JPH11138412A - Wire saw having fixed abrasive grains and its cutting method of workpiece to be cut - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately cut a workpiece by sensing cutting resistance of the workpiece during cutting, and controlling feeding speed of the workpiece so as to obtain a set value of cutting resistance. SOLUTION: An endless wire saw 10 having fixed abrasive grains is provided with a cutting unit 12, in which wire lines 28 are formed by sequentially wrapping a wire 26 having fixed abrasive grains along grooves of grooved rollers 24A, 24B from an inlet side to an outlet side. A workpiece (ingot) In is fed by a feeding unit 14, and cut into plural pieces by means of the cutting unit 12. The workpiece In is attached to a column 56 movable on a guide rail 54 of the feeding unit 14 through a tilting unit 64. A cutting resistance meter is arranged on a workpiece holding part 54a of the unit 64. Cutting resistance of the workpiece In is sensed during cutting, and the feeding speed of the workpiece In is controlled so as to obtain a set value of cutting resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire saw with fixed abrasive grains and a method of cutting a workpiece, and more particularly, to a method of cutting silicon,
The present invention relates to a wire saw with fixed abrasives for cutting a workpiece made of a hard and brittle material such as glass and ceramic, and a method of cutting the workpiece.

[0002]

2. Description of the Related Art A wire saw with fixed abrasive grains is one of devices for cutting a wafer from an ingot of a hard brittle material such as silicon. This wire saw with fixed abrasives is a device that cuts the ingot by pressing the ingot against the wire with fixed abrasives that has run at high speed.

[0003] When a cylindrical ingot is cut with the wire saw with fixed abrasives, the contact length of the ingot with the wire changes according to the cutting position. When an ingot having a contact length that changes in this way is cut at a constant feed speed, the cutting resistance changes. When the cutting resistance of the ingot changes, the traveling direction and the amount of deflection of the wire change, so that the cutting accuracy of the wafer decreases.

For this reason, in the conventional wire saw with fixed abrasives, in order to keep the cutting resistance constant, the feed speed of the ingot is changed according to the contact length with the ingot.

[0005]

However, the cutting resistance actually generated in the ingot varies depending on the degree of clogging of the wire and the degree of supply of the coolant. Therefore, simply changing the feed speed of the ingot results in high accuracy. The wafer could not be cut. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a wire saw with fixed abrasives that can cut a workpiece with high accuracy, and a method of cutting the workpiece.

[0006]

The invention according to claim 1 is
In order to achieve the above object, a workpiece to be processed is sent to a traveling fixed abrasive wire, and the workpiece is cut by pressing the workpiece against the fixed abrasive wire. In the object cutting method, a cutting resistance of the workpiece during cutting is detected, and a feed speed of the workpiece is controlled such that the cutting resistance has a preset value.

According to the present invention, the cutting resistance of the workpiece during cutting is detected, and the feed speed of the workpiece is controlled so that the cutting resistance has a preset target value. In order to achieve the above object, the invention according to claim 3 sends a workpiece toward a traveling fixed abrasive wire and cuts the workpiece by pressing the workpiece against the fixed abrasive wire. In the method for cutting a workpiece with a fixed-abrasive wire saw, the cutting speed of the fixed-abrasive wire is detected such that the cutting resistance of the workpiece during cutting is detected and the cutting resistance becomes a preset value. Is controlled.

According to the present invention, the cutting resistance of the workpiece during cutting is detected, and the traveling speed of the wire with fixed abrasive grains is controlled so that the cutting resistance becomes a preset value. In order to achieve the above object, the invention according to claim 5 sends a workpiece toward a traveling fixed abrasive wire and cuts the workpiece by pressing the workpiece against the fixed abrasive wire. In the method for cutting a workpiece with a fixed-abrasive wire saw, the cutting speed of the fixed-abrasive wire is detected such that the cutting resistance of the workpiece during cutting is detected and the cutting resistance becomes a preset value. And controlling the feed speed of the workpiece.

