A sawing and fine hole drilling composite processing method for hard and brittle ceramic matrix composite materials

Abstract

The application discloses a sawing and fine hole drilling composite processing method for hard and brittle ceramic matrix composite materials. The method comprises the following steps: pumping liquid carbon dioxide fluid into a hollow diamond composite cutter and maintaining a basic pressure, and in-situ sawing rough machining by using bottom coarse-grained diamond abrasive grains; lifting the fluid static pressure to a working pressure, driving a radial elastic deformation of a micron-level closed flexible hinge of a side wall, forcibly pulling apart a dynamic variable cross-section throttling micro-channel, triggering liquid carbon dioxide throttling expansion phase change into a gas-solid mixed phase; forming a cryogenic environment by using the impact of the sprayed gas-solid mixed phase on the hole wall to promote low-temperature embrittlement of the reinforcing fibers, and using fine-grained diamond abrasive grains expanding with the side wall to perform micro-extrusion and same-direction brittle shear on the hole wall; and unloading the fluid pressure to make the cutter shrink inward and reversely exit under the action of elastic restoring force. The application realizes in-situ switching of rough and fine machining and synchronous brittle removal of two-phase materials, and eliminates the contact interference scratch of the tool.

Description

Technical Field

[0001] This invention relates to the field of hard and brittle composite material processing technology, specifically to a sawing and precision hole processing method for hard and brittle ceramic matrix composite materials. Background Technology

[0002] Hard and brittle ceramic matrix composites are widely used in aerospace and high-end manufacturing due to their physical properties such as high temperature resistance, low density, and high specific strength. However, these materials face many technical bottlenecks in hole machining. In existing hole machining processes, roughing and sawing of the blanking material and finishing of the hole wall usually require different tools to be performed in steps. This step-by-step machining mode requires a second tool change and repositioning when switching between processes, which inevitably introduces spindle centering runout error, making it difficult to guarantee the machining dimensional accuracy and severely restricting the overall machining efficiency.

[0003] Meanwhile, hard-brittle ceramic matrix composites consist of a ceramic matrix and reinforcing fibers. Under normal room temperature processing conditions, there are significant differences in the mechanical properties between these two material components. The ceramic matrix exhibits hard and brittle characteristics, while the reinforcing fibers possess higher fracture toughness. When the abrasive grains of a cutting tool apply cutting action to the material, the reinforcing fibers at room temperature are prone to plasticity, causing the tool to bend and the interface to detach, preventing them from achieving brittle fracture simultaneously with the ceramic matrix. This heterogeneous removal mode can produce surface defects such as fiber pull-out and matrix tearing on the machined hole walls, making it difficult to achieve the surface integrity requirements of finished holes.

[0004] Furthermore, in machining equipment involving minute adjustment of hole diameter or expansion finishing, when the spindle retracts after the hole wall machining is completed, the cutting edge of the tool often struggles to achieve mechanical timing synchronization with the system's decompression command. If the cutting edge cannot retract to its initial safe size in time, the abrasive grains on the outer edge of the tool will interfere with the machined finished hole wall during the retraction process, directly scratching the ceramic-based hole wall surface, which is extremely sensitive to microcracks, causing severe secondary damage. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a combined sawing and precision drilling method for hard and brittle ceramic matrix composites, which solves the technical problems existing in the processing of hard and brittle ceramic matrix composites, such as reinforcing fiber pull-out, matrix tearing, and positioning errors during secondary tool changes.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of the present invention provides a method for sawing and precision drilling of hard and brittle ceramic matrix composite materials, based on a composite machining system. The composite machining system includes a CNC spindle unit, a fluid pumping and temperature control unit, a hollow diamond composite tool, and a multi-field collaborative control unit. The hollow diamond composite tool has a liquid-containing cavity inside, a micron-level closed flexible hinge on its sidewall, and a dynamically variable cross-section throttling microchannel spatially nested with the micron-level closed flexible hinge. Coarse-grained diamond abrasive grains are fixed to the bottom end face, and fine-grained diamond abrasive grains are fixed to the outer surface of the sidewall. The machining method includes the following steps: Step S100, Initialization of the processing system and pressure maintenance of the medium base: The control fluid pumping and temperature control unit pumps liquid carbon dioxide fluid into the liquid cavity of the hollow diamond composite tool to maintain the actual fluid static pressure in the liquid cavity at the base pressure. The base pressure is set to be less than the critical opening pressure threshold for the micron-level closed flexible hinge to yield and deform, thus maintaining the mechanical closure of the micron-level closed flexible hinge and maintaining the throat of the dynamic variable cross-section throttling microchannel at the preset micron-level leakage gap. Step S200, closed-state high-rigidity in-situ sawing roughing: control the CNC spindle unit to drive the hollow diamond composite tool to rotate and feed along the workpiece axis, use coarse-grained diamond abrasive to perform roughing, maintain the liquid cavity at the basic pressure during roughing, and control the fluid to leak out through the micron-level leakage gap. Step S300, In-situ Fluid-Structure Coupling Micro-diameter Variable and Phase Transformation Excitation: When the multi-field collaborative control unit determines that the set machining hole depth has been reached, it controls the CNC spindle unit to stop the axial feed motion and maintain the in-situ rotation of the hollow diamond composite tool, raising the actual hydrostatic pressure of the fluid in the liquid cavity to the working pressure. The working pressure is set to be greater than the critical opening pressure threshold, driving the micron-level closed flexible hinge to generate radial elastic deformation. The radial expansion displacement of the tool sidewall follows the stiffness equation; the radial expansion displacement forcibly opens the throat of the dynamic variable cross-section throttling microchannel, triggering the isenthalpic throttling expansion of the liquid carbon dioxide fluid. The temperature drop when the fluid is injected into the external cutting zone follows the thermodynamic integral equation; the liquid carbon dioxide fluid phase changes to a gas-solid mixed phase and is injected into the external cutting zone; Step S400, Gas-solid mixed phase targeted chilling and micro-extrusion fine grinding: The sprayed gas-solid mixed phase impacts the rough-machined hole wall, and the dry ice snow particles sublimate and absorb latent heat to form a cryogenic environment, which promotes the low-temperature embrittlement of the reinforcing fibers inside the hard and brittle ceramic matrix composite material. The real-time elastic modulus of the reinforcing fibers increases with the decrease of local temperature, and its change relationship is a negative correlation function of temperature. Fine-grained diamond abrasive grains with radial expansion displacement with the sidewalls are used to conduct micron-level radial interference with the rough-machined hole wall. A single fine-grained diamond abrasive grain applies contact extrusion force to the hole wall material, and the maximum local contact stress generated satisfies the contact mechanics equation. When the local contact stress exceeds the critical brittle fracture strength, the hole wall is controlled to undergo unidirectional brittle shear. Step S500, flow field unloading and tool non-destructive retraction: The fluid supply is cut off, and the multi-field collaborative control unit outputs a controlled linear pressure relief curve to release the actual static pressure of the fluid in the liquid cavity to the environmental pressure of the external cutting zone. In order to maintain the micron-level closed flexible hinge in a quasi-static recovery equilibrium state, the pressure relief rate is set to be limited by the kinematic synchronous control constraint equation. The micron-level closed flexible hinge closes under the action of elastic restoring force, and the throat of the dynamic variable cross-section throttling microchannel is synchronously contracted to the micron-level leakage gap. The CNC spindle unit drives the hollow diamond composite tool, whose outer diameter has recovered to the initial size, to retract in the reverse direction.

[0007] Furthermore, in the processing system initialization and medium base pressure maintenance in step S100, the base pressure is set to be greater than the saturated vapor pressure of liquid carbon dioxide at the current fluid temperature in the liquid cavity, so as to maintain the liquid carbon dioxide in a single liquid phase flow state.

[0008] Furthermore, in the in-situ fluid-structure interaction micro-diameter change and phase change excitation in step S300, the multi-field collaborative control unit outputs a continuous ramp pressurization command curve, and sets the target working pressure transient value as a linear function of time; combined with the pipeline transient pressure collected by the pipeline built-in pressure sensor and the dynamic pressure drop calculated by the fluid pipeline empirical resistance model, the actual fluid static pressure feedback value of the liquid cavity is calculated in real time; based on the pressure deviation between the target working pressure transient value and the actual fluid static pressure feedback value, a closed-loop proportional-integral-derivative control algorithm is run to control the actual fluid static pressure to rise to the working pressure.

