A numerical control machine tool cutting force dynamic control method and system for blisk machining

Abstract

This invention discloses a dynamic control method and system for cutting force in CNC machine tools for machining integral bladed disks, comprising: a geometric mapping module between the tool and the blade surface, which considers the complex surface features of the blade and solves in real time the contact point position and surface normal of the tool and the blade surface; a cutting force model construction module, which constructs a theoretical model of infinitesimal cutting force using the infinitesimal method and calculates the total cutting force of the CNC machine tool using integral summation; and a dynamic closed-loop control module for cutting force, which projects the elastic displacement of the blade and the vibration displacement of the tool tip onto the normal of the surface contact point to form a chip thickness correction amount, thereby correcting the undeformed chip thickness in the next time step and realizing the dynamic correction of the theoretical calculation model of cutting force. This invention effectively reduces the prediction error of chip thickness in the machining of thin-walled blades with complex surfaces by introducing the surface contact point normal vector, dynamic coupling, and closed-loop correction mechanism, thus improving the machining stability of CNC machine tools.

Description

Technical Field

[0001] This invention relates to the field of CNC machine tool machining technology, specifically to a dynamic control method and system for cutting force of CNC machine tools for machining integral impeller disks. Background Technology

[0002] With the increasing demands for precision and efficiency in the machining of bladed disks for aero-engines, five-axis CNC machine tools are widely used in the machining of integral bladed disks. However, integral bladed disk blades are typical complex free-form thin-walled structures. During five-axis CNC machining, the contact state between the tool and the blade surface changes in real time with the tool position. Affected by the elastic deformation of the blade and the vibration of the tool-spindle system, the actual chip thickness dynamically shifts along the normal direction of the surface. This makes it difficult for traditional cutting force models based on ideal geometry and fixed direction assumptions to accurately describe the actual machining process, thus limiting machining stability and accuracy.

[0003] Therefore, there is a need for a dynamic control and correction method for cutting force that can combine the kinematics of five-axis machine tools with the contact geometry of blade surfaces, and comprehensively consider the deformation of thin-walled blades, tool vibration, and surface geometric characteristics, so as to achieve dynamic closed-loop control of the cutting force of CNC machine tools in the high-precision machining process. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a dynamic control method and system for cutting force in CNC machine tools for machining integral bladed disks. First, the normal direction of the contact point between the tool and the blade surface is introduced as a unified control direction. The blade elastic deformation and the chip thickness deviation caused by tool tip vibration are dynamically quantified. The cutting force model input is then fed back to correct the dynamic closed-loop control of the cutting force.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks includes the following steps:

[0007] Step 1: Perform geometric mapping between the tool and the blade surface. Considering the complex surface features of the blade, solve the contact point position between the tool and the complex surface of the blade and the surface normal at the contact point in real time.

[0008] Step 2: Based on the contact point position and surface normal, construct a theoretical model of infinitesimal cutting force using the infinitesimal element method, and calculate the total cutting force of the CNC machine tool by integrating and summing the infinitesimal cutting force.

[0009] Step 3: Project the elastic displacement of the blade under the current cutting force and the vibration displacement of the tool tip under the current cutting force onto the normal direction of the surface to form a chip thickness correction amount. Then, use this chip thickness correction amount to correct the undeformed chip thickness at the next moment, thereby realizing the dynamic closed-loop correction of the cutting force theoretical model.

[0010] Further, step 1 includes: parsing the CNC G-code to extract the coordinates, rotation angles, and feed rate information of each axis; constructing a total transformation matrix from the tool coordinate system to the workpiece coordinate system based on the information; calculating the tool tip position and tool axis direction vector in the workpiece coordinate system according to the total transformation matrix, and further calculating the ball center coordinates of the ball end mill; solving for the minimum distance between the ball center coordinates and the parameterized blade surface to determine the contact point between the tool and the blade surface, and obtaining the unit normal vector at the contact point through the cross product operation of the surface parameters.

[0011] Furthermore, the blade surface is mathematically represented using parametric surfaces, where the surface parameters correspond to the circumferential and spanwise directions of the blade, respectively.

[0012] Further, step 2 includes: calculating the undeformed chip thickness, length, and width of the micro-element cutting edge based on the feed per tooth, the radial and axial tangential angles of the micro-element cutting edge, the tool helix angle, and the micro-element thickness; constructing a micro-element cutting force model containing tangential, radial, and axial components; converting the micro-element cutting force to the XYZ axis directions of the tool coordinate system; integrating and summing all the micro-element cutting forces involved in cutting to obtain the instantaneous cutting force in the tool coordinate system, and further converting it to the workpiece coordinate system.

