Method and apparatus for surface strengthening of materials by three-dimensional multidirectional time-sharing force

Abstract

The application provides a material surface strengthening method and device of three-dimensional multidirectional time-sharing force, which comprises applying different forces to a workpiece in two time periods in one stroke. The strengthening device is assembled by a piston, a base, an outer hoop, a cross screw, a spring, a positioning ring, a ball, a lower anvil, an elastic body, an inclined pin and a force applying body. Different forces are applied to the surface of the metal material in time, including hammering force perpendicular to the surface of the material and outward pushing force in several directions in the tangent plane of the force applying point on the surface of the material. Under the comprehensive action of the forces, the surface layer of the material is plastically deformed by stretching, and a residual compressive stress layer is formed on the surface of the material after the deformation. The existence of the compressive stress layer delays the generation and expansion of fatigue cracks, thereby improving the fatigue life of the parts.

Description

Technical Field

[0001] This invention belongs to the field of surface strengthening technology for metallic materials, and more specifically, relates to a three-dimensional multi-directional time-division force application surface strengthening method and apparatus. Background Technology

[0002] Currently, in the three-dimensional multi-directional impact technology for metallic materials, the multi-directional impact force is applied simultaneously, resulting in insufficient residual compressive stress on the material surface and an unsatisfactory strengthening effect. Consequently, the fatigue strength and fatigue life are difficult to meet the actual production requirements. To address this, a three-dimensional multi-directional time-sharing force application surface strengthening method and device has been invented. Summary of the Invention

[0003] This application aims to address the problems existing in the prior art and related technologies.

[0004] As mentioned earlier, the method of applying force simultaneously in three dimensions and multiple directions has the problem of insufficient strengthening effect.

[0005] To address this issue, we used finite element method to analyze and compare the strengthening effects of simultaneous and time-sharing force application under the same processing conditions. The results show that the time-sharing force application method resulted in a larger residual compressive stress on the workpiece surface and a better strengthening effect than the simultaneous force application method.

[0006] Therefore, this application proposes a three-dimensional multi-directional time-division force application surface strengthening method and apparatus.

[0007] During the process of strengthening the workpiece surface using the method and apparatus of this application, the force application process on the workpiece surface can be divided into two time periods: a first time period and a second time period. The first time period refers to the period from the moment the force-applying body contacts the workpiece until the lower end boss of the piston contacts the lower anvil; the second time period refers to the period from the moment the lower end boss of the piston contacts the lower anvil until the end of the impact strengthening loading in one stroke. During the first time period, multiple force-applying bodies of the apparatus of this application apply a vertically downward unidirectional impact force to the workpiece surface; during the second time period, multiple force-applying bodies simultaneously apply a vertically downward force and an outward thrust in multiple directions in the horizontal plane to the workpiece surface, that is, apply forces in multiple directions in three-dimensional space to achieve three-dimensional multi-directional impact. Because the force is applied unidirectionally in the first time period, the force-applying body and the workpiece are in close contact and exert considerable pressure. Therefore, when the force-applying body is pushed outward in the second time period, the friction between the force-applying body and the workpiece surface increases. Compared with the simultaneous application of force, a greater outward pushing force is generated. At the point of force application, the workpiece surface can generate greater tensile plastic deformation and residual compressive stress. Since the greater the residual compressive stress on the material surface, the greater the tendency to suppress the generation and propagation of fatigue cracks, its strengthening effect is better than the simultaneous application of force method.

[0008] The surface strengthening method and apparatus for three-dimensional multi-directional time-sharing force application proposed in this application is assembled from a piston, a base, an outer hoop, a lower anvil, multiple force-applying bodies, multiple inclined pins, an elastic body, a positioning ring, multiple balls, multiple springs, and screws. The upper end of the piston is usually fixedly connected to the punch of an impact device or the punch of a pneumatic impactor, and the piston can reciprocate up and down in the inner cavity of the base.

[0009] The base's inner cavity consists of stepped holes of varying inner diameters, with the largest diameter at the bottom. This inner hole is used to position and install the locating ring, preventing it from moving within the device during impact. The diameter of the inner hole in the middle of the base is equal to the piston's maximum outer diameter, and they are fitted with a clearance fit to facilitate the piston's reciprocating motion. The outer diameter of the locating ring is larger than the piston's maximum outer diameter; that is, the largest inner diameter of the locating ring on the base is larger than the piston's maximum outer diameter. This creates a shoulder at the junction of these two inner holes on the base. This shoulder ensures that the base is locked in place vertically, maintaining a 3-4 mm gap between the base and the force-applying body during piston movement.

