Drilling force calculation method based on unit cutter linear synthesis method and transfer learning

Abstract

The invention discloses a drilling force calculation method based on a unit cutter linear synthesis method and transfer learning, which comprises the following steps of: firstly, dividing a drilling cutter into a plurality of unit cutters by adopting the unit cutter linear synthesis method, and calculating and synthesizing the cutting force on each unit cutter to obtain the cutting force on a whole drilling edge; on the basis, an existing drilling force calculation neural network model is migrated to a new drilling task by utilizing a migration learning technology, and rapid and accurate calculation of the drilling force is realized by finely adjusting the weight of the model. According to the method, the accuracy of a unit tool linear synthesis method and the high efficiency of transfer learning are combined, the influence of multiple factors such as the geometrical shape of the twist drill and the workpiece material can be fully considered, and the accuracy and reliability of drilling force calculation are improved; the method has a wide application prospect in machining, can be used for optimizing cutting parameters and improving the machining efficiency and the workpiece quality, and provides effective reference and guidance for machining personnel.

Description

Technical Field

[0001] The present invention relates to the field of mechanical processing technology, and specifically to a method for calculating drilling force in drilling processing. The method combines a unit tool linear synthesis method with a transfer learning technology to improve the calculation accuracy and efficiency of the drilling force. Background Art

[0002] In drilling processing, drilling force has an important influence on workpiece quality and drill life. Studying the calculation (prediction) method of drilling force not only helps to deeply understand the mechanical characteristics of the drilling process, but also provides a theoretical basis for optimizing processing parameters, improving processing efficiency and reducing costs. At present, the main methods for calculating drilling force are theoretical analysis, empirical formula method, finite element method and neural network method: ① The theoretical analysis method decomposes the cutting edge of the drill into multiple tiny cutting units (microelements) when calculating the drilling force. The cutting force of each unit is calculated by a simple microelement cutting force calculation model, and then the cutting forces of all units are superimposed to obtain the drilling force of the whole twist drill. This method ignores the nonlinear effects in the drilling process (such as the influence of drilling thermal effects, tool wear, built-up edge, etc. on drilling force). Only under the condition of a very accurate microelement cutting force calculation model, the calculated drilling force is relatively accurate. ② The empirical formula method uses experimental data to establish the mathematical relationship between drilling force, drilling amount and drill structure parameters through regression analysis. The accuracy and extrapolation of this method are poor. ③ The finite element method uses numerical methods to simulate the interaction between the material and the drill bit during the drilling process, and then calculates the drilling force of the twist drill. This method is computationally intensive and time-consuming. The accuracy of the drilling force is greatly affected by factors such as the selection of material constitutive model parameters and meshing accuracy. It is difficult to handle complex working conditions and requires a large amount of experimental data for verification and calibration. ④ The neural network method uses a large amount of experimental data to automatically learn the relationship between input variables (such as drilling amount and drill bit structural parameters) and drilling force. This method is highly dependent on data and requires a large amount of high-quality experimental data to train the model. When data is insufficient or feature selection is inappropriate, overfitting problems are prone to occur, resulting in poor model generalization ability.

[0003] In summary, most of the existing methods for calculating drilling force require a large amount of experimental data, and the calculation accuracy and efficiency of drilling force need to be further improved. Summary of the invention

[0004] The purpose of the present invention is to provide a drilling force calculation method based on unit tool linear synthesis method and transfer learning, so as to overcome the problems of large amount of experimental data and low precision required for calculating drilling force in existing methods. The method decomposes the drill cutting edge into multiple unit tools, calculates the cutting force of each unit tool using a neural network model, and combines the linear synthesis method and transfer learning technology to realize accurate calculation of drilling force.

[0005] To achieve the above content, the present invention proposes the following technical solutions.

[0006] The drilling force calculation method based on unit tool linear synthesis method and transfer learning includes the following steps:

[0007] S1: Unit tool division

[0008] The two main cutting edges and the chisel edge of the drill bit are divided into a series of unit tools connected end to end, each of which cuts with different rake angles, edge inclination angles and cutting amounts;

[0009] S2: Neural network model for right-angle cutting force calculation

[0010] A series of theoretical calculation results of right-angle cutting force are obtained by using the unequal shear zone model as the source domain data set to train the initial neural network model for right-angle cutting force calculation.

