Tool for finish-processing cylindrical bore and method for finish-processing cylindrical bore

Abstract

To provide a tool for finish-processing a cylindrical bore that can finish-process an inner peripheral surface of a cylindrical bore, which includes an inlet portion and an outlet portion of the cylindrical bore, with high accuracy and with high processing efficiency.SOLUTION: A tool 3 for finish-processing a cylindrical bore is attachably and detachably fixed to a front end in an axial direction of a carbide arbor 2 held by a shrinkage fitting holder 1 when used, and is moved spirally around a center of a cylindrical bore H of a work-piece W while being rotated by a machining center, so as to finish-process an inner peripheral surface of the cylindrical bore H. An outer peripheral cutting edge 24 that finish-processes the inner peripheral surface of the cylindrical bore H is constituted of a straight cutting edge 27, a first inclined cutting edge 28 whose cutting edge diameter gradually reduces from the front end in the axial direction of the straight cutting edge 27 toward a front side in the axial direction, and a second inclined cutting edge 29 whose cutting edge diameter gradually reduces from a rear end in the axial direction of the straight cutting edge 27 toward a rear side in the axial direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a tool for finishing a cylindrical hole and a method for finishing a cylindrical hole using the tool. [Background technology]

[0002] A boring head is generally used when finishing the inner peripheral surface of a cylindrical hole formed in a workpiece (for example, Patent Document 1). An example of a boring head 50 is shown in FIG. 10. The boring head 50 has a tapered shank portion 53 that is inserted and fixed into a tapered hole 52 of a spindle 51 of a machine tool, a rod-shaped shaft portion 54 that extends in the axial direction from the tapered shank portion 53, and a cutting portion 55 provided at the tip of the shaft portion 54. The cutting portion 55 is supported so as to be movable in the radial direction relative to the shaft portion 54, and the radial position of the cutting portion 55 can be adjusted by operating an adjustment screw 56.

[0003] An example of use of the boring head 50 will be described. First, as shown in Fig. 11, the boring head 50 is set on a tool presetter 57, and the adjustment screw 56 of the boring head 50 is operated to adjust the radial position of the cutting edge 55 at the tip of the boring head 50 to a position slightly offset radially inward from the radial position corresponding to the finishing dimension of the inner diameter of the cylindrical hole H of the workpiece W. Next, as shown in Fig. 10, the boring head 50 is set on a spindle 51 of a machine tool, and the boring head 50 is inserted into the cylindrical hole H of the workpiece W while rotating at a fixed position (the center position of the cylindrical hole H), thereby cutting the inner peripheral surface of the cylindrical hole H over the entire axial length.

[0004] Thereafter, the inner diameter of the cylindrical hole H is measured, and the difference between the measured value and the finishing dimension of the inner diameter of the cylindrical hole H is obtained. Then, as shown in FIG. 11, the boring head 50 is set again on the tool presetter 57, and the position of the blade 55 at the tip of the boring head 50 is manually adjusted so that the radial position of the blade 55 at the tip of the boring head 50 moves radially outward by the amount of the difference between the measured value of the inner diameter of the cylindrical hole H and the finishing dimension of the inner diameter of the cylindrical hole H. Thereafter, as shown in FIG. 10, the boring head 50 is set again on the spindle 51 of the machine tool, and the boring head 50 is inserted into the cylindrical hole H of the workpiece W while rotating at a fixed position, thereby cutting the inner peripheral surface of the cylindrical hole H over the entire axial length, and finishing the inner diameter of the cylindrical hole H to a predetermined finishing dimension. As described above, the finishing process of the inner peripheral surface of the cylindrical hole H of the workpiece W is generally performed using the boring head 50. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-079517 A Summary of the Invention [Problem to be solved by the invention]

[0006] As shown in FIGS. 10 and 11, when finishing the inner peripheral surface of a cylindrical hole H using a boring head 50, the following problems arise.

[0007] As shown in FIG. 10, the inner peripheral surface of the cylindrical hole H is cut, and then, as shown in FIG. 11, the position of the cutting edge 55 at the tip of the boring head 50 is moved radially outward by the difference between the measured value of the inner diameter of the cylindrical hole H and the finished dimension of the inner diameter of the cylindrical hole H. This requires human skill to manually adjust the position of the cutting edge 55, and the work takes time. In addition, the process of inserting the boring head 50 into the cylindrical hole H of the workpiece W while rotating it at a fixed position is likely to produce long, continuous chips, which tend to get entangled with the boring head 50 and cause problems such as machine stoppage. In addition, when finishing a plurality of cylindrical holes H with different inner diameters, it is necessary to prepare a plurality of boring heads 50 with different shaft diameters, which is costly.

[0008] Therefore, the inventors of this invention investigated a method that does not require human skill, is less likely to cause machine stoppages due to entanglement of cutting chips, and can finish the inner surfaces of multiple cylindrical holes H with different inner diameters at low cost.

[0009] As a result of this investigation, the inventors came up with the idea of ​​using a combination of a shrink fit holder 60, which fixes a tool by shrink fitting, and a carbide arbor 61 made of cemented carbide, as shown in Figure 12, and finishing the inner surface of a cylindrical hole H in a workpiece W with a tool 62 attached to the axial front end of the carbide arbor 61.

[0010] In other words, by using a combination of a shrink-fit holder 60, which fixes a tool by shrink-fitting, and a carbide arbor 61 formed of a cemented carbide alloy, the shrink-fit holder 60 can significantly reduce tool vibration compared to a typical collet-type holder, and the carbide arbor 61 has significantly higher rigidity in the direction perpendicular to the axis compared to a typical steel arbor. Therefore, the inventors have come up with the idea that by attaching a tool 62 to the axial front end of the carbide arbor 61 held by the shrink-fit holder 60 and rotating the tool 62 in a machining center while moving it spirally around the center of the cylindrical hole H of the workpiece W to finish the inner surface of the cylindrical hole H of the workpiece W, it will be possible to machine the inner surface of the cylindrical hole H of the workpiece W with finishing accuracy (referring to the shape accuracy, dimensional accuracy, surface roughness, etc. after finishing; the same applies below) equal to or greater than that of finishing with a boring head 50.

