A method and automatic shot blasting device for eliminating turning marks on the surface of a harmonic reducer flexspline

Abstract

The application provides a method and an automatic shot blasting device for eliminating turning marks on the surface of a harmonic reducer flexspline, and relates to the technical field of metal processing.The application rotates 210 degrees for each shot blasting and then proceeds to the next shot blasting, the shot blasting positions are basically symmetrical, and the whole outer surface is fully covered, so that no unshot blasting area and repeated shot blasting area appear.Because the positions are relatively symmetrical, the residual stress caused by one shot blasting is small, and the stress cannot cause deformation of the residual stress.The device of the application can realize repeated and continuous symmetrical automatic shot blasting, eliminate the turning marks on the surface of the harmonic reducer flexspline under the condition of ensuring the size precision of the harmonic reducer flexspline, and improve the service life of the harmonic reducer flexspline.

Description

Technical Field

[0001] This invention relates to the field of metal processing technology, and in particular to a method for eliminating turning marks on the surface of the flexible wheel of a harmonic reducer and an automatic shot peening device. Background Technology

[0002] Harmonic reducers are a new type of mechanical transmission that relies on the controllable elastic deformation of flexible gears to transmit motion and force. They consist of four main components: a cam (wave generator), a flex wheel, an input shaft, and a rigid wheel. When the wave generator rotates, it forces the flex wheel to undergo elastic deformation, causing its teeth to interact with the teeth of the rigid wheel, thus achieving the purpose of transmission. The most unique component is the flex wheel, which undergoes two elliptical deformations per revolution during service. To meet this service characteristic, the flex wheel's wall thickness is generally designed to be thin, around 0.5mm. This thin-walled dimensional characteristic, along with the alternating stress generated by repeated deformation during service, makes the flex wheel highly susceptible to failure. Testing of domestically produced harmonic reducers has revealed that flex wheel failure accounts for over 99% of reducer failures. Many causes of flex wheel failure are attributed to stress conditions within the flex wheel itself.

[0003] Extensive failure analysis studies by our research group have revealed that machining marks left during the flexible wheel machining process are the primary location for surface stress concentration. Figure 1 As shown. Therefore, eliminating machining marks on the surface of flexible wheels is of great significance for improving their service performance.

[0004] Currently, the main mechanism for shot blasting transmission components and elastic components in industry is to use high-speed airflow generated by a fan to carry small solid particles such as diamond abrasive (SiO2) to impact the surface. Its main function is to remove some rusted areas and burrs during the processing. Therefore, its main function cannot solve the defects on the substrate of the component such as those caused by surface turning.

[0005] Furthermore, the main principle of eliminating surface defects using shot peening is that the impact of the shot causes micro-area plastic deformation on the surface. For example, the impact load of steel balls can polish and flatten surface tool marks, resulting in residual stress on the surface. In addition, shot peening with an air compressor involves a relatively large load on the surface. This load is relatively small on conventional thicker components and will not cause significant impact. However, it will cause problems on metal components with a wall thickness of 0.5mm, such as flexible wheels. Because the wall is relatively thin, and the conventional shot peening process is a gradual and continuous process, the first peened area will have residual stress. When the area of ​​the first peened area reaches a certain size, the accumulated stress and the unpeened area (where the stress is smaller at this time) will become unbalanced, that is, there is a stress imbalance between the peened and unpeened areas. For a flexible wheel with a wall thickness of only 0.5mm, this unbalanced stress will cause it to deform during the shot peening process, seriously affecting the dimensional accuracy of the flexible wheel. Summary of the Invention

[0006] The purpose of this invention is to provide a method and an automatic shot peening device for eliminating machining marks on the surface of the flexible wheel of a harmonic reducer, which can eliminate surface machining marks while ensuring the dimensional accuracy of the flexible wheel and improve its service life.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for eliminating machining marks on the surface of a harmonic reducer flexure, comprising the following steps: using compressed air to drive stainless steel shot to repeatedly peel the surface of the flexure to be treated; each shot peeling creates a shot peeling area with a coverage angle of 30-60° on the side of the flexure; after each shot peeling, the flexure is rotated 210° before the next shot peeling is performed, until the side of the flexure is completely covered.