[0011] A target domain data set is obtained through a small number of right-angle cutting experiments, and a neural network model for right-angle cutting force calculation is trained using the transfer learning method.

[0012] S3: Neural network model for calculating bevel cutting forces

[0013] The equivalent plane method is used to transform the bevel cutting condition into an equivalent right-angle cutting condition. The equivalent rake angle and equivalent right-angle cutting amount are calculated in the equivalent plane. The right-angle cutting force neural network model is used to obtain the equivalent right-angle cutting force and transform it into the bevel cutting force.

[0014] The bevel cutting force data obtained from a small number of bevel cutting experiments are used as the target domain dataset, and the final neural network model for bevel cutting force calculation is trained using the transfer learning method.

[0015] S4: Linear synthesis method

[0016] The cutting forces of each unit tool are accumulated by linear synthesis method to obtain the theoretical calculation result of the drilling force of the whole twist drill.

[0017] S5: Transfer Learning

[0018] Obtain a series of theoretical calculation results of drilling force under different diameter twist drills and drilling amount conditions, and use them as source domain data sets to train an initial neural network model for drilling force calculation;

[0019] Conduct a small number of drilling experiments to obtain the measured data of drilling force experiments and use it as the target domain data set;

[0020] Using the transfer learning method, part of the structure, weights or parameters of the initial drilling force calculation neural network model are transferred to the final drilling force calculation neural network, the weights of the first few layers of the neural network are frozen, and a small amount of actual drilling force experimental data is used for secondary training to obtain the final drilling force calculation neural network.

[0021] Furthermore, each cutting edge of the drill bit is divided into a number of unit tools connected end to end, specifically including:

[0022] Divide the drill radius into n equal parts, and get n radii ρ1, ρ2, ρ3, ... ρ arranged from large to small i With the drill axis as the axis and the radius of each equally divided cylinder as the radius, draw n coaxial cylinders. The tool part sandwiched between two adjacent cylindrical surfaces and located on the same cutting edge of the drill bit is defined as a unit tool, that is, the unit tool on the same cutting edge sandwiched between the i-th cylindrical surface and the i+1-th cylindrical surface is defined as the i-th unit tool, and the corresponding cutting edge is P i P i+1 ;

[0023] The position radius ρ of the unit tool is calculated using formula (1): i :

[0024] ρ i =x i i+y i j+z i k#(1)

[0025] Among them, x i ,y i , z i (i=1,2,……,n) is the dividing point (P i P i+1 The coordinates of the midpoint of the center point (i, j, k) are the unit vectors in the x, y, and z directions respectively;

[0026] Calculate the orientation b of the unit tool using formula (2): i :

[0027]

[0028] The synthetic cutting speed vector V of the unit tool is calculated using formula (3): all :

[0029] V all =V c +V f =ρ i ×2πNj+Nf / 1000j#(3)

[0030] Among them, V cis the main motion linear velocity of the unit tool, V f is the feed motion of the unit tool, f is the feed per revolution of the drill (mm / r), and N is the spindle speed (r / min);

[0031] Formula (4) is used to calculate the unit normal vector of the working base surface r, working cutting plane s and working main section o of the unit tool:

[0032]

[0033] The working edge inclination angle λ of the unit tool is calculated using formula (5): se , working front angle γ oe and working principal deflection angle k re :

[0034]

[0035] Wherein, f' is the unit vector in the projection direction of the unit vector f in the feed direction on the working base surface,

[0036] The cutting amount (cutting width a) of the unit tool is calculated using formula (6) c and cutting thickness a w ):

[0037]

[0038] Where z is the number of teeth, for a drill, z = 2; u is the angle between the synthetic cutting speed of the unit tool and the main motion linear speed, sinu = j·r

[0039] Furthermore, formula (7) is used to calculate the normal front angle α of the unit tool at the transverse edge of the twist drill: n :

[0040]

[0041] in, is the cutting edge angle, ψ is the bevel angle of the chisel edge.