[0011] However, when the inventors performed finish machining of the inner surface of a cylindrical hole H using a general tool 62 as shown in Figure 12 and evaluated the finishing accuracy, they found that the finishing accuracy of the inner surface of the cylindrical hole H may be reduced at the entrance of the cylindrical hole H (the upper opening of the cylindrical hole H in the figure) and the exit of the cylindrical hole H (the lower opening of the cylindrical hole H in the figure).

[0012] The inventors then investigated the cause of the decrease in finishing accuracy at the entrance and exit of the cylindrical hole H, and found that when the axial front end (lower end in the figure) of the outer cutting edge 63 of the tool 62 begins to cut the inner circumferential surface of the entrance portion of the cylindrical hole H (upper opening portion in the figure), the cutting resistance of the tool 62 increases suddenly, causing the outer cutting edge 63 of the tool 62 to dig deeply into the inner circumferential surface of the entrance portion of the cylindrical hole H, resulting in chattering of the tool 62 and enlargement of the entrance portion of the cylindrical hole H. Also, just before the axial rear end (upper end in the figure) of the outer cutting edge 63 of the tool 62 passes through the exit portion of the cylindrical hole H (lower opening portion in the figure), the deflection of the carbide arbor 61 and the tool 62 suddenly returns to its original state, causing the outer cutting edge 63 of the tool 62 to dig deeply into the inner circumferential surface of the exit portion of the cylindrical hole H, resulting in chattering of the tool 62 and enlargement of the exit portion of the cylindrical hole H, which is the cause of the decrease in finishing accuracy.

[0013] Also, when finishing a cylindrical hole H using a general tool 62 as shown in FIG. 12, a method is considered in which the inner peripheral surface of the cylindrical hole H formed as a pilot hole is first cut with the tool 62 to perform semi-finishing, and then, in a state in which the spiral diameter of the movement of the tool 62 is increased by the amount of the machining allowance for the finish machining, the inner peripheral surface of the cylindrical hole H is again cut with the tool 62 as shown in FIG. 12 to perform finish machining. Semi-finishing is a process for cutting the inner peripheral surface of the cylindrical hole H while leaving the machining allowance for the finish machining in order to perform the subsequent finish machining with high accuracy. In other words, since the cylindrical hole H formed as a pilot hole usually has low shape accuracy, dimensional accuracy, and surface roughness, if the finish machining is performed as it is, the machining allowance of the inner peripheral surface of the cylindrical hole H is not constant, and the cylindrical hole H cannot be finished with high accuracy. Therefore, in order to make the machining allowance of the inner peripheral surface of the cylindrical hole H in the finish machining constant and to finish the cylindrical hole H with high accuracy, semi-finishing is generally performed before the finish machining. Here, the inventors of the present application have also investigated ways to improve the machining efficiency when the above-mentioned semi-finishing and finishing processes are performed.

[0014] The problem to be solved by this invention is to provide a tool for finishing cylindrical holes that is capable of finishing the inner surface of a cylindrical hole, including the entrance and exit portions of the cylindrical hole, with high precision and high machining efficiency. [Means for solving the problem]

[0015] In order to solve the above problems, the present invention provides a tool for finishing a cylindrical hole having the following configuration. [Configuration 1] A cylindrical hole finishing tool that is removably fixed to a tool attachment hole at an axial front end of a carbide arbor held by a shrink fit holder, and that finishes an inner peripheral surface of a cylindrical hole formed in a workpiece by moving the tool in a spiral shape around the center of the cylindrical hole while rotating the workpiece in a machining center, A tool for finishing cylindrical holes, in which an outer cutting edge for finishing the inner surface of the cylindrical hole is composed of a straight blade having a constant cutting edge diameter along the axial direction, a first inclined blade whose cutting edge diameter gradually decreases from the axial front end of the straight blade toward the front in the axial direction, and a second inclined blade whose cutting edge diameter gradually decreases from the axial rear end of the straight blade toward the rear in the axial direction.

[0016] When this configuration is adopted, the outer cutting edge of the finishing tool has a straight blade with a constant cutting edge diameter along the axial direction and a first inclined blade with a cutting edge diameter that gradually decreases from the axial front end of the straight blade toward the axial front, so that when the outer cutting edge of the finishing tool starts to cut the inner peripheral surface of the entrance of the cylindrical hole, the cutting resistance of the finishing tool increases gradually and slowly. Therefore, it is possible to prevent chattering of the tool caused by the outer cutting edge of the finishing tool biting deeply into the inner peripheral surface of the entrance of the cylindrical hole and the enlargement of the entrance of the cylindrical hole. In addition, the outer cutting edge of the finishing tool has a straight blade with a constant cutting edge diameter along the axial direction and a second inclined blade with a cutting edge diameter that gradually decreases from the axial rear end of the straight blade toward the axial rear, so that the bending of the carbide arbor and the finishing tool gradually and slowly returns to normal just before the outer cutting edge of the finishing tool exits the exit of the cylindrical hole. This makes it possible to prevent chattering of the tool caused by the outer cutting edge of the finishing tool biting deeply into the inner peripheral surface of the outlet of the cylindrical hole and to prevent the diameter of the outlet of the cylindrical hole from expanding.