[0013] Furthermore, the tillage force cutting coefficient and shear force cutting coefficient in the infinitesimal cutting force model were obtained through cutting experiments.

[0014] Furthermore, in step 3, when solving for the elastic displacement of the bladed disk, the total cutting force is applied as an excitation load to the finite element physical analysis model of the bladed disk, and the finite element equilibrium equation of the model is solved to obtain the elastic displacement of the bladed disk.

[0015] Furthermore, when establishing the finite element physical analysis model of the bladed disk, the initial deformation caused by the clamping force is applied to the model as a constraint condition.

[0016] Furthermore, in step 3, when solving for the tool tip vibration displacement, the total cutting force is applied as a dynamic excitation to the tool-spindle system dynamic model, and the dynamic equation of the model is solved to obtain the tool tip vibration displacement.

[0017] Furthermore, in step 3, the elastic displacement and vibration displacement are projected onto the surface normal and superimposed to obtain the total chip thickness correction amount. This correction amount is then used to update the undeformed chip thickness at the next moment. The updated undeformed chip thickness is then used as input to the cutting force model construction step to complete the closed-loop control.

[0018] This invention provides a dynamic control system for cutting force in CNC machine tools for machining integral bladed disks, used to implement the aforementioned dynamic control method for cutting force in CNC machine tools for machining integral bladed disks, comprising:

[0019] The module for geometric mapping between the tool and the blade surface performs geometric mapping between the tool and the blade surface, taking into account the complex surface features of the blade, and solves in real time the position of the contact point between the tool and the complex surface of the blade and the surface normal at the contact point.

[0020] The cutting force model construction module constructs a theoretical model of infinitesimal cutting force based on the contact point position and surface normal, and calculates the total cutting force of the CNC machine tool by integrating and summing the infinitesimal cutting forces.

[0021] The cutting force dynamic closed-loop control module projects the elastic displacement of the blade under the current cutting force and the vibration displacement of the tool tip under the current cutting force onto the normal direction of the curved surface to form a chip thickness correction amount. This chip thickness correction amount is then used to correct the undeformed chip thickness at the next moment, thereby realizing the dynamic closed-loop correction of the cutting force theoretical model.

[0022] Beneficial effects:

[0023] 1. This invention addresses the complex curved surface features of blades by proposing to analyze the NC (numerical control code) and combine it with the kinematics of a five-axis CNC machine tool, introducing the normal vector of the contact point between the tool and the blade surface, thus achieving a consistent expression of the chip thickness correction under complex free-form surface machining conditions;

[0024] 2. This invention quantifies and feeds back the elastic deformation of the blade and the vibration displacement of the cutting tip in a unified manner, and constructs a dynamic closed-loop control framework for cutting force in the five-axis machining scenario of the overall bladed disk, thereby improving the machining stability of CNC machine tools. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the CNC machine tool cutting force dynamic control method and system for machining integral bladed disks according to the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0027] like Figure 1 As shown, the present invention provides a dynamic control method for cutting force in CNC machine tools for machining integral bladed disks, comprising: geometric mapping between the tool and the blade surface, construction of a cutting force model, and dynamic closed-loop control of the cutting force. The specific steps are as follows:

[0028] Step (1), geometric mapping between the tool and the blade surface, including:

[0029] Step (1.1): Extract key information from the G-code: Use the NC interpreter to parse m lines of CNC machine tool G-code and extract the key information from the i-th line of G-code to obtain the set KS. i ={G i ,X i ,Y i Z i A i C i ,F i}, where G i The G-code interpolation mode for line i, X i Y i Z i Refers to the XYZ linear coordinates of the i-th row, A i Refers to the rotation angle of the A-axis in the i-th row, C i F refers to the rotation angle along the C-axis of the i-th row. i This refers to the feed rate of the i-th row.