[0042] Furthermore, a neural network model for calculating right-angle cutting force is established, which specifically includes:

[0043] (1) Using the unequal shear zone model, a series of theoretical calculation results of right-angle cutting force under different rake angles and cutting parameters are obtained as the source domain data set to train an initial neural network model for right-angle cutting force calculation;

[0044] (2) Conduct a small number of right-angle cutting experiments to obtain a target domain data set containing the measured data of right-angle cutting force experiments;

[0045] (3) Using the transfer learning method, part of the structure, weights or parameters of the initial right-angle cutting force calculation neural network model are transferred to the final right-angle cutting force calculation neural network, and the weights of the first few layers of the final neural network are frozen. A small amount of right-angle cutting force experimental measured data is used for secondary training to obtain the final right-angle cutting force calculation neural network.

[0046] Furthermore, the final neural network model for calculating the bevel cutting force is established, which specifically includes:

[0047] (1) The equivalent plane method is used to transform the bevel cutting condition into an equivalent right-angle cutting condition. The equivalent rake angle and equivalent right-angle cutting amount are calculated in the equivalent plane. The right-angle cutting force neural network model is used to obtain the equivalent right-angle cutting force and transform it into the bevel cutting force.

[0048] (2) A series of theoretical calculation results of oblique cutting forces under different cutting angles and cutting parameters based on the equivalent plane method and the right-angle cutting force calculation neural network are used as the source domain data set;

[0049] (3) Conduct a small number of oblique cutting experiments to obtain experimental measured data of oblique cutting force as the target domain data set;

[0050] (4) Using the transfer learning method, part of the structure, weights or parameters of the initial bevel cutting force calculation neural network model are transferred to the final bevel cutting force calculation neural network, and the weights of the first few layers of the final neural network are frozen. A small amount of experimental measured data of the bevel cutting force is used for secondary training to obtain the final bevel cutting force calculation neural network.

[0051] Furthermore, the equivalent plane method is used to transform the bevel cutting condition into an equivalent right-angle cutting condition, which specifically includes:

[0052] The equivalent plane P is defined according to the chip flow direction u' of the oblique cutting and the normal direction n' of the rake face equ ;

[0053] In the equivalent plane, use formula (8) to calculate the equivalent rake angle α e :

[0054] tanα n =tanα e ·cosη#(8)

[0055] Among them, α n is the normal to forward angle, η is the chip flow angle;

[0056] Establish a rectangular coordinate system xyz, where x is the unit vector of the main cutting motion direction and y is the unit vector of the feed motion direction. Rotate the rectangular coordinate system xyz around the x-axis by λ0 (edge ​​inclination angle) and then rotate it around the transformed y-axis by α n(normal forward angle), and finally rotate η (chip angle) around the transformed x-axis to obtain the coordinate system x'y'z', where x', y', and z' are unit vectors in the x', y', and z' directions;

[0057] In the equivalent plane, the equivalent feed f is calculated using formula (9): equ :

[0058] f equ =f e / (D fe ·z')#(9)

[0059] Among them, f e is the feed rate in the bevel cutting condition, D fe is the unit vector in the equivalent feed direction,

[0060] In the equivalent plane, the equivalent cutting speed V is calculated using formula (10): equ :

[0061] V equ =V e ·(D fe ·z′)#(10)

[0062] Among them, V e is the cutting speed in the bevel cutting condition, D te is the unit vector in the direction of the equivalent cutting main motion,

[0063] In the equivalent plane, the equivalent cutting width w is calculated using formula (11): equ :

[0064] w equ =w e / (D te ·x')#(11)where w e is the cutting width in the bevel cutting condition;

[0065] The equivalent right-angle cutting force is converted into the oblique cutting force using formula (12):

[0066]

[0067] Among them, F t is the main cutting force under the equivalent right-angle cutting condition, F f is the feed resistance under equivalent right-angle cutting conditions; F r is the main cutting force under oblique cutting conditions, F s is the feed resistance under oblique cutting conditions, F o It is the cutting depth resistance under oblique cutting conditions.

