Grinding pin for grinding the inner surface of a cavity

Abstract

Grinding pin (10) for grinding an internal surface (11) of a cavity, comprising - an elongated base body (12) with a longitudinal axis (13) and a drive shaft (14) which can be detachably connected to a drive shaft of a drive machine, - and an abrasive body (15) arranged concentrically around the base body (12) and its longitudinal axis (13), wherein - the base body (12) extends substantially over the entire length of the grinding body (15) and has a central blind bore (16) running longitudinally along the base body (12), which is closed at its end facing away from the drive shaft (14), and through which a cooling and / or lubricating medium can be supplied into the base body (12), and - the grinding pin (10) has at least one coolant groove (17) which extends over the entire length of the grinding body (15) and whose depth extends from an outer cylindrical surface (18) of the grinding body (15) to the central blind bore (16) in the base body, so that coolant and / or lubricant can be transported directly from the central blind bore (16) to the outer cylindrical surface (18) of the grinding body (15), and wherein the base body (12) and the grinding body (15) are cylindrical in shape.

Description

[0001] The invention relates to a grinding pin for grinding an inner surface of a cavity, comprising an elongated base body with a longitudinal axis and a drive shaft which can be detachably connected to a drive shaft of a drive machine, and an abrasive body arranged around the base body concentrically around its longitudinal axis.

[0002] Such grinding pins are used, for example, for internal grinding of cylindrical bores, such as guide bores in the nozzle bodies of fuel injectors. Needle-shaped valve elements for opening and closing the injector are movably mounted in these guide bores. Towards the tip of the nozzle body, which, when installed, protrudes into the combustion chamber of an internal combustion engine, a fuel volume with a high-pressure supply line and a nozzle needle seat adjoin the guide bore. The guide bore and fuel volume form part of a nozzle needle recess in the nozzle body. This nozzle needle recess opens at the nozzle body tip into a blind hole, from which one or more injection holes lead to inject fuel into the combustion chamber.

[0003] For the injection valve to operate reliably in the long term with consistent friction conditions, the quality of the inner surface of the guide bore is essential.

[0004] Up to now, grinding pins with a central coolant bore have been used to machine guide bores. Coolant or lubricant is supplied through this bore during the grinding process, entering the nozzle needle recess via an opening at the end of the grinding pin. The coolant flows into the blind hole and from there back into the guide bore and onto the inner surface being ground. Due to the coolant exiting at the end of the grinding pin, the coolant is flushed between the blind hole and the grinding pin, resulting in some of the coolant being flushed unused through the high-pressure supply line. Achieving a uniform coolant distribution on the inner surface of the guide bore is difficult. This leads to a less than optimal cooling and lubrication effect during grinding and, in some cases, high frictional forces.This means that, on the one hand, only partial grinding is possible with conventional machines and the known grinding pins. In partial grinding, the length of the grinding pin is shorter than the length of the internal surface to be machined, so that only a portion of the internal surface can be machined at a time. On the other hand, insufficient cooling or lubrication can lead to inaccuracies in the shape of the cylindrical guide bore.

[0005] Furthermore, grinding pins are known in which coolant is guided through a central base body, which extends approximately to the middle of the grinding pin, into a cavity in the grinding pin and from there transported via coolant grooves laterally and end-face into the bore to be machined.

[0006] One disadvantage of partial sanding is the increased time required compared to full sanding, where the entire surface to be treated is processed simultaneously.

[0007] Against this background, the invention is based on the objective of providing an improved grinding pin in which the surface quality of the inner surface of bores can be further improved and which enables full-coverage grinding.

[0008] DE 100 32 036 A1 discloses a countersinking tool with a central blind bore which is connected via several distribution channels along the longitudinal direction of the blind bore and at the end face of the blind bore to a recess groove arranged on a cylindrical area of ​​a grinding surface.

