Grinding method and grinding device

Abstract

A grinding device (100) performs internal grinding of a workpiece (1) by rotating a grindstone (13) attached to a grindstone shaft (12) protruding from a base (11). A jetting unit (21) for jetting a grinding fluid is disposed to cover an outer peripheral surface of the base (11). The jetting unit (21) is provided with a jetting hole (22) so that the grinding fluid discharged from the jetting unit (21) is supplied to a grinding portion of the workpiece (1).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a grinding method and a grinding device.BACKGROUND ART

[0002] A conventional grinding device for internal grinding of a workpiece uses a grindstone with a shaft, which is a grindstone attached to a grindstone shaft rotated by a wheel head (see Patent Document 1).

[0003] The internal grinding applies a grinding load to the grindstone, and the grindstone shaft deflects. The deflection is not negligible compared to the machining accuracy required for grinding. Thus, high-precision internal grinding requires spark-out grinding, which is a process of suspending the axial movement of the grindstone shaft for several seconds until the deflection is eliminated. If a target hole to be machined is long and narrow, the grindstone shaft needs to be long and narrow as well. Such a grindstone shaft is less rigid, and takes long time to perform the spark-out grinding to recover the deflection of the grindstone shaft, increasing machining time.

[0004] The internal grinding requires a grinding fluid to be supplied to a grinding portion of the workpiece. For machining a narrow hole having a small diameter, it is necessary to dispose a port for jetting the grinding fluid so that the grinding fluid smoothly enters a gap between the grindstone shaft and the target hole. If the target hole is a blind hole, the grinding fluid needs to be supplied to the grinding portion of the workpiece from the same side from which the grindstone shaft is inserted. Patent Document 1 discloses that a supply pipe for the grinding fluid is bent along the axial direction of the grindstone shaft to face the port for jetting the grinding fluid toward the target hole.CITATION LISTPATENT DOCUMENT

[0005] Patent Document 1: Japanese Unexamined Patent Publication No. 2014-69303SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0006] If the grindstone shaft is shortened to improve the rigidity and reduce the time for the spark-out grinding and the machining time, the distance between the workpiece and the wheel head decreases too much when the innermost portion of the target hole is ground. This makes it difficult to appropriately dispose the port for jetting the grinding fluid. Insufficient supply of the grinding fluid to the grinding portion causes problems such as grinding burn involving a temperature rise of the grinding portion to 500°C or higher, shortened life of the grindstone, or the like.

[0007] An object of the present disclosure is to provide a grinding method and a grinding device capable of sufficiently supplying a grinding fluid to a grinding portion of a workpiece, with a grindstone shaft shortened to ensure its rigidity.SOLUTION TO THE PROBLEM

[0008] A first aspect is directed to a grinding method for performing internal grinding of a workpiece (1) by rotating a grindstone (13) attached to a grindstone shaft (12) protruding from a base (11), wherein a distance between the base (11) and the workpiece (1) during the grinding changes, and the distance is equal to or less than 5 mm when the innermost portion of the workpiece (1) is ground, and a grinding fluid discharged from a jetting unit (21) disposed to cover an outer peripheral surface of the base (11) is supplied to a grinding portion of the workpiece (1).

[0009] In the first aspect, although the grindstone shaft (12) is shortened to set the distance between the base (11) and the workpiece (1) during the grinding equal to or less than 5 mm, the jetting unit (21) covering the outer peripheral surface of the base (11) can sufficiently supply the grinding fluid to the grinding portion of the workpiece (1). This can reduce grinding burn, and can provide a grindstone with a shaft with longer life by reducing the wear of the grindstone (13).

[0010] A second aspect is directed to a grinding device configured to perform internal grinding of a workpiece (1) by rotating a grindstone (13) attached to a grindstone shaft (12) protruding from a base (11), the device including: a jetting unit (21) disposed to cover an outer peripheral surface of the base (11) and configured to jet a grinding fluid, wherein the jetting unit (21) is provided with a jetting hole (22) so that the grinding fluid discharged from the jetting unit (21) is supplied to a grinding portion of the workpiece (1).

[0011] In the second aspect, although the grindstone shaft (12) is shortened to set the distance between the base (11) and the workpiece (1) during the grinding equal to or less than 5 mm, the grinding fluid can be sufficiently supplied to the grinding portion of the workpiece (1) from the injection hole (22) of the jetting unit (21) covering the outer peripheral surface of the base (11). This can reduce grinding burn, and can provide a grindstone with a shaft with longer life by reducing the wear of the grindstone (13).

[0012] A third aspect is an embodiment of the second aspect. In the third aspect, the jetting hole (22) includes a plurality of holes (22) each having a small diameter equal to or smaller than 2 mm and disposed near the outer peripheral surface of the base (11).

[0013] In the third aspect, the holes (22) each having a small diameter are disposed near the outer peripheral surface of the base (11), and the grinding fluid discharged from each of the holes (22) easily enters a gap between an inner wall surface of a target hole of the workpiece (1) and the grindstone shaft (12), allowing easy supply of the grinding fluid to the grinding portion of the workpiece (1).

[0014] A fourth aspect is an embodiment of the third aspect. In the fourth aspect, a center line of each of the plurality of holes (22) has an inclination angle α of 20 degrees or less with respect to the grindstone shaft (12), and the plurality of holes (22) are bored so that an extension line of the center line hits an outer peripheral surface of the grindstone (13).

[0015] In the fourth aspect, the grinding fluid can be efficiently supplied to the grinding portion of the workpiece (1) through the gap between the inner wall surface of the target hole of the workpiece (1) and the grindstone shaft (12).

[0016] A fifth aspect is an embodiment of any one of the second to fourth aspects. In the fifth aspect, the base (11) includes a truncated conical portion (15) having the grindstone shaft (12) at the top, and an inclination angle θ of an outer peripheral surface of the truncated conical portion (15) with respect to the grindstone shaft (12) is 0° or more and 20° or less at the top of the truncated conical portion (15).

[0017] In the fifth aspect, the jetting hole (22) facing the grinding portion of the workpiece (1) can be easily provided in the jetting unit (21) covering the outer peripheral surface of the truncated conical portion (15).BRIEF DESCRIPTION OF THE DRAWINGS

[0018] [FIG. 1] FIG. 1 is a side view of a grinding device according to an embodiment (a view seen from a direction perpendicular to a grindstone shaft). [FIG. 2] FIG. 2 is a perspective view of the grinding device according to the embodiment. [FIG. 3] FIG. 3 is a cross-sectional view of the grinding device according to the embodiment. [FIG. 4] FIG. 4 is a cross-sectional view of a jetting unit of the grinding device according to the embodiment (a cross section perpendicular to the grindstone shaft). [FIG. 5] FIG. 5 is a perspective view of the jetting unit of the grinding device according to the embodiment (half of the jetting unit is shown in cross section (a cross section perpendicular to the grindstone shaft)). [FIG. 6] FIG. 6 is a perspective view of a grindstone with a shaft of the grinding device according to the embodiment. [FIG. 7] FIG. 7 is a side view of the grindstone with the shaft of the grinding device according to the embodiment (a view seen from a direction perpendicular to the grindstone shaft). [FIG. 8] FIG. 8 is a cross-sectional view showing details of the jetting unit and the grindstone with the shaft of the grinding device according to the embodiment. [FIG. 9] FIG. 9 is a perspective view of a grinding device according to a variation. [FIG. 10] FIG. 10 is a cross-sectional view of a grinding device according to Comparative Example 1. [FIG. 11] FIG. 11 is a cross-sectional view of a grinding device according to Comparative Example 2. DESCRIPTION OF EMBODIMENTS(Embodiment)

[0019] An embodiment of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to the embodiment shown below, and various changes can be made within the scope without departing from the technical concept of the present disclosure. Since each of the drawings is intended to illustrate the present disclosure conceptually, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for ease of understanding. The numerical values in the following embodiment are merely examples, and the present disclosure is not limited to them.<Grinding Device>

[0020] As illustrated in FIGS. 1 to 7, a grinding device (100) mainly includes a grindstone (10) with a shaft for internal grinding of a workpiece (1), a wheel head (20) for rotating the grindstone (10) with the shaft, a jetting unit (21) for jetting a grinding fluid, and a grinding fluid supply unit (30) for supplying the grinding fluid to the jetting unit (21).