[0068] Furthermore, the cutting forces of each unit tool are superimposed using the linear synthesis method, including:

[0069] Through coordinate transformation, the tangential force F of the i-th unit tool in the drill bit global coordinate system xyz is obtained using formula (13): eli , radial force F emi and axial force F eni :

[0070]

[0071] Among them, l i 、m i 、n i Represents the unit vectors in the tangential, radial and axial directions of the position of the i-th unit tool; r i 、s i , o i They represent the unit normal vector of the unit tool working base surface, the unit normal vector of the working cutting plane, and the unit normal vector of the working orthogonal plane respectively; F eri 、F esi 、F eoi They represent the cutting forces in the main motion direction, feed motion direction, and cutting depth direction of the unit tool respectively.

[0072] Using formula (14), we can get the torque T of the unit tool: ei :

[0073]

[0074] Among them, x i 、z i Respectively represent the coordinates of the i-th unit tool in the x and z directions in the global coordinate system xyz;

[0075] Using formula (15), we can get the torque T and axial force F of the twist drill as a whole: N :

[0076]

[0077] Beneficial effects of the present invention:

[0078] 1. Compared with obtaining drilling force by empirical formula method or neural network method, the method proposed in the present invention can obtain more accurate drilling force without a large amount of experimental data;

[0079] 2. Compared with obtaining the drilling force by the finite element method, the method proposed in the present invention greatly reduces the calculation time;

[0080] 3. Compared with obtaining the drilling force through theoretical analytical method, the calculation accuracy of the drilling force is improved by the method proposed in the present invention.

[0081] Instruction Manual

[0082] Figure 1 The drilling force calculation process based on unit tool linear synthesis method and transfer learning;

[0083] Figure 2 It is the global coordinate system of the twist drill and the local coordinate system of the unit tool;

[0084] Figure 3 Schematic diagram of the equivalent plane method. DETAILED DESCRIPTION

[0085] The scheme of the present invention is described in more detail and completely below.

[0086] Specific embodiment 1,

[0087] The drilling force calculation method based on unit tool linear synthesis method and transfer learning includes the following steps:

[0088] S1: Unit tool decomposition

[0089] Decomposing the drill bit cutting edge into a series of unit tools connected end to end, each cutting with different rake angles, edge inclination angles and cutting amounts;

[0090] S2: Final neural network model for right-angle cutting force calculation

[0091] A series of theoretical calculation results of right-angle cutting force are obtained by using the unequal shear zone model as the source domain data set to train the initial neural network model for right-angle cutting force calculation.

[0092] A target domain data set is obtained through a small number of right-angle cutting force experiments, and the final neural network model for right-angle cutting force calculation is trained using the transfer learning method.

[0093] S3: Neural network model for calculating bevel cutting forces

[0094] The equivalent plane method is used to transform the bevel cutting condition into an equivalent right-angle cutting condition. The equivalent rake angle and equivalent right-angle cutting amount are calculated in the equivalent plane. The right-angle cutting force neural network model is used to obtain the equivalent right-angle cutting force and transform it into the bevel cutting force.

[0095] A target domain data set is obtained through a small number of oblique cutting experiments, and the final neural network model for oblique cutting force calculation is trained using the transfer learning method.

[0096] S4: Linear synthesis method

[0097] The cutting forces of each unit tool are superimposed by linear synthesis method to obtain the theoretical calculation result of the drilling force of the whole twist drill.

[0098] S5: Transfer Learning

[0099] A series of theoretical calculation results of drilling force under different diameter twist drills and drilling amount conditions are obtained as source domain data sets, and an initial neural network model for drilling force calculation is trained;

[0100] Conduct a small number of drilling experiments and obtain drilling force experimental results as the target domain data set;

[0101] Using the transfer learning method, part of the structure, weights or parameters of the initial drilling force calculation neural network model are transferred to the final drilling force calculation neural network, and the weights of the first few layers of the final neural network are frozen. A small amount of drilling force experimental results are used for secondary training to obtain the final drilling force calculation neural network.

