JP5481870B2 - Grinding machine and grinding method - Google Patents

Description

The present invention relates to a grinding machine and a grinding method for forming a screw by grinding a screw groove on an inner peripheral surface of a workpiece.

  2. Description of the Related Art Conventionally, a grinding machine that forms a female thread by grinding a screw groove on an inner peripheral surface of a cylindrical workpiece has a spindle device that holds the workpiece rotatably around the axis of the workpiece, and a workpiece with respect to the spindle device. A grinding wheel that is relatively movable in the axial direction and the direction orthogonal to the axis of the article and is rotatable around the grinding wheel axis. The grinding wheel can be turned around an axis orthogonal to the grinding wheel axis, and the grinding wheel is turned so that the inclination angle of the grinding wheel shaft with respect to the screw shaft (workpiece axis) matches the lead angle of the screw. And grinding.

  However, in the grinding machine as described above, when the lead angle or depth of the female screw is large or when the internal diameter of the female screw is small, the grinding wheel or the support shaft member that supports the grinding wheel interferes with the mouth of the workpiece. There is a risk. In order to avoid this interference, it is conceivable to reduce the diameter of the grinding wheel and the support shaft member. However, the support rigidity of the grinding wheel, that is, the bending rigidity of the support shaft member is lowered. As a result, there has been a problem that the processing accuracy cannot be increased due to the bending of the support shaft member. Furthermore, the grinding time cannot be shortened because a sufficient grinding force cannot be applied due to a decrease in the bending rigidity of the support shaft member.

  Therefore, as a grinding machine in which the lead angle of the female screw and the inclination angle of the grinding wheel shaft do not coincide with each other, for example, Japanese Patent Publication No. 8-11329 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2003-11022 (Patent Document 2) describe. There is something that was done. Patent Document 1 discloses a processing method for grinding a female screw in a state in which the axis of a workpiece and the axis of a grinding wheel are parallel to each other. Patent Document 2 discloses a processing method for grinding a female screw in a state where the grinding wheel is inclined smaller than the lead angle of the female screw.

  Here, each of the grinding wheels described in Patent Documents 1 and 2 has a disk shape. On the other hand, for example, there is one described in JP-A-10-43943 (Patent Document 3). Patent Document 3 discloses a grinding wheel having a plurality of disk-shaped protrusions that match the pitch of the female screw. It is said that by grinding this grinding wheel, grinding can be performed at high speed and the tool life of the grinding wheel can be extended.

  An example of a grinding machine that forms a male thread by grinding a thread groove on the outer peripheral surface of a cylindrical or columnar workpiece is disclosed in Japanese Patent Application Laid-Open No. 2004-90215 (Patent Document 4). . Patent Document 4 describes that grinding is performed by turning the grinding wheel so that the inclination angle of the shaft of the grinding wheel with respect to the screw shaft of the male screw matches the lead angle of the male screw.

Japanese Patent Publication No. 8-11329 JP 2003-11022 A JP 10-43943 A JP 2004-90215 A

  However, since the grinding wheels described in Patent Documents 1 to 3 are all disk-shaped, grinding may not be possible when the lead angle or depth of the female screw is large or when the internal diameter of the female screw is small. there were.

  Also, when forming the external thread on the outer peripheral surface of the workpiece, if the grinding wheel shaft can be turned due to the configuration of the grinding machine, it cannot be ground as in the case of forming the internal thread on the inner peripheral surface. There is no. However, a space for turning the grinding wheel around an axis orthogonal to the axis of the workpiece and a turning mechanism are required. As a result, the grinding machine becomes larger and the cost becomes higher. Therefore, when a male screw is formed on the outer peripheral surface of the workpiece, a grinding method in which the grinding wheel is not made to coincide with the lead angle is required as in the case of forming the female screw. Then, as described above, when the lead angle and depth of the male screw are large, grinding may not be possible.

The present invention has been made in view of the above problems. Even when the lead angle and depth of the screw are large, the inner peripheral surface of the workpiece is formed even when the inner diameter of the female screw is small particularly when forming the female screw. An object of the present invention is to provide a grinding machine and a grinding method capable of grinding to form a screw.

In order to solve the above problems, the structural features of the invention described in claim 1 are:
A workpiece holding means for holding a shaft-shaped workpiece;
It is rotatable around a grindstone axis parallel to the axis of the workpiece, is movable relative to the workpiece in the axial direction and the axis orthogonal direction of the workpiece, and the grindstone axis is moved to the workpiece A grinding wheel that is rotatable relative to the workpiece about the axis of the workpiece;
With
In a grinding machine that forms a screw by grinding a screw groove on the inner peripheral surface of the workpiece,
The grinding wheel is
The base,
A ridge formed in a spiral shape in the grinding wheel axis direction on the outer peripheral surface of the base, and set at a lead angle different from the lead angle of the screw;
Equipped with a,
Wherein the parallel axis of the workpiece and said grinding wheel shaft, a grinding to Rukoto the thread groove by relatively moving the grinding wheel in the axial direction of the workpiece.

The structural feature of the invention described in claim 2 is that in claim 1,
In the case of forming an internal thread on the inner peripheral surface of the workpiece,
The outermost diameter of the ridge is set smaller than the root diameter of the female screw.

The structural feature of the invention described in claim 3 is that in claim 1 or 2,
Grinding wheel rotating means for rotating the grinding wheel around the grinding wheel axis;
Workpiece rotation means for rotating the workpiece around the axis of the workpiece;
Axis moving means for moving the grinding wheel relative to the workpiece in the axial direction and the axis orthogonal direction of the workpiece;
Control means for controlling the grinding wheel rotating means, the workpiece rotating means, and the axis moving means;
It is to provide.

The constitutional feature of the invention described in claim 4 is that in claim 1 or 2,
Bed and
Grinding wheel rotating means for rotating the grinding wheel around the grinding wheel axis;
Axis moving means for moving the grinding wheel relative to the workpiece in the axial direction and the axis orthogonal direction of the workpiece;
Revolving means for relatively rotating and driving the grindstone shaft around the workpiece axis;
Control means for controlling the grinding wheel rotating means, the shaft moving means, and the revolution means;
With
The workpiece holding means fixes the workpiece to the bed so as not to rotate.

The structural feature of the invention according to claim 5 is the structure according to any one of claims 1 to 4,
The ridges are formed in a spiral shape so as to extend over a plurality of circumferences around the grindstone axis.
The structural feature of the invention according to claim 6 is that in claim 5,
The ridge is set to a lead angle larger than the lead angle of the screw.

The structural feature of the invention according to claim 7 is the structure according to any one of claims 1 to 4,
The ridges are formed in a spiral shape so as to be less than one turn around the grindstone axis.
The structural feature of the invention according to claim 8 is the structure according to any one of claims 1 to 7,
The ridges are formed in multiple stripes.

The structural feature of the invention according to claim 9 is the structure according to any one of claims 1 to 8,
The grinding machine
A surface shape acquisition means for calculating a contact line between a thread groove surface of the thread groove of a grinding target and the grinding wheel, and acquiring a surface shape by rotating the contact line around a central axis of the grinding wheel;
Grinding wheel forming means for forming the outer peripheral surface of the grinding wheel into the surface shape acquired by the surface shape acquisition means;
It is to provide.

The structural feature of the invention described in claim 10 is that in claim 9,
The grinding wheel forming means is an NC truing device that forms an outer peripheral surface of the grinding wheel by NC control.

