JP3051576B2 - Workpiece deformation prevention clamp method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clamping method for preventing excessive deformation of a workpiece to be machined in a machine tool.
In particular, in an NC machine tool, the amount of deformation of a workpiece which is generated when a workpiece having a hollow shape, a small shape, or a thin and easily deformable shape is clamped by a clamping device on a work table is determined for each machining portion before starting the NC machining. And the maximum allowable clamping force of the clamping device is determined for each processing portion within a range where the amount of deformation does not exceed the allowable value, and N
Workpiece that enables high-precision automatic machining with deformation of the work within an allowable range by automatically changing the clamping force of the clamp device in accordance with the above-mentioned determination when performing the C processing. The present invention relates to a method for preventing deformation of a clamp.

[0002]

2. Description of the Related Art Generally, when performing machining, it is necessary to firmly fix a work to a work table surface against a cutting force of a tool so that a position of a work to be processed does not shift. A clamping device for that purpose is provided on the work table. However, when the work has a hollow shape or a small or thin flexible shape, the work may be deformed by the clamping force of the clamp device. When automatic machining is performed by the NC machine tool, deformation of the workpiece due to the clamp adversely affects machining accuracy. That is, in NC machine tools,
Since the work is automatically processed in accordance with the NC program stored in advance, when the work is deformed at the time of clamping, between the coordinate value of the processing part specified by the NC program and the processing part on the work to be actually processed. As a result of performing the machining, a desired part shape and machining accuracy cannot be obtained.

Conventionally, in order to avoid such a problem, a method of appropriately adjusting an engagement position and a clamping force of a clamp device according to a material and a shape of a work to be processed has been generally performed. In other words, for a work of a material and a shape that does not cause deformation even if the clamping force is increased, the work is fixed with sufficient force to perform stable processing, while, for example, a small thin-walled shape that is easily deformed For workpieces of a certain type, the clamping position and clamping force must be determined and adjusted in advance before machining, such as by reducing the clamping force to the limit where machining is possible to ensure machining accuracy. Is trying to obtain the processing accuracy of Also, while the machining part moves on one workpiece,
In some cases, the clamping force that was appropriate in the previously machined part may be inappropriate (large deformation or weak clamping force) in the next machined part. After adjusting or moving the clamp position to apply an appropriate clamping force to the next processing portion, a method of performing the processing is adopted. In these methods, in general, the adjustment of the clamping force of the clamping device is performed by adjusting the fastening force of the bolt in the case of the bolt fastening type, and adjusting the supply pressure in the case of the hydraulic or pneumatic type.

[0004]

As described above, the deformation of the work caused by clamping by the clamping device is a factor that reduces the processing accuracy in the automatic processing. It is indispensable to fix the work with a force that can withstand the cutting force. In particular, when there is an increasing demand for precision processing of small and thin work as in today, clamp the work in a state that satisfies both requirements. This is an essential requirement for improving the processing accuracy. In addition, the ATC (Automatic Tool Change) in machining centers and the use of robots to load and unload workpieces reduce machining time per unit workpiece and save labor in setting up various types of NC machining processes. At this time, changing the clamp position during the machining process or adjusting the clamping force for each workpiece or machining portion generally requires the intervention of an artificial operation, which hinders automation of machining.

The present invention has been made intensively and devised to solve the above-mentioned problems in the prior art.
Its purpose is to be able to reliably clamp small or thin-walled workpieces without hindering automation and labor-saving by NC, and to eliminate the fear of a decrease in machining accuracy due to workpiece deformation due to clamps. It is an object of the present invention to provide a method for clamping a workpiece to prevent deformation.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to an NC machine tool, which deforms a workpiece which is easily deformed when the workpiece is clamped on a work table by a clamp device. The amount is automatically detected for each machined part before the start of machining, and the maximum clamping force within the range where the amount of deformation does not exceed the allowable maximum value is determined for each machined part, taken into the NC device, and executed. It is an object of the present invention to provide a workpiece deformation preventing and clamping method which enables a clamping force to be automatically changed in accordance with the above-mentioned determination in accordance with a processing portion in accordance with a command from an NC device.

