Precise slender triangular spline internal broach machining method

Abstract

The invention relates to a precision slender triangular spline inner broach machining method. The problems that an existing method is poor in quality and low in production efficiency are solved. The method comprises the steps that 1, a broach is subjected to repeated upsetting and drawing forging from a blank, and carbide segregation after forging is guaranteed; 2, rough machining is carried out to control bending deformation out-of-tolerance, straightening is carried out after machining is completed, and machining stress is eliminated; 3, bending deformation is controlled through four times of outer circle grinding, straightening and bearing grinding measures in semi-finish machining; 4, tooth profile rough grinding is carried out, and grinding of all tooth profiles is completed through one-time clamping machining; straightening is conducted after machining is completed, and machining stress is eliminated; and 5, the starting stroke and the stopping stroke of a workbench are changed, involute tooth profile parameters are input for accurate grinding, the consistency of the centers of the triangular spline teeth and the involute spline teeth is guaranteed, and when the M value of the two sections of tooth profiles is ground to be close to the measured value of a finished product, the feeding amount of a grinding wheel is reduced, smooth grinding is repeated, and spark-free grinding is carried out. The machining efficiency is high, the part machining quality is stable, and the batch production requirement can be met.

Description

Technical Field

[0001] The invention relates to a mechanical processing method, in particular to a precision slender triangular spline internal broach processing method. Background Art

[0002] Broaching is one of the preferred processing methods for machining internal splines. Spline internal broaches are a type of tool specifically used for machining spline holes and are widely used in the machinery manufacturing industry. Spline internal broaches can generally achieve one-time forming through broaching, and can efficiently machine spline holes that meet precision requirements. They have high processing efficiency and accurate positioning, and can achieve precise machining of spline holes. For internal splines with smaller inner diameters, precision slender triangular spline internal broaches are often used. The main features of this type of broach are: the front part of the broach uses round rough cutting teeth to remove most of the cutting allowance for initial forming, and the remaining part is left for the rear spline cutting teeth to expand the key forming, which can reduce the contact between the teeth and the workpiece surface, reduce the cutting amount and cutting force, reduce noise and vibration, and have a good surface roughness and a long tool life. At the same time, the rear part of the broach is designed as a type of spline cutting teeth for machining splines and a calibration spline tooth arrangement, which can simultaneously broach the large and small diameters of triangular splines, thereby ensuring good coaxiality and meeting the centering accuracy requirements of the workpiece.

[0003] The material hardness requirement of a product part is HB≤217, and its internal profile is an involute triangular spline tooth. The part requires a broach to broach an involute triangular spline internal hole. Therefore, a combined involute precision slender triangular spline internal broach with 28 teeth, a maximum outer diameter of 37.14, a tooth profile half angle of 40°21′13″±10′, a length of 670, and a structure of cutting teeth and calibration teeth is designed for this part. The shape of the broach is as follows: Figure 1 , Figure 2 , Figure 3 , Figure 4 shown.

[0004] The main technical parameters of the precision slender triangular spline internal broach are: number of teeth: 28, pressure angle: 40°, triangular spline tooth profile half angle 40°21′13″±10′ length 670 long, specification: 24.968×1115mm.

[0005] The main technical requirements are as follows:

[0006] 1. The consistency of the outer diameter of the calibration tooth and its precision-cut tooth of the same size is 0.007, and positive taper is not allowed.

[0007] 2. The radial runout of the outer diameter of the precision slender triangular spline internal broach should be in the same direction.

[0008] 3. The cumulative tolerance of the spline tooth pitch of the precision slender triangular spline internal broach is 0.03.

[0009] 4. The parallelism tolerance of the longitudinal grinding of the spline tooth side surface of the precision slender triangular spline internal broach to the broach reference axis is 0.025 for every 500MM length of the tooth part.

[0010] 5. There is no positive taper allowed on the side surfaces of the spline tooth along the axis of the broach, and the taper is measured with three needles and is allowed to be within the M value tolerance range.

[0011] 6. Heat treatment requirements: handle neck 40 ~ 52HRC, blade 63 ~ 66HRC.

[0012] After analysis and research, it was found that this precision and slender triangular spline internal broach could not meet the accuracy requirements of the drawing for the broach if it was turned, milled, quenched and ground once according to the conventional process. It was also easy to deform, the quality of the broach processing was too poor, and the yield rate and production efficiency were extremely low.

[0013] Analysis of the processing difficulties of this broach:

[0014] Precision slender triangular spline internal broaches have strict requirements on the cumulative error of the tooth pitch, and their small outer diameter and long length make them very easy to deform during processing. In addition, they have a large number of teeth, which leads to strict requirements on the indexing of the broach grinder accessory - the indexing plate. Any change in these processing processes will increase the angle and pitch error of the part, affecting the processing quality of the broach.

[0015] It is mainly manifested in:

[0016] (1) Due to its small diameter-to-length ratio, the maximum diameter is 37.44, while the length reaches 670, and the slenderness ratio is 18, it is very easy to deform during fine processing after quenching.

