Straight fluted tap tapping torque prediction method based on bevel angle cutting model

Abstract

The invention discloses straight fluted tap tapping based on an oblique angle cutting model, and relates to a straight fluted tap mechanical modeling and torque prediction method. The method aims at solving the problems that in the tapping process of the straight fluted tap, the cutting torque time is too long, and the precision of a calculation result is low. The method comprises the following steps: step 1, establishing a straight fluted tap tapping bevel angle cutting model; 2, establishing a straight fluted tap cutting edge mechanical model; 3, establishing a workpiece geometric model; 4, calculating a unit mechanical model according to the step 2 and the step 3; 5, performing overall mechanical model calculation according to the tool and workpiece contact mechanical model; and 6, finite element simulation of the tool and workpiece contact model is carried out. Through comparison of a simulation result and a calculation result, the accuracy of the method is verified. Through comparison with simulation time of a single linear model, high efficiency of the torque prediction method based on the bevel angle cutting model is verified. The method is applied to the field of tapping manufacturing.

Description

Technical Field

[0001] The invention relates to the field of tapping manufacturing, and in particular to a method for mechanical modeling of a straight groove tap and predicting its torque during the tapping process. Background Art

[0002] Tapping is a common method for internal thread processing, but the core diameter of the tap is small and the strength is low. The semi-closed state during the processing makes the cutting conditions poor, resulting in easy breakage of the tap, poor quality of the processed thread, and low production efficiency. Most of the tap breakage is caused by excessive torque. The breakage of the tap leads to huge waste in production. The tapping process is a highly complex process, which requires high precision and mechanical properties of the tap. Flexible tapping methods can effectively reduce the tapping torque and have good adaptability to different tapping conditions. However, there is no complete research theory on the size of the tapping torque. In order to obtain the best performance at the lowest processing cost, some procedures must be strictly calculated. However, the determination of the tapping torque not only needs to consider the type of reaming drill bit, but also the influence of processing parameters. This also leads to an increase in the factors affecting the tapping torque, making the prediction of the tapping torque more difficult, and the prediction results have large errors, long prediction results, and low reliability. Problems make it difficult to be widely used in processing practice. Summary of the invention

[0003] The present invention aims to solve the problems of low simulation accuracy and slow calculation speed of the existing tapping mechanics model, and proposes a straight groove tap tapping torque prediction method based on an oblique cutting model.

[0004] The tapping torque prediction method for straight groove taps based on the bevel cutting model is implemented in the following steps:

[0005] Step 1: Establish a straight groove tap tapping bevel cutting model;

[0006] Step 2: Establish the mechanical model of the straight groove tap cutting edge;

[0007] Step 3: Establishment of workpiece geometric model;

[0008] Step 4: Calculate the unit mechanical model according to steps 2 and 3;

[0009] Step 5: Calculate the overall mechanical model based on the contact mechanical model between the tool and the workpiece;

[0010] Step 6: Perform finite element simulation of the tool-workpiece contact model.

[0011] Effect of the invention:

[0012] In order to achieve the purpose of taking into account both accuracy and simulation speed, the present invention proposes a straight groove tap tapping torque prediction method based on an angle cutting model, and conducts simulation test verification. The processing of threads by straight groove taps indicates that the workpiece is about to be processed. Therefore, tapping is one of the most noteworthy processes in the machining process. Once the tapping fails, it means that the entire machined part is scrapped. Therefore, the research on the mechanical modeling and torque prediction method of the angle cutting of straight groove taps is an urgent problem to be solved in machining operations. In order to establish a torque prediction model that is both accurate and can improve the calculation speed, the present invention proposes to carry out research on the torque prediction of straight groove taps based on the angle cutting model. First, a straight groove tap angle cutting mechanical model is established; then, based on the angle cutting mechanical model, the torque size of the tapping mechanical model is calculated; finally, the straight groove tap mechanical model is simulated and calculated based on the finite element simulation theory. The accuracy of the model is verified by comparing the simulation results with the calculation results, and the efficiency of the established model is verified by comparing the simulation time with the calculation time.