[0102] Furthermore, each cutting edge of the drill bit is divided into a number of unit tools connected end to end, specifically including:

[0103] Divide the drill radius into n equal parts, and get n radii ρ1, ρ2, ρ3, ... ρ arranged from large to small i With the drill axis as the axis and the radius of each equally divided cylinder as the radius, draw n coaxial cylinders. The tool part sandwiched between two adjacent cylindrical surfaces and located on the same cutting edge of the drill bit is defined as a unit tool, that is, the unit tool on the same cutting edge sandwiched between the i-th cylindrical surface and the i+1-th cylindrical surface is defined as the i-th unit tool, and the corresponding cutting edge is P i P i+1 ;

[0104] The position radius ρ of the unit tool is calculated using formula (1): i :

[0105] ρ i =x i i+y i j+z i k#(1)

[0106] Among them, x i ,y i , z i (i=1,2,……,n) is the dividing point (P i P i+1 The coordinates of the midpoint of the center point (i, j, k) are the unit vectors in the x, y, and z directions respectively;

[0107] Calculate the orientation b of the unit tool using formula (2): i :

[0108]

[0109] The synthetic cutting speed vector V of the unit tool is calculated using formula (3): all :

[0110] V all =V c +V f =ρ i ×2πNj+Nf / 1000j#(3)

[0111] Among them, V c is the main motion linear velocity of the unit tool, V f is the feed motion of the unit tool, f is the feed per revolution of the drill (mm / r), and N is the spindle speed (r / min);

[0112] Formula (4) is used to calculate the unit normal vector of the working base surface r, working cutting plane s and working main section o of the unit tool:

[0113]

[0114] The working edge inclination angle λ of the unit tool is calculated using formula (5): se , working front angle γ oe and working principal deflection angle k re :

[0115]

[0116] Wherein, f' is the unit vector in the projection direction of the unit vector f in the feed direction on the working base surface,

[0117] The cutting amount (cutting width a) of the unit tool is calculated using formula (6) c and cutting thickness a w ):

[0118]

[0119] Where z is the number of teeth, for a drill, z = 2; u is the angle between the synthetic cutting speed of the unit tool and the main motion linear speed, sinu = j·r

[0120] Furthermore, formula (7) is used to calculate the normal front angle α of the unit tool at the transverse edge of the twist drill: n :

[0121]

[0122] in, is the cutting edge angle, ψ is the bevel angle of the chisel edge.

[0123] Furthermore, a neural network model for calculating right-angle cutting force is established, which specifically includes:

[0124] (1) Using the unequal shear zone model (Reference Zhou Danyu. Improvement of the unequal shear zone model and its application in modeling the sudden change of chip angle in face turning [D / OL]. Huazhong University of Science and Technology, 2022.) to obtain a series of theoretical calculation results of right-angle cutting forces under different rake angles and cutting parameters as the source domain data set, an initial neural network model for right-angle cutting force calculation is trained;

[0125] (2) Conduct a small number of right-angle cutting experiments to obtain a target domain dataset containing right-angle cutting force experimental results;

[0126] (3) Using the transfer learning method, part of the structure, weights or parameters of the initial right-angle cutting force calculation neural network model are transferred to the final right-angle cutting force calculation neural network, the weights of the first few layers of the final neural network are frozen, and a small amount of right-angle cutting force experimental results are used for secondary training to obtain the final right-angle cutting force calculation neural network.

[0127] Furthermore, a neural network model for calculating the bevel cutting force is established, which specifically includes:

[0128] (1) The equivalent plane method is used to transform the bevel cutting condition into an equivalent right-angle cutting condition. The equivalent rake angle and equivalent right-angle cutting amount are calculated in the equivalent plane. The right-angle cutting force neural network model is used to obtain the equivalent right-angle cutting force and transform it into the bevel cutting force.

[0129] (2) A series of theoretical calculation results of oblique cutting forces under different cutting angles and cutting parameters based on the equivalent plane method and the right-angle cutting force calculation neural network are used as the source domain data set;

[0130] (3) Conduct a small number of oblique cutting experiments and obtain the experimental results of oblique cutting force as the target domain data set;

[0131] (4) Using the transfer learning method, part of the structure, weights or parameters of the initial bevel cutting force calculation neural network model are transferred to the final bevel cutting force calculation neural network, and the weights of the first few layers of the final neural network are frozen. A small amount of bevel cutting force experimental results are used for secondary training to obtain the final bevel cutting force calculation neural network.

