Honing tool and its application

Abstract

The present invention relates to a honing tool for smoothing the inner surface of a hollow cylinder with an inner diameter iH, using a guide wire whose outer diameter aF is smaller than the inner diameter iH of the hollow cylinder. The invention further comprises the use of this honing tool in a honing machine, its use in a honing process, and the resulting product.

Description

[0001] The present invention relates to a honing tool for smoothing an inner surface of a hollow cylinder with an inner diameter i H , using a guide wire whose outer diameter a F smaller than the inner diameter i H of the hollow cylinder. The invention further comprises the use of this honing tool in a honing machine, its use in a honing process, and the resulting product.

[0002] Honing is a precision machining process used to improve surface finish and reduce dimensional tolerances of cylindrical workpieces. It involves drawing a rotating honing tool loaded with abrasive material through the workpiece, usually a hollow cylinder, removing material from the surface and creating a smooth, uniform finish.

[0003] Honing plays a crucial role in the manufacture of implants and other medical devices due to the extremely high quality requirements. These requirements necessitate precise fits and tolerances to ensure safe and reliable performance. Honing enables the achievement of these tight tolerances and ensures an optimal fit between components. Furthermore, the surface finish of medical devices and implants is critical for their biocompatibility and functionality. Honing reduces surface roughness and creates smooth, uniform surfaces that offer fewer points of attachment for bacteria and prevent the formation of biofilms.

[0004] In this context, wire honing is frequently used. Wire honing is a special form of honing in which a wire is used to machine the surface of workpieces. It is drawn lengthwise through the hollow cylinder, thus smoothing the inner surface. The longitudinal movement can be oscillated in both directions, and rotating the wire for smoothing is also possible.

[0005] Wire honing is used in medical technology for the high-precision machining of the inner surfaces of hollow cylinders, including the finishing of tubes made of Nitinol. Nitinol is a nickel-titanium alloy and one of the best-known shape-memory alloys. Hollow cylinders made of this alloy can be demonstrably cleaned and machined effectively using wire honing. This enables high-precision machining of the inner surfaces of tubes.

[0006] When using wire honing for hollow cylinders made of magnesium or magnesium alloys, those skilled in the art face the problem that the wire engages a relatively large surface area of ​​the hollow cylinder, resulting in significant friction in the typically 1 to 1.5 m long soft magnesium tubes manufactured for implants. This friction and the resulting heat are problematic: the heat generated leads to local heating of the hollow cylinder material and thus to expansion, which in turn can cause local grain growth and a consequent weakening of the material. The wire, which is drawn through the tube during the process, therefore has an uncontrolled effect and can even cause local fluctuations, i.e., varying degrees of honing.On the other hand, the total amount of heat can be so large that heat must be dissipated, which is possible with cooling lubricants, but carries a high risk of contamination.

[0007] Furthermore, with the softer magnesium material, if the force applied when pulling the wire through, especially when overcoming static friction, becomes too high, material can literally be torn out of the very thin and soft tubes. This results in damage in the form of indentations and even holes.

[0008] It is therefore an object of the invention to provide a device and an associated method with which a smoothing of the inner surface and a homogenization of the wall thickness of hollow cylinders is reliably ensured, regardless of the material used and in particular for hollow cylinders made of magnesium or magnesium alloys, without damage or contamination occurring.

[0009] This problem is solved by a honing tool having the features of claim 1.

[0010] The honing tool comprises a guide wire, which is preferably high-strength and corrosion-resistant. The outer diameter of the guide wire is smaller than the inner diameter of the hollow cylinder being machined, allowing the guide wire to pass through the hollow cylinder. The guide wire is designed so that it is not a conical wire with geometrically undefined cutting edges throughout.

[0011] At least one, preferably several, spheres are attached to this guide wire to ensure optimal smoothing of the inner surface. This at least one sphere has geometrically undefined cutting edges, so that this at least one sphere, and not the wire, performs the cleaning and material removal tasks. This is achieved by establishing a linear contact between the sphere and the hollow cylinder along the circumference of the sphere, rather than a surface contact (the wire's outer surface). This drastically reduces the friction between the honing wire and the inner surface, thereby significantly decreasing the amount of heat generated and its associated disadvantages.