[0021] The grindstone (10) with the shaft includes a base (11) made of metal, a long and narrow grindstone shaft (12) having one end supported by the base (11), and a grindstone (13) exchangeably attached to the grindstone shaft (12). The base (11) has, for example, a truncated conical portion (15) having the grindstone shaft (12) at the top and a cylindrical portion (16) connected to the bottom of the truncated conical portion (15) (see FIG. 7). The cylindrical portion (16) may be chamfered so that a spanner can be used for attachment to the wheel head (20). The grindstone shaft (12) may be made of the same material as the base (11) and integrally formed with the base (11). For higher rigidity of the grindstone shaft (12), the grindstone shaft (12) may be made of a superhard material and inserted and joined to the base (11). The grindstone (13) may have, for example, a cylindrical shape, and may be fixed to the grindstone shaft (12) with the grindstone shaft (12) inserted into a cylindrical hole of the grindstone (13). The grindstone (13) rotates together with the grindstone shaft (12) to perform the internal grinding of the workpiece (1). The diameter of the grindstone (13) is smaller by about several millimeters than the diameter of a hole formed in the workpiece (1).

[0022] The base (11) of the grindstone (10) with the shaft has a fixing member (14) on the opposite side of the grindstone shaft (12) for attaching the grindstone (10) with the shaft to a rotating mechanism (not shown) of the wheel head (20). The fixing member (14) may be, for example, a mounting screw or a draw-in taper (a fastener). The wheel head (20) is configured to move the grindstone (10) with the shaft back and forth in the axial direction of the grindstone shaft (12).

[0023] The jetting unit (21) is disposed to cover at least part of an outer peripheral surface of the base (11). The jetting unit (21) is supported by an outer wall (non-rotating portion) of the wheel head (20) via a support member (21a), and the jetting unit (21) does not rotate when the base (11) rotates. The jetting unit (21) is formed in an annular shape when viewed from the axial direction of the grindstone shaft (12), and an opening (21b) is formed in a center portion of the jetting unit (21) to receive at least the top of the base (11). Jetting holes (22) for discharging the grinding fluid to a grinding portion of the workpiece (1) are formed in an end face of the jetting unit (21) facing the grindstone (13). The plurality of jetting holes (22) are formed to surround the opening (21b) of the jetting unit (21). By providing the plurality of jetting hole (22), it is possible to ensure a sufficient flow rate of the grinding fluid supplied to the grinding portion of the workpiece (1).

[0024] An introduction hole (23) connected to the grinding fluid supply unit (30) is formed in the outer periphery of the jetting unit (21). An annular connection hole (24) is formed in the inner periphery (a portion adjacent to the opening (21b)) of the jetting unit (21). The connection hole (24) is connected to each of the jetting holes (22) and the introduction hole (23). Thus, the grinding fluid supplied from the grinding fluid supply unit (30) to the jetting unit (21) is supplied to the grinding portion of the workpiece (1) from the jetting holes (22) through the introduction hole (23) and the connection hole (24). A pipe of the grinding fluid supply unit (30) to the introduction hole (23) of the jetting unit (21) may be disposed along the outer wall (non-rotating portion) of the wheel head (20).

[0025] In the grinding device (100), the grindstone (13) may be rotated at a high speed, and the workpiece (1) may be rotated at a low speed. In this case, the workpiece (1) may be held on a worktable that is rotatable. Alternatively or in addition to the configuration in which the grindstone (10) with the shaft is moved back and forth in the axial direction of the grindstone shaft (12) together with the wheel head (20), the workpiece (1) may be moved back and forth in the axial direction of the grindstone shaft (12) together with a worktable holding the workpiece (1).<Jetting Unit>

[0026] For the internal grinding of the workpiece (1), the grindstone (13) is inserted in a recess (a target hole to be machined) formed in the workpiece (1) and rotated to grind the inner surface of the target hole. The grindstone (13) inserted in the target hole of the workpiece (1) is movable in the axial direction of the grindstone shaft (12) and also movable in the radial direction of the grindstone shaft (12). This makes it possible to process the inner surface of the target hole into a desired shape.

[0027] When the internal grinding of the workpiece (1) is performed by the grinding method of the present embodiment, the grindstone (13) is moved in the axial direction of the grindstone shaft (12), which changes the distance between the base (11) and the workpiece (1) (an end surface of the workpiece (1) facing the base (11)). In the present embodiment, the grindstone (10) with the shaft that has the short grindstone shaft (12) is used so that the distance between the base (11) and the workpiece (1) is equal to or less than 5 mm when the innermost portion of the target hole of the workpiece (1) is ground with the grindstone (13) without bringing the base (11) and the workpiece (1) into contact. Thus, the jetting unit (21) for jetting the grinding fluid is disposed to cover the outer peripheral surface of the base (11) of the grindstone (10) with the shaft, and the jetting holes (22) are formed in the jetting unit (21) so that the grinding fluid discharged from the jetting unit (21) is supplied to the grinding portion of the workpiece (1).

[0028] When the jetting unit (21) is attached to cover the outer peripheral surface of the base (11) at least around the top of the base (11), the plurality of jetting holes (22) can be arranged in a circular pattern around the grindstone shaft (12) (see FIG. 2). This allows the grinding fluid to be directly jetted from the jetting unit (21) to the grinding portion of the workpiece (1) inside the target hole.

[0029] As illustrated in FIG. 8, the grinding fluid discharged from the jetting holes (22) needs to be supplied toward the grinding portion through a narrow gap between the inner wall surface of the target hole of the workpiece (1) and the grindstone shaft (12). For this reason, the diameter of the jetting holes (22) is about 2 mm or less, preferably about 1 mm or less. The jetting holes (22) are disposed within a range of about 3 mm or less from the outer peripheral surface of the base (11) to shorten the distance between the jetting holes (22) and the grindstone shaft (12). Providing the plurality of jetting hole (22) can ensure a sufficient flow rate of the grinding fluid supplied to the grinding portion of the workpiece (1) although the diameter of the jetting holes (22) is small.