[0013] 1. The straight groove tap tapping torque prediction method based on the bevel cutting model can meet the accuracy of the torque calculated during the machining process.

[0014] This study aims to establish a mechanical model for the angled cutting of straight groove taps, and proposes to divide the entire process into two stages: the establishment of the mechanical model and the calculation of torque based on the angled cutting mechanical model. The mechanical model calculation results are compared with the simulation test results to verify the accuracy of the method.

[0015] 2. The straight groove tap tapping torque prediction method based on the bevel cutting model can meet the high efficiency of the torque calculated during the machining process.

[0016] This study aims to establish a mechanical model for the oblique cutting of straight groove taps, and proposes to divide the entire process into two stages: the establishment of the mechanical model and the calculation of torque based on the oblique cutting mechanical model. The time used for the mechanical model calculation results is compared with the time used for the simulation results to verify the advantage of the straight groove tap tapping torque prediction method based on the oblique cutting model in terms of calculation speed.

[0017] 3. The simulation process is carried out in the ABAQUS environment, and the processing conditions can be strictly simulated during the process.

[0018] The accuracy of the established model was verified by comparing the simulation results with the calculation results of the established model. The efficiency of the straight groove tap tapping torque prediction method based on the bevel cutting model in terms of calculation speed was verified by comparing the time used for the calculation results of the mechanical model with the time used for the simulation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Attached Figure 1This is a schematic diagram of the force on the tap.

[0020] Attached Figure 2 It is the tapping process tap tooth cutting model

[0021] Attached Figure 3 The contact area between the cutter teeth and the workpiece during tapping

[0022] Attached Figure 4 Tap cutting teeth extrusion chip diagram

[0023] Attached Figure 5 Torque calculation flow chart DETAILED DESCRIPTION

[0024] Specific implementation method 1: A method for predicting the torque of a straight groove tap based on an oblique cutting model, characterized in that the method for predicting the torque of an oblique cutting model comprises the following steps:

[0025] Step 1: Establish a straight groove tap tapping bevel cutting model;

[0026] Step 2: Establish the mechanical model of the straight groove tap cutting edge;

[0027] Step 3: Establishment of workpiece geometric model;

[0028] Step 4: Calculate the unit mechanical model according to steps 2 and 3;

[0029] Step 5: Calculate the overall mechanical model based on the contact mechanical model between the tool and the workpiece;

[0030] Step 6: Perform finite element simulation of the tool-workpiece contact model.

[0031] Specific implementation method 2: This implementation method is different from the specific implementation method 1 in that: the step 1 in which the straight groove tap tapping bevel cutting model is established is specifically as follows:

[0032] In the process of tapping with a straight groove tap, the cutting direction of the cutting edge is along the guide of the thread, while the tangential component perpendicular to the tooth surface is not along this direction. Therefore, the process of tapping with a straight groove tap is essentially an oblique cutting process. According to Stabler's law, assuming that the chip flow angle η c Like the bevel cutting angle i, the bevel cutting angle is related to the geometric characteristics of the tap, that is, the thread lead angle ζ and the groove helix angle γ can be expressed as:

[0033] i=η c =π / 2+ζ-γ (1)

[0034] The other steps and parameters are the same as those in the first specific implementation.

[0035] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that: the mechanical model of the straight groove tap cutting edge is established in step two as follows:

[0036] According to the oblique cutting model, let the unit positive cutting force on the rake face of the i-th tap tooth at time t be dF ni (t) and the unit friction cutting force is dF fi (t), let c i (t) is the radial distance from the center of mass of the interference area of ​​the teeth to the axis of the tap. The tangential force and friction force can be along the axial direction of the tap (T h ), radial (F r ) and tangential (T o ) decomposed. Therefore, the unit torque dT of the i-th tap tooth at time t is oi (t), axial force dT hi (t) and radial force dF ri (t) can be expressed as:

[0037]

[0038] where α n It is the front angle of the straight groove tap.