[0132] Furthermore, the equivalent plane method is used to transform the bevel cutting condition into an equivalent right-angle cutting condition, which specifically includes:

[0133] The equivalent plane P is defined according to the chip flow direction u' of the oblique cutting and the normal direction n' of the rake face equ ;

[0134] In the equivalent plane, use formula (8) to calculate the equivalent rake angle α e :

[0135] tanα n =tanα e ·cosη#(8)

[0136] Among them, α n is the normal to forward angle, η is the chip flow angle;

[0137] Establish a rectangular coordinate system xyz, where x is the unit vector of the main cutting motion direction and y is the unit vector of the feed motion direction. Rotate the rectangular coordinate system xyz around the x-axis by λ0 (edge ​​inclination angle) and then rotate it around the transformed y-axis by α n (normal forward angle), and finally rotate η (chip angle) around the transformed x-axis to obtain the coordinate system x'y'z', where x', y', and z' are unit vectors in the x', y', and z' directions;

[0138] In the equivalent plane, the equivalent feed f is calculated using formula (9): equ :

[0139] f equ =f e / (D fe ·z')#(9)

[0140] Among them, f e is the feed rate in the bevel cutting condition, D fe is the unit vector in the equivalent feed direction,

[0141] In the equivalent plane, the equivalent cutting speed V is calculated using formula (10): equ :

[0142] V equ =V e ·(D fe ·z′)#(10)

[0143] Among them, V e is the cutting speed in the bevel cutting condition, D te is the unit vector in the direction of the equivalent cutting main motion,

[0144] In the equivalent plane, the equivalent cutting width w is calculated using formula (11): equ :

[0145] w equ =w e / (D te ·x')#(11)where w e is the cutting width in the bevel cutting condition;

[0146] The equivalent right-angle cutting force is converted into the oblique cutting force using formula (12):

[0147]

[0148] Among them, F t is the main cutting force under the equivalent right-angle cutting condition, F f is the feed resistance under equivalent right-angle cutting conditions; F r is the main cutting force under oblique cutting conditions, F s is the feed resistance under oblique cutting conditions, F o It is the cutting depth resistance under oblique cutting conditions.

[0149] Furthermore, the cutting forces of each unit tool are accumulated using a linear synthesis method, including:

[0150] Through coordinate transformation, the tangential force F of the i-th unit tool in the drill bit global coordinate system xyz is obtained using formula (13): eli , radial force F emi and axial force F eni :

[0151]

[0152] Among them, l i 、m i 、n i Represents the unit vectors in the tangential, radial and axial directions of the position of the i-th unit tool; r i 、s i , o i They represent the unit normal vector of the unit tool working base surface, the unit normal vector of the working cutting plane, and the unit normal vector of the working orthogonal plane respectively; F eri 、F eso 、F eoi They represent the cutting forces in the main motion direction, feed motion direction, and cutting depth direction of the unit tool respectively.

[0153] Using formula (14), we can get the torque T of the unit tool: ei :

[0154]

[0155] Among them, x i 、z i Respectively represent the coordinates of the i-th unit tool in the x and z directions in the global coordinate system xyz;

[0156] Using formula (15), we can get the torque T and axial force F of the twist drill as a whole: N :

[0157]

[0158] In summary, the present invention provides a drilling force calculation method based on unit tool linear synthesis method and transfer learning. This method combines the advantages of multiple technologies, has the characteristics of high calculation accuracy, small amount of required experimental data and high calculation efficiency, is suitable for various drilling processing scenarios, and has broad application prospects.