According to the present invention, the cutting speed of the wire with the fixed abrasive grains and the feeding of the workpiece are detected so that the cutting resistance of the workpiece during cutting is detected so that the cutting resistance becomes a preset value. Control the speed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a wire saw with fixed abrasive grains and a method of cutting a workpiece according to the present invention will be described below in detail with reference to the accompanying drawings. First, the overall configuration of a wire saw with fixed abrasives to which the present invention is applied will be described. The wire saw with fixed abrasive described below is an endless wire saw with fixed abrasive, that is, a wire saw with fixed abrasive using an endless wire with fixed abrasive.

As shown in FIGS. 1 and 2, the wire saw with fixed abrasives 10 mainly comprises a cutting unit 12 for cutting the ingot In and a work feed unit 14 for feeding the ingot In. . First,
The configuration of the cutting unit 12 will be described. Anti-vibration table 16, 1
A pair of spindle brackets 20, 20 are vertically set on a gantry 18 installed horizontally through 6,. A pair of left and right spindle units 22A and 22B are disposed on the spindle brackets 20 and 20 at predetermined intervals in the vertical direction.

The pair of spindle units 22A, 22A
Groove rollers 24A, 24B having spiral grooves formed on the outer periphery are rotatably supported by 2B. The wire row 28 is formed by sequentially winding the wire 26 with the fixed abrasive grains along the grooves of the groove rollers 24A and 24B. In front of the groove rollers 24A, 24B, a wire 2 with fixed abrasive grains having a wire row 28 is formed.
6 for guiding the roller 6 from one end of the groove rollers 24A, 24B to the other end.
L, 30R and 30R are installed. The guide rollers 30L, 30L, 30R, and 30R are provided in a pair at each of one end and the other end of the groove rollers 24A and 24B, and rotate on a frame (not shown) installed on the gantry 18. It is freely supported. The wire 26 with the fixed abrasive which has been fed out from one end of the groove rollers 24A, 24B is connected to the guide rollers 30L, 3L.
It is guided to the other end side by sequentially winding around 0L, 30R, and 30R. Then, on the other end side, the both end portions are joined by laser welding or the like to form an endless shape.

The groove rollers 24A, 24B
A tension unit 32 for applying a predetermined tension to the traveling fixed abrasive wire 26 is provided in front of the wire. The tension unit 32 includes a pair of fixed guide rollers 34, 34, and the fixed guide rollers 34, 34.
The fixed guide rollers 34, 34 are provided between the mount 18 and the tension roller 36.
It is rotatably supported on a frame (not shown) installed above. On the other hand, the tension roller 36 is rotatably supported on a slider 40 slidably supported on a guide rail 38 in a vertical direction, and a tension weight 42 having a predetermined load is suspended. The fixed abrasive grain-attached wire 26 whose both ends are joined to each other is wound around the fixed guide rollers 34, 34 and the tension roller 36 of the tension unit 32, so that a predetermined tension is applied.

The traveling of the wire array 28 constructed as described above is performed by rotating the groove roller 24B located at the lower side at a high speed. That is, the rotation is performed by rotating one groove roller 24B at a high speed by the drive motor 44. The drive motor 44 sends the groove roller 24
B is transmitted by a belt 50 and a spindle pulley 46 connected to one end of the groove roller 24B.
And a motor pulley 48 connected to the output shaft of the drive motor 40 by a belt 50, thereby transmitting the rotation of the drive motor 44 to the groove roller 24B.

The drive motor 44 is connected to the controller 7
The driving speed of the wire train 28 is controlled by controlling the output of the driving motor 44. The cutting unit 12 is configured as described above. Next, the configuration of the cutting and feeding unit 14 will be described.

As shown in FIG. 2, the cutting unit 12
A base 52 is installed on the gantry 18 on which is installed the right side of the cutting unit 12 in the drawing. This base 5
A pair of guide rails 54, 54 are laid on the upper part of 2, and a column 56 is slidably supported on the guide rails 54, 54. A screw rod 58 is provided inside the base 52 along the guide rails 54, 54.
The screw rod 58 is rotatably supported at both ends by brackets 60, 60. An output shaft of a work feed motor 62 installed on the gantry 18 is connected to one end of the screw rod 58, and by driving the work feed motor 62, the screw rod 58 rotates. A nut member 56A screwed to the screw bar 58 is fixed to the lower surface of the column 56, and the column 56 moves by rotating the screw bar 58.