[0039] The other steps and parameters are the same as those in the first or second embodiment.

[0040] Specific implementation method 4: This implementation method is different from any one of the specific implementation methods 1 to 3 in that the establishment of the workpiece geometric model in step 3 is specifically as follows:

[0041] Construct a general model for calculating chip load. Chip load is calculated as a function of time and is expressed as the undeformed area between the tool and the workpiece. In addition, the hole formed after drilling is usually not ideal, so the change in hole diameter needs to be considered when calculating chip load. As the tap penetrates the workpiece, the chip load begins to increase and reaches a steady state when the tapered part of the tap is fully entered into the workpiece. In the scenario of tapping a through hole, the chip load will begin to decrease as the tap gradually emerges from the other end of the hole.

[0042] The other steps and parameters are the same as those in Specific Embodiments 1 to 3.

[0043] Specific implementation method 5: This implementation method is different from the specific implementation methods 1 to 4 in that the specific process of calculating the unit mechanical model in step 4 is:

[0044] Step 41: For a tap with a specific geometry, determining the torque and the axial force in the Z axis requires determining the unit normal force and friction. In the process of constructing the tapping mechanism model, the unit normal force dF generated during the cutting process ni(t) and unit friction force dF fi (t) and chip load (i.e., undeformed chip area) dA ci (t), the proportional coefficients are defined as normal and friction cutting specific energy, respectively, and are expressed as K n and K f , which can be expressed as:

[0045]

[0046] Studies have confirmed that K n and K f Depending on the tool-workpiece material, cutting thickness and cutting speed, it can be expressed as:

[0047]

[0048] where t c is the cutting thickness coefficient; a0, a1, a2, a3, b0, b1, b2, and b3 are called specific cutting energy coefficients.

[0049] The above coefficients are determined by calibration tests for a given tool-workpiece combination and a given range of cutting conditions.

[0050] Step 42: The holes are not uniform along the axial and radial directions. The holes distributed along the circumferential direction are marked with j, and the holes distributed along the axial direction are marked with k.

[0051] The increase in chip load during the tap entry phase is determined by the area difference between adjacent teeth. Assuming T i and T i-1 is the adjacent teeth of the tap, H(r jk ) is a variable radius r jk The radius may vary along the circumference j and depth k of the hole. Then the increment of chip load can be expressed as:

[0052] dA ci =[T i ∩H(r jk )]-[T i-1 ∩H(r jk )] (5)

[0053] In the calculation of the chip load increment, the evaluation of the Boolean expression can be performed by means of coordinate geometry. The interference area increment of the i-th tap tooth is represented by unit 1234. For any given hole diameter r jk , the coordinate point (u jk1 ,x jk1 ),(u jk2 ,x jk2 ),(u jk3 ,x jk3), and (u jk4 ,x jk4 ) can be determined. These coordinate points are therefore a function of the tap tooth number i and the tap position in the hole, which in turn is determined by the spindle speed N and the time t. The chip thickness is defined as the ratio of this incremental area to the cutting length, which can be expressed as the cutting cone angle and the cutting thickness. The following formula provides the chip load increment dA at the i-th tap tooth at time t ci (t). With a small increase in the tap rotation angle, the chip load experienced by all meshing tap teeth will change. Therefore, after each tap rotation time increment dt, the chip load needs to be recalculated according to the following formula.

[0054]

[0055] In cutting mechanics, the radial distance between the center of mass of the tap teeth interference area and the tap axis, that is, the force arm c i (t), can be calculated by the following expression: The above expression involves calculating the determinant of two triangles (the quadrilateral formed by the interference of the tap teeth and the hole can be divided into), then adding the values ​​of these two determinants and multiplying them by the sum of the corresponding x-coordinates. This result will be related to the undeformed chip area dA ci (t) is used to determine the radial distance from the center of mass of the interference area. This is an important calculation in tap design and process analysis, which can affect the distribution of cutting forces and the stability of the tap.