[0159] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0160] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A drilling force calculation method based on unit tool linear synthesis method and transfer learning, characterized in that: The following steps are involved: S1: Unit tool division The two main cutting edges and the chisel edge of the drill bit are divided into a series of unit tools connected end to end, each of which cuts with different rake angles, edge inclination angles and cutting amounts; S2: Neural network model for right-angle cutting force calculation A series of theoretical calculation results of right-angle cutting force are obtained by using the unequal shear zone model as the source domain data set to train the initial neural network model for right-angle cutting force calculation. A target domain data set is obtained through a small number of right-angle cutting experiments, and a neural network model for right-angle cutting force calculation is trained using the transfer learning method. S3: Neural network model for calculating bevel cutting forces The equivalent plane method is used to transform the bevel cutting condition into an equivalent right-angle cutting condition. The equivalent rake angle and equivalent right-angle cutting amount are calculated in the equivalent plane. The right-angle cutting force neural network model is used to obtain the equivalent right-angle cutting force and transform it into the bevel cutting force. The bevel cutting force data obtained from a small number of bevel cutting experiments are used as the target domain dataset, and the final neural network model for bevel cutting force calculation is trained using the transfer learning method. S4: Linear synthesis method The cutting forces of each unit tool are accumulated by linear synthesis method to obtain the theoretical calculation result of the drilling force of the whole twist drill. S5: Transfer Learning Obtain a series of theoretical calculation results of drilling force under different diameter twist drills and drilling amount conditions, and use them as source domain data sets to train an initial neural network model for drilling force calculation; Conduct a small number of drilling experiments to obtain the measured data of drilling force experiments and use it as the target domain data set; Using the transfer learning method, part of the structure, weights or parameters of the initial drilling force calculation neural network model are transferred to the final drilling force calculation neural network, the weights of the first few layers of the neural network are frozen, and a small amount of actual drilling force experimental data is used for secondary training to obtain the final drilling force calculation neural network.

2. The drilling force calculation method based on unit tool linear synthesis method and transfer learning according to claim 1 is characterized in that: The drill cutting edge is divided into several unit tools, including: The drill radius is divided into n equal parts, and n radii are arranged from large to small: ρ1, ρ2, ρ3, ... ρ i With the drill axis as the axis and the radius of each equally divided cylinder as the radius, draw n coaxial cylinders. The tool part sandwiched between two adjacent cylindrical surfaces and located on the same cutting edge of the drill bit is defined as a unit tool, that is, the unit tool on the same cutting edge sandwiched between the i-th cylindrical surface and the i+1-th cylindrical surface is defined as the i-th unit tool, and the corresponding cutting edge is P i P i+1 ; The position radius ρ of the unit tool is calculated using formula (1): i : ρ i =x i i+y i j+z i k#(1) Among them, x i ,y i , z i (i=1,2,……,n) is the dividing point (P i P i+1 The coordinates of the midpoint of the center point (i, j, k) are the unit vectors in the x, y, and z directions respectively; Calculate the orientation b of the unit tool using formula (2): i : The synthetic cutting speed vector V of the unit tool is calculated using formula (3): all : V all =V c +V f =ρ i ×2πNj+Nf / 1000j#(3) Among them, V c is the main motion linear velocity of the unit tool, V f is the feed motion of the unit tool, f is the feed per revolution of the drill (mm / r), and N is the spindle speed (r / min); Formula (4) is used to calculate the unit normal vector of the working base surface r, working cutting plane s and working main section o of the unit tool: The working edge inclination angle λ of the unit tool is calculated using formula (5): se , working front angle γ oe and working principal deflection angle k re : Wherein, f' is the unit vector in the projection direction of the unit vector f in the feed direction on the working base surface, The cutting amount (cutting width a) of the unit tool is calculated using formula (6) c and cutting thickness a w ): Among them, z is the number of teeth. For a drill, z=2; u is the angle between the synthetic cutting speed of the unit tool and the main motion linear speed, sinu=j·r.

3. The drilling force calculation method based on unit tool linear synthesis method and transfer learning according to claim 1 is characterized in that: Formula (7) is used to calculate the normal front angle α of the unit tool at the transverse edge of the twist drill: n : in, is the cutting edge angle, ψ is the bevel angle of the chisel edge.

4. The drilling force calculation method based on unit tool linear synthesis method and transfer learning according to claim 1 is characterized in that: Establish a neural network model for right-angle cutting force calculation, including: (1) Using the unequal shear zone model, a series of theoretical calculation results of right-angle cutting force under different rake angles and cutting parameters are obtained as the source domain data set to train an initial neural network model for right-angle cutting force calculation; (2) Conduct a small number of right-angle cutting experiments to obtain a target domain data set containing the measured data of right-angle cutting force experiments; (3) Using the transfer learning method, part of the structure, weights or parameters of the initial right-angle cutting force calculation neural network model are transferred to the final right-angle cutting force calculation neural network, and the weights of the first few layers of the final neural network are frozen. A small amount of right-angle cutting force experimental measured data is used for secondary training to obtain the final right-angle cutting force calculation neural network.

