Method for realizing large-size chip-resistant tap

Abstract

The application relates to a realization method of a large-size anti-broken-edge tap, which solves the broken-edge problems of the tap during the tap feeding and retreating by respectively obtaining the best point of a shoveling bit through a main cutting edge load uniform distribution strategy and obtaining the best chamfer angle through a terminal complete tooth chamfer strategy to optimize the anti-broken-edge structure of the tap. The application makes the load on the cutting tooth uniformly distributed, reduces the stress borne by the tap, reduces the friction between the complete tooth and the machined thread, provides more space for the blocked chip to discharge, reduces the reverse torque borne by the tap during the retreating, and finally reduces the broken-edge problem of the tap.

Description

Technical Field

[0001] This invention relates to a technology in the field of machining, specifically a method for implementing a large-size anti-chipping tap. Background Technology

[0002] During tapping of difficult-to-machine materials, excessive cutting forces can easily be generated, exceeding the tolerance of the tap cutting edge and leading to chipping. Chipping of large-diameter spiral flute taps mainly occurs during the tapping feed and retraction processes. Chipping during the feed process is primarily caused by excessive cutting force, uneven load distribution on the cutting teeth, stress concentration, and tool vibration. Chipping during the retraction process is mainly caused by chip accumulation generating reverse cutting forces and reverse torque causing wear and chipping of the weaker, intact teeth. Current technologies mainly focus on optimizing the tap cutting edge structure and coating processes. However, for large-diameter taps (greater than 16 mm), optimizing the surface microtexture structure of the cutting edge does not significantly improve the load distribution on the cutting edge. Furthermore, the high temperatures during tapping may cause the coating to lose adhesion due to thermal shock, affecting its service life. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, this invention proposes a method for implementing large-size anti-chipping taps. By uniformly distributing the load on the cutting teeth and chamfering the end teeth, the load distribution on the cutting teeth is made uniform, reducing the stress on the tap. At the same time, it reduces the friction between the end teeth and the machined threads, allowing more space for blocked chips to be discharged, reducing the reverse torque on the tap during retraction, and ultimately reducing the tap chipping problem.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for implementing a large-size anti-chipping tap. The method optimizes the tap anti-chipping structure by obtaining the optimal point of the shovel tip through a strategy of uniformly distributing the load on the main cutting edge and obtaining the optimal chamfer angle through a strategy of chamfering the complete teeth at the end, thereby solving the chipping problem during tap feed and retraction.

[0006] The aforementioned strategy for uniform load distribution on the main cutting edge refers to: simulating the tapping process based on the starting point of the cutting edge, thereby obtaining the stress cloud diagram corresponding to the tapping process, determining the candidate cutting edge point when the load is uniform, and obtaining the optimal cutting edge point after iterating through several candidate cutting edge points.

[0007] After setting the starting point of the scraper tip to 50%~90% of the original distance from the tap axis, the starting point of the scraper tip is obtained by simulating the stress cloud diagram to obtain the starting point of the scraper tip when the load is uniform and minimal during the feed process. This is used as the final starting point of the scraper tip, thereby increasing the scraper tip length.

[0008] The aforementioned end complete tooth chamfering strategy refers to: simulating the tapping process based on the initial chamfer angle to obtain the stress cloud diagram corresponding to the tapping process; determining when there is a force interaction between the end complete tooth and the material; resetting the chamfer angle; and obtaining the optimal chamfer angle after several iterations.

[0009] The initial chamfer angle is 15°~30°.

[0010] Technical effect

[0011] This invention effectively reduces chipping during the feed process by employing a strategy of uniform load distribution on the main cutting edge. For chipping during the retraction of large-diameter taps, this invention proposes a chamfering strategy for the complete teeth at the end. By chamfering the tip of the complete teeth along the width of the cutting edge, this reduces chipping of the complete tap teeth. Compared to existing technologies, this invention targets an M18 tap with a 7.5mm tip length and an 11.5° angle, containing four incomplete teeth. As the number of incomplete teeth increases, the load distribution becomes more uniform, reducing stress concentration, increasing the strength of the main cutting teeth, and reducing chipping during the feed. Attached Figure Description

[0012] Figure 1 This is a flowchart of the present invention;

[0013] Figure 2 This is a schematic diagram of the original tap cutting the toothed tip;

[0014] Figure 3 This is a schematic diagram of the cutting tooth tip of the anti-chipping tap of the present invention;

[0015] Figure 4 This is a diagram showing the stress distribution on the cutting teeth during the tapping process of the original tap.