Accordingly, the present invention provides a Ruwa chromatography click processed I <br/> by the NC machine tool is placed on the work table in a predetermined posture, the positions of a plurality of machining sites on the workpiece, depending on the clamping device measurement Mr and before and after clamping the word over click
Each measured value to the control device of the NC machine tool.
To clamp multiple processing sites based on the measured values
The control unit determines the amount of displacement
The these displacement, compared with pre-stored predetermined displacement tolerance value to the control device, varying the clamping force of the clamping device
By reduction, the permissible clamping force as displacement does not exceed the allowable displacement value determined for each of the plurality of processing sites, the control device is stored, in processing <br/> a plurality of machining sites to, depending on a plurality of <br/> permissible clamping force stored to correspond to each of the machining area, provides a deformation preventing clamping method of the workpiece, characterized in that the clamp ring over click.

[0008]

The amount of deformation of a work generated when a work to be processed is clamped on a work table by a clamping device is determined based on measured values of a plurality of work sites on the work before and after clamping. Is calculated in the NC device as the displacement amount of. Therefore, this displacement is NC
In the apparatus, the displacement is compared with a predetermined allowable value. If the allowable value is exceeded, the clamping force of the clamping device is changed so that the displacement amount becomes equal to or less than the allowable value. In this way, the maximum allowable clamping force of the clamp device for reducing the work deformation amount to the allowable value or less for each of the plurality of processing parts is determined. When performing NC machining, the workpiece is clamped with the maximum allowable clamping force corresponding to the machining area, and when the machining area moves, the clamping force is changed to the maximum allowable clamping force corresponding to the next machining area, and the workpiece continues. Clamp. All of these operations are automatically performed by the command of the NC device of the NC machine tool.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the preferred embodiments shown in the accompanying drawings. In the following description, an example in which the clamping method according to the present invention is applied to a vertical NC drilling machine will be described. However, any other NC that clamps a work to be processed on a work table using a clamping device is described.
It goes without saying that the present invention is applicable to machine tools.

Referring first to FIG. 2, a known vertical NC drilling machine 1 to which a clamping method according to an embodiment of the present invention is applied.
0 (hereinafter referred to as the drill press 10) is shown. Drilling machine 10, the working column 14 erected on a bed 12 installed on a floor, the spindle head 16 vertically (Z axis direction) movably feed by driving the Z axis feed motor M _Z in column 14 Erect. The spindle head 16 has a spindle 18 in front of it.
Is rotatably supported, and a tool (not shown) held at the tip of the main shaft 18 by the driving of the main shaft motor Ms performs drilling. Also, a saddle 20 is placed on the bed 12,
Y-axis feed motor (not shown) in the Y-axis direction orthogonal to the Z-axis
It is installed so that it can be moved by driving. Saddle 2
The work table 22 is mounted on the upper surface of the camera 0 so that the work table 22 can be moved by driving an X-axis feed motor (not shown) in the X-axis direction orthogonal to both the Z-axis and the Y-axis. Thus, the spindle 1
8 and the worktable 22 are mutually orthogonal X axis, Y
The feed is relatively movable in an orthogonal three-axis coordinate system composed of an axis and a Z axis.

The drilling machine 10 is further provided with an NC device 24 for performing various control operations in NC machining such as a feed operation in accordance with an NC program. The NC program 26, which numerically represents command information such as position coordinates, a feed speed, and a rotational speed of a tool, is generally input after being created on an NC tape. Although not shown, the drilling machine 10 is provided with an automatic tool changer (ATC), and a desired tool can be selected from a plurality of tools stored in a tool magazine by the NC program 26.
In accordance with the tool exchange program described in the above, it is possible to automatically attach / detach / replace the spindle 18 to / from the spindle 18. In the tool magazine, together with various tools, a touch probe 28 generally used for measuring a surface position such as a processing reference point of a workpiece to be processed.
(See FIG. 3) is accommodated, and is similarly attached to and detached from the main shaft 18 by an automatic tool changer.

As shown in FIG. 3, the work table 22 of the drilling machine 10 is provided with a clamp device 30 for clamping the work W to be processed. The clamp device 30 includes a base 32 fixed on the work table 22, a claw 34 that contacts the work W, and a cylinder 36 that moves the claw 34 with respect to the base 32. The cylinder 36 is operated by hydraulic pressure or air pressure, and can clamp the work W with a clamping force that can oppose the cutting force at the time of machining, and can change the clamping force as desired.