[0010] The inner diameter of the locating ring is slightly larger than the outer diameter of the lower end boss of the piston and the outer diameter of the upper end boss of the lower anvil, so as to avoid sliding friction between the lower end boss of the piston and the upper end boss of the lower anvil and the inner wall of the locating ring when the piston moves up and down.

[0011] The upper end of the positioning ring has a blind hole for installing the spring. This blind hole serves to position the spring and prevent it from being damaged by lateral shear. If the positioning ring is not used and the spring is directly installed and positioned on the force-applying body, the spring will move laterally and be subjected to lateral shear force due to the outward pushing action of the force-applying body during use, resulting in shear fatigue failure and reducing the service life of the device.

[0012] A 3-4mm gap is provided between the base and the force-applying body. The purpose of this gap is to prevent sliding friction between the base and the force-applying body when the force-applying body pushes outward in multiple directions within the tangential plane of the force application point during the second time period, thereby ensuring that the outward pushing force of the force-applying body mainly acts on the workpiece;

[0013] A 2-3mm gap is provided between the force-applying body and the positioning ring. The purpose of this gap is to prevent sliding friction between the force-applying body and the positioning ring when the force-applying body pushes outward in multiple directions within the tangential plane of the force application point during the second time period, thereby ensuring that the outward pushing force of the force-applying body mainly acts on the workpiece;

[0014] The lower end of the positioning ring is provided with radial rectangular grooves for installing multiple balls; the diameter of the balls is 2-3 mm larger than the depth of these radial rectangular grooves to ensure that these balls leave a set gap between the positioning ring and the force-applying body; in the second time period, these balls roll when the force-applying body moves outward in multiple directions in the tangential plane of the point of force application to avoid sliding friction between the positioning ring and the force-applying body.

[0015] A certain distance is maintained between the protrusion at the lower end of the piston and the protrusion at the upper end of the anvil. The magnitude of this distance is set by the duration of the first time period. The duration of the first time period is affected by factors such as the spring stiffness coefficient, the spring length in the reset state, the piston speed, and the distance between the protrusion at the lower end of the piston and the protrusion at the upper end of the anvil. Typically, to ensure sufficient impact force in the second time period, the spring stiffness coefficient, the spring length in the reset state, and the piston speed are set to constant values, while the duration of the first time period is achieved by designing the distance between the protrusion at the lower end of the piston and the protrusion at the upper end of the anvil. Specifically, in the device design stage of this application, after the distance between the protrusion at the lower end of the piston and the protrusion at the upper end of the anvil is set as required, the size of the protrusion at the upper end of the anvil remains unchanged, while the height of the protrusion at the lower end of the piston is set by calculation.

[0016] The piston has several blind holes for mounting springs. The base and the outer surface of the force-applying body have slots; the outer clamp is fitted into these slots to encapsulate the device, and is secured to the base with fastening screws.

[0017] The outer hoop has a semi-circular cross-section, divided into left and right sections. This division facilitates the installation of the outer hoop into the slots of the base and the force-applying body. The outer hoop has a certain degree of elasticity. During the reinforcement process of the device in this application, when the force-applying body moves outward in the horizontal plane, the outer hoop undergoes a certain degree of elastic deformation. During the retraction and unloading process after the force application process of the device in this application ends, the elastic force of the slightly elastically deformed outer hoop allows the force-applying body to return to its reset state.

[0018] The material of the elastomer is usually hard rubber. During operation, the elastomer can produce a certain elastic compression deformation under the pressure of the lower anvil. After the force application process of the device in this application ends, during the retraction and unloading process, the lower anvil is restored to the reset state by the elastic restoring force of the elastically deformed elastomer.