[0016] Figure 5 This is a diagram showing the stress distribution on the cutting teeth during the tapping process of the anti-chipping tap of this invention.

[0017] Figure 6 This is a schematic diagram of the complete tooth chamfer at the end of the anti-chipping tap of the present invention;

[0018] Figure 7 This is a schematic diagram of the force analysis on the cutting edge of a spiral groove tap;

[0019] Figure 8 This is a schematic diagram of a spiral groove tap for tapping. Detailed Implementation

[0020] like Figure 1As shown, this embodiment relates to a method for implementing a large-size anti-chipping tap. The optimal point of the chipping tip is obtained by a strategy of uniformly distributing the load on the main cutting edge, and the optimal chamfer angle is obtained by a strategy of chamfering the end teeth to optimize the anti-chipping structure of the tap, thereby solving the chipping problem during tap entry and exit.

[0021] The aforementioned strategy for uniform load distribution on the main cutting edge refers to: simulating the tapping process based on the starting point of the cutting edge, thereby obtaining the stress cloud diagram corresponding to the tapping process, determining the candidate cutting edge point when the load is uniform, and obtaining the optimal cutting edge point after iterating through several candidate cutting edge points.

[0022] The aforementioned end complete tooth chamfering strategy refers to: simulating the tapping process based on the initial chamfer angle to obtain the stress cloud diagram corresponding to the tapping process; determining when there is a force interaction between the end complete tooth and the material; resetting the chamfer angle; and obtaining the optimal chamfer angle after several iterations.

[0023] The end teeth are subjected to forces with the material. A discrete method is used to analyze the forces on the spiral flute tap. This involves dividing the tap along the cutting edge into multiple small units, and performing a force analysis on each unit with a short straight cutting edge and rake / rare face. Specifically, this includes:

[0024] Step 1: Take any one of the teeth of the tap, such as... Figure 6 The forces distributed on the cutting teeth are simplified to concentrated forces. Let the total cutting force F be the force acting on the cutting teeth. The total cutting force F can be decomposed into the main cutting force F0. c Radial component F p and axial component F a There is a positive pressure N between the workpiece and the sides and top of the cutting tooth flank. i and frictional force R i .

[0025] Step 2: During tapping, each tooth is equivalent to a fluted lathe tool. Based on experimental analysis of the cutting force of fluted lathe tools, the friction on both sides and the top flank of the tooth increases the main cutting force by 20% to 30%. The main cutting force plays a major cutting role, with the main cutting force per tooth... , where: k c A is the cutting force per unit area. D This represents the cutting area.

[0026] Step 3: Depending on the workpiece material, the cutting force per unit area of ​​the tap is: , Where: A is the shear yield strength coefficient; n is the material strengthening coefficient; Ψ is the angle between the shear plane and the resultant cutting force; δ is the deformation coefficient; γ is the actual working rake angle of the tool; γ p ω is the face angle of the tool end face; K is the groove helix angle; rThe cutting cone angle.

[0027] Step 4: When the number of flutes on the spiral tap is N and the pitch is P, the basic tooth profile of a standard thread is used. During the tapping process, the tap advances one pitch, the rear cutting tooth reaches the position of the front cutting tooth and cuts off a portion of the material, and all cutting teeth perform cutting simultaneously. A schematic diagram of the tapping process is shown below. Figure 7 As shown. Cutting thickness of each cutting tooth. Where: а is the thickness of metal removed by each tooth of the tap in one revolution; P is the pitch; N is the number of chip flutes; K r The cutting cone angle.