[0009] In DE 94 188 76 U1 a grinding pin is described which has a longitudinal bore which widens and opens towards its end face in the area of ​​a diamond coating which is used for grinding.

[0010] In GB 1 226 435 A, a one-piece grinding tool is described, consisting of a conically shaped abrasive body with a central, longitudinally oriented blind hole. An odd number of longitudinally oriented grooves are machined into the abrasive body.

[0011] JP H05-269669 A discloses a two-part grinding tool consisting of a shaft with a blind hole and a grinding wheel mounted on the shaft. Both the shaft and the grinding wheel have interconnected radial bores.

[0012] JP S58-143 162 U describes a one-piece grinding tool with a centrally located, longitudinally extending blind hole. The grinding tool has longitudinally and circumferentially milled grooves on an outer cylindrical surface, which are connected to the blind hole via bores.

[0013] The problem is solved by a grinding pin according to the independent claim. Advantageous further developments are specified in the dependent claims.

[0014] A grinding pin according to the invention is suitable for grinding the inner surface of a cavity. A grinding pin according to the invention comprises an elongated base body with a longitudinal axis and a drive shaft, which can be detachably connected to a drive shaft of a drive machine. Preferably, the base body is made of steel. A grinding element is arranged concentrically around the longitudinal axis of the base body. The base body extends substantially over the entire length of the grinding element. For the purposes of this application, this means that the grinding element projects beyond the base body by no more than 10%, preferably no more than 5%, of its length. The base body has a central blind bore extending longitudinally along the base body, which is closed at its end facing away from the drive shaft. A coolant and / or lubricant, e.g.,The coolant is supplied from the drive motor to the base body. Furthermore, the grinding pin has at least one coolant groove that extends over the entire length of the grinding body and whose depth extends from the outer surface of the grinding body to the central blind bore in the base body, so that coolant and / or lubricant can be transported directly from the central blind bore to the outer surface of the grinding body.

[0015] The abrasive body of the grinding pin according to the invention can, for example, be cylindrical or conical. The outer surface of the abrasive body forms the working surface of the grinding pin, which interacts with the surface to be ground. For a grinding operation, the grinding pin according to the invention can be set in rotation by means of a drive shaft of a drive machine. For this purpose, the abrasive body is preferably non-rotatably connected to the base body. For machining the inner surface of cylindrical bores, the base body and / or the abrasive body are preferably cylindrical. A preferred application of the grinding pin according to the invention is the internal grinding of guide bores in nozzle bodies of injection valves, which, for example, have a diameter of less than or equal to 6 mm.The outer diameter of the grinding pin according to the invention is preferably less than or equal to 6 mm. Typical dimensions of the grinding body according to the invention are lengths greater than 7 mm, preferably greater than or equal to 10 mm and less than 20 mm, preferably less than or equal to 15 mm, and diameters greater than or equal to 3 mm and less than or equal to 10 mm, preferably less than or equal to 7 mm.

[0016] The at least one coolant groove preferably extends radially outwards from the blind bore in the base body to the outer surface of the grinding wheel body. This allows coolant and / or grinding fluid to be delivered directly to the working surface of the grinding wheel and the surface to be ground via this at least one groove.

[0017] The grinding pin according to the invention enables improved cylindrical shape quality in cylindrical bores without negatively impacting the average surface roughness Rz. Improved cooling by the grinding pin allows for a longer service life. A further advantage is a reduction in cycle time during full-coverage grinding.

[0018] According to a preferred embodiment of the grinding pin according to the invention, the at least one coolant groove extends over the entire length of the grinding element body. The at least one coolant groove preferably runs in the longitudinal direction of the grinding pin, i.e., parallel to the longitudinal axis. However, other shapes or configurations are also conceivable, e.g., spirally twisted, oblique, straight, or helical. Extending the coolant groove over the entire length of the grinding element body offers the advantage of enabling a uniform distribution of the coolant and / or lubricant over the entire length of the working or grinding surface.