[0012] Honing with the tool according to the invention functions analogously to existing processes. However, instead of an existing wire with geometrically undefined cutting edges, a guide wire is now used, which also serves to hold the at least one ball. The actual material removal is now achieved by this at least one ball, rather than by the wire as before. The guide wire is therefore always smaller than the inner diameter of the tube to be machined, but should be as thick and thus as stiff as possible. It is therefore intended that the ratio between the outer diameter of the at least one ball and the inner diameter of the corresponding tube is at least minimally greater than 1 and is selected such that optimal smoothing of the inner surface of the tube is achieved. It is therefore preferred that the difference between the outer diameter a K the ball and inner diameter i H of the hollow cylinder lies in the range of 0.01 to 50 µm. Differences in the range of 0.1 to 25 µm are preferred, more preferably in the range of 0.5 to 20 µm, even more preferably in the range of 0.75 to 15 µm, and most preferably in the range of 1 to 10 µm.

[0013] For the purposes of the invention, the term "spherical shape" is understood to mean not only exact spheres according to the geometric definition, but also three-dimensional shapes that deviate from this definition and are round in cross-section. In some cases, the shape also resembles an ellipsoid, whereby it is also true that the presence of an exact ellipsoid of revolution is not required for it to be considered ellipsoidal.

[0014] The balls are attached to the guide wire by passing the wire through a bore and along an axis intersecting the ball, preferably the axis intersecting its center. Fixation is achieved either within the ball by clamping, shrink-fitting, and / or welding, or outside the ball by gluing and / or other suitable methods. This allows for very simple manufacturing of the honing tool with high flexibility regarding the properties of the specific balls used.

[0015] The guide wire is preferably made of a metal or metal alloy to ensure sufficient rigidity when guiding the balls through the hollow cylinder and, at the same time, good manufacturability of the honing tool. Any type of stainless steel is particularly suitable, as these materials exhibit virtually no wear, especially when processing magnesium and magnesium alloys, and therefore there is no risk of contamination.

[0016] In a supplementary or alternative embodiment, the at least one sphere is made of a material whose hardness on the Mohs scale is at least 1, preferably 2 or more degrees greater than the hardness of the material from which the hollow cylinder is formed. This ensures sufficient material abrasion. Suitable materials include, in addition to the aforementioned stainless steel, hard materials.

[0017] It is therefore preferred that the balls are made of hard materials. Hard materials are materials that form intermetallic phases and are characterized by particularly high hardness and abrasion resistance. Particularly suitable are hard materials such as metal nitrides (e.g., boron nitride, titanium nitride, silicon nitride, or titanium aluminum nitride), metal carbides (e.g., silicon carbide, boron carbide, tungsten carbide, vanadium carbide, titanium carbide, or tantalum carbide), metal oxides (e.g., aluminum oxide varieties such as ruby, corundum, or sapphire), or even diamond. However, cemented carbides or metal matrix composites in which the aforementioned hard materials are added as aggregates to the metal matrix are also suitable. As mentioned above, all types of stainless steel are also suitable. It is particularly preferred that at least one ball is made of corundum. Due to the hardness of corundum (Mohs hardness 9), good abrasion can be achieved with just a few movements.At the same time, there is no contamination inside the hollow cylinder from ball abrasion. Furthermore, since synthetic corundum is widely used industrially as an abrasive in toolmaking, many years of experience with its use can be drawn upon.

[0018] Furthermore, it has proven advantageous to provide at least two, preferably three or more balls in a row on the guide, since at least two balls arranged in a row lead to a higher relative coverage of the hollow cylinder to be machined or its inner surface, thus increasing efficiency and reducing machining times.

[0019] When using multiple balls, it is preferred that two balls arranged one behind the other have the same outer diameter. a K are provided for. This allows for very uniform processing of the tool.

