A large-length-diameter-ratio shaft tooth part and a machining method thereof

Abstract

The application discloses a machining method for a large-length-diameter-ratio shaft tooth part, which comprises the following steps: removing excess material from a forging blank; performing heat treatment and quenching and tempering to obtain a quenched and tempered blank; straightening the quenched and tempered blank; performing annealing stress relief treatment on the straightened blank to obtain an annealed blank; performing rough grinding on the outer circle of the annealed blank to obtain a ground blank; clamping and fixing the ground blank on a clamping mechanism to perform rough turning to obtain a rough blank; pre-grinding the rough blank to a target size; clamping and fixing the rough blank on the clamping mechanism to perform finish turning, and thus the large-length-diameter-ratio shaft tooth part is obtained. The machining method reduces the deflection of the large-length-diameter-ratio shaft tooth part to the maximum extent, effectively solves the technical problems of low qualified rate, high production cost and machining precision failing to meet product requirements in the machining of the large-length-diameter-ratio shaft tooth part, effectively enhances the rigidity of the large-length-diameter-ratio shaft tooth part, and effectively reduces the research and development cost of enterprises.

Description

Technical Field

[0001] This invention belongs to the field of machining tools, specifically relating to a large length-to-diameter ratio shaft gear part and its machining method. Background Technology

[0002] The power take-off (PTO) connecting shaft is one of the important components of a tractor transmission, mainly used to transmit torque between the transmission and the PTO. It is a typical high length-to-diameter ratio (L / D ratio) shaft gear part, and its manufacturing precision has a significant impact on the performance of the tractor transmission. However, the existing processing methods for high L / D ratio shaft gear parts have the following drawbacks: After forging, high L / D ratio shaft gear parts need to undergo quenching and tempering treatment, which will cause quenching and tempering cracks on the surface of the parts, and the bending deformation of the parts is large, affecting the subsequent processing and use of the forging blank; The structural characteristics of the parts determine that the rigidity of this type of part is extremely poor, and it is easily affected by cutting forces and its own weight during processing, making it prone to cutting chatter and processing deformation.

[0003] Due to the existence of the two bottleneck problems mentioned above, the pass rate of shaft gear parts with large length-to-diameter ratio is relatively low, the production cost remains high, and large-scale production is not possible. Therefore, it is urgent to develop a perfect processing method suitable for this type of part. Summary of the Invention

[0004] The purpose of this invention is to provide a machining method for shaft gear parts with a large length-to-diameter ratio, so as to solve the technical problems of low pass rate, high production cost and inability to meet the requirements of machining accuracy in the prior art for shaft gear parts with a large length-to-diameter ratio.

[0005] The technical solution adopted in this invention is:

[0006] A method for machining shaft gear parts with a large length-to-diameter ratio includes the following steps:

[0007] Step 1: Remove excess material from the forging billet to obtain the workpiece to be processed;

[0008] Step 2: Heat-treat and temper the workpiece to obtain the tempered workpiece;

[0009] Step 3: Make straightening center holes at both ends of the heat-treated blank; use the straightening center holes to position the heat-treated blank and complete the straightening to obtain the straightened blank;

[0010] Step 4: Anneal the straightened blank to relieve stress, and obtain the annealed blank.

[0011] Step 5: Mill the end faces of both ends of the annealed blank flat; re-drill the center hole at the location of the center hole for straightening; rough grind the outer diameter of the annealed blank on an external cylindrical grinding machine with the center hole as the positioning hole to obtain the rounded blank.

[0012] Step 6: Clamp and fix the rounded blank on the clamping mechanism to rough turn it to obtain a rough blank;

[0013] Step 7: After the rough blank is pre-ground to the target size, the outer diameter is ground.

[0014] Step 8: Precision machining.

[0015] The present invention also has the following technical features:

[0016] Specifically, the clamping mechanism includes a base, a three-jaw chuck disposed on the base, and a tail tip disposed opposite the three-jaw chuck. An intermediate support is also disposed between the three-jaw chuck and the tail tip.

[0017] Furthermore, the center hole for straightening includes a first center hole and a second center hole, with the first center hole and the second center hole being coaxially arranged.

[0018] Furthermore, in steps 6 and 8, the clamping position of the intermediate support satisfies the following conditions:

[0019]

[0020] In the formula:

[0021] L is the length of a gear-type part with a large length-to-diameter ratio, in mm;

[0022] 'a' represents the distance between the center point of the top surface of the central support and the front face of the three-jaw chuck, in mm.

[0023] Furthermore, in the precision machining process described in step 8, the cutting tool moves from the three-jaw chuck towards the tail tip.

[0024] Furthermore, in step 3, the warpage of the straightened blank is ≤0.3mm.