[0019] According to one embodiment of the grinding pin according to the invention, the at least one coolant groove does not have the same depth over the entire length of the grinding pin body. Instead, the length of the coolant groove increases from the blind bore, to which it is connected only over a relatively short section of its length, towards the outer surface of the grinding pin body in the longitudinal direction of the grinding pin. Advantageously, as described above, it can extend over the entire length of the grinding pin body along the outer surface.

[0020] In a preferred alternative embodiment of the grinding pin according to the invention, the at least one coolant groove has essentially the same depth over its entire length. Only for the connection with the blind bore in the base body is it pierced through in a portion of its length, thus exhibiting a greater depth at this point. This embodiment offers the advantage that the grinding pin is easier to manufacture.

[0021] Preferably, the grinding pin has a plurality of coolant grooves, which are arranged around the circumference of the grinding pin body, preferably in a radially uniform manner. The multiple coolant grooves can be identical or differently configured. A variant with three identically shaped coolant grooves, each arranged offset by 120° around the longitudinal axis, is particularly preferred. However, two, four, or more coolant grooves are also conceivable, for example.

[0022] In a further preferred embodiment of the grinding pin according to the invention, the preferably steel base body has a section with a reduced outer diameter at its end facing away from the drive shaft, and the abrasive body has a section with a reduced inner diameter at its end facing away from the drive shaft. The reduced inner diameter essentially corresponds to the reduced outer diameter of the base body in this section. This embodiment is particularly advantageous when the coolant grooves extend to the end face of the abrasive body facing away from the drive shaft. Even if the grooves open to a constant depth along the longitudinal direction up to the end face, a continuous ring of abrasive body material can thus exist in the section with the reduced diameter. This ensures good stability of the grinding pin.This is particularly advantageous when the grinding pin has several coolant grooves that extend to the end face of the grinding pin at a constant depth. Without the section with the reduced inner diameter of the abrasive body and the reduced outer diameter of the base body, the abrasive body would be divided into separate sectors at the end face of the grinding pin.

[0023] The grinding pin according to one of the previously described variants is particularly suitable for the inventive method for grinding the inner surface of a cavity. According to the inventive method for grinding the inner surface of a cavity, a grinding pin is used which has an elongated base body with a longitudinal axis and an abrasive body arranged concentrically around its longitudinal axis and around the base body. According to the inventive method, the grinding pin is set into rotation about the longitudinal axis of the base body by means of a drive motor. The grinding pin is then, or even before, inserted into the cavity and a circumferential surface of the abrasive body is brought into contact with the inner surface to be ground.According to the invention, a cooling or lubricating medium is further supplied in a radial direction through the outer surface directly to the inner surface of the cavity to be ground, wherein the cooling or lubricating medium is first guided into a blind bore in the interior of the base body, and from there through at least one groove in the abrasive body extending over the entire length of the abrasive body and at least in a partial section of this length from its outer surface to the blind bore.

[0024] Furthermore, a method for the complete internal grinding of cylindrical cavities can be applied. For this purpose, the abrasive body of the grinding pin is cylindrical, and its diameter and length essentially correspond to the diameter and length of the cylindrical inner surface of the cylindrical cavity.

[0025] All features of the grinding pin according to the invention described herein can be implemented individually or in combination in the method. In particular, the base body of the grinding pin preferably extends substantially over the entire length of the abrasive body in the method as well.

[0026] The invention will now be described with reference to the invention described in the Fig. The exemplary embodiments shown in 1 to 5 are explained in more detail. They show schematically: Fig. 1: a nozzle body of an injection valve with a guide bore to be ground; Fig. 2: a grinding pin according to a first variant according to the invention in longitudinal section; Fig. 3: a cross-sectional view of the grinding pin according to the invention made of Fig. 2, Fig. 4 or Fig. 5 on average along lines AA; Fig. 4: a longitudinal section view through a grinding pin according to a second embodiment according to the invention; Fig. 5: a longitudinal section view through a grinding pin according to a third embodiment.