The driving of the work feed motor 62 is controlled by a control device 70. By controlling the drive of the work feed motor 62, the feed speed V of the column 56 is controlled. The column 56 is formed in an L-shape, and a tilting unit 64 is provided at the top. Workpiece Ingot In
Is a work holding portion 64a of the tilting unit 64.
Attached to. And the attached ingot In,
The tilting unit 64 inclines the crystal at a predetermined angle and performs a predetermined crystal orientation alignment.

The mounting of the ingot In to the tilting unit 64 is performed via a mounting block M, and the ingot In adhered to the mounting block M via the slice base S is attached to a work holding portion of the tilting unit 64. 64a and fixed with screws or the like. The work holding portion 64a of the tilting unit 64 is provided with a cutting resistance meter (not shown), and the ingot I is being cut by the cutting resistance meter.
The n cutting resistances F are detected. The cutting resistance meter uses, for example, a piezo element, and electrically detects X, Y, and Z components of a cutting load applied to the ingot In during cutting. Then, the detection value is output to the control device 70. Note that the X direction is the traveling direction of the wire row 28, and the Y direction is a direction orthogonal to the wire row 28. The Z direction is the ingot feed direction.

The wire saw with fixed abrasives 10 is configured as described above, and the ingot In is cut as follows. First, the ingot In is bonded to the mounting block M via the slice base S, and the ingot In bonded to the mounting block M is mounted on the work mounting portion of the tilting unit 64. After mounting, the ingot In is inclined by a predetermined angle with respect to the wire row 28 by the tilting unit 64 so that the ingot In is cut in a predetermined crystal orientation.

Next, the drive motor 44 is driven to rotate the groove roller 24B at a high speed.
The wire row 28 stretched between A and 24B is run at high speed. Next, the work feed motor 62 is driven to drive the column 5
6 is sent toward the cutting unit 12 at a constant feed speed V. As a result, the ingot In is pressed against the high-speed running wire array 28.

The ingot In pressed against the wire row 28 is ground at a contact portion with the wire row 28 into fixed abrasive grains fixed to the peripheral surface of the wire 26 with fixed abrasive grains. Cut into wafers. At the time of this cutting, a coolant is supplied to a contact portion between the ingot In and the wire row 28 from a coolant supply nozzle 66 installed above the contact portion. Then, the supplied coolant is collected and discarded by a drain pan 68 provided below the groove roller 24B.

Next, the wire saw 10 with the fixed abrasive described above is used.
A first embodiment of a workpiece cutting method according to the present invention applied to the present invention will be described. First, the operator sets a reference value F of the cutting resistance and inputs the reference value F to the control device 70. Here, as shown in FIG. 3A, the cutting resistance is set so as to be always a constant value F regardless of the cutting position of the ingot In.

Next, the operator operates the fixed abrasive wire 26.
The reference value of the traveling speed v is set and input to the control device 70. Here, a cylindrical ingot In is formed.
The traveling speed v is set in accordance with the contact length of. That is, as shown in FIG. 3B, the travel speed v is set to be the maximum at the center of the ingot In where the contact length is the maximum.

Next, the operator sets an initial value V _O of the feed speed of the ingot In and inputs it to the control device 70.
When the above setting is completed, the cutting of the ingot In is started. That is, the control device 70 drives each motor and the like based on the above settings. The cutting resistance of the ingot In during cutting is detected by a cutting resistance meter, and the detected value is output to the control device 70. Control device 70
Controls the feed speed V of the ingot In such that the detected value becomes the reference value F. For example, when the detected value is higher than the reference value F, the feed speed V of the ingot In is reduced, and when the detected value is lower than the reference value F, the feed speed V of the ingot In is increased.

As a result, the ingot In is always cut while maintaining a constant cutting resistance, and the cutting accuracy is improved. That is, by keeping the cutting resistance of the ingot In constant, the traveling direction of the fixed abrasive wire 26 is stabilized and the run-out is reduced.
A small wafer such as a TV can be obtained. Next, a second embodiment of the workpiece cutting method according to the present invention will be described.

In the above-described first embodiment, control for making the cutting resistance constant is performed by controlling the feed speed V of the ingot In. In the second embodiment, by controlling the traveling speed v of the fixed abrasive wire 26,
The cutting resistance of the ingot In is controlled to be constant. Specifically, the following control is performed. First, the operator sets a reference value F of the cutting resistance and inputs the reference value F to the control device 70. Here, as in the first embodiment, the ingot I
The cutting resistance is set so that it always becomes a constant value F regardless of the cutting position of n (see FIG. 4A).