[0009] Furthermore, in the in-situ fluid-structure interaction micro-diameter change and phase change excitation in step S300, the initial fluid temperature of liquid carbon dioxide is controlled to be lower than the Joule-Thomson conversion temperature of carbon dioxide corresponding to the working pressure, so that the single liquid fluid at the working pressure is transformed into a gas-solid mixture containing dry ice particles and carbon dioxide gas at a level below the triple point parameter.

[0010] Furthermore, in the flow field unloading and tool non-destructive retraction in step S500, when the actual fluid static pressure drops to the environmental pressure of the external cutting zone, the multi-field collaborative control unit initiates the elastic recovery delay waiting program, constructs the viscoelastic recovery equation based on the mechanical relaxation time constant of the alloy material and the set maximum radial expansion displacement, sets a safe waiting time until the dynamic residual radial displacement decays to below the allowable radial safety gap, and generates a state determination trigger signal; in response to the state determination trigger signal, the multi-field collaborative control unit cuts off the rotation drive voltage of the vertical spindle motor and drives the hollow diamond composite tool to move upward.

[0011] The second aspect of the present invention provides a sawing and precision drilling composite machining system for hard and brittle ceramic matrix composite materials, for performing the sawing and precision drilling composite machining method described above, including a CNC spindle unit, a fluid pumping and temperature control unit, a multi-field collaborative control unit, and a hollow diamond composite tool clamped at the execution end of the CNC spindle unit; The hollow diamond composite tool has a cylindrical body with an internal liquid-containing cavity. The sidewalls of the hollow diamond composite tool have micron-level closed flexible hinges and dynamically variable cross-section throttling microchannels nested with the micron-level closed flexible hinges. The bottom end face of the hollow diamond composite tool is fixed with coarse-grained diamond abrasive grains, and the outer surface of the sidewalls of the hollow diamond composite tool is fixed with fine-grained diamond abrasive grains. The liquid-containing cavity is connected to the output pipeline of the fluid pump and temperature control unit. The fluid pumping and temperature control unit includes a cryogenic insulated storage tank, a pneumatic liquid booster pump set, a pipeline subcooler, an electric proportional pressure regulating valve, and a Coriolis mass flow meter, which are connected in series through high-pressure resistant pipelines. The multi-field collaborative control unit is bidirectionally connected to the CNC spindle unit, fluid pumping and temperature control unit, respectively. It is used to adjust the valve core opening of the electro-proportional pressure regulating valve to perform dynamic closed-loop setting and linear pressure relief curve control of the actual fluid static pressure, and to control the CNC spindle unit to provide machining motion.

[0012] Furthermore, the micron-level closed flexible hinge is distributed longitudinally in multiple segments along the axial direction of the hollow diamond composite tool. The movable sidewall of the micron-level closed flexible hinge directly constitutes the structural boundary of the throat of the dynamic variable cross-section throttling microchannel, converting the radial expansion displacement of the micron-level closed flexible hinge into the continuous change of the fluid throttling area.

[0013] This invention provides a combined sawing and precision drilling method for hard and brittle ceramic matrix composites. It offers the following advantages: 1. This invention establishes a fluid-structure interaction driving mechanism and uses internal hydrostatic pressure to control the outer diameter deformation of the sidewall of the hollow diamond composite tool. This enables in-situ continuous switching between high-rigidity roughing and micro-extrusion finishing in the same spindle step, avoiding the centering and runout error introduced by secondary tool changes in conventional processes, and improving the dimensional accuracy and overall machining efficiency of composite machining.

[0014] 2. This invention binds the mechanical expansion action of the tool sidewall with the sudden expansion area of ​​the fluid throttling microchannel, triggering isenthalpic expansion to generate a cryogenic gas-solid mixed phase impact cutting zone in situ. This causes the reinforcing fibers inside the hard and brittle ceramic matrix composite material to become brittle at low temperature, reducing the mechanical difference between the fibers and the ceramic matrix, promoting the simultaneous brittle fracture of the two phases, and suppressing the plastic deflection and pull-out defects that are prone to occur in the reinforcing fibers at room temperature.

[0015] 3. By combining the viscoelastic relaxation characteristics of the tool alloy material, this invention sets a controlled linear pressure relief curve and an elastic recovery delay waiting program to ensure that the radial contraction displacement of the hollow diamond composite tool and the flow field pressure relief command are synchronized in time. This allows the outer diameter of the tool to be completely restored to its initial size before the tool is retracted, eliminating the risk of contact interference and scratches on the finishing hole wall and ensuring the integrity of the machined surface. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method of the present invention. Figure 2 This is a system flowchart of the present invention. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] See attached document Figures 1-2 This invention provides a combined sawing and precision drilling method for hard and brittle ceramic matrix composite materials.

[0019] The composite machining system provided in this embodiment includes, at the hardware level, a CNC spindle unit, a fluid pumping and temperature control unit, a hollow diamond composite tool, and a multi-field collaborative control unit. The multi-field collaborative control unit is bidirectionally connected to the CNC spindle unit and the fluid pumping and temperature control unit via an industrial electrical bus. The hollow diamond composite tool is mounted at the end of the CNC spindle unit, and its internal flow channels are physically connected to the output piping of the fluid pumping and temperature control unit.

[0020] The CNC spindle unit is configured to provide the main motion and feed motion required for composite machining. In specific implementations, the CNC spindle unit comprises a mechanical assembly of a vertical spindle motor, a Z-axis linear guide, a servo-driven ball screw mechanism, and a central rotary joint. The vertical spindle motor has a central through-hole that runs through the axis of its rotating spindle, forming the system's main hollow fluid injection channel. The top end of the main hollow fluid injection channel is dynamically sealed to the output pipeline of an external fluid pump and temperature control unit via the central rotary joint, while the bottom end is connected to the machine tool's hydraulic tool holder. For the calculation of the transmission displacement of the servo-driven ball screw mechanism and the vector torque control principle of the vertical spindle motor, those skilled in the art can consult machining equipment design manuals, as these are well-known technologies in the field and will not be elaborated upon here.

[0021] The fluid pumping and temperature control unit is configured to provide the CNC spindle unit and cutting tools with adjustable pressure and flow rate of liquid carbon dioxide fluid. Specifically, the fluid pumping and temperature control unit includes a cryogenic insulated storage tank, a pneumatic-liquid booster pump set, a pipeline subcooler, an electro-proportional pressure regulating valve, an accumulator, and a Coriolis mass flow meter, connected in series via high-pressure resistant pipelines. The cryogenic insulated storage tank is used to contain and maintain the initial liquid phase state of the liquid carbon dioxide. The pneumatic-liquid booster pump set receives control signals and pressurizes the liquid carbon dioxide from its initial storage pressure to a set operating pressure range. The pipeline subcooler is configured to perform secondary cooling of the pressurized liquid carbon dioxide to offset the heat absorbed by the fluid during pipeline transmission and high-speed spindle rotation friction, preventing premature vaporization. The electro-proportional pressure regulating valve is configured to adjust the static pressure amplitude of the output fluid in real time according to analog control commands. The accumulator is connected in parallel in the main fluid supply circuit to absorb fluid pressure pulsations caused by the reversing stroke of the booster pump set, maintaining a constant pressure in the downstream pipeline system. The Coriolis mass flow meter is installed at the end of the pipeline to obtain the real-time transient flow rate and density parameters of liquid carbon dioxide before it enters the main shaft, and feeds this data back to the multi-field collaborative control unit.

[0022] The hollow diamond composite tool is clamped within the aforementioned hydraulic tool chuck. The hollow diamond composite tool is a hollow cylinder with a blind-hole-shaped fluid-containing cavity inside. The open top of the fluid-containing cavity is connected to the main hollow fluid injection channel of the vertical spindle motor, forming a closed, pressurized flow field space. The sidewalls of the hollow diamond composite tool are arrayed with micron-sized closed flexible hinges, and the solid structure of the sidewalls is machined with dynamic variable cross-section throttling microchannels that connect the fluid-containing cavity to the external environment of the tool. The throat of the dynamic variable cross-section throttling microchannels coincides with and nests within the spatial deformation zone of the micron-sized closed flexible hinges. The bottom end face of the hollow diamond composite tool is bonded with a coarse-grained diamond abrasive array using a metal binder, and the outer surface of its cylindrical sidewalls is electroplated with a fine-grained diamond abrasive layer.