The constitutional feature of the invention according to claim 11 is that
A grinding wheel parallel to the axis of the workpiece is rotated around the grinding wheel axis, moved relative to the workpiece in the axial direction and the axis orthogonal direction of the workpiece, and the grinding wheel axis is moved to the workpiece. In a grinding method for forming a screw by grinding a screw groove on an inner peripheral surface of the workpiece by rotating the workpiece relatively around an axis of the workpiece,
The grinding wheel is
The base,
A ridge formed in a spiral shape in the grinding wheel axis direction on the outer peripheral surface of the base, and set at a lead angle different from the lead angle of the screw;
With
And parallel with said wheel spindle and the axis of the workpiece, by relatively moving the grinding wheel in the axial direction of the workpiece, is to grind the thread groove I by prior Kitotsujo .

The structural feature of the invention according to claim 12 is that
The grinding wheel is rotated about the grinding wheel axis, the workpiece is rotated about the axis of the workpiece, and the grinding wheel is relative to the workpiece in an axial direction and an axis orthogonal direction. The screw groove is formed by grinding the thread groove on the inner peripheral surface of the workpiece.

The structural feature of the invention according to claim 13 is that
The workpiece is fixed to the bed in a non-rotatable manner, the grinding wheel is rotated about the grinding wheel axis, and the grinding wheel is moved relative to the workpiece in an axial direction and an axis orthogonal direction of the workpiece. By moving and rotating the grindstone shaft relatively around the workpiece axis , the thread groove is ground on the inner peripheral surface of the workpiece to form a screw.

According to the invention which concerns on Claim 1, the spiral protruding item | line in a grinding wheel can form a screw groove in the internal peripheral surface of a workpiece. In particular, a screw having a large lead angle and thread depth can be ground without turning the grinding wheel in the direction perpendicular to the axis of the workpiece. That is, the grinding machine of the present invention can grind the screw that could not be ground by the conventional disc-shaped grinding wheel. Further, in a screw that can be ground by a conventional disk-shaped grinding wheel, the outer diameter of the grinding wheel of the present invention can be increased as compared with a conventional disk-shaped grinding wheel. Therefore, the rigidity of the grinding wheel can be increased, and the life of the grinding wheel can be prolonged. Here, like the present invention, the thread groove can be ground by the spiral ridges for the reason described later in the column of the embodiment.

  Moreover, it is not necessary to incline the axis of the grinding wheel with respect to the axis of the workpiece. Therefore, even if the internal diameter of the female screw is small, grinding can be performed without interference between the workpiece and the grinding wheel or the support shaft member that supports the grinding wheel. Furthermore, a sufficient grinding force can be applied to the grinding wheel without lowering the bending rigidity of the support shaft member that supports the grinding wheel. Therefore, the grinding time can be shortened.

  According to the second aspect of the present invention, a non-contact gap is formed between the inner peripheral surface of the workpiece and the outer peripheral surface of the grinding wheel, particularly when an internal thread is formed on the inner peripheral surface of the workpiece. This gap makes it easier to discharge chips and allows coolant to be inserted into the gap.

  According to the third aspect of the invention, the workpiece and the grinding wheel rotate together, and the grinding wheel moves relative to the workpiece in the radial direction of the workpiece, thereby changing the processing point of the grinding process. it can. The present invention can be applied to a conventional grinding machine, and the processing points of grinding can be at the same position (same phase) in the rotation direction of the workpiece. Therefore, it is possible to reliably supply the coolant to the processing point, and it is possible to perform grinding to efficiently and reliably form the thread groove.

  According to the invention which concerns on Claim 4, the processing point of grinding can be moved to the circumferential direction of a workpiece by rotating and revolving only a grinding wheel in the state which fixed the workpiece. Thereby, since the support rigidity of a workpiece can be made high, a highly accurate grinding process is attained. Further, it is possible to prevent an error caused by rotating both the workpiece and the grinding wheel.

According to the fifth aspect of the present invention, since a plurality of locations can be ground at the same time by a plurality of spiral ridges in the grinding wheel, the grinding speed can be increased. Moreover, the lifetime of a grinding wheel can be extended by providing many convex parts which can be ground. In this case, it is necessary that the spiral ridge lead matches the lead of the screw.
According to the invention which concerns on Claim 6, a female screw can be reliably grind-processed by the helical convex shape by which the circumference | surroundings were carried out in multiple times.
According to the invention which concerns on Claim 7, since it is not necessary to make the lead of a spiral protruding item | line coincide with the lead of a screw, the design freedom degree of protruding item | lines, such as a lead angle, can be improved. Moreover, it is lighter than a multiple-turn grinding wheel, is less likely to bend, and enables high-precision finishing.
According to the invention which concerns on Claim 8, even when forming a multi-thread screw in a workpiece, there exists the same effect and it can form a screw groove.
According to the ninth aspect of the invention, since the outer peripheral surface of the grinding wheel is formed to have a surface shape obtained by the contact line, it is possible to reliably grind the thread groove of the grinding target, which is extremely high. Screws can be formed with high accuracy.

  Here, the thread groove surface of the target thread groove for grinding is an ideal thread groove surface of a portion to be ground by a grinding wheel, and can be expressed as an equation of a cylindrical spiral surface. Then, when considering a certain moment of grinding, a portion where the thread groove surface and the grinding wheel come into contact is linear. This line is the contact line described above. And this contact line is not necessarily parallel to the axis of a screw shaft or a grinding wheel. When the angle formed by the workpiece axis and the grinding wheel axis is different from the lead angle of the screw, the contact line is usually not parallel to the screw axis and the grinding wheel axis.

  In the surface shape acquisition means, the surface shape is acquired by rotating the contact line around the axis of the grinding wheel. In the grinding wheel forming means, the outer peripheral surface of the grinding wheel is formed so as to have this surface shape. Therefore, the outer peripheral surface of the grinding wheel has a surface shape obtained by the contact line.

Here, the screw shaft corresponds to the rotation center axis of the workpiece. The lead is a distance that travels in the screw axis direction when it makes a round around the screw axis. Further, the lead angle is an angle formed by the hypotenuse and the base of the triangle when considering a right triangle with the circumference of the screw cylinder as the base and the lead as the height.
According to the invention which concerns on Claim 10, the outer peripheral surface of arbitrary grinding wheels can be shape | molded. As a truer of the NC truing apparatus, a rotary dresser or a single stone dresser can be used.

According to the invention which concerns on Claim 11, there exists an effect similar to the effect as the said grinding machine. That is, according to the grinding method of the present invention, the spiral ridges in the grinding wheel can form thread grooves on the inner peripheral surface of the workpiece. In particular, a screw having a large lead angle and thread depth can be ground without turning the grinding wheel in the direction perpendicular to the axis of the workpiece. That is, the grinding machine of the present invention can grind the screw that could not be ground by the conventional disc-shaped grinding wheel. Further, in a screw that can be ground by a conventional disk-shaped grinding wheel, the outer diameter of the grinding wheel of the present invention can be increased as compared with a conventional disk-shaped grinding wheel. Therefore, the rigidity of the grinding wheel can be increased, and the life of the grinding wheel can be prolonged.

  Moreover, it is not necessary to incline the axis of the grinding wheel with respect to the axis of the workpiece. Therefore, even if the internal diameter of the female screw is small, grinding can be performed without interference between the workpiece and the grinding wheel or the support shaft member that supports the grinding wheel. Furthermore, a sufficient grinding force can be applied to the grinding wheel without lowering the bending rigidity of the support shaft member that supports the grinding wheel. Therefore, the grinding time can be shortened.

  According to the twelfth aspect of the present invention, grinding is performed by rotating the workpiece and the grinding wheel together and performing grinding by moving the grinding wheel relative to the workpiece in the radial direction of the workpiece. The point has changed. The present invention can be implemented with a conventional grinding machine, and the processing point of the grinding process is the same position (same phase) in the rotation direction of the workpiece. As a result, the coolant can be reliably supplied to the machining point, and a more efficient and more reliable screw groove can be formed.