[0017] In addition, the outer cutting edge of the finishing tool has a first inclined blade whose cutting edge diameter gradually decreases from the axial front end of the straight blade toward the axial front, and a second inclined blade whose cutting edge diameter gradually decreases from the axial rear end of the straight blade toward the axial rear. Therefore, it is possible to perform the semi-finishing and finishing of the cylindrical hole with only one reciprocating machining (specifically, an outward semi-finishing process in which the finishing tool is rotated and moved axially forward in a spiral of a constant diameter so that the first inclined blade and straight blade cut the inner surface of the cylindrical hole while passing through the cylindrical hole from the axial rear side to the axial front side, and a return-way finishing process in which, after the outward semi-finishing process, the finishing tool is rotated and moved axially backward in a spiral of a diameter larger than the constant diameter by the amount of the finishing allowance) and it is possible to finish the inner surface of the cylindrical hole with high machining efficiency.

[0018] As described above, by employing the above-described configuration, it is possible to finish the inner peripheral surface of the cylindrical hole, including the entrance and exit portions of the cylindrical hole, with high precision and high machining efficiency.

[0019] In the above configuration, the first inclined blade is not limited to a blade extending linearly, but may include a blade extending curved in a convex arc, a blade extending curved in a concave arc, etc. In short, it is sufficient that the blade extends in a direction in which the cutting edge diameter gradually decreases from the axial front end of the straight blade toward the axial front when viewed from the direction of rotation. Similarly, it is sufficient that the second inclined blade extends in a direction in which the cutting edge diameter gradually decreases from the axial rear end of the straight blade toward the axial rear when viewed from the direction of rotation.

[0020] [Configuration 2] The first inclined blade is gently curved with a radius of curvature greater than the radius of the cutting edge of the straight blade when viewed in the direction of rotation, and is formed such that the angle between the tangent direction of the curve and the axial direction at any position on the curve is 30° or less; The tool for finishing cylindrical holes as described in configuration 1, wherein the second inclined blade is also gently curved with a radius of curvature greater than at least the cutting edge radius of the straight blade when viewed in the direction of rotation, and the angle between the tangent direction of the curve and the axial direction at any position on the curve is 30° or less.

[0021] With this configuration, the first inclined blade is formed in a gentle curve with an angle of 30° or less in the tangential direction with respect to the axial direction, so that chatter of the tool caused by the outer cutting edge of the finishing tool biting deeply into the inner circumferential surface of the entrance portion of the cylindrical hole and enlargement of the diameter of the entrance portion of the cylindrical hole can be effectively prevented. Also, the second inclined blade is formed in a gentle curve with an angle of 30° or less in the tangential direction with respect to the axial direction, so that chatter of the tool caused by the outer cutting edge of the finishing tool biting deeply into the inner circumferential surface of the exit portion of the cylindrical hole and enlargement of the diameter of the exit portion of the cylindrical hole can be effectively prevented.

[0022] [Configuration 3] The first inclined blade is formed in a straight line inclined at an angle of 30° or less with respect to the axial direction, 2. The tool for finishing a cylindrical hole according to claim 1, wherein the second inclined blade is also formed linearly and inclined at an angle of 30° or less with respect to the axial direction.

[0023] With this configuration, the first inclined blade is formed in a straight line inclined at an angle of 30° or less with respect to the axial direction, so that chatter of the tool caused by the outer cutting edge of the finishing tool biting deeply into the inner peripheral surface of the entrance portion of the cylindrical hole and enlargement of the diameter of the entrance portion of the cylindrical hole can be effectively prevented. Also, the second inclined blade is formed in a straight line inclined at an angle of 30° or less with respect to the axial direction, so that chatter of the tool caused by the outer cutting edge of the finishing tool biting deeply into the inner peripheral surface of the exit portion of the cylindrical hole and enlargement of the diameter of the exit portion of the cylindrical hole can be effectively prevented.

[0024] [Configuration 4] A tool for finishing a cylindrical hole according to any one of configurations 1 to 3, wherein the first inclined blade and the second inclined blade are formed symmetrically with respect to a virtual plane perpendicular to the axial direction.

[0025] When this configuration is adopted, the first inclined blade and the second inclined blade have a symmetrical shape, so that stable machining is possible when performing reciprocating machining (specifically, a semi-finishing process on the outward path in which the finishing tool is rotated so that the first inclined blade and the straight blade cut the inner surface of the cylindrical hole while passing through the cylindrical hole from the axial rear side to the axial front side and moved in a spiral of a constant diameter toward the axial front, and a finishing process on the return path in which, after the semi-finishing process on the outward path, the finishing tool is rotated so that the second inclined blade and the straight blade cut the inner surface of the cylindrical hole while passing through the cylindrical hole from the axial front side to the axial front side and moved in a spiral of a diameter larger than the constant diameter by the amount of the finishing machining allowance).

[0026] [Configuration 5] The finishing tool for cylindrical holes according to any one of configurations 1 to 4, has a single insert tip in which the outer cutting edge is formed at two locations circumferentially spaced 180° apart, and a tool body to which the insert tip is attached.

[0027] This configuration uses a single insert tip with two outer cutting edges spaced 180° apart in the circumferential direction, making it easy to position the insert tip radially, and therefore makes it possible to finish the inner surface of a cylindrical hole with high precision without requiring human skill.

[0028] [Configuration 6] The tool for finishing a cylindrical hole according to configuration 5, wherein the tool body has a radial positioning fitting shaft portion that fits into the tool mounting hole at the axial front end of the carbide arbor to position it in the radial direction, and a threaded shaft portion that extends axially rearward from the axial rear end of the fitting shaft portion.

[0029] With this configuration, when the tool body is fixed to the axial front end of the carbide arbor, the fitting shaft of the tool body fits into the tool mounting hole of the carbide arbor, automatically positioning the finishing tool in the radial direction. This makes it possible to finish the inner surface of a cylindrical hole with high precision without requiring human skill.