[0023] The multi-field collaborative control unit serves as the system's central control unit, specifically an industrial programmable logic controller (PLC) hardware system integrating a motion control card and an analog data acquisition card. The multi-field collaborative control unit incorporates a force-position collaborative control module and a fluid thermodynamics calculation module. The force-position collaborative control module reads the absolute position encoder values ​​of the Z-axis linear guide of the CNC spindle unit via a bus to determine the current machining hole depth position of the tool face, thereby determining whether the system is currently in the roughing or finishing stage.

[0024] The fluid thermodynamics calculation module interacts with the fluid pumping and temperature control unit to execute dynamic closed-loop settings for the hydrostatic pressure of the fluid within the tool cavity. The multi-field collaborative control unit incorporates an empirical resistance model for fluid pipelines, used to calculate the frictional and local resistance losses generated by fluid flow within the pipeline. The multi-field coordinated control unit will control the pressure output from the electrical proportional pressure regulating valve. and The difference serves as the predicted value of the actual hydrostatic pressure within the fluid-filled cavity of the hollow diamond composite tool. The fluid pressure transmission within the system follows the following equilibrium equation: In the formula, The hydrostatic pressure within the fluid cavity of the cutting tool; The target control pressure is issued by the control system to the electric proportional pressure regulating valve; It is the total pressure loss of the fluid flowing from the regulating valve through the rotary joint, the spindle through-hole, and into the inner cavity of the tool.

[0025] The multi-field collaborative control unit adjusts... Variables, forcing actual hydrostatic pressure The system switches between the anti-clogging base pressure value and the high-pressure working value, forming a fluid pressure switching process. The state control threshold for the above fluid pressure switching process is set as the critical opening pressure threshold at which the micron-level closed flexible hinge on the tool sidewall yields and deforms. At the hardware topology level, the system correlates and controls the spindle displacement, system fluid pressure, and microchannel structure deformation, providing a hardware execution basis for subsequent sawing and precision hole machining steps.

[0026] The sawing and precision hole machining method provided in this embodiment is executed based on the aforementioned composite machining system. The system achieves in-situ switching between roughing and finishing through multi-physics field timing control. The specific implementation process includes the following steps.

[0027] Step S100: Machining system initialization and media base pressure holding. The hard and brittle ceramic matrix composite workpiece is fixed to the machine tool table. The system's central control unit controls the fluid pumping and temperature control unit to pump liquid carbon dioxide fluid into the liquid-containing cavity of the hollow diamond composite tool through the spindle's central through-hole. The fluid thermodynamics calculation module calculates the actual hydrostatic pressure of the liquid-containing cavity. Set and maintain at base pressure The basic pressure setting meets the conditions. ,in The critical opening pressure threshold is defined as the pressure at which the micron-level closed flexible hinge on the sidewall of the hollow diamond composite tool yields. Under this pressure boundary condition, the flexible hinge remains mechanically closed due to the material's own stiffness, maintaining a preset micron-level leakage gap at the throat of the dynamically variable cross-section throttling microchannel nested within the flexible hinge. The hollow diamond composite tool as a whole exhibits a highly rigid solid structure.

[0028] Step S200: Closed-state high-rigidity in-situ sawing roughing. The CNC spindle unit drives the hollow diamond composite tool at a predetermined speed. Rotate and apply a feed rate along the workpiece axis. The coarse-grained diamond abrasive grains, fixed to the bottom end face of the hollow diamond composite tool, cut into the workpiece for downward nesting or sawing operations. During roughing, the fluid cavity continuously maintains the base pressure. The fluid seeps outwards in minute quantities through the aforementioned micron-level leakage gaps due to a positive pressure difference, preventing hard and brittle abrasive chips generated during cutting from clogging the microchannels on the tool sidewalls. Regarding the spindle speed... With axial feed rate For specific numerical matching selections, those skilled in the art can consult the manual on cutting processes for hard and brittle materials, which is a well-known technology in the field and will not be elaborated here.

[0029] Step S300: In-situ fluid-structure interaction with micro-diameter change and phase transformation excitation. When the force-position coordination control module determines that the tool end face has reached the set machining hole depth, it controls the CNC spindle unit to stop the axial feed motion, i.e., the axial feed speed... The pressure drops to zero, and the hollow diamond composite tool maintains its in-situ rotation within the hole. The multi-field coordinated control unit sends a pressurization command to the fluid pump and temperature control unit, increasing the actual hydrostatic pressure of the fluid within the cavity to the working pressure. Work pressure meets the conditions. The internal hydrostatic pressure overcomes the yield strength of the tool sidewall material, driving the flexible hinge to produce radial elastic deformation. The radial expansion displacement of the tool sidewall... It follows the stiffness equation.

[0030] The radial expansion displacement of the flexible hinge forcibly opens the throat of the dynamically variable cross-section throttling microchannel, triggering the Joule-Thomson throttling expansion effect of high-pressure liquid carbon dioxide. The temperature drop when the fluid is injected into the external cutting zone... Following thermodynamic equations, the high-pressure fluid undergoes a phase change via a sudden expansion through microchannels, transforming from a liquid phase into a gas-solid mixture of extremely low-temperature dry ice and carbon dioxide gas.

[0031] Step S400: Targeted cryogenic cooling and micro-extrusion finishing of the gas-solid mixture. The ultra-low temperature gas-solid mixture generated in step S300 is targeted and sprayed to impact the rough-machined hole wall. Heat exchange occurs between the ultra-low temperature fluid and the hole wall. The localized deep-cryogenic environment causes low-temperature embrittlement of the reinforcing fibers inside the hard and brittle ceramic matrix composite material, reducing the difference in elastic modulus and fracture toughness between the reinforcing fibers and the ceramic matrix. Simultaneously, due to the radial expansion displacement of the tool sidewall... Fine-grained diamond abrasive grains electroplated on the outer surface of the sidewall cylinder undergo micron-level radial interference with the rough-machined hole wall. Under in-situ rotation, the fine-grained diamond abrasive grains apply constant compressive stress to the hole wall, performing co-directional brittle shearing on the embrittled reinforcing fibers and ceramic matrix, removing the surface damage layer remaining from rough machining, and achieving fine finishing of the hole wall.

[0032] Step S500: Flow field unloading and tool retraction without damage. After finishing, the multi-field collaborative control unit sends a pressure relief command to the electro-proportional pressure regulating valve to cut off the high-pressure fluid supply, releasing the actual static pressure of the fluid in the liquid cavity to the ambient pressure of the external cutting zone. The flexible hinge closes under the elastic restoring force of the structural material, and the radial expansion displacement is... Returning to zero, the throat of the dynamically variable cross-section throttling microchannel synchronously contracts to the preset micron-level leakage gap. The phase change jet stops, and the outer diameter of the hollow diamond composite tool returns to its initial size under system initialization conditions. The CNC spindle unit drives the hollow diamond composite tool to withdraw from the machining hole in the reverse axial direction, ending the entire sawing and precision hole machining process.

[0033] The hollow diamond composite tool body is integrally molded from a high-elasticity modulus alloy material, and its overall shape is a hollow cylinder. An axially extending blind hole is formed inside the body, constituting a fluid-containing cavity. The open top end of the fluid-containing cavity is equipped with a standard tool holder interface for mechanical engagement with the hydraulic tool chuck of the CNC spindle unit, and for achieving fluid-sealed communication with the main hollow fluid injection channel. The bottom of the fluid-containing cavity is a closed end face, creating a closed flow field space capable of withstanding the static pressure of the internal high-pressure fluid.

[0034] The closed-state high-rigidity in-situ sawing roughing described in step S200, and the gas-solid mixed-phase targeted chilling and micro-extrusion fine grinding described in step S400, constitute a composite machining process that includes roughing sub-steps to finishing sub-steps. In detailing the tool structure supporting these sub-steps, the cutting execution part of the hollow diamond composite tool is divided axially into a roughing end face area and a finishing sidewall area. These two areas employ different abrasive bonding processes and grain size configurations to respectively meet the mechanical requirements of high-rigidity sawing and micro-extrusion fine grinding.

