-assisted surface milling is performed, which can effectively reduce the surface roughness of the processed ceramic matrix composites. Attached Figure Description

[0052] The present invention will now be further described in detail with reference to the accompanying drawings and specific embodiments:

[0053] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0054] Example 1

[0055] See Figure 1 A method for determining the amplitude parameters of ultrasonic milling of ceramic matrix composites includes the following steps:

[0056] a. Based on the fracture mode of fibers in the macroscopic brittle fracture domain, the fiber orientation angle is divided into 0°≤θ<γ. n γ n ≤θ<90°+γ n and 90°+γ n The three intervals are ≤θ<180°, where θ is the fiber orientation angle and γ is the fiber orientation angle. n The rake angle of the cutting tool;

[0057] b. Propose a critical criterion for the micro-macro brittle fracture transition in three fiber orientation angle ranges;

[0058] c. Calculate the critical cutting depth by selecting the corresponding critical cutting depth model for each of the three fiber orientation angle intervals;

[0059] d. Based on the calculated critical cutting depth of the 0°-180° full fiber orientation angle, select the minimum value as the amplitude value of ultrasonic vibration-assisted face milling of ceramic matrix composites.

[0060] This embodiment is the most basic implementation method. The minimum value of the critical depth of cut for the micro-to-macro brittle fracture transition of the full fiber orientation angle is used as the amplitude value of ultrasonic vibration-assisted surface milling of ceramic matrix composites, and is used for ultrasonic vibration-assisted machining of ceramic matrix composites, which greatly reduces the surface roughness of the machined ceramic matrix composites.

[0061] Example 2

[0062] See Figure 1 A method for determining the amplitude parameters of ultrasonic milling of ceramic matrix composites includes the following steps:

[0063] a. Based on the fracture mode of fibers in the macroscopic brittle fracture domain, the fiber orientation angle is divided into 0°≤θ<γ. n γ n ≤θ<90°+γ n and 90°+γ n The three intervals are ≤θ<180°, where θ is the fiber orientation angle and γ is the fiber orientation angle. n The rake angle of the cutting tool;

[0064] b. Propose a critical criterion for the micro-macro brittle fracture transition in three fiber orientation angle ranges;

[0065] c. Calculate the critical cutting depth by selecting the corresponding critical cutting depth model for each of the three fiber orientation angle intervals;

[0066] d. Based on the calculated critical cutting depth of the 0°-180° full fiber orientation angle, select the minimum value as the amplitude value of ultrasonic vibration-assisted face milling of ceramic matrix composites.

[0067] In step b, the critical criteria for the micro-to-macro brittle fracture transition include critical criterion one, critical criterion two, and critical criterion three.

[0068] Preferably, in step b, when the fiber orientation angle is 0°≤θ<γ n At that time, the critical criterion one is adopted: under the driving force of cutting force, interfacial slippage occurs between the fiber and the matrix, resulting in interfacial debonding, and the maximum shear stress at the fiber-matrix interface reaches the interfacial shear strength, expressed as:

[0069] τ t，maX =τ s，interphase Formula 1

[0070] Where, τ t，max τ is the maximum shear stress at the fiber-matrix interface. s，interphase The interfacial shear strength.

[0071] In step b, when the fiber orientation angle is γ n ≤θ<90°+γ nAt that time, the second critical criterion is adopted: during cutting, the cutting edge of the tool first contacts the fiber, forming a contact area between the cutting edge and the fiber. The local high stress in the contact area causes the fiber to break. Based on the maximum tensile stress criterion, the maximum tensile stress in the fiber-cutting edge contact area reaches the fiber tensile strength, and the expression is:

[0072] σ t，max，c =σ T，fiber Formula 2

[0073] Where, σ t，max，c The maximum tensile stress in the fiber-edge contact area is σ. T，fiber This represents the tensile strength of the fiber.

[0074] In step b, when the fiber orientation angle is 90°+γ n When ≤θ<180°, the third critical criterion is adopted: the fiber undergoes bending deformation under the action of the tool's rake face. Based on the maximum tensile stress criterion, the maximum tensile stress on the fiber reaches the fiber's tensile strength, and the expression is:

[0075] σ t，max =σ T，fiber Formula 3

[0076] Where, σ t，max σ is the maximum tensile stress on the fiber. T，fiber This represents the tensile strength of the fiber.