[0013] By the clamping device 30, for example, FIG.
When the work W in a thin plate shape as shown in FIG. 3A is clamped, the work W is deformed by the clamping force of the clamp device 30 as shown in FIG. When machining is performed in this state, a deviation due to the deformation occurs between the coordinate value of the machining portion in the NC program and the actual coordinate value of the machining portion on the work W to be actually machined, so that machining accuracy is reduced. It is a problem of the conventional NC machine tool to decrease. Therefore, in the present invention, the above-mentioned displacement, that is, the amount of displacement due to the clamping force at the machining portion of the workpiece W is measured and calculated before machining, and the maximum allowable clamping force within a range where the amount of displacement does not exceed a predetermined allowable value is determined. Then, the NC processing is performed while clamping the work W with the maximum allowable clamping force corresponding to the processing portion. Hereinafter, an embodiment of the present invention will be described with reference to the block diagram of FIG. 1 and the flowcharts of FIGS.

As shown in FIG. 1, an NC device 24 for implementing the clamping method according to the present invention inputs an NC program 26 including NC command data such as a tool operation mode, a movement position, and a feed speed. Unit 38 for performing calculations such as positioning and interpolation based on the NC command data input from the input unit 38; a storage unit 42 for recording the calculation results and control programs; This is a known NC device including at least a servo control unit 44 that controls a feed drive motor and a spindle motor of each axis based on the information. In practicing the present invention, the displacement amounts of the workpiece clamped by the clamping device on the work table are calculated at a plurality of machining sites, and the displacement amounts are calculated with a predetermined displacement allowable value recorded in the storage unit 42. The maximum allowable clamping force is determined based on the comparison operation unit 46 to be compared and the operation result of the comparison operation unit 46, and the clamping force of the clamp device 30 is set and changed to the maximum allowable clamping force in accordance with the movement of the processing part. Clamp control unit 4
8 is further provided. According to a preferred embodiment of the present invention, the data 50 for calculating the work displacement amount is, according to a preferred embodiment of the present invention,
Using the touch probe 28 attached to the tip of the spindle, the coordinate value of the processed part of the workpiece is measured before and after the clamp, that is, before and after the displacement. Hereinafter, FIG.
A series of processes of a clamping method according to an embodiment of the present invention will be described with reference to FIGS.

In FIGS. 4 to 9, first, as preparation,
The NC program 26 and the allowable displacement values (α _X , α _Y , α _Z ) at each processing portion are input to the NC device 24 of the drilling machine 10, and the workpiece W is placed at a predetermined position on the work table 22 in a posture at the time of processing. , The start button of the NC device 24 is pressed. Thus, the machining operation of the drill press 10 is started. In the present invention, first, in step 61, the touch probe 28 is attached to the spindle 18 by the automatic tool changer. Here, the clamp device 30 is released (step 62), and the work W is brought into a state without deformation (FIG. 3A).
reference).

Next, at step 63, the touch probe 2
8 to the machining part coordinate value data (X
_P , Y _P , Z _P ), and then approach the processing portion on the work W in the X-axis direction (that is, operate the feed drive motors of each axis to move the tip of the main shaft 18 to Y = Y _P and Z = Z _P). Line
Is moved toward the point X = X _P), to determine if it can reach the processing site (the direction of moving the touch probe 28 is the positive direction of the X axis along). Here, in this embodiment, since drilling with an NC drilling machine is assumed, the processing position is not at the end face of the work W, and the processing surface is generally X direction perpendicular to the feed direction of the main shaft 18, that is, the Z-axis direction.
-In the Y plane. Therefore the above in that to reach the touch probe 28 to accurately machined portion is method is virtually impossible, and therefore by setting the predetermined tolerances 2.alpha, the position coordinates of the touch probe 28 is in contact with the workpiece W X _p -α ≦ X ≦ At but within tolerances ranges (i.e. step 63
If ( _Xp + α), it is determined that the workpiece can be reached.

When it is determined that the processing portion can be approached from the X-axis direction in this way, in step 64, the feed movement of the main spindle 18 is stopped at a position where the touch probe 28 abuts on the work W (switch ON). Let it. On the other hand, if it is determined that the workpiece cannot be approached from the X-axis direction in step X, the touch probe 28 is slightly shifted in the Y-axis direction in step 65 to similarly approach the workpiece W from the X-axis direction. The feed movement of the main shaft 18 is stopped at the position where it comes into contact with W (switch ON).

When the touch probe 28 is turned on and the movement of the spindle 18 stops, the X coordinate value X ₁ at this time is recorded in the storage unit 36 of the NC unit 24 in step 66. Similarly, the Y-coordinate value Y ₁ of the first point of the machining area or processing site near measured and recorded in step 67 to 70, also measures and records the Z coordinate value Z ₁ at step 71-74.