[0035] The bottom face of the hollow diamond composite tool body is configured as a roughing end face area. This area is sintered and solidified with a coarse-grained diamond abrasive array using a metal binder. Multiple chip removal grooves are formed along the circumferential direction on the end face, and these grooves radially penetrate the inner and outer walls to accommodate and remove large, hard, and brittle material chips generated during downward nesting or sawing. The metal binder provides high-strength mechanical holding force to resist the impact load caused by brittle fracture of the material during the roughing stage. For the powder metallurgy sintering process of the metal binder and the specific geometric calculations of the chip removal grooves, those skilled in the art can refer to the Superhard Abrasives Manufacturing Manual, which is well-known in the field and will not be elaborated upon here.

[0036] The cylindrical outer surface of the sidewall of the hollow diamond composite tool is configured as a finished sidewall area. This area is deposited with a fine-grained diamond abrasive layer using an electroplating process. The particle size of the fine-grained diamond abrasive is smaller than that of the coarse-grained diamond abrasive on the bottom face, and the specific selection is determined based on the surface roughness requirements of the target machined hole. The single or multiple layers of fine-grained diamond abrasive formed by the electroplating process expose more sharp micro-cutting edges, suitable for micro-compression and shearing of the hole wall under radial expansion of the tool.

[0037] On the solid structure of the pipe wall corresponding to the precision-machined sidewall region, micron-level closed flexible hinges and dynamically variable cross-section throttling microchannels are machined. The inner diameter of the liquid-containing cavity... , outer diameter of the cylinder outer surface foundation Yield strength of the alloy material itself These factors collectively determine the opening threshold of the hollow diamond composite tool's sidewall under internal pressure. Without considering the local deformation of the micron-level closed flexible hinge, the mechanical relationship of the tube wall under the action of internal hydrostatic pressure satisfies the Lamé formula for thick-walled cylinders. The maximum circumferential stress on the inner surface of the tube wall... Compared with actual hydrostatic pressure The relationship is: In the formula, The basic outer diameter of the cylindrical outer surface of the hollow diamond composite tool does not include the thickness of the electroplated fine-grained diamond abrasive layer. This is the inner diameter of the liquid-containing cavity.

[0038] Based on the aforementioned maximum circumferential stress, the critical opening pressure threshold for a micrometer-scale closed flexible hinge to undergo yield deformation is determined. The following yield criterion equation must be satisfied: In the formula, This refers to the yield strength of the high-elasticity modulus alloy material used in the tool body. This equation clarifies the critical opening pressure threshold. The physical calculations are based on this. Once the high-pressure liquid carbon dioxide fluid in the inner cavity reaches this pressure threshold, it is ejected outwards through microchannels in the pipe wall, simultaneously driving the outer diameter... Micrometer-level changes occur.

[0039] In the finishing sidewall region of the hollow diamond composite tool, multiple micron-sized closed flexible hinges are uniformly arrayed along the circumferential direction within the tube wall solid structure. As a subordinate feature of the general technical feature of the micron-sized closed flexible hinges in the claims, its specific physical structure is manifested as a geometric combination of micron-sized gaps formed by slow wire EDM or femtosecond laser processing and elliptical stress concentration holes. These micron-sized closed flexible hinges are distributed longitudinally in multiple segments along the axial direction of the hollow diamond composite tool to ensure that the tool sidewall maintains cylindricity under pressure and avoids tapered deformation.

[0040] Before the actual hydrostatic pressure within the fluid cavity falls below the critical opening pressure threshold, the two side walls of the micron-sized gap in the micron-sized closed flexible hinge adhere to each other under the initial internal stress of the alloy material. This closed state maintains the overall annular cross-sectional shape of the hollow diamond composite tool's sidewalls, ensuring its mechanical stiffness in both torsional and bending directions.

[0041] The in-situ fluid-structure interaction micro-diameter change and phase transition excitation described in step S300 are executed. Step S300 specifically includes a system pressurization sub-step followed by a microchannel sudden expansion sub-step. In explaining the hinge deformation mechanism supporting the subsequent sub-steps, the multi-field cooperative control unit increases the actual hydrostatic pressure of the liquid cavity to the working pressure. Work pressure The structural critical opening pressure threshold required to overcome the pre-tightening force of the gap bonding is greater than the threshold value. Furthermore, the pressure is strictly less than the ultimate pressure required for plastic yielding in the thin-walled region of the hinge. Ultra-high pressure hydrostatic pressure acts directly on the inner wall of the micron-sized closed flexible hinge, overcoming the initial fit stiffness of the structure and forcing the thin-walled region of the hinge to undergo purely elastic bending deformation. The two side walls of the micron-sized gap are then forcibly opened, and the micron-sized closed flexible hinge macroscopically exhibits a minute geometric displacement radially outward along the tool. For finite element stress field analysis and low-cycle fatigue life verification of the elastic deformation of the flexible hinge, those skilled in the art can consult relevant theories in materials mechanics and elasticity mechanics, which are well-known techniques in this field and will not be elaborated upon here.

[0042] To control the variable outer diameter of the tool, the system treats an array structure consisting of multiple micrometer-scale closed flexible hinges distributed on the sidewalls as an equivalent radial elastic mechanical system. This radial elastic mechanical system operates under working pressure... Radial expansion displacement generated under drive The following stiffness equation must be satisfied: In the formula, The effective pressure-bearing area is where hydrostatic pressure directly acts on the inner wall of a single micrometer-scale closed flexible hinge and generates effective thrust in the radial direction. It is the equivalent radial stiffness coefficient of a micrometer-scale closed flexible hinge array.

[0043] The equivalent radial stiffness coefficient This represents the inherent structural constants of the hollow diamond composite tool. Its specific value is determined by the wall thickness of the tube, the radial penetration depth of the micron-sized slit, the minor axis dimension of the elliptical stress concentration hole, and the material thickness at the hinge thin-walled connection. By changing the combination of these geometric parameters, the structure can be set... Specific values, thereby establishing work pressure With radial expansion displacement A linear or nonlinear mapping relationship is established between them. This design, which binds the topology to the mechanical parameters, provides a structural basis for the radial interference of fine-grained diamond abrasive grains on the hole wall during the finishing stage.

[0044] In the finishing sidewall region of the hollow diamond composite tool, a dynamically variable cross-section throttling microchannel penetrates the solid structure of the tube wall, connecting the fluid cavity with the cutting zone environment outside the tool. As a subordinate feature of the dynamically variable cross-section throttling microchannel in the claim, its internal spatial structure is configured as a converging-expanding microchannel. This converging-expanding microchannel is sequentially divided into a converging section, a throat, and an expanding section along the fluid flow direction from the inside out. The fluid inlet of the converging section is connected to the fluid cavity, and the fluid outlet of the expanding section opens towards the fine-grained diamond abrasive layer on the outer surface of the sidewall cylinder.

[0045] The dynamically variable cross-section throttling microchannel and the aforementioned micrometer-scale closed flexible hinge form a spatial nesting and mechanical linkage relationship in terms of spatial topology. Specifically, the throat position of the tapered-expanding microchannel coincides with the micrometer-scale gap space of the micrometer-scale closed flexible hinge. The movable sidewall of the micrometer-scale closed flexible hinge directly constitutes the structural boundary of this throat.

[0046] The processing system initialization and media base pressure maintenance described in step S100 are executed. Step S100 specifically includes a media injection sub-step and a state locking sub-step. When explaining the hardware mechanism supporting the subsequent anti-clogging sub-step, the liquid cavity maintains the base pressure. The micron-level closed flexible hinge maintains structural closure under this basic pressure. Its physical gaps are not completely closed; instead, a pre-set micron-level leakage gap is preserved through the kerf allowance of the slow wire EDM process. This pre-set micron-level leakage gap directly constitutes the initial cross-sectional area of ​​the throat of the dynamic variable cross-section throttling microchannel. This structural feature allows liquid carbon dioxide to leak out in small amounts through the microchannels due to the positive pressure difference between the inside and outside, providing a fluid channel for chip removal and anti-clogging in step S200.