5. The drilling force calculation method based on unit tool linear synthesis method and transfer learning according to claim 1 is characterized in that: A neural network model for calculating bevel cutting force is established, including: (1) The equivalent plane method is used to transform the bevel cutting condition into an equivalent right-angle cutting condition. The equivalent rake angle and equivalent right-angle cutting amount are calculated in the equivalent plane. The right-angle cutting force neural network model is used to obtain the equivalent right-angle cutting force and transform it into the bevel cutting force. (2) A series of theoretical calculation results of oblique cutting forces under different cutting angles and cutting parameters based on the equivalent plane method and the right-angle cutting force calculation neural network are used as the source domain data set; (3) Conduct a small number of oblique cutting experiments to obtain experimental measured data of oblique cutting force as the target domain data set; (4) Using the transfer learning method, part of the structure, weights or parameters of the initial bevel cutting force calculation neural network model are transferred to the final bevel cutting force calculation neural network, and the weights of the first few layers of the final neural network are frozen. A small amount of experimental measured data of the bevel cutting force is used for secondary training to obtain the final bevel cutting force calculation neural network.

6. The drilling force calculation method based on unit tool linear synthesis method and transfer learning according to claim 5 is characterized in that: The equivalent plane method is used to transform the bevel cutting condition into an equivalent right-angle cutting condition, including: The equivalent plane P is defined according to the chip flow direction u' of the oblique cutting and the normal direction n' of the rake face equ ; In the equivalent plane, use formula (8) to calculate the equivalent rake angle α e : tanα n =tanα e ·cosη#(8) Among them, α n is the normal forward angle, η is the chip flow angle; Establish a rectangular coordinate system xyz, where x is the unit vector of the main cutting motion direction and y is the unit vector of the feed motion direction. Rotate the rectangular coordinate system xyz around the x-axis by λ0 (edge ​​inclination angle) and then rotate it around the transformed y-axis by α n (normal forward angle), and finally rotate η (chip angle) around the transformed x-axis to obtain the coordinate system x'y'z', where x', y', and z' are unit vectors in the x', y', and z' directions; In the equivalent plane, the equivalent feed f is calculated using formula (9): equ : f equ =f e / (D fe ·z')#(9) Among them, f e is the feed rate in the bevel cutting condition, D fe is the unit vector in the equivalent feed direction, In the equivalent plane, the equivalent cutting speed V is calculated using formula (10): equ : In equ =V e ·(D fe ·z′)#(10) Among them, V e is the cutting speed in the bevel cutting condition, D te is the unit vector in the direction of the equivalent cutting main motion, In the equivalent plane, the equivalent cutting width w is calculated using formula (11): equ : w equ =w e / (D te ·x')#(11) Among them, w e is the cutting width in the bevel cutting condition; The equivalent right-angle cutting force is converted into the oblique cutting force using formula (12): Among them, F t is the main cutting force under the equivalent right-angle cutting condition, F f is the feed resistance under equivalent right-angle cutting conditions; F r is the main cutting force under oblique cutting conditions, F s is the feed resistance under oblique cutting conditions, F o It is the cutting depth resistance under oblique cutting conditions.

7. The drilling force calculation method based on unit tool linear synthesis method and transfer learning according to claim 1 is characterized in that: The cutting forces of each unit tool are superimposed using the linear synthesis method, including: Through coordinate transformation, the tangential force F of the i-th unit tool in the drill bit global coordinate system xyz is obtained using formula (13): eli , radial force F emi and axial force F eni : Among them, l i 、m i 、n i Represents the unit vectors in the tangential, radial and axial directions of the position of the i-th unit tool; r i 、s i , o i They represent the unit normal vector of the unit tool working base surface, the unit normal vector of the working cutting plane, and the unit normal vector of the working orthogonal plane respectively; F eri 、F esi 、F eoi They represent the cutting forces in the main motion direction, feed motion direction, and cutting depth direction of the unit tool respectively. Using formula (14), we can get the torque T of the unit tool: ei : Among them, x i 、z i Respectively represent the coordinates of the i-th unit tool in the x and z directions in the global coordinate system xyz; Using formula (15), we can get the torque T and axial force F of the twist drill as a whole: N : 。

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