[0019] In the first time period, the device of this application generates elastic force due to the compression of the spring. This force acts on the positioning ring and is then distributed to multiple force-applying bodies through multiple ball bearings. Because the lower end of each force-applying body is designed as a truncated cone, the force generates a vertically downward force and an eccentric moment at the contact surface between the force-applying body and the workpiece. The vertically downward force completes the unidirectional impact on the workpiece surface in the first time period, while the eccentric moment helps the force-applying bodies to hold each other tightly, preventing gaps between them. In the second time period, the boss at the bottom of the base and the boss at the top of the lower anvil collide, generating a certain impact force. Under the action of this impact force, the elastic body undergoes elastic deformation and, guided by multiple inclined pins, causes the multiple force-applying bodies to exert a combined effect of outward thrust in several directions within the tangential plane at the point of force application and a vertically downward impact force on the workpiece surface. Attached Figure Description

[0020] Figure 1 It refers to the stress distribution on the workpiece surface after three-dimensional multi-directional impact strengthening with simultaneous and time-division force application;

[0021] Figure 2 This is a schematic diagram of the structure of the three-dimensional multi-directional time-division force-applying material surface strengthening device provided in the embodiments of this application;

[0022] in:

[0023] 1-Piston; 2-Base; 3-Outer clamp; 4-Screw; 5-Spring; 6-Positioning ring; 7-Ball bearing; 8-Lower anvil; 9-Elastomer; 10-Angled pin; 11-Force-applying body;

[0024] Figure 3 This is a three-dimensional exploded view provided to more intuitively show the device structure of the embodiments of this application; wherein region A is a blind hole on the positioning ring used for positioning and installing the spring;

[0025] Figure 4 This is a 3D view of the piston. Area B is the blind hole at the lower end of the piston; area C is the boss at the lower end of the piston.

[0026] Figure 5 This is a three-dimensional display of the force-applying body. Area D is the slot for installing the outer clamp, and area E is the circular plane at the point of force application.

[0027] Figure 6 This is a 3D display of the positioning ring; area F is the radial rectangular groove at the lower end of the positioning ring.

[0028] Figure 7 The image shows a 3D view of the base. Area G is the slot for mounting the outer clamp to the base, and area H is the shoulder. Detailed Implementation

[0029] To more clearly illustrate the purpose of this application, the applicant used ABAQUS software to perform finite element calculations on two strengthening methods: simultaneous force application and time-sharing force application. A specific example is given below.

[0030] Impact strengthening of Q235 steel surface was performed under the conditions of initial impact velocity of 30 m / s, contact surface friction coefficient of 0.2, and punch weight of 5 kg (where the ratio of the first and second time periods of force application was 1:1). The calculated stress distribution on the surface of the strengthened workpiece is as follows: Figure 1 As shown:

[0031] Figure 1 Tensile stress is represented by positive values, and compressive stress by negative values; the horizontal axis represents the horizontal distance on the workpiece surface, and the vertical axis represents the stress. As can be seen from the curves in the figure, although both simultaneous and time-sharing force application methods result in compressive stress (negative values) on the workpiece surface, the absolute value of the residual compressive stress in the impact strengthening method using time-sharing force application is greater than that of the simultaneous application method. A larger residual compressive stress is more effective in suppressing the initiation and propagation of fatigue cracks, thereby improving the fatigue life of the workpiece. This example is universal and fully demonstrates that the time-sharing force application method is more effective than the simultaneous force application method in strengthening.

[0032] When the device described in this application uses an air impactor as the power source, the piston of the device is typically mounted and fixed to the punch head of the air impactor. The air impactor is mounted on the end effector of an industrial robot, and the robot control system adjusts the posture of the air impactor to ensure that the impact direction is perpendicular to the workpiece surface. The robot's path planning enables the robot arm to move along a predetermined trajectory. During operation, the robot arm and the air impactor are controlled to impact the workpiece surface, ultimately achieving full-coverage surface strengthening of the area to be processed. If a hammer impactor is used as the power source, the piston of the device described in this application is mounted and fixed to the hammer head of the hammer, while the workpiece to be strengthened is mounted on a robot CNC turntable. During operation, the hammer impactor only performs up-and-down reciprocating motion, while the robot CNC turntable continuously adjusts its posture according to the shape of the workpiece surface. Similarly, during the movement trajectory, the hammer impacts the workpiece surface, ultimately achieving full coverage of the area to be strengthened. To better understand the technical solution of this application, the following description is provided in conjunction with the embodiments in the accompanying drawings: It should be noted that in the description of this application, the terms "upper", "lower", "left", "right", "horizontal", etc., which indicate the direction and positional relationship, are based on the direction and positional relationship shown in the accompanying drawings, and are only for the convenience of description.

[0033] Combined with appendix Figure 2The reinforcing device of this application is assembled from a piston 1, a base 2, an outer clamp 3, a Phillips head screw 4, a spring 5, a positioning ring 6, a ball bearing 7, a lower anvil 8, an elastic body 9, a beveled pin 10, and a force-applying body 11. The device is fastened to the hammer head of a power-driven punching device or the punch head of a pneumatic punch via the piston 1.