[0030] As illustrated in FIG. 8, each of the jetting holes (22) is bored so that an extension line C of the center line of the jetting hole (22) hits the outer peripheral surface of the grindstone (13) and the grinding fluid discharged from the jetting holes (22) is prevented from hitting and splashing back from the end surfaces of the workpiece (1) and the grindstone (13) facing the base (11). Specifically, the extension line C has an inclination angle α of 20 degrees or less with respect to the grindstone shaft (12) (a center axis J of the grindstone shaft (12)). The length of each jetting hole (22), that is, the distance from the junction with the connection hole (24) to the opening facing the grindstone (13), is made greater than the diameter of the jetting hole (22) so that the grinding fluid is discharged from the jetting holes (22) in the direction of the extension line C.

[0031] The end surface of the jetting unit (21) facing the grindstone (13) is flush with the end surface of the base (11) facing the grindstone (13), or is located farther from the grindstone (13) than the end surface of the base (11) facing the grindstone (13). Conversely, if the jetting unit (21) is located closer to the grindstone (13) than the end surface of the base (11) facing the grindstone (13), the grindstone shaft (12) (specifically, a portion between the base (11) and the grindstone (13)) should be longer to avoid contact between the jetting unit (21) and the workpiece (1). This results in low rigidity of the grindstone shaft (12).<Grindstone with Shaft>

[0032] As described above, the grindstone (10) with the shaft may be configured as follows to reduce the distance between the jetting holes (22) of the jetting unit (21) and the grindstone shaft (12) and to set the inclination angle α of the center line of each jetting hole (22) (extension line C) with respect to the grindstone shaft (12) (center axis J) to 20 degrees or less.

[0033] As illustrated in FIG. 7, the base (11) of the grindstone (10) with the shaft may have a truncated conical portion (15) having the grindstone shaft (12) at the top. An inclination angle θ of an outer peripheral surface of the truncated conical portion (15) with respect to the grindstone shaft (12) (center axis J) is 0° or more and about 20° or less at the top of the truncated conical portion (15). The outer peripheral surface of the truncated conical portion (15) and the outer peripheral surface of the grindstone shaft (12) have a level difference of about 5 mm or less at the top of the truncated conical portion (15).

[0034] If the inclination angle θ of the entire outer peripheral surface of the truncated conical portion (15) is set to 20° or less, the rigidity of the truncated conical portion (15), that is, the base (11), decreases. Thus, as illustrated in FIG. 7, the outer peripheral surface of the truncated conical portion (15) of the base (11) may be formed into a concave surface (15a) to keep a space for disposing the jetting unit (21) with the jetting holes (22) (extension line C) facing the grinding portion of the workpiece (1). This makes it easy to bore the jetting holes (22) in a desired direction with less adverse effects on the rigidity of the base (11), that is, the grindstone (10) with the shaft. For example, the inclination angle θ of the concave surface (15a) of the truncated conical portion (15) with respect to the grindstone shaft (12) (center axis J) may be 0° or more and 20° or less at the top of the truncated conical portion (15), the inclination angle θ may increase from the top to the bottom of the truncated conical portion (15), and the concave surface (15a) may be connected to the outer peripheral surface of the cylindrical portion (16) at the bottom of the truncated conical portion (15) at an angle φ of 40° or more and 90° or less. The angle φ is equal to the inclination angle of the concave surface (15a) with respect to the center axis J of the grindstone shaft (12) at the bottom of the truncated conical portion (15).

[0035] The shape of the base (11) is obtained by combining the truncated conical portion (15) having the outer peripheral surface inclined at an angle of, for example, 45°, with respect to the bottom surface and the cylindrical portion (16) in which the fixing member (14) for fixing the base (11) to the wheel head (20) is inserted. However, in the example shown in FIG. 7, the outer peripheral surface of the truncated conical portion (15) is shaped into the curved concave surface (15a). As illustrated in FIG. 7, when the grindstone (10) with the shaft is viewed from a direction perpendicular to the grindstone shaft (12), a curve (e.g., a parabola or an arc) which is the concave surface (15a) starts to extend from the top of the truncated conical portion (15) having a diameter slightly larger (e.g., by about 1 to 2 mm) than the diameter of the grindstone (13) at an inclination angle θ of about 0° to 20° with respect to the grindstone shaft (12), and the inclination angle θ greatly changes toward the bottom of the truncated conical portion (15). The curve is connected to the outer peripheral surface of the cylindrical portion (16) having a larger diameter than the grindstone (13) at an angle φ of 40° or more and 90° or less.

[0036] The rigidity of the base (11) shaped as shown in FIG. 7 slightly decreases compared to when the outer peripheral surface of the truncated conical portion (15) is not formed into the concave surface (15a). However, the decrease in the rigidity of the base (11) is negligible compared to the increase in the rigidity by shortening the grindstone shaft (12).

[0037] The configuration of the grindstone (10) with the shaft shown in FIG. 7 is an example. The jetting holes (22) can be bored in the desired direction although the entire outer peripheral surface of the truncated conical portion (15) is not formed into the concave surface (15a) as long as the inclination angle θ of the outer peripheral surface of the truncated conical portion (15) with respect to the grindstone shaft (12) (center axis J) is 0° or more and about 20° or less at the top of the truncated conical portion (15) (at an end portion facing the grindstone (13)). Specifically, only the outer peripheral surface of the truncated conical portion (15) around the top may be formed into the concave surface. Alternatively, the outer peripheral surface of the truncated conical portion (15) may include a plurality of flat inclined surfaces having different inclination angles, and only the flat inclined surface near the top of the truncated conical portion (15) may have an inclination angle of 0° or more and about 20° or less.<Position of Jetting Holes>

[0038] The jetting unit (21) and the grindstone (10) with the shaft illustrated in FIG. 8 may be configured as follows so that the grinding fluid discharged from the jetting holes (22) of the jetting unit (21) hits the outer peripheral surface of the grindstone (13).

[0039] The minimum distance L1 between the base (11) and the workpiece (1) during the grinding is equal to or less than 5 mm, for example, 4 mm. The distance L2 between the end surface of the base (11) facing the grindstone (13) and the end surface of the grindstone (13) facing the base (11), that is, the axial length of a portion of the grindstone shaft (12) without the grindstone (13), is, for example, 7.5 mm. Each jetting hole (22) has a diameter of about 2 mm or less, for example, 1 mm. The inclination angle α of the center line (extension line C) of the jetting hole (22) with respect to the grindstone shaft (12) (center axis J) is 20 degrees or less, for example, 16 degrees. The radius D2 of the top of the base (11) is larger than the radius D1 of the grindstone (13) by about 1 to 3 mm. For example, D1 is 5.75 mm, and D2 is 7 mm.

[0040] In the above configuration, the distance L3 between the center of the opening of the jetting hole (22) and the grindstone shaft (12) (center axis J) is set to be larger than "D1 + L2 × tan(α)" (7.85 mm in this example), for example, 8.21 mm. This is because the grinding fluid discharged from the jetting holes (22) does not reach the outer peripheral surface of the grindstone (13) if L3 is less than "D1 + L2 × tan(α)."<Variation of Jetting Unit>

[0041] In the embodiment shown in FIG. 2 or others, the jetting unit (21) is disposed to surround the entire outer periphery of the base (11) (truncated conical portion (15)) of the grindstone (10) with the shaft. This can easily increase the number of jetting holes (22) to be arranged.

