Micro-texturing functional curved surface machining method based on structured grinding tool

Abstract

The invention belongs to the technical field of advanced manufacturing, and particularly relates to a microtexture functional curved surface machining method based on a structured grinding tool, which comprises the following steps of: determining an artificial joint type and an artificial joint surface microtexture array form; a grinding wheel is selected according to the microtexture array form; the grinding wheel is provided with an upper convex part and a lower concave part; mounting the artificial joint and the grinding wheel on a five-axis numerical control ultra-precision machine tool; setting a moving track of a grinding wheel according to the artificial joint type; and polishing the surface of the artificial joint to form a micro-texture array. The micro-texture array is machined on the surface of the artificial joint in a structured grinding mode, and the method has the advantages of being high in machining efficiency, good in process continuity, low in cost and the like, and is wide in applicability and high in flexibility.

Description

Technical Field

[0001] The present invention belongs to the field of advanced manufacturing technology, and particularly relates to a method for machining a micro-textured functional curved surface based on a structured grinding tool. Background Art

[0002] An artificial joint is a medical device used to replace a natural joint that has lost its function due to joint diseases or injuries. It is implanted into the human body through surgery to restore joint function and relieve pain.

[0003] The market value of artificial joints is very considerable. However, since the service life of existing commercial artificial joints is between 15 and 20 years, this is not sufficient for half of the patients who undergo total joint replacement (TJR), especially young patients, which may lead them to have to undergo revision surgery. The revision surgery is higher than the primary surgery both in terms of cost and risk. Therefore, in the medical field, extending the service life of artificial joints is an urgent problem to be solved.

[0004] Preparing a functional micro-texture array on the curved surface of an artificial joint is one of the effective methods to improve its service life. Currently, the most widely used micro-texture preparation methods are micro-milling and laser processing, but they both have certain limitations. Micro-milling is not suitable for processing ceramic materials with high hardness values, and only one micro-texture can be processed each time, resulting in low processing efficiency. Laser processing requires a set of laser processing equipment, with high energy consumption and low processing efficiency, and may generate products in the processing area, which may have a negative impact on the tribological properties. Machining a micro-texture array on the curved surface of an artificial joint by structured grinding is expected to make up for the above deficiencies. Therefore, we propose a method for machining a micro-textured functional curved surface based on a structured grinding tool. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for machining a micro-textured functional curved surface based on a structured grinding tool to solve the above problems.

[0006] To achieve the above purpose, the present invention provides the following solution:

[0007] A method for machining a micro-textured functional curved surface based on a structured grinding tool includes the following steps:

[0008] Determine the type of artificial joint and the morphology of the micro-texture array on the surface of the artificial joint;

[0009] Select a grinding wheel according to the morphology of the micro-texture array;

[0010] The grinding wheel has a convex part and a concave part;

[0011] Install the artificial joint and the grinding wheel on a five-axis CNC ultra-precision machine tool;

[0012] Set the moving trajectory of the grinding wheel according to the type of artificial joint;

[0013] Grind the surface of the artificial joint to form the micro-texture array.

[0014] Optionally, the convex part of the grinding wheel is one of a triangle, an ellipse, a rectangle, and a spiral.

[0015] Optionally, the design process of the moving trajectory includes the following steps:

[0016] According to the type of artificial joint, discretize the artificial joint surface into a number of discrete curves;

[0017] The rotation center of the grinding wheel moves along any one of the discrete curves to form a grinding trajectory.

[0018] Optionally, the equation of the discrete curve is y = f(x).

[0019] Optionally, the equation of the grinding trajectory is y = g(x).

[0020] Optionally, according to the discrete curve and the principle of normal machining, y = g(x) is expressed as:

[0021]

[0022] where R is the nominal radius of the grinding wheel, a p is the grinding depth.

[0023] Optionally, the n x and the n y are expressed by the following formula:

[0024]

[0025] Optionally, the N is expressed by the following formula:

[0026]

[0027] Optionally, the discrete curve equation y = f(x) is parametrically represented to obtain a parametric equation as:

[0028]

[0029] Derive the parametric equation to obtain

[0030]

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] 1. The present invention proposes to process a micro-texture array on the surface of an artificial joint by means of structured grinding. This method features high processing efficiency. After selecting the form of the structured grinding wheel, it is only necessary to control the structured grinding wheel to move along the grinding trajectory related to the shape of the artificial joint, and the micro-texture array can be directly formed on the surface of the artificial joint.

