JPH04372331A - Machining method of correcting workpiece deformation caused by clamp - Google Patents

Abstract

PURPOSE:To enable NC machining of high accuracy by finding/correcting the deformation quantity of a workpiece even if being deformed by a jig clamp in an NC machine tool. CONSTITUTION:An NC device is provided with an NC program input part 32, an arithmetic control part 34 for performing operation for positioning, interpolation, and the like on the basis of NC command data, a storage part 36 for recording the arithmetic result and a control program, and a servo control part 38 for controlling a feed-driving motor for each shaft and a spindle motor. There is further provided a correcting arithmetic part 40 for computing the displacement quantity in the machined part of a workpiece clamped by a jig on a work-table so as to correct the machining part coordinate value data assigned by an NC program 26 stored in the storage part 36. The machined part coordinate value of the workpiece is measured before and after being clamped using a touch probe 28 fitted to a machining spindle, and the displacement quantity obtained from the difference is set as correction value to corect the data of the NC program 26 for the execution of NC machining.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a machining method that corrects workpiece deformation due to jig clamping in an NC machine tool, and in particular, to a method for clamping a hollow or easily deformable workpiece on a work table using a jig. The amount of deformation of the workpiece that occurs when machining is automatically detected and imported into the NC control device before the start of machining, and when machining is executed, the coordinate value data of the machined part in the NC program is calculated by the detected value of the deformation that is taken in. The present invention relates to a machining method in which highly accurate automatic machining is performed with automatic self-correction function of an NC machine tool by correcting the program.

0002

2. Description of the Related Art Generally, when machining is carried out, it is necessary to firmly fix the workpiece to the work table surface so as to withstand the cutting force of the tool and prevent the workpiece from shifting. For this purpose, the workpiece is generally fixed by using a plurality of clamping jigs and clamping the workpiece between these jigs and a work table or between the jigs. Therefore, if the workpiece has a hollow shape or a shape that is easily bent, the workpiece may be deformed by the clamping force when clamped. N
When automatic machining is performed using a C machine tool, the deformation of the workpiece due to the jig clamp has a negative effect on machining accuracy. In other words, in NC machine tools, workpieces are automatically machined according to pre-stored NC programs, so if the workpiece is deformed during clamping, the coordinate values of the machining area specified in the NC program and the actual workpiece to be machined are A misalignment occurs between the upper part and the part to be machined, and as a result of machining, the desired part shape and machining accuracy cannot be obtained. In order to avoid such problems, the conventional method has been to appropriately adjust the engagement position of the jig and the clamping force depending on the shape of the workpiece to be machined. In other words, for workpieces made of materials and shapes that do not cause deformation even if the clamping force of the jig is increased, the workpiece can be fixed with sufficient force for stable machining, but For example, for small, thin-walled workpieces, it is necessary to reduce the clamping force to the limit that can be processed to ensure machining accuracy by determining and adjusting the clamping position, clamping force, etc. in advance for each workpiece. The aim was to obtain machining accuracy of Also, if the displacement in the next machining part is large while moving the machining part on one workpiece, move the clamp position to a position where this displacement becomes smaller before machining the next machining part. There were also methods of implementation.

0003

[Problems to be Solved by the Invention] As described above, the deformation of the workpiece caused by clamping with a clamp jig is a factor that reduces the machining accuracy in automatic machining, but on the contrary, it is necessary to perform stable machining. It is essential to secure the workpiece with a force that can withstand the cutting force.Especially as today's demands for precise machining of small, thin-walled workpieces increase, it is essential to secure the workpiece in a state that satisfies both requirements. is extremely difficult to clamp. In addition, when trying to reduce the machining time per unit workpiece, including workpiece loading and unloading, by adopting ATC (automatic tool change) and robots in machining centers, and to save labor in setting up various NC machining processes. In addition, changing the clamping position of the workpiece with a jig during the machining process or adjusting the clamping force for each workpiece requires human intervention, which impedes automation of machining and is virtually impossible. become.

[0004] The present invention has been devised and improved in order to solve such problems, and its purpose is to prevent the workpiece from being deformed to some extent due to the clamping force of the clamping jig in NC machine tools. It is an object of the present invention to provide a machining method that makes it possible to achieve highly accurate NC machining without interfering with automation and labor-saving by NC by finding the amount of deformation and correcting it even in the state of deformation.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention enables a machine to automatically detect the amount of deformation of a workpiece due to the clamping force of a clamping jig before machining. NC machine tools This provides the desired high-precision machining method.

That is, according to the present invention, a workpiece to be machined by an NC machine tool according to a predetermined NC program is clamped on a work table in a predetermined machining posture with a jig, and the machined part of the clamped workpiece is The amount of displacement at any predetermined position near the machined part is detected and calculated as the amount of component in each axis direction in the same coordinate system as the orthogonal three-axis coordinate system of the NC machine tool, and each axis of the amount of displacement calculated above is The directional component amount is incorporated into each axis coordinate value of the coordinate value data of the designated machining part in each block of the NC program, and the coordinate value data of these designated machining parts is corrected in advance, and the coordinate value of the corrected machining part is obtained. A machining method that corrects workpiece deformation due to clamping is provided, which is characterized in that NC machining is performed for each program block based on data.