[0042] On the other hand, as a variation shown in FIG. 9, the jetting unit (21) is formed in, for example, a semicircular shape or a U-shape, to surround part of the outer periphery of the base (11) (truncated conical portion (15)) (about half of the outer periphery in this example) so as to easily conduct detachment of the jetting unit (21) or the like. If the grinding fluid supply unit (30) is made of a flexible pipe separate from the wheel head (20), the jetting unit (21) may be detached together with the pipe.<Features of Embodiment (and Variation)>

[0043] The grinding method of the embodiment is a method for internal grinding the workpiece (1) by rotating the grindstone (13) attached to the grindstone shaft (12) protruding from the base (11). The distance between the base (11) and the workpiece (1) during the grinding changes, the distance is equal to or less than 5 mm when the innermost portion of the workpiece (1) is ground, and the grinding fluid discharged from the jetting unit (21) disposed to cover the outer peripheral surface of the base (11) is supplied to the grinding portion of the workpiece (1).

[0044] By the grinding method of the embodiment, although the grindstone shaft (12) is shortened to set the distance between the base (11) and the workpiece (1) during the grinding equal to or less than 5 mm, the jetting unit (21) covering the outer peripheral surface of the base (11) can sufficiently supply the grinding fluid to the grinding portion of the workpiece (1). This can reduce grinding burn, and can provide a grindstone with a shaft with longer life by reducing the wear of the grindstone (13). Further, with the grindstone shaft (12) shortened, the machining accuracy can be kept from decreasing due to deflection of the grindstone shaft (12), and the time required for the spark-out grinding can be reduced. This shortens the machining time, that is, improves the machining speed.

[0045] The grinding device (100) of the embodiment performs the internal grinding of the workpiece (1) by rotating the grindstone (13) attached to the grindstone shaft (12) protruding from the base (11). The grinding device (100) includes the jetting unit (21) disposed to cover the outer peripheral surface of the base (11). The jetting unit (21) has the jetting holes (22) for jetting the grinding fluid. The jetting holes (22) are provided in the jetting unit (21) so that the grinding fluid discharged from the jetting holes (22) is supplied to the grinding portion of the workpiece (1).

[0046] In the grinding device (100) of the embodiment, although the grindstone shaft (12) is shortened to set the distance between the base (11) and the workpiece (1) during the grinding equal to or less than 5 mm, the grinding fluid can be sufficiently supplied to the grinding portion of the workpiece (1) from the jetting holes (22) of the jetting unit (21) covering the outer peripheral surface of the base (11). This can reduce grinding burn, and can provide a grindstone with a shaft with longer life by reducing the wear of the grindstone (13). Further, with the grindstone shaft (12) shortened, the machining accuracy can be kept from decreasing due to deflection of the grindstone shaft (12), and the time required for the spark-out grinding can be reduced. This shortens the machining time, that is, improves the machining speed.

[0047] On the other hand, when a supply pipe for the grinding fluid is bent along the axial direction of the grindstone shaft so that the jetting port of the grinding fluid supply pipe is disposed toward the target hole as in the previous manner, the grinding fluid jetting port (31) can be disposed toward the target hole if the grindstone shaft (12) is long as in Comparative Example 1 shown in FIG. 10, but the grinding fluid jetting port (31) cannot be disposed toward the target hole if the grindstone shaft (12) is short as in Comparative Example 2 shown in FIG. 11. In Comparative Examples 1 and 2 shown in FIGS. 10 and 11, the same components as those of the embodiment shown in FIG. 3 are denoted by the same reference numerals. As described above, the grindstone shaft should be kept as short as possible to ensure the rigidity. However, when the distance between the workpiece and the base of the grindstone shaft or the wheel head is about 5 mm or less, the target hole of the workpiece is blocked by the base or the wheel head as in Comparative Example 2 shown in FIG. 11, and the grinding fluid jetting port cannot be appropriately disposed. In this case, the grinding fluid cannot be sufficiently supplied to the grinding portion of the workpiece, causing problems such as grinding burn involving the temperature rise of the grinding portion to 500°C or higher, shortened life of the grindstone, or the like.

[0048] In the grinding device (100) of the embodiment, the plurality of jetting holes (22) each having a small diameter of 2 mm or less may be disposed as the jetting holes (22) near the outer peripheral surface of the base (11). This makes it easy for the grinding fluid discharged from the jetting holes (22) to enter the gap between the inner wall surface of the target hole of the workpiece (1) and the grindstone shaft (12), allowing easy supply of the grinding fluid to the grinding portion of the workpiece (1). In this case, the inclination angle α of the center line (extension line C) of each jetting hole (22) with respect to the grindstone shaft (12) (center axis J) may be 20 degrees or less, and the jetting holes (22) may be bored so that the extension line C hits the outer peripheral surface of the grindstone (13). This allows efficient supply of the grinding fluid to the grinding portion of the workpiece (1) through the gap between the inner wall surface of the target hole of the workpiece (1) and the grindstone shaft (12).

[0049] In the grinding device (100) of the embodiment, the base (11) may include the truncated conical portion (15) having the grindstone shaft (12) at the top, and the inclination angle θ of the outer peripheral surface of the truncated conical portion (15) with respect to the grindstone shaft (12) at the top of the truncated conical portion (15) may be 0° or more and 20° or less. Thus, the jetting holes (22) facing the grinding portion of the workpiece (1) can be easily provided in the jetting unit (21) covering the outer peripheral surface of the truncated conical portion (15).(Other Embodiments)

[0050] It will be understood that the embodiments and variations described above can be modified with various changes in form and details without departing from the spirit and scope of the claims. The foregoing embodiments and variations may be appropriately combined or replaced as appropriate.INDUSTRIAL APPLICABILITY

[0051] As described above, the present disclosure is useful for a grinding method and a grinding device.DESCRIPTION OF REFERENCE CHARACTERS

[0052] 1Workpiece 11Base 12Grindstone Shaft 13Grindstone 15Truncated Conical Portion 21Jetting Unit 22Jetting Hole 100Grinding Device

Examples

embodiment

(Embodiment)

[0019]An embodiment of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to the embodiment shown below, and various changes can be made within the scope without departing from the technical concept of the present disclosure. Since each of the drawings is intended to illustrate the present disclosure conceptually, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for ease of understanding. The numerical values in the following embodiment are merely examples, and the present disclosure is not limited to them.

[0020]As illustrated in FIGS. 1 to 7, a grinding device (100) mainly includes a grindstone (10) with a shaft for internal grinding of a workpiece (1), a wheel head (20) for rotating the grindstone (10) with the shaft, a jetting unit (21) for jetting a grinding fluid, and a grinding fluid supply unit (30) for supplying the grinding fluid to the jetting unit (21).

[0021...

TECHNICAL FIELD

[0001] The present disclosure relates to a grinding method and a grinding device.BACKGROUND ART

[0002] A conventional grinding device for internal grinding of a workpiece uses a grindstone with a shaft, which is a grindstone attached to a grindstone shaft rotated by a wheel head (see Patent Document 1).

[0003] The internal grinding applies a grinding load to the grindstone, and the grindstone shaft deflects. The deflection is not negligible compared to the machining accuracy required for grinding. Thus, high-precision internal grinding requires spark-out grinding, which is a process of suspending the axial movement of the grindstone shaft for several seconds until the deflection is eliminated. If a target hole to be machined is long and narrow, the grindstone shaft needs to be long and narrow as well. Such a grindstone shaft is less rigid, and takes long time to perform the spark-out grinding to recover the deflection of the grindstone shaft, increasing machining time.