[0020] Alternatively, or if the total number of balls is more than two, at least two balls are arranged one behind the other, whose outer diameter a K are unequal. The outer diameter is... a K The smaller of the two balls is the one positioned on the guide wire in such a way that, when the honing tool is used, it is first inserted into or drawn through the hollow cylinder. Conversely, this means that the honing tool has a device for securing it in a honing machine, either directly at or adjacent to one end of the guide wire. The ball facing this mounting point has the larger of the two outer diameters. a K .

[0021] This allows larger burrs to be ground off first before the surface is further smoothed. It also enables a targeted increase in the inner diameter of the hollow cylinder or a reduction in its wall thickness. This reduces the forces required and the associated risk of tool damage. The difference in outer diameters a K The size is between 0.01 and 50 µm, preferably between 1 and 10 µm.

[0022] In this context, the possibility of a group of at least two spheres with an identical outer diameter is considered. a K pointed out that there is at least one other ball with a different, preferably larger, outer diameter a K This follows. The advantages of both designs are thus combined. A further embodiment of this design provides that different materials with different degrees of hardness are used for the at least two balls. In this embodiment, either balls with the same outer diameter are possible. a K can be used or with different outer diameters a K . In such an embodiment, the first ball(s) is / are made of a softer, preferably more cost-effective material, while the rear ball(s) are made of a harder material. This allows larger burrs to be ground off first, before the surface with stubborn irregularities is further smoothed. As already described above, the rear ball(s) can have a larger outer diameter. a K . The tool shall be provided with the following: The first ball(s) shall be the one(s) positioned on the guide wire in such a way that, when the honing tool is used, it is the first ball(s) inserted into or drawn through the hollow cylinder. Similarly, the rear ball(s) shall be the one(s) positioned on the guide wire in such a way that, when the honing tool is used, it is inserted into or drawn through the hollow cylinder after the first ball(s).

[0023] To increase stiffness, the diameter of the guide wire could be increased analogously to the ball diameter. However, increasing the guide wire diameter is not strictly necessary for increasing stiffness, as the increases are only a few hundredths of a millimeter.

[0024] The invention further comprises a honing machine which has a holding device for the honing tool according to the invention. This holding device ensures a secure and stable positioning of the honing tool during the machining process. The feed mechanism enables controlled and uniform progress of the honing tool along the longitudinal axis of the hollow cylinder.

[0025] The honing machine can be equipped with various control and monitoring systems to optimize the honing process and ensure the quality of the machined surface. These include, for example, pressure or tension sensors that monitor the contact between the honing tool and the inner surface of the hollow cylinder, as well as automatic control systems that can adjust the feed rate and movement of the honing tool according to the defined parameters.

[0026] The invention further comprises a honing method which utilizes the honing tool according to the invention in one of its described embodiments. In this method, in at least one honing step, the honing tool is drawn through the hollow cylinder in such a way that it is moved in the direction of its longitudinal axis. This allows the ball or balls of the honing tool to pass through the entire diameter of the hollow cylinder, thereby smoothing out unevenness, roughness, and other defects on the inner surface.

[0027] Additional honing steps can be performed to achieve specific surface structures or surface treatments. These include, for example, oscillating or rotating movements of the honing tool. A rotating movement of the tool is called flat honing and can improve the smoothing effect.

[0028] The process also encompasses long-stroke honing, in which the tool rotates around its own axis and simultaneously moves up and down along the entire length of the bore. This allows for the reliable reduction of burrs on the surface. The invention also illustrates short-stroke honing, in which the workpiece performs the rotational movement and the tool the oscillating movement, resulting in overall higher degrees of smoothness.

[0029] Finally, the inventive method also includes a honing process with at least two steps, in which the first and second honing steps are performed with different honing tools. The essential aspect of the invention is that the at least one ball of the second honing tool has a larger outer diameter. a K than the ball of the first honing tool. The difference in outer diameters a K The diameter of the two balls on the first and second honing tools is in the range of 0.01 to 50 µm, preferably 1 to 10 µm. This allows coarser burrs to be ground away in the first step and the surface to be further smoothed in the second step. The inner diameter of the hollow cylinder can also be subsequently enlarged in this way.