  According to the invention which concerns on Claim 13, the processing point of a grinding process is moved to the circumferential direction of a workpiece by rotating and revolving only a grinding wheel in the state which fixed the workpiece. Thereby, since the support rigidity of a workpiece can be made high, a highly accurate grinding process is attained. Further, it is possible to prevent an error caused by rotating both the workpiece and the grinding wheel.

  Further, other characteristic portions as the grinding machine of the present invention can be similarly applied to the grinding method of the present invention. And also about the effect in this case, there exists an effect similar to the effect as the said grinding machine. In addition, each "means" in the grinding machine of this invention can be grasped | ascertained as the grinding method of this invention by replacing with a "step".

1st embodiment: (a) It is a side view which sees through and shows the internal peripheral surface of the workpiece 100. FIG. (B) It is an AA cross-sectional enlarged view. 1 is a plan view of a grinding machine 1. FIG. 3 is a control block diagram of a control device 50. FIG. It is the side view which looked at the grinding wheel 33 from the axis orthogonal direction. (A) It is an axial sectional view of the state where the inner peripheral surface of the workpiece 100 is ground at the reference position (phase 0 degree). (B) It is the figure seen from the axial direction in phase 0 degree. (A) It is an axial sectional view of the state where the inner peripheral surface of the workpiece 100 is ground at a phase of 90 degrees. (B) It is the figure seen from the axial direction in 90 degrees of phases. (A) It is an axial sectional view of the state where the inner peripheral surface of the workpiece 100 is ground at a phase of 180 degrees. (B) It is the figure seen from the axial direction in 180 degrees of phases. (A) It is an axial sectional view of the state where the inner peripheral surface of the workpiece 100 is ground at a phase of 270 degrees. (B) It is the figure seen from the axial direction in phase 270 degree | times. (A) It is an axial sectional view of the state where the inner peripheral surface of the workpiece 100 is ground at a phase of 360 degrees. (B) It is the figure seen from the axial direction in 360 degrees of phases. It is explanatory drawing (when inclination angle (SIGMA) and lead angle (gamma) correspond) that the outer peripheral surface shape of the grinding wheel 60 changes with the outer diameter of the grinding wheel 60. FIG. It is explanatory drawing (when inclination angle (SIGMA) and lead angle (gamma) differ) that the outer peripheral surface shape of the grinding wheel 60 changes with the outer diameter of the grinding wheel 60. FIG. It is explanatory drawing of a helical equation. It is explanatory drawing of a helical equation. It is a figure which shows a certain state which grinds the nut member of the ball screw as the workpiece 100 with the grinding wheel 60, Comprising: It is a figure which shows each coordinate system. It is a figure which shows a contact line and the protruding item | line 33b. 2nd embodiment: It is sectional drawing which shows operation | movement of the grinding wheel 33. FIG.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a grinding machine and a grinding method according to the present invention will be described with reference to the drawings.
<First embodiment>
(1) Description of Workpiece First, a work piece 100 (also referred to as “internal thread”) to be ground by the grinding machine of the present invention will be described with reference to FIG. FIG. 1A is an axial sectional view of the workpiece 100, and FIG. 1B is an AA partial sectional enlarged view of FIG.

  As shown in FIG. 1A, the workpiece 100 is a nut member of a ball screw. That is, a screw groove 101 formed of a ball groove on which a ball (not shown) can roll is formed in a spiral shape on the inner peripheral surface of the workpiece 100. That is, the workpiece 100 has a cylindrical shape, and a thread groove 101 is formed on the inner peripheral surface thereof. The thread groove surface of the thread groove 101 has a Gothic arc shape as shown in FIG. Of course, it can also be a circular arc shape.

  The thread groove 101 is a single thread having a pitch P. The lead angle is γ. Here, the lead is a distance traveled in the direction of the screw shaft 102 when it makes a round around the screw shaft 102 of the female screw 100. The screw shaft 102 of the female screw 100 corresponds to a rotation center axis of the workpiece 100 and a spindle shaft described later. The lead angle γ is an angle formed by the hypotenuse and the base of the triangle when considering a right triangle with the circumference of the inner circumferential surface of the screw cylinder as the base and the lead as the height.

The thread groove surface of the thread groove 101 has a Gothic arc shape as described above. Specifically, one side from the groove bottom portion 103 of the screw groove surface (right side in FIG. 1 (b)), the central and C _R, a circular arc shape having a radius r _C. The other side from the groove bottom portion 103 of the screw groove surface (the left side in FIG. 1 (b)), the central and C _L, which is a circular arc shape having a radius r _C. Thus, the thread groove surface has a shape obtained by connecting two kinds of arcs.

(2) Configuration of Grinding Machine Next, the mechanical configuration of the grinding machine of the present embodiment will be described with reference to FIG. FIG. 2 is a plan view of the grinding machine 1. As shown in FIG. 2, the grinding machine 1 includes a bed 10, a spindle device 20, a grindstone support device 30, an NC truing device 40, and a control device 50.

The bed 10 has a substantially rectangular shape and is disposed on the floor. On the upper surface of the bed 10, the grinding wheel head guide rails 11 and 12 on which the grinding wheel base traverse base 31 constituting the grinding wheel support device 30 is slidable are on the upper side of FIG. (Axial direction) and are formed in parallel to each other. Further, on the upper surface of the bed 10, below the grinding wheel guide rails 11 and 12, below the FIG. 2 are spindle head guide rails 13 and 14 on which the head stock 21 constituting the spindle device 20 can slide. They extend in the left-right direction (Z-axis direction) in FIG. 2 and are parallel to each other.
Further, on the bed 10, a grinding wheel base Z-axis ball screw 16 for driving the grinding wheel base traverse base 31 in the left-right direction in FIG. 2 is disposed between the grinding wheel base guide rails 11, 12. A grinding wheel base Z-axis motor 15 for rotating the base Z-axis ball screw 16 is disposed. Further, a Z-axis ball screw (not shown) for the headstock for driving the headstock 21 in the left-right direction in FIG. 2 is disposed between the guide rails 13 and 14 for the headstock in the bed 10. A headstock Z-axis motor 17 for rotating the headstock Z-axis ball screw is disposed.

  The spindle device 20 includes a headstock 21, a spindle 22 (corresponding to “workpiece rotating means” of the present invention), and a chuck 23 (corresponding to “workpiece holding means” of the present invention). The head stock 21 is slidably disposed on the head stock guide rails 13 and 14 on the upper surface of the bed 10. The headstock 21 is coupled to the nut member of the headstock Z-axis ball screw, and moves along the headstock guide rails 13 and 14 by driving the headstock Z-axis motor 17. The headstock 21 is formed with a hole penetrating in the left-right direction in FIG. The main shaft 22 is inserted into and supported by the through hole of the main shaft base 21 so as to be rotatable around the main shaft axis (around the Z axis in FIG. 2). A chuck 23 that holds one end of the workpiece 100 in the axial direction is attached to the right end of the main shaft 22. The headstock 21 rotates the workpiece 100 held by the chuck 23 via the spindle 22 by a workpiece rotating motor (not shown).

  The grinding wheel support device 30 includes a grinding wheel base traverse base 31, a grinding wheel base 32, a grinding wheel 33, a grinding wheel rotation motor 34, and a support shaft member 35. The grinding wheel base traverse base 31 is formed in a rectangular flat plate shape, and is slidably disposed on the grinding wheel head guide rails 11 and 12 on the upper surface of the bed 10. The wheel head traverse base 31 is connected to a nut member of the wheel head Z-axis ball screw 16 and moves along the wheel head guide rails 11 and 12 by driving the wheel head Z-axis motor 15. X-axis guide rails 31a and 31b on which the grindstone table 32 can slide are formed on the upper surface of the traverse base 31 so as to extend in the vertical direction (X-axis direction) in FIG. 2 and to be parallel to each other. Has been. Further, an X-axis ball screw 31c for driving the grinding wheel base 32 in the vertical direction in FIG. 2 is disposed between the X-axis guide rails 31a and 31b on the grinding wheel base traverse base 31. An X-axis motor 31d that rotates 31c is disposed.