[0033] 2. This method has the advantage of good process continuity. Structured grinding essentially still belongs to the category of grinding processing. In the production process arrangement of micro-textured artificial joints, the process of manufacturing the micro-texture array by structured grinding can be arranged after the shape grinding of the artificial joint, without the need to replace other equipment, and only the arc grinding wheel needs to be replaced with a structured grinding wheel.

[0034] 3. This method has the advantage of low cost. Due to good process continuity, structured grinding does not require an additional set of processing equipment like laser processing, and avoids the steps of disassembling and reinstalling the artificial joint during the production process, saving labor and time costs. Therefore, the cost of producing micro-textured artificial joints using this method is lower, and it is more suitable for mass production in batches.

[0035] 4. This method has wide applicability. Since the type of structured grinding wheel can be a superabrasive grinding wheel, this method can process all materials commonly used for artificial joints, including ceramic materials with relatively high hardness.

[0036] 5. This method has high flexibility. This method can process various types of micro-textures. Only by designing a structured grinding wheel once according to the target micro-texture form and selecting a reasonable grinding process, the target micro-texture array can be processed on the surface of the artificial joint. For micro-texture arrays of the same type but different sizes, there is no need to design a new structured grinding wheel additionally, and the micro-texture arrays of the same type but different sizes can be processed by appropriately modifying the grinding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts:

[0038] Figure 1 It is a schematic structural diagram of a structured grinding device for a micro-textured artificial joint based on a five-axis ultra-precision machine tool of the present invention;

[0039] Figure 2 It is a schematic diagram of the structured grinding principle of the curved surface of a micro-textured artificial joint of the present invention;

[0040] Figure 3Schematic diagram of the kinematic principle of structured grinding for the micro-textured curved surface of the present invention;

[0041] Figure 4 Cross-sectional view of the micro-texture in the form of gradual increase and gradual decrease of the present invention;

[0042] Figure 5 Cross-sectional view of the micro-structure in the form where the side wall is perpendicular to the bottom surface of the present invention;

[0043] Figures 6 to 11 Data graph of the fluid-structure interaction finite element simulation results of different forms of micro-textures of the present invention;

[0044] Figure 12 Schematic diagram of the surface of the structured grinding wheel in different forms of the present invention;

[0045] Figure 13 Schematic diagram of the surface of different forms of micro-textures of the present invention; Detailed implementation manners

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0047] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0048] Refer to Figures 1 to 13 , the present invention discloses a method for machining a micro-textured functional curved surface based on a structured grinding tool, including the following steps:

[0049] Determine the type of artificial joint and the morphology of the micro-texture array on the surface of the artificial joint;

[0050] Select a grinding wheel according to the morphology of the micro-texture array;

[0051] The grinding wheel has a convex part and a concave part;

[0052] Install the artificial joint and the grinding wheel on a five-axis CNC ultra-precision machine tool;

[0053] Set the movement trajectory of the grinding wheel according to the type of artificial joint;

[0054] Grind the surface of the artificial joint to form the micro-texture array.

[0055] During use, after determining the type of artificial joint to be processed, select a suitable grinding wheel according to the morphology of the micro-texture array to be polished on the surface of the artificial joint, and install both on a five-axis CNC ultra-precision machine tool. Plan the movement trajectory of the grinding wheel according to the type of artificial joint. After starting the equipment, the grinding wheel grinds on the surface of the artificial joint. Since the grinding wheel has a convex part and a concave part, the convex part of the grinding wheel removes the surface material of the artificial joint, while the concave part of the grinding wheel does not contact the surface of the artificial joint, so a micro-texture array can be formed.

[0056] This method is built based on a five-axis ultra-precision machine tool. The linear axes X-axis and Z-axis of the five-axis ultra-precision machine tool are arranged in a "T" shape. The linear axis Y-axis is installed on the X-axis, the rotary axis C-axis is installed on the Y-axis, the artificial joint to be processed is fixed to the C-axis through a fixture, the rotary axis B-axis is installed on the Z-axis, the base is installed on the B-axis, the grinding spindle is installed on the base through a fixture, the structured grinding wheel is installed on the grinding shaft, and the linkage of the B-axis and the Z-axis can be used to adjust the posture of the grinding wheel.