[0028] Step 5: Set the cutting thickness α per tooth of the tap, typically 0.02~0.2mm. Since the cutting thickness is very small, the cutting area can be approximated as a rectangle. Let the cutting width of each tooth be α. wi Then the cutting area During the tapping process, a spiral flute tap advances one pitch P with each revolution, and the next cutting tooth reaches the position of the previous cutting tooth to perform the cutting. A schematic diagram of the spiral flute tap tapping process is shown below. Figure 7 As shown, during the continuous advance of the tap, the cutting width 'a' of each tooth... W1 >a W2 >a W3 When the cutting cone section is fully engaged, the total cutting width of the tap is: Where: H is the tooth height; a Wi This represents the cutting width.

[0029] Step 6 calculates the total cutting area when tapping with a spiral flute tap. .

[0030] like Figure 6 The figure shows the force analysis of a spiral flute tap during the tapping process. The total tapping torque is the sum of the torque components generated by each component force on the Z-axis. The torque components generated by each component force on the Z-axis are as follows: cutting force F c Torque component generated on the Z-axis radial force F p The force arm on the Z-axis is 0, so the torque component... ; Axial force F a The direction of action is parallel to the Z-axis, so the torque component... The positive pressure on the back face of the cutter teeth is 𝑁 𝑖 Torque component on the Z-axis The frictional force R on both sides of the back face of the cutting tooth i Torque component on the Z-axis ; Main back face normal pressure N i Torque component on the Z-axis Friction R on the main flank face i Torque component on the Z-axis , where: d i γ is the diameter at the i-th tooth of the tap; M is the torque component on the Z-axis; γ is the tooth profile angle; β is the thread helix angle of the tap; μ is the coefficient of friction between the tap and the workpiece; α p It is the back angle of the tap.

[0031] Because the helix angle β of the spiral groove tap thread is very small, sinβ is approximately 0 and cosβ is approximately 1, which means the torque of the normal force on the back face of the cutter teeth is zero. hour, Let be the Coulomb coefficient of friction between the tool and the workpiece. The torque exerted by the normal force on the main flank face and the torque exerted by the frictional force are equal in magnitude and opposite in direction, so the sum of the two equations is zero. Adding the above torque components yields the total torque for each tooth of the spiral flute tap. From the above equation, it can be seen that, without considering the interaction between the tap and the chip, the tapping torque of the spiral flute tap mainly comes from the cutting force F. c The frictional force R between the cutting teeth and the workpiece i Each tooth of a spiral flute tap can be considered as a fluted cutting tool. Cutting experiments with fluted cutting tools show that the mutual friction between the two flank faces and the workpiece increases the main cutting force by 20% to 30%. Depending on the workpiece material, let's assume a proportionality coefficient k for the increase in main cutting force; then the friction force R... i With the main cutting force F c The relationship between them satisfies: The tapping torque for each cutting tooth is: The total tapping torque is: Mechanical analysis of the tapping process shows that the net force on the tap is constantly changing, as is the torque on the tap during the tapping process. Mainly due to cutting force and friction force The resulting cutting torque and friction torque Composition, that is The torque on the tap is then... , where: r i Where is the radius of rotation of the cutting edge; m is the number of cutting teeth; N is the number of working teeth for both cutting and calibration teeth; therefore, during the tapping process, in order to reduce the problem of uneven load distribution and stress concentration on the cutting teeth, two M18 taps with different numbers of cutting teeth are structurally optimized, with 3 and 4 cutting teeth respectively, as follows: Figure 1 , Figure 2 As shown, tapping simulations were performed to compare and analyze the stress distribution on the cutting teeth during the tapping process.

[0032] like Figure 3 , Figure 4 The figure shows the simulated stress distribution results of tapping with different numbers of cutting teeth. When tapping through holes, with only 3 cutting teeth, significant stress concentration occurs on the three incomplete teeth, with higher Mises stress on the first two teeth. With 4 cutting teeth, the stress distribution is more uniform, with no obvious stress concentration, and the Mises stress is also lower. This indicates that increasing the number of cutting teeth, i.e., the number of incomplete teeth, or increasing the backing length, helps to distribute the load evenly on the cutting teeth, reduces the stress on the tap, and ultimately reduces tap chipping and improves tool life.