  The grinding wheel base 32 is slidably disposed on the X-axis guide rails 31 a and 31 b in the upper surface of the grinding wheel base traverse base 31. The grinding wheel base 32 is connected to the nut member of the X-axis ball screw 31c, and moves along the X-axis guide rails 31a and 31b by driving the X-axis motor 31d. That is, the grindstone base 32 can move relative to the bed 10 and the spindle device 20 in the X-axis direction and the Z-axis direction.

  And the hole penetrated in the left-right direction of FIG. 2 is formed in the lower part of FIG. A support shaft member 35, which is a grinding wheel rotating shaft member, is supported in the through hole of the grinding wheel base 32 so as to be rotatable around the grinding wheel center axis (around the Z axis). A grinding wheel 33 is coaxially attached to one end of the support shaft member 35 (left end in FIG. 2). A grindstone rotating motor 34 is fixed to the other end side of the support shaft member 35. That is, the grinding wheel 33 rotates around the grinding wheel axis by driving the grinding wheel rotating motor 34. The shape and grinding method of the grinding wheel 33 will be described later.

  Here, the details of the grinding wheel 33 will be described with reference to FIG. FIG. 4 is an enlarged side view of the grinding wheel 33 viewed from the direction perpendicular to the axis. As shown in FIG. 4, the grinding wheel 33 includes a columnar base portion 33a and a spiral ridge 33b. The base 33a forms the main body of the grinding wheel 33, and is rotationally driven by receiving power from the grinding wheel rotation motor 34 via a grinding wheel rotary shaft member such as the support shaft member 35.

  The ridge 33b is a part where the grinding wheel 33 rotates relative to the workpiece 100 and grinds the thread groove 101 (shown in FIG. 1) of the workpiece 100. The ridge 33b is formed on the outer peripheral surface of the base 33a so as to be spiral in the direction of the grindstone axis. The protrusions 33b are wound by about 3 turns in the circumferential direction of the grindstone shaft so as to have the same pitch as the pitch of the thread grooves 101 of the workpiece 100. Furthermore, the outermost diameter of the ridge 33 b is set smaller than the root diameter of the thread groove 101 of the workpiece 100. The cross-sectional shape in the axial direction of the ridge 33b has a shape that approximates an arcuate convex shape in which the thread groove 101 is inverted. The ridge 33b is formed by a large number of abrasive grains. Further, acquisition of the spiral surface shape of the ridge 33b will be described later.

  Returning to FIG. The NC truing device 40 is arranged on the bed 10 above the spindle device 20 in FIG. The NC truing device 40 is supported by the bed 10 so as to be pivotable about the vertical axis (Y axis) (B axis) with respect to the bed 10 and the horizontal axis (A And a rotary dresser 42 supported rotatably on the shaft). The rotary dresser 42 has a disk shape and is used for forming the outer peripheral surface of the grinding wheel 33. The outer peripheral edge of the rotary dresser 42 is formed in an acute angle shape. That is, the outer peripheral surface shape of the grinding wheel 33 can be formed into an arbitrary shape by appropriately moving the grinding wheel base 32 in the X axis direction and the Z axis direction while rotating the rotary dresser 42 on the B axis.

  The control device 50 performs NC control of the rotation of the spindle device 20 and the rotation of the grinding wheel base 32, the X-axis position, and the Z-axis position. Furthermore, NC control is also performed for the B-axis angle of the NC truing device 40.

  The control device 50 shapes the outer peripheral surface of the grinding wheel 33 so as to have an outer peripheral surface shape corresponding to the outer diameter of the grinding wheel 33. A control block diagram of the control device 50 in this regard is shown in FIG. As shown in FIG. 3, the control device 50 includes an outer diameter detection unit 51, a surface shape acquisition unit 52, and a grindstone forming processing unit 53.

  The outer diameter detection unit 51 detects the outer diameter of the grinding wheel 33. In the present embodiment, the outer diameter detection unit includes the following means. For example, there is means for detecting the outer diameter of the grinding wheel 33 based on the number of times dressed by the rotary dresser 42 of the NC truing device 40.

  Further, the rotary dresser 42 and the grinding wheel 33 can be slightly brought into contact with each other, and the outer diameter of the grinding wheel 33 can be detected based on the position of the grinding wheel base 32 at the time of contact between the rotary dresser 42 and the grinding wheel 33. The contact between the rotary dresser 42 and the grinding wheel 33 can be detected by, for example, an acoustic emission sensor (AE sensor) or a change in the resistance of the grinding wheel rotation motor 34 for driving the grinding wheel 33. The AE sensor is a sensor that detects an elastic wave when the rotary dresser 42 and the grinding wheel 33 come into contact with each other. The AE sensor can be provided on the grinding wheel base 32 or can be provided on the support member 41 that supports the rotary dresser 42.

  In addition to the above, it is possible to use a means for calculating the outer diameter of the grinding wheel 33 based on the outer diameter of the workpiece 100 and the position of the grinding wheel base 32. The outer diameter of the workpiece 100 at this time can be obtained by a known sizing device or the like.

  In this way, it is possible to detect the outer diameter of the grinding wheel 33 using the existing rotary dresser 42 without separately providing a dedicated device for detecting the outer diameter of the grinding wheel 33.

  The surface shape acquisition unit 52 determines the grinding wheel 33 after molding based on the outer diameter of the grinding wheel 33 detected by the outer diameter detection unit 51 and the reduced diameter of the grinding wheel 33 formed by the grinding wheel molding processing unit 53 described later. Calculate the outer diameter. Then, the surface shape acquisition unit 52 acquires the outer diameter of the grinding wheel 33 according to the calculated outer diameter of the grinding wheel 33 after molding and the lead of the thread groove 101 of the female screw 100. As the outer peripheral surface shape, a large number of shapes corresponding to the outer diameter of the grinding wheel 33 are determined in advance and stored in advance as a map, a function expression, or the like. This calculation method will be described later.

  The grinding wheel molding processing unit 53 forms the grinding wheel 33 by performing NC control of the NC truing device 40 based on the outer peripheral surface shape of the grinding wheel 33 acquired by the surface shape acquisition unit 52. That is, the grindstone forming means in the present invention corresponds to the grindstone forming processing unit 53 and the NC truing device 40 in the present embodiment.

(3) Grinding Method Using Grinding Wheel 33 In the grinding machine of the present embodiment, a grinding method for grinding the thread groove 101 on the inner peripheral surface of the workpiece 100 to form an internal thread using the grinding wheel 33 is shown in FIGS. This will be described with reference to FIG. FIG. 5A is an axial cross-sectional view in a state where the inner peripheral surface of the workpiece 100 is ground at the reference position (phase 0 degree), and FIG. 5B is an axial direction at phase 0 degree. FIG. FIG. 6A is an axial cross-sectional view showing a state in which the inner peripheral surface of the workpiece 100 is ground at a phase of 90 degrees, and FIG. 6B is a diagram viewed from the axial direction at a phase of 90 degrees. is there. FIG. 7A is an axial cross-sectional view of the state in which the inner peripheral surface of the workpiece 100 is ground at a phase of 180 degrees, and FIG. 7B is a diagram viewed from the axial direction at a phase of 180 degrees. is there. FIG. 8A is an axial sectional view of the state in which the inner peripheral surface of the workpiece 100 is ground at a phase of 270 degrees, and FIG. 8B is a diagram viewed from the axial direction at the phase of 270 degrees. is there. FIG. 9A is an axial sectional view of the state in which the inner peripheral surface of the workpiece 100 is ground at a phase of 360 degrees, and FIG. 9B is a diagram viewed from the axial direction at a phase of 360 degrees. is there.