[0009] Preferably, the shot peening pressure is 0.5 to 0.8 MPa.

[0010] Preferably, the stainless steel shot is 304 stainless steel shot.

[0011] Preferably, the diameter of the stainless steel projectile is 0.1 mm.

[0012] Preferably, the diameter of the shot peening nozzle is 4.5 to 7.5 mm.

[0013] Preferably, the shot peening distance is 15-30 mm.

[0014] Preferably, the coverage angle of the shot peening zone formed on the side of the flexible wheel each time is 40-60°.

[0015] This invention provides an automatic shot peening device, comprising: an incomplete gear, a screw, a connecting rod, a sliding rod, and a shot peening device; the screw is used to drive a flexible wheel to rotate;

[0016] The incomplete gear meshes with the screw, and the resulting meshing area causes the flexible wheel to rotate only 210°.

[0017] The incomplete gear is connected to one end of the sliding rod via the connecting rod; the other end of the sliding rod is connected to the nozzle of the shot peening equipment.

[0018] Preferably, the connecting rod and the sliding rod are connected by a hinged bearing.

[0019] Preferably, the incomplete gear and the connecting rod are movably connected.

[0020] This invention provides a method for eliminating machining marks on the surface of a harmonic reducer flexure, comprising the following steps: using compressed air to drive stainless steel shot to repeatedly peen the surface of the flexure to be treated; each shot peening creates a peening area with a coverage angle of 30-60° on the side of the flexure; after each shot peening, the flexure is rotated 210° before the next shot peening, until the entire side of the flexure is covered. This invention rotates 210° after each shot peening before the next shot peening, ensuring that the shot peening positions are basically symmetrical and completely cover the entire outer surface, eliminating unpeened areas and repeated shot peening areas. Due to the relative symmetry and the relatively small residual stress from each shot peening, the stress will not cause deformation due to residual stress.

[0021] This invention also provides an automatic shot peening device. Through the continuous motion of an incomplete gear, the shot peening gun head reciprocates. The meshing of the incomplete gear with a screw causes the flexible wheel to move in a directional circular motion, thereby achieving continuous shot peening of the target area of ​​the flexible wheel under continuous power output. Using this device, repeated, continuous, symmetrical automatic shot peening can be achieved, eliminating surface machining marks on the flexible wheel of the harmonic reducer while ensuring its dimensional accuracy, thus improving its service life. Attached Figure Description

[0022] Figure 1 This is a picture of a flexspline with surface scratches.

[0023] Figure 2 This is a schematic diagram of the automatic shot peening device of the present invention;

[0024] Figure 3 This is a front view of the connection position between the incomplete gear and the connecting rod.

[0025] Figure 4 This is a side view of the incomplete gear connection point with the connecting rod.

[0026] Figure 5 This is a front view of the connection point between the connecting rod and the sliding rod.

[0027] Figure 6 This is a side view of the connection point between the connecting rod and the sliding rod.

[0028] Figures 7-11 The diagram shows the working state of the automatic shot peening device of the present invention at different times.

[0029] Figure 12 Here are enlarged views of a portion of the top hat-shaped flexible wheel before shot peening and an overall photograph of the actual object in Example 1;

[0030] Figure 13 The images shown are magnified views of a portion of the top hat-shaped flexible wheel after shot peening in Example 1, as well as an overall photograph of the finished product.