[0004] The internal grinding requires a grinding fluid to be supplied to a grinding portion of the workpiece. For machining a narrow hole having a small diameter, it is necessary to dispose a port for jetting the grinding fluid so that the grinding fluid smoothly enters a gap between the grindstone shaft and the target hole. If the target hole is a blind hole, the grinding fluid needs to be supplied to the grinding portion of the workpiece from the same side from which the grindstone shaft is inserted. Patent Document 1 discloses that a supply pipe for the grinding fluid is bent along the axial direction of the grindstone shaft to face the port for jetting the grinding fluid toward the target hole.CITATION LISTPATENT DOCUMENT

[0005] Patent Document 1: Japanese Unexamined Patent Publication No. 2014-69303SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0006] If the grindstone shaft is shortened to improve the rigidity and reduce the time for the spark-out grinding and the machining time, the distance between the workpiece and the wheel head decreases too much when the innermost portion of the target hole is ground. This makes it difficult to appropriately dispose the port for jetting the grinding fluid. Insufficient supply of the grinding fluid to the grinding portion causes problems such as grinding burn involving a temperature rise of the grinding portion to 500°C or higher, shortened life of the grindstone, or the like.

[0007] An object of the present disclosure is to provide a grinding method and a grinding device capable of sufficiently supplying a grinding fluid to a grinding portion of a workpiece, with a grindstone shaft shortened to ensure its rigidity.SOLUTION TO THE PROBLEM

[0008] A first aspect is directed to a grinding method for performing internal grinding of a workpiece (1) by rotating a grindstone (13) attached to a grindstone shaft (12) protruding from a base (11), wherein a distance between the base (11) and the workpiece (1) during the grinding changes, and the distance is equal to or less than 5 mm when the innermost portion of the workpiece (1) is ground, and a grinding fluid discharged from a jetting unit (21) disposed to cover an outer peripheral surface of the base (11) is supplied to a grinding portion of the workpiece (1).

[0009] In the first aspect, although the grindstone shaft (12) is shortened to set the distance between the base (11) and the workpiece (1) during the grinding equal to or less than 5 mm, the jetting unit (21) covering the outer peripheral surface of the base (11) can sufficiently supply the grinding fluid to the grinding portion of the workpiece (1). This can reduce grinding burn, and can provide a grindstone with a shaft with longer life by reducing the wear of the grindstone (13).

[0010] A second aspect is directed to a grinding device configured to perform internal grinding of a workpiece (1) by rotating a grindstone (13) attached to a grindstone shaft (12) protruding from a base (11), the device including: a jetting unit (21) disposed to cover an outer peripheral surface of the base (11) and configured to jet a grinding fluid, wherein the jetting unit (21) is provided with a jetting hole (22) so that the grinding fluid discharged from the jetting unit (21) is supplied to a grinding portion of the workpiece (1).

[0011] In the second aspect, although the grindstone shaft (12) is shortened to set the distance between the base (11) and the workpiece (1) during the grinding equal to or less than 5 mm, the grinding fluid can be sufficiently supplied to the grinding portion of the workpiece (1) from the injection hole (22) of the jetting unit (21) covering the outer peripheral surface of the base (11). This can reduce grinding burn, and can provide a grindstone with a shaft with longer life by reducing the wear of the grindstone (13).

[0012] A third aspect is an embodiment of the second aspect. In the third aspect, the jetting hole (22) includes a plurality of holes (22) each having a small diameter equal to or smaller than 2 mm and disposed near the outer peripheral surface of the base (11).

[0013] In the third aspect, the holes (22) each having a small diameter are disposed near the outer peripheral surface of the base (11), and the grinding fluid discharged from each of the holes (22) easily enters a gap between an inner wall surface of a target hole of the workpiece (1) and the grindstone shaft (12), allowing easy supply of the grinding fluid to the grinding portion of the workpiece (1).

[0014] A fourth aspect is an embodiment of the third aspect. In the fourth aspect, a center line of each of the plurality of holes (22) has an inclination angle α of 20 degrees or less with respect to the grindstone shaft (12), and the plurality of holes (22) are bored so that an extension line of the center line hits an outer peripheral surface of the grindstone (13).

[0015] In the fourth aspect, the grinding fluid can be efficiently supplied to the grinding portion of the workpiece (1) through the gap between the inner wall surface of the target hole of the workpiece (1) and the grindstone shaft (12).

[0016] A fifth aspect is an embodiment of any one of the second to fourth aspects. In the fifth aspect, the base (11) includes a truncated conical portion (15) having the grindstone shaft (12) at the top, and an inclination angle θ of an outer peripheral surface of the truncated conical portion (15) with respect to the grindstone shaft (12) is 0° or more and 20° or less at the top of the truncated conical portion (15).

[0017] In the fifth aspect, the jetting hole (22) facing the grinding portion of the workpiece (1) can be easily provided in the jetting unit (21) covering the outer peripheral surface of the truncated conical portion (15).BRIEF DESCRIPTION OF THE DRAWINGS

[0018] [FIG. 1] FIG. 1 is a side view of a grinding device according to an embodiment (a view seen from a direction perpendicular to a grindstone shaft). [FIG. 2] FIG. 2 is a perspective view of the grinding device according to the embodiment. [FIG. 3] FIG. 3 is a cross-sectional view of the grinding device according to the embodiment. [FIG. 4] FIG. 4 is a cross-sectional view of a jetting unit of the grinding device according to the embodiment (a cross section perpendicular to the grindstone shaft). [FIG. 5] FIG. 5 is a perspective view of the jetting unit of the grinding device according to the embodiment (half of the jetting unit is shown in cross section (a cross section perpendicular to the grindstone shaft)). [FIG. 6] FIG. 6 is a perspective view of a grindstone with a shaft of the grinding device according to the embodiment. [FIG. 7] FIG. 7 is a side view of the grindstone with the shaft of the grinding device according to the embodiment (a view seen from a direction perpendicular to the grindstone shaft). [FIG. 8] FIG. 8 is a cross-sectional view showing details of the jetting unit and the grindstone with the shaft of the grinding device according to the embodiment. [FIG. 9] FIG. 9 is a perspective view of a grinding device according to a variation. [FIG. 10] FIG. 10 is a cross-sectional view of a grinding device according to Comparative Example 1. [FIG. 11] FIG. 11 is a cross-sectional view of a grinding device according to Comparative Example 2. DESCRIPTION OF EMBODIMENTS(Embodiment)

[0019] An embodiment of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to the embodiment shown below, and various changes can be made within the scope without departing from the technical concept of the present disclosure. Since each of the drawings is intended to illustrate the present disclosure conceptually, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for ease of understanding. The numerical values in the following embodiment are merely examples, and the present disclosure is not limited to them.<Grinding Device>

[0020] As illustrated in FIGS. 1 to 7, a grinding device (100) mainly includes a grindstone (10) with a shaft for internal grinding of a workpiece (1), a wheel head (20) for rotating the grindstone (10) with the shaft, a jetting unit (21) for jetting a grinding fluid, and a grinding fluid supply unit (30) for supplying the grinding fluid to the jetting unit (21).