  First, the grinding wheel 33 is rotationally driven around the grinding wheel axis, and the workpiece 100 is rotationally driven around the axis. Here, the rotation direction of the grinding wheel 33 (the rotation direction around the grinding wheel shaft) and the direction in which the grinding wheel shaft revolves relative to the workpiece 100 are the same direction. At this time, the grinding wheel 33 is moved in the axial direction of the workpiece 100 in synchronization with the rotational driving of the grinding wheel 33 and the workpiece 100 by the control device 50. Then, when the spiral ridge 33 b formed on the grinding wheel 33 contacts the inner peripheral surface of the workpiece 100, the screw groove 101 is ground.

  In the present embodiment, the workpiece 100 rotates once in the reverse direction of the grinding wheel 33 with respect to one rotation of the grinding wheel 33, and the grinding wheel 33 moves by one lead in the axial direction of the workpiece 100. It is controlled synchronously. Further, since the spiral ridge 33b is formed in a spiral shape around the grindstone axis on the outer peripheral surface of the base portion 33a, a plurality of locations are ground simultaneously on the inner peripheral surface of the workpiece 100. .

  A state where the thread groove 101 is ground will be described. As shown in FIGS. 5A and 5B, the grinding wheel 33 grinds the thread groove 101 on the inner peripheral surface of the workpiece 100 at a machining point 104. Here, the actual machining points are linear, and in the description of the grinding method, the machining points will be described as one point for easy explanation. Further, this state in which the grinding wheel reference point 33c and the workpiece reference point 103 are in the same phase is defined as a reference state (phase 0 degree). Further, counterclockwise in FIG. 5B is positive, and clockwise is negative. The processing point 104 at this time is at the position P0. The grinding wheel reference point 33 c is a point positioned on the grinding wheel 33, and the workpiece reference point 103 is a point positioned on the workpiece 100.

  Next, in FIG. 5B, the grinding wheel 33 rotates 90 degrees counterclockwise, and the workpiece 100 rotates 90 degrees clockwise. At this time, the point to be machined out of the thread groove 101 of the workpiece 100 is shifted to the left in FIG. Therefore, in synchronization with the rotation, the grinding wheel 33 moves to the left so that the processing point 104 is at the position P1. Then, as shown in FIGS. 6A and 6B, the processing point 104 is at the lowest point on the inner peripheral surface of the workpiece 100 and is at the position P1. At this time, the grinding wheel reference point 33c moves to a position of 90 degrees phase, and the workpiece reference point 103 moves to a position of -90 degrees phase (equal to 270 degrees). That is, the grinding wheel reference point 33c and the workpiece reference point 103 are located in directions away from each other.

  Further, in FIG. 6B, the grinding wheel 33 rotates 90 degrees counterclockwise, and the workpiece 100 rotates 90 degrees clockwise. At this time, the point to be machined out of the thread groove 101 of the workpiece 100 is shifted to the left in FIG. Therefore, in synchronization with the rotation, the grinding wheel 33 moves to the left so that the processing point 104 is at the position P2. 7A and 7B, the processing point 104 is at the lowest point on the inner peripheral surface of the workpiece 100, and is at the position P2. At this time, the grinding wheel reference point 33c moves to a position of 180 degrees in phase, and the workpiece reference point 103 moves to a position of phase -180 degrees (equal to 180 degrees). That is, the grinding wheel reference point 33c and the workpiece reference point 103 are in the same phase.

  In FIG. 7B, the grinding wheel 33 rotates 90 degrees counterclockwise, and the workpiece 100 rotates 90 degrees clockwise. At this time, the point to be machined out of the thread groove 101 of the workpiece 100 is shifted to the left in FIG. Therefore, in synchronization with the rotation, the grinding wheel 33 moves to the left so that the processing point 104 is at the position P3. Then, as shown in FIGS. 8A and 8B, the machining point 104 is at the lowest point on the inner peripheral surface of the workpiece 100 and at the position P3. At this time, the grinding wheel reference point 33c moves to the position of phase 270 degrees, and the workpiece reference point 103 moves to the position of phase -270 degrees (equal to 90 degrees).

  Finally, in FIG. 8B, the grinding wheel 33 rotates 90 degrees counterclockwise, and the workpiece 100 rotates 90 degrees clockwise. At this time, the point to be machined out of the thread groove 101 of the workpiece 100 is shifted to the left in FIG. Therefore, in synchronization with the rotation, the grinding wheel 33 moves to the left so that the processing point 104 is at the position P4. 9A and 9B, the machining point 104 is at the lowest point on the inner peripheral surface of the workpiece 100 and at the position P4. The grinding wheel reference point 33c moves to a position of phase 360 degrees (equal to 0 degrees), and the workpiece reference point 103 moves to a phase of -360 degrees (equal to 0 degrees). That is, the grinding wheel reference point 33c and the workpiece reference point 103 are in the same phase.

  Thus, when the grinding wheel 33 and the workpiece 100 make one rotation, the grinding wheel 33 moves by one lead in the axial direction of the workpiece 100. By repeating this, the thread groove 101 is ground on the inner peripheral surface of the workpiece 100 to form a screw.

(4) Description of concept of acquisition of outer peripheral surface shape of grinding wheel 33 A concept necessary for calculating an appropriate spiral surface shape of the spiral ridge 33b of the grinding wheel 33 will be described. Here, even if the thread groove 101 of the workpiece 100 has the same diameter, when the outer diameter of the spiral ridge 33b is different, the shape of the spiral ridge 33b is different. The reason for this will be described below. However, in order to facilitate the explanation, not the spiral ridge 33b but the disk-like ridge will be described. When the lead on the spiral ridge 33b is set to 0, the ridge 33b has a disk shape. That is, the reason why the shape of the spiral ridge 33b is different as described above is the same as the case of the disk-like ridge.

  When the outer diameter of the grinding wheel 60 is different, the inclination angle Σ of the central axis (grinding wheel axis) of the grinding wheel 60 with respect to the screw shaft 102 of the female screw 100 coincides with the lead angle γ, and the inclination angle Σ is 0. With reference to FIG. 10 and FIG. 11, the outer peripheral surface shape of the grinding wheel 60 will be described.

  FIG. 10 shows the case where the inclination angle Σ coincides with the lead angle γ, and FIG. 11 shows the case where the inclination angle Σ is 0 °. 10 and 11, (a) the positions of the workpiece 100 and the grinding wheel 60 during grinding are shown. (B1) is a view of the grinding wheel 60 as viewed from the grinding wheel axis direction when the outer diameter of the grinding wheel 60 is relatively large, and (b2) is a cross-sectional view taken along the line CC in (b1), or The outer peripheral surface shape of the grinding wheel 60 in FF sectional drawing is shown. (C1) is a diagram of a state seen from the grinding wheel axis direction during grinding when the outer diameter of the grinding wheel 60 is relatively small, and (c2) is a sectional view taken along the line DD of (c1), or The outer peripheral surface shape of the grinding wheel 60 in GG sectional drawing is shown.

  As shown in FIGS. 10B2 and 10C2, when the inclination angle Σ is made to coincide with the lead angle γ, the outer peripheral surface shape in the axial cross section of the grinding wheel 60 is the same regardless of the outer diameter of the grinding wheel 60. It is. On the other hand, when the inclination angle Σ is different from the lead angle γ, the outer peripheral surface shape in the axial section of the grinding wheel 60 differs depending on the outer diameter of the grinding wheel 60.