[0047] The in-situ fluid-structure interaction micro-diameter variation and phase change excitation described in step S300 are executed. Step S300 specifically includes a system pressurization sub-step followed by a microchannel sudden expansion sub-step. When specifically explaining the structural linkage mechanism supporting the subsequent phase change excitation sub-step, the actual hydrostatic pressure of the liquid cavity is increased to the working pressure. When the micron-sized closed flexible hinge exceeds its opening threshold, it undergoes purely elastic bending deformation, resulting in radial expansion displacement of the tool sidewall. Because the throat structure boundary is directly mechanically bound to the hinge wall, the radial expansion of the micron-level closed flexible hinge forcibly pulls open the throat of the tapered-expanding microchannel, causing a physical expansion of the throat cross-section.

[0048] Under the aforementioned mechanical linkage, the effective cross-sectional area of ​​the microchannel throat This manifests as radial expansion displacement. The function of . Its cross-sectional area changes according to the following geometric mapping equation: In the formula, The initial cross-sectional area of ​​the microchannel throat when it is in a preset micron-level leakage gap; The effective solid width of the microchannel throat along the axial direction of the hollow diamond composite tool; This is the structural linkage conversion coefficient. This structural linkage conversion coefficient... Defined as the ratio of the radial coordinate value of the microchannel throat to the radial coordinate value of the outer cylindrical surface of the tool.

[0049] The aforementioned geometric mapping equations clarify the correspondence between the local deformation of the hollow diamond composite tool and the change in the cross-sectional area of ​​the fluid channel. The dynamic variable cross-section throttling microchannel, through this spatial nesting design, transforms the radial displacement of the tool sidewall into a continuous change in the fluid throttling area. For the fluid dynamics simulation boundary settings of the Mach number distribution and pressure drop gradient inside the tapered-expanding microchannel, those skilled in the art can consult relevant computational fluid dynamics theories, which are well-known techniques in the field and will not be elaborated upon here.

[0050] During the operation of the composite machining system, the fluid thermodynamics calculation module and the fluid pumping and temperature control unit within the multi-field collaborative control unit work together to regulate the flow state and pressure of liquid carbon dioxide in the tool fluid cavity. As a subordinate feature of the general technical feature of dynamic closed-loop setting of fluid pressure in the claims, the system adjusts the valve core opening of the electro-proportional pressure regulating valve through a closed-loop proportional-integral-derivative control algorithm.

[0051] The processing system initialization and media base pressure holding described in step S100 are executed. Step S100 specifically includes a media injection sub-step and a state locking sub-step. When specifically describing the control logic supporting the subsequent anti-blocking sub-step, the multi-field collaborative control unit sets the target control pressure to the base pressure. To ensure that liquid carbon dioxide does not prematurely vaporize during the transportation and basic pressure holding stages, the fluid thermodynamics calculation module sets the basic pressure in the control logic. It must be strictly greater than the saturated vapor pressure at the current fluid temperature. The controlling boundary conditions for this physical state satisfy the following thermodynamic criterion: In the formula, The current fluid temperature of liquid carbon dioxide within the liquid cavity. The saturated vapor pressure below; The set safety pressure margin is used to offset the local pressure pulsations generated when the fluid flows through the rotary joint and blind orifice. Based on this boundary condition, liquid carbon dioxide maintains a single liquid phase flow state under the basic pressure-holding state, exhibiting the physical characteristics of an incompressible fluid, and providing a stable source of micro-positive pressure leakage for the microchannel.

[0052] The in-situ fluid-structure interaction micro-diameter variation and phase change excitation described in step S300 are executed. Step S300 specifically includes a system pressurization sub-step to a microchannel sudden expansion sub-step. When specifically explaining the variable pressure drive logic supporting the subsequent phase change excitation sub-step, the multi-field collaborative control unit triggers the system pressurization sub-step based on the machining hole depth arrival signal fed back by the force-position collaborative control module. To avoid the liquid hammer effect caused by transient high pressure from causing transient impact on the micron-level closed flexible hinge, the fluid thermodynamics calculation module outputs a continuous ramp pressurization command curve, rather than an instantaneous step signal.

[0053] During the ramp pressurization phase, the system sets the target transient working pressure value. It is expressed as a linear function of time: In the formula, This is the initial moment when the boost command is triggered; The set constant boost rate; This refers to the current moment. The target working pressure transient value. The maximum value is limited to the set final working pressure. .

[0054] During the pressurization process, a Coriolis mass flow meter installed at the end of the pipeline and a pressure sensor built into the pipeline collect transient fluid parameters in real time before entering the spindle. The multi-field collaborative control unit compensates for the transient pressure collected by the pipeline's built-in pressure sensor by combining the dynamic pressure drop calculated using the aforementioned empirical resistance model of the fluid pipeline, and calculates the actual hydrostatic pressure feedback value of the liquid cavity in real time. And calculate its real-time pressure deviation. The multi-field coordinated control unit operates based on this pressure deviation using a proportional-integral-derivative (PID) control algorithm, outputting a control voltage. To the electric proportional pressure regulating valve. Its closed-loop control equation follows: In the formula, This is the proportional gain coefficient; This is the integral gain coefficient; The differential gain coefficient; This is the time variable for integration.

[0055] Through the closed-loop control logic described above, the actual hydrostatic pressure of the liquid cavity is steadily increased and maintained at the working pressure. For the internal electromagnetic response hysteresis compensation of the electro-proportional pressure regulating valve and the tuning methods of the aforementioned proportional-integral-derivative parameters, those skilled in the art can consult relevant theories of industrial automatic control system design, which are well-known technologies in this field and will not be elaborated here.

[0056] As the internal pressure increases, the stress state of the hollow diamond composite tool changes from basic pressure holding to high-pressure expansion. The aforementioned variable pressure drive logic ensures that the radial expansion displacement of the flexible hinge and the sudden expansion action of the throat of the dynamically variable cross-section throttling microchannel are within a controlled and gradual change range, providing the thermodynamic initial conditions for the subsequent throttling expansion and targeted quenching of high-pressure liquid carbon dioxide in the microchannel.

[0057] During the radial expansion of the hollow diamond composite tool, the throat cross-sectional area of ​​the dynamically variable cross-section throttling microchannel continuously expands. This mechanical displacement triggers a change in the fluid thermodynamic state between the internal fluid cavity and the external cutting zone of the tool. As a subordinate feature of the general technical feature of phase change excitation in the claims, the system utilizes the Joule-Thomson effect generated when high-pressure fluid enters a low-pressure environment through micropores to achieve in-situ generation of the cryogenic cooling medium.

[0058] The in-situ fluid-structure interaction micro-diameter variation and phase change excitation described in step S300 are performed. Step S300 specifically includes a system pressurization sub-step followed by a microchannel sudden expansion sub-step. When describing the subsequent phase change excitation sub-step, the liquid carbon dioxide in the liquid cavity is at a high working pressure. With initial fluid temperature The thermodynamic initial state. When the radial expansion of the micron-sized closed flexible hinge forcibly opens the throat of the tapered-expanding microchannel, high-pressure liquid carbon dioxide is injected at high speed through the suddenly expanded throat section to the ambient pressure. The external cutting zone.

[0059] Because the fluid travels through the microchannel for an extremely short time and there is virtually no heat exchange between the system and the external environment, the aforementioned high-speed jetting process is thermodynamically equivalent to an isenthalpic expansion process. The temperature-pressure relationship of a fluid under isenthalpic conditions is determined by the Joule-Thomson coefficient. The partial derivative is defined by the following equation: In the formula, The fluid thermodynamic temperature; For fluid pressure; is the enthalpy of the fluid system.

[0060] To ensure that the throttling expansion produces a cooling effect, the fluid pumping and temperature control unit is configured to maintain the initial fluid temperature... Strictly control carbon dioxide levels corresponding to operating pressure Below the Joule-Thomson conversion temperature, a temperature-controlled boundary condition is established. Based on the above temperature-controlled boundary condition, the Joule-Thomson coefficient of liquid carbon dioxide is... Always greater than zero. High-pressure fluid is injected into a low-pressure environment through a microchannel, resulting in a negative abrupt change in pressure difference. This represents the temperature change of the fluid as it passes through the dynamic microchannel to reach the external cutting zone. Following the thermodynamic integral equation: because and The negative result of the definite integral indicates a decrease in fluid temperature. The final temperature of the fluid after reaching the cutting zone... satisfy As the pressure and temperature of the fluid drop simultaneously below the triple point parameter of carbon dioxide (0.517 MPa, -56.6 °C), the original single liquid phase fluid transforms into a gas-solid mixture containing dry ice particles and carbon dioxide gas the instant it exits the microchannel.