[0017] (2) When grinding the tooth profile on a broach grinder, how to ensure that the center hole, tailstock and grinding wheel center are always on the same center line, and after the grinding wheel is worn, it can still be ensured to be on the same center with the tailstock after being repaired with a grinding wheel dresser, which is a difficult point.

[0018] (3) 28 teeth need to be divided on the broach grinder, and the pitch error should be ≤0.03, which requires a higher indexing accuracy of the indexing plate.

[0019] (4) The measurement of the finished product after grinding is the difficulty of the final inspection. Summary of the invention

[0020] The present invention is directed to a method for processing a precision slender triangular spline internal broach. The process route, processing difficulties, technical principles and other aspects are analyzed and compared, and a relatively feasible processing method is found after repeated research and processing tests. This processing method is not only suitable for the processing of precision slender triangular spline internal and external broaches, but also suitable for the processing of slender precision involute triangular spline internal broaches, and also suitable for trapezoidal spline broaches, which will play a role in promoting and drawing lessons for the future mass production, scientific research trial production and non-standard customization of this type of tools.

[0021] The present invention is achieved by the following technical solutions:

[0022] A method for machining a precision elongated triangular spline internal broach comprises the following steps:

[0023] Step 1: The broach is repeatedly forged from the blank to ensure carbide segregation after forging;

[0024] Step 2: Use external cylindrical grinding for rough machining, and take measures to control the bending deformation tolerance, including: use tops to tighten on both sides, use the tool rest to support in the middle, speed 2000 / min, feed rate 0.08mm-0.1mm, straighten after machining to eliminate machining stress; use vacuum furnace heat treatment, the neck of the handle reaches HRC40-52, and the blade reaches HRC63-66;

[0025] Step 3: Semi-finishing: The bending deformation is controlled by grinding the outer circle, straightening and grinding the support four times. The allowance after each processing is 0.2mm, 0.15mm, 0.1mm and 0.05mm respectively.

[0026] Step 4: Rough grinding of tooth profile. First, calculate the reasonable half angle of triangular spline tooth profile. The grinding wheel shape is trimmed into a triangular shape and ensured to be included in the complete involute tooth profile. Select broach grinder for processing. Complete all tooth profile grinding in one clamping process. Rough grinding speed is 3200 / min, feed rate is 0.08mm-0.1mm, and straighten after processing to eliminate processing stress.

[0027] Step 5: After the triangular spline tooth profile is qualified, fine grinding is performed, the start and end strokes of the workbench are changed, the involute tooth profile parameters are input, and the grinding wheel shape is re-dressed to the involute shape. The center of the grinding wheel dresser remains unchanged to ensure the consistency of the centers of the triangular spline teeth and the involute spline teeth. When the M value of the two-stage tooth profile is close to the measured value of the finished product, the grinding wheel feed amount is reduced to 0.03mm-0.05mm, and the polishing is repeated to implement spark-free grinding;

[0028] After each processing sequence is completed, it should be hung vertically for more than 20 hours to prevent stress release and bending deformation.

[0029] Beneficial effects of the present invention:

[0030] 1. Use precise processing technology and heat treatment technology to ensure the accuracy and durability of the tool; use appropriate testing equipment and means to monitor and adjust the processing quality in real time to ensure the technical requirements of the tool. This method has high processing efficiency, stable parts processing quality, and can meet mass production requirements;

[0031] 2. It meets the precision requirements of broach processing and ensures the quality.

[0032] 3. It is not only suitable for the processing of precision slender triangular spline internal and external broaches, but also for the processing of slender precision involute triangular spline internal broaches. It is also suitable for trapezoidal spline broaches, which will promote and refer to the mass production, scientific research trial production and non-standard customization of this type of tools in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the structure diagram of the broach;

[0034] Figure 2 It is the structure diagram of broach tooth shape;

[0035] Figure 3 It is a triangular spline tooth grinding wheel shape;

[0036] Figure 4 It is the shape of an involute spline tooth grinding wheel. DETAILED DESCRIPTION

[0037] like Figure 1 , 2 As shown, it is the broach involved in the present invention. Since its diameter-to-length ratio is small, the maximum diameter is 37.44, while the length reaches 670, and the slenderness ratio reaches 18, it is very easy to bend and deform during cold working and heat treatment, so the following processing method is used.

[0038] 1. The broach is forged by repeated forging and pulling from the blank to ensure carbide segregation after forging.

[0039] 2. In the rough machining process, multiple measures should be taken to control the bending deformation, such as: use the top to tighten on both sides, use the tool rest to support in the middle, the speed is 2000 / min, and the feed rate is (0.08mm-0.1mm). Straighten after machining to eliminate machining stress.

[0040] 3. After heat treatment in vacuum furnace, the neck of the handle reaches HRC40-52, and the blade reaches HRC63-66.

[0041] 4. Semi-finishing controls the bending deformation by grinding the outer circle, straightening, and grinding the support four times. The allowance after each processing is 0.2mm, 0.15mm, 0.1mm, and 0.05mm respectively.