[0077] This embodiment is a preferred implementation. Compared with the Chinese patent document with publication number CN111755083A and publication date of October 9, 2020, which only analyzes the macroscopic brittle fracture domain, the previous theoretical and experimental research found that there are two material removal mechanisms in the machining of ceramic matrix composites: microscopic brittle fracture and macroscopic brittle fracture. Moreover, the quality is best when cutting in the microscopic brittle fracture domain. The minimum value of the critical depth of cut for the transition from microscopic to macroscopic brittle fracture at the full fiber orientation angle was determined as the amplitude value of ultrasonic vibration-assisted face milling of ceramic matrix composites, which greatly reduces the surface roughness of the machined ceramic matrix composites.

[0078] Example 3

[0079] See Figure 1 A method for determining the amplitude parameters of ultrasonic milling of ceramic matrix composites includes the following steps:

[0080] a. Based on the fracture mode of fibers in the macroscopic brittle fracture domain, the fiber orientation angle is divided into 0°≤θ<γ. n γ n ≤θ<90°+γ n and 90°+γ n The three intervals are ≤θ<180°, where θ is the fiber orientation angle and γ is the fiber orientation angle. n The rake angle of the cutting tool;

[0081] b. Propose a critical criterion for the micro-macro brittle fracture transition in three fiber orientation angle ranges;

[0082] c. Calculate the critical cutting depth by selecting the corresponding critical cutting depth model for each of the three fiber orientation angle intervals;

[0083] d. Based on the calculated critical cutting depth of the 0°-180° full fiber orientation angle, select the minimum value as the amplitude value of ultrasonic vibration-assisted face milling of ceramic matrix composites.

[0084] In step b, the critical criteria for the micro-to-macro brittle fracture transition include critical criterion one, critical criterion two, and critical criterion three.

[0085] In step b, when the fiber orientation angle is 0°≤θ<γ n At that time, the critical criterion one is adopted: under the driving force of cutting force, interfacial slippage occurs between the fiber and the matrix, resulting in interfacial debonding, and the maximum shear stress at the fiber-matrix interface reaches the interfacial shear strength, expressed as:

[0086] τ t，max =τ s，interphase Formula 1

[0087] Where, τ t，max τ is the maximum shear stress at the fiber-matrix interface. s，interphase The interfacial shear strength.

[0088] In step b, when the fiber orientation angle is γ n ≤θ<90°+γ n At that time, the second critical criterion is adopted: during cutting, the cutting edge of the tool first contacts the fiber, forming a contact area between the cutting edge and the fiber. The local high stress in the contact area causes the fiber to break. Based on the maximum tensile stress criterion, the maximum tensile stress in the fiber-cutting edge contact area reaches the fiber tensile strength, and the expression is:

[0089] σ t，max，c =σ T，fiber Formula 2

[0090] Where, σ t，max，c The maximum tensile stress in the fiber-edge contact area is σ. T，fiber This represents the tensile strength of the fiber.

[0091] In step b, when the fiber orientation angle is 90°+γ n When ≤θ<180°, the third critical criterion is adopted: the fiber undergoes bending deformation under the action of the tool's rake face. Based on the maximum tensile stress criterion, the maximum tensile stress on the fiber reaches the fiber's tensile strength, and the expression is:

[0092] σ t，max =σT，fiber Formula 3

[0093] Where, σ t，max σ is the maximum tensile stress on the fiber. T，fiber This represents the tensile strength of the fiber.

[0094] More preferably, in step c, when the fiber orientation angle range is 0°≤θ<γ n At that time, the critical cutting depth model one is adopted;

[0095] When subjected to cutting force, the maximum shear stress τ at the fiber-matrix interface is... t，max for:

[0096]

[0097] Among them, c fiber n represents the relative fiber content in ceramic matrix composites. composite σ represents the porosity of the ceramic matrix composite material. T，matrix For the strength of the matrix, u c，micro The tangential cutting energy is the tangential cutting energy of the micro-brittle fracture domain, w is the cutting width, and a is the cutting width. p N represents the depth of cut. fiber r is the number of fibers that come into contact with the cutting edge across the cutting width. fiber The radius of the fiber;

[0098] Substituting Equation 4 into the critical criterion 1, we obtain the fiber orientation angle range as 0°≤θ<γ. n The critical depth of cut at that time.