[0061] During the aforementioned phase transition process, the multi-field coordinated control unit needs to maintain a stable supply of cryogenic medium. The initial mass flow rate of the gas-solid mixture injected into the cutting zone. Controlled by the fluid dynamics throttling equation: In the formula, The flow coefficient of the tapered-expanding microchannel is affected by the roughness of the channel wall and the cone angle of the tapered section. The real-time effective cross-sectional area of ​​the throat of the dynamically variable cross-section throttling microchannel; This represents the real-time fluid density of high-pressure liquid carbon dioxide within the liquid cavity.

[0062] The above equations clarify the quantitative relationship between the thermodynamic phase transition process and the physical cross-sectional area of ​​the microchannel. Through the structural expansion of the dynamically variable cross-section throttling microchannel, the system converts the high-pressure fluid potential energy within the liquid cavity into the latent heat and kinetic energy of the gas-solid mixture in the cutting zone. For consulting isenthalpic distribution charts and specific enthalpy data of carbon dioxide under different pressure and temperature coordinates, those skilled in the art can refer to the Chemical Engineering Thermodynamics Phase Diagram Handbook, which is well-known in the field and will not be elaborated upon here.

[0063] In the processing of hard and brittle ceramic matrix composites, the residual processing damage on the hole wall surface mainly stems from the anisotropy of the internal components of the material. At room temperature, the ceramic matrix exhibits hard and brittle characteristics, while the reinforcing fibers exhibit relatively high fracture toughness. When the abrasive grains of the cutting tool apply shear stress to the hole wall, the reinforcing fibers are prone to bending deformation and interlaminar debonding, resulting in fiber pull-out and matrix tearing defects. As a subordinate feature of the general technical feature of targeted cryogenic treatment and material embrittlement in the claims, the system constructs a localized deep cryogenic environment and utilizes the coupling effect of thermodynamics and material mechanics to change the physical parameters of the reinforcing fibers.

[0064] The gas-solid mixture targeted cryogenic treatment and micro-extrusion grinding described in step S400 are performed. Step S400 specifically includes a targeted material embrittlement sub-step followed by a unidirectional brittle shearing sub-step. In detail, the subsequent targeted material embrittlement sub-step involves an ultra-low temperature gas-solid mixture ejected through a dynamically variable cross-section throttling microchannel directly impacting the rough-machined hole wall. This gas-solid mixture contains dry ice particles and carbon dioxide gas at temperatures below the triple point. At the moment of impact with the hole wall, convective heat transfer and phase change heat transfer occur between the hole wall surface and the cryogenic fluid. Its local heat flux density... The following composite heat transfer equation is satisfied: In the formula, is the equivalent convective heat transfer coefficient between the gas-solid mixture and the pore wall surface; This represents the real-time temperature of the hole wall surface; The cryogenic temperature of the gas-solid mixture; The mass flux of dry ice particles impacting the borehole wall; This refers to the latent heat absorbed when dry ice particles undergo a phase transition and sublimate.

[0065] When dry ice particles contact the hole wall in the cutting zone, they sublimate and absorb latent heat, causing a local temperature drop on the hole wall surface and the shallow subsurface, creating a cryogenic environment that targets and covers the contact area between the cutting edge and the material. Under the influence of this cryogenic environment, the reinforcing fibers inside the hard and brittle ceramic matrix composite undergo a low-temperature embrittlement transformation.

[0066] With local temperature The decrease in the real-time elastic modulus of the reinforcing fiber It exhibits a negative correlation function with temperature, and the relationship satisfies: In the formula, To enhance the fiber's performance at room temperature reference temperature The initial elastic modulus; To enhance the temperature coefficient of elastic modulus of fiber materials. Because... and The cryogenic environment leads to an increase in the elastic modulus of the reinforcing fibers.

[0067] At the same time, it enhances the fiber's tensile toughness. The temperature decreases as the material transitions from a ductile fracture mode at room temperature to a brittle fracture mode. Furthermore, the cryogenic environment induces thermal mismatch stress at the interface between the reinforcing fiber and the ceramic matrix, increasing the interfacial shear strength and suppressing radial slippage of the fiber under stress. Through this targeted chilling effect, the difference in elastic modulus and fracture toughness between the reinforcing fiber and the ceramic matrix decreases, and their overall mechanical properties tend to be consistent under cryogenic conditions. For dynamic thermomechanical analysis and lattice phase transition parameter acquisition of different types of reinforcing fibers in the cryogenic temperature range, those skilled in the art can consult standards and atlases for low-temperature mechanical testing of composite materials, which are well-known techniques in the field and will not be elaborated upon here.

[0068] The aforementioned construction and heat transfer process of the local cryogenic environment provides a physical modification basis for the synchronous brittle cutting of two-phase materials in hard and brittle ceramic matrix composites.

[0069] In the machining of hard and brittle ceramic matrix composites, the formation of finished hole walls depends on the microscopic forces and motion interference between abrasive grains and the surface of the workpiece. As a subordinate feature of the general technical feature of micro-extrusion grinding and unidirectional brittle shearing in the claims, the system establishes a fixed-distance cutting trajectory of the abrasive cutting edge by controlling the radial expansion scale of the hollow diamond composite tool and the in-situ rotation of the spindle.

[0070] The gas-solid mixed-phase targeted chilling and micro-extrusion grinding described in step S400 specifically includes a targeted material embrittlement sub-step followed by a co-directional brittle shearing sub-step. In explaining the kinematic mechanism supporting the subsequent co-directional brittle shearing sub-step, the sidewall solid structure of the hollow diamond composite tool undergoes radial expansion displacement under internal pressure. The fine-grained diamond abrasive layer electroplated on the outer surface of the sidewall moves radially outward synchronously with the tool body.

[0071] Let the inner radius of the rough hole formed when the preliminary step S200 rough machining is completed be... The outer radius of the fine-grained diamond abrasive layer of a hollow diamond composite tool in an unpressurized state is... Before the system is pressurized, there is an initial radial clearance between the outer edge of the tool and the hole wall. The initial radial clearance satisfies the geometric equation: As the actual hydrostatic pressure of the fluid inside the cavity steadily increases, the radial expansion displacement of the tool sidewall... Continuously increasing. When the control system prompts... At this point, the fine-grained diamond abrasive layer crosses the initial radial clearance, and its sharp cutting edge physically interferes with the coarse hole wall. The actual micro-radial depth of cut generated by the system... Constrained by displacement interference conditions, its numerical model is expressed as: The spindle drives the tool at a predetermined speed. Under the motion boundary of in-situ rotation, enter the radial depth of cut. A single, fine-grained diamond abrasive grain moves tangentially along the circumferential direction on the surface of the borehole. The cutting edge simultaneously applies tangential shear force and radial compressive force to the borehole wall material in a cryogenic environment.

[0072] Since the aforementioned targeted material embrittlement sub-step has reduced the difference in fracture toughness between the reinforcing fiber and the ceramic matrix, the processed hole wall exhibits homogeneous, hard, and brittle physical properties. The contact compression effect exerted by the fine-grained diamond abrasive grains on the hole wall material approximately obeys Hertz's law of contact mechanics. The maximum local contact stress generated in the contact area between the abrasive grains and the material... Satisfies the contact mechanics equations: In the formula, The normal compressive force transmitted radially outward by a single diamond abrasive grain along the tool; It is the equivalent contact circle radius of the microscopic contact area between the abrasive cutting edge and the workpiece material.

[0073] To clarify the normal extrusion force of a single diamond abrasive grain The macroscopic mechanical source is set under working pressure. The total macroscopic radial thrust transmitted outward by a single micrometer-scale closed flexible hinge is The number of dynamically effective abrasive grains interfering with the hole wall in the corresponding area on the outer side of the hinge is Under the assumption of uniformly distributed load, the normal compressive force borne by a single abrasive grain satisfies .