[0021] The grindstone (10) with the shaft includes a base (11) made of metal, a long and narrow grindstone shaft (12) having one end supported by the base (11), and a grindstone (13) exchangeably attached to the grindstone shaft (12). The base (11) has, for example, a truncated conical portion (15) having the grindstone shaft (12) at the top and a cylindrical portion (16) connected to the bottom of the truncated conical portion (15) (see FIG. 7). The cylindrical portion (16) may be chamfered so that a spanner can be used for attachment to the wheel head (20). The grindstone shaft (12) may be made of the same material as the base (11) and integrally formed with the base (11). For higher rigidity of the grindstone shaft (12), the grindstone shaft (12) may be made of a superhard material and inserted and joined to the base (11). The grindstone (13) may have, for example, a cylindrical shape, and may be fixed to the grindstone shaft (12) with the grindstone shaft (12) inserted into a cylindrical hole of the grindstone (13). The grindstone (13) rotates together with the grindstone shaft (12) to perform the internal grinding of the workpiece (1). The diameter of the grindstone (13) is smaller by about several millimeters than the diameter of a hole formed in the workpiece (1).

[0022] The base (11) of the grindstone (10) with the shaft has a fixing member (14) on the opposite side of the grindstone shaft (12) for attaching the grindstone (10) with the shaft to a rotating mechanism (not shown) of the wheel head (20). The fixing member (14) may be, for example, a mounting screw or a draw-in taper (a fastener). The wheel head (20) is configured to move the grindstone (10) with the shaft back and forth in the axial direction of the grindstone shaft (12).

[0023] The jetting unit (21) is disposed to cover at least part of an outer peripheral surface of the base (11). The jetting unit (21) is supported by an outer wall (non-rotating portion) of the wheel head (20) via a support member (21a), and the jetting unit (21) does not rotate when the base (11) rotates. The jetting unit (21) is formed in an annular shape when viewed from the axial direction of the grindstone shaft (12), and an opening (21b) is formed in a center portion of the jetting unit (21) to receive at least the top of the base (11). Jetting holes (22) for discharging the grinding fluid to a grinding portion of the workpiece (1) are formed in an end face of the jetting unit (21) facing the grindstone (13). The plurality of jetting holes (22) are formed to surround the opening (21b) of the jetting unit (21). By providing the plurality of jetting hole (22), it is possible to ensure a sufficient flow rate of the grinding fluid supplied to the grinding portion of the workpiece (1).

[0024] An introduction hole (23) connected to the grinding fluid supply unit (30) is formed in the outer periphery of the jetting unit (21). An annular connection hole (24) is formed in the inner periphery (a portion adjacent to the opening (21b)) of the jetting unit (21). The connection hole (24) is connected to each of the jetting holes (22) and the introduction hole (23). Thus, the grinding fluid supplied from the grinding fluid supply unit (30) to the jetting unit (21) is supplied to the grinding portion of the workpiece (1) from the jetting holes (22) through the introduction hole (23) and the connection hole (24). A pipe of the grinding fluid supply unit (30) to the introduction hole (23) of the jetting unit (21) may be disposed along the outer wall (non-rotating portion) of the wheel head (20).

[0025] In the grinding device (100), the grindstone (13) may be rotated at a high speed, and the workpiece (1) may be rotated at a low speed. In this case, the workpiece (1) may be held on a worktable that is rotatable. Alternatively or in addition to the configuration in which the grindstone (10) with the shaft is moved back and forth in the axial direction of the grindstone shaft (12) together with the wheel head (20), the workpiece (1) may be moved back and forth in the axial direction of the grindstone shaft (12) together with a worktable holding the workpiece (1).<Jetting Unit>

[0026] For the internal grinding of the workpiece (1), the grindstone (13) is inserted in a recess (a target hole to be machined) formed in the workpiece (1) and rotated to grind the inner surface of the target hole. The grindstone (13) inserted in the target hole of the workpiece (1) is movable in the axial direction of the grindstone shaft (12) and also movable in the radial direction of the grindstone shaft (12). This makes it possible to process the inner surface of the target hole into a desired shape.

[0027] When the internal grinding of the workpiece (1) is performed by the grinding method of the present embodiment, the grindstone (13) is moved in the axial direction of the grindstone shaft (12), which changes the distance between the base (11) and the workpiece (1) (an end surface of the workpiece (1) facing the base (11)). In the present embodiment, the grindstone (10) with the shaft that has the short grindstone shaft (12) is used so that the distance between the base (11) and the workpiece (1) is equal to or less than 5 mm when the innermost portion of the target hole of the workpiece (1) is ground with the grindstone (13) without bringing the base (11) and the workpiece (1) into contact. Thus, the jetting unit (21) for jetting the grinding fluid is disposed to cover the outer peripheral surface of the base (11) of the grindstone (10) with the shaft, and the jetting holes (22) are formed in the jetting unit (21) so that the grinding fluid discharged from the jetting unit (21) is supplied to the grinding portion of the workpiece (1).

[0028] When the jetting unit (21) is attached to cover the outer peripheral surface of the base (11) at least around the top of the base (11), the plurality of jetting holes (22) can be arranged in a circular pattern around the grindstone shaft (12) (see FIG. 2). This allows the grinding fluid to be directly jetted from the jetting unit (21) to the grinding portion of the workpiece (1) inside the target hole.

[0029] As illustrated in FIG. 8, the grinding fluid discharged from the jetting holes (22) needs to be supplied toward the grinding portion through a narrow gap between the inner wall surface of the target hole of the workpiece (1) and the grindstone shaft (12). For this reason, the diameter of the jetting holes (22) is about 2 mm or less, preferably about 1 mm or less. The jetting holes (22) are disposed within a range of about 3 mm or less from the outer peripheral surface of the base (11) to shorten the distance between the jetting holes (22) and the grindstone shaft (12). Providing the plurality of jetting hole (22) can ensure a sufficient flow rate of the grinding fluid supplied to the grinding portion of the workpiece (1) although the diameter of the jetting holes (22) is small.

[0030] As illustrated in FIG. 8, each of the jetting holes (22) is bored so that an extension line C of the center line of the jetting hole (22) hits the outer peripheral surface of the grindstone (13) and the grinding fluid discharged from the jetting holes (22) is prevented from hitting and splashing back from the end surfaces of the workpiece (1) and the grindstone (13) facing the base (11). Specifically, the extension line C has an inclination angle α of 20 degrees or less with respect to the grindstone shaft (12) (a center axis J of the grindstone shaft (12)). The length of each jetting hole (22), that is, the distance from the junction with the connection hole (24) to the opening facing the grindstone (13), is made greater than the diameter of the jetting hole (22) so that the grinding fluid is discharged from the jetting holes (22) in the direction of the extension line C.

[0031] The end surface of the jetting unit (21) facing the grindstone (13) is flush with the end surface of the base (11) facing the grindstone (13), or is located farther from the grindstone (13) than the end surface of the base (11) facing the grindstone (13). Conversely, if the jetting unit (21) is located closer to the grindstone (13) than the end surface of the base (11) facing the grindstone (13), the grindstone shaft (12) (specifically, a portion between the base (11) and the grindstone (13)) should be longer to avoid contact between the jetting unit (21) and the workpiece (1). This results in low rigidity of the grindstone shaft (12).<Grindstone with Shaft>

[0032] As described above, the grindstone (10) with the shaft may be configured as follows to reduce the distance between the jetting holes (22) of the jetting unit (21) and the grindstone shaft (12) and to set the inclination angle α of the center line of each jetting hole (22) (extension line C) with respect to the grindstone shaft (12) (center axis J) to 20 degrees or less.