Next, the operator sets a reference value F for the feed speed V of the ingot In and inputs it to the control device 70.
Here, the feed speed V is set according to the contact length of the ingot In.
Set. That is, as shown in FIG. 4B, the feed speed V is set to be the maximum at the center of the ingot In where the contact length is the maximum. Next, the operator sets an initial value v _O of the traveling speed of the wire with fixed abrasive grains 26,
Input to the controller 70.

When the above setting is completed, the cutting of the ingot In is started. That is, the control device 70 drives each motor and the like based on the above settings. The cutting resistance of the ingot In during cutting is detected by a cutting resistance meter, and the detected value is output to the control device 70. The control device 70 controls the traveling speed v of the wire 26 with the fixed abrasive so that the detected value becomes the reference value F. For example, when the detected value is higher than the reference value F, the traveling speed v of the fixed abrasive wire 26 is decreased, and when the detected value is lower than the reference value, the traveling speed v is increased.

Thus, the ingot In is always cut while maintaining a constant cutting resistance, and the cutting accuracy is improved. Next, a third embodiment of the workpiece cutting method according to the present invention will be described. The first mentioned above,
In the second embodiment, control is performed to control the cutting resistance to be constant by controlling either the feed speed V of the ingot In or the traveling speed v of the wire 26 with the fixed abrasive. In the third embodiment, the cutting resistance of the ingot In is controlled to be constant by simultaneously controlling the feed speed V of the ingot In and the traveling speed v of the wire 26 with the fixed abrasive.

That is, first, the operator sets a reference value F of the cutting resistance and inputs the reference value F to the control device 70. Here, as in the first and second embodiments, the ingot I
The cutting resistance is set so as to be always constant irrespective of the cutting position of n (see FIGS. 3A and 4A). Next, the operator sets the initial value v of the traveling speed of the wire 26 with the fixed abrasive.
An initial value V _O of the feed speed of _O and the ingot In is set and input to the control device 70.

When the above setting is completed, the cutting of the ingot In is started. That is, the control device 70 drives each motor and the like based on the above settings. The cutting resistance of the ingot In during cutting is detected by a cutting resistance meter, and the detected value is output to the control device 70. The controller 70 controls the traveling speed v of the wire 26 with fixed abrasive grains and the feed speed V of the ingot In such that the detected value becomes the reference value. For example, when the detected value is higher than the reference value F, the traveling speed v of the wire with fixed abrasive grains 26 is increased and the feed speed V of the ingot In is decreased. When the detected value is lower than the reference value F, the traveling speed of the wire 26 with the fixed abrasive is reduced and the feed speed V of the ingot In is increased.

As a result, the ingot In is always cut while maintaining a constant cutting resistance, and the cutting accuracy is improved. Note that the traveling speed v of the wire 26 with the fixed abrasive and the feed speed V of the ingot In may be controlled simultaneously, or in some cases, only one of them may be controlled. As described above, by cutting while keeping the cutting resistance of the ingot In constant, the cutting accuracy of the wafer is improved.

However, the above method is not applied to all ingots. Depending on the material and shape of the ingot to be cut, it is possible to cut the wafer with higher precision by changing the cutting resistance according to the cutting position. There are cases. In some cases, changing the cutting resistance according to the cutting position can efficiently cut a highly accurate wafer. In such a case, the reference cutting resistance is varied and set in accordance with the cutting position based on past experimental data and the like. For example, FIG.
As shown in (2), the curve is set so that the cutting resistance becomes maximum when cutting the center of the ingot.

As described above, the cutting resistance is not only constant,
It may be set to be variable depending on the material and shape of the ingot to be cut. In the wire saw 10 with fixed abrasive grains of the present embodiment, the cutting resistance of the ingot In during cutting is detected by a cutting resistance meter. However, the detected value of the cutting resistance of the ingot In and the preset value are set in advance. By using the reference value of the cutting resistance, it is possible to detect the abnormal cutting of the wire saw 10 with the fixed abrasive.