[0030] In summary, compared to conventional wire honing, this method reduces friction within the workpiece. This results in more stable mechanical properties across the entire length of the semi-finished product, as less frictional heat alters the mechanical characteristics. Consequently, the highly uniform honing process with reduced frictional heat enables more precise geometric properties of the semi-finished product while reliably preventing contamination from the tool.

[0031] The hollow cylinder machined according to this process also exhibits an exceptionally low variation in its inner diameter, typically less than 5 µm, which makes it particularly suitable for high-precision applications in medical technology or for medical devices such as implants. The invention therefore fundamentally encompasses hollow cylinders and implants, preferably made of magnesium or magnesium alloys, which possess this property.

[0032] Furthermore, the invention expressly includes all hollow cylinders processed according to the inventive method and the workpieces resulting from the further processing of such hollow cylinders.

[0033] Further embodiments of the invention are shown in the figures and their accompanying descriptions. Each feature, individually and in any combination, is considered disclosed. Some of the illustrations are simplified and schematic.

[0034] They show: Fig. 1 : a perspective view of a honing tool according to the invention; Fig. 2 : a section in the yz-axis through the honing tool according to the invention during use in a hollow cylinder and Fig. 3 : a section in the xy-axis through the honing tool according to the invention during use in a hollow cylinder;

[0035] Figur 1 Figure 1 shows a honing tool 1 according to the invention, wherein several balls 3a, 3b, and 3c are arranged one behind the other on a guide wire 2, which represents a preferred embodiment of the invention. The essential feature of the invention is only the presence of one ball 3.

[0036] Each of the spheres 3a, 3b and 3c has an outer diameter a K This can be the same or different from the outer diameter of other balls. In the case of varying outer diameters, it is advantageous if the ball with the smallest outer diameter enters the workpiece to be honed first and grinds down particularly prominent burrs before larger outer diameter balls proceed. a K A finer smoothing effect is achieved.

[0037] Figur 2 Figure 1 shows, as a cross-section through the yz-axis of a sphere 3, the ratio of the individual inner and outer diameters when the honing tool 1 according to the invention is used in a hollow cylinder 4. This hollow cylinder 4 has an inner diameter i H . It is essential that this inner diameter, in the sense of the invention, can be understood as both the average inner diameter and the minimum or maximum inner diameter.

[0038] The outer diameter a K The ball that is guided through the hollow cylinder for honing the surface of the inside of this hollow cylinder corresponds either to the inner diameter in of the hollow cylinder, or it is larger. The greater the difference between the inner diameter, the greater the difference between the inner diameter and the hollow cylinder. i H and the outer diameter a K The greater the difference, the more material is removed, resulting in a smoother surface, but this also increases the risk of damaging the workpiece, e.g., the hollow cylinder. It is therefore preferable that the difference between the outer diameter a K the ball and inner diameter in of the hollow cylinder lies in the range of 0.01 to 50 µm. Differences in the range of 0.1 to 25 µm are preferred, more preferably in the range of 0.5 to 20 µm, even more preferably in the range of 0.75 to 15 µm, and most preferably in the range of 1 to 10 µm.

[0039] The fixing wire 2 is guided in an axis through a bore through an axis intersecting the sphere, preferably the axis intersecting the center. Its outer diameter a F is equal to or smaller than the bore in the axis of the ball 3, so that it can penetrate it and the ball 3 is attached either inside or outside the bore at at least one, preferably two points on the guide wire 2 by clamping, shrinking, welding, gluing or other suitable methods.

[0040] Figur 3 Figure 1 shows a section along the xy-axis of a honing tool 1 according to the invention during use in a hollow cylinder 4. The honing tool 1 has four balls 3a, 3b, 3c and 3d arranged on the guide wire, which again have the same or different, preferably increasing, outer diameters. a K exhibit.