  For example, as shown in FIGS. 11 (b2) and 11 (c2), the widths W3 and W4 of the outer peripheral surface shape in the axial section of the grinding wheel 60 change. 10B2 and 10C2 show that the width W of the outer peripheral surface shape in the axial section of the grinding wheel 60 is the same. On the other hand, as shown in FIGS. 11 (b2) and (c2), when the inclination angle Σ is different from the lead angle γ, the grinding wheel 60 has a larger outer diameter, that is, FIGS. 11 (b1) and (b2). The width W3 of the outer peripheral surface shape in the axial cross section of the grinding wheel 60 is smaller in the state shown in FIG. On the other hand, the smaller the outer diameter of the grinding wheel 60, that is, the state shown in FIGS. 11C1 and 11C2, the width W4 of the outer peripheral surface shape in the axial cross section of the grinding wheel 60 becomes larger. That is, even if the diameter of the screw groove 101 and the lead are the same, the width of the spiral ridge 33b changes due to the different outer diameter of the spiral ridge 33b.

  In the spiral ridge 33 b of the present embodiment, the outermost diameter of the ridge 33 b is set smaller than the valley diameter of the female screw 100. Therefore, the circumferential length of the base portion 33a of the grinding wheel 33 and the circumferential length of the thread groove of the female screw 100 are different. The lead angle of the ridge 33b is set larger than the lead angle of the female screw so that the pitch of the ridge 33b is equal to the pitch of the female screw 100. Here, the grinding wheel 60 wears as grinding continues. Therefore, as described in (4-1) above, when the inclination angle Σ is set to 0 °, the outer peripheral surface shape of the grinding wheel 60 changes due to the change in the outer diameter of the grinding wheel 60. That is, in the present embodiment, the outer peripheral surface shape of the grinding wheel 60 is determined by calculation according to the outer diameter of the grinding wheel 60. This will be described in detail in the next section.

(5) Detailed description of acquisition of outer peripheral surface shape of grinding wheel 33 (5-1) Outline As described above, the outer peripheral surface shape of the disc-shaped grinding wheel 60 varies depending on the outer diameter of the grinding wheel 60. Therefore, an equation of a spiral surface corresponding to the thread groove surface obtained by grinding is derived, and thereafter, a contact line between the grinding wheel 60 and the spiral surface (thread groove surface) is calculated. Then, on the outer peripheral surface of the base portion 33a of the grinding wheel 33, the contact line is rotated around the central axis while moving in the axial direction by the lead amount, whereby the outer circumference of the grinding wheel 33 formed with the spiral ridges 33b. A surface shape corresponding to the surface shape is obtained. Below, each calculation process is demonstrated in detail.

(5-2) Derivation of the helical surface equation Derivation of the helical surface equation will be described with reference to FIGS. Here, a spiral surface 201 having an arc cross-sectional shape is considered on the inner peripheral surface of a cylindrical member 200, such as a ball screw nut member as shown in FIG. 13B is a cross-sectional view orthogonal to the traveling direction of the spiral surface 201 of FIG. 12, and FIG. 13A is a plan view of the coordinate system of FIG. 13B. Here, as shown in FIG. 12, each unit vector in the spatial coordinate system (o-xyz) is defined as shown in Expression (1).

  Further, the coordinate system (ou, v) is a plane coordinate system defined in a right-angle cross section of the spiral surface (thread groove) 201 as shown in FIGS. 12 and 13. As shown in FIGS. 12 and 13, v is a radial coordinate axis of the cylindrical member 200 of FIG. 12. That is, v is located on the xy plane and passes through the z axis. However, in FIG. 12 and FIG. 13, v is shown in a state that coincides with the x-axis. u is a coordinate axis that passes through v and is orthogonal to the traveling direction of the spiral surface 201. That is, a cross-sectional view orthogonal to the traveling direction of the spiral surface 201 in FIG. 12 as shown in FIG. 13B can be expressed in the (ou, v) plane coordinate system.

Here, as shown in FIG. 13, the shape of the spiral surface 201 is a Gothic arc shape. That is, the right-hand helical surface 201 in FIG. 13, the central and _{C R,} a circular arc shape having a radius _{r C.} It left helical surface 201, the central and _{C L,} which is a circular arc shape having a radius _{r C.} The cross-sectional shape of the spiral surface 201 includes a diameter da of the ball 202 arranged on the spiral surface 201, a pitch circle radius (PCR) at the center of the ball 202, a contact angle α ₀ between the ball 202 and the spiral surface 201, If the radius r _C , the lead, and the screw outer diameter are determined, the spiral surface 201 is determined.

Then, as shown in FIG. 12, (equation of the vector r ₀₎ vector equation of any curve Γ in space is expressed by Equation (2). That is, the arbitrary curve Γ is expressed as a function of the auxiliary function τ.

When this is expressed in the coordinate system (o-xyz), it can be expressed as in Expression (3). That is, arbitrary points x, y, and z are values determined when τ is determined. Note that τ is an angle around the centers C _R and C _L in the (ou, v) plane coordinate system. τ = 0 is an angle when parallel to the v-axis.

  Here, the movement of rotating the curve Γ around the z axis at a constant speed and simultaneously moving the curve Γ at a constant speed parallel to the z axis is a uniform spiral movement. In this uniform spiral motion, the locus of the curve Γ becomes a spiral surface 201 with the z axis as the central axis. Here, this curve Γ is referred to as a generatrix of the spiral surface 201.

  Then, the equation of the spiral surface 201 of the right-hand cylinder (vector r) is expressed as in equation (4). At this time, p can be expressed as shown in Equation (5).

From the above, if the vector r ₀ (τ) of the bus Γ and the lead are known, the spiral surface 201 formed from the vector r ₀ can be obtained from the equation (4). In addition, although the above has illustrated the nut member of the ball screw, the helical surface equation can be similarly applied to other female screws. Further, the present invention can be applied to the male screw substantially in the same manner.

(5-3) Calculation of Contact Line Next, calculation of the contact line between the grinding wheel 60 and the spiral surface (thread groove surface) 201 (101) will be described with reference to FIG. FIG. 14 is a diagram showing a state in which a nut member of a ball screw as the workpiece 100 is ground by the grinding wheel 60, and shows each coordinate system. Among the coordinate systems, the same symbols as those in FIGS. 12 and 13 indicate the same coordinate system.
Here, in the grinding machine 1 described above, when grinding the screw groove 101 of the nut member 100 of the ball screw by the grinding wheel 60, attention is paid to the fact that there is only one contact line in the space. That is, when this contact line is spirally moved around the center axis 102 (screw axis) of the nut member 100 of the ball screw, the thread groove 101 is obtained. On the other hand, when this contact line is spirally moved around the central axis of the grinding wheel 60, the outer peripheral surface of the grinding wheel 60 is obtained. Here, first, derivation of the contact line will be described.

  As shown in FIG. 14, a coordinate system (o-xyz) of the nut member 100 of the ball screw and a coordinate system (o′-XYZ) of the grinding wheel 60 are defined. Here, the Z axis coincides with the central axis of the grinding wheel 60, and the z axis coincides with the central axis of the workpiece 100. The x axis and the X axis are always coaxial and have the same orientation. Here, the central axis (Z axis) of the grinding wheel 60 is parallel to the central axis (z axis) of the workpiece 100. The distance between the coordinate center o ′ of the grinding wheel 60 and the coordinate center o of the workpiece 100 is a. This center-to-center distance a varies depending on the outer diameter of the grinding wheel 60 if the workpiece shape is the same. Specifically, as the outer diameter of the grinding wheel 60 decreases, the center distance a increases. At this time, the relationship between both coordinate systems is expressed as shown in Equation (6).