[0033] As illustrated in FIG. 7, the base (11) of the grindstone (10) with the shaft may have a truncated conical portion (15) having the grindstone shaft (12) at the top. An inclination angle θ of an outer peripheral surface of the truncated conical portion (15) with respect to the grindstone shaft (12) (center axis J) is 0° or more and about 20° or less at the top of the truncated conical portion (15). The outer peripheral surface of the truncated conical portion (15) and the outer peripheral surface of the grindstone shaft (12) have a level difference of about 5 mm or less at the top of the truncated conical portion (15).

[0034] If the inclination angle θ of the entire outer peripheral surface of the truncated conical portion (15) is set to 20° or less, the rigidity of the truncated conical portion (15), that is, the base (11), decreases. Thus, as illustrated in FIG. 7, the outer peripheral surface of the truncated conical portion (15) of the base (11) may be formed into a concave surface (15a) to keep a space for disposing the jetting unit (21) with the jetting holes (22) (extension line C) facing the grinding portion of the workpiece (1). This makes it easy to bore the jetting holes (22) in a desired direction with less adverse effects on the rigidity of the base (11), that is, the grindstone (10) with the shaft. For example, the inclination angle θ of the concave surface (15a) of the truncated conical portion (15) with respect to the grindstone shaft (12) (center axis J) may be 0° or more and 20° or less at the top of the truncated conical portion (15), the inclination angle θ may increase from the top to the bottom of the truncated conical portion (15), and the concave surface (15a) may be connected to the outer peripheral surface of the cylindrical portion (16) at the bottom of the truncated conical portion (15) at an angle φ of 40° or more and 90° or less. The angle φ is equal to the inclination angle of the concave surface (15a) with respect to the center axis J of the grindstone shaft (12) at the bottom of the truncated conical portion (15).

[0035] The shape of the base (11) is obtained by combining the truncated conical portion (15) having the outer peripheral surface inclined at an angle of, for example, 45°, with respect to the bottom surface and the cylindrical portion (16) in which the fixing member (14) for fixing the base (11) to the wheel head (20) is inserted. However, in the example shown in FIG. 7, the outer peripheral surface of the truncated conical portion (15) is shaped into the curved concave surface (15a). As illustrated in FIG. 7, when the grindstone (10) with the shaft is viewed from a direction perpendicular to the grindstone shaft (12), a curve (e.g., a parabola or an arc) which is the concave surface (15a) starts to extend from the top of the truncated conical portion (15) having a diameter slightly larger (e.g., by about 1 to 2 mm) than the diameter of the grindstone (13) at an inclination angle θ of about 0° to 20° with respect to the grindstone shaft (12), and the inclination angle θ greatly changes toward the bottom of the truncated conical portion (15). The curve is connected to the outer peripheral surface of the cylindrical portion (16) having a larger diameter than the grindstone (13) at an angle φ of 40° or more and 90° or less.

[0036] The rigidity of the base (11) shaped as shown in FIG. 7 slightly decreases compared to when the outer peripheral surface of the truncated conical portion (15) is not formed into the concave surface (15a). However, the decrease in the rigidity of the base (11) is negligible compared to the increase in the rigidity by shortening the grindstone shaft (12).

[0037] The configuration of the grindstone (10) with the shaft shown in FIG. 7 is an example. The jetting holes (22) can be bored in the desired direction although the entire outer peripheral surface of the truncated conical portion (15) is not formed into the concave surface (15a) as long as the inclination angle θ of the outer peripheral surface of the truncated conical portion (15) with respect to the grindstone shaft (12) (center axis J) is 0° or more and about 20° or less at the top of the truncated conical portion (15) (at an end portion facing the grindstone (13)). Specifically, only the outer peripheral surface of the truncated conical portion (15) around the top may be formed into the concave surface. Alternatively, the outer peripheral surface of the truncated conical portion (15) may include a plurality of flat inclined surfaces having different inclination angles, and only the flat inclined surface near the top of the truncated conical portion (15) may have an inclination angle of 0° or more and about 20° or less.<Position of Jetting Holes>

[0038] The jetting unit (21) and the grindstone (10) with the shaft illustrated in FIG. 8 may be configured as follows so that the grinding fluid discharged from the jetting holes (22) of the jetting unit (21) hits the outer peripheral surface of the grindstone (13).

[0039] The minimum distance L1 between the base (11) and the workpiece (1) during the grinding is equal to or less than 5 mm, for example, 4 mm. The distance L2 between the end surface of the base (11) facing the grindstone (13) and the end surface of the grindstone (13) facing the base (11), that is, the axial length of a portion of the grindstone shaft (12) without the grindstone (13), is, for example, 7.5 mm. Each jetting hole (22) has a diameter of about 2 mm or less, for example, 1 mm. The inclination angle α of the center line (extension line C) of the jetting hole (22) with respect to the grindstone shaft (12) (center axis J) is 20 degrees or less, for example, 16 degrees. The radius D2 of the top of the base (11) is larger than the radius D1 of the grindstone (13) by about 1 to 3 mm. For example, D1 is 5.75 mm, and D2 is 7 mm.

[0040] In the above configuration, the distance L3 between the center of the opening of the jetting hole (22) and the grindstone shaft (12) (center axis J) is set to be larger than "D1 + L2 × tan(α)" (7.85 mm in this example), for example, 8.21 mm. This is because the grinding fluid discharged from the jetting holes (22) does not reach the outer peripheral surface of the grindstone (13) if L3 is less than "D1 + L2 × tan(α)."<Variation of Jetting Unit>

[0041] In the embodiment shown in FIG. 2 or others, the jetting unit (21) is disposed to surround the entire outer periphery of the base (11) (truncated conical portion (15)) of the grindstone (10) with the shaft. This can easily increase the number of jetting holes (22) to be arranged.

[0042] On the other hand, as a variation shown in FIG. 9, the jetting unit (21) is formed in, for example, a semicircular shape or a U-shape, to surround part of the outer periphery of the base (11) (truncated conical portion (15)) (about half of the outer periphery in this example) so as to easily conduct detachment of the jetting unit (21) or the like. If the grinding fluid supply unit (30) is made of a flexible pipe separate from the wheel head (20), the jetting unit (21) may be detached together with the pipe.<Features of Embodiment (and Variation)>

[0043] The grinding method of the embodiment is a method for internal grinding the workpiece (1) by rotating the grindstone (13) attached to the grindstone shaft (12) protruding from the base (11). The distance between the base (11) and the workpiece (1) during the grinding changes, the distance is equal to or less than 5 mm when the innermost portion of the workpiece (1) is ground, and the grinding fluid discharged from the jetting unit (21) disposed to cover the outer peripheral surface of the base (11) is supplied to the grinding portion of the workpiece (1).