[0041] As shown, the balls are guided parallel to the course of the interior of the hollow cylinder 4 and can also be rotated, so that abrasion occurs at least in the longitudinal direction of movement, preferably also additionally in the orthogonally running second direction of movement. Reference symbol list

[0042] 1 Honing tool (according to the invention) 2 Guide wire 3, 3a-d Ball 4 Hollow cylinder in Inner diameter of hollow cylinder a K Outer diameter of ball a F Outer diameter of guide wire

Claims

1. Honing tool (1) for smoothing an inner surface of a hollow cylinder (4) with an inner diameter in with a guide wire (2) whose outer diameter a F smaller than the inner diameter in of the hollow cylinder (4) is, characterized by the fact that on the guide wire (2) at least one ball (3, 3a, 3b, 3c, 3d) is arranged, the outer diameter of which a K equal to or larger than the inner diameter in of the hollow cylinder (4) but larger than the outer diameter a F of the guide wire (2) and that the arrangement of the at least one ball (3, 3a, 3b, 3c, 3d) on the guide wire (2) is effected by the guide wire (2) being guided through an axis of the at least one ball (3, 3a, 3b, 3c, 3d) by means of a bore arranged in the at least one ball (3, 3a, 3b, 3c, 3d) and at least one fixing for fastening the at least one ball (3, 3a, 3b, 3c, 3d) inside or outside the ball (3, 3a, 3b, 3c, 3d).

2. Honing tool (1) according to claim 1, characterized by the fact that The fixing of at least one ball (3, 3a, 3b, 3c, 3d) to the guide wire (2) is carried out by clamping, shrinking, welding and / or gluing.

3. Honing tool (1) according to claim 1 or 2, characterized by the fact that the guide wire (2) is made of a metal or a metal alloy.

4. Honing tool (1) according to one of the preceding claims, characterized by the fact thatthe at least one sphere (3, 3a, 3b, 3c, 3d) is made of a material whose hardness on the Mohs scale is at least 1 degree greater than the hardness of the material from which the hollow cylinder (4) is formed.

5. Honing tool (1) according to any one of the preceding claims, characterized by the fact that which contains at least one sphere (3, 3a, 3b, 3c, 3d) a hard material.

6. Honing tool (1) according to one of the preceding claims, characterized by the fact that at least two balls (3a, 3b, 3c, 3d) arranged one behind the other along the guide wire (2) are provided.

7. Honing tool (1) according to claim 6, characterized by the fact that at least two spheres (3a, 3b, 3c, 3d) have the same outer diameter a K have.

8. Honing tool (1) according to claim 6 or 7, characterized by the fact that the at least two spheres (3a, 3b, 3c, 3d) in their outer diameter a K are unequal, with the outer diameter a K the smaller of the balls which is arranged on the guide wire (2) in such a way that it is first inserted into the hollow cylinder (4) when using the honing tool (1).

9. Honing machine, characterized by the fact that it has a fastening device for the honing tool (1) according to one of claims 1 to 8 and a drive for feeding the honing tool (1).

10. Method for machining an inner surface of a hollow cylinder for medical technology or for a medical device, in particular for an implant, characterized by the fact that In a first honing step, the honing tool according to one of claims 1 to 8 is drawn through the hollow cylinder along its longitudinal axis, so that the at least one ball completely passes through the hollow cylinder.

11. Method according to claim 10, characterized by the fact that The honing tool rotates around the longitudinal axis of the hollow cylinder.

12. Method according to claim 10, characterized by the fact thatThe honing tool moves in an oscillating motion along the longitudinal axis of the hollow cylinder.

13. Method according to any one of claims 10 to 12, characterized by the fact that The first honing step is followed by a second honing step with a second honing tool according to one of claims 1 to 8, wherein the at least one ball of the second honing tool has a larger outer diameter a K than which has at least one ball of the first honing tool.

14. Hollow cylinder for medical technology or for a medical device, in particular for an implant, wherein an inner diameter of the hollow cylinder has fluctuations of <5 µm.

15. Hollow cylinder made of a magnesium alloy and machined using a method according to any one of claims 10 to 13, and products thereof.

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