  Here, in FIG. 14, unit vectors in the coordinate system (o-xyz) of the workpiece 100 are respectively defined as the above-described equation (1). Further, each unit vector in the coordinate system (o′-XYZ) of the grinding wheel 60 is defined as shown in Expression (7).

  Then, vectors of an arbitrary point M in the space in both coordinate systems are expressed by equations (8) and (9), respectively. Note that (x, y, z) are values having τ and θ as variables, respectively. Furthermore, the center distance a that affects the outer diameter of the grinding wheel 60 is also a variable.

Next, assuming that the rotational angular velocity of the grinding wheel 60 is ω and the rotational angular velocity of the spiral surface (thread groove) is ω ′, the speed and relative speed of the grinding wheel 60 and the spiral surface (thread groove) 201 at the above point M are calculate. A velocity vector v ₁ when the point M moves along the spiral surface 201 is expressed by Expression (10). On the other hand, the velocity vector v ₂ when the point M is movement along the plane of rotation of the grinding wheel 60 is expressed by equation (11). The relative velocity vector _{v 12} of the grinding wheel 60 and the spiral surface (thread groove) 201, the equation (10) (11), the formula (12).

The first relational expression of Expression (13) can be derived using Expression (10) indicating the velocity vector v ₁ and the normal vector n obtained from Expression (4).

A procedure for deriving the first relational expression (13) will be described. First, equation (10) indicating the velocity vector v ₁ is expressed as equation (14) when equation (9) is substituted and converted.

  Here, when Equation (4) is partially differentiated by θ, it is expressed as Equation (15).

  From Expression (14) and Expression (15), it can be seen that both are located on the same line. That is, the velocity of an arbitrary point M on the spiral surface 201 is in the tangential direction of the point, and is orthogonal to the normal vector n of the arbitrary point M (x, y, z) on the curved surface r. From this, equation (13) can be derived.

  Here, since the normal vector n can be expressed as in Expression (16), when Expression (13) is expressed as a coordinate expression, it is expressed as Expression (17).

  Next, based on the first relational expression (13) and the contact condition between the grinding wheel 60 and the spiral surface (thread surface) 201, the conditional expression of the contact line on the spiral surface 201 is expressed by the following expression (18). expressed.

  Thus, if the center-to-center distance a is determined from the contact line conditional expression (18), θ for each τ can be obtained, and the contact lines (x, y, z) can be derived. The center-to-center distance a is a value that varies depending on the outer diameter of the grinding wheel 60 as described above.

(5-4) Acquisition of the spiral surface shape of the grinding wheel The calculated grinding wheel 33, the thread groove 101 of the workpiece 100, and the contact lines (x, y, z) are linear as shown in FIG. Become. Then, by causing this contact line to spirally move around the central axis (Z axis) of the grinding wheel 33, the ridge 33b having the spiral surface shape of the grinding wheel 33 is obtained. Specifically, the contact line is converted from the coordinate system (o-xyz) of the workpiece 100 to the coordinate system (o′-XYZ) of the grinding wheel 60 based on the relationship of the expression (6).

  Next, the rotation angle φ from the X axis of each point of the contact line in the XZ plane is calculated according to the equation (19). The rotation angle φ is shown in FIG. And the coordinate (U, W) of the contact line in the XZ plane of the protruding item | line 33b of the grinding wheel 60 is calculated. U is the X-axis value of the coordinate system (o'-XYZ) of the grinding wheel 60, and W is the Z-axis value of the coordinate system (o'-XYZ) of the grinding wheel 60. (U, W) is expressed as in Expression (20), and represents the cross-sectional shape in the axial direction of the grinding wheel 60 on the ridge 33b. Therefore, the shape of the ridge 33b is obtained by spirally moving this (U, W) so as to advance one lead per rotation around the axis of the grinding wheel 60.

As described above, in the present embodiment, the ridge 33b of the grinding wheel 33 is determined by calculation based on the outer diameter of the grinding wheel 33. The determination by this calculation is performed when the surface shape acquisition unit 62 described above determines the outer peripheral surface shape of the grinding wheel 33. In the above calculation, the center-to-center distance a that varies depending on the outer diameter of the grinding wheel 60 is obtained not by the outer diameter of the grinding wheel 60 before molding, but by the outer diameter of the grinding wheel 33 after molding. Accordingly, the center-to-center distance a is calculated by estimating the outer diameter of the grinding wheel 33 after molding in consideration of the reduced diameter due to molding of the grinding wheel 33.
(6) Effect By applying the calculation method described above, the shape of the ridge 33b of the grinding wheel 33 capable of grinding the thread groove 101 of the workpiece 100 can be determined. Moreover, since it considers that the helical surface shape of the grinding wheel 33 changes according to the outer diameter of the grinding wheel 33, the protruding item | line 33b of the grinding wheel 33 which can be ground with higher precision can be formed.

  Further, when forming the female thread of the workpiece 100, a non-contact gap is formed between the inner peripheral surface of the workpiece 100 and the outer peripheral surface of the grinding wheel 33. This gap makes it easier to discharge chips and allows coolant to be inserted into the gap.

  Further, a screw having a large lead angle and screw depth can be ground without turning the grinding wheel 33 in the direction orthogonal to the axis of the workpiece 100. In other words, the grinding machine 1 of the present invention can grind the screws that could not be ground by the conventional disc-shaped grinding wheel. Further, in a screw that can be ground by a conventional disk-shaped grinding wheel, the outer diameter of the grinding wheel 33 of the present invention can be made larger than that of a conventional disk-shaped grinding wheel. Therefore, the rigidity of the grinding wheel 33 can be increased and the life of the grinding wheel 33 can be extended.

  Further, it is not necessary to incline the axis of the grinding wheel 33 with respect to the axis of the workpiece 100. Therefore, even if the internal diameter of the internal thread 101 is small, the workpiece 100 and the grinding wheel 33 or the support shaft member 35 can be ground without interference. Furthermore, a sufficient grinding force can be applied to the grinding wheel 33 without reducing the bending rigidity of the support shaft member 35. Therefore, the grinding time can be shortened.

  Furthermore, since a plurality of ridges 33b are circulated, a plurality of locations can be ground simultaneously. As a result, the grinding process can be speeded up. Moreover, the lifetime of the grinding wheel 33 can be extended by providing many parts of the protrusion 33b which can be ground.

  Further, as described above, as the outer diameter of the grinding wheel 33 changes, the spiral surface shape of the grinding wheel 33 to be formed changes. Therefore, by forming the ridge 33b of the grinding wheel 33 using the NC truing device 50, it is possible to finely cope with changes in the outer diameter of the grinding wheel 33, and as a result, the screw groove 101 can be ground with high accuracy.

  In the grinding method of the first embodiment, the workpiece 100 and the grinding wheel 33 rotate together, and the grinding wheel 33 moves relative to the workpiece 100 in the radial direction of the workpiece 100, so that the thread groove 101 is obtained. Is grinding. Therefore, the processing point of grinding can be set at the same position (same phase) in the rotation direction of the workpiece 100. Therefore, it becomes possible to reliably supply the coolant to the processing point, and it is possible to perform grinding to efficiently and reliably form the thread groove 101.

<Second embodiment>
Next, the grinding method by the grinding machine of 2nd embodiment is demonstrated with reference to FIG. FIG. 16 is a diagram illustrating a grinding method according to the second embodiment. Here, the grinding machine of the second embodiment is different from the grinding machine of the first embodiment in the following points. First, the workpiece 100 is fixed to the bed 10 so as not to rotate. The spindle device 20 in the first embodiment is for simply holding the workpiece 100. Second, the axis of the grinding wheel 33 operates so as to revolve around the axis of the workpiece 100. Specifically, the grindstone base 32 is configured to be further movable in the Y-axis direction with respect to the bed 10.