[0030] Step (1.2): Construct the total transformation matrix from the tool coordinate system to the workpiece coordinate system:

[0031] Based on the key information obtained in step (1.1), according to Calculate the linear axis translation matrix ;

[0032] according to Calculate the rotation matrix of axis A ;

[0033] according to Calculate the C-axis rotation matrix ;

[0034] The XYZ coordinates of the intersection point Q of axis A and axis C in the workpiece coordinate system were measured when the motion of each axis of the CNC machine tool was 0. ,according to Calculate the transformation matrix of the rotation center ;

[0035] This machine tool uses a typical five-axis XYZAC type. The C-axis is the rotary axis located on the machine tool's worktable, rotating around the Z-axis. The A-axis is the tilting axis that allows the C-axis worktable to tilt as a whole, tilting around the X-axis. The machine operates in the following order: "workpiece → C-axis worktable → A-axis worktable → bed → X-axis tool post → Y-axis tool post → Z-axis tool post → cutting tool". The total transformation matrix from the tool coordinate system to the workpiece coordinate system is calculated. .

[0036] Calculated As shown below:

[0037] ;

[0038] Step (1.3): Calculate the coordinates of the tool sphere center.

[0039] Based on the total transformation matrix obtained in step (1.2) ,in accordance with Calculate the tool tip position coordinates in the workpiece coordinate system ;

[0040] in, Let L be the position coordinates of the tool tip in the tool coordinate system, and L be the tool length.

[0041] according to Find the tool axis direction vector ;

[0042] according to Calculate the coordinates of the center of the ball end mill. , where R is the radius of the sphere head.

[0043] Step (1.4): Solve for the normal vector of the contact point between the tool and the blade surface:

[0044] Based on parametric surfaces The geometric shape of the blade is mathematically characterized, where For surface parameters, This usually corresponds to the circumferential direction of the blade (from the leading edge to the trailing edge). This usually corresponds to the direction of leaf spread (from leaf root to leaf tip). These are the three-dimensional coordinate functions of points on the surface.

[0045] The above parameterization is achieved using NURBS surfaces:

[0046] ;

[0047] in, It is The grid points for the blade The direction usually corresponds to the circumferential direction (from the leading edge to the trailing edge). The direction corresponds to the span (from leaf root to leaf tip). Indicates the weighting factor. and As basis functions, express The number of times the parameter direction is, express The number of times the parameter direction is measured.

[0048] ;

[0049] ;

[0050] ;

[0051] according to Solve for the coordinates of the center of the sphere With curved surfaces The surface coordinates corresponding to the minimum distance between them, where The value of the independent variable that causes the variable to reach its minimum value. The norm represents the straight-line distance between two points in space.

[0052] in accordance with Determine the contact point between the tool and the blade surface in the current state. ;

[0053] According to the cross product operation Calculate the surface At the contact point The unit normal vector at the location .

[0054] Step (2): Construct the cutting force model, including:

[0055] Step (2.1), Calculation of cutting force related parameters:

[0056] in accordance with Calculate the thickness of the undeformed chip ,in Refers to the current time.

[0057] in accordance with Calculate the length of the infinitesimal cutting edge .

[0058] in accordance with Calculate the width of the infinitesimal cutting edge.

[0059] in, The feed per tooth. The radial tangential angle of the micro-element cutting edge. The axial tangential angle is the angle between the micro-element points on the cutting edge. The helix angle of the cutting tool. The thickness of the micro-element cutting edge.

[0060] Step (2.2), Construction of the infinitesimal cutting force model:

[0061] The cutting force is decomposed into tangential cutting force, radial cutting force, and axial cutting force. Based on the relevant parameters obtained in step (2.1), according to... Construct a micro-element cutting force model, where db is the length of the micro-element cutting edge.

[0062] in, , , Let represent the tillage force cutting coefficients of the infinitesimal element cutting edge in the tangential, radial, and secondary normal directions, respectively. , , The cutting coefficients representing the shear forces in the tangential, radial, and sub-normal directions of the micro-element cutting edge are respectively obtained from cutting experiments. Indicates tangential force. Indicates radial force. This indicates axial force.

[0063] Step (2.3): Transform the three-directional cutting forces onto the tool coordinate system XYZ axes:

[0064] Based on the tangential force obtained in step (2.2) radial force and axial force ,in accordance with The cutting forces in the X, Y, and Z directions of the tool coordinate system are calculated. .

[0065] Wherein, the transformation matrix .

[0066] Step (2.4), Solving for instantaneous cutting force:

[0067] Based on the results obtained in step (2.3) ,in accordance with Obtain the cutting force of the tool ,in This refers to the number of teeth on the cutting tool. , These represent the contact area boundaries of the cutting edge of the tool.

[0068] in accordance with The cutting force in the workpiece coordinate system is obtained through transformation calculation. .