[0056]

[0057] By substituting equations (6) and (7) into equation (3), the normal force and friction force of each element during the tapping process can be derived.

[0058] The other steps and parameters are the same as those in Specific Embodiments 1 to 4.

[0059] Specific implementation method 6: This implementation method is different from the specific implementation methods 1 to 5 in that: the specific process of calculating the overall mechanical model of the contact mechanical model between the tool and the workpiece in step 5 is:

[0060] Step 51: Let the unit positive cutting force of the i-th tap tooth on the rake face at time t be dF ni (t) and the unit friction cutting force is dF fi (t), let c i (t) is the radial distance from the center of mass of the interference area of ​​the teeth to the axis of the tap. The tangential force and friction force can be along the axial direction of the tap (T h ), radial (F r ) and tangential (T o) decomposition. The unit torque dT of the i-th tap tooth at time t oi (t), axial force dT hi (t) and radial force dF ri (t) can be expressed as:

[0061]

[0062] Step 52: During the whole process of tapping, as the tap gradually cuts into the workpiece, the total force can be obtained by integrating the cutting force of each unit. If at a specific time t, m(t) tap teeth cut into the hole, the total torque, total axial force and total radial force can be expressed as:

[0063]

[0064] Step 53: Assume that the time required to increase the number of tap teeth by one is dt seconds, that is, m(t+dt)=m(t)+1. With the setting of the new position of the tap, the unit normal pressure and friction force need to be recalculated to obtain the new unit torque, axial force and radial force. Therefore, at the moment t+dt, the total torque, total axial force and total radial force can be expressed as:

[0065]

[0066] The time increment dt can be expressed as:

[0067]

[0068] Where N is the spindle speed, n f is the number of grooves of the tap, P is the pitch, P eff is the effective pitch of a particular tap, taking into account the time increment dt.

[0069] The relationship between the effective pitch and the tap geometric parameters can be expressed as:

[0070]

[0071] For ordinary straight-flute taps, the helix angle γ is 90°, so the effective pitch is equal to the thread pitch.

[0072] The other steps and parameters are the same as those in Specific Embodiments 1 to 5.

[0073] Specific implementation method 7: This implementation method is different from any one of the specific implementation methods 1 to 6 in that: the specific process of the finite element simulation of the tool and workpiece contact model in step 6 is:

[0074] Step 61: Set the working directory;

[0075] Step 62: Modeling and assembling of tool workpiece;

[0076] Step 63: Create tool workpiece attributes;

[0077] Step 64: Workpiece and tool meshing;

[0078] Step 65: Workpiece-tool interaction settings;

[0079] Step 66: Create analysis steps;

[0080] Step 67: Workpiece tool load setting;

[0081] Step 68: Submit the assignment;

[0082] Step 69: End.

[0083] The calculation process of tapping torque of straight groove tap based on the bevel cutting model is as follows: Figure 5 As shown in the figure, the entire calculation process is divided into the calculation of tapping force during bevel cutting and the calculation of the load per unit area of ​​the tap. In order to verify the accuracy of the calculation results, the simulation results are compared with the model calculation results, and the final results tend to be consistent, proving that the torque prediction method of the bevel cutting model proposed in this study can accurately express the mechanical characteristics of the tap during working, and is even closer to experimental data than the calculation results of existing simulation software.

[0084] In order to further analyze the performance of the torque calculation method of the straight groove tap tapping bevel cutting model in terms of calculation time, a multi-factor analysis method was used in the simulation process. The multi-factors were set as grid size, iteration step, and initial load, and the simulation time under different conditions was recorded. The results show that under all simulation conditions, the torque prediction method of the bevel cutting model is superior to the simulation calculation in terms of calculation efficiency.