[0025] Furthermore, the stress-relieving annealing process described in step 4 specifically includes placing the straightened billet into a pit furnace for suspension and hoisting, heating it to 450±10℃, holding it at that temperature for 2.5 hours, cooling it in the furnace to 200℃, and then removing it from the furnace and cooling it to room temperature.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The processing method provided by this invention effectively solves the problems of low yield, high production cost, and inability to meet product requirements for shaft and gear parts with large length-to-diameter ratios. The method eliminates forging cracks by removing excess material from the forging billet and then performing heat treatment. Stress-relieving annealing heat treatment on the straightened parts eliminates residual stress, stabilizes the part's size and shape, and reduces deformation and cracking during subsequent processing and use. The intermediate support effectively reduces the deflection of shaft and gear parts with large length-to-diameter ratios. The clamping mechanism provided by this invention has a simple structure, is easy to use, and is worthy of promotion. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the precision turning clamping of the part to be processed in Example 1;

[0029] Figure 2 The simulation results of deflection calculation for the large aspect ratio gear part obtained in Example 1 are shown.

[0030] Figure 3 The simulation results for the deflection calculation of the large length-to-diameter ratio gear part obtained in Comparative Example 1 are shown.

[0031] Figure 4 The simulation results for the deflection calculation of the large length-to-diameter ratio gear part obtained in Comparative Example 2 are shown.

[0032] Figure 5 A simplified mechanical calculation model for a high aspect ratio gear part constructed for Example 1;

[0033] Figure 6 A schematic diagram of the tool path for machining existing parts;

[0034] Figure 7 This is a schematic diagram of the tool path direction for machining the part in Example 1.

[0035] The labels in the diagram indicate:

[0036] 1-Three-jaw chuck, 2-Tail tip, 3-Intermediate support, 4-Part to be processed. Detailed Implementation

[0037] Following the above technical solutions, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0038] The technical terms involved in this invention are explained as follows:

[0039] High length-to-diameter ratio parts: Parts with a length-to-diameter ratio ≥ 25.

[0040] Allowance: Thickness of the material to be processed

[0041] Remove excess material: Remove the excess material to be processed.

[0042] The present invention will be further described in detail below with reference to the embodiments.

[0043] Example 1

[0044] This embodiment provides a machining method for shaft gear parts with a large length-to-diameter ratio, in order to obtain qualified shaft gear parts with a large length-to-diameter ratio, specifically including the following steps:

[0045] Step 1: Remove excess material from the forging billet to obtain the workpiece. Forging cracks exist on the surface of the forging billet; direct tempering will cause these cracks to expand further, severely impacting the quality of the machined part. Therefore, it is necessary to remove excess material from the forging billet.

[0046] Step 2: Heat-treat the blank to be processed to obtain the tempered blank. The surface hardness of the tempered blank is 31-35 HRC. Due to the presence of heat stress during tempering, the tempered blank will warp to a certain extent. Because the warping is large, the tempered blank cannot be directly precision machined. Therefore, the tempered blank needs to be straightened and annealed to relieve stress.

[0047] Step 3: Open straightening center holes at both ends of the tempered blank. The straightening center holes include a first center hole and a second center hole, which are coaxially arranged. Position the tempered blank with the straightening center holes and complete the straightening to obtain the straightened blank. The warpage of the straightened blank is ≤0.3mm.

[0048] Step 4: To prevent deformation rebound caused by the release of residual stress in the straightened blank, the straightened blank needs to be annealed to relieve stress, resulting in an annealed blank.

[0049] The stress-relieving annealing process specifically includes: placing the straightened billet into a pit furnace and suspending it, heating it to 450±10℃ and holding it at that temperature for 2.5 hours; cooling it in the furnace to 200℃ and then removing it from the furnace and cooling it to room temperature.

[0050] Step 5: Mill the two end faces of the annealed blank flat, ensuring that the milled length is greater than or equal to the total length of the part; re-drill the center hole at the location of the center hole for straightening; rough grind the outer diameter of the annealed blank on an external cylindrical grinding machine with the center hole as the positioning hole to obtain the rounded blank.

[0051] In this embodiment, the width of the center support used is 40mm. Therefore, a reference with a width of 44mm or more is ground at the middle position of the length of the blank after annealing, and the runout of the machined outer surface is ensured to be less than or equal to 0.02mm, so as to ensure that the center support used for support does not interfere during rough turning.