[0027] A nozzle body 21 for an injection valve of an internal combustion engine can be machined with a grinding pin and the inventive method to grind the inner surfaces of the guide bore 22. The nozzle body has a nozzle needle recess, which includes, among other things, the guide bore 22, the fuel volume 23, and the nozzle needle seat 25. At the tip of the nozzle body, the nozzle needle recess opens into a blind hole 26, from which injection holes lead into a combustion chamber (not shown). The fuel volume 23 has a high-pressure fuel supply line 24, through which pressurized fuel enters the nozzle body during operation. With the conventional grinding pin and method described above for machining the inner surfaces 21 of the guide bore, coolant introduced into the nozzle needle recess can be flushed out unused through the high-pressure fuel supply line.

[0028] A first embodiment of the grinding pin according to the invention is described in Fig. Figure 2 shows the grinding pin 10. It has an elongated base body 12 with a drive shaft 14, which allows it to be connected to the drive shaft of a drive machine. The base body is made of steel, for example. From the end of the drive shaft 14, the base body 12 is provided with a blind bore 16 extending along its longitudinal axis, through which coolant or lubricant can be flushed into the base body. In the illustrated embodiment, the base body is cylindrical, and a grinding element 15, also substantially cylindrical, is arranged concentrically around it.The abrasive body 15 projects only slightly beyond the base body 12 at the end pointing away from the drive shaft 14. This projection of the abrasive body 15 beyond the base body 12 is preferably less than 10% or 5% of the length of the abrasive body 15, so that the base body extends substantially over the entire length of the abrasive body 15. At this end face of the grinding pin 10, the abrasive body 15 can project either ring-shaped beyond the base body 12 or form a closed surface. The outer circumferential surface 18 of the abrasive body 15 serves as the working or effective surface of the grinding pin 10.

[0029] Distributed around its circumference, the grinding pin 10 has three identically shaped coolant grooves 17, only one of which is visible in the sectional view of the Fig. 2 can be seen. The coolant groove 17 extends over the entire length of the abrasive body and is only penetrated in the central region of the abrasive body up to the blind bore 16 of the base body 12. The penetration of a second in Fig. The coolant groove 17, not shown in the diagram, can be seen schematically in the sectional view of the blind bore 16. The coolant groove 17 does not have a constant depth along its entire length but is shallower towards the ends of the abrasive body. The coolant groove 17, which, for example, has a width of 0.4 mm, can be cut into the abrasive body 15 and the base body 12 using a cutting disc. The length of the abrasive body is 10.5 mm. The diameter of the grinding pin is approximately 3.8 mm. The abrasive body 15 consists of a ceramic material with abrasive particles, for example, CBN particles (CBN = cubic boron nitride), distributed throughout it.

[0030] In Fig. 3 is a cross-sectional view of the in Fig. The grinding pin 10 shown in Figure 2 is depicted along section line AA. The cross-section of the grinding pin and the abrasive body 15 is round. Three coolant grooves 17 are arranged radially evenly spaced around the axis 13 of the base body, offset by 120° each. In the central area of ​​the grinding pin, which the sectional view in Figure 2 shows, the grinding pin is shown along section line AA. Fig. Figure 3 shows that the coolant grooves 17 are pierced through to the blind bore 16 in the base body.

[0031] In Fig. Figure 4 shows a second embodiment of the grinding pin according to the invention. Identical components and parts are provided with the same reference numerals as in Figure 4. Fig. 2. In contrast to the one in Fig. In the embodiment shown in Figure 2, the coolant groove 17 is open towards the end face of the grinding pin and has a constant depth extending over the entire thickness of the grinding body 15. At the end of the grinding body 15 facing the drive shaft 14, the coolant groove 17 runs as in the embodiment shown in Figure 2. Fig. In the embodiment shown in Figure 2, the grinding pin is flatter. In this variant of the grinding pin, the abrasive body 15 is divided into three separate sectors in the front area of ​​the grinding pin at the end pointing away from the drive shaft 14 by the three coolant grooves 17.