[0099] In step c, when the fiber orientation angle range is γ n ≤θ<90°+γ n At that time, the critical cutting depth model two is adopted;

[0100] The maximum tensile stress in the fiber-edge contact area is calculated using Equation 5;

[0101]

[0102] Among them, F r E is the radial component of the force acting on a single fiber. * For the equivalent contact modulus, r tool Let {F1(e)} be the radius of the cutting edge blunt circle of the tool. -2 v is the eccentricity correction factor for the ellipse. fiber Let be the Poisson's ratio of the fiber, and e be the eccentricity of the ellipse. It is the ratio of the minor axis radius to the major axis radius of the elliptical contact region;

[0103] Substituting Equation 5 into the critical criterion 2, we obtain the fiber orientation angle range as γ. n≤θ<90°+γ n The critical depth of cut at that time.

[0104] In step c, when the fiber orientation angle range is 90°+γ n When ≤θ<180°, the critical cutting depth model three is adopted;

[0105] The maximum tensile stress on the fiber is calculated using Equation 6;

[0106]

[0107] Among them, M max I is the maximum bending moment of the fiber. fiber Let x be the moment of inertia of the fiber cross section. f For the horizontal displacement of the fiber, z f This refers to the vertical displacement of the fiber.

[0108] Substituting Equation 6 into the critical criterion 3, we obtain the fiber orientation angle range as 90° + γ. n Critical depth of cut when ≤θ<180°.

[0109] This embodiment is the best implementation method. For different grades of ceramic matrix composites, the amplitude of ultrasonic vibration-assisted surface milling is quickly determined by calculation before processing, and then ultrasonic vibration-assisted surface milling is performed, which can effectively reduce the surface roughness of the processed ceramic matrix composites.

[0110] The invention will now be illustrated with specific examples:

[0111] SiC prepared by a combined process of chemical vapor infiltration and precursor impregnation pyrolysis f Taking SiC ceramic matrix composites as an example, the material dimensions are 100mm × 100mm × 3mm, the fibers are continuous silicon carbide fibers with a volume fraction of 38%-43%, and the fiber diameter is 12μm-18μm. According to calculations, SiC... f The minimum critical depth of cut for the micro-to-macro brittle fracture transition of SiC ceramic matrix composites under different fiber orientation angles is 8.12 μm. Therefore, the longitudinal amplitude value of ultrasonic vibration-assisted face milling of ceramic matrix composites is set to 8 μm.

[0112] Ultrasonic vibration-assisted face milling was performed on a CNC machining center using a longitudinal-torsion composite rotary ultrasonic tool holder with a longitudinal-torsion ratio of 14:5. During machining, the ultrasonic tool holder was mounted on the spindle of the CNC machining center, and the ultrasonic frequency was set to 20.06 kHz with a longitudinal ultrasonic amplitude of 8 μm. An 8 mm diameter straight fluting cutter was used for face milling. Machining parameters were set as follows: spindle speed 2000 rpm, feed rate 40 mm / min, axial depth of cut 0.5 mm, and radial width of cut 3 mm. A conventional face milling process was also used as a control group, with milling parameters identical to the above parameters, but without ultrasonic vibration applied during the process.

[0113] The surface roughness of the ceramic matrix composite material machined using ultrasonic vibration-assisted face milling was 1.53 μm, while that of the ceramic matrix composite material machined using conventional milling was 3.17 μm. In the ultrasonic vibration-assisted face milling process, the fibers of the ceramic matrix composite material were largely removed within the microscopic brittle fracture domain, resulting in good fiber fracture height uniformity, fewer inclined fracture surfaces, and significantly reduced machining damage. Therefore, this invention can significantly improve the surface quality of machined ceramic matrix composite materials.