Claims

1. A method for predicting the tapping torque of a straight groove tap based on an angle cutting model, characterized in that: The torque prediction method of the bevel cutting model comprises the following steps: Step 1: Establish a straight groove tap tapping bevel cutting model; Step 2: Establish the mechanical model of the straight groove tap cutting edge; Step 3: Establishment of workpiece geometric model; Step 4: Calculate the unit mechanical model according to steps 2 and 3; Step 5: Calculate the overall mechanical model based on the contact mechanical model between the tool and the workpiece; Step 6: Perform finite element simulation of the tool-workpiece contact model.

2. The method for predicting tapping torque of a straight groove tap based on an angle cutting model according to claim 1, characterized in that: The establishment of the straight groove tap tapping bevel cutting model in step 1 is specifically as follows: In the process of tapping with a straight groove tap, the cutting direction of the cutting edge is along the guide of the thread, while the tangential component perpendicular to the tooth surface is not along this direction. Therefore, the process of tapping with a straight groove tap is essentially an oblique cutting process. According to Stabler's law, assuming that the chip flow angle η c Like the bevel cutting angle i, the bevel cutting angle is related to the geometric characteristics of the tap, that is, the thread lead angle ζ and the groove helix angle γ can be expressed as: i=η c =π / 2+ζ-γ (1) 3. The method for predicting the tapping torque of a straight groove tap based on an angle cutting model according to claim 2, characterized in that: The mechanical model of the straight groove tap cutting edge established in step 2 is specifically as follows: According to the oblique cutting model, let the unit positive cutting force on the rake face of the i-th tap tooth at time t be dF ni (t) and the unit friction cutting force is dF fi (t), let c i (t) is the radial distance from the center of mass of the interference area of ​​the teeth to the axis of the tap. The tangential force and friction force can be along the axial direction of the tap (T h ), radial (F r ) and tangential (T o ) decomposed. Therefore, the unit torque dT of the i-th tap tooth at time t is oi (t), axial force dT hi (t) and radial force dF ri (t) can be expressed as: where α n It is the front angle of the straight groove tap.

4. The method for predicting tapping torque based on a straight groove bevel cutting model according to claim 3, characterized in that: The establishment of the workpiece geometric model in step 3 is specifically as follows: Construct a general model for calculating chip load. Chip load is calculated as a function of time and is expressed as the undeformed area between the tool and the workpiece. In addition, the hole formed after drilling is often not ideal, so the change in hole diameter needs to be considered when calculating chip load. As the tap penetrates the workpiece, the chip load begins to increase and reaches a steady state when the tapered part of the tap is fully inserted into the workpiece. In the scenario of tapping a through hole, the chip load will begin to decrease as the tap gradually emerges from the other end of the hole.