[0052] Step 6: Clamp and fix the rounded blank on the clamping mechanism to rough turn it to obtain a rough blank;

[0053] The clamping mechanism includes a base, a three-jaw chuck 1 mounted on the base, and a tail tip 2 positioned opposite the three-jaw chuck 1. An intermediate support 3 is also provided between the three-jaw chuck 1 and the tail tip 2. The three-jaw chuck 1 and the tail tip 2 positioned opposite the three-jaw chuck 1 are used to fix the two ends of the workpiece 4 (blank) to be processed. The intermediate support 3 supports the workpiece 4 (blank), which can effectively reduce the deflection of the workpiece. If the workpiece is bent and deformed, it will inevitably cause vibration, and in severe cases, tool breakage may occur, which will damage the accuracy of the machine tool. The intermediate support 3 can effectively solve the above problems.

[0054] First, a rectangular coordinate system is established with the center of the front face of the three-jaw chuck 1 as the origin, the axis of the workpiece 4 (blank) to be processed as the X-axis, and the direction in the same horizontal plane as the X-axis and perpendicular to the X-axis as the Y-axis. The distance between the center point of the top surface of the center support 4 and the front face of the three-jaw chuck 1 is defined as a.

[0055] Using the central support as the fulcrum, the large length-to-diameter ratio shaft gear parts are divided into two segments: one segment is from the center point of the top surface of the three-jaw chuck 1 to the center point of the top surface of the intermediate support 4, and the other segment is from the center point of the top surface of the intermediate support 4 to the right end face of the part to be processed 4 (blank). These two segments correspond to two different deflection states and different models.

[0056] For any point on a gear-type part with a large length-to-diameter ratio, when 0 ≤ x ≤ a, the mechanical model of this segment is a beam model with both ends fixed. When a ≤ x ≤ L (the length of the gear-type part with a large length-to-diameter ratio), the mechanical model of this segment is a beam model with one end fixed and the other end simply supported.

[0057] The deflection equation for any point on a gear-type part with a large length-to-diameter ratio is as follows:

[0058]

[0059] In the formula:

[0060] q is the self-distributed load of the shaft gear part with a large length-to-diameter ratio, and q = mg / L, with the unit being N / mm;

[0061] L is the length of a gear-type part with a large length-to-diameter ratio, in mm;

[0062] 'a' is the distance between the center point of the top surface of the central support and the front end face of the three-jaw chuck, in mm.

[0063] E is Young's modulus, in MPa;

[0064] x is the distance between any point on the high length-to-diameter ratio geared part and the three-jaw chuck, in mm;

[0065] y represents the deflection at any point on a gear-type part with a large length-to-diameter ratio, in mm;

[0066] I represents the moment of inertia of the cross section of a gear-type part with a large length-to-diameter ratio. The unit is mm. 4 ;

[0067] D is the diameter of the shaft gear part with a length-to-diameter ratio to be machined, in mm.

[0068] Differentiating the two deflection equations above and setting the derivatives to zero, we obtain the X-coordinates of the maximum values ​​of the two deflection functions. Substituting these two X-coordinates into the corresponding deflection equations, we obtain the maximum values ​​y1 and y2 of the two deflection equations. Setting y1 = y2, we obtain the clamping position of the intermediate support, that is, the equation relating the position a of the central support to L:

[0069]

[0070] Solving the equation reveals that when a = 0.545L, the deflection of gear parts with a large length-to-diameter ratio is minimal.

[0071] Step 7: After the rough blank is pre-ground to the target size, the outer diameter is ground.

[0072] To ensure the quality of precision turning, the rough blank can be pre-ground to a reference point before precision turning. The outer diameter of the center support and the clamping point of the three-jaw chuck can be ground to ensure that the runout of these two positions is less than 0.02mm. Ultimately, it can be ensured that the runout of all outer diameters of the machined part is less than 0.03mm.

[0073] Step 8: Fix the rough blank processed in step 7 onto the clamping mechanism and finish turn it to obtain the final product. In the finish turning process, the tool moves from the three-jaw chuck towards the tail tip. This tool movement direction setting can significantly reduce the axial force on the part.

[0074] In this step, the clamping position of the central support is also determined by the following formula:

[0075]

[0076] Finally, a was determined to be 0.545L.

[0077] Specifically, such as Figure 6As shown, according to the existing tool feed direction, that is, from the tail tip to the three-jaw chuck, the relationship between the axial pressure FB applied to the part by the tail tip, the axial cutting force FC borne by the part, and the axial support force FA applied to the part by the three-jaw chuck is: FA=FB+FC. The axial forces on the parts at both ends of the intermediate support are: FB+2FC and FB-FC, respectively.

[0078] from Figure 7 As can be seen from the data, when using the tool path direction provided in this embodiment, the axial cutting force FC and the axial pressure FB applied to the part by the tail tip are in opposite directions. The axial forces on the parts at both ends of the intermediate support are FB-2FC and FB+FC, respectively, and the axial force on the parts is significantly reduced.