In each of the steps up to this point, the position coordinate values (X ₁ , Y ₁ , Z ₁₎ of the processing part or one point in the vicinity thereof on the work W without deformation before being clamped by the clamping device 30 on the work table 22. ) Is measured and recorded. Therefore, the workpiece W is then firmly clamped at the same position on the work table 22 in the same posture by the maximum clamping force of the clamp device 30 (step 7).
5).

[0020] Subsequently, in step 76, based on the machining area coordinate values measured before clamping of the _{(X 1, Y 1, Z} 1), moved close to the measurement position a touch probe 28 is first in the X-axis direction (i.e. the tip of the spindle 18 actuates the feed drive motor of each axis Y = Y _P and along the line of the Z = Z _P is moved toward the point of X = X _1), a touch probe 28
Is in contact with the workpiece W (switch ON).
Stop the feed movement of And recording the X-coordinate value X ₂ of this time in the storage unit 36 of the NC device 24 at step 77. Similarly, in steps 78 and 79, the Y coordinate value Y ₂ at the machining site after clamping or at one point near the machining site is obtained.
Is measured and recorded, and the Z coordinate value Z ₂ is measured and recorded in steps 80 and 81 similarly.

In this manner, the position coordinate values (X ₁ , Y ₁ , Z ₁ ) before and after clamping (ie, before displacement) and at one point near or near the machining portion of the workpiece W (and before displacement) and When (X ₂ , Y ₂ , Z ₂ ) is measured and recorded, in step 82, the comparison operation unit 46 of the NC device 24 calculates the displacement amount (ε _X , ε _Y , ε _Z ),
Next, the axial component amounts of the displacement amounts (ε _X , ε _Y , ε _Z ) are stored in the storage unit 36 in advance as the displacement allowable values (α _X ,
α _Y , α _Z ). In step 83, first, the X-axis components are compared.

As a result of the comparison, the displacement amount ε _X becomes the displacement allowable value α.
_{If it is} larger than _X , first, in step 84, it is determined whether or not the work deformation by the clamp has brought the processed portion closer to the touch probe 28, that is, whether or not X ₂ <X ₁ . If X ₂ <X ₁ , the clamp device 30 is opened in step 85, and in step 86, the touch probe 28 is moved along the line of Y = Y _P and Z = Z _P to X = X ₁ −α.
_It is fixedly arranged at the position of _X. In this state, the clamp device 30 is gradually closed in step 87, and the clamping force of the clamp device 30 is fixed when the work W is gradually deformed and comes into contact with the touch probe 28.

[0023] In step 84, if it is determined not X ₂ <X _1, closing the clamping device 30 in step 88, in step 89, whether the touch probe 28 Y = Y _P
And fixedly arranged at the position of X = X ₁ + α _X on the line of Z = Z _P. In this state, the clamp device 30 is gradually released in step 90, and the clamping force of the clamp device 30 is fixed when the deformed work W is gradually restored and comes into contact with the touch probe 28. Thus, the X component ε of the displacement amount
Maximum clamping force P _X in the range _{of X} becomes equal to or less than the allowable value alpha _X
Is determined, and in step 91, this clamping force P _{X is set} to NC.
It is recorded in the storage unit 36 of the device. When the displacement amount ε _X is smaller than the displacement allowable value α _{X as} a result of the comparison in step 83,
The clamping force used in step 75 is converted to the maximum clamping force P _X
Is recorded in the storage unit 36 of the NC device (step 92).

[0024] Then in step ninety-three to one hundred and two, Y component epsilon _Y of displacement in the same manner the maximum clamping force P _Y in a range of equal to or less than the allowable value alpha _Y are determined, NC device of the storage unit 36
Will be recorded. Further, in step 103-112, the same way the displacement amount of the Z component epsilon _Z and is determined maximum clamping force P _Z in the range of the allowable value or less alpha _Z is recorded in the storage unit 36 of the NC device. Then, the maximum clamping forces P _X , P _Y , and P _Z thus obtained are compared with each other, and the minimum clamping force among them is determined as the maximum allowable clamping force P.
(Step 113).