[0032] Fig. Figure 5 shows a third embodiment of a grinding pin according to the invention as a further development of the one described in Figure 5. Fig.As in the exemplary embodiment shown in Figure 4, the coolant groove 17 is also formed with a constant depth towards the end of the grinding body 15 facing away from the drive shaft 14. However, in this case, the base body 12 and the grinding body 15 have a reduced outer and inner diameter, respectively, in a partial section of length 20 at the end of the grinding pin facing away from the drive shaft 14. Thus, despite the coolant grooves 17 tapering straight towards the end face, a small web of the grinding body 15 remains, so that the grinding body is also ring-shaped at the end face of the grinding pin. This offers advantages for stability and improves the service life of the grinding pin when used, for example, in the method according to the invention.

[0033] When using a grinding pin according to the invention in the inventive method, the grinding pin is set into rotation about the longitudinal axis 13 by means of a drive motor (not shown). The outer circumferential surface 18 of the grinding body 15 is brought into contact with the surface to be machined. Coolant and / or lubricant is fed from the drive motor through the blind bore 16 in the base body into the blind bore and exits from there through the openings 19 into the coolant grooves 17. Through these grooves, the coolant and / or lubricant is guided directly radially outwards to the inner surface 11 of the cavity to be machined. With the grinding pin according to the invention and the inventive method for grinding an inner surface of a cavity, more efficient cooling during the grinding process is thus possible.This can improve the quality of the inner surface, the quality of the cylindrical shape of bores, and the service life of the grinding pins.

Claims

[1] Grinding pin (10) for grinding an internal surface (11) of a cavity, comprising - an elongated base body (12) with a longitudinal axis (13) and a drive shaft (14) which can be detachably connected to a drive shaft of a drive machine, - and an abrasive body (15) arranged concentrically around the base body (12) and its longitudinal axis (13), wherein - the base body (12) extends substantially over the entire length of the grinding body (15) and has a central blind bore (16) running longitudinally along the base body (12), which is closed at its end facing away from the drive shaft (14), and through which a cooling and / or lubricating medium can be supplied into the base body (12), and - the grinding pin (10) has at least one coolant groove (17) which extends over the entire length of the grinding body (15) and whose depth extends from an outer cylindrical surface (18) of the grinding body (15) to the central blind bore (16) in the base body, so that coolant and / or lubricant can be transported directly from the central blind bore (16) to the outer cylindrical surface (18) of the grinding body (15), and wherein the base body (12) and the grinding body (15) are cylindrical in shape. [2] Grinding pin (10) according to claim 1, wherein the extension in the longitudinal direction of the at least one coolant groove (17) increases from the central blind bore (16) towards the outer circumferential surface (18) of the grinding body (15). [3] Grinding pin (10) according to claim 1, wherein the at least one coolant groove (17) has substantially the same depth over its entire length and has a greater depth up to the blind bore (16) in a partial region of its length only for the connection with the blind bore (16) in the base body (12). [4] Grinding pin (10) according to one of the preceding claims, wherein a plurality of coolant grooves (17) are provided which are arranged radially and uniformly distributed around the circumference of the grinding body (15). [5] Grinding pin (10) according to claim 4, wherein 3 identically shaped coolant grooves (17) are arranged offset by 120° each. [6] Grinding pin (10) according to one of the preceding claims, wherein the base body (12) has a partial section (20) with a reduced outer diameter at its end pointing away from the drive shaft and wherein the abrasive body (15) has a partial section (20) with a reduced inner diameter at its end pointing away from the drive shaft, which essentially corresponds to the reduced outer diameter of the base body (12) in its partial section (20).

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