That is, in the above-described series of embodiments, the feed speed V of the ingot In or the traveling of the wire 26 with the fixed abrasive grains is adjusted so that the cutting resistance of the ingot In becomes constant based on the detection value of the cutting resistance meter. Although the speed v is controlled, if the cutting resistance is not constant even by such control, it can be clearly determined that the cutting is abnormal (abnormal coolant supply, deterioration of sharpness of the wire, etc.). If exceeds a predetermined value, the operation of the wire saw 10 with fixed abrasives is stopped.

In this embodiment, the cutting resistance of the ingot In is measured using a piezo element in the cutting resistance meter, but the method of detecting the cutting resistance is not limited to this. For example, if the cutting resistance increases,
Since the load of the drive motor 44 for running the wire increases,
By detecting the load (change in current value) of the drive motor 44, the traveling speed of the fixed abrasive wire 26 or the feed speed of the ingot In is controlled. That is, the reference value of the load applied to the drive motor 44 is set in advance,
The running speed of the wire 26 with fixed abrasive grains or the feed speed of the ingot In is controlled so as to be the reference value.

As another method, the traveling speed of the wire 26 with fixed abrasive grains or the feed speed of the ingot In is controlled by detecting the number of rotations of the groove roller or the guide roller. That is, when the cutting resistance increases,
Since the rotation speed of the groove roller or the like decreases, a reference value for the rotation speed of the groove roller or the like is set in advance, and the traveling speed of the wire 26 with the fixed abrasive grains or the feed speed of the ingot In is set to this reference value. Control.

Even if the cutting resistance is detected by the above method, the same effect as that of the above-described embodiment can be obtained. Further, in the present embodiment, the example in which the cutting method of the present invention is applied to the endless type wire saw with fixed abrasive grains 10 has been described. However, the cutting method of the present invention is also applicable to other wire saws with fixed abrasive grains. Can be applied to

For example, in the wire saw 100 with fixed abrasive grains shown in FIG. 6, a wire 114 with fixed abrasive grains running between a pair of wire reels 112A and 112B is wound around three groove rollers 122, 122 and 122. Row 12
This is a fixed-abrasive wire saw of the type that forms No. 4, and the cutting method of the present invention can also be applied to this type of fixed-abrasive wire saw.

The wire saw 1 with fixed abrasive grains shown in FIG.
Reference numeral 60 denotes a fixed-abrasive wire saw in which a large number of fixed-abrasive wires 164, 164,... Are stretched at a constant pitch on a rectangular frame 162 to form a wire row 166. Is reciprocated along the direction in which the wires are stretched, so that the wire row 166 runs. The cutting method according to the present invention can be similarly applied to this type of wire saw with fixed abrasive grains.

Further, a wire saw 1 with fixed abrasive grains shown in FIG.
Reference numeral 70 denotes a number of fixed abrasive-coated wires 174, 174 formed endlessly on a pair of groove rollers 172, 172;
Are stretched at a constant pitch to form a wire row 176.
By rotating 72, the wire array 176 is run. The cutting method according to the present invention can be similarly applied to this type of wire saw with fixed abrasive grains.

The endless type wire saw with fixed abrasives 10 is a wire saw with fixed abrasives shown in FIG.
In comparison with the above, there is an advantage that the wire with fixed abrasive grains is run by one drive motor 44, so that the speed of the wire can be increased and the running control thereof can be easily performed. That is, the wire saw 100 with fixed abrasive grains shown in FIG.
Since the driving motors 118A and 118B connected to the motor must be driven in synchronization, there is a problem in terms of running control and speeding up. Considering this point, it can be said that the endless type wire saw 10 with fixed abrasive shown in FIG. 1 is superior to the wire saw 100 with fixed abrasive shown in FIG.

The endless type wire saw with fixed abrasives 10 is a wire saw with fixed abrasives shown in FIG.
In comparison with the above, since the wire row 28 is formed by one endless fixed abrasive wire 26, there is an advantage that a wafer with uniform accuracy can be cut. That is, the wire saw 100 with fixed abrasive grains shown in FIG.
Because each wire is independent, the behavior of each wire at the time of cutting varies due to differences in the distribution of abrasive grains and the degree of clogging, etc., and the accuracy of the cut wafer is one by one. It will be different. Considering this point, it can be said that the endless type wire saw 10 with fixed abrasives shown in FIG. 1 is superior to the wire saw 100 with fixed abrasives shown in FIG.