Claims

1. A method for determining the amplitude parameters of ultrasonic milling of ceramic matrix composites, characterized in that, The method comprises the following steps: a、According to the breaking mode of the fiber in the macroscopic brittle fracture domain, the fiber orientation angle is divided into three intervals of 0°≤θ<γ n , γ n ≤θ<90°+γ n and 90°+γ n ≤θ<180°, wherein θ is the fiber orientation angle, and γ n is the tool rake angle; b. proposing micro-macro brittle fracture transition critical criterion for three fiber orientation angle intervals; c. selecting corresponding critical depth model to calculate critical depth for the three fiber orientation angle intervals respectively; d. selecting the minimum value as the amplitude value of the ultrasonic vibration assisted face milling of the ceramic matrix composite according to the calculated critical depth of the full fiber orientation angle of 0°-180°; In the step b, the micro-macro brittle fracture transition critical criterion comprises critical criterion one, critical criterion two and critical criterion three; In step b, when the fiber orientation angle is 0°≤θ<90°, γ n At this time, the critical criterion one is adopted: the interface slip occurs between the fiber and the matrix under the driving of the cutting force, the interface debonding occurs, and the maximum shear stress at the fiber-matrix interface reaches the interface shear strength, which is expressed as: Formula 1 wherein, is the maximum shear stress at the fiber-matrix interface, is the interfacial shear strength; The step b is: γ n ≤θ<90°+ γ n When the fiber orientation angle is The second critical criterion is adopted: the cutting tool edge contacts the fiber first when cutting, forming a contact area between the edge blunt circle and the fiber, and the local high stress of the contact area causes the fiber to break. Based on the maximum tensile stress criterion, the maximum tensile stress of the fiber-edge contact area reaches the fiber tensile strength, and the expression is: Formula 2 wherein, is the maximum tensile stress in the fiber-edge contact zone, is the tensile strength of the fiber; The step b, when the fiber orientation angle is 90° γ n When ≤θ<180°, the critical criterion three is adopted: the fiber is bent and deformed under the action of the rake face of the tool, the maximum tensile stress on the fiber reaches the tensile strength of the fiber based on the maximum tensile stress criterion, and the expression is: Formula 3 wherein, is the maximum tensile stress on the fiber, is the tensile strength of the fiber; In the step c, when the fiber orientation angle interval is 0°≤θ ＜ γ n , the critical depth model one is adopted. Maximum shear stress at the fiber-matrix interface when bearing the cutting force is: Formula 4 wherein, is the relative content of fibers in the ceramic matrix composite, is the porosity of the ceramic matrix composite, is the strength of the matrix, is the tangential specific cutting energy of the micro-brittle fracture zone, is the cutting width, is the cutting depth, is the number of fibers in contact with the cutting edge over the cutting width, is the radius of the fibers; Substitute formula 4 into critical criterion one, and the critical depth of cut when the fiber orientation angle interval is 0°≤θ<γ is obtained. n Substitute formula 4 into critical criterion one, and the critical depth of cut when the fiber orientation angle interval is 0°≤θ<γ is obtained. In the step c, when the fiber orientation angle interval is γn≤θ<90°+γn, the critical depth model two is adopted; The maximum tensile stress of the fiber-blade contact area is calculated by formula 5; Formula 5 wherein, is the radial component of force acting on the individual fiber, is the equivalent contact modulus, is the tool edge radius, is the elliptical eccentricity correction factor, is the Poisson's ratio of the fiber, is the eccentricity of the ellipse, is the ratio of the minor axis radius to the major axis radius of the elliptical contact area; Substituting formula 5 into the critical criterion two, the fiber orientation angle interval is γ n ≤θ<90°+γ n The critical depth when In the step c, when the fiber orientation angle interval is 90°+γ n ≤θ<180°, the critical depth model three is used. The maximum tensile stress on the fiber is calculated by formula 6; Formula 6 wherein, is the maximum bending moment of the fiber, is the moment of inertia of the fiber cross-section, is the horizontal displacement of the fiber, is the vertical displacement of the fiber; Substitute formula 6 into critical criterion three, and the fiber orientation angle interval is 90°+γ n Critical depth when ≤θ<180°.

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