[0034] The lower end of piston 1 is in the shape of a boss (e.g.) Figure 4 In the design phase of the device in this application (region C), the height of the boss was calculated from the piston displacement during the reserved first time period.

[0035] The force-applying component consists of several independent force-applying bodies 11 of the same shape and size (such as...) Figure 5 These force-applying bodies 11 are assembled together and are referred to as the force-applying body group. The more force-applying bodies 11 there are, the more outward thrusts in different directions will be provided on the horizontal plane during the second time period.

[0036] At the lower part of piston 1 (such as...) Figure 4 (area B) and the upper part of positioning circle 6 (such as) Figure 3 Area A has several blind holes for installing the positioning spring 5; the lower surface of the positioning ring 6 has several radial rectangular grooves (such as...). Figure 6 The F area is used to install the ball bearing 7; the depth of the rectangular groove is 1-2 mm less than the diameter of the ball bearing, so as to ensure that the ball bearing 7 rolls when the force-applying body 11 makes an outward pushing motion on the horizontal plane during the second time period, and to leave a gap of 1-2 mm between the positioning ring 6 and the force-applying body 7, so as to avoid sliding friction between the positioning ring 6 and the force-applying body 11.

[0037] After the device of this application is assembled, a shoulder is provided in the inner hole of the base 2 for installing the positioning ring 6 (e.g., Figure 7 The base is fixed to the positioning ring using the shoulder slot, so that the base will not move up and down with the reciprocating motion of the piston during operation. The height of the positioning ring 6 is 2-3 mm greater than the depth of the inner hole of the base 2 used to install the positioning ring 6, and a gap of 3-4 mm is left between the base 2 and the force-applying body 11. This gap can prevent the base 2 from sliding and rubbing due to direct contact with the force-applying body.

[0038] The lower anvil 8, the elastic body 9, and the inclined pin 10 are embedded in the force-applying body group; the elastic body 9 can produce a certain elastic compression deformation under the pressure of the lower anvil 8; the inclined pin 10 is installed in several hemispherical recesses on the lower end plane of the lower anvil and the inner surface of the force-applying body 11; when the elastic body 9 is compressed and produces elastic deformation, the inclined pin 10 can guide the force-applying body 11 to perform an outward pushing motion in the horizontal plane.

[0039] The outer hoop 3 is divided into two identical left and right parts and has a certain degree of elasticity. The outer hoop 3 encapsulates the device of this application together; when the force-applying body group makes outward pushing motion in the tangential plane of the force application point, the outer hoop 3 can produce a small amount of outward elastic deformation; when the force impact of the device of this application on the workpiece ends and it retracts, the outer hoop 3 uses elastic force to return the force-applying body group to the reset state.

[0040] The outer contours of the base 2 and the force-applying body 11 are machined with slots for mounting the outer hoop 3 (e.g., Figure 7 H region and Figure 5 (Region D).

[0041] The working principle and process of the strengthening device of this application are further explained in detail below:

[0042] The strengthening device of this application is installed on the hammer head of the punch or the punch head of the pneumatic punch, and the strengthening device moves up and down reciprocating with the hammer head of the punch or the punch head of the pneumatic punch.

[0043] Furthermore, when the strengthening device of this application moves downward, from the moment the force-applying body 11 touches the workpiece to the moment the boss of the piston 1 touches the lower anvil 8, the workpiece undergoes strengthening within a first time period. That is, as the piston 1 moves downward, the spring 5 undergoes compressive elastic deformation, and the elastic deformation force acts on the workpiece through the positioning ring 6, the ball 7, and the force-applying body 11. Since the lower part of the force-applying body 11 is truncated cone-shaped, the contact area between the force-applying body 11 and the workpiece is a small circular plane (e.g., ...). Figure 5 The E region generates a vertically downward force and an inward eccentric moment on the workpiece at this circular plane; the vertically downward force is used to strengthen the workpiece, while the inward eccentric moment helps the multiple force-applying bodies 11 to hold together.

[0044] Furthermore, as the strengthening device of this application continues to move downward, from the moment the piston 1 touches the lower anvil 8 until the end of the load application, the workpiece undergoes strengthening during the second time period. That is, as the piston 1 continues to move downward, the piston 1 touches the lower anvil 8 and causes it to move downward. The lower anvil 8 compresses the elastic body 9, causing it to undergo compressive elastic deformation. Under the guidance of the inclined pin 10, the force-applying body 11 makes an outward pushing motion in the horizontal plane. At this time, the surface of the workpiece is subjected to a vertically downward force and an outward pushing force in the horizontal plane by the force-applying body 11. When the force-applying body 11 makes an outward pushing motion, the outer hoop 3 undergoes a small amount of elastic deformation under the outward pushing force of the force-applying body 11.