[0033] Regarding the issue of wear and chipping of the weaker intact teeth during tap retraction due to reverse torque, it can be inferred from the actual chipping location of the tap that there is interference between the width of the cutting edge and the machined thread. This interference mainly stems from two aspects: First, poor chip removal during tapping causes residual chips to block the gap between the intact teeth of the tap and the thread during tap retraction, resulting in greater reverse torque. Ultimately, this causes chipping of the tap's cutting edge and damages the quality of the thread. Second, the tap's central axis may not coincide with the central axis of the bottom hole during tapping, leading to abnormal vibration during retraction. This causes the intact teeth of the tap to scrape and impact the machined thread, resulting in chipping of the tool.

[0034] Based on the stress analysis of spiral flute taps and the actual chipping location, the chipping problem is suppressed by chamfering the tooth tip of the complete tooth along the width of the cutting edge. Figure 5 As shown. Since the intact teeth do not participate in cutting, chamfering the tops of the last few intact teeth will not affect thread machining or thread quality. On the contrary, the chamfer on the back of the cutting edge can reduce the friction between the intact teeth and the machined thread during retraction, allowing more space for clogged chips to escape, reducing the reverse torque on the tap during retraction, and effectively reducing chipping problems.

[0035] Through specific experiments, an M18 tap with optimized multi-cutting teeth and end-complete tooth chamfer structure was created using 3D modeling software. This was then imported into finite element simulation software for tapping simulation, and stress cloud diagrams were extracted. Figure 3 , Figure 4 As shown, the improved tap of this invention has a more uniform stress distribution and lower stress value on the cutting edge compared to the unimproved tap. During tapping with large-diameter taps, the stress distribution on the cutting edge is more uniform and the stress is lower, which can reduce tool breakage and extend tool life.

[0036] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for implementing a large-size anti-chipping tap, characterized in that, The optimal point of the scraper tip is obtained by uniformly distributing the load on the main cutting edge, and the optimal chamfer angle is obtained by the complete end tooth chamfering strategy, so as to optimize the tap anti-chipping structure and solve the chipping problem during tap infeed and retraction respectively. The aforementioned end complete tooth chamfering strategy refers to: simulating the tapping process based on the initial chamfer angle, thereby obtaining the stress cloud diagram corresponding to the tapping process, determining when there is a force interaction between the end complete tooth and the material, resetting the chamfer angle, and obtaining the optimal chamfer angle after several iterations; The end teeth are subjected to forces with the material. A discrete method is used to analyze the forces on the spiral flute tap. This involves dividing the tap along the cutting edge into multiple small units, and performing a force analysis on each unit with a short straight cutting edge and rake / rare face. Specifically, this includes: Step 1: Take any one tooth of the tap and simplify the force distributed on the tooth into a concentrated force. Let the force on the tooth be the total cutting force F. The total cutting force F is decomposed into the main cutting force F. c Radial component F p and axial component F a There is a positive pressure N between the workpiece and the sides and top of the cutting tooth flank. i and frictional force R i ; Step 2: During tapping, each tooth is equivalent to a fluted lathe tool. Based on experimental analysis of the cutting force of the fluted lathe tool, the friction on both sides and the top flank of the tooth increases the main cutting force by 20%~30%. This main cutting force plays a major cutting role, and the main cutting force per tooth... , where: k c A is the cutting force per unit area. D The cutting area; Step 3: Depending on the workpiece material, the cutting force per unit area of ​​the tap is: , Where: A is the shear yield strength coefficient; n is the material strengthening coefficient; Ψ is the angle between the shear plane and the resultant cutting force; δ is the deformation coefficient; γ is the actual working rake angle of the tool; γ p ω is the face angle of the tool end face; K is the groove helix angle; r The cutting cone angle; Step 4: When the number of flutes on the spiral tap is N, the pitch is P, and the basic tooth profile of a standard thread is used, during the tapping process, the tap advances one pitch, the rear cutting tooth reaches the position of the front cutting tooth and cuts off a portion of the material, and all cutting teeth cut simultaneously. The cutting thickness of each cutting tooth is... Where: а is the thickness of metal removed by each tooth of the tap in one revolution; P is the pitch; N is the number of chip flutes; K r The cutting cone angle; Step 5: Set the cutting thickness α per tooth of the tap, which is generally 0.02~0.2mm. Since the cutting thickness is very small, the cutting area is approximated as a rectangle, and the cutting width of each tooth is set as α. wi Then the cutting area During the tapping process, a spiral flute tap advances one pitch P with each revolution, and the next cutting tooth reaches the position of the previous cutting tooth to perform cutting. As the tap continues to advance, the cutting width a of each tooth increases. W1 >a W2 >a W3 When the cutting cone section is fully engaged, the total cutting width of the tap is: Where: H is the tooth height; a Wi This refers to the cutting width; Step 6 calculates the total cutting area when tapping with a spiral flute tap. .