[0069] Step (3), dynamic closed-loop control of cutting force, including:

[0070] Step (3.1): Solve for the elastic displacement of the bladed disk:

[0071] The clamping force itself causes initial elastic deformation and stress in the bladed disk, especially in its thin-walled blade section. Therefore, this preloaded state needs to be applied as part of the constraint conditions to the physical analysis model of the bladed disk.

[0072] In finite element analysis software, a detailed finite element model of the impeller and fixture is established, and the key properties of the impeller material are defined, including elastic modulus E, Poisson's ratio v, and density. Using the "bolt preload" function in the software, a specified preload force is applied to the element simulating the clamp bolt. Static nonlinear analysis is then performed, and the initial stress field, strain field, and displacement field inside the impeller under clamping force are read from the result file and used as the initial conditions.

[0073] The material properties of the entire bladed disc are shown in Table 1:

[0074] Table 1 Material properties of the integral bladed disk

[0075]

[0076] The result calculated in step (2.4) As the excitation load in the finite element physical analysis model of the bladed disk, according to the finite element equilibrium equations Solve for the elastic displacement of the bladed disk. .

[0077] in, , , These are the mass matrix, damping matrix, and stiffness matrix of the bladed disk, respectively.

[0078] in accordance with The normal vector projected onto the contact point of the surface The chip thickness correction component caused by the elastic deformation of the bladed disk is obtained above. .

[0079] Step (3.2), solve for the tool tip vibration displacement:

[0080] The result calculated in step (2.4) As a dynamic excitation in the dynamic model of the tool-spindle system, according to the dynamic equations Calculate the vibration displacement of the tool tip .

[0081] in, , , These are the mass, damping, and stiffness matrices of the tool-spindle system, respectively.

[0082] in accordance with The normal vector projected onto the contact point of the surface The chip thickness correction component caused by tool tip vibration is obtained above. .

[0083] Step (3.3), dynamic closed-loop control of cutting force:

[0084] Based on the results obtained in step (3.1) And obtained from step (3.2) ,in accordance with Calculate the current time Total cutting thickness correction .

[0085] in accordance with Calculate the next time The actual undeformed chip thickness is calculated and corrected for the thickness value corresponding to that time. The time interval is indicated, and its value needs to take into account both the frequency of cutting force changes and the real-time requirements of the system. Preferably, The spindle speed is determined based on the feed cycle per tooth of the tool, assuming it is... The number of teeth on the cutting tool is To ensure that at least one cutting tooth is completed within one cutting cycle The time interval is calculated and corrected. satisfy .

[0086] The revised As the next time The input is fed back to step (2.2) and the cutting force model is corrected. This enables dynamic closed-loop compensation during the processing.

[0087] In summary, this invention discloses a dynamic control method and system for cutting force in CNC machine tools for machining integral bladed disks, including geometric mapping between the tool and the blade surface, a cutting force model construction module, and dynamic closed-loop control of the cutting force. This invention combines the kinematics of a five-axis machine tool with the contact geometry of the blade surface, comprehensively considering the deformation of thin-walled blades, tool vibration, and surface geometric characteristics to achieve dynamic closed-loop control of the cutting force in high-precision machining processes.

[0088] like Figure 1 As shown, the present invention also provides a dynamic control system for cutting force of CNC machine tools for machining integral bladed disks, used to implement the above-mentioned dynamic control method for cutting force of CNC machine tools for machining integral bladed disks, including:

[0089] The module for geometric mapping between the tool and the blade surface performs geometric mapping between the tool and the blade surface, taking into account the complex surface features of the blade, and solves in real time the position of the contact point between the tool and the complex surface of the blade and the surface normal at the contact point.

[0090] The cutting force model construction module constructs a theoretical model of infinitesimal cutting force based on the contact point position and surface normal, and calculates the total cutting force of the CNC machine tool by integrating and summing the infinitesimal cutting forces.

[0091] The cutting force dynamic closed-loop control module projects the elastic displacement of the blade under the current cutting force and the vibration displacement of the tool tip under the current cutting force onto the normal direction of the curved surface to form a chip thickness correction amount. This chip thickness correction amount is then used to correct the undeformed chip thickness at the next moment, thereby realizing the dynamic closed-loop correction of the cutting force theoretical model.