[0030] The present invention also provides a method for finishing a cylindrical hole using the above-mentioned finishing tool, which has the following configuration. [Configuration 7] A method for finishing an inner peripheral surface of a cylindrical hole formed in a workpiece, comprising the steps of: a shrink fit holder having a chuck cylinder portion whose axial front end is open and a tapered shank portion that is inserted into and fixed to a tapered hole in a spindle of a machining center; a cemented carbide arbor having a base end portion inserted into the chuck cylinder portion and fixed thereto by shrink fitting, a rod-shaped shaft portion extending axially forward from the base end portion outside the chuck cylinder portion, and a tool attachment hole opening at an axial front end of the shaft portion; A tool for finishing a cylindrical hole according to any one of configurations 1 to 6, which is removably fixed to the tool mounting hole at the axial front end of the carbide arbor; A cylindrical hole finishing method in which the finishing tool is rotated in the machining center while being moved spirally around the center of the cylindrical hole in the workpiece, thereby finishing the inner surface of the cylindrical hole.

[0031] By adopting this configuration, the shrink fit holder can suppress the tool runout significantly smaller than a general collet type holder, and the carbide arbor has a significantly higher rigidity in the axial direction than a general steel arbor, so that the inner surface of the cylindrical hole of the workpiece can be machined to a specified inner diameter with finishing accuracy equal to or higher than that of finishing with a boring head. In addition, the spiral diameter when the finishing tool moves in a spiral shape can be automatically adjusted by the numerical control of the machining center so that the inner diameter of the cylindrical hole of the workpiece becomes a specified finishing dimension. Therefore, manual adjustment of the position of the blade is not required, and no human skill is required. In addition, since the finishing tool moves in a spiral shape around the center of the cylindrical hole of the workpiece while rotating, the chips when machining the inner surface of the cylindrical hole of the workpiece are broken into small pieces, and long connected chips are less likely to be generated. Therefore, machine stoppage due to entanglement of chips is less likely to occur. In addition, when finishing cylindrical holes of multiple workpieces with different inner diameters, the spiral diameter when the finishing tool moves in a spiral shape can be changed by the numerical control of the machining center, so that the cylindrical holes of multiple workpieces with different inner diameters can be finished, which is low cost.

[0032] [Configuration 8] an intermediate finishing process in which the finishing tool is rotated and moved in a spiral shape of a constant diameter toward the axial front side so that the first inclined blade and the straight blade cut the inner peripheral surface of the cylindrical hole and pass through the cylindrical hole from the axial rear side to the axial front side; The cylindrical hole finishing method described in configuration 7, in which after the intermediate finishing process on the outward path, a return finishing process is performed in which the finishing tool is rotated and moved axially rearward in a spiral shape with a diameter larger than the constant diameter by the amount of the finishing allowance while passing through the cylindrical hole from the axial front side to the axial rear side while the second inclined blade and the straight blade cut the inner surface of the cylindrical hole.

[0033] By adopting this configuration, semi-finishing and finishing of the cylindrical hole can be performed by simply inserting the finishing tool into the cylindrical hole of the workpiece once, making it possible to finish the inner surface of the cylindrical hole with high machining efficiency.

[0034] [Configuration 9] A method for finishing a cylindrical hole as described in configuration 8, in which the axial length of the straight blade is set to a length equal to or greater than the lead length of the spiral when the finishing tool is moved in a spiral manner in the intermediate finishing process on the outward path, and equal to or greater than the lead length of the spiral when the finishing tool is moved in a spiral manner in the finishing process on the return path.

[0035] When this configuration is adopted, the axial length of the straight blade is greater than or equal to the spiral lead length of the finishing tool when it moves spirally in the intermediate finishing process on the outbound path, and greater than or equal to the spiral lead length of the finishing tool when it moves spirally in the finishing process on the return path.Therefore, the axial machining range of the straight blade before the finishing tool has made one spiral movement overlaps with the axial machining range of the straight blade after the finishing tool has made one spiral movement, thereby making it possible to effectively improve the shape accuracy and surface roughness of the inner surface of the cylindrical hole. Effect of the Invention

[0036] The cylindrical hole finishing tool of the present invention is capable of finishing the inner peripheral surface of a cylindrical hole, including the entrance and exit portions of the cylindrical hole, with high precision and high machining efficiency. [Brief description of the drawings]

[0037] [Figure 1] FIG. 1 is a partial cross-sectional view showing a state in which the cylindrical hole inner surface is finished using a cylindrical hole finishing tool according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged view of the finish machining tool of FIG. 1 and its surroundings. [Diagram 3] A view of the finishing tool shown in Figure 2 from the axial front side. [Figure 4] A view of the vicinity of the outer cutting edge of the finishing tool shown in Figure 2 when starting to cut the inner surface of the entrance of the cylindrical hole shown in Figure 1, viewed from the direction of rotation. [Diagram 5] The finishing tool shown in Figure 4 cuts the inner surface of the cylindrical hole while moving forward in the axial direction, and is positioned in the middle of the cylindrical hole shown in Figure 1. This is a view of the vicinity of the outer cutting edge of the finishing tool as seen from the direction of rotation. [Figure 6] The view of the vicinity of the outer cutting edge of the finishing tool shown in Figure 5, seen from the direction of rotation, when the finishing tool moves further forward in the axial direction while cutting the inner surface of the cylindrical hole and is in a position just before passing through the exit part of the cylindrical hole shown in Figure 1. [Figure 7] This is a view of the vicinity of the peripheral cutting edge of the finishing tool shown in Figure 6, viewed from the direction of rotation, just before the finishing tool moves axially backward after passing through the exit of the cylindrical hole and starts cutting the inner surface of the cylindrical hole again. [Figure 8] FIG. 3 is an enlarged view of the axial front end of a finishing tool showing a modified example of the peripheral cutting edge shown in FIG. [Figure 9] FIG. 3 is an enlarged view of an axial front end portion of a finishing tool showing another modified example of the peripheral cutting edge shown in FIG. [Figure 10] A partial cross-sectional view showing the state in which the inner surface of a cylindrical hole is finished using a conventional boring head. [Figure 11] FIG. 11 shows how the position of the cutting edge of the boring head shown in FIG. 10 is adjusted by a tool presetter. [Figure 12] FIG. 11 is a partial cross-sectional view showing a state in which the inner peripheral surface of a cylindrical hole is finished using a tool of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] FIG. 1 shows a state in which a shrink fit holder 1, a carbide arbor 2 held by the shrink fit holder 1, and a finishing tool 3 according to an embodiment of the present invention are used to finish the inner surface of a cylindrical hole H formed through a workpiece W.