[0079] In this embodiment, deflection testing was performed on the final manufactured part, including: placing the central support at positions a = 0.4L, a = 0.7L, and a = 0.545L respectively, and then obtaining deflection curves at different positions on the part. The results are as follows. Figure 2 As shown in the figure:

[0080] When a = 0.4L, the maximum deflection occurs in the segment a ≤ x ≤ L, and the maximum deflection is 0.003 mm.

[0081] When a = 0.7L, the maximum deflection occurs in the segment 0 ≤ x ≤ a, and the maximum deflection is 0.0027 mm.

[0082] When a = 0.545L, the maximum deflection of the two segments is equal, and the maximum deflection is 0.001mm.

[0083] The results above show that the part deflection is minimized when the central support is located at a distance of 0.545L from the three jaws, which is more conducive to machining.

[0084] Comparative Example 1

[0085] This comparative example provides a machining method for shaft gear parts with a large length-to-diameter ratio. The operation steps of this comparative example are the same as those of Example 1. The difference is that in steps 6 and 8, when clamping, the clamping method is to clamp one end with three jaws and leave the other end suspended.

[0086] The deflection of the final part prepared in this comparative example was tested, and the results are as follows: Figure 4 As shown, the maximum deflection occurs at the suspended end, with a maximum deflection of -0.546 mm.

[0087] Comparative Example 2

[0088] This comparative example provides a machining method for shaft gear parts with a large length-to-diameter ratio. The operation steps of this comparative example are the same as those of Example 1. The difference is that in steps 6 and 8, when clamping, the clamping method is to clamp one end with three jaws and clamp the other end with the tail tip.

[0089] The deflection of the final part prepared in this comparative example was tested, and the results are as follows: Figure 5 As shown, the maximum deflection occurs at the suspended end. The maximum deflection occurs at the middle of the workpiece, with a maximum deflection of -0.023 mm.

[0090] As can be seen from Example 1, Comparative Example 1, and Comparative Example 2:

[0091] The deflection of large aspect ratio gear parts prepared by the method of the present invention is significantly reduced, thereby effectively enhancing the rigidity of the parts.

[0092] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0093] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0094] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for machining shaft gear parts with a large length-to-diameter ratio, characterized in that, Includes the following steps: Step 1: Remove excess material from the forging billet to obtain the workpiece to be processed; Step 2: Heat-treat and temper the workpiece to obtain the tempered workpiece; Step 3: Make straightening center holes at both ends of the heat-treated blank; use the straightening center holes to position the heat-treated blank and complete the straightening to obtain the straightened blank; Step 4: Anneal the straightened blank to relieve stress, and obtain the annealed blank. Step 5: Mill the end faces of both ends of the annealed blank flat; re-drill the center hole at the location of the center hole for straightening; rough grind the outer diameter of the annealed blank on an external cylindrical grinding machine with the center hole as the positioning hole to obtain the rounded blank. Step 6: Clamp and fix the rounded blank on the clamping mechanism to rough turn it to obtain a rough blank; Step 7: After the rough blank is pre-ground to the target size, the outer diameter is ground. Step 8: Precision machining; The clamping mechanism includes a base, a three-jaw chuck disposed on the base, and a tail point disposed opposite the three-jaw chuck. An intermediate support is also provided between the three-jaw chuck and the tail point. In steps 6 and 8, the clamping position of the intermediate support is determined by the following formula: In the formula: L represents the length of a geared shaft with a large length-to-diameter ratio, expressed in mm. 'a' represents the distance between the center point of the top surface of the intermediate support and the front face of the three-jaw chuck, in mm. In the precision machining process described in step 8, the cutting tool moves from the three-jaw chuck towards the tail tip.

2. The machining method for shaft gear parts with a large length-to-diameter ratio as described in claim 1, characterized in that, The straightening center hole includes a first center hole and a second center hole, which are coaxially arranged.

3. The machining method for shaft gear parts with a large length-to-diameter ratio as described in claim 1, characterized in that, In step 3, the warpage of the straightened blank is ≤0.3mm.

4. The machining method for shaft gear parts with a large length-to-diameter ratio as described in claim 1, characterized in that, The stress-relieving annealing process described in step 4 specifically includes placing the straightened billet into a pit furnace for suspension and hoisting, heating it to 450±10℃, holding it at that temperature for 2.5 hours, cooling it in the furnace to 200℃, and then removing it from the furnace and cooling it to room temperature.

5. The machining method for shaft gear parts with a large length-to-diameter ratio as described in claim 1, characterized in that, In step 7, when grinding the outer diameter, the runout of the outer diameter of the machining end face at the three-jaw chuck and the intermediate support is less than 0.02mm.

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