[0044] By the grinding method of the embodiment, although the grindstone shaft (12) is shortened to set the distance between the base (11) and the workpiece (1) during the grinding equal to or less than 5 mm, the jetting unit (21) covering the outer peripheral surface of the base (11) can sufficiently supply the grinding fluid to the grinding portion of the workpiece (1). This can reduce grinding burn, and can provide a grindstone with a shaft with longer life by reducing the wear of the grindstone (13). Further, with the grindstone shaft (12) shortened, the machining accuracy can be kept from decreasing due to deflection of the grindstone shaft (12), and the time required for the spark-out grinding can be reduced. This shortens the machining time, that is, improves the machining speed.

[0045] The grinding device (100) of the embodiment performs the internal grinding of the workpiece (1) by rotating the grindstone (13) attached to the grindstone shaft (12) protruding from the base (11). The grinding device (100) includes the jetting unit (21) disposed to cover the outer peripheral surface of the base (11). The jetting unit (21) has the jetting holes (22) for jetting the grinding fluid. The jetting holes (22) are provided in the jetting unit (21) so that the grinding fluid discharged from the jetting holes (22) is supplied to the grinding portion of the workpiece (1).

[0046] In the grinding device (100) of the embodiment, although the grindstone shaft (12) is shortened to set the distance between the base (11) and the workpiece (1) during the grinding equal to or less than 5 mm, the grinding fluid can be sufficiently supplied to the grinding portion of the workpiece (1) from the jetting holes (22) of the jetting unit (21) covering the outer peripheral surface of the base (11). This can reduce grinding burn, and can provide a grindstone with a shaft with longer life by reducing the wear of the grindstone (13). Further, with the grindstone shaft (12) shortened, the machining accuracy can be kept from decreasing due to deflection of the grindstone shaft (12), and the time required for the spark-out grinding can be reduced. This shortens the machining time, that is, improves the machining speed.

[0047] On the other hand, when a supply pipe for the grinding fluid is bent along the axial direction of the grindstone shaft so that the jetting port of the grinding fluid supply pipe is disposed toward the target hole as in the previous manner, the grinding fluid jetting port (31) can be disposed toward the target hole if the grindstone shaft (12) is long as in Comparative Example 1 shown in FIG. 10, but the grinding fluid jetting port (31) cannot be disposed toward the target hole if the grindstone shaft (12) is short as in Comparative Example 2 shown in FIG. 11. In Comparative Examples 1 and 2 shown in FIGS. 10 and 11, the same components as those of the embodiment shown in FIG. 3 are denoted by the same reference numerals. As described above, the grindstone shaft should be kept as short as possible to ensure the rigidity. However, when the distance between the workpiece and the base of the grindstone shaft or the wheel head is about 5 mm or less, the target hole of the workpiece is blocked by the base or the wheel head as in Comparative Example 2 shown in FIG. 11, and the grinding fluid jetting port cannot be appropriately disposed. In this case, the grinding fluid cannot be sufficiently supplied to the grinding portion of the workpiece, causing problems such as grinding burn involving the temperature rise of the grinding portion to 500°C or higher, shortened life of the grindstone, or the like.

[0048] In the grinding device (100) of the embodiment, the plurality of jetting holes (22) each having a small diameter of 2 mm or less may be disposed as the jetting holes (22) near the outer peripheral surface of the base (11). This makes it easy for the grinding fluid discharged from the jetting holes (22) to enter the gap between the inner wall surface of the target hole of the workpiece (1) and the grindstone shaft (12), allowing easy supply of the grinding fluid to the grinding portion of the workpiece (1). In this case, the inclination angle α of the center line (extension line C) of each jetting hole (22) with respect to the grindstone shaft (12) (center axis J) may be 20 degrees or less, and the jetting holes (22) may be bored so that the extension line C hits the outer peripheral surface of the grindstone (13). This allows efficient supply of the grinding fluid to the grinding portion of the workpiece (1) through the gap between the inner wall surface of the target hole of the workpiece (1) and the grindstone shaft (12).

[0049] In the grinding device (100) of the embodiment, the base (11) may include the truncated conical portion (15) having the grindstone shaft (12) at the top, and the inclination angle θ of the outer peripheral surface of the truncated conical portion (15) with respect to the grindstone shaft (12) at the top of the truncated conical portion (15) may be 0° or more and 20° or less. Thus, the jetting holes (22) facing the grinding portion of the workpiece (1) can be easily provided in the jetting unit (21) covering the outer peripheral surface of the truncated conical portion (15).(Other Embodiments)

[0050] It will be understood that the embodiments and variations described above can be modified with various changes in form and details without departing from the spirit and scope of the claims. The foregoing embodiments and variations may be appropriately combined or replaced as appropriate.INDUSTRIAL APPLICABILITY

[0051] As described above, the present disclosure is useful for a grinding method and a grinding device.DESCRIPTION OF REFERENCE CHARACTERS

[0052] 1Workpiece 11Base 12Grindstone Shaft 13Grindstone 15Truncated Conical Portion 21Jetting Unit 22Jetting Hole 100Grinding Device

Examples

embodiment

(Embodiment)

[0019]An embodiment of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to the embodiment shown below, and various changes can be made within the scope without departing from the technical concept of the present disclosure. Since each of the drawings is intended to illustrate the present disclosure conceptually, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for ease of understanding. The numerical values in the following embodiment are merely examples, and the present disclosure is not limited to them.

[0020]As illustrated in FIGS. 1 to 7, a grinding device (100) mainly includes a grindstone (10) with a shaft for internal grinding of a workpiece (1), a wheel head (20) for rotating the grindstone (10) with the shaft, a jetting unit (21) for jetting a grinding fluid, and a grinding fluid supply unit (30) for supplying the grinding fluid to the jetting unit (21).

[0021...

Claims

1. A grinding method for performing internal grinding of a workpiece (1) by rotating a grindstone (13) attached to a grindstone shaft (12) protruding from a base (11), wherein a distance between the base (11) and the workpiece (1) during the grinding changes, and the distance is equal to or less than 5 mm when the innermost portion of the workpiece (1) is ground, and a grinding fluid discharged from a jetting unit (21) disposed to cover an outer peripheral surface of the base (11) is supplied to a grinding portion of the workpiece (1).

2. A grinding device configured to perform internal grinding of a workpiece (1) by rotating a grindstone (13) attached to a grindstone shaft (12) protruding from a base (11), the device comprising: a jetting unit (21) disposed to cover an outer peripheral surface of the base (11) and configured to jet a grinding fluid, wherein the jetting unit (21) is provided with a jetting hole (22) so that the grinding fluid discharged from the jetting unit (21) is supplied to a grinding portion of the workpiece (1).

3. The grinding device of claim 2, wherein the jetting hole (22) includes a plurality of holes (22) each having a small diameter equal to or smaller than 2 mm and disposed near the outer peripheral surface of the base (11).

4. The grinding device of claim 3, wherein a center line of each of the plurality of holes (22) has an inclination angle α of 20 degrees or less with respect to the grindstone shaft (12), and the plurality of holes (22) are bored so that an extension line of the center line hits an outer peripheral surface of the grindstone (13).

5. The grinding device of any one of claims 2 to 4, wherein the base (11) includes a truncated conical portion (15) having the grindstone shaft (12) at the top, and an inclination angle θ of an outer peripheral surface of the truncated conical portion (15) with respect to the grindstone shaft (12) is 0° or more and 20° or less at the top of the truncated conical portion (15).

Images