[0057] Before processing, it is necessary to design a structured grinding wheel according to the target micro-texture form. For each micro-texture form, only one structured grinding wheel needs to be designed. Subsequently, if a certain micro-texture surface needs to be processed, the corresponding structured grinding wheel can be directly used.

[0058] As an optional implementation method, the convex part of the grinding wheel is one of a triangle, an ellipse, a rectangle, and a spiral.

[0059] In the present invention, the grinding wheel is a structured grinding wheel, which refers to constructing various concave and convex structures on the surface of a conventional arc and cylindrical grinding wheel. Refer to Figure 12 , Figure 12 are the surfaces of 4 different forms of structured grinding wheels. Figure 12 a) is a structured grinding wheel with triangular protrusions. Figure 12 b) is a structured grinding wheel with elliptical protrusions. Figure 12 c) is a structured grinding wheel with rectangular protrusions. Figure 12 d) is a structured grinding wheel with spiral protrusions. During the structured grinding process, different forms of structured grinding wheels can generate different forms of micro-textures on the surface of the artificial joint.

[0060] Before starting the processing, it is necessary to control the Y-axis and the C-axis to drive the artificial joint to rotate to a suitable position, and the so-called suitable position is different for different artificial joints.

[0061] Specifically, if the femoral head of the artificial hip joint is spherical and rotationally symmetrical, there is no difference along the C-axis direction, and the starting point of the processing can be selected. In order to make the micro-texture of the structured grinding process have good uniformity and consider the processing feasibility of the arc structured grinding wheel on the spherical surface, the Y-axis can be controlled to drive the artificial hip joint so that its rotation center and the maximum diameter of the structured grinding wheel are in the same horizontal plane, and the Y-axis position remains unchanged during the entire structured grinding process.

[0062] For artificial knee joints, their shape is relatively complex, so the position of the C-axis needs to be adjusted before processing so that the continuity contour of its surface is parallel to the horizontal plane. Then, during processing, the position of the C-axis remains unchanged, and the height of the Y-axis is adjusted according to different processing positions.

[0063] Since different artificial joints have different shapes, different processing strategies will be adopted according to their shape characteristics.

[0064] As an optional implementation, the design process of the movement trajectory includes the following steps:

[0065] According to the type of artificial joint, the artificial joint surface is discretized into a number of discrete curves;

[0066] The rotation center of the grinding wheel moves along any discrete curve to form a grinding trajectory.

[0067] For an artificial hip joint, it can be discretized into several circular arc curves distributed around its rotation center; for the surface of an artificial knee joint, it can be discretized into several free curves parallel to the horizontal plane.

[0068] During processing, the motion trajectory of the structured grinding wheel needs to be planned according to the discrete curve of the artificial joint, and each processing corresponds to a discrete curve. Figure 2 As shown, for the artificial hip joint, structured grinding is performed along a discrete arc curve each time. The surface of the structured grinding wheel includes a convex part and a concave part. When the structured grinding wheel moves along the grinding track, only the convex part contacts the surface of the artificial joint and realizes material removal, while the concave part does not contact the surface of the artificial joint, that is, the corresponding part will be retained during the grinding process. In this way, under the alternating action of the concave and convex structures, a micro-texture array with a certain regular distribution can be formed on the surface of the artificial joint.

[0069] After completing processing along a discrete curve, the C-axis needs to be rotated a small angle to make the next discrete curve parallel to the horizontal plane, and then the structured grinding wheel is controlled to return to the starting point of processing. At this point, a cycle of structured grinding is completed and the next structured grinding can be started, and so on, until the micro-texture of the entire artificial hip joint surface meets the design requirements.

[0070] For artificial knee joints, the processing principle of the micro-texture array is the same as that of artificial hip joints. The regular distributed micro-textures are generated by the concave-convex structure of the structured grinding wheel during the grinding process. The difference is that after each structured grinding along a discrete curve, it is necessary to control the Y-axis to move a small distance so that the next discrete curve parallel to the horizontal plane moves to the corresponding height of the structured grinding wheel. And because the surface shape of the artificial knee joint is a complex free-form surface, the shapes of its discrete curves are different. Therefore, during processing, it should be noted that after each Y-axis movement, the grinding trajectory of the corresponding structured grinding wheel should be changed according to the corresponding discrete curve. Then, control the structured grinding wheel to move to the processing starting point and start the next processing, and so on until the micro-textures on the surface of the entire artificial knee joint meet the design requirements.

[0071] As an alternative implementation, the equation of the discrete curve is y = f(x).