[0031] Figure 14This is a magnified view of a cup-shaped flexible wheel before and after shot peening in Example 2;

[0032] Figure 15 This is an overall photograph of the cup-shaped flexible wheel before and after shot peening in Example 2;

[0033] Figure 16 This is an enlarged photograph of the tooth root of the cup-shaped flexible wheel before and after shot peening in Example 2;

[0034] Figure 17 These are optical photographs of the cup-shaped flexible wheel before and after shot peening in Example 2. Detailed Implementation

[0035] This invention provides a method for eliminating machining marks on the surface of a harmonic reducer flexure, comprising the following steps: using compressed air to drive stainless steel shot to repeatedly peel the surface of the flexure to be treated; each shot peeling creates a shot peeling area with a coverage angle of 30-60° on the side of the flexure; after each shot peeling, the flexure is rotated 210° before the next shot peeling is performed, until the side of the flexure is completely covered.

[0036] In this invention, the stainless steel shot is preferably 304 stainless steel shot; the diameter of the stainless steel shot is preferably 0.1 mm. In this invention, the nozzle diameter of the shot peening is preferably 4.5–7.5 mm, more preferably 5.0–7.0 mm, and even more preferably 5.5–6.5 mm. In this invention, the shot peening distance is preferably 15–30 mm, more preferably 18–26 mm, and even more preferably 20–25 mm. In this invention, the shot peening pressure is preferably 0.5–0.8 MPa, more preferably 0.6–0.7 MPa. Controlling the shot peening conditions within the above ranges in this invention helps to reduce the residual stress caused by a single shot peening operation.

[0037] In this invention, the coverage angle of the shot peening zone formed on the side of the flexible wheel each time is 30 to 60°. Considering that in actual engineering, the spray intensity on both sides of the shot peening fan is lower than that in the middle, this invention preferably controls the coverage angle to be 40 to 60° to ensure that both sides of the fan are sprayed repeatedly, which is beneficial to achieving uniform shot peening.

[0038] For a flexible peening wheel, if one area is peened, then the second, and then the third, and these three areas are connected, assuming each area is 30°, then the three consecutive areas after peening will be 90°, occupying one-quarter of the entire circumference of the flexible peening wheel. The stress in this one-quarter area will be unbalanced with the stress in the other three-quarters of the unpeened area. Therefore, this invention aims to avoid continuous area shot peening. Ideally, symmetrical shot peening involves peening one side and then rotating 180° to peen. However, in practice, this would only peen two symmetrical areas. If another 180° rotation is performed, it returns to the position of the first peening, and so on, requiring constant angle adjustments. This is difficult to modify the mechanical components and hinders automation. This invention rotates the flexible peening wheel 210° after each shot peening cycle. This ensures that the shot peening position is basically symmetrical during automation and fully covers the entire outer surface, eliminating unpeened areas and repeated shot peening areas. Symmetrical shot peening and multiple coverage methods prevent deformation of the flexible peening wheel caused by shot peening stress.

[0039] like Figure 2 As shown, the present invention provides an automatic shot peening device, comprising: an incomplete gear, a screw, a connecting rod, a sliding rod, and a shot peening device; the screw is used to drive the flexible wheel to rotate;

[0040] The incomplete gear meshes with the screw, and the resulting meshing area causes the flexible wheel to rotate only 210°.

[0041] The incomplete gear is connected to one end of the sliding rod via the connecting rod; the other end of the sliding rod is connected to the nozzle of the shot peening equipment.

[0042] The present invention does not impose any special limitations on the incomplete gear and screw, as long as the meshing area formed by the two is such that the flexible wheel only rotates 210°.

[0043] In this invention, the incomplete gear and the connecting rod are movably connected. For example... Figure 3 and Figure 4 As shown, in one embodiment of the present invention, the incomplete gear and the connecting rod are connected by a hinge bearing 2. Specifically, a washer 1 is provided on the incomplete gear to fix the outer ring of the hinge bearing 2 to the incomplete gear; a bolt 3 passes through the center of the hinge bearing 2 to fasten the connecting rod. When the incomplete gear rotates, the bolt 3 and the connecting rod are integrated and rotate freely with the hinge bearing 2 to transmit torque.

