Manufacturing process of a high-precision small module and small diameter centering composite slender broach

Abstract

The present invention discloses a manufacturing process for a high-precision small module and small-diameter centering composite slender broach, including a first-stage manufacturing process and a second-stage manufacturing process of the broach. The content of the first-stage manufacturing process of the broach sequentially includes (1) making the broach blank, (2) turning the outer circle of the broach, (3) turning the chip flutes and the outer circle of the circular cutting teeth of the broach, (4) heat treatment of the broach, (5) cryogenic treatment and aging treatment of the broach, (6) grinding the center hole of the broach, (7) grinding the outer circle of the support points of the broach, (8) grinding the outer circles of the front and rear handles, the outer circle of the cutting edge and the back angle of the broach, (9) grinding the chip flutes and the front cutting surface of the broach, (10) grinding the tooth profile of the broach, (11) trial broaching of the broach, (12) measuring the trial broaching parts, and (13) coating. The present invention improves the manufacturing precision of the small module and small-diameter centering composite slender broach, and further realizes high-precision broaching of internal splines with small-diameter centering of the broach.

Description

Technical Field

[0001] The present invention relates to the technical field of broach manufacturing, and particularly to a manufacturing process for a high-precision small-module small-diameter centering composite slender broach. Background Art

[0002] Most of the disk gears in the gear industry adopt spline hole structures. In the new national and international standards, involute splines are preferably recommended. The design datum of the involute spline hole is the pitch circle of the involute. In production, due to the limitations of the structures of fixtures and measuring tools, it is difficult to use the pitch circle as the process datum. The traditional involute spline broaches pull out the spline and the large diameter simultaneously. Therefore, the traditional processing method generally uses the large diameter of the spline as the process datum to reduce the error caused by datum conversion. When the large diameter of the spline hole is used as the process datum, the positioning element must be a spline, which not only increases the complexity of the tooling but is also inconvenient to use. Therefore, in production, it is hoped to use the small diameter of the spline hole as the process datum so as to use a smooth shaft as the positioning element.

[0003] At present, the vast majority of involute broaches produced by domestic tool factories are ordinary involute broaches, and generally the circular cutting teeth are in front of or behind the spline teeth. In this way, the centering circular hole of the spline and the spline hole are broached separately. During the broaching process, due to the bending of the broach, the sag caused by the self-weight of the broach, the movement of the workpiece, etc., will cause the offset between the spline and the centering circular hole.

[0004] The small-diameter centering composite broach is a new generation of advanced tool for processing high transmission accuracy and high service life. The structural feature of this kind of tool is that the circular cutting teeth and the spline teeth are staggered in the rear part of the broach. Therefore, the small diameter of the spline and the spline are broached simultaneously, so as to ensure a very high coaxiality between the spline and its small diameter. Therefore, in industries where a large number of high-precision gears are used, small-diameter centering composite broaches are required.

[0005] However, since the structure of the high-precision small-module small-diameter centering composite slender broach is different from that of the conventional broach, the use of the conventional broach manufacturing process can no longer meet its high-precision requirements. Therefore, there is an urgent need to develop a manufacturing technology specifically for the high-precision small-module small-diameter centering composite slender broach to meet the needs of modern processing technology. Summary of the Invention

[0006] In order to solve the above problems, the present invention proposes a manufacturing process for a high-precision small-module small-diameter centering composite slender broach, aiming to improve the manufacturing precision of the small-module small-diameter centering composite slender broach, and further achieve high-precision broaching of the internal spline with small-diameter centering of the broach.

[0007] The so-called high precision means that the technical indexes of broaching the internal spline reach above level 5 of the national standard GB / T3478 or above level 9 of the German standard DIN 5480.

[0008] The so-called small module refers to the module range of the broach being 0.3 - 0.9 mm.

[0009] The so-called small-diameter centering compound refers to the simultaneous broaching of the small diameter and the large diameter of the internal spline.

[0010] For this reason, the specific technical solution of the present invention is as follows:

[0011] A manufacturing process for a high-precision small-module small-diameter centering compound slender broach, including a first-stage manufacturing process and a second-stage manufacturing process of the broach. The content of the first-stage manufacturing process of the broach includes the following steps in sequence:

[0012] (1) Broach blank production: Select powder high-speed steel manufacturing technology, formulate the material composition according to the tool characteristics, atomize the powder, and perform static pressure treatment to make the broach blank of the high-precision small-module small-diameter centering compound slender broach; among them, the powder high-speed steel material selected for the broach blank is the molten steel melted by a high-frequency induction furnace, and the molten steel is sprayed and atomized with high-pressure argon or nitrogen, and quickly cooled to fine and uniform high-speed steel powder. The high-speed steel powder is made into a tool blank through high temperature and high pressure, and then further forged and rolled to form the broach blank;

[0013] (2) Turning the outer circle of the broach: Use a precision CNC lathe equipped with a self-centering hydraulic steady rest to turn the outer circle of the broach;

[0014] (3) Turning the chip flutes and the outer circle of the circular cutting teeth of the broach; Use a precision CNC lathe equipped with a steady rest, and perform CNC programming to turn the chip flutes and the outer circle of the circular cutting teeth of the broach;

[0015] (4) Heat treatment of the broach: Perform heat treatment of salt bath quenching and salt bath tempering on the broach. The heat treatment is carried out strictly in accordance with the process flow, and each process is coordinated; among them, the broach is straightened during the cooling process after salt bath quenching to obtain good comprehensive mechanical properties and a small workpiece deformation;

[0016] (5) Cold treatment and aging treatment of the broach: Adopt low-temperature cryogenic technology to perform sizing treatment and aging treatment on the broach to remove heat treatment stress and grinding stress;

[0017] (6) Grinding the center hole of the broach: Use a precision CNC center hole grinding machine to grind the center hole of the broach;