[0039] The shrink fit holder 1 has a flange portion 4, a tapered shank portion 5 extending axially rearward (upward in the figure) from the flange portion 4, and a chuck cylinder portion 6 extending axially forward (downward in the figure) from the flange portion 4. A circumferential groove 7 is formed on the outer periphery of the flange portion 4 for gripping with a tool changing manipulator (not shown) of a machining center.

[0040] The tapered shank portion 5 is a part that is inserted and fixed into a tapered hole 9 of a spindle 8 of a machining center. The machining center used is one that is capable of simultaneously controlling the movement in a total of three axial directions: the Z-axis direction (up and down direction in the figure), which is the axial direction of the spindle 8, the X-axis direction (left and right direction in the figure), which is perpendicular to the Z-axis direction, and the Y-axis direction (direction perpendicular to the paper surface in the figure).

[0041] The chuck cylinder portion 6 is formed in a cylindrical shape with an opening at its axial front end (the lower end in the drawing). The tapered shank portion 5, the flange portion 4, and the chuck cylinder portion 6 are integrally formed from a steel material. The steel material constituting the chuck cylinder portion 6 is preferably a steel material (e.g., austenitic steel) having a larger linear expansion coefficient than the steel materials constituting the flange portion 4 and the tapered shank portion 5, and the two are preferably integrated together by welding or the like.

[0042] The carbide arbor 2 has a base end 10 that is inserted into the chuck cylinder 6 of the shrink fit holder 1 and fixed by shrink fit, a rod-shaped shaft portion 11 that extends axially forward (downward in the figure) from the base end 10 outside the chuck cylinder 6, and a tool attachment hole 12 that opens at the axial front end (lower end in the figure) of the shaft portion 11. The base end 10 and the shaft portion 11 are cylindrical and elongated in the axial direction, and are integrally formed from cemented carbide. In the figure, a carbide arbor 2 in which the outer diameter of the shaft portion 11 is slightly smaller than the outer diameter of the base end 10 is shown, but it is also possible to use a carbide arbor 2 in which the outer diameter of the shaft portion 11 and the outer diameter of the base end 10 are the same size.

[0043] As shown in FIG. 2, tool mounting hole 12 has a threaded hole portion 13 having a female thread on its inner circumference, and a mating hole portion 14 formed on the axial front end side (the lower end in the figure) of shaft portion 11 relative to threaded hole portion 13.

[0044] The finishing tool 3 is detachably fixed to a tool mounting hole 12 at the axial front end (lower end in the figure) of the carbide arbor 2. The finishing tool 3 has a tool body 15 and an insert tip 16 attached to the tool body 15. The tool body 15 has an engagement shaft portion 17 extending axially rearward (upward in the figure) from the tool body 15, and a threaded shaft portion 18 extending axially rearward from the axial rear end (upper end in the figure) of the engagement shaft portion 17. The threaded shaft portion 18 is threadedly engaged with the threaded hole portion 13 of the tool mounting hole 12. The engagement shaft portion 17 is engaged with the engagement hole portion 14 of the tool mounting hole 12 to position the tool body 15 in the radial direction.

[0045] 2 and 3, the tool body 15 is formed with a pair of opposed pieces 19 that protrude forward in the axial direction. The pair of opposed pieces 19 face each other in a direction perpendicular to the axis, sandwiching the rotation center of the finishing tool 3 therebetween, and the insert tip 16 is inserted between the pair of opposed pieces 19. The insert tip 16 is fixed to the pair of opposed pieces 19 by tightening bolts 20. The insert tip 16 is made of cemented carbide.

[0046] 3, one of the pair of opposing pieces 19 is formed with a screw hole 21 that is threadedly engaged with the screw shaft of the bolt 20, and the other opposing piece 19 is formed with a seat surface 22 on which the head of the bolt 20 sits. The insert tip 16 is formed with a through hole 23 through which the bolt 20 is inserted.

[0047] The insert tip 16 has two outer cutting edges 24 formed at 180° intervals in the circumferential direction. The outer cutting edge 24 is an intersecting ridge between a rake face 25 facing forward in the rotation direction of the finishing tool 3 and a clearance face 26 facing radially outward, and this portion cuts the inner circumferential surface of the cylindrical hole H of the workpiece W, as shown in FIG.

[0048] As shown in Figure 4, the peripheral cutting edge 24 is composed of a straight blade 27 having a constant cutting edge diameter along the axial direction, a first inclined blade 28 having a cutting edge diameter that gradually decreases from the axial front end of the straight blade 27 toward the front in the axial direction, and a second inclined blade 29 having a cutting edge diameter that gradually decreases from the axial rear end of the straight blade 27 toward the rear in the axial direction.

[0049] The axial length of the straight blade 27 is set to be equal to or greater than the lead length of the spiral when the finishing tool 3 is moved in a spiral manner in the semi-finishing machining process on the outward path described below, and specifically, when the lead length of the spiral when the finishing tool 3 is moved in a spiral manner is 1 mm or less, the axial length of the straight blade 27 is set to be equal to or greater than 1 mm (preferably equal to or greater than 2 mm). Also, the radial width of the first inclined blade 28 is set to be equal to or greater than the cutting depth (machining allowance) when cutting the inner circumferential surface of the cylindrical hole H in the semi-finishing machining process on the outward path described below, and specifically, to be equal to or greater than 0.1 mm.