Using the grinding machine having such a configuration, the thread groove 101 of the workpiece 100 is ground as follows. Simultaneously three-axis control is performed so that the grinding wheel shaft revolves around the axis of the workpiece 100 while the grinding wheel 33 rotates around the grinding wheel axis while the workpiece 100 is fixed.
That is, the grinding method of the first embodiment rotates the workpiece 100 and the grinding wheel 33, whereas the grinding method of the second embodiment rotates the grinding wheel 33 with the workpiece 100 fixed. And it is revolving. However, the relative positions of the workpiece 100 and the grinding wheel 33 match between the grinding method of the first embodiment and the grinding method of the second embodiment. That is, also in the grinding method of the second embodiment, the same effect as that of the first embodiment is obtained.

  However, according to the grinding method of the second embodiment, the following effects are further achieved due to the difference in the machine configuration. Since grinding is performed with the workpiece 100 fixed, the support rigidity of the workpiece 100 can be increased. Thereby, highly accurate grinding can be performed. Moreover, it can prevent that the error by rotating both the workpiece 100 and the grinding wheel 33 arises.

<Others>
In the above embodiment, the single thread groove 101 of the workpiece 100 is ground by using the protrusion 33b as a single thread. In addition to this, a multi-thread can be formed on the workpiece 100 by making the ridges 33b into multi-strands. Moreover, you may form the protruding item | line 33b in a spiral shape so that it may become less than 1 round around the axis | shaft of the grinding wheel 33. FIG. In this case, since it is not necessary to match the lead of the spiral ridge 33b with the lead of the screw, the degree of freedom in designing the ridge 33b such as the lead angle can be improved. Further, it is lighter than the multiple-turn grinding wheel 33, is less likely to be bent, and enables high-precision finishing.

DESCRIPTION OF SYMBOLS 1: Grinding machine, 10: Bed, 11, 12: Grinding wheel guide rail 13, 14: Spindle head guide rail, 15: Grinding wheel Z-axis motor 16: Grinding wheel Z-axis ball screw, 17: Spindle head Z-axis motor 20: Spindle device, 21: Spindle base (workpiece rotating means), 22: Spindle 23: Chuck (workpiece holding means)
30: Whetstone support device 31: Whetstone traverse base 31a, b: X-axis guide rail 31c: X-axis ball screw 31d: X-axis motor 32: Whetstone base
33: Grinding wheel, 33a: Base, 33b: Projection, 33c: Grinding wheel reference point 34: Grinding wheel motor (grinding wheel rotating means), 35: Support shaft member 40: NC truing device, 41: Support member, 42 : Rotary dresser 50: Control device (control means) 51: Outer diameter detection unit 52: Surface shape acquisition unit 53: Grinding wheel forming processing unit 60: Grinding wheel (disk shape)
100: Workpiece (internal thread) 101: Screw groove 102: Screw shaft 103: Workpiece reference point 104: Machining point

Claims (13)

A workpiece holding means for holding a shaft-shaped workpiece;
It is rotatable around a grindstone axis parallel to the axis of the workpiece, is movable relative to the workpiece in the axial direction and the axis orthogonal direction of the workpiece, and the grindstone axis is moved to the workpiece A grinding wheel that is rotatable relative to the workpiece about the axis of the workpiece;
With
In a grinding machine that forms a screw by grinding a screw groove on the inner peripheral surface of the workpiece,
The grinding wheel is
The base,
A ridge formed in a spiral shape in the grinding wheel axis direction on the outer peripheral surface of the base, and set at a lead angle different from the lead angle of the screw;
Equipped with a,
Grinder said to parallel the axis of the workpiece and said grinding wheel shaft and the screw groove, wherein the grinding to Rukoto by relatively moving the grinding wheel in the axial direction of the workpiece. In claim 1,
In the case of forming an internal thread on the inner peripheral surface of the workpiece,
A grinding machine, wherein an outermost diameter of the ridge is set smaller than a root diameter of the female screw. In claim 1 or 2,
Grinding wheel rotating means for rotating the grinding wheel around the grinding wheel axis;
Workpiece rotation means for rotating the workpiece around the axis of the workpiece;
Axis moving means for moving the grinding wheel relative to the workpiece in the axial direction and the axis orthogonal direction of the workpiece;
Control means for controlling the grinding wheel rotating means, the workpiece rotating means, and the axis moving means;
A grinding machine comprising: In claim 1 or 2,
Bed and
Grinding wheel rotating means for rotating the grinding wheel around the grinding wheel axis;
Axis moving means for moving the grinding wheel relative to the workpiece in the axial direction and the axis orthogonal direction of the workpiece;
Revolving means for relatively rotating and driving the grindstone shaft around the workpiece axis;
Control means for controlling the grinding wheel rotating means, the shaft moving means, and the revolution means;
With
The workpiece holding means fixes the workpiece so as not to rotate with respect to the bed. In any one of Claims 1-4,
The ridge is formed in a spiral shape so as to extend over a plurality of circumferences around the grindstone axis. In claim 5,
The grinding machine according to claim 1, wherein the protrusion is set to a lead angle larger than a lead angle of the screw. In any one of Claims 1-4,
The grinding machine is characterized in that the ridge is formed in a spiral shape so as to be less than one turn around the grindstone axis. In any one of Claims 1-7,
The grinding machine according to claim 1, wherein the protrusions are formed in multiple lines. In any one of Claims 1-8,
The grinding machine
A surface shape acquisition means for calculating a contact line between a thread groove surface of the thread groove of a grinding target and the grinding wheel, and acquiring a surface shape by rotating the contact line around a central axis of the grinding wheel;
Grinding wheel forming means for forming the outer peripheral surface of the grinding wheel into the surface shape acquired by the surface shape acquisition means;
A grinding machine comprising: In claim 9,
The grinding machine according to claim 1, wherein the grinding wheel forming means is an NC truing device that forms an outer peripheral surface of the grinding wheel by NC control. A grinding wheel parallel to the axis of the axial workpiece is rotated around the grinding wheel axis, moved relative to the workpiece in the axial direction and the axis orthogonal direction of the workpiece, and the grinding wheel shaft is In a grinding method for forming a screw by grinding a screw groove on an inner peripheral surface of the workpiece by rotating the workpiece relative to the workpiece about the axis of the workpiece,
The grinding wheel is
The base,
A ridge formed in a spiral shape in the grinding wheel axis direction on the outer peripheral surface of the base, and set at a lead angle different from the lead angle of the screw;
With
Wherein the shaft of the workpiece and the said wheel spindle and parallel, by relatively moving the grinding wheel in the axial direction of the workpiece, grinding the said screw groove I by prior Kitotsujo Grinding method. In claim 11,
The grinding wheel is rotated about the grinding wheel axis, the workpiece is rotated about the axis of the workpiece, and the grinding wheel is relative to the workpiece in an axial direction and an axis orthogonal direction. A grinding method characterized in that a screw groove is formed by grinding a screw groove on the inner peripheral surface of the workpiece by relative movement. In claim 11,
The workpiece is fixed to the bed in a non-rotatable manner, the grinding wheel is rotated about the grinding wheel axis, and the grinding wheel is moved relative to the workpiece in an axial direction and an axis orthogonal direction of the workpiece. A grinding method characterized in that a screw is formed by grinding a thread groove on an inner peripheral surface of the workpiece by moving and rotating the grindstone shaft relatively around the axis of the workpiece.

Images