2. The method for implementing a large-size anti-chipping tap according to claim 1, characterized in that, The aforementioned strategy for uniform load distribution on the main cutting edge refers to: simulating the tapping process based on the starting point of the cutting edge, thereby obtaining the stress cloud diagram corresponding to the tapping process, determining the candidate cutting edge point when the load is uniform, and obtaining the optimal cutting edge point after iterating through several candidate cutting edge points.

3. The method for implementing a large-size anti-chipping tap according to claim 2, characterized in that, After setting the starting point of the scraper tip to 50%~90% of the original distance from the tap axis, the starting point of the scraper tip is obtained by simulating the stress cloud diagram to obtain the starting point of the scraper tip when the load is uniform and minimal during the feed process. This is used as the final starting point of the scraper tip, thereby increasing the scraper tip length.

4. The method for implementing a large-size anti-chipping tap according to claim 1, characterized in that, The initial chamfer angle is 15°~30°.

5. The method for implementing a large-size anti-chipping tap according to claim 1, characterized in that, The aforementioned resetting of the chamfer angle refers to: analyzing the force on the spiral flute tap during the tapping process. The total tapping torque is the sum of the torque components generated by each force on the Z-axis. The torque components generated by each force on the Z-axis are, in order: cutting force F... c Torque component generated on the Z-axis radial force F p The force arm on the Z-axis is 0, so the torque component... ; Axial force F a The direction of action is parallel to the Z-axis, so the torque component... The positive pressure on the back face of the cutter teeth is 𝑁 𝑖 Torque component on the Z-axis The frictional force R on both sides of the back face of the cutting tooth i Torque component on the Z-axis ; Main back face normal pressure N i Torque component on the Z-axis Friction R on the main flank face i Torque component on the Z-axis , where: d i γ is the diameter at the i-th tooth of the tap; M is the torque component on the Z-axis; γ is the tooth profile angle; β is the thread helix angle of the tap; μ is the coefficient of friction between the tap and the workpiece; α p Let β be the tap relief angle. Since the helix angle β of a spiral flute tap is very small, sinβ is approximately 0 and cosβ is approximately 1. Therefore, the torque of the normal force on the relief face of the cutter teeth is zero. hour, Let be the Coulomb coefficient of friction between the tool and the workpiece. The torque exerted by the normal force on the main flank face and the torque exerted by the frictional force are equal in magnitude and opposite in direction, so the sum of the two equations is zero. Adding the above torque components together gives the total torque for each tooth of the spiral flute tap. From the above equation, it can be seen that, without considering the interaction between the tap and the chip, the tapping torque of the spiral flute tap mainly comes from the cutting force F. c The frictional force R between the cutting teeth and the workpiece i Treating each tooth of the spiral flute tap as a fluted cutting tool, cutting experiments with fluted cutting tools show that the mutual friction between the two flank faces and the workpiece increases the main cutting force by 20% to 30%. Depending on the workpiece material, let's assume a proportionality coefficient k for the increase in main cutting force, then the friction force R... i With the main cutting force F c The relationship between them satisfies: The tapping torque for each cutting tooth is: The total tapping torque is: Mechanical analysis of the tapping process shows that the net force on the tap is constantly changing, and the torque on the tap during the tapping process is also constantly changing. Mainly due to cutting force and friction force The resulting cutting torque and friction torque Composition, that is The torque on the tap , where: r i is the radius of rotation of the cutting edge; m is the number of cutting teeth; N is the number of working teeth of the cutting teeth and the calibration teeth.

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