[0072] To facilitate the representation of relatively complex discrete curves and grinding trajectories, a parametric equation is used here to describe the equation of the discrete curve, and its parametric equation is:

[0073]

[0074] where u is the parameter term, which is directly related to the form of the curve.

[0075] Its derivative can be directly obtained according to the parametric equation, which is:

[0076]

[0077] The length of the normal vector at each point on the discrete curve can be obtained by the following formula:

[0078]

[0079] The normalized normal vector can be expressed by the following formula:

[0080]

[0081] As an alternative implementation, the equation of the grinding trajectory is y = g(x).

[0082] According to the discrete curve of the artificial joint and the principle of normal processing, the grinding trajectory y = g(x) of the center of the grinding wheel rotation can be expressed by the following formula:

[0083]

[0084] where R is the nominal radius of the grinding wheel, and a p is the grinding depth.

[0085] As an alternative embodiment, the grinding trajectory equation of each abrasive point on the grinding wheel is

[0086]

[0087] where v s is the rotational speed of the structured grinding wheel; θ is the angle between the abrasive point on the structured grinding wheel and the machining starting point; h(u) is the angle between the normal of the discrete curve and the machining starting point; v w is the feed speed of the structured grinding wheel. To ensure a uniform distribution of the micro-texture array on the artificial joint surface, the feed speed of the grinding wheel should vary with the curvature of the discrete curve being machined; p(u) is the cosine function of the angle between the feed speed of the structured grinding wheel and the x-direction, used to represent the x-direction component of the feed speed; q(u) is the cosine function of the angle between the feed speed of the structured grinding wheel and the y-direction, used to represent the y-direction component of the feed speed; t is the machining time.

[0088] The discrete polar coordinates of each abrasive point on the structured grinding wheel are where is the angle of each point, and R ci is the radius corresponding to each point, and its size can reflect the concavity and convexity of the structured grinding wheel surface.

[0089] Since the subsequent deeper grinding trajectories will cover the previous shallower grinding trajectories, the equation of the micro-texture topography on the artificial joint surface can be calculated by the following formula:

[0090]

[0091] In the formula, t i is the time when the abrasive point i on the structured grinding wheel reaches a point x in the x-direction of the workpiece; y i (t i (x)) is the height when the abrasive point i on the structured grinding wheel reaches a point x in the x-direction.

[0092] According to the characteristics of the structured grinding process, the profile of the micro-texture that can be machined by this method is a gradually emerging and gradually disappearing type, while micro-milling and laser processing can machine micro-textures with side walls perpendicular to the bottom surface. This is the most obvious difference between the structured grinding method and these two methods. Schematic cross-sectional diagrams of the two different forms are as Figures 4 to 5 shown. To verify whether the cross-sectional profile of the micro-texture has a significant effect on its tribological performance, the fluid-structure interaction finite element simulation method was used to study these two different forms of micro-textures, taking the artificial hip joint as an example here.

[0093] A ball-and-socket type of micro-textured artificial hip joint is established, where the acetabulum is located above, its upper boundary is a fixed boundary, the femoral head is located below, and it is subjected to a vertically upward load. There is synovial fluid filled between the acetabulum and the femoral head, and three micro-textures are constructed on the top of the femoral head. The simulation results of fluid-structure interaction finite element are as Figures 6 to 11 shown. It can be found that when the femoral head is subjected to the load, it moves vertically upward, the synovial fluid is squeezed and moves towards the outlet, the synovial fluid at the top bears the maximum pressure, and the synovial fluid near the outlet has a faster flow rate. The synovial fluid stored in both micro-textures will flow out of the micro-textures after being squeezed, playing a role in supplementing the synovial fluid and prolonging the duration of the liquid lubrication state. By comparing two micro-textures with different cross-sectional forms, it is found that the maximum pressure of the synovial fluid is 1293.7 Pa for the progressive-in and progressive-out type and 1293.5 Pa for the sidewall vertical type, and the maximum flow rate of the synovial fluid is 0.11531 m / s for the progressive-in and progressive-out type and 0.11551 m / s for the sidewall vertical type. Therefore, the difference between the two micro-textures with different cross-sectional forms is not significant.