[0042] 5. Rough grinding of tooth profile: First calculate the reasonable half angle of triangular spline tooth profile, and adjust the grinding wheel shape to Figure 3 The shape of the tooth is ensured to be contained within the complete involute tooth profile. The consistency of the front and rear tooth profile centers must be ensured. A special broach grinder is selected for processing, and all tooth profile grinding is completed in one clamping process. The speed is 3200 / min during rough grinding, and the feed rate is (0.08mm-0.1mm). After processing, straighten and eliminate processing stress.

[0043] 6. After the triangular spline tooth profile is qualified, fine grinding is performed, the start and end strokes of the workbench are changed, the involute tooth profile parameters are input, and the grinding wheel is re-dressed. The shape of the grinding wheel at this time is as follows: Figure 4 In this way, since the center of the grinding wheel dresser remains unchanged, the consistency of the centers of the triangular spline teeth and the involute spline teeth is guaranteed. It should be noted that when the M value of the two-stage tooth profile is close to the measured value of the finished product, the grinding wheel feed should be reduced (0.03mm-0.05mm), repeated polishing, and spark-free grinding should be implemented to improve the tooth profile accuracy and the use effect of the broach.

[0044] After each processing sequence is completed, it should be hung vertically for more than 20 hours to prevent stress release and bending deformation.

[0045] Implementation of the program:

[0046] 1. According to the process analysis and processing difficulties, after research, we first processed samples with the same outer diameter as the drawn material for trial production, and designed a dividing plate with higher processing accuracy and a grinding wheel dresser for grinding the grinding wheel according to the drawings and the actual needs of the equipment (broach grinder). We also calculated the measuring needle diameter and three-needle coefficient, and repeatedly adjusted the broach grinder so that its center, tailstock and grinding wheel dresser were always kept on the same center line.

[0047] 2. Adjust the gear shape from the fine grinding after one processing to three semi-fine processing, fully age and release the processing stress before fine grinding the gears, and add a straightening process after each processing sequence to eliminate the processing stress.

[0048] 3. Use three needles to correctly measure the M value and provide powerful scientific data for inspection.

[0049] Through the trial production of samples, and the corresponding auxiliary second-class tooling, and repeated aging during the rough processing, fully releasing the processing stress, and then semi-finishing and finishing after straightening, multiple effective measurements and metrology are combined in the process. Through these effective measures, the deformation of the precision slender triangular spline internal broach during the processing is effectively overcome. And the cumulative error of the tooth pitch is well guaranteed to meet the needs of the broach parts, and the processing accuracy of the broach parts is guaranteed, which provides a good basis and reference for better processing of precision slender triangular spline internal broaches.

Claims

1. A method for machining a precision elongated triangular spline internal broach, characterized in that: The following steps are involved: Step 1: The broach is repeatedly forged from the blank to ensure carbide segregation after forging; Step 2: Use external cylindrical grinding for rough machining, and take measures to control the bending deformation tolerance, including: tightening the tops on both sides, supporting the tool rest in the middle, straightening after machining to eliminate machining stress; using vacuum furnace heat treatment, the handle neck reaches HRC40-52, and the blade reaches HRC63-66; Step 3: Semi-finishing: Control bending deformation by grinding the outer circle four times, straightening, and grinding the support; Step 4: Rough grinding of tooth profile. First, calculate the reasonable half angle of triangular spline tooth profile. The grinding wheel shape is trimmed into a triangular shape and ensured to be included in the complete involute tooth profile. Select broach grinder for processing. Use one-time clamping to complete all tooth profile grinding. Straighten after processing to eliminate processing stress. Step 5: After the triangular spline tooth profile is qualified, fine grinding is performed, the start and end strokes of the workbench are changed, the involute tooth profile parameters are input, and the grinding wheel shape is re-dressed to the involute shape. The center of the grinding wheel dresser remains unchanged to ensure the consistency of the centers of the triangular spline teeth and the involute spline teeth. When the M value of the two sections of the tooth profile is close to the measured value of the finished product, the grinding wheel feed amount is reduced, and the polishing is repeated to implement spark-free grinding.

2. A method for machining a precision elongated triangular spline internal broach according to claim 1, characterized in that: After each processing sequence is completed, it should be hung vertically for more than 20 hours to prevent stress release and bending deformation.

3. A method for machining a precision elongated triangular spline internal broach according to claim 1, characterized in that: In step 2, the grinding machine speed is 2000 / min and the feed rate is 0.08mm-0.1mm.

4. A method for machining a precision elongated triangular spline internal broach according to claim 1, characterized in that: In step 3, the allowances after each processing are 0.2mm, 0.15mm, 0.1mm, and 0.05mm respectively.

5. The method for machining a precision elongated triangular spline internal broach according to claim 1, characterized in that: In step 4, the speed during rough grinding is 3200 / min and the feed rate is 0.08mm-0.1mm.

6. The method for machining a precision elongated triangular spline internal broach according to claim 1, characterized in that: In step 5, reduce the grinding wheel feed to a certain 0.03mm-0.05mm.

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