[0092] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks, characterized in that, Includes the following steps: Step 1: Perform geometric mapping between the tool and the blade surface. Considering the complex surface features of the blade, solve the contact point position between the tool and the complex surface of the blade and the surface normal at the contact point in real time. Step 2: Based on the contact point position and surface normal, construct a theoretical model of infinitesimal cutting force using the infinitesimal element method, and calculate the total cutting force of the CNC machine tool by integrating and summing the infinitesimal cutting force. Step 3: Project the elastic displacement of the blade under the current cutting force and the vibration displacement of the tool tip under the current cutting force onto the normal direction of the surface to form a chip thickness correction amount. Then, use this chip thickness correction amount to correct the undeformed chip thickness at the next moment, thereby realizing the dynamic closed-loop correction of the cutting force theoretical model.

2. The method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks as described in claim 1, characterized in that, Step 1 includes: parsing the CNC G-code to extract the coordinates, rotation angles, and feed rates of each axis; constructing a total transformation matrix from the tool coordinate system to the workpiece coordinate system based on the information; calculating the tool tip position and tool axis direction vector in the workpiece coordinate system according to the total transformation matrix, and further calculating the ball center coordinates of the ball end mill; solving for the minimum distance between the ball center coordinates and the parameterized blade surface to determine the contact point between the tool and the blade surface, and obtaining the unit normal vector at the contact point through the cross product operation of the surface parameters.

3. The method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks as described in claim 2, characterized in that, The blade surface is mathematically represented using parametric surfaces, where the surface parameters correspond to the circumferential and spanwise directions of the blade, respectively.

4. The method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks as described in claim 1, characterized in that, Step 2 includes: calculating the undeformed chip thickness, length, and width of the micro-element cutting edge based on the feed per tooth, the radial and axial tangential angles of the micro-element cutting edge, the tool helix angle, and the micro-element thickness; constructing a micro-element cutting force model containing tangential, radial, and axial components; converting the micro-element cutting force to the XYZ axis directions of the tool coordinate system; integrating and summing all the micro-element cutting forces involved in cutting to obtain the instantaneous cutting force in the tool coordinate system, and further converting it to the workpiece coordinate system.

5. The method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks as described in claim 4, characterized in that, The tillage force cutting coefficient and shear force cutting coefficient in the infinitesimal cutting force model were obtained through cutting experiments.

6. The method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks as described in claim 1, characterized in that, In step 3, when solving for the elastic displacement of the bladed disk, the total cutting force is applied as an excitation load to the finite element physical analysis model of the bladed disk, and the finite element equilibrium equation of the model is solved to obtain the elastic displacement of the bladed disk.

7. The method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks as described in claim 6, characterized in that, When establishing the finite element physical analysis model of the bladed disk, the initial deformation caused by the clamping force is applied to the model as a constraint condition.

8. The method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks as described in claim 1, characterized in that, In step 3, when solving for the tool tip vibration displacement, the total cutting force is applied as a dynamic excitation to the tool-spindle system dynamic model, and the dynamic equation of the model is solved to obtain the tool tip vibration displacement.

9. The method for dynamic control of cutting force in CNC machine tools for machining integral bladed disks as described in claim 1, characterized in that, In step 3, the elastic displacement and vibration displacement are projected onto the surface normal and superimposed to obtain the total chip thickness correction amount. This correction amount is then used to update the undeformed chip thickness at the next moment. The updated undeformed chip thickness is then used as input to the cutting force model construction step to complete the closed-loop control.

10. A dynamic control system for cutting force of a CNC machine tool for machining integral bladed disks, used to implement the dynamic control method for cutting force of a CNC machine tool for machining integral bladed disks as described in any one of claims 1-9, characterized in that, include: The module for geometric mapping between the tool and the blade surface performs geometric mapping between the tool and the blade surface, taking into account the complex surface features of the blade, and solves in real time the position of the contact point between the tool and the complex surface of the blade and the surface normal at the contact point. The cutting force model construction module constructs a theoretical model of infinitesimal cutting force based on the contact point position and surface normal, and calculates the total cutting force of the CNC machine tool by integrating and summing the infinitesimal cutting forces. The cutting force dynamic closed-loop control module projects the elastic displacement of the blade under the current cutting force and the vibration displacement of the tool tip under the current cutting force onto the normal direction of the curved surface to form a chip thickness correction amount. This chip thickness correction amount is then used to correct the undeformed chip thickness at the next moment, thereby realizing the dynamic closed-loop correction of the cutting force theoretical model.

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