[0094] Based on Figure 12 the model of the structured grinding wheel shown in Figure 13 , the micro-textured surface of the artificial joint shown in s can be obtained. Due to the influence of the grinding wheel speed v w and the feed speed v Figure 13 a) The micro-textured surface formed by machining with a triangular protrusion structured grinding wheel is pentagonal in shape; Figure 13 b) The micro-textured surface formed by machining with an elliptical protrusion structured grinding wheel is approximately elliptical in shape; Figure 13 c) The micro-textured surface formed by machining with a rectangular protrusion structured grinding wheel is quadrilateral in shape; Figure 13 d) The micro-textured surface formed by machining with a spiral protrusion structured grinding wheel is diamond-shaped and shows a staggered distribution.

[0095] Compared with the prior art, the present invention has the following advantages:

[0096] 1. The present invention proposes to machine a micro-texture array on the surface of an artificial joint by means of structured grinding. This method has the characteristic of high processing efficiency. After selecting the form of the structured grinding wheel, only by controlling the movement of the structured grinding wheel along the grinding trajectory related to the shape of the artificial joint, the micro-texture array can be directly formed on the surface of the artificial joint;

[0097] 2. This method has the advantage of good process continuity. Structured grinding essentially still belongs to the category of grinding processing. In the production process arrangement of micro-textured artificial joints, the process of manufacturing micro-texture arrays by structured grinding can be arranged after the shape grinding of artificial joints without replacing other equipment, and only the arc grinding wheel needs to be replaced with a structured grinding wheel.

[0098] 3. This method has the advantage of low cost. Due to good process continuity, structured grinding does not require an additional set of processing equipment like laser processing, and avoids the steps of disassembling and reinstalling artificial joints during production, saving labor and time costs. Therefore, the cost of producing micro-textured artificial joints using this method is lower and it is more suitable for mass production in batches.

[0099] 4. This method has wide applicability. Since the type of structured grinding wheel can be a superabrasive grinding wheel, this method can process all materials commonly used for artificial joints, including ceramic materials with relatively high hardness.

[0100] 5. This method has high flexibility. This method can process various types of micro-textures. Only by designing a structured grinding wheel once according to the target micro-texture form and selecting reasonable grinding processes, the target micro-texture array can be processed on the surface of artificial joints. For micro-texture arrays of the same type but different sizes, there is no need to design a new structured grinding wheel additionally, and the same type of micro-texture arrays with different sizes can be processed by appropriately modifying the grinding processes.

[0101] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention.

[0102] The above-described embodiments are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for processing a micro-textured functional surface based on a structured abrasive tool, characterized in that: include: Determining the type of artificial joint and the morphology of the micro-texture array on the surface of the artificial joint; selecting a grinding wheel according to the micro-texture array morphology; The grinding wheel has an upper convex portion and a lower concave portion; Mounting the artificial joint and the grinding wheel on a five-axis CNC ultra-precision machine tool; Setting the moving track of the grinding wheel according to the type of the artificial joint; The surface of the artificial joint is polished to form the micro-texture array.

2. The method for processing micro-textured functional surfaces based on a structured abrasive tool according to claim 1, characterized in that: The convex part of the grinding wheel is one of a triangle, an ellipse, a rectangle and a spiral.

3. The method for processing micro-textured functional surfaces based on a structured abrasive tool according to claim 1, characterized in that: The design process of the moving trajectory includes the following steps: According to the type of the artificial joint, discretizing the artificial joint curved surface into a plurality of discrete curves; The rotation center of the grinding wheel moves along any of the discrete curves to form a grinding track.

4. The method for processing micro-textured functional surfaces based on a structured abrasive tool according to claim 3, characterized in that: The equation of the discrete curve is y=f(x).

5. The method for processing micro-textured functional surfaces based on a structured abrasive tool according to claim 4, characterized in that: The equation of the grinding trajectory is y=g(x).

6. The method for processing micro-textured functional surfaces based on a structured abrasive tool according to claim 5, characterized in that: According to the discrete curve and the principle of normal processing, y=g(x) is expressed as: Among them, R is the nominal radius of the grinding wheel, a p is the grinding depth.

7. The method for machining a micro-textured functional surface based on a structured abrasive tool according to claim 6, characterized in that: The x and the n y It is expressed by the following formula:

8. The method for processing micro-textured functional surfaces based on a structured abrasive tool according to claim 7, characterized in that: The N is represented by the following formula:

9. The method for processing micro-textured functional surfaces based on a structured abrasive tool according to claim 8, characterized in that: The discrete curve equation y=f(x) is expressed parameterized to obtain the parameterized equation: Derivative the parameterized equation to obtain

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