[0050] The first inclined blade 28 is formed in a straight line, inclined at an angle of 3° or more and 30° or less (preferably 15° or less, more preferably 10° or less) with respect to the axial direction, and the second inclined blade 29 is also formed in a straight line, inclined at an angle of 3° or more and 30° or less (preferably 15° or less, more preferably 10° or less) with respect to the axial direction.

[0051] Here, the first inclined blade 28 and the second inclined blade 29 are described as being linear when viewed in the direction of rotation as shown in Fig. 4, but the first inclined blade 28 and the second inclined blade 29 may be gently curved with a large radius of curvature when viewed in the direction of rotation. In this case, the first inclined blade 28 and the second inclined blade 29 are gently curved (e.g., gently convex arc) with a radius of curvature greater than at least 1 time (preferably 1.5 times, more preferably 2 times (= cutting edge diameter)) the cutting edge radius of the straight blade 27, and are preferably formed so that the angle that the tangent direction of the curve forms with the axial direction is 30° or less (preferably 15° or less, more preferably 10° or less) at any position where semi-finishing or finishing is performed, which will be described later.

[0052] In addition, the first inclined blade 28 and the second inclined blade 29 may be curved in a convex arc shape as shown in Figure 8, or may be curved in a concave arc shape as shown in Figure 9.

[0053] As shown in FIG. 4, the first inclined blade 28 and the second inclined blade 29 are formed symmetrically with respect to an imaginary plane perpendicular to the axial direction (the vertical direction in the drawing).

[0054] An example of a finishing method for finishing the inner surface of the cylindrical hole H of the workpiece W shown in FIG. 1 using the above-mentioned shrink fit holder 1, carbide arbor 2, and finishing tool 3 will be described.

[0055] 1 is rotated to rotate the finishing tool 3, while the machining center simultaneously controls the XYZ three axes to move the finishing tool 3 in a spiral shape around the center of the cylindrical hole H in the workpiece W, cutting the inner surface of the cylindrical hole H over the entire axial length (rough machining). At this time, cutting is performed so that the inner diameter of the cylindrical hole H after cutting is slightly smaller than the finishing dimension (target dimension).

[0056] After that, the inner diameter of the cylindrical hole H is measured with a touch probe (not shown) of the machining center. After that, by again rotating the spindle 8 shown in Fig. 1 to rotate the finishing tool 3 as shown in Fig. 2, the finishing tool 3 is moved spirally around the center of the cylindrical hole H of the workpiece W by simultaneous three-axis control of XYZ of the machining center, thereby cutting the inner surface of the cylindrical hole H over the entire axial length, and the inner diameter of the cylindrical hole H is made to match the finishing dimension (target dimension).

[0057] This machining is performed by reciprocating machining. That is, as shown in Fig. 4 to Fig. 6, first, a semi-finishing machining process is performed on the way to the front of the cylindrical hole H in the axial direction (downward in the figure) while rotating the finishing tool 3 so that the first inclined blade 28 and the straight blade 27 cut the inner peripheral surface of the cylindrical hole H and pass through the cylindrical hole H from the axial rear side (upper side in the figure) to the axial front side (lower side in the figure). Then, as shown in Fig. 7, a finishing machining process is performed on the way to the back, in which the finishing tool 3 is rotated and moved spirally toward the rear of the axial direction (upper side in the figure) so that the second inclined blade 29 and the straight blade 27 cut the inner peripheral surface of the cylindrical hole H and pass through the cylindrical hole H from the axial front side (lower side in the figure) to the axial rear side (upper side in the figure).

[0058] Here, when the finishing tool 3 is moved in a spiral shape in the return finish machining step, the spiral diameter of the movement of the finishing tool 3 is set to be larger than the spiral diameter when the finishing tool 3 is moved in a spiral shape in the outward semi-finish machining step by an amount corresponding to the finishing machining allowance (radius of about 0.03 mm to 0.1 mm). By performing this return finish machining step, the uncut portion on the inner peripheral surface of the cylindrical hole H caused by slight bending of the carbide arbor 2 and the tool 3 in the outward semi-finish machining step can be removed, and the accuracy of the inner diameter dimension of the cylindrical hole H can be improved.

[0059] When the inner surface of the cylindrical hole H is finished using the above method, the shrink-fit holder 1 shown in Figure 1 is able to significantly reduce tool runout compared to a typical collet-type holder, and the carbide arbor 2 has significantly higher rigidity perpendicular to the axis compared to a typical steel arbor, so the inner surface of the cylindrical hole H in the workpiece W can be finished to the specified inner diameter with accuracy equal to or greater than that achieved by finishing with a boring head.

[0060] Furthermore, when the inner surface of the cylindrical hole H is finished using the above method, the spiral diameter when the finishing tool 3 moves in a spiral shape can be automatically adjusted by the numerical control of the machining center so that the inner diameter of the cylindrical hole H in the workpiece W shown in Figure 1 has a specified finishing dimension. Therefore, there is no need to manually adjust the position of the cutting edge, and no human skill is required.

[0061] Furthermore, when the inner periphery of the cylindrical hole H is finished by the above method, the finishing tool 3 shown in Fig. 1 is rotated while moving in a spiral around the center of the cylindrical hole H in the workpiece W, so that the chips produced when machining the inner periphery of the cylindrical hole H in the workpiece W are broken into small pieces and long continuous chips are unlikely to be produced. Therefore, machine stoppages due to entanglement of chips are unlikely to occur.

[0062] Furthermore, when finishing cylindrical holes H of multiple workpieces W having different inner diameters, the spiral diameter when the finishing tool 3 moves in a spiral shape can be changed by the numerical control of the machining center, thereby making it possible to finish cylindrical holes H of multiple workpieces W having different inner diameters. Therefore, the cost is low.

[0063] Furthermore, when the inner surface of the cylindrical hole H is finished using the above-described method, as shown in Figures 4 to 7, semi-finishing and finishing of the cylindrical hole H in the workpiece W can be performed by simply inserting the finishing tool 3 into the cylindrical hole H in the workpiece W once, making it possible to finish the inner surface of the cylindrical hole H with high machining efficiency.