[0044] In this invention, the connecting rod and the sliding rod are connected by a hinged bearing, and the length between the two rods can be adjusted by adjusting the relative distance between them to meet rotational requirements. More specifically: as... Figure 5 and Figure 6As shown, 4 is the bearing mounting bracket; 5 is the mounting bolt, which fixes the bearing mounting bracket 4 to the sliding rod; 6 is the hinged bearing; 7 is the bolt, which is fixed in the inner hole of the bearing and used to fix the connecting rod; 8 is the inner groove on the sliding rod, in which the bearing mounting bracket 4 can slide. By loosening the mounting bolt 5, the bearing mounting bracket 4 can be moved within the groove to adjust the length of the sliding rod; 9 is the inner groove on the connecting rod, in which the position of the connecting rod within the inner groove can be adjusted by the bolt 7 to achieve the length adjustment of the connecting rod. The connecting rod and the sliding rod are connected by a hinged bearing, and by loosening bolts 5 and 7 respectively, the hinged bearing can be moved within the sliding grooves 8 and 9, thereby allowing the lengths of the connecting rod and the sliding groove to be adjusted relative to each other to meet the requirements.

[0045] In this invention, the working principle of the automatic shot peening device is as follows:

[0046] like Figure 7 As shown, the gear and screw partially mesh, initially causing the screw to drive the flexible wheel to rotate. The meshing area ensures that the flexible wheel rotates only 210°. The shot peening nozzle reaches its rightmost position under the gear's influence. The nozzle does not stop peening, but the peening zone has moved away from the flexible wheel surface. This is equivalent to stopping the shot peening of the rotating flexible wheel.

[0047] like Figure 8 As shown, with the rotation of the incomplete gear, after the incomplete gear has left the screw, the flexible wheel rotates 210° and stops. Driven by the incomplete gear, the nozzle returns to the working area, aligns with the wheel wall, and begins shot peening, continuing to move to the left.

[0048] like Figure 9 As shown, the incomplete gear continues to rotate, the nozzle continues to move to the left and prepares to move to the right after reaching the left end of the flexible wheel.

[0049] like Figure 10 As shown, the incomplete gear continues to rotate, the nozzle moves to the right and covers the shot peening, while the flexible wheel remains stationary.

[0050] like Figure 11 As shown, the incomplete gear and screw re-engage, preparing to promote the flexible wheel to rotate 210°. The nozzle, driven by the gear, reaches its rightmost position again, and the blasting zone has left the surface of the flexible wheel. Shot peening of the rotating flexible wheel is paused. This completes one shot peening cycle, and preparation begins for the next.

[0051] This invention utilizes the continuous motion of an incomplete gear to reciprocate the spray gun head. The meshing of the incomplete gear with a screw causes the flexible wheel to move in a directional circular motion, thus achieving continuous shot peening of the target area of ​​the flexible wheel under continuous power output. Using this device, repeated, continuous, symmetrical, automatic shot peening can be achieved, eliminating surface machining marks on the flexible wheel of the harmonic reducer while ensuring its dimensional accuracy, thereby improving its service life.

[0052] In this invention, when the automatic shot peening device is used for actual shot peening, the rotational speed of the incomplete gear is preferably 5 to 10 rpm, corresponding to a shot peening scanning rate of 0.4 to 0.6 mm / s. This invention adjusts the shot peening scanning rate by controlling the rotational speed of the incomplete gear; for example, a faster rotational speed results in a faster sweep of the nozzle across the flexible wheel, leading to a weaker shot peening force.

[0053] The following detailed description, in conjunction with embodiments, of the method for eliminating machining marks on the surface of the flexible wheel of a harmonic reducer and the automatic shot peening device provided by the present invention, but these should not be construed as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] Taking the top hat-shaped flexible wheel as an example, the lack of shot peening led to rapid fatigue failure, causing it to crack in less than 3,000 hours. Figure 12 The left image shows severe machining marks on the surface of the flexible gear, while the right image shows the flexible gear breaking directly during service. Failure analysis revealed typical cracking along the machining marks at the tooth root.