In each of the above steps, the maximum allowable clamping force P for one processing site is obtained, and the maximum allowable clamping force P for another processing site is determined in the same manner.
All are recorded in the storage unit 36 of the NC device (step 11
4). Next, at step 115, the touch probe 28 attached to the tip of the spindle is replaced with a desired tool used for machining by the automatic tool changing device. And step 116
Under the control of the clamp controller 48 of the NC device 24,
The workpiece W is clamped by setting the clamp device 30 to the maximum allowable clamping force P, and then NC processing is performed in step 117. At this time, as the machining portion specified in the NC program 28 moves, the clamp device 30 is set to the maximum allowable clamping force determined corresponding to the machining portion as needed, that is, the workpiece W is changed by changing the clamping force as needed. Clamp. In this way, during the execution of the NC machining, the work W is always controlled by the optimal clamping force that causes the deformation below the allowable value in all the machined parts of the work W.
Can be reliably clamped.

In the above-described embodiment, the data for calculating the workpiece displacement, that is, the coordinate values of the processed parts before and after the clamp or the vicinity thereof are measured by using the touch probe 28 for measuring the work surface position of the NC drilling machine. However, the work shape is complicated and the touch probe 28 cannot approach the processing part,
Even if the vicinity of the machined part is measured, a large error may be expected between the obtained displacement and the actual displacement of the machined part. In such a case, for example, the touch probe 28
A method is conceivable in which a projection that can be contacted is attached by a magnet or the like, and a position as close as possible to the processing site is measured. However, in this method, manual work is required when attaching and detaching the projections to and from the work, which hinders complete automation. Therefore, various data when clamping the work are
It is convenient to input to the device 24 and calculate the work displacement amount by a predetermined calculation such as a finite element method.

[0027]

As is apparent from the above description, according to the present invention, the amount of deformation of a work generated when a work to be processed is clamped on a work table by a clamp device is determined by a predetermined tolerance in the NC device. By comparing with
For each of the plurality of machining parts, the maximum allowable clamping force of the clamp device for reducing the work deformation amount to the allowable value or less is determined, and when performing the NC machining, the NC device is automatically instructed by the command of the NC device. The workpiece to be processed is clamped by setting and changing the clamping force of the clamping device to the maximum allowable clamping force in accordance with the movement, so that workpieces that are easily deformed without hindering automation and labor saving by NC. Can be reliably clamped while eliminating the fear of a decrease in machining accuracy due to the deformation of the workpiece by the clamp, and the machining accuracy and work efficiency of the NC machine tool are improved.

[Brief description of the drawings]

FIG. 1 shows an N for performing a clamping method according to the invention.
It is a functional block diagram of C apparatus.

FIG. 2 is a schematic view of a vertical NC drilling machine to which the present invention can be applied.

3A and 3B are diagrams showing a clamp device provided on a work table of the drilling machine shown in FIG. 2 and a deformed state of a workpiece to be processed clamped by the clamp device.
(B) The state after clamping.

FIG. 4 is a flowchart illustrating a process of a clamping method according to an embodiment of the present invention.

FIG. 5 is a flowchart showing a process following FIG. 4;

FIG. 6 is a flowchart showing a process following FIG. 5;

FIG. 7 is a flowchart showing a process following FIG. 6;

FIG. 8 is a flowchart showing a process following FIG. 7;

FIG. 9 is a flowchart showing a process following FIG. 8;

[Explanation of symbols]

 18 Spindle 22 Work table 24 NC device 26 NC program 28 Touch probe 30 Clamp device 40 Operation control unit 46 Comparison operation unit 48 Clamp control unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B23Q 15/00 G05B 19/404 B23Q 3/06 304

Claims (1)

(57) [Claims] 1. A a Ruwa over click is processed me by the NC machine tool is placed on the work table in a predetermined posture, the positions of a plurality of machining sites on the workpiece, 該Wa chromatography click by a clamping device to measure in the before and after clamping the,
Each measured value is sent to the NC machine tool controller.
Inclusive, the clamping of a plurality of machining areas on the basis of the measured values
The amount of displacement is determined by the controller,
The amount of displacement that is, compared to the previously stored predetermined displacement tolerance value to the control unit, in varying the clamping force of the clamping device
The displacement does not exceed the displacement allowance.
Seeking a clamping force to each of the plurality of processing sites
Umate, is stored in the control device, when processing a plurality of machining sites, depending on the allowable clamping force stored to correspond to each of the machining area of the plurality of
Te, which clamp the workpiece, deformation preventing clamping method of the workpiece, characterized in that.