[0074] When local contact stress When the critical brittle fracture strength of the composite material exceeds that under cryogenic conditions, microcracks form inside the material and propagate rapidly. The embrittled reinforcing fibers and the ceramic matrix undergo brittle fracture synchronously under the guidance of tangential motion, forming tiny chips that detach from the pore wall. This unidirectional brittle shearing sub-step removes the subsurface damage layer remaining on the coarse pore wall, avoiding the tool deformation and shear hysteresis caused by plastic bending of the reinforcing fibers at room temperature.

[0075] The tiny chips that break off are discharged outward along the tool's chip removal grooves under the blowing force of the high-pressure gas-solid mixture ejected from the dynamically variable cross-section throttling microchannel. The continuous microscopic brittle fracture removal volumes of multiple abrasive grains during in-situ rotation superimpose spatially, creating a cylindrical hole wall that meets the design dimensions and surface roughness requirements. For statistical methods of the microscopic cutting edge morphology parameters of diamond abrasive grains and the construction of a single abrasive grain cutting thickness model, those skilled in the art can consult relevant theories of precision grinding mechanisms and contact mechanics; these are well-known techniques in the field and will not be elaborated upon here.

[0076] After finishing, the system needs to restore the safe state of the hollow diamond composite tool from the high-pressure expansion interference state to the initial non-interference state to avoid secondary scratches on the machined hole wall during the tool retraction process. As a subordinate feature of the general technical feature of flow field unloading and tool non-destructive retraction in the claims, the system controls the rate of decrease of the hydrostatic pressure of the fluid in the liquid cavity by adjusting the opening of the unloading valve of the electro-proportional pressure regulating valve through a multi-field collaborative control unit.

[0077] The execution of step S500 involves flow field unloading and non-destructive tool retraction. Step S500 specifically includes the flow field pressure relief sub-step followed by the non-destructive tool retraction step. In detail, the mechanical synchronization mechanism supporting the subsequent flow field pressure relief sub-step is explained: the multi-field coordinated control unit issues a pressure relief command to the fluid pumping and temperature control unit, cutting off the main supply path of high-pressure liquid carbon dioxide. The actual hydrostatic pressure within the liquid cavity... Work pressure It begins to descend. As the internal hydrostatic pressure decreases, the effective thrust acting on the inner wall of the micron-level closed flexible hinge decreases accordingly, and the tool sidewall contracts inward under the elastic restoring force of the alloy material.

[0078] To prevent fluid cavitation impact caused by sudden internal pressure drops, and to avoid the tool sidewalls failing to contract in time due to material elastic hysteresis, the multi-field collaborative control unit outputs a controlled linear pressure relief curve in the flow field pressure relief sub-step, rather than an instantaneous cutoff command. The transient pressure drop equation of this linear pressure relief curve satisfies: In the formula, This is the starting moment when the multi-field coordinated control unit triggers the pressure relief command; This represents the current moment during the depressurization process; The set control pressure relief rate.

[0079] During this depressurization process, the dynamic radial contraction displacement of the tool sidewall Limited by the structural damping and elastic relaxation time of the alloy material, to ensure that mechanical contraction and fluid depressurization remain synchronized, the micron-sized closed flexible hinge is kept in a quasi-static restoring equilibrium state, thus controlling the depressurization rate. It must be constrained by the structural response characteristics of the tool. Its kinematic synchronization control constraint equation is: In the formula, It is the equivalent radial stiffness coefficient of a micrometer-scale closed flexible hinge array; The effective pressure-bearing area of ​​the flexible hinge under hydrostatic pressure; is the mechanical relaxation time constant of hollow diamond composite tool alloy material, which characterizes the intrinsic hysteresis time of the material recovering from stress deformation to a stress-free state; The radial shrinkage safety margin limit value set for the system.

[0080] The multi-field coordinated control unit calculates the target control decompression rate based on the above kinematic synchronization control constraint equations. This is then converted into a continuously decreasing analog control voltage signal and sent to the electro-proportional pressure regulating valve. The fluid pumping and temperature control unit executes this linear pressure relief curve by smoothly reducing the valve opening of the electro-proportional pressure regulating valve. The above valve opening adjustment process ensures the dynamic radial contraction displacement of the tool sidewall. Follow the actual hydrostatic pressure The descent trajectory controls the dynamic tracking error of the radial displacement within a safe margin limit. With the actual hydrostatic pressure... Reduced to cutting zone environmental pressure The micron-sized closed flexible hinge completely closes under the action of its structural elastic restoring force. The throat of the dynamically variable cross-section throttling microchannel synchronously contracts to the preset micron-sized leakage gap, thereby blocking the phase change jet.

[0081] At this point, the basic outer diameter of the cylindrical outer surface of the hollow diamond composite tool has been restored to its initial size before pressurization, and the contact interference between the fine-grained diamond abrasive layer and the machined cylindrical hole wall has been completely eliminated. The aforementioned flow field depressurization sub-step, by controlling the rate of decrease in fluid pressure, matches the elastic recovery mechanical characteristics of the solid material, providing a structurally interference-free prerequisite for the subsequent safe axial withdrawal of the spindle-driven tool from the machined hole. Regarding the mechanical relaxation time constant of the alloy material... The experimental calibration method can be found in the relevant specifications for dynamic thermomechanical analysis and viscoelasticity testing of materials by those skilled in the art. It is a well-known technology in the field and will not be described in detail here.

[0082] At the end of the pressure relief process in the composite machining system, it is essential to ensure that the sidewall of the hollow diamond composite tool is completely restored to its base outer diameter, eliminating contact interference between the fine-grained diamond abrasive grains and the machined hole wall. As a subordinate feature of the general technical feature of state determination and non-destructive tool retraction in the claims, the system performs composite calculations on the real-time fluid pressure feedback value and the material mechanical relaxation time through a multi-field collaborative control unit, and performs a safety state confirmation before tool retraction.

[0083] The flow field unloading and non-destructive tool retraction described in step S500 are executed. Step S500 specifically includes the flow field pressure relief sub-step to the non-destructive tool retraction step. In detailing the subsequent non-destructive tool retraction step, the multi-field collaborative control unit continuously monitors the fluid pressure parameters fed back by the pressure sensor built into the pipeline. When the actual hydrostatic pressure inside the liquid cavity... Reduced to external cutting zone environmental pressure At that time, the multi-field collaborative control unit recorded the unloading completion time as... .

[0084] At this moment, although the hydrostatic pressure has been unloaded, due to the viscoelastic constitutive characteristics of the high-modulus alloy material, the micron-sized closed flexible hinge still exhibits a small amount of residual deformation. The dynamic residual radial displacement of the tool sidewall... It exhibits an exponential decay over time, and its viscoelastic recovery equation satisfies: In the formula, The time when uninstallation is complete The corresponding initial residual radial displacement; The mechanical relaxation time constant of the alloy material; This is the current moment after uninstallation is complete.

[0085] To prevent the tool from scratching the finishing hole wall due to axial movement while in a partially retracted state, the multi-field collaborative control unit operates at all times. Then, the elastic recovery delay waiting procedure is initiated. This is the system-defined safe waiting time. The dynamic residual radial displacement must be ensured Attenuation to the allowable radial safety clearance The following is the radial safety clearance. The value of is strictly less than the design surface roughness tolerance of the finished hole wall.

[0086] To ensure the engineering feasibility of the formula and provide safety redundancy, the multi-field collaborative control unit extracts the working pressure generated in step S300. The corresponding maximum radial expansion displacement is directly assigned to Used for calculation. Based on the above viscoelastic recovery equation, the safe waiting time... The control threshold equation is set as follows: Once the internal timer of the multi-field collaborative control unit confirms that the delay satisfies the above equation condition, the system internally generates a state determination trigger signal indicating that radial interference has been eliminated. This safety state confirmation process, combined with the fluid pressure state and material attenuation model, provides a definite timing control node for non-destructive tool retraction.