[0056] The automatic shot peening device of the present invention is used to shot peen a hat-shaped flexible wheel. The shot peening pressure is controlled at 0.8 MPa, the diameter of the 304 stainless steel shot is 0.1 mm, the diameter of the shot peening nozzle is 7 mm, the spraying distance is 20 mm, the coverage angle of each shot peening is 30°, the rotation speed of the incomplete gear is 10 rpm, and after each shot peening is completed, the flexible wheel is rotated 210° before the next shot peening is performed until the side of the flexible wheel is completely covered.

[0057] After shot peening using the method of this invention, on the one hand, the machining marks on the surface are reduced (see...). Figure 13 (Left image) On the other hand, thin-walled parts received uniform shot peening treatment without significant deformation (see image). Figure 13 (Middle right image). Lifespan extended by more than 5 times.

[0058] Example 2

[0059] Taking a cup-shaped flexible wheel as an example, the machining marks before shot peening are obvious (see...). Figure 14 Middle left image and Figure 15 (Left figure) The automatic shot peening device of this invention is used to shot peen a cup-shaped flexible wheel. The shot peening pressure is controlled at 0.6 MPa, the diameter of the 304 stainless steel shot is 0.1 mm, the diameter of the shot peening nozzle is 6 mm, the spray distance is 15 mm, the coverage angle of each shot peening is 40°, and the rotation speed of the incomplete gear is set to 8 rpm. After each shot peening, the flexible wheel is rotated 210° before the next shot peening is performed until the entire side of the flexible wheel is covered. After shot peening, machining marks are significantly reduced (see...). Figure 14 (middle right figure), and no thin-wall deformation caused by residual stress was observed (e.g.) Figure 15 (As shown in the middle right figure).

[0060] Figure 16 The images shown are magnified photos of the tooth root before and after shot peening of the cup-shaped flexible wheel in Example 2. The left image shows the area before shot peening, which shows obvious signs of tearing. The right image shows the area after shot peening, which shows that the signs of tearing have been significantly reduced.

[0061] The flexible rollers before and after shot peening were further observed using an optical microscope (20x magnification). The results are shown in [Figure number missing]. Figure 17 The left image shows obvious machining marks before shot peening, such as discontinuous or interrupted lines. These are areas of stress concentration and are sensitive to notches. The right image shows that after shot peening, the directional machining marks have been completely eliminated, reducing notch sensitivity.

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for eliminating machining marks on the surface of the flexspline of a harmonic reducer, characterized in that, The process includes the following steps: using compressed air to drive stainless steel shot to repeatedly peel the surface of the flexible wheel; each shot peeling creates a peeling zone with a coverage angle of 40~60° on the side of the flexible wheel; after each shot peeling, the flexible wheel is rotated 210° before the next shot peeling, until the entire side of the flexible wheel is covered; the flexible wheel moves in a directional circular motion, thereby achieving continuous symmetrical shot peeling of the target area of ​​the flexible wheel under continuous power output. The shot peening pressure is 0.5~0.8MPa; The stainless steel shot is 304 stainless steel shot; The diameter of the stainless steel shot is 0.1 mm; The diameter of the shot peening nozzle is 4.5~7.5mm; The shot peening distance is 15~30mm.

2. An automatic shot peening device for implementing the method of claim 1, characterized in that, include: Incomplete gears, screws, connecting rods, sliding rods, and shot peening equipment; the screw is used to drive the flexible wheel to rotate; The incomplete gear meshes with the screw, and the resulting meshing area causes the flexible wheel to rotate only 210°. The incomplete gear is connected to one end of the sliding rod via the connecting rod; the other end of the sliding rod is connected to the nozzle of the shot peening equipment.

3. The automatic shot peening device according to claim 2, characterized in that, The connecting rod and the sliding rod are connected by a hinged bearing.

4. The automatic shot peening device according to claim 2, characterized in that, The incomplete gear and the connecting rod are movably connected.

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