[0018] (7) Grinding the outer circle of the broach support points: Using a high-precision CNC external grinder, with the center hole of the broach as the reference, grind several outer circles of the support points on the outer circle of the broach as the auxiliary reference for broach grinding; applying the reference ring technology to precisely grind the outer circles of the broach support points, ensuring the roundness and radial runout of each outer circle of the support points, making the roundness of each outer circle of the support points not greater than 0.001 mm and the radial runout not greater than 0.005 mm, and the radial runout positions of the highest points or the lowest points of each outer circle of the support points are in the same circumferential angle direction;

[0019] (8) Grinding the outer circles of the front and rear handles, the cutting edge outer circle and the back angle of the broach: Using a high-precision CNC external grinder, with the center hole of the broach and the outer circles of the support points as the reference, grind the outer circles of the front and rear handles, the cutting edge outer circle and the back angle of the broach;

[0020] (9) Grinding the chip flutes and the front cutting surface of the broach: On a high-precision CNC broach grinder, use the conical surface of the grinding wheel to grind the chip flutes and the front cutting surface of the broach, ensuring the rake angle and surface roughness of the broach;

[0021] (10) Grinding the tooth profile of the broach: Use a high-precision CNC spline grinder to grind the tooth profile of the broach. The center holes at both ends of the broach are positioned between the two center points of the CNC spline grinder, and several center rests are preset in the middle. Adjust the upper and side generatrices of the broach. Adopt a CBN grinding wheel formed by external dressing with a diamond roller and internal precision dressing. On the CNC spline grinder, use the generation method to grind the tooth profile of the front section spline teeth through grinding, ensuring the tooth profile accuracy and generating a small amount of side relief angle. The tooth profile of the intersecting part of the spline teeth and the circular cutting teeth adopts the form grinding process of the same profile method, and a side relief angle of 1 degree to 2 degrees is formed on the tooth surface to improve the broaching accuracy of the workpiece;

[0022] (11) Broach trial broaching: The material and hardness of the trial broaching piece are the same as those of the workpiece. The trial broaching piece is placed on the broaching machine workbench. Adopt an upward-pulling vertical broaching machine for the workpiece. The broach passes through the workpiece and is installed in the broach chuck. The upper guide sleeve on the broaching machine holds the rear handle of the broach, ensuring that the broach is perpendicular to the workbench surface. After the calibration teeth are removed from the workpiece, the upper guide sleeve then withdraws, and the workpiece broaching is completed;

[0023] (12) Measuring the trial broaching piece: Correctly install the trial broaching piece between the precision chuck and the lower center point of the gear detector. Select the positioning reference compensation method for the internal spline of the trial broaching piece, align the position of the internal spline according to the positioning reference compensation method, place the 3D probe at the measured part, and detect the parameters such as the tooth profile, tooth direction, and tooth thickness of the internal spline by the 3D probe through programming and inputting the basic parameters;

[0024] (13) Coating: After sandblasting and cleaning the broach before coating, put it into the PVD coating furnace and perform PVD coating on the surface of the broach according to the coating operation process regulations.

[0025] In the present invention, the content of the manufacturing process of the second stage of the broach is as follows:

[0026] When the pull test data measured during the pull test of the test piece in step (12) is qualified, the content of the second-stage manufacturing process of the broach adopts steps (1) to (10) and step (13) in the first-stage manufacturing process of the broach, and omits steps (11) and (12).

[0027] When the broach parameters measured during the pull test of the test piece in step (12) are out of tolerance, a 3D model containing the broach machining error is established using the broach machining error data measured during the pull test of the test piece in step (12), the parts that need error correction are determined, and then during the CNC grinding process of steps (7) to (9), an error compensation amount is set in the CNC grinding program to obtain a CNC grinding program with error compensation; the content of the second-stage manufacturing process of the broach adopts steps (1) to (10) and step (13) in the first-stage manufacturing process of the broach, and omits steps (11) and (12); at the same time, the CNC grinding program used in steps (7) to (9) is replaced with the CNC grinding program with error compensation for the CNC grinding program used in steps (7) to (9) in the first-stage manufacturing process of the broach.

[0028] Preferably, when the second-stage manufacturing process of the broach is adopted, during the coating in step (13) of the second-stage manufacturing process of the broach, the thickness of the PVD coating in the second-stage manufacturing process of the broach is optimized according to the pull test results of the test piece in step (12) of the first-stage manufacturing process of the broach. The method is as follows:

[0029] Preferably, when the internal spline tooth thickness dimension of the test piece is at the upper limit within the design tolerance range, the coating thickness of the broach in the second-stage manufacturing process of the broach is set at the lower limit within the design tolerance range of the broach coating thickness; when the internal spline tooth thickness dimension of the test piece is at the lower limit within the design tolerance range, the coating thickness of the broach in the second-stage manufacturing process of the broach is set at the upper limit within the design tolerance range of the broach coating thickness, which is beneficial to improving the overall accuracy level of broach manufacturing.

[0030] In the present invention, when turning the outer circle of the broach in step (2): the broach is placed between the three-jaw chuck, the hydraulic tool rest and the tail center, the three-point support cylindrical surface on the hydraulic tool rest is supported on the machined outer circle surface of the broach, the three-point support cylindrical surface on the hydraulic tool rest expands and contracts synchronously with the broach in the radial and axial directions, and the center of the broach is always kept coaxial with the rotation center of the lathe spindle, thereby increasing the rigidity of the broach; a precise tool rest system is used for turning to ensure the outer circle size and radial runout of the broach, the center of the center rest is strictly coaxial with the center of the spindle, and the center of the center rest needs to be readjusted when the center rest position or the clamping pressure is changed; a single tool rest or a double tool rest is selected according to the length-to-diameter ratio of the broach, the single tool rest is located on the right side of the turning tool, and the double tool rest is located on both sides of the turning tool, the outer circle runout of the broach at one end clamped by the lathe chuck and the runout at one end against the center hole of the lathe tail center are less than 0.01 mm.

[0031] In the present invention, in step (3), when machining the broach chip groove and the outer circle of the circular cutting tooth, the upper busbar and the side busbar runout of the broach are pre-adjusted to within 0.05 mm. According to the length of the broach, multiple center frames can be placed or the center frames can be installed in sections; and a suitable diamond blade is selected according to the shape of the chip groove.

[0032] When turning, it is preferred to use diamond-shaped blades, which have sharp cutting properties, small deformation of the workpiece after processing, and good surface roughness.

[0033] In the present invention, during the heat treatment of the broach in step (4), the broach is quenched and tempered in a salt bath furnace, preheated twice before quenching, and the preheating temperatures are 450°C and 850°C respectively. After quenching, secondary graded cooling is adopted, and the broach is straightened in time during the first cooling at 620°C. After tempering, hot straightening is performed again to obtain excellent broach straightness.

[0034] In the present invention, in the step (5) of cold treatment and aging treatment of the broach, the cold treatment of the broach is to vertically hang the broach into a liquid nitrogen-cooled low-temperature box for low-temperature treatment to shape the internal structure of the material and ensure the stability of the size; the aging treatment of the broach is to vertically hang the broach into a pit furnace for aging treatment to remove stress; in the grinding processing of the steps (8), (9) and (10), the broach after grinding is also placed in an oil furnace for aging treatment to remove the surface stress generated during the grinding process and reduce grinding deformation, thereby further improving the processing accuracy.

[0035] For the broach to maintain its accuracy and good performance in the long term, the broach must be cryogenically treated in a low-temperature chamber cooled by liquid nitrogen below -185°C after tempering. The low-temperature chamber and liquid nitrogen are the basic facilities for the cryogenic treatment of the broach. Grinding stresses will occur during heat treatment and grinding. After heat treatment and grinding respectively, the broaches must be aged in a pit furnace at 240°C - 260°C for 12 hours to reduce the stresses. After the broach is precision ground, it is aged in an oil furnace at 150°C - 170°C for 12 hours to remove the surface stresses generated during the grinding process. When undergoing cryogenic treatment and aging treatment, the broach must be suspended vertically to prevent bending. The pit furnace and oil furnace are the basic facilities for the aging treatment of the broach.

[0036] As a further improvement of the present invention, when grinding the center hole of the broach in step (6), the outer circle of the broach is positioned by a three-point support fixture. First, grind the outer circle and then grind the center holes at both ends, repeating at least twice to make the roundness of the center hole not greater than 0.005 mm; during grinding, the broach rotates around its own axis, and the grinding wheel on the numerically controlled center hole grinding machine makes a compound movement of self-rotation and reciprocating circumferential movement, so that the conical surface of the center hole of the broach is ground into a high-precision conical surface with reticulated cross-grinding lines.

[0037] Preferably, when grinding the outer circles of the front and rear handles, the outer circle of the cutting edge, and the back angle of the broach in step (8), the center holes at both ends of the broach are positioned between the two center points of the numerically controlled external cylindrical grinding machine. By presetting several center rests in the middle of the broach, the upper generatrix and side generatrix of the broach are adjusted, and the parallelism tolerance of the side surface of the broach teeth along the longitudinal direction with respect to the reference axis of the broach is within 0.02 mm; control the tooth height increment of the outer circle of the cutting teeth and the width of the land, the width of the land of the cutting teeth of the broach is less than 0.05 mm, and the width of the land of the correcting teeth is 0.2 - 0.3 mm, and the width of the land on the circumference is consistent.

[0038] Preferably, when grinding the chip flutes and the front cutting face of the broach in step (9), the center holes at both ends of the broach are positioned between the two center points of the high-precision numerically controlled broach grinding machine. Several center rests are preset in the middle. The broach adjusts the side generatrix of the broach through multiple center rests, and the parallelism tolerance of the side surface of the broach teeth along the longitudinal direction with respect to the reference axis of the broach is within 0.02 mm; the conical surface of the CBN grinding wheel dressed by a diamond roller is used to grind the front cutting face of the broach on the numerically controlled broach grinding machine, so as to obtain a correct front cutting face and good surface roughness.

[0039] When grinding the front cutting face of the broach using the conical surface method as described above, compared with the circumferential method, the roughness of grinding the front cutting face using the conical surface method is better, the front angle part is a straight line, and the front angle of each cutting tooth can be guaranteed to be consistent.

[0040] Preferably, in order to prevent the interference between the outer edge of the grinding wheel and the front cutting face, according to the results of theoretical calculation and experimental verification, the diameter D of the grinding wheel should satisfy the following formula:

[0041] D ≤ 0.85 × d × sin(β - γ) ÷ sinγ;

[0042] In the formula, d is the broach diameter, β is the grinding wheel mounting angle, and γ is the rake angle of the broach tooth.

[0043] Preferably, when grinding the broach tooth profile in step (10), the broach adjusts the side generatrix of the broach through multiple steady rests, and the parallelism tolerance of the side surface of the broach tooth along the longitudinal direction with respect to the reference axis of the broach is within 0.01 mm.

[0044] When using a high-precision CNC spline grinding machine to grind the broach tooth profile, in addition to using high-quality CBN grinding wheels, ultra-precision diamond rollers, precision CNC spline grinding, and in-body dressing devices of the grinding wheel dressing system to ensure the diamond shape and motion accuracy, accurate in-machine clamping accuracy of the broach on multiple steady rests is also required. The parallelism tolerance of the side surface of the broach tooth along the longitudinal direction with respect to the reference axis of the broach being within 0.01 mm can meet the requirements of tooth profile machining.

[0045] In the present invention, the self-centering hydraulic steady rest 1 includes a steady rest body, three movable clamping arms arranged on the steady rest body, and clamping wheels respectively arranged at the front ends of the three movable clamping arms. A cam mechanism connected to the three movable clamping arms is disposed inside the steady rest body; wherein, the three movable clamping arms include a pair of rotating clamping arms and a movable clamping arm, and the three clamping wheels achieve self-centering clamping through the cam mechanism connected to the movable clamping arms and driven by a hydraulic cylinder; the hydraulic cylinder is disposed inside the steady rest body and is connected to a hydraulic source through a hydraulic pipeline.

[0046] As a further improvement of the self-centering hydraulic steady rest, a compressed air cleaning nozzle is provided on one side of the front end of the movable clamping arm facing the turning tool direction, and the air outlet of the compressed air cleaning nozzle faces the self-centering center of the self-centering hydraulic steady rest; the compressed air cleaning nozzle is connected to a compressed air source through a compressed air pipeline.

[0047] In the present invention, the powder high-speed steel used for the broach blank has fine carbides, no segregation, small heat treatment deformation, and good mechanical properties, and is an ideal material for high-speed steel cutting tools.

[0048] The beneficial effects of the present invention are as follows:

[0049] First, for the manufacturing process of a high-precision small module small-diameter centering composite slender broach of the present invention, a new overall improvement design is carried out on the manufacturing process flow of the broach, thereby improving the manufacturing accuracy of the small module small-diameter centering composite slender broach. After measurement, the technical indicators of the broach have reached above level 5 of the national standard GB / T3478 or above level 9 of the German standard DIN5480.

[0050] Second, in the manufacturing process of a high-precision small module and small-diameter centering composite slender broach of the present invention, an error compensation is set in the grinding process used in the second-stage manufacturing process of the broach. The basis of the error compensation is derived from the measured errors of the trial broach in the first-stage manufacturing process of the broach, thereby further improving the manufacturing precision of the broach.

[0051] Third, in the manufacturing process of a high-precision small module and small-diameter centering composite slender broach of the present invention, according to the measurement data of the trial broach in the first-stage manufacturing process of the broach, the precise value of the broach coating thickness is also optimized in the second-stage manufacturing process of the broach, which is beneficial to improving the overall precision level of broach manufacturing.

[0052] Fourth, in the manufacturing process of a high-precision small module and small-diameter centering composite slender broach of the present invention, the structure of the self-centering hydraulic follower rest is improved. When turning, three compressed air cleaning nozzles are arranged on the movable clamping arm of the follower rest to clean the outer circle surface of the broach in real time during the processing, thereby effectively preventing the influence of dirt on the outer circle surface of the broach on the centering precision of the self-centering hydraulic follower rest. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a schematic process flow diagram of the manufacturing process of a high-precision small module and small-diameter centering composite slender broach of the present invention (the first-stage manufacturing process of the broach);

[0054] Figure 2 is a schematic structural diagram of the self-centering hydraulic follower rest;

[0055] Figure 3 is a schematic diagram of using the conical surface of the grinding wheel to grind the chip flutes of the broach;

[0056] Figure 4 is Figure 3 the top view of

[0057] Figure 5 is a schematic structural diagram of a high-precision small module and small-diameter centering composite slender broach;

[0058] Figure 6 is Figure 5 the cross-sectional view of the middle circular cutting teeth and spline teeth in

[0059] Figure 7 is an embodiment of the relief angle of the side working edge of the spline teeth after grinding.

[0060] In the figure: 1. Self-centering hydraulic follower rest, 2. Follower rest body, 3. Movable clamping arm, 4. Clamping wheel, 5. Rotating clamping arm, 6. Moving clamping arm, 7. Hydraulic pipeline, 8. Compressed air cleaning nozzle, 9. Compressed air pipeline, 10. Broach, 11. Lubrication pipeline, 12. Grinding wheel. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0061] The following further describes the specific implementation manners of the present invention in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present invention.

[0062] As Figures 1 to 7 shown in the embodiment of the manufacturing process of a high-precision small module small-diameter centering composite slender broach of the present invention, it includes the first-stage manufacturing process and the second-stage manufacturing process of the broach. The content of the first-stage manufacturing process of the broach successively includes the following steps:

[0063] (1) Broach blank manufacturing: Select the powder high-speed steel manufacturing technology, formulate the material composition according to the characteristics of the tool, atomize the powder, and perform static pressure treatment to make the broach blank of the high-precision small module small-diameter centering composite slender broach; among them, the powder high-speed steel material selected for the broach blank is the molten steel melted by a high-frequency induction furnace, and the molten steel is sprayed and atomized with high-pressure argon or nitrogen, and rapidly cooled to fine and uniform high-speed steel powder. The high-speed steel powder is made into a tool blank through high temperature and high pressure, and then further forged and rolled to form the broach blank;

[0064] (2) Turning the outer diameter of the broach: Use a precision CNC lathe equipped with a self-centering hydraulic follower rest to turn the outer diameter of the broach;

[0065] (3) Turning the chip flutes and the outer diameter of the circular cutting teeth of the broach; Use a precision CNC lathe equipped with a steady rest, and perform CNC programming to turn the chip flutes and the outer diameter of the circular cutting teeth of the broach;

[0066] (4) Broach heat treatment: Perform heat treatment on the broach successively by salt bath quenching and salt bath tempering. The heat treatment is carried out strictly in accordance with the technological process, and each process is coordinated; among them, the broach is straightened during the cooling process after salt bath quenching to obtain good comprehensive mechanical properties and small workpiece deformation;

[0067] (5) Broach cryogenic treatment and aging treatment: Adopt low-temperature cryogenic technology to perform sizing treatment and aging treatment on the broach to remove the heat treatment stress and grinding stress;

[0068] (6) Grinding the center hole of the broach: Use a precision CNC center hole grinder to grind the center hole of the broach;

[0069] [[ID=

[0070] (8) Grinding the outer circles of the front and rear handles, the outer circle of the cutting edge, and the back angle of the broach: Using a high-precision CNC external cylindrical grinding machine, with the center hole of the broach and the outer circle of the support points as the reference, grind the outer circles of the front and rear handles, the outer circle of the cutting edge, and the back angle of the broach;

[0071] (9) Grinding the chip flutes and the front cutting face of the broach: On a high-precision CNC broach grinding machine, use the conical surface of the grinding wheel to grind the chip flutes and the front cutting face of the broach to ensure the rake angle and surface roughness of the broach;

[0072] (10) Grinding the tooth profile of the broach: Use a high-precision CNC spline grinding machine to grind the tooth profile of the broach. The center holes at both ends of the broach are positioned between the two center points of the CNC spline grinding machine, and several center supports are preset in the middle. Adjust the upper and side generatrices of the broach. Adopt a CBN grinding wheel formed by external dressing with a diamond roller and internal precision dressing. On the CNC spline grinding machine, use the generation method to grind the tooth profile of the front section spline teeth through grinding, ensure the tooth profile accuracy and generate a small amount of side back angle. The tooth profile of the intersecting part of the spline teeth and the circular cutting teeth adopts the form grinding process of the same profile method, and a side back angle of 1 degree to 2 degrees is formed on the tooth surface to improve the broaching accuracy of the workpiece;

[0073] (11) Broach trial broaching: The material and hardness of the trial broaching part are the same as those of the workpiece. The trial broaching part is placed on the workbench of the broaching machine. Adopt an upward-pulling vertical broaching machine for the workpiece. The broach is inserted into the broach chuck through the workpiece. The upper guide sleeve on the broaching machine holds the rear handle of the broach to ensure that the broach is perpendicular to the workbench surface. After the correction teeth are removed from the workpiece, the upper guide sleeve then withdraws, and the workpiece broaching is completed;

[0074] (12) Measuring the trial broaching part: Correctly install the trial broaching part between the precision chuck and the lower center point of the gear detector. Select the positioning reference compensation method for the internal spline of the trial broaching part, align the position of the internal spline according to the positioning reference compensation method, place the 3D probe at the measured part, and input the basic parameters through programming. The 3D probe detects parameters such as the tooth profile, tooth direction, and tooth thickness of the internal spline;

[0075] (13) Coating: After the broach is subjected to pre-coating sandblasting and cleaning treatment, it is placed in a PVD coating furnace, and the PVD coating of the broach surface is carried out according to the coating operation process specifications.

[0076] In this embodiment, the content of the second-stage manufacturing process of the broach is as follows:

[0077] When the measured pull detection data is qualified during the measurement of the trial broaching part in step (12), the content of the second-stage manufacturing process of the broach adopts steps (1) to (10) and step (13) in the first-stage manufacturing process of the broach, and omits steps (11) and (12);

[0078] When the broach parameters measured during the trial broaching in step (12) are out of tolerance, a 3D model containing the broach machining error is established using the broach machining error data measured during the trial broaching in step (12), the parts that need error correction are determined, and then during the CNC grinding process in steps (7) to (9), an error compensation amount is set in the CNC grinding program to obtain a CNC grinding program with error compensation; the content of the second-stage manufacturing process of the broach adopts steps (1) to (10) and step (13) in the first-stage manufacturing process of the broach, and omits steps (11) and (12); at the same time, the CNC grinding program used in steps (7) to (9) is replaced with a CNC grinding program with error compensation instead of the CNC grinding program used in steps (7) to (9) in the first-stage manufacturing process of the broach.

[0079] Preferably, when adopting the second-stage manufacturing process of the broach, during the coating in step (13) of the second-stage manufacturing process of the broach, the thickness of the PVD coating in the second-stage manufacturing process of the broach is optimized according to the measurement result of the trial broach in step (12) of the first-stage manufacturing process of the broach, and the method is as follows:

[0080] Preferably, when the internal spline tooth thickness dimension of the trial broach is at the upper limit within the design tolerance range, the coating thickness of the broach in the second-stage manufacturing process of the broach is set to the lower limit within the design tolerance range of the broach coating thickness; when the internal spline tooth thickness dimension of the trial broach is at the lower limit within the design tolerance range, the coating thickness of the broach in the second-stage manufacturing process of the broach is set to the upper limit within the design tolerance range of the broach coating thickness, which is beneficial to improving the overall precision level of broach manufacturing.

[0081] In this embodiment, during the turning of the broach outer circle in step (2): the broach is placed between a three-jaw chuck, a hydraulic follower rest and a tailstock center. The three-point supporting cylindrical surface on the hydraulic follower rest supports on the machined outer circle surface of the broach. The three-point supporting cylindrical surface on the hydraulic follower rest expands and contracts synchronously with the broach in the radial and axial directions, always keeping the center of the broach coaxial with the rotation center of the lathe spindle, thereby increasing the rigidity of the broach; precision follower rest systems are used for turning to ensure the outer circle size and radial runout of the broach. The center of the steady rest is strictly coaxial with the center of the spindle. When the position of the steady rest or the clamping pressure is changed, the center of the steady rest needs to be readjusted; a single follower rest or a double follower rest is selected according to the length-diameter ratio of the broach. The single follower rest is located on the right side of the turning tool, and the double follower rest is located on both sides of the turning tool. The outer circle runout of the broach at the end clamped by the lathe chuck and the runout at the end where the lathe tailstock center holds the center hole are less than 0.01 mm.

[0082] In this embodiment, when turning the chip flutes and the outer circle of the circular cutting teeth of the broach in step (3), the runout of the upper generatrix and the side generatrix of the broach is pre-adjusted to be within 0.05 mm. According to the length of the broach, multiple steady rests can be placed or the steady rests can be installed in sections; a suitable diamond blade is selected according to the shape of the chip flutes.

[0083] When turning, it is preferable to use a diamond blade, which has sharp cutting edges, causes little deformation of the workpiece after machining, and has good surface roughness.

[0084] In this embodiment, when heat-treating the broach in step (4), the broach is quenched and tempered in a salt bath furnace. It is pre-heated twice before quenching, and the pre-heating temperatures are 450 °C and 850 °C respectively. After quenching, secondary staged cooling is adopted, and the broach is straightened in time when cooling at 620 °C for the first time. After tempering, it is straightened thermally again to obtain excellent straightness of the broach.

[0085] In this embodiment, in the cold treatment and aging treatment of the broach in step (5), the cold treatment of the broach is to vertically suspend the broach and place it in a low-temperature box cooled by liquid nitrogen for cryogenic treatment to fix the internal structure of the material and ensure the dimensional stability; the aging treatment of the broach is to vertically suspend the broach and place it in a pit furnace for aging treatment to remove stress; in the grinding processes of steps (8), (9), and (10), the broach after grinding is also placed in an oil furnace for aging treatment to remove the surface stress generated during the grinding process and reduce the grinding deformation, thereby further improving the machining accuracy.

[0086] For the broach to maintain its accuracy and good performance for a long time, the broach must be placed in a low-temperature box cooled by liquid nitrogen below -185 °C for cryogenic treatment after tempering. The low-temperature box and liquid nitrogen are the basic facilities for the cold treatment of the broach. Grinding stresses will be generated during heat treatment and grinding. The broach after heat treatment and the broach after grinding must be placed in a pit furnace at 240 °C - 260 °C for 12 hours of aging treatment to reduce the stress. After fine grinding of the broach, it is placed in an oil furnace at 150 °C - 170 °C for 12 hours of aging treatment to remove the surface stress generated during the grinding process. When performing cold treatment and aging treatment, the broach must be suspended vertically to prevent bending. The pit furnace and the oil furnace are the basic facilities for the aging treatment of the broach.

[0087] As a further improvement of this embodiment, when grinding the center hole of the broach in step (6), the outer circle of the broach is positioned by a three-point support fixture. First, the outer circle is ground and then the center holes at both ends are ground, and this is repeated at least twice to make the roundness of the center hole not greater than 0.005 mm; during grinding, the broach makes a rotational motion around its own axis, and the grinding wheel on the CNC center hole grinding machine makes a compound motion of self-rotation and reciprocating circumferential rotation, so that the conical surface of the center hole of the broach is ground into a high-precision conical surface with a reticulated cross-grinding pattern.

[0088] Preferably, when grinding the outer circles of the front and rear handles, the outer circle of the cutting edge, and the back angle of the broach in step (8), the center holes at both ends of the broach are positioned between the two center points of the CNC cylindrical grinder. By presetting several center rests in the middle of the broach, the upper and side generatrices of the broach are adjusted. The parallelism tolerance of the flank of the broach teeth along the longitudinal direction with respect to the reference axis of the broach is within 0.02 mm. Control the tooth height increment of the outer circle of the cutting teeth and the width of the land. The width of the land of the cutting teeth of the broach is less than 0.05 mm, and the width of the land of the correcting teeth is 0.2 - 0.3 mm. The width of the land on the circumference is consistent.

[0089] Preferably, when grinding the chip flutes and the front rake face of the broach in step (9), the center holes at both ends of the broach are positioned between the two center points of the high-precision CNC broach grinder. Several center rests are preset in the middle. The broach adjusts the side generatrix of the broach through multiple center rests. The parallelism tolerance of the flank of the broach teeth along the longitudinal direction with respect to the reference axis of the broach is within 0.02 mm. Use the conical surface of the CBN grinding wheel dressed by a diamond roller to grind the front rake face of the broach on the CNC broach grinder, so as to obtain the correct front rake face and good surface roughness.

[0090] When grinding the front rake face of the broach using the conical surface method as described above, compared with the circumferential method, the roughness of the front rake face ground by the conical surface method is better. The front angle part is a straight line and can ensure that the front angle of each cutting tooth is consistent.

[0091] Preferably, in order to prevent the interference between the outer edge of the grinding wheel and the front tool face, according to the results of theoretical calculation and experimental verification, the diameter D of the grinding wheel should satisfy the following formula:

[0092] D ≤ 0.85 × d × sin(β - γ) ÷ sinγ;

[0093] In the formula, d is the diameter of the broach, β is the installation angle of the grinding wheel, and γ is the front angle of the broach teeth.

[0094] Preferably, when grinding the tooth profile of the broach in step (10), the broach adjusts the side generatrix of the broach through multiple center rests. The parallelism tolerance of the flank of the broach teeth along the longitudinal direction with respect to the reference axis of the broach is within 0.01 mm.

[0095] Use a high-precision CNC spline grinder to grind the tooth profile of the broach. In addition to using high-quality CBN grinding wheels, ultra-precision diamond rollers, precision CNC spline grinding, and in-body dressing devices of the grinding wheel dressing system to ensure the diamond shape and motion accuracy, the accurate in-machine clamping accuracy of the broach on multiple center rests is also required. The parallelism tolerance of the flank of the broach teeth along the longitudinal direction with respect to the reference axis of the broach is within 0.01 mm to meet the requirements of tooth profile machining.

[0096] Such as Figure 2As shown in the figure, the self-centering hydraulic follower rest 1 in this embodiment includes a follower rest body 2, three movable clamping arms 3 provided on the follower rest body 2, and clamping wheels 4 provided at the front ends of the three movable clamping arms 3 respectively. A cam mechanism (not shown in the figure) connected to the three movable clamping arms 3 is built in the follower rest body 2. Among them, the three movable clamping arms 3 include a pair of rotating clamping arms 5 and a movable clamping arm 6. The three clamping wheels 4 achieve self-centering clamping of the three clamping wheels 4 through the cam mechanism connected to the movable clamping arms 3 and driven by a hydraulic cylinder. The hydraulic cylinder is built in the follower rest body 2 and is connected to a hydraulic source through a hydraulic pipeline 7.

[0097] As a further improvement of the self-centering hydraulic follower rest, a compressed air cleaning nozzle 8 is provided on one side of the front end of the movable clamping arm 3 facing the direction of the turning tool. The air blowing port of the compressed air cleaning nozzle 8 faces the center of the self-centering of the self-centering hydraulic follower rest 1. The compressed air cleaning nozzle 8 is connected to a compressed air source through a compressed air pipeline 9.

[0098] In this embodiment, the carbide of the powder high-speed steel used for broaching blanks is fine, has no segregation, has small heat treatment deformation, and has good mechanical properties, which is an ideal material in high-speed steel tools.

[0099] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A manufacturing process for a high-precision, small-module, small-diameter, centering, composite, slender broach, characterized in that: The method includes a first-stage manufacturing process for a broach and a second-stage manufacturing process for a broach. The first-stage manufacturing process for a broach includes the following steps in sequence: (1) Production of broach blanks: Use powder high-speed steel manufacturing technology, formulate the material composition according to the characteristics of the tool, atomize the powder, and perform static pressure treatment to produce broach blanks for high-precision, small-module, small-diameter, centering, composite, and slender broaches. The powder high-speed steel material used for the broach blanks is the molten steel melted in a high-frequency induction furnace, which is sprayed and atomized with high-pressure argon or nitrogen, and rapidly cooled to fine and uniform high-speed steel powder. The high-speed steel powder is made into a blade blank under high temperature and high pressure, and then further forged and rolled to form the broach blank. (2) Turning the outer circle of the broach: Use a precision CNC lathe equipped with a self-centering hydraulic tool holder to turn the outer circle of the broach; (3) Turning the broach chip groove and the outer circle of the circular cutting gear; using a precision CNC lathe equipped with a center stand, CNC programming to turn the broach chip groove and the outer circle of the circular cutting gear; (4) Heat treatment of broaches: The broaches are subjected to salt bath quenching and salt bath tempering heat treatments in sequence. The heat treatment is carried out strictly in accordance with the process flow, and each process is coordinated. Among them, the broaches are straightened during the cooling process after salt bath quenching to obtain good comprehensive mechanical properties and small workpiece deformation. (5) Cold treatment and aging treatment of broaches: Use low-temperature ice-cooling technology to perform shaping and aging treatment on the broaches to remove heat treatment stress and grinding stress; (6) Grinding the center hole of the broach: Use a precision CNC center hole grinder to grind the center hole of the broach; (7) Grinding the outer circle of the broach support point: Using a high-precision CNC external cylindrical grinder, with the broach center hole as the reference, grind out several outer circles of the support points on the outer circle of the broach as auxiliary references for broach grinding; using the reference ring technology to accurately grind the outer circle of the broach support point, ensuring the roundness and radial runout of the outer circle of each support point, so that the roundness of the outer circle of each support point is not greater than 0.001mm, the radial runout is not greater than 0.005mm, and the highest point position or the lowest point radial runout position of the outer circle of each support point is in the same circumferential angle direction; (8) Grinding the outer circle of the front and rear handles, the outer circle of the blade and the back angle of the broach: Using a high-precision CNC cylindrical grinder, with the outer circle of the broach center hole and the support point as the reference, grind the outer circle of the front and rear handles, the outer circle of the blade and the back angle of the broach; (9) Grinding the broach chip groove and front edge surface: On a high-precision CNC broach grinding machine, use the conical surface of the grinding wheel to grind the broach chip groove and front edge surface to ensure the broach rake angle and surface roughness; (10) Grinding the tooth profile of the broach: Use a high-precision CNC spline grinder to grind the tooth profile of the broach. The center holes at both ends of the broach are positioned in the two thimbles of the CNC spline grinder. Several center racks are pre-set in the middle to adjust the upper and side busbars of the broach. A CBN grinding wheel formed by external dressing and internal finishing with a diamond roller is used. The tooth profile of the front section of the spline teeth is ground by the gradual method on the CNC spline grinder to ensure the tooth profile accuracy and generate a slight side clearance angle. The tooth profile of the interlaced part of the spline teeth and the circular cutting teeth adopts the same profile method of relief grinding process. The tooth surface forms a side clearance angle of 1 to 2 degrees to improve the broaching accuracy of the workpiece. (11) Broach test: The material and hardness of the test piece are the same as the workpiece. The test piece is placed on the broaching table. A vertical broaching machine with the workpiece pulled upward is used. The broach is passed through the workpiece and inserted into the broaching sleeve. The guide sleeve on the broaching machine holds the rear handle of the broach to ensure that the broach is perpendicular to the worktable. After the correction teeth are removed from the workpiece, the upper guide sleeve is withdrawn and the workpiece broaching is completed. (12) Test piece measurement: correctly install the test piece between the precision chuck and the lower center of the gear tester, select the positioning reference compensation method of the internal spline of the test piece, align the position of the internal spline according to the positioning reference compensation method, place the 3D probe on the part to be tested, and input the basic parameters through programming to allow the 3D probe to detect the tooth shape, tooth direction, and tooth thickness parameters of the internal spline; (13) Coating: After sandblasting and cleaning the broach before coating, put it into the PVD coating furnace and apply PVD coating on the broach surface according to the coating operation process regulations; The contents of the second stage manufacturing process of the broach are as follows: When the pulling test data obtained during the measurement of the test piece in step (12) is qualified, the contents of the second stage manufacturing process of the broach adopt steps (1) to (10) and step (13) of the first stage manufacturing process of the broach, and steps (11) and (12) are omitted; When the broach parameters measured during the test piece measurement in step (12) are out of tolerance, the broach processing error data measured during the test piece measurement in step (12) are used to establish a 3D model including the broach processing error, determine the location that needs error correction, and then set the error compensation amount in the CNC grinding process from step (7) to step (9) to obtain a CNC grinding program with error compensation; the content of the second stage manufacturing process of the broach adopts steps (1) to (10) and step (13) in the first stage manufacturing process of the broach, and omits steps (11) and (12); at the same time, the CNC grinding program used in steps (7) to (9) adopts the CNC grinding program with error compensation to replace the CNC grinding program used in steps (7) to (9) of the first stage manufacturing process of the broach.

2. The manufacturing process of a high-precision, small-module, small-diameter, centering, composite, slender broach according to claim 1, characterized in that: When turning the outer circle of the broach in step (2): the broach is placed between the three-jaw chuck, the hydraulic tool rest and the tail center, the three-point support cylindrical surface on the hydraulic tool rest is supported on the machined outer circle surface of the broach, the three-point support cylindrical surface on the hydraulic tool rest expands and contracts synchronously with the broach in the radial and axial directions, and the center of the broach is always kept coaxial with the rotation center of the lathe spindle, thereby increasing the rigidity of the broach; a precise tool rest system is used for turning to ensure the outer circle size and radial runout of the broach, the center of the center rest is strictly coaxial with the center of the spindle, and the center of the center rest needs to be readjusted when the center rest position or clamping pressure is changed; a single tool rest or a double tool rest is selected according to the length-diameter ratio of the broach, the single tool rest is located on the right side of the turning tool, and the double tool rest is located on both sides of the turning tool, the outer circle runout of the broach at one end clamped by the lathe chuck and the runout at one end against the center hole of the lathe tail center are less than 0.01 mm.

3. The manufacturing process of a high-precision, small-module, small-diameter, centering, composite, slender broach according to claim 1, characterized in that: When turning the broach chip groove and the outer circle of the circular cutting tooth in step (3), the upper and side busbar runouts of the broach are pre-adjusted to within 0.05 mm. Multiple center racks can be placed or the center racks can be installed in sections according to the length of the broach; and a suitable diamond blade is selected according to the shape of the chip groove.

4. The manufacturing process of a high-precision, small-module, small-diameter, centering, composite, slender broach according to claim 1, characterized in that: During the heat treatment of the broach in step (4), the broach is quenched and tempered in a salt bath furnace, preheated twice before quenching, and the preheating temperatures are 450°C and 850°C respectively. After quenching, secondary graded cooling is adopted, and the broach is straightened in time during the first cooling at 620°C. After tempering, hot straightening is performed again to obtain excellent broach straightness.

5. The manufacturing process of a high-precision, small-module, small-diameter, centering, composite, slender broach according to claim 1, characterized in that: In the step (5) of cold treatment and aging treatment of the broach, the cold treatment of the broach is to vertically hang the broach into a liquid nitrogen cooling low temperature box for low temperature treatment to shape the internal structure of the material and ensure the stability of the size; the aging treatment of the broach is to vertically hang the broach into a pit furnace for aging treatment to remove stress; in the grinding processing of the steps (8), (9) and (10), the broach after grinding is also placed in an oil furnace for aging treatment to remove the surface stress generated during the grinding process and reduce grinding deformation, thereby further improving the processing accuracy.

6. The manufacturing process of a high-precision, small-module, small-diameter, centering, composite, slender broach according to claim 1, characterized in that: When grinding the center hole of the broach in step (6), the outer circle of the broach is positioned by a three-point support fixture, and the outer circle is ground first and then the center holes at both ends, and this is repeated at least twice, so that the roundness of the center hole is not greater than 0.005 mm; during grinding, the broach rotates around its own axis, and the grinding wheel on the CNC center hole grinder performs a composite motion of self-rotation and circumferential reciprocating rotation, so that the conical surface of the broach center hole is ground into a high-precision conical surface of the center hole with a mesh-like cross-grinding pattern.

7. The manufacturing process of a high-precision, small-module, small-diameter, centering, composite, slender broach according to claim 1, characterized in that: In the step (8), when grinding the outer circles of the front and rear handles, the outer circles of the blades and the back angles of the broaches, the center holes at both ends of the broaches are positioned in the two thimbles of the CNC cylindrical grinder. By pre-setting a number of center racks in the middle of the broaches, the upper and side busbars of the broaches are adjusted, and the parallelism tolerance of the broach tooth side surfaces to the reference axis of the broaches along the longitudinal direction is within 0.02 mm; the tooth outer circle tooth lift and the edge band width are controlled, the broach cutting tooth edge band width is less than 0.05 mm, the correction tooth edge band width is 0.2 to 0.3 mm, and the circumferential edge band width is consistent.

8. The manufacturing process of a high-precision, small-module, small-diameter, centering, composite, slender broach according to claim 1, characterized in that: When grinding the chip groove and the front edge of the broach in step (9), the center holes at both ends of the broach are positioned in the two thimbles of a high-precision CNC broach grinder, and a plurality of center racks are pre-set in the middle. The broach side busbar is adjusted by the plurality of center racks, and the parallelism tolerance of the broach tooth side surface to the reference axis of the broach in the longitudinal direction is within 0.02 mm; the front edge of the broach is ground on the CNC broach grinder using the conical surface of a CBN grinding wheel trimmed by a diamond roller, thereby obtaining a correct front edge and good surface roughness.

9. The manufacturing process of a high-precision, small-module, small-diameter, centering, composite, slender broach according to claim 1, characterized in that: When grinding the broach tooth shape in step (10), the broach is adjusted to have a broach side busbar through a plurality of center stands, and the parallelism tolerance of the broach tooth side surface to the broach reference axis in the longitudinal direction is within 0.01 mm.

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