[0007] Also, according to a preferred embodiment of the present invention,
The step of detecting and calculating the amount of displacement at either the machining part of the clamped workpiece or a predetermined position near the machining part is performed by using the touch probe attached to the tip of the machining spindle of the NC machine tool. Measure in advance the coordinate values of the machined part of the workpiece or a predetermined position near the machined part before workpiece clamping, then measure the coordinates of the same part after workpiece clamping with the above jig, and calculate the coordinate values of both. It consists of determining the difference in the NC controller.

[0008]

[Operation] In the machining method of the present invention, the displacement of the machining part that occurs when the workpiece is clamped on the work table with a jig is detected at the machining part or at a predetermined position near the machining part before machining. do. This displacement amount is calculated as the component amount in each axis direction of the orthogonal three-axis coordinate system, and this is added to each axis coordinate value of the coordinate value data of the machining part specified in the NC program to correct the machining part coordinate value data. do. Based on this corrected machining part coordinate value data, N
By performing C machining, it becomes possible to perform machining with desired accuracy on a workpiece that has been deformed by the clamping force.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail by way of preferred embodiments with reference to the accompanying drawings. Here, an example will be shown in which the processing method according to the present invention is applied to a vertical NC drilling machine.
It goes without saying that the present invention is applicable to any other NC machine tools that require clamping of a workpiece onto a worktable using a clamping jig.

Referring first to FIG. 2, a well-known vertical NC drilling machine 10 (
A drilling machine (hereinafter referred to as a drilling machine 10) is shown. The drilling machine 10 has a column 14 erected on a bed 12 installed on the floor, and a spindle head 16 is mounted on the column 14 in the vertical direction (Z
It has a structure that allows it to be moved in the axial direction) by the drive of a Z-axis feed motor MZ. The spindle head 16 rotatably supports, at its front lower end, a machining spindle 18 having an axis in the vertical direction (Z-axis direction) via bearing means, and this machining spindle 18 is driven by the spindle motor Ms. Drilling is performed using a rotating tool (not shown) held at its tip.

[0011] Furthermore, a saddle 20 is placed on the bed 12 on which the column 14 is erected, and can be moved forward and backward relative to the column 14 in the horizontal direction, that is, in the Y-axis direction perpendicular to the Z-axis, by driving a feed motor (not shown). Install. Furthermore, a work table 22 is installed on the upper surface of the saddle 20 so that it can be fed and moved in the left and right horizontal directions relative to the column 14, that is, in the X-axis direction perpendicular to both the Z-axis and the Y-axis, by driving a feed motor (not shown). . As a result, the machining spindle 18 and the work table 22 are arranged in a three-dimensional orthogonal three-axis coordinate system composed of mutually orthogonal X, Y, and Z axes.
It is possible to relatively feed and move via the column 14.

Note that the drilling machine 10 shown in FIG.
It is equipped with an NC device 24 that performs various control operations in NC machining, such as feeding operations, according to a program. The NC program 26, which numerically indicates command information such as tool position coordinates, feed rate, rotation speed, etc., is generally created on an NC tape and then input. Also, although not shown, the drilling machine 1
0 is equipped with an automatic tool changer (ATC device), and the desired tool is transferred from the plurality of tools stored in the tool magazine to the above-mentioned NC.
According to the tool change program in program 26,
It can be automatically attached to and detached from the processing spindle 18 and replaced. The tool magazine houses various tools as well as a touch probe 28 (Fig. 3), which is generally used to measure the surface position of a workpiece's machining reference point, etc., and can be attached to and detached from the machining spindle 18 by an automatic tool changer. It is possible.

When drilling a hole in a workpiece using the above-mentioned drilling machine 10, the workpiece W to be machined is firmly clamped on the worktable 22 by a clamping jig 30, as shown in FIG. In the example of FIG. 3, the jig 30 includes a base 301 fixed on the work table 22, a claw 302 that comes into contact with the workpiece W, and a claw 302 that is attached to the base 301.
The workpiece W can be clamped with a holding force that can withstand the cutting force during machining (see FIG. 3(a)). Therefore, for example, when a workpiece W having an internal hollow shape as shown in the drawing is clamped as shown in the drawing, the workpiece W is deformed by the clamping force of the jig 30 as shown in a slightly emphasized diagram in FIG. 3(b). If processing is performed in this state, the NC
In conventional NC machining, machining accuracy decreases because a discrepancy occurs due to the above deformation between the coordinate values of the machining part in the program and the actual coordinate values of the machining part on the workpiece W to be actually machined. It was a mechanical issue. Therefore, in the present invention, the above-mentioned deviation, that is, the displacement amount due to the clamping force in the machining part of the workpiece W, is calculated before machining, the machining position coordinate data of the NC program is corrected using this displacement amount as a correction value, and then the corrected coordinate Provides a method for performing NC machining based on. