Aircraft small module gear tooth root ultrasonic rolling strengthening device and method

Abstract

An aviation small modulus gear tooth root ultrasonic rolling strengthening device and method, comprising: an ultrasonic rolling mechanism and a workpiece clamping mechanism connected thereto, ultrasonic vibration is generated by the ultrasonic rolling mechanism and transmitted to the workpiece clamping mechanism containing the gear sample to realize rolling strengthening. The invention can effectively perform ultrasonic rolling strengthening treatment on the narrow tooth root area of the aviation gear by designing a rolling head for the geometric profile characteristics of the aviation gear, especially the tooth root transition fillet part prone to fatigue crack, optimizing the tooth root surface integrity, and is beneficial to improving the bending fatigue performance of the gear.

Description

Technical Field

[0001] This invention relates to a technology in the field of machining, specifically an ultrasonic rolling strengthening device and method for the tooth root of small module gears in aerospace applications. Background Technology

[0002] The common machining method for existing aerospace gears involves first rough machining the gear shape using hobbing or shaping, then grinding to ensure tooth profile accuracy and surface integrity, and finally using mechanical shot peening to strengthen the gear surface and improve its service performance. However, aerospace gears typically have a small module and limited geometric space at the tooth root, making mechanical shot peening difficult to implement and significantly limiting the strengthening effect, resulting in little improvement in fatigue resistance. Therefore, it is necessary to develop new equipment and corresponding technologies to strengthen the gear root. Furthermore, it is important to note that fatigue sources during service are generally located at the transition fillets at the tooth root; therefore, when strengthening the tooth root, special attention should be paid to the strengthening effect at these transition fillets. Summary of the Invention

[0003] This invention addresses the problems inherent in existing technologies during the rolling process, such as the roller tip inevitably making complete contact with the tooth root and the transition fillet of the tooth root failing to effectively contact the roller. It also addresses the shortcomings of existing tooth root rolling devices, which are difficult to apply to variable cross-section parts like bevel gears and cannot effectively strengthen the transition fillet area at the tooth root. The invention proposes an ultrasonic rolling strengthening device and method for the tooth root of small-module aerospace gears. A rolling head designed specifically for the geometric contours of aerospace gears is incorporated, enabling effective ultrasonic rolling strengthening of the narrow tooth root area. It particularly strengthens the transition fillet area at the tooth root, where fatigue cracks are prone to initiation, optimizing the surface integrity of the tooth root and improving the gear's bending fatigue performance.

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

[0005] This invention relates to an ultrasonic rolling strengthening device for the tooth root of small module gears in aerospace applications, comprising: an ultrasonic rolling mechanism and a workpiece clamping mechanism connected thereto. The ultrasonic rolling mechanism generates ultrasonic vibrations and transmits them to the workpiece clamping mechanism, which holds a gear sample, thereby achieving rolling strengthening.

[0006] The ultrasonic rolling mechanism includes an ultrasonic generator, a transducer, an amplitude transformer, and a rolling head connected in sequence. The ultrasonic generator generates an ultrasonic vibration signal, which is transmitted to the amplitude transformer via a transducer driven by compressed air. The amplitude transformer is fixedly connected to the rolling head, causing the amplitude transformer to drive the rolling head to vibrate ultrasonically with a corresponding amplitude and frequency.

[0007] The workpiece clamping mechanism includes: a chuck, and a fixed stepped shaft and a gear sample disposed inside the two chucks, wherein: the fixed stepped shaft positions and clamps the gear sample, and the chuck is used to fix the stepped shaft for positioning and clamping, that is, to fix the tooth root of the gear to be rolled in a suitable position, so as to ensure that the rolling head maintains full contact with the tooth root under the static pressure generated by compressed air.

[0008] Technical effect

[0009] This invention employs compressed air to drive the rolling head to generate radial motion, enabling a constant-force rolling process. Targeting the geometric characteristics of small-module aerospace gears, the outermost part of the rolling head is designed with a specific ω-shaped structure to ensure full contact between the rolling head and the tooth root transition fillet during the rolling process, resulting in a better rolling effect. By applying ultrasonic technology to strengthen the tooth root of small-module aerospace gears, the high-frequency impact effect of ultrasonic vibration allows for effective rolling strengthening with a relatively small static load. Compared to existing technologies, this invention can perform ultrasonic rolling strengthening not only on the roots of common cylindrical gears but also on the roots of gears with variable cross-sections along the axial direction, such as bevel gears, with high automation efficiency and a good strengthening effect on the transition fillet of the gear tooth root. This invention achieves a good rolling strengthening effect on the gear tooth root using a lower static load than ordinary rolling. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the device of the present invention;

[0011] Figure 2 This is a schematic diagram of the roller head structure;

[0012] In the figure: a is the front view, b is the top view, c is the axonometric view, d is the AA section view, e is the front view of the roller, and f is the axonometric view of the roller.

[0013] Figure 3 A field illustration of an example of ultrasonic rolling of small module gears for aircraft.

[0014] Figure 4 A schematic diagram of the residual stress distribution at the tooth root before and after ultrasonic rolling of a small-module aero-engine gears;

[0015] In the figure: 1. Ultrasonic rolling mechanism; 2. Workpiece clamping mechanism; 101. Ultrasonic generator; 102. Transducer; 103. Amplitude rod; 104. Rolling head; 201. Chuck; 202. Stepped shaft; 203. Gear; 204. Chuck; 3. Bearing; 4. Cylindrical pin; 5. Carbide roller; 6. Protective sleeve; 7. Threaded fit; 8. Spring; 9. Support seat; 10. Connecting seat; 11. Internal thread. Detailed Implementation

[0016] like Figure 1As shown in the figure, this embodiment relates to an ultrasonic rolling strengthening device for the tooth root of a small module gear in aerospace, including: an ultrasonic rolling mechanism 1 and a workpiece clamping mechanism 2 connected thereto. The ultrasonic rolling mechanism 1 generates ultrasonic vibration and transmits it to the workpiece clamping mechanism 2, which holds the gear sample, to achieve rolling strengthening.

[0017] The ultrasonic rolling mechanism 1 includes: an ultrasonic generator 101, a transducer 102, an amplitude transformer 103, and a rolling head 104 connected in sequence. The ultrasonic generator 101 generates an ultrasonic vibration signal, which is transmitted to the amplitude transformer 103 through the transducer 102 driven by compressed air. The amplitude transformer 103 is fixedly connected to the rolling head 104, so that the amplitude transformer 103 drives the rolling head 104 to vibrate ultrasonically with corresponding amplitude and frequency.

[0018] The compressed air indirectly acts on the amplitude transformer, generating a certain amount of static load to push the rolling head to maintain contact with the workpiece to be processed.

[0019] The workpiece clamping mechanism 2 includes: chucks 201 and 204, and a fixed stepped shaft 202 and a gear sample 203 disposed inside the two chucks. The fixed stepped shaft 202 positions and clamps the gear sample 203. The chucks 201 and 204 are used to fix the stepped shaft for positioning and clamping, that is, to fix the tooth root of the gear 203 to be rolled in a suitable position, so as to ensure that the rolling head maintains full contact with the tooth root under the static pressure generated by the compressed air.

[0020] To ensure sufficient ultrasonic rolling reinforcement of the narrow root area of ​​small-module aerospace gears, with particular attention to the reinforcement effect at the transition fillet of the tooth root, the selection of the rolling head is crucial. For example... Figure 2 As shown, the rolling head 104 includes: a bearing 3, a cylindrical pin 4, a carbide roller 5, a support seat 9, and a connecting seat 10. The carbide roller 5 of the tool head used for ultrasonic rolling of tooth roots is mounted on the support seat 9 through the bearing 3 and the fixed cylindrical pin 4. The carbide roller 5 can rotate around the cylindrical pin 4. The support seat 9 and the connecting seat 10 are fitted together.

[0021] The geometric dimensions of the carbide roller 5 are matched with the tooth root of the gear 203 to be rolled.

[0022] The cylindrical pin 4 is fixed to the support base 9 by a small plane.

[0023] The support base 9 is provided with a protective sleeve 6 by a spring 8, and the protective sleeve 6 and the connecting base 10 are engaged by a fine thread 7 to realize the overall fixed structure of the rolling head and enable the support base to withstand static load and transmit it to the roller, while transmitting ultrasonic vibration displacement.

[0024] The connecting seat 10 is provided with a fine thread 11 for connecting with the amplitude rod.

[0025] like Figure 2 As shown, the overall geometric dimensions of the carbide roller 5 match the geometric dimensions of the gear tooth root.

[0026] In order to fully strengthen the tooth root transition fillet area where fatigue cracks are prone to occur, the top of the cemented carbide roller 5 is a "ω" shaped structure, as shown in the enlarged part of the figure. In this way, under the action of external static load pressure, the protruding fillets on both sides of the roller will always keep in contact with the transition fillet of the gear during the rolling process, so as to exert a better ultrasonic rolling effect on the tooth root fillet.

[0027] This embodiment relates to a method for ultrasonic rolling reinforcement of gear tooth roots using the aforementioned device, including:

[0028] S1. Determine the corresponding carbide roller geometry and size based on the geometric parameters of the small module aerospace gear to be ultrasonically rolled and assemble it with other parts into an independent rolling head. The specific confirmation process of the carbide roller is as follows: If the module of the gear to be processed is m, the theoretical value of the tooth root transition fillet radius can be calculated as r = 0.38m. In actual processing, it is generally necessary to round it upwards and use the rounded value as the final roller fillet radius.

[0029] S2. Fix the gear sample in the workpiece clamping mechanism. The stepped shaft is fixed and clamped by the machine tool chuck, and the gear sample is fixed and clamped by the stepped shaft. The gear can rotate around the machine tool spindle at a certain pitch angle. The pitch angle can be calculated based on the number of gear teeth.

[0030] S3. Connect the roller head and amplitude transformer assembled in S1 via threaded connection. Adjust the position of the roller head to produce a significant ultrasonic vibration effect. Simultaneously, adjust the position of the carbide roller to align it with the first tooth root to be ultrasonically rolled, ensuring that the roller remains in full contact with the tooth root throughout the subsequent ultrasonic rolling process. This process can be accomplished using the static load provided by compressed air. First, do not lock the stepped shaft; use the static load to make the roller protrude forward. Utilizing the principle of meshing between the roller and the tooth groove, the gear fixed on the stepped shaft rotates slightly within the slightly loose chuck under the action of the roller, thus automatically aligning the first tooth root. After the roller and tooth root are fully engaged, lock the stepped shaft, then remove the static load, and the roller retracts.

[0031] S4. Select appropriate ultrasonic rolling parameters, including rolling force and ultrasonic frequency, to ensure that the ultrasonic vibration amplitude reaches the set value under these parameters. Program the parameters in the machine tool CNC system, specifically including:

[0032] 4.1 Set the position where the roller and the tooth root are fully engaged as the zero point of the workpiece rotation. When this position is marked with R1=0, use the SPOS=R1 command to lock the spindle and set the program start flag N10 at this position. Set the start and end positions of the rolling head along the gear axis during the ultrasonic rolling process according to the gear width.

[0033] 4.2 Determine the number of times a single tooth root is rolled, and in each cycle, program the code to set two actions: the rolling head advances with air M12 and retreats with air M13; set the number of times the tooth root is rolled in this cycle Px (x is a specific value). When this single tooth root ultrasonic rolling cycle is a small cycle, the program flag is N15.

[0034] 4.3 After the ultrasonic rolling of the first tooth root is completed, exit the small cycle, rotate the spindle by the pitch angle θ, execute the R1 = R1 + θ command, and start the ultrasonic rolling process of the next tooth root. Use the SPOS = R1 command to lock the spindle at this angle, repeat the small cycle, that is, execute REPEAT N15 Py (y is the specific value of the number of large cycles, and satisfies y = Z - 1, Z is the number of teeth of the gear). Finally, stop the test after all the tooth roots of a gear product have been ultrasonically rolled.

[0035] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description, in conjunction with the accompanying drawings and preferred embodiments, provides a detailed explanation of the specific implementation of the ultrasonic rolling device for the tooth root of small-module aerospace gears proposed according to the present invention. Figure 3 The test site shown has the following main parameters for the aerospace small-module gear sample: module m = 2mm, number of teeth Z = 30, pressure angle α = 20°, clearance coefficient c* = 0.25, addendum coefficient ha* = 1, displacement coefficient x = 0, and tooth width b = 20mm. First, a stepped shaft is used to fix the gear sample in the workpiece clamping mechanism. The stepped shaft is fixed and clamped by the machine tool chuck and can rotate around the machine tool spindle at a certain pitch angle. The pitch angle can be calculated based on the number of gear teeth.

[0036] Furthermore, appropriate ultrasonic rolling parameters were selected. Based on previous basic experiments, the final selected test parameters were: static load F = 550 N, ultrasonic frequency f = 28 kHz, corresponding ultrasonic amplitude A = 12 μm, roller feed speed along gear axis Fz = 100 mm / min, and each gear tooth root was rolled 5 times.

[0037] Furthermore, in the CNC system programming of the machine tool, the position where the roller is fully engaged with the tooth root is first determined as the zero point of the workpiece rotation, and the command R1=0, SPOS=R1 is executed; according to the gear width, the starting and ending positions Zs and Zf of the rolling head feed along the gear axis during ultrasonic rolling are set, and then each tooth root is rolled five times. In each time, two actions are set: the rolling head advances with air and retreats with air release. Specifically, the following commands are executed: N10 G90 G94 G00 Zs; M12 G01 Zs+1F20; G01ZfF100; M13 G01 Zf+1F20; N15 REPEAT N10 P5; Since the rolling head needs a certain amount of time to advance and retreat, this invention sets a 1mm lateral movement margin in the rolling head advance and retreat action command. At this time, a lower feed speed F=20mm / min is used to complete the operation, which can ensure that the starting and ending positions of the gear tooth root can be effectively rolled.

[0038] After the ultrasonic rolling of the first tooth root is completed, the spindle rotates 12° to begin the ultrasonic rolling process of the next tooth root. The instructions R1 = R1 + 12, SPOS = R1Z are executed, and the cycle is repeated. The instructions REPEAT N15 P29 are then executed. Finally, after all the tooth roots of a gear product have been ultrasonically rolled, the test is stopped, and the M02 instruction is executed. In this invention, only one programming is required to achieve fully automated ultrasonic rolling strengthening treatment of all tooth roots of the entire gear, significantly improving production efficiency.

[0039] Furthermore, the distribution of residual stress at the tooth root before and after ultrasonic rolling was measured using X-ray diffraction, and the results are as follows: Figure 4 As shown, the ultrasonic rolling strengthening device designed in this invention can introduce residual compressive stress with large amplitude and deep layer at the root of small module gears in aerospace applications, which is expected to significantly improve the bending fatigue performance of the gears.

[0040] Compared with existing technologies, this device introduces ultrasonic technology into the gear tooth root rolling process. With the help of a rolling head of a certain shape, it can achieve excellent rolling effect under low static load and the action of a single roller mechanism, and introduce a larger and deeper residual compressive stress layer at the tooth root transition fillet. The rolling device is driven by compressed air and is used with a corresponding machine tool to realize fully automatic rolling treatment of all gear tooth roots with one programming, which greatly improves production efficiency.

[0041] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. An ultrasonic rolling strengthening device for the tooth root of small module aerospace gears, characterized in that, include: The ultrasonic rolling mechanism and the workpiece clamping mechanism connected thereto generate ultrasonic vibrations through the ultrasonic rolling mechanism and transmit them to the workpiece clamping mechanism equipped with the gear sample to achieve rolling strengthening. The ultrasonic rolling mechanism includes: an ultrasonic generator, a transducer, an amplitude transformer, and a rolling head connected in sequence, wherein: the ultrasonic generator generates an ultrasonic vibration signal, which is transmitted to the amplitude transformer through a transducer driven by compressed air; the amplitude transformer is fixedly connected to the rolling head and drives the rolling head to vibrate ultrasonically with corresponding amplitude and frequency. The workpiece clamping mechanism includes: a chuck and a fixed stepped shaft and a gear sample disposed inside the two chucks, wherein: the fixed stepped shaft positions and clamps the gear sample, and the chuck is used to fix the stepped shaft for positioning and clamping, that is, to fix the tooth root of the gear to be rolled in a suitable position, so as to ensure that the rolling head maintains full contact with the tooth root under the static pressure generated by the compressed air; The roller head includes: a bearing, a cylindrical pin, a carbide roller, a support base, and a connecting base. The carbide roller of the tool head used for ultrasonic roller milling of tooth roots is mounted on the support base via a bearing and a fixed cylindrical pin. The carbide roller can rotate around the cylindrical pin. The support base and the connecting base are fitted together. The geometric dimensions of the carbide roller are matched with the tooth root of the gear to be rolled, and the top of the carbide roller has an ω-shaped structure. The cylindrical pin is fixed to the support base by a small plane; The support base is equipped with a protective sleeve by a spring, and the protective sleeve and the connecting base are engaged by a fine thread to realize the overall fixed structure of the rolling head and enable the support base to withstand static load and transmit it to the roller, while transmitting ultrasonic vibration displacement.

2. A method for ultrasonic rolling strengthening of the tooth root of small-module aerospace gears based on the device described in claim 1, characterized in that, include: S1. Determine the corresponding carbide roller geometry and size based on the geometric parameters of the small module aerospace gear to be ultrasonically rolled and assemble it with other parts into an independent rolling head. Specifically, when the module of the gear to be processed is m, calculate the theoretical value of the tooth root transition fillet radius as r=0.38m, and then round it upwards, using the rounded value as the final roller fillet radius. S2. Fix the gear sample in the workpiece clamping mechanism. The stepped shaft is fixed and clamped by the machine tool chuck. The gear sample is fixed and clamped by the stepped shaft, and the gear can rotate around the machine tool spindle at a certain pitch angle. Calculate the pitch angle based on the number of gear teeth. ; S3. Connect the roller head and amplitude transformer assembled in S1 with threads, adjust the position of the roller head to produce a significant ultrasonic vibration effect, and simultaneously adjust the position of the carbide roller to face the first tooth root to be ultrasonically rolled, thus ensuring that the roller is always in full contact with the tooth root during the subsequent ultrasonic rolling process. This process can be completed with the static load provided by compressed air. That is, do not lock the stepped shaft first, use the static load to make the roller protrude forward, and use the principle of the roller's design to mesh with the tooth groove to make the gear fixed on the stepped shaft rotate slightly in the slightly loose chuck under the action of the roller, thereby achieving automatic alignment of the first tooth root position. After the roller and tooth root are fully meshed and in contact, lock the stepped shaft, and then remove the static load, and the roller moves backward. S4. Select appropriate ultrasonic rolling parameters to ensure that the ultrasonic vibration amplitude reaches the set value, and program the process in the machine tool CNC system, specifically including: 4.1 Set the position where the roller is fully engaged with the tooth root as the zero point of the workpiece rotation. When this position is marked with R1=0, use the SPOS=R1 command to lock the spindle and set the program start flag N10 at this position. Set the start and end positions of the rolling head along the gear axis during ultrasonic rolling according to the gear width. 4.2 Determine the number of times a single tooth root is rolled, and in each cycle, program the code to set two actions: the rolling head advances with air M12 and retreats with air M13; set the number of times the tooth root is rolled in this cycle, Px, where: x is a specific value. When this single tooth root ultrasonic rolling cycle is a small cycle, the program flag is N15. 4.3 After the ultrasonic rolling of the first tooth root is completed, the small cycle ends, the spindle rotates by the pitch angle θ, and the R1=R1+θ command is executed to start the ultrasonic rolling process of the next tooth root. The spindle is locked at this angle using the SPOS=R1 command, and the small cycle is repeated, i.e., the REPEAT N15 Py command is executed, where: y is the specific value of the number of large cycles, and satisfies y=Z-1, Z is the number of teeth of the gear, until the ultrasonic rolling of all tooth roots of a gear product is completed.

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