[0064] As shown in Fig. 2, the finishing tool 3 of this embodiment has a peripheral cutting edge 24 that has a straight edge 27 with a constant cutting edge diameter along the axial direction and a first inclined edge 28 with a cutting edge diameter that gradually decreases from the axial front end of the straight edge 27 toward the axial front, so that as shown in Fig. 4, when the peripheral cutting edge 24 starts to cut the inner peripheral surface of the entrance portion of the cylindrical hole H, the cutting resistance gradually increases slowly. Therefore, it is possible to prevent chattering of the tool 3 and expansion of the diameter of the entrance portion of the cylindrical hole H caused by the peripheral cutting edge 24 deeply biting into the inner peripheral surface of the entrance portion of the cylindrical hole H.

[0065] In addition, as shown in FIG. 2, the outer peripheral cutting edge 24 of the finishing tool 3 has a straight blade 27 with a constant cutting edge diameter along the axial direction and a second inclined blade 29 with a cutting edge diameter gradually decreasing from the axial rear end of the straight blade 27 toward the axial rear, so that the flexure of the carbide arbor 2 and the finishing tool 3 gradually and slowly returns to normal just before the outer peripheral cutting edge 24 exits the exit portion of the cylindrical hole H, as shown in FIG. 6. This makes it possible to prevent chattering of the tool 3 and expansion of the diameter of the exit portion of the cylindrical hole H caused by the outer peripheral cutting edge 24 deeply biting into the inner peripheral surface of the exit portion of the cylindrical hole H. Therefore, it is possible to accurately finish the inner peripheral surface of the cylindrical hole H, including the entrance portion and the exit portion of the cylindrical hole H.

[0066] As shown in FIG. 2, the outer peripheral cutting edge 24 of the finishing tool 3 has a first inclined blade 28 whose cutting edge diameter gradually decreases from the axial front end of the straight blade 27 toward the axial front, and a second inclined blade 29 whose cutting edge diameter gradually decreases from the axial rear end of the straight blade 27 toward the axial rear. Therefore, one reciprocating machining (specifically, a cutting edge 29 is moved forward in the axial direction while rotating the finishing tool 3 so that the first inclined blade 28 and the straight blade 27 pass through the cylindrical hole H from the axial rear side (upper side in the figure) to the axial front side (lower side in the figure) while cutting the inner peripheral surface of the cylindrical hole H) is performed. The semi-finishing and finishing of cylindrical hole H can be performed simply by performing the semi-finishing on the outward path, in which the second inclined blade 29 and the straight blade 27 are moved in a spiral shape of a constant diameter by rotating the finishing tool 3 so that they pass through the cylindrical hole H from the axial front side (the bottom side in the figure) to the axial rear side (the top side in the figure) while cutting the inner surface of the cylindrical hole H, and then performing the finishing on the return path, in which the second inclined blade 29 and the straight blade 27 are moved in a spiral shape of a diameter larger than the constant diameter by the amount of the finishing machining allowance while rotating the finishing tool 3, and it is possible to finish the inner surface of the cylindrical hole H with high machining efficiency.

[0067] Furthermore, this finishing tool 3 has the first inclined blade 28 shown in Figure 2 formed in a straight line inclined at an angle of 30° or less (preferably 15° or less, and more preferably 10° or less) with respect to the axial direction, so that when the outer cutting edge 24 begins to cut the inner surface of the entrance portion of the cylindrical hole H, as shown in Figure 4, it is possible to effectively prevent vibration of the tool 3 and expansion of the entrance portion of the cylindrical hole H caused by the outer cutting edge 24 biting deeply into the inner surface of the entrance portion of the cylindrical hole H.

[0068] In addition, this finishing tool 3 has the second inclined blade 29 shown in Figure 2 formed in a straight line inclined at an angle of 30° or less (preferably 15° or less, more preferably 10° or less) with respect to the axial direction, so that, as shown in Figure 6, it is possible to effectively prevent vibration of the tool 3 and expansion of the exit portion of the cylindrical hole H caused by the outer cutting edge 24 deeply biting into the inner surface of the exit portion of the cylindrical hole H just before the outer cutting edge 24 passes through the exit portion of the cylindrical hole H.

[0069] In addition, since the first inclined blade 28 and the second inclined blade 29 of this finishing tool 3 have a symmetrical shape as shown in FIG. 2, stable machining is possible when performing reciprocating machining as shown in FIGS. 4 to 7.

[0070] 3, the finishing tool 3 uses a single insert tip 16 on which two outer peripheral cutting edges 24 are formed at 180° intervals in the circumferential direction, making it easy to position the insert tip 16 in the radial direction. Therefore, it is possible to finish the inner peripheral surface of the cylindrical hole H with high precision without requiring human skill.

[0071] 2, when the tool body 15 of the finishing tool 3 is fixed to the axial front end of the carbide arbor 2, the fitting shaft portion 17 of the tool body 15 fits into the tool mounting hole 12 of the carbide arbor 2, so that the finishing tool 3 is automatically positioned in the radial direction. Therefore, the inner peripheral surface of the cylindrical hole H can be finished with high precision without requiring human skill.

[0072] In addition, the axial length of the straight blade 27 of the outer cutting edge 24 shown in Figure 2 of this finishing tool 3 is greater than or equal to the spiral lead length when the finishing tool 3 moves spirally in the intermediate finishing process on the outward path, and greater than or equal to the spiral lead length when the finishing tool 3 moves spirally in the finishing process on the return path. Therefore, the axial machining range of the straight blade 27 before the finishing tool 3 moves one spiral revolution overlaps with the axial machining range of the straight blade 27 after the finishing tool 3 has moved one spiral revolution. As a result, it is possible to effectively improve the shape accuracy and surface roughness of the inner surface of the cylindrical hole H.