[0044]

As described above, according to the present invention,
By detecting the cutting resistance of the workpiece during cutting and controlling the traveling speed of the wire or the feed rate of the workpiece so that the cutting resistance becomes a preset value, the workpiece can be accurately detected. Can be cut.

[Brief description of the drawings]

FIG. 1 is a front view showing the configuration of a wire saw with fixed abrasive grains.

FIG. 2 is a side view showing a configuration of a wire saw with fixed abrasive grains.

FIG. 3 is an explanatory view of a first embodiment of a workpiece cutting method according to the present invention.

FIG. 4 is an explanatory view of a second embodiment of the workpiece cutting method according to the present invention.

FIG. 5 is an explanatory diagram of another embodiment of the work cutting method according to the present invention.

FIG. 6 is a perspective view of another embodiment of a wire saw with fixed abrasive grains.

FIG. 7 is a perspective view of another embodiment of a wire saw with fixed abrasive grains.

FIG. 8 is a perspective view of another embodiment of a wire saw with fixed abrasive grains.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Wire saw with fixed abrasive 24A, 24B ... Groove roller 26 ... Wire with fixed abrasive 28 ... Wire row 30L, 30R ... Guide roller 36 ... Tension roller 44 ... Drive motor 56 ... Column 62 ... Work feed motor 64 ... Tilting Unit 70: Control device In: Ingot

Claims (6)

[Claims] 1. A method for cutting a workpiece with a fixed-abrasive wire saw in which a workpiece is fed toward a traveling fixed-abrasive wire and the workpiece is pressed against the fixed-abrasive wire to cut the workpiece. A wire saw with fixed abrasive grains, characterized in that a cutting resistance of the workpiece during cutting is detected, and a feed speed of the workpiece is controlled so that the cutting resistance has a preset value. Workpiece cutting method. 2. A fixed-abrasive wire saw for feeding a workpiece toward a traveling fixed-abrasive wire and pressing the workpiece against the fixed-abrasive wire to cut the workpiece. A cutting resistance meter for detecting the cutting resistance of the workpiece, and a feed rate of the workpiece so that the cutting resistance of the workpiece becomes a preset value based on a detection value of the cutting resistance meter. A wire saw with fixed abrasive grains, comprising: 3. A method for cutting a workpiece with a fixed-abrasive wire saw, in which a workpiece is fed toward a traveling fixed-abrasive wire, and the workpiece is pressed against the fixed-abrasive wire to cut the workpiece. In the fixed abrasive, detecting a cutting resistance of the workpiece during cutting, and controlling a traveling speed of the wire with the fixed abrasive so that the cutting resistance becomes a preset value. For cutting workpiece with wire saw. 4. A fixed-abrasive wire saw for sending a workpiece toward a traveling fixed-abrasive wire and pressing the workpiece against the fixed-abrasive wire to cut the workpiece. A cutting resistance meter for detecting the cutting resistance of the workpiece, based on the detection value of the cutting resistance meter, so that the cutting resistance of the workpiece becomes a preset set value, A wire saw with fixed abrasive grains, comprising: a control device for controlling a traveling speed. 5. A method of cutting a workpiece with a fixed-abrasive wire saw, in which a workpiece is fed toward a traveling fixed-abrasive wire, and the workpiece is pressed against the fixed-abrasive wire to cut the workpiece. Detecting the cutting resistance of the workpiece during cutting, and controlling the traveling speed of the wire with the fixed abrasive grains and the feed rate of the workpiece so that the cutting resistance has a preset value. A method for cutting a workpiece of a wire saw with fixed abrasive grains, comprising: 6. A fixed-abrasive wire saw for sending a workpiece toward a traveling fixed-abrasive wire and cutting the workpiece by pressing the workpiece against the fixed-abrasive wire. A cutting resistance meter for detecting the cutting resistance of the workpiece, based on the detection value of the cutting resistance meter, so that the cutting resistance of the workpiece becomes a preset set value, A control device for controlling a running speed and a feed speed of the workpiece, and a wire saw with fixed abrasive grains.