5. The method for predicting tapping torque of a straight groove tap based on an oblique cutting model according to claim 4, characterized in that: The specific process of calculating the unit mechanical model in step 4 is as follows: Step 41: For a tap with a specific geometry, determining the torque and the axial force in the Z axis requires determining the unit normal force and friction. In the process of constructing the tapping mechanism model, the unit normal force dF generated by cutting ni (t) and unit friction force dF fi (t) and chip load (i.e., undeformed chip area) dA ci (t), the proportional coefficients are defined as normal and friction cutting specific energy, respectively, and are expressed as K n and K f , which can be expressed as: Studies have confirmed that K n and K f Depending on the tool-workpiece material, cutting thickness and cutting speed, it can be expressed as: where t c is the cutting thickness coefficient; a0, a1, a2, a3, b0, b1, b2 and b3 are called specific cutting energy coefficients. The above coefficients are determined by calibration tests for a given tool-workpiece combination and a given range of cutting conditions. Step 42: The holes are not uniform along the axial and radial directions. The holes distributed along the circumferential direction are marked with j, and the holes distributed along the axial direction are marked with k. The increase in chip load during the tap entry phase is determined by the area difference between adjacent teeth. Assuming T i and T i-1 is the adjacent teeth of the tap, H(r jk ) is a variable radius r jk The radius may vary along the circumference j and depth k of the hole. Then the increment of chip load can be expressed as: dA ci =[T i ∩H(r jk )]-[T i-1 ∩H(r jk )] (5) In the calculation of the chip load increment, the evaluation of the Boolean expression can be performed by coordinate geometry methods. The interference area increment of the i-th tap tooth is represented by unit 1234. For any given hole diameter r jk , the coordinate point (u jk1 ,x jk1 ),(u jk2 ,x jk2 ),(u jk3 ,x jk3 ), and (u jk4 ,x jk4 ) can be determined. These coordinate points are therefore a function of the tap tooth number i and the tap position in the hole, which in turn is determined by the spindle speed N and the time t. The chip thickness is defined as the ratio of this incremental area to the cutting length, which can be expressed as the cutting cone angle and the cutting thickness. The following formula provides the chip load increment dA for the i-th tap tooth at time t ci (t). With a small increase in the tap rotation angle, the chip load experienced by all meshing tap teeth will change. Therefore, after each tap rotation time increment dt, the chip load needs to be recalculated according to the following formula. In cutting mechanics, the radial distance between the center of mass of the tap teeth interference area and the tap axis, that is, the force arm c i (t), can be calculated by the following expression: The above expression involves calculating the determinant of two triangles (the quadrilateral formed by the interference of the tap teeth and the hole can be divided into), then adding the values ​​of these two determinants and multiplying them by the sum of the corresponding x-coordinates. This result will be related to the undeformed chip area dA ci (t) is used to determine the radial distance from the center of mass of the interference area. This is an important calculation in tap design and process analysis, which can affect the distribution of cutting forces and the stability of the tap. By substituting equations (6) and (7) into equation (3), the normal force and friction force of each element during the tapping process can be derived.

6. The torque prediction method based on the straight groove tap tapping bevel cutting model according to claim 5 is characterized in that: The specific process of calculating the overall mechanical model of the tool and workpiece contact mechanical model in step 5 is as follows: Step 51: Let the unit positive cutting force on the rake face of the i-th tap tooth at time t be dF ni (t) and the unit friction cutting force is dF fi (t), let c i (t) is the radial distance from the center of mass of the interference area of ​​the teeth to the axis of the tap. The tangential force and friction force can be along the axial direction of the tap (T h ), radial (F r ) and tangential (T o ) decomposition. The unit torque dT of the i-th tap tooth at time t oi (t), axial force dT hi (t) and radial force dF ri (t) can be expressed as: Step 52: During the whole process of tapping, as the tap gradually cuts into the workpiece, the total force can be obtained by integrating the cutting force of each unit. If at a specific time t, m(t) tap teeth cut into the hole, the total torque, total axial force and total radial force can be expressed as: Step 53: Assume that the time required to increase the number of tap teeth by one is dt seconds, that is, m(t+dt)=m(t)+1. With the setting of the new position of the tap, the unit normal pressure and friction force need to be recalculated to obtain the new unit torque, axial force and radial force. Therefore, at the moment t+dt, the total torque, total axial force and total radial force can be expressed as: The time increment dt can be expressed as: Where N is the spindle speed, n f is the number of grooves of the tap, P is the pitch, P eff is the effective pitch of a particular tap, taking into account the time increment dt. The relationship between the effective pitch and the tap geometric parameters can be expressed as: For ordinary straight-flute taps, the helix angle γ is 90°, so the effective pitch is equal to the thread pitch.

7. The method for predicting the tapping torque of a straight groove tap based on an oblique cutting model according to claim 6, characterized in that: The specific process of the finite element simulation of the tool-workpiece contact mechanics model in step 6 is as follows: Step 61: Set the working directory; Step 62: Modeling and assembling of tool workpiece; Step 63: Create tool workpiece attributes; Step 64: Workpiece and tool meshing; Step 65: Workpiece-tool interaction settings; Step 66: Create analysis steps; Step 67: Workpiece tool load setting; Step 68: Submit the assignment; Step 69: End.

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