[0073] In the above embodiment, in order to effectively prevent vibration of the tool 3 and expansion of the entrance and exit portions of the cylindrical hole H, the first inclined blade 28 and the second inclined blade 29 are formed in a straight line inclined at an angle of 30° or less (preferably 15° or less, more preferably 10° or less) with respect to the axial direction when viewed from the direction of rotation. However, even if the first inclined blade 28 and the second inclined blade 29 are formed in a gentle curve such that the tangent angle with the axial direction when viewed from the direction of rotation is 30° or less (preferably 15° or less, more preferably 10° or less), it is possible to effectively prevent vibration of the tool 3 and expansion of the entrance and exit portions of the cylindrical hole H caused by the outer cutting edge 24 deeply digging into the inner surface of the entrance and exit portions of the cylindrical hole H. [Explanation of symbols]

[0074] 1 Shrink fit holder 2 Carbide Arbor 3. Tools for finishing cylindrical holes 5 Tapered shank 6 Chuck barrel 8 main axis 9 Tapered hole 10 Proximal end 11 Shaft 12 Tool mounting hole 15 Tool body 16 Insert Chip 17 Mating shaft 18 Screw shaft 24 Peripheral cutting edge 27 Straight blade 28 1st inclined blade 29 2nd inclined blade Double work H Cylindrical bore

Claims

1. A cylindrical hole finishing tool that is removably fixed to a tool attachment hole (12) at an axial front end of a carbide arbor (2) held by a shrink fit holder (1), and that finishes an inner peripheral surface of a cylindrical hole (H) formed in a workpiece (W) by moving the tool in a spiral shape around the center of the cylindrical hole (H) while rotating the workpiece in a machining center, A tool for finishing cylindrical holes, in which an outer cutting edge (24) for finishing the inner surface of the cylindrical hole (H) is composed of a straight blade (27) having a constant cutting edge diameter along the axial direction, a first inclined blade (28) whose cutting edge diameter gradually decreases from the axial front end of the straight blade (27) toward the front in the axial direction, and a second inclined blade (29) whose cutting edge diameter gradually decreases from the axial rear end of the straight blade (27) toward the rear in the axial direction.

2. The first inclined blade (28) is gently curved with a radius of curvature larger than the cutting edge radius of at least the straight blade (27) when viewed in the direction of rotation, and is formed so that the angle between the tangent direction of the curve and the axial direction at any position on the curve is 30° or less; 2. A tool for finishing cylindrical holes as described in claim 1, wherein the second inclined blade (29) is also gently curved with a radius of curvature larger than at least the cutting edge radius of the straight blade (27) when viewed in the direction of rotation, and is formed so that the angle between the tangent direction of the curve and the axial direction at any position on the curve is 30° or less.

3. The first inclined blade (28) is formed in a straight line inclined at an angle of 30° or less with respect to the axial direction, 2. The tool for finishing a cylindrical hole according to claim 1, wherein the second inclined blade (29) is also formed linearly inclined at an angle of 30 degrees or less with respect to the axial direction.

4. 4. The tool for finishing a cylindrical hole according to claim 1, wherein the first inclined blade (28) and the second inclined blade (29) are formed symmetrically with respect to an imaginary plane perpendicular to the axial direction.

5. The finishing tool for cylindrical holes as described in any one of claims 1 to 3 has a single insert chip (16) in which the outer cutting edge (24) is formed at two locations circumferentially spaced 180° apart, and a tool body (15) to which the insert chip (16) is attached.

6. 6. The tool for finishing a cylindrical hole as described in claim 5, wherein the tool body (15) has a radial positioning fitting shaft portion (17) that fits into the tool mounting hole (12) at the axial front end of the carbide arbor (2) to position it in the radial direction, and a threaded shaft portion (18) that extends axially rearward from the axial rear end of the fitting shaft portion (17).

7. A method for finishing an inner peripheral surface of a cylindrical hole (H) formed in a workpiece (W), comprising the steps of: A shrink fit holder (1) having a chuck cylinder portion (6) whose axial front end is open and a tapered shank portion (5) inserted into and fixed to a tapered hole (9) of a spindle (8) of a machining center; a cemented carbide arbor (2) having a base end (10) inserted into the chuck cylinder portion (6) and fixed by shrink fitting, a rod-shaped shaft portion (11) extending axially forward from the base end (10) outside the chuck cylinder portion (6), and a tool attachment hole (12) opening at the axial front end of the shaft portion (11); a cylindrical hole finishing tool (3) according to any one of claims 1 to 3, which is detachably fixed to the tool mounting hole (12) at the axial front end of the carbide arbor (2); A cylindrical hole finishing method in which the inner surface of the cylindrical hole (H) of the workpiece (W) is finished by rotating the finishing tool (3) in the machining center while moving it spirally around the center of the cylindrical hole (H).

8. an intermediate finishing process in which the finishing tool (3) is rotated and moved axially forward in a spiral shape of a constant diameter so that the first inclined blade (28) and the straight blade (27) cut the inner peripheral surface of the cylindrical hole (H) and pass through the cylindrical hole (H) from the axial rear side to the axial front side; 8. The method for finishing a cylindrical hole as described in claim 7, wherein after the intermediate finishing process on the outward path, a finishing process on the return path is performed in which the finishing tool (3) is rotated and moved axially rearward in a spiral shape with a diameter larger than the constant diameter by an amount corresponding to a finishing machining allowance, so that the second inclined blade (29) and the straight blade (27) cut the inner surface of the cylindrical hole (H) while passing through the cylindrical hole (H) from the axial front side to the axial rear side.

9. 9. The method for finishing a cylindrical hole as described in claim 8, wherein the axial length of the straight blade (27) is set to a length equal to or greater than the lead length of the spiral when the finishing tool (3) is moved in a spiral manner in the intermediate finishing processing step on the outward path, and equal to or greater than the lead length of the spiral when the finishing tool (3) is moved in a spiral manner in the finishing processing step on the return path.

Images