[0087] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for combined sawing and precision drilling of hard and brittle ceramic matrix composites, characterized in that, The process employs a hollow diamond composite tool, the hollow diamond composite tool having an internal liquid-containing cavity, and its sidewalls having micron-level closed flexible hinges and dynamically variable cross-section throttling microchannels spatially nested within these hinges. The bottom end face of the hollow diamond composite tool is bonded with coarse-grained diamond abrasive grains, and the outer surface of its sidewalls is bonded with fine-grained diamond abrasive grains. The process includes the following steps: Step S100, Initialization of the processing system and pressure maintenance of the medium: Liquid carbon dioxide fluid is pumped into the liquid cavity of the hollow diamond composite tool to maintain the actual hydrostatic pressure of the liquid cavity at the base pressure. The base pressure is set to be less than the critical opening pressure threshold for the micron-level closed flexible hinge to yield and deform, so as to maintain the mechanical closure of the micron-level closed flexible hinge and maintain the throat of the dynamic variable cross-section throttling microchannel at the preset micron-level leakage gap. Step S200, closed-state high-rigidity in-situ sawing roughing: drive the hollow diamond composite tool to rotate and feed along the workpiece axis, use the coarse-grained diamond abrasive to perform roughing, maintain the liquid cavity at the base pressure during roughing, and allow the fluid to leak out through the micron-level leakage gap; Step S300, In-situ fluid-structure coupling micro-diameter change and phase change excitation: When the set machining hole depth is reached, the axial feed motion is stopped and the hollow diamond composite tool is kept rotating in situ. The actual hydrostatic pressure of the liquid cavity is increased to the working pressure. The working pressure is set to be greater than the critical opening pressure threshold. The micron-level closed flexible hinge is driven to generate radial elastic deformation, which forcibly opens the throat of the dynamic variable cross-section throttling microchannel, triggering the liquid carbon dioxide fluid to throttle and expand and change phase to gas-solid mixed phase and spray it to the external cutting zone. Step S400, gas-solid mixed phase targeted cooling and micro-extrusion fine grinding: the sprayed gas-solid mixed phase impacts the rough-machined hole wall, causing the reinforcing fibers inside the hard and brittle ceramic matrix composite material to undergo low-temperature embrittlement. The fine-grained diamond abrasive grains that generate radial expansion displacement with the sidewalls interact with the rough-machined hole wall at the micron level, applying extrusion stress to the hole wall and performing unidirectional brittle shear. Step S500, flow field unloading and tool non-destructive retraction: cut off the fluid supply, release the actual fluid static pressure of the liquid cavity to the external cutting zone environmental pressure, the micron-level closed flexible hinge closes under the action of elastic restoring force, and simultaneously shrinks the throat of the dynamic variable cross-section throttling microchannel to the micron-level leakage gap, driving the hollow diamond composite tool, whose outer diameter has been restored to the initial size, to retract in the opposite direction.

2. The method for combined sawing and precision drilling of hard and brittle ceramic matrix composite materials according to claim 1, characterized in that, In the processing system initialization and medium base pressure maintenance in step S100, the base pressure is set to be greater than the saturated vapor pressure of liquid carbon dioxide at the current fluid temperature in the liquid cavity, so as to maintain the liquid carbon dioxide in a single liquid phase flow state.

3. The method for combined sawing and precision drilling of hard and brittle ceramic matrix composite materials according to claim 1, characterized in that, In step S300, during the in-situ fluid-structure interaction micro-diameter change and phase change excitation, a continuous ramp pressurization command curve is output, and the target working pressure transient value is set as a linear function of time. Combining the collected pipeline transient pressure and the dynamic pressure drop calculated by the fluid pipeline empirical resistance model, the actual fluid static pressure feedback value of the liquid cavity is calculated in real time. Based on the pressure deviation between the target working pressure transient value and the actual fluid static pressure feedback value, a closed-loop proportional-integral-derivative control algorithm is run to control the actual fluid static pressure to rise to the working pressure.

4. The method for combined sawing and precision drilling of hard and brittle ceramic matrix composite materials according to claim 1, characterized in that, In the in-situ fluid-structure interaction micro-diameter change and phase change excitation in step S300, the initial fluid temperature of the liquid carbon dioxide is controlled to be lower than the Joule-Thomson conversion temperature of carbon dioxide corresponding to the working pressure, triggering isenthalpic expansion of the fluid, and transforming the single liquid phase fluid at the working pressure into the gas-solid mixed phase containing dry ice particles and carbon dioxide gas at a level below the triple point parameter.

5. The method for combined sawing and precision drilling of hard and brittle ceramic matrix composite materials according to claim 1, characterized in that, The cylindricity of the sidewall under pressure is maintained by the micron-level closed flexible hinge, which is distributed in multiple segments longitudinally along the axis of the hollow diamond composite tool. The structural boundary of the throat of the dynamic variable cross-section throttling microchannel is directly formed by the movable sidewall surface of the micron-level closed flexible hinge. In step S300, the radial expansion displacement of the micron-level closed flexible hinge is converted into the continuous change of the fluid throttling area.

6. The method for combined sawing and precision drilling of hard and brittle ceramic matrix composite materials according to claim 1, characterized in that, In step S400, the gas-solid mixed phase targeted cooling and micro-extrusion fine grinding, the gas-solid mixed phase impacts the rough-machined hole wall to generate convective heat transfer and phase change heat transfer. The dry ice snow particles sublimate and absorb latent heat to reduce the local temperature and form a cryogenic environment, which forces the elastic modulus of the reinforcing fibers inside the hard and brittle ceramic matrix composite material to increase and the fracture toughness to decrease.

7. The method for combined sawing and precision drilling of hard and brittle ceramic matrix composite materials according to claim 1, characterized in that, In step S400, during the gas-solid mixed-phase targeted chilling and micro-extrusion fine grinding, the working pressure of the liquid cavity is converted into the normal extrusion force transmitted outward by the micron-level closed flexible hinge. The fine-grained diamond abrasive grains move radially outward synchronously with the sidewall of the hollow diamond composite tool, crossing the initial radial gap. Each fine-grained diamond abrasive grain applies tangential shear force and radial extrusion force to the hole wall material in the cryogenic environment, forcing the local contact stress to exceed the critical brittle fracture strength, and controlling the reinforcing fiber and the ceramic matrix to simultaneously undergo brittle fracture and detach from the hole wall.

8. The method for combined sawing and precision drilling of hard and brittle ceramic matrix composite materials according to claim 1, characterized in that, In step S500, during the unloading of the flow field and the non-destructive retraction of the tool, a controlled linear pressure relief curve is output. The pressure relief rate is set to be limited by the equivalent radial stiffness coefficient of the micron-level closed flexible hinge array and the mechanical relaxation time constant of the hollow diamond composite tool alloy material. The dynamic radial contraction displacement of the sidewall of the hollow diamond composite tool is controlled to follow the downward trajectory of the actual fluid static pressure, maintaining the micron-level closed flexible hinge in a quasi-static recovery equilibrium state.

9. A method for combined sawing and precision drilling of hard and brittle ceramic matrix composites according to claim 1, characterized in that, In step S500, during the unloading of the flow field and the non-destructive retraction of the tool, when the actual hydrostatic pressure of the fluid drops to the environmental pressure of the external cutting zone, an elastic recovery delay waiting program is initiated. Based on the mechanical relaxation time constant of the alloy material and the set maximum radial expansion displacement, a viscoelastic recovery equation is constructed. A safe waiting time is set until the dynamic residual radial displacement decays to below the allowable radial safety gap, and a state determination trigger signal is generated. In response to the state determination trigger signal, the rotary drive voltage is cut off, driving the hollow diamond composite tool to move upward.

10. A sawing and precision drilling combined machining system for hard and brittle ceramic matrix composites, used to perform the sawing and precision drilling combined machining method according to any one of claims 1-9, characterized in that, It includes a CNC spindle unit, a fluid pumping and temperature control unit, and a multi-field collaborative control unit. The fluid pumping and temperature control unit includes a cryogenic insulated storage tank, a pneumatic liquid booster pump set, a pipeline subcooler, an electrical proportional pressure regulating valve, and a Coriolis mass flow meter connected in series. In step S100, the fluid pumping and temperature control unit is controlled by the multi-field collaborative control unit to pressurize the fluid through the pneumatic liquid booster pump group and cool it through the pipeline subcooler before pumping it into the liquid-containing cavity. In steps S200 and S500, the hollow diamond composite tool is driven to rotate, feed axially, and retract in the reverse direction by the CNC spindle unit. In steps S300 and S500, the valve core opening of the electro-proportional pressure regulating valve is adjusted by the multi-field collaborative control unit to execute the actual fluid static pressure increase to the working pressure and the linear pressure relief curve control.

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