[0045] Furthermore, during the unloading process after the application of force to the workpiece by this strengthening device is completed, the elastic deformation force of the outer hoop 3 and the elastic body 9 causes the force-applying body 11 and the lower anvil 8 to return to their initial positions.

[0046] The outward thrust of the force-applying body 11 in the horizontal plane can have several directions, and the number of force directions depends on the number of force-applying bodies 11. All force-applying bodies 11 are assembled together to form a force-applying body group that applies external force to the workpiece. This utility model uses four force-applying bodies 11, but the scope of protection of this application is not limited to the specific number of force-applying bodies 11. Any technical solution that uses the method of this application to generate outward thrust in several directions falls within the scope of protection of this application.

Claims

1. A three-dimensional multi-directional time-sharing force-applying material surface strengthening device, characterized in that, include: The piston (1) is installed inside the base (2). The lower end of the piston (1) is in the shape of a boss (C). The height of the boss is calculated from the piston displacement during the first time period. In the reset state, there is a distance between the piston (1) and the lower anvil (8) for the piston (1) to move back and forth during the first time period. The first time period refers to the time period from the moment the force-applying body contacts the workpiece until the lower end of the piston's boss contacts the lower anvil. A positioning ring (6) is set between the base (2), the piston (1), the lower anvil (8), and the force-applying body (11). The positioning ring (6) is connected to the base (2). The spring (5) and the ball (7) are provided. The upper end of the positioning ring (6) is provided with several blind holes (A) for installing the spring (5). The lower end of the positioning ring (6) is machined with several radial rectangular grooves (F) for installing the ball (7). The bottom surface of the lower anvil (8) is connected to the inclined pin (10) and the elastic body (9). The spring (5) is installed and positioned in the blind holes of the piston (1) and the positioning ring (6). The ball (7) is set between the positioning ring (6) and the force-applying body (11). The ball (7) is installed in the radial rectangular groove (F) provided at the lower end of the positioning ring (6). The lower anvil (8), the elastic body (9) and the inclined pin (10) are embedded in multiple force-applying bodies (11).

2. The material surface strengthening device with three-dimensional multi-directional time-sharing force application according to claim 1, characterized in that, The height of the positioning ring (6) is 2-3 mm greater than the depth of the maximum inner hole (H) in the base.

3. The material surface strengthening device with three-dimensional multi-directional time-sharing force application according to claim 1, characterized in that, A gap of 1-2 mm is left between the force-applying body (11) and the positioning ring (6).

4. The material surface strengthening device with three-dimensional multi-directional time-sharing force application according to claim 1, characterized in that, A gap of 3 to 4 mm is left between the base (2) and the force-applying body (11).

5. A method for strengthening the surface of materials by applying three-dimensional multi-directional time-sharing force, characterized in that, The material surface strengthening device according to any one of claims 1-4 applies different types of hammering forces perpendicular to the material surface and outward pushing forces in several directions within the tangential plane of the force application point on the material surface to the surface of a metal material in a time-division manner. In one stroke, the device applies different types of force to the workpiece in two time periods, including the following steps in the two consecutive time periods: During the first time period, the hammer or punch that provides the power source drives the piston (1) to move downward, and the compressed spring (5) passes through the positioning ring (6) and the ball (7) to make the force-applying body (11) apply a vertical downward force to the workpiece; During the second time period, the hammer head drives the piston (1) to continue moving downwards, and the lower anvil (8) is struck by the boss (C) at the lower end of the piston (1). The lower anvil (8) drives the inclined pin (10) and the elastic body (9) to exert force on the force-applying body (11), so that the force-applying body (11) applies a combined effect of a vertically downward force and an outward thrust in several directions in the tangent plane of the force application point to the workpiece. The second time period refers to the time period from the moment when the lower end boss of the piston contacts the lower anvil until the end of the impact strengthening loading in one stroke. Under the combined action of these forces, the surface of the material undergoes tensile plastic deformation, and a residual compressive stress layer is formed on the surface of the material after deformation. The presence of this compressive stress layer will delay the initiation and propagation of fatigue cracks, thereby improving the fatigue life of the components.

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