JP7814775B2 - Skiving tools, devices and methods - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. Name of the meeting: 2023 Autumn Meeting of the Japan Society for Precision Engineering. Date held: September 15, 2023. Date of publication of the conference proceedings on the website: August 31, 2023. Address of publication: https://2023-09autumn.jspe.or.jp/proceedings/

Embodiments of the present invention relate to skiving tools, devices, and methods.

A known method for cutting the rotationally symmetric surface of a rotating workpiece (object to be machined) is the skiving method, in which a cutting edge (straight blade) positioned at an angle to the workpiece's axis of rotation is introduced along the rotating workpiece in a linear feed motion that crosses the axis of rotation while making contact with the workpiece. When cutting the workpiece using this method, the inclination angle of the straight blade relative to the axis of rotation is set to a range greater than 0° and less than 90°.

Patent Document 1 discloses a technology for reducing the surface roughness of the outer peripheral surface of a workpiece cut by skiving using a straight blade.

Patent No. 6428919

However, when skiving using a straight blade, it is necessary to control three axes: the extension direction of the workpiece's rotation axis (Z-axis), the direction in which the cutting tool cuts into the workpiece (X-axis), and the tangential direction (Y-axis) perpendicular to both the Z-axis and X-axis. On the other hand, a typical lathe machine tool performs cutting using two-axis control. In other words, there is no Y-axis direction, and cutting is performed by controlling the feed rate in the Z-axis and the depth of cut in the X-axis.

This invention was developed through extensive research focused on these issues, and its purpose is to provide a machining technology that enables skiving to be performed even on two-axis controlled lathe machine tools.

To solve the above problem, the present invention provides a skiving tool equipped with a helical blade, which performs skiving without using both ends of the cutting edge of the helical blade.

The present invention is a skiving device that uses a machine tool equipped with a chuck that rotatably holds a workpiece on a first axis and a tool rest that mounts a skiving tool having a helical blade, and that sets the feed rate of the helical blade in the first axial direction and the cutting depth of the helical blade in a second axis perpendicular to the first axial direction, and the skiving tool performs skiving without using both ends of the cutting edge of the helical blade.

The present invention is a skiving method using a machine tool equipped with a chuck that rotatably holds a workpiece on a first axis and a tool rest to which a skiving tool having a twisted blade is attached. The skiving method involves fixing the workpiece to the chuck, rotating the chuck, aligning the skiving tool with the first axis, setting the feed rate of the twisted blade in the first axial direction, and setting the cutting depth of the twisted blade in a second axis perpendicular to the first axial direction.

The present invention provides a machining technology that enables skiving to be performed even on two-axis controlled lathe machine tools.

1 is a perspective view of a cutting tool according to a first embodiment of the present invention; 3A to 3C are diagrams illustrating a method for manufacturing a twisted blade according to the first embodiment of the present invention. 1 is a diagram illustrating skiving using a twisted blade according to a first embodiment of the present invention. FIG. FIG. 4 is an enlarged view of a part of FIG. 3. 3A and 3B are diagrams for explaining the contact area of the blade according to the degree of twist of the twisted blade according to the first embodiment of the present invention. FIG. 1 is a front view of a skiving device according to a first embodiment of the present invention. 1 is a flowchart of a skiving method according to a first embodiment of the present invention. 10A to 10C are diagrams illustrating a method for manufacturing a twisted blade according to a second embodiment of the present invention. FIG. 10 is a perspective view of a cutting tool according to a third embodiment of the present invention. FIG. 10 is a perspective view of a twisted blade according to a third embodiment of the present invention. 10A and 10B are diagrams for explaining a cutting tool according to a fourth embodiment of the present invention. 10A and 10B are diagrams illustrating a twisted blade according to a fourth embodiment of the present invention. 10A and 10B are diagrams for explaining a cutting tool according to a modified example of the fourth embodiment of the present invention. 10A and 10B are diagrams for explaining a cutting tool according to a fifth embodiment of the present invention. FIG. 13 is a diagram for explaining components of a cutting force according to a fifth embodiment of the present invention. FIG. 13 is a diagram for explaining components of cutting force according to a helix angle according to a fifth embodiment of the present invention. 10A and 10B are diagrams for explaining a finished surface and a surface shape according to a fifth embodiment of the present invention. FIG. 10 is a diagram for explaining surface roughness according to a fifth embodiment of the present invention. FIG. 10 is a diagram for explaining residual stress according to the fifth embodiment of the present invention. FIG. 1 is a diagram for explaining an analysis model of inner diameter mill skiving. FIG. 1 is a diagram for explaining an analysis model of outer diameter mill skiving. FIG. 10 is a diagram for explaining an end mill model. FIG. 10 is a diagram for explaining the azimuth angle of a workpiece. FIG. 13 is a diagram for explaining components of a cutting force according to a sixth embodiment of the present invention. FIG. 10 is a diagram illustrating skiving using a twisted blade according to a sixth embodiment of the present invention. 13 is a graph of cutting force components according to a comparative example and the sixth embodiment of the present invention. 10 is a graph of cutting force components according to a sixth embodiment of the present invention. FIG. 13 is a diagram for explaining the cutting depth and cutting force components according to the sixth embodiment of the present invention. FIG. 13 is a diagram for explaining the cutting depth and cutting force components according to a comparative example compared to the sixth embodiment of the present invention. 10A and 10B are diagrams for explaining a finished surface and a surface shape according to a sixth embodiment of the present invention. 13A and 13B are diagrams for explaining a finished surface and a surface shape according to a comparative example of the sixth embodiment of the present invention. FIG. 13 is a diagram for explaining residual stress according to the sixth embodiment of the present invention. FIG. 13 is a diagram for explaining end face cutting according to a comparative example to the seventh embodiment of the present invention. 13A and 13B are diagrams for explaining end face cutting according to a seventh embodiment of the present invention. 13A to 13C are diagrams for explaining a finished surface and a surface shape according to a seventh embodiment of the present invention. 13A and 13B are diagrams for explaining a finished surface and a surface shape according to a comparative example of the seventh embodiment of the present invention. FIG. 13 is a diagram illustrating residual stress according to the seventh embodiment of the present invention.

An embodiment of the present invention will be described with reference to the drawings. Common parts in each drawing will be given the same reference numerals, and duplicate explanations will be omitted. The Z-axis direction is the direction in which the rotation axis of the workpiece extends, the X-axis direction is the direction in which the cutting tool cuts into the workpiece, and the Y-axis direction is the tangential direction perpendicular to both the Z-axis and the X-axis.

General lathe machine tools perform cutting using two-axis control. In other words, there is no Y-axis direction, and cutting is performed using the feed amount in the Z-axis direction and the depth of cut in the X-axis direction.

(First embodiment)
FIG. 1 is a perspective view of a cutting tool according to a first embodiment of the present invention. The cutting tool 100 includes a twisted cutting edge 110, a shank 120 that holds the twisted cutting edge 110, a clamp 130 that fixes the twisted cutting edge 110 to the shank 120, and a screw 140 for tightening the clamp. The cutting tool 100 is also called a cutting tool, and the shank 120 is also called a cutting tool holder. The twisted cutting edge 110 is replaceable and is also called a throw-away tip. The cutting tool 100 is also called a throw-away cutting tool.

The twisted blade 110 is the tip of the cutting edge of a three-blade end mill, which will be described later. The twisted blade 110 cuts the outer diameter of the workpiece between point A and point B. For this reason, the twisted blade 110 is also called an outer diameter throw-away tip. In addition, the twisted blade 110's three twisted cutting edges can be used by loosening the screw 140 and rotating it around the Y axis.

In this embodiment, the thickness of the twisted blade 110 is, for example, 5 mm, and the distance between point A and point B is, for example, 1 mm. In this way, the radial cutting depth of the workpiece can be controlled between, for example, 0.05 mm and 0.1 mm.

Figure 2 is a diagram illustrating a method for manufacturing a helical blade according to the first embodiment of the present invention. The end mill 200 in Figure 2(b) is a commercially available three-blade product. For three-blade end mills, the helix angle is generally 45°. The diameter of the end mill is 8 to 10 mm.

By cutting off a portion approximately 5 mm from the tip of the cutting edge of the end mill 200 in Figure 2(b) (shown by the two-dot chain line), the twisted blade 110 in Figure 2(a) can be produced. Chips cut by the twisted blade 110 are discharged along the flutes 230. The portion 210 surrounded by the dotted line is the relief groove of the end cutting edge of the end mill 200. The twisted blade is not limited to the tip of the cutting edge of the end mill 200; after cutting the twisted blade 110 in Figure 2(b), the next tip portion can be cut off and used as the twisted blade 110'. Unlike the twisted blade 110, the twisted blade 110' does not have the relief groove of the end cutting edge of the end mill 200.

Figure 3 is a diagram illustrating skiving using a twisted blade according to the first embodiment of the present invention. Figure 3(a) shows the state in which the chuck 310 of the machine tool is holding the workpiece W1. The workpiece W1 has a round rod shape. The entire machine tool is not shown, but the chuck 310 holds the workpiece W1 so that it can rotate around the Z axis. When the machine tool rotates the chuck 310, the workpiece W1 also rotates. In Figure 3(a), the twisted blade 110 is hidden behind the workpiece W1, so it is represented by a dotted line.

Figure 1(b) is a cross-sectional view showing the twist blade 110 cutting the outer diameter of the workpiece W1. The Z-axis is the rotation axis of the workpiece W1, and allows the feed amount of the twist blade 110 to be determined. The X-axis is the cutting axis, and the twist blade 110 is used to cut into the workpiece W1 from point A to point B. The Y-axis is a direction perpendicular to both the Z-axis and the X-axis, and indicates the tangent direction to the cross-sectional circle of the workpiece W1. A typical lathe machine tool moves along only two axes, the Z and X directions, but in the case of a multi-tasking machine, the Y-axis is also used.

Figure 4 is an enlarged view of a portion of Figure 3, enlarging the area surrounded by the two-dot chain line in Figure 3(b). Point A indicates the start point where the helical blade cuts into the workpiece rotating around the Z axis. Point B indicates the state where the helical blade has reached the finished surface while cutting into the workpiece. In this way, it is possible to perform outer diameter cutting with a cutting depth of 0.05 mm to 0.1 mm. The cutting depth can also be considered the depth of cut toward the center of the Z axis.

Returning to Figure 3, the twisted blade 110 is then advanced a predetermined distance in the Z-axis direction, making it possible to cut the outer diameter of the workpiece W1. Because skiving is performed using the tip of the end mill's cutting edge in this way, this can be called mill skiving.

Figure 5 is a diagram illustrating the blade contact area according to the degree of twist of the helical blade according to the first embodiment of the present invention. Figure 5(a) shows the state in which the end mill 200 itself is used to cut the outer diameter of a rotating workpiece W1 without cutting off the tip of the end mill 200. The end mill 200 is not rotating; it is simply moving at a predetermined feed rate in the direction of the rotation axis Z of the workpiece W1. Here, the only part of the helical blade of the end mill 200 used for cutting the outer diameter is the part surrounded by the two-dot chain line. This part surrounded by the two-dot chain line corresponds to the helical blade 110. Furthermore, while the end mill 200 is composed of three helical blades, there is no particular limit to the number of helical blades; it is sufficient if a portion of the helical blade at the tip of the end mill 200 can cut into the outer diameter of the workpiece W1.

Figure (b) shows the cutting portion AB of the twisted blade 110-1 when the twist angle is 20°. Figure (c) shows the cutting portion AB of the twisted blade 110-2 when the twist angle is 45°. The cutting portion AB is the area where the twisted blade 110 comes into contact with the workpiece W1. The length of the cutting portion AB when the twist angle is weak (20° in Figure (b)) is longer than the length of the cutting portion AB when the twist angle is strong (45° in Figure (c)).

The length of the cutting portion of the twist blade 110 changes depending on the twist angle of the twist blade 110 used in cutting. In this way, the feed amount of the twist blade 110 (or end mill 200) per rotation of the workpiece W1 can be set by taking into account or calculating the length of the cutting portion of the twist blade 110. Here, it is preferable to set the twist angle of the twist blade between 15° and 50°.

Figure 6 is a front view of a skiving device according to a first embodiment of the present invention. Figure 6(a) shows the cutting tool 100 attached to a machine tool 300. The machine tool 300 is a two-axis (X-axis and Z-axis) controlled lathe. The chuck 310 of the machine tool 300 holds a cylindrical workpiece W1 so that it can rotate around the Z-axis. The cutting tool 100 has a helical blade 110, which is the tip of an end mill cut off, attached to a shank 120. The shank 120 is attached from bottom to top (in the X direction) to the tool post 320 of the machine tool 300.

The tool rest 320 is movable in three axial directions. The cutting edge of the twist blade 110 is raised vertically (X direction) from the central axis (Z axis) of the workpiece W1 and aligned with the tangent direction of the circle (Y direction). The cutting depth of the twist blade 110 is set in the X direction, and the feed rate of the twist blade 110 is set in the Z direction. By attaching the twist blade 110 to the machine tool 300 in this way, it is possible to provide a skiving processing device.

Figure 1(b) is a front view of a skiving device that uses an end mill 200 instead of the cutting tool 100. The end mill 200 is attached to the tool post 321 from left to right (in the Z direction). As in Figure 1(a), the cutting edge of the end mill 200 is aligned in the Y direction, the cutting depth of the end mill 200 is set in the X direction, and the feed rate of the end mill 200 is set in the Z direction. In this way, by attaching the end mill 200 to a three-axis controlled machine tool 300 (e.g., a machining center or multi-tasking machine), it is possible to provide a skiving device.

In Figure 3(a), a twisted blade with the tip of an end mill cut off is attached to the machine tool 300, and in Figure 3(b), the end mill 200 itself is attached to the machine tool 300. These skiving machines are collectively called mill-skiving machines.

Figure 7 is a flowchart of the skiving method according to the first embodiment of the present invention. Here, the explanation will be based on the case of Figure 6(a). The workpiece W1 is fixed to the chuck 310 of the machine tool 300 (S1). The chuck 310 is rotated by a predetermined amount (S2). The cutting tool 100 attached to the tool rest 320 of the machine tool 300 is aligned in the Z-axis direction (S3). The amount by which the cutting tool is fed in the Z-axis direction (cutting feed amount) is set (S4). The depth of cut is set (S5).

Figure 6(a) shows a two-axis controlled machine tool, so it is necessary to align the cutting tool 100 in the Y direction before aligning it in the Z direction in S3. The cutting feed amount in S4 is set per rotation in the Z direction, and the start and end points in the Z direction are also set. The cutting depth in S5 is set as the cutting depth in the X direction.

The skiving method described in Figure 7 can be applied not only to two-axis controlled machine tools, but also to three-axis controlled machining centers. In this case, the cutting depth of S5 can be set as the cutting depth in either the X or Y direction. The tool post 320 corresponds to the tool spindle of a machining center. The flowchart in Figure 7 may be controlled by the hardware of the machine tool 300, or as a software program executable by a computer that operates the machine tool 300.

Second Embodiment
FIG. 8 is a diagram illustrating a method for manufacturing a helical blade according to a second embodiment of the present invention. The end mill 201 in FIG. 8(b) is a commercially available two-blade product. In the case of a two-blade end mill, the helix angle is generally 30°. The diameter of the end mill is 8 to 10 mm.

By cutting off approximately 5 mm of the tip of the end mill 201 in Figure (b) (shown by the two-dot chain line), the twisted cutting edge 111 in Figure (a) can be produced. Note that the area 211 surrounded by the dotted line is the clearance groove for the bottom cutting edge of the end mill 201.

(Third embodiment)
9 is a perspective view of a cutting tool according to a third embodiment of the present invention. The cutting tool 101 includes a helical cutting edge 112 for cutting the outer diameter of a cylindrical workpiece, a shank 120 for holding the helical cutting edge 112, a clamp 131 for fixing the helical cutting edge 112 to the shank 120, and a screw 140 for tightening the clamp.

Figure 9 differs from Figure 1 in that the twisted blade 112 has a single blade and is hollow in the center. Therefore, the tip pin of the clamp 131 is longer than in Figure 1, reaching all the way to the shank 120 and securing the twisted blade 112 to the shank 120.

Figure 10 is a perspective view of a twisted blade according to a third embodiment of the present invention. The twisted blade 112 can be manufactured by cutting the material of a throw-away tip into a rectangular parallelepiped shape approximately 5 mm thick, hollowing out the center, and then removing the area indicated by the two-dot chain line through cutting and grinding. The twisted blade angle is 45°. As explained in Figure 4, points A and B are the cutting start point and the point where the cutting reaches the finished surface. The twisted blade 112 can also be called an outer diameter throw-away tip.

(Fourth embodiment)
11A and 11B are diagrams illustrating a cutting tool according to a fourth embodiment of the present invention. Fig. 11A is a perspective view of a cutting tool 102. The cutting tool 102 includes a helical cutting edge 113 for cutting the inner diameter of a cylindrical workpiece, a shank 121 for holding the helical cutting edge 113, and a screw 141 for directly (without a clamp) fixing the helical cutting edge 113 to the shank 121.

The difference between Figure 11(a) and Figure 9 is that the twist blade 113 has a female thread in the center, and the part of the shank 121 that secures the twist blade 113 also has a female thread. The twist blade 113 is then secured to the shank 121 by tightening the male screw 141. Figure 11(b) is a cross-sectional view of a cylindrical workpiece W2. The cutting tool 102 is inserted into the cylindrical workpiece W2, and the twist blade 113 cuts the inner diameter of the workpiece W2.

Figure 12 is a diagram illustrating a twisted blade according to a fourth embodiment of the present invention. Figure 12(a) is a view of the twisted blade 113 from the arrow line A in Figure 11(a). The twisted blade 113 can be manufactured by cutting the material of the throw-away tip into a rectangular parallelepiped with a thickness of 4 mm, and then removing the portion indicated by the two-dot chain line outside the twisted blade 113 by cutting and grinding, in the same manner as described in Figure 10.

Figure 12(b) is a view of the helical blade 113 from the arrow line B in Figure 11(a). As explained in Figure 4, points A and B are the cutting start point and the point where the cutting reaches the finished surface. The thickness of the helical blade 113 is 4 mm, and the helix angle is 30°. The helical blade 113 can also be called an internal diameter throw-away tip. As in the first embodiment, the helical blade used to cut the inner diameter of a cylindrical workpiece may be the tip of an end mill or the entire end mill. Figure 13 is a diagram for explaining a cutting tool according to a modified example of the fourth embodiment of the present invention. This figure is a cross-sectional view of a cylindrical workpiece W2. The figure shows the cylindrical workpiece W2 inserted into the end mill 200, with the helical blade 110 cutting the inner diameter of the workpiece W2.

Fifth Embodiment
FIG. 14 is a diagram illustrating a cutting tool according to a fifth embodiment of the present invention. FIG. 14(a) is a side view of a cutting tool 103. The cutting tool 103 is an end mill. FIG. 14(a) omits the shank portion of the end mill and shows the body portion with a helical cutting edge 114 attached to the outer peripheral side surface. Chips cut by the helical cutting edge 114 are discharged along flutes 231. In addition, a bottom cutting edge 221 is attached to the tip surface of the body portion. FIG. 14(b) shows a cross section 1-2 of the cutting tool 103 in FIG. 14(a). FIG. 14(c) shows a cross section 3-4 of the cutting tool 103 in FIG. 14(a).

FIG. 14 shows the cutting mode of the cutting tool 103 for finishing the inner surface of a cylindrical workpiece (labeled "Workpiece"). The helix cutting edge 114 incises into the inner surface of the workpiece, feeding it longitudinally to remove a cutting area (labeled "Removal Area"). Because the helix cutting edge 114 has a helix angle, it bites into the workpiece surface at point A, continuously incising the workpiece radially toward the right in FIG. 14(a), reaching a predetermined depth of cut at point B. Therefore, the orientation of the bottom cutting edge 220 is set according to the helix angle and the set depth of cut so that the helix cutting edge 114 at point B achieves the set depth of cut. If the azimuth angle of the end mill at point A is _φA , the cutting edge length L involved in material removal is expressed by the following equation:

where R _T and γ are the radius and helix angle of the end mill. When the feed per revolution of the workpiece is f, the set depth of cut is achieved at L/f revolutions, and the inner surface is finished. Therefore, as will be described later, a good finished surface is obtained, and the residual stress also tends to be compressive.

On the other hand, chips are discharged along the flutes of the end mill. Generally, when machining the inner surface of a hollow hole, chip abrasion against the finished surface is often a problem. In this embodiment, the flutes guide the chips and discharge them out of the hole, preventing them from abrading the finished surface.

Figure 15 is a diagram illustrating the components of cutting forces in a fifth embodiment of the present invention. Figure 15 explains the cutting force components when cutting the inner surface of the cylindrical workpiece described in Figure 14. Figure 15(a) shows the vector components of cutting forces when a general-purpose turning cermet tool (Kyocera TN620) 400 is used (labeled "Turning"), and Figure 15(b) shows the vector components of cutting forces when a 10 mm diameter, two-flute end mill (UNION TOOL CSS2100-1500, helix angle 30°) 103 is used (labeled "Mill skiving").

To measure the cutting forces, each tool was attached to the turret of a CNC lathe (OKUMA SPACE TURN LB3000 EX) via a piezoelectric cutting dynamometer (Kistler 9251A). Therefore, the principal force _Fz , thrust force _Fy , and feed force _Fx were measured. It should be noted that the coordinate axes are different from those in the case where the extension direction of the rotation axis of the workpiece is the Z-axis direction.

The workpiece was carbon steel (S45C) with an inner diameter of 26 mm. The cutting conditions were a cutting speed of 150 m/min, a feed rate of 0.1 mm/rev, and a radial depth of cut of 0.05 mm, and the cutting was performed dry.

In the case of the conventional turning tool 400 shown in Figure 1(a), the normal to the main cutting edge is inclined in the feed direction, resulting in a large feed force _Fx . On the other hand, the normal to the cutting edge of the end mill 103 in this embodiment is inclined in the radial direction of the workpiece, resulting in a cutting force being applied in the direction shown in Figure 1(b). As a result, the feed force _Fx is smaller than in conventional turning. Note that the Y component in Figure 1 is shown as a negative value based on the direction of the measured cutting force.

Figure 16 is a diagram illustrating the components of cutting forces according to the helix angle in the fifth embodiment of the present invention. The figure compares the cutting force components of an end mill 103 with a helix angle of 25°, 30°, or 40°, and a general turning tool 400 (Turning). According to equation (1), when the helix angle γ is small, the cutting edge length L acting in cutting becomes long. Therefore, the cutting force is large at a helix angle of 25°.

Figure 17 is a diagram illustrating the finished surface and surface profile according to the fifth embodiment of the present invention. The finished surface roughness was measured using a laser confocal microscope (KEYENCE VX-X100). Figure 17(a) shows the finished surface and surface profile (surface profile) obtained by mill skiving using an end mill 103 with a 30° helix angle. Figure 17(b) shows the finished surface and surface profile obtained by turning using a general-purpose turning tool 400. In turning, cutting marks corresponding to the tool nose radius and feed rate can be observed. However, in mill skiving, continuous cutting is achieved by the rotation of the workpiece and the axial movement of the tool. This results in a uniform surface profile.

Figure 18 is a diagram illustrating surface roughness according to the fifth embodiment of the present invention. The figure compares the surface roughness in cutting tests using end mills 103 with helix angles of 25°, 30°, and 40°, as well as a general turning tool 400 (Turning). Figure (a) shows Ra (arithmetic mean roughness). Figure (b) shows Rz (maximum height roughness). According to equation (1), the smaller the helix angle γ in mill skiving, the longer the cutting edge length L, and the greater the number of rotations of the workpiece until the set depth of cut is reached. Therefore, at a helix angle of 25°, the depth of cut per rotation of the workpiece is smaller. This results in a better finished surface.

Figure 19 is a diagram illustrating residual stresses related to the fifth embodiment of the present invention. Here, residual stresses in the axial and circumferential directions of the finished surface were measured using a residual stress measuring device (PULSREC μ-X360n). The figure compares residual stresses in mill skiving with a 30° helix angle and turning. In turning, tensile stress is generated at the tip of the cutting edge, separating the chips from the finished surface. As a result, tensile residual stress is likely to occur on the surface, as shown in this figure. In contrast, in mill skiving, the depth of cut is gradually increased as the workpiece rotates and the tool feeds, resulting in a smaller depth of cut on the final finished surface. As a result, the cutting edge's pushing force is relatively greater than the chip-forming force. Furthermore, when the depth of cut falls below the minimum chip thickness, no chips are generated, and the cutting edge acts to smooth the finished surface. As a result, the residual stress in the surface layer becomes compressive.

(Analysis model of mill skiving)
The analytical model for mill skiving will be explained separately for inner diameter cutting and outer diameter cutting.

(1. Inner diameter mill skiving)
FIG. 20 is a diagram for explaining an analytical model of internal mill skiving. FIG. 20(a) shows the geometric relationships when an end mill (labeled "Tool") cuts the internal diameter of a cylindrical workpiece (labeled "Workpiece"). FIG. 20(b) is an enlarged view of a portion of FIG. 20(a). FIG. 20(c) is a table of symbols indicating the geometric relationships. FIG. 20(d) is a diagram for supplementary explanation of the geometric relationships. Please note that the radius _Rw of the cylindrical workpiece (workpiece) is the value obtained by adding the finishing depth of cut d to the internal diameter of the hole, not the value obtained by adding the wall thickness to the internal diameter of the hole.

First, we will explain the geometric relationships in mill skiving. The radius _ri from the center of the workpiece to any point _Pi on the end mill cutting edge is expressed by the following equation by applying the law of cosines to the triangle _OO'Pi .

The azimuth angle θ _i from the center of the workpiece and the angle α _Ri between the normal to the cutting speed direction and the rake face are expressed by the following equations according to the sine theorem:

The axial length L of the cutting edge involved in cutting is expressed by the following equation, where the azimuth angle of the bottom cutting edge is φ _0. This L corresponds to the length in the Z-axis direction from point A to point B in Figure 4.

Next, the cutting region model will be explained. In a situation where cutting starts from the bottom position of the end mill, the cutting region model can be expressed by the following equation, with r ₀ =R _w -d in equation (2).

The cutting edge of the end mill is divided into n micro cutting edges, and points P _i (i=0, 1, ..., n) are defined in a cylindrical coordinate system (r _i , φ _i , z _i ). Point P ₀ corresponds to point A in Figure 4, and point P _n corresponds to point B in Figure 4. The length dz of one micro cutting edge in the Z direction is expressed by the following equation using equation (7):

The relative positional relationship between points P _i+1 and P _i on a square end mill with a radius of R _T is expressed by the following equation:

The position r _Pi of the cutting edge at point _Pi is expressed by the following equation:

Since point P cuts point Q, which was cut an angle (2π+dφ) ago, the following equation is expressed.

Since dφ=φ _Q −φ _Pi , the following equation is obtained from the second equation of equation (12).

The position of the cutting edge at point Q is expressed by the following equation:

The cutting thickness h _i in the radial direction at point P _i is expressed by the following equation:

In addition, when z _i < f, there are no cutting marks from the previous rotation, so the cutting edge position is the depth of cut, which can be expressed by the following equation.

(2. Outer diameter mill skiving)
21 is a diagram illustrating an analytical model for external mill skiving, where R _T is the tool radius, R _w is the workpiece radius, dθ _T is the parting angle on the tool cutting edge, dθ _w is the parting angle on the workpiece surface, φ is the helix angle, and y _o is the end mill center in the Y-axis direction.

22 is a diagram for explaining an end mill model. In the coordinate system in the figure, the coordinates of the cutting edge relative to the azimuth angle θ _T of the end mill are expressed by the following equation:

Next, we will explain how the cutting edge coordinates change over time in the workpiece Cartesian coordinate system. Since the tool origin coordinates in the workpiece coordinate system at time t in the analysis model of Figure 21 are (0, y _o , ft), the coordinates of the tool cutting edge are expressed by the following equation.

However, y _o in Figure 21 is a negative value. In the actual model, the workpiece rotates, but in the analytical model, the workpiece is considered to be fixed and the end mill rotates around the workpiece at an angular velocity ω _w . In this case, the (x, y, z) of the cutting edge in the Cartesian coordinate system of the workpiece is expressed by the following equation:

The workpiece is cut when the following conditions are met:
In addition, the radius of the workpiece is reduced by the removal thickness during cutting.

The analysis of cutting thickness will now be explained. Figure 23 is a diagram for explaining the azimuth angle of the workpiece. The preceding cutting point Q is found for point P at height _xp in the axial direction (X axis) of the end mill cutting edge. Please note that the Y axis (cutting axis) in Figure 23 is the X axis in Figure 5. The azimuth angle θ _T,P of point P is expressed by the following equation using the first equation of equation (17):

Therefore, with reference to the end mill model of FIG. 22, (y _p , z _p ) is expressed by the following equation.

The azimuth angle θ _W,P of the workpiece relative to the cutting edge point Pi is expressed by the following equation.
However, y _o is a negative value in FIG. 21, and y _T,P is a positive value in FIG.

Consider the position of the leading cutting edge Q, which is cut by point P. On the end mill cutting edge, point Q is below point P (X _Q < X _P ), and if the helix angle φ is positive, the Z direction is in the feed direction (Z _Q > Z _P ). On the other hand, assuming point Q, the azimuth angle θ _W,Q of the workpiece relative to point Q can be obtained from equation (20) in the same way as equation (22).

The azimuth angle difference dθ _W between points P and Q is expressed by the following equation.

If the feed per revolution is f, then point P will cut the position cut by point Q an angle (2p-dθ _W ). Therefore, point Q is ahead of point P in the Z direction by the following formula: dz _w .

On the other hand, for point Q, Z _T,Q can be obtained from equation (22), so dz _w satisfies the following equation.

Therefore, point Q is obtained by the following five steps.
In step 1, the X coordinate (x _P ) of point P is set, and the Y and Z coordinates are found using equations (21) and (22).
In step 2, the X coordinate (x _Q ) of point Q is set, and the Y and Z coordinates are found using equations (21) and (22).
In step 3, the azimuth angles q _W,P and q _W,Q on the workpiece are found using equation (22), and dθ _W and dz _w are found using equations (24) and (25).
In step 4, dz _w is calculated from z _T,P and z _T,Q calculated in steps 1 and 2 using equation (26).
In step 5, the assumption of the X coordinate (x _Q ) of point Q is repeated until dz _w in steps 3 and 4 become equal.

The radii R _W,P and R _W, Q of points P and Q on the workpiece are expressed by the following equations:

Therefore, the radial cutting depth d _p at point P is expressed by the following equation:

In the analysis, the cutting edge of the end mill is divided into n minute cutting edges, the leading cutting edge _Qi is determined for the cutting edge element _Pi , and the distribution of the cutting depth is calculated using equations (27) and (28).

We will now explain the finished surface analysis. The workpiece is divided into infinitesimal elements in the circumferential and axial directions, and a cylindrical coordinate system of (r _ij , θ _ij , z _ij ) is considered. In the analysis model, the tool is fixed, and the workpiece is considered to move in the -Z direction at a feed rate of f. In other words, the following relationship is satisfied.

The coordinate system of the cutting edge in the model where the tool is fixed is given by the following equation.

The second equation in equation (29) and the third equation in equation (30) give the following equation:

The minute element (r _ij , θ _ij , z _ij ) of interest interferes with the tool when the following equation is satisfied.

At this time, the coordinates of the cutting edge on the XY plane are expressed by the following equation.

However, θ _T , _i,j is expressed by the following equation from equation (31).

The workpiece is cut when this (x _T , _i,j , y _T , _i,j ) is on a straight line connecting the center of the workpiece and a point on the circumference rotating at angular velocity ω.

(Action and effect)
As described above, according to this embodiment, skiving is performed using a portion of the cutting edge of the helical blade (other than both ends). Therefore, unlike a straight blade, it may be performed using two-axis control. In the case of two-axis control, it is necessary to control only the X-axis (cutting direction) and the Z-axis (rotation axis), and it is not necessary to control the Y-axis (tangential direction). In this way, skiving is possible using two-axis control because the cutting depth of a portion of the cutting edge of the helical blade increases from the point where it bites into the workpiece to another point. Therefore, it is possible to provide a machining technology that enables skiving to be performed even on a general two-axis controlled lathe machine tool.

Sixth Embodiment
In the sixth embodiment, we will explain how mill skiving reduces vibration compared to general cutting processes, using the cutting of the outer peripheral surface of a workpiece as an example. Please note that the coordinate axes are set differently from those in the first to fifth embodiments in order to compare with general cutting processes. The workpiece material used is S45C steel with a diameter of 8.5 mm. The cutting conditions are a cutting speed of 35 m/min, a feed rate of 0.05 mm per rotation, a depth of cut of 0.4 mm, and no cutting fluid. The helix angle of the end mill 201 is 30°.

FIG. 24 is a diagram illustrating the components of cutting forces according to the sixth embodiment. Here, the general-purpose turning cermet tool 400 described in FIG. 15( a) is used as the general cutting tool (labeled "Turning"). The workpiece W1 is held in the X-axis direction and can rotate in the N-axis direction. The general-purpose cutting tool 400 performs cutting at a feed rate f in the X-axis direction to cut the outer surface of the workpiece W1. The cutting force components can be expressed as the principal force _Fz , the thrust force _Fy , and the feed force _Fx . The black arrow indicates the combination of the three force components, which can be considered the cutting force. The general-purpose cutting tool 400 is a 16 mm square steel bit equipped with a finishing carbide tip with a nose radius of 0.4 mm.

Figure 25 is a diagram illustrating skiving using a helix blade according to the sixth embodiment. Figure 25(a) shows the state in which the chuck 310 of the machine tool is holding the workpiece W1. The workpiece W1 has a round rod shape. As with Figure 3, the entire machine tool is not shown, but the chuck 310 holds the workpiece W1 so that it can rotate around the X-axis. When the machine tool rotates the chuck 310, the workpiece W1 also rotates. In Figure 25(a), the end mill 201 is hidden behind the workpiece W1, so it is represented by a dotted line. As explained in Figure 8, the end mill 201 is a commercially available two-blade product with a helix angle of 30° (labeled Mill skiving).

Figure 25 (b) is a cross-sectional view showing the end mill 201 cutting the outer diameter of the workpiece W1. The X-axis is the rotation axis of the workpiece W1, and allows the feed rate of the end mill 201 to be determined. The Z-axis is the cutting axis, and the end mill 201 is used to cut into the workpiece W1 from point A to point B. The Y-axis is a direction perpendicular to both the X-axis and Z-axis, and indicates the tangent direction to the cross-sectional circle of the workpiece W1. A typical lathe machine tool moves only in the X and Z directions, but in the case of a multi-axis machine, the Y-axis is also used.

26 is a graph of cutting force components for a comparative example (Turning) of the sixth embodiment. Here, for each cutting force, X is the feed direction, Y is the tool axial direction, and Z is the downward positive direction. In the case of general cutting, it can be seen that the principal force _Fz is larger than the feed force _Fx and the thrust force _Fy , which causes the workpiece W1 to vibrate (or bend) significantly in the cutting axial direction Z.

27 is a graph of cutting force components according to the sixth embodiment (mill skiving with a helix angle of 30°). Here, for each cutting force, X is the feed direction, Y is the axial direction of the tool, and Z is the downward direction, which are positive. X and Y are negative values for the forces applied to the tool (end mill), with the feed force _Fx and thrust force _Fy being the largest. It can also be seen that a constant principal force _Fz is generated in the positive Z direction as the depth of cut increases.

In the case of mill skiving, unlike general cutting processes, it can be seen that the principal force (Z direction) is smaller than the feed force (X direction) and thrust force (Y direction).

Figure 28 is a diagram explaining the cutting depth and cutting force components for the sixth embodiment (mill skiving). In mill skiving, as the cutting depth (also known as the depth of cut) increases, the feed force (X direction) and thrust force (Y direction) also increase. However, the principal force (Z direction) remains approximately the same magnitude.

Figure 29 is a diagram illustrating the cutting depth and cutting force components for a comparative example (Turning) compared to the sixth embodiment. In the case of general cutting, when the cutting depth is increased, the feed force (X direction), thrust force (Y direction), and principal force (Z direction) all increase. In particular, the principal force (Z direction) becomes the largest.

As such, the principal component of force (Z direction) in Figure 28 (Mill skiving) differs from the principal component of force (Z direction) in Figure 29 (Turning). Even if the cutting depth is increased, the principal component of force (Z direction) remains roughly the same magnitude, and vibration of the workpiece W1 toward the center of the rotation axis can be suppressed.

Figure 30 is a diagram illustrating the finished surface and surface shape for the sixth embodiment (mill skiving). The finished surface roughness was measured using a laser confocal microscope (KEYENCE VX-X100). The surface roughness was Ra (arithmetic mean roughness) of 0.881 μm and Rz (maximum height) of 9.840 μm.

Figure 31 is a diagram illustrating the finished surface and surface shape for a comparative example (Turning) compared to the sixth embodiment. The surface roughness is Ra (arithmetic mean roughness) of 4.097 μm and Rz (maximum height) of 27.33 μm.

As can be seen, the surface in Figure 30 (Mill skiving) has a much better finish than the surface in Figure 31 (Turning).

Figure 32 is a diagram illustrating residual stress in the sixth embodiment. Here, residual stress in the axial direction of the finished surface was measured using a residual stress measuring device (PULSREC μ-X360n). The figure compares residual stress in mill skiving and conventional turning. In conventional turning, tensile stress occurs at the tip of the cutting edge, separating the chip from the finished surface. As a result, tensile residual stress is likely to occur on the surface, as shown here. On the other hand, in mill skiving, the depth of cut is gradually increased as the workpiece rotates and the tool feeds, resulting in a smaller depth of cut on the final finished surface. As a result, the cutting edge's pushing force is relatively greater than the chip-forming force. Furthermore, when the depth of cut falls below the minimum chip thickness, no chips are generated, and the cutting edge acts to smooth the finished surface. As a result, the residual stress in the surface layer becomes compressive.

Seventh Embodiment
In the seventh embodiment, we will use the cutting of the end face of a workpiece as an example to explain how mill skiving can produce a better finished surface than general cutting. The workpiece is made of S45C steel with a diameter of 35 mm. The cutting conditions are a cutting speed of 35 m/min, a feed rate of 0.1 mm per revolution, and a depth of cut of 0.2 mm for turning and 0.1 mm for mill skiving. The end face of the workpiece is cut from the large diameter side to the center.

Figure 33 is a diagram illustrating end surface cutting in a comparative example to the seventh embodiment. Here, as with the sixth embodiment, a cermet tool 400 for general turning is used as the general cutting tool (labeled "Turning"). The chuck 310 of the machine tool rotatably holds the workpiece W1, and the general cutting tool 400 cuts the end surface ES of the workpiece W1.

Figure 34 is a diagram illustrating end face cutting according to the seventh embodiment of the present invention. As with the sixth embodiment, an end mill 201 is used as a mill skiving tool (labeled "Mill skiving"). The chuck 310 of the machine tool rotatably holds the workpiece W1, and the end mill 201 cuts the end face ES of the workpiece W1.

Figure 35 is a diagram illustrating the finished surface and surface shape for the seventh embodiment (mill skiving). The finished surface roughness was measured using a laser confocal microscope (KEYENCE VX-X100). The surface roughness was Ra (arithmetic mean roughness) of 0.452 μm and Rz (maximum height) of 4.824 μm.

Figure 36 is a diagram illustrating the finished surface and surface shape for a comparative example (Turning) compared to the seventh embodiment. The surface roughness is Ra (arithmetic mean roughness) of 0.918 μm and Rz (maximum height) of 7.63 μm.

As can be seen, the surface in Figure 35 (Mill skiving) has a much better finish than the surface in Figure 36 (Turning).

Figure 37 is a diagram illustrating residual stresses in the seventh embodiment. Here, residual stress in the axial direction of the finished surface was measured using a residual stress measuring device (PULSREC μ-X360n). The figure compares residual stresses in mill skiving and conventional turning. Unlike the sixth embodiment (peripheral surface machining), conventional turning does not generate tensile stress at the cutting edge, and chips are separated from the finished surface. As a result, slight compressive residual stresses tend to occur on the surface, as shown in this result. On the other hand, in mill skiving, the depth of cut is gradually increased as the workpiece rotates and the tool is fed, resulting in a smaller depth of cut on the final finished surface. As a result, the cutting edge's pushing force is relatively greater than the chip-forming force. Furthermore, when the depth of cut is below the minimum chip thickness, no chips are generated, and the cutting edge acts to smooth the finished surface. As a result, significant compressive residual stress occurs in the surface layer.

Please note that because regular skiving uses a straight blade, unlike a helical blade, it is not possible to cut the end face of the workpiece from the large diameter side to the center. In other words, even if the workpiece is sufficiently thin, using a straight blade will simply result in a thin cut at the end face.

The above describes embodiments of the present invention, but two or more of these examples may be combined and implemented. Alternatively, one of these examples may be implemented partially.

Furthermore, the present invention is in no way limited to the above-described embodiments. Various modifications within the scope of the claims and within the scope that can be easily conceived by a person skilled in the art are also included in the present invention.

100, 101, 102, 103 Cutting tool 110, 110', 111, 112, 113, 114 Helical cutting edge 120, 121 Shank 130, 131 Clamp 140, 141 Screw 200, 201 End mill 210, 211 End cutting edge relief groove 220, 221 End cutting edge 230, 231 Flute 300 Machine tool 310 Chuck 320, 321 Tool post 400 General turning tool W1, W2 Workpiece

Claims (13)

A skiving tool having a twisted blade used for skiving,
The cutting edge of the helical blade is twisted in the cutting direction of the skiving process ,
A skiving tool characterized in that the cutting edge of the helical blade has different azimuth angles at a first point and a second point in the cutting direction . The skiving tool according to claim 1, which is integral with the twisted blade. The skiving tool according to claim 1, wherein the helix angle of the helical blade is between 15° and 50°. The skiving tool according to claim 3 , wherein the helix angle of the helical blade is 30°. The skiving tool described in claim 1, wherein the helical blade is manufactured by cutting a portion of an end mill. A skiving tool as described in claim 5 , wherein when the twisted blade is formed by cutting the tip of the end mill, one end of the peripheral blade of the tip on the bottom blade side of the tip is used for the skiving. The skiving tool according to claim 5 , wherein the end mill has three blades. The skiving tool according to claim 5 , wherein the end mill has two blades. The skiving tool according to claim 1, wherein the helical blade is an outer diameter throw-away tip. The skiving tool according to claim 1, wherein the helical blade is an internal diameter throw-away tip. The skiving tool according to claim 1, wherein the helical blade performs skiving on the end face of the workpiece. a chuck for rotatably holding the workpiece on the first axis;
A tool rest for mounting a skiving tool having a twisted blade used for skiving,
a feed amount of the twist blade is set in the first axial direction;
A skiving processing device using a machine tool that sets the cutting amount of the twist blade to a second axis perpendicular to the first axis direction,
A skiving device characterized in that the cutting edge of the helical blade is twisted in the cutting direction of the skiving. a chuck for rotatably holding the workpiece on the first axis;
A skiving method using a machine tool including a tool rest to which a skiving tool having a twisted blade used for skiving is attached,
The workpiece is fixed to the chuck;
Rotating the chuck;
Aligning the skiving tool with a first axis;
a feed amount of the twist blade is set in the first axial direction;
The cutting amount of the twisted blade is set to a second axis perpendicular to the first axial direction, so that the skiving tool performs the skiving process,
A skiving method, characterized in that the cutting edge of the helical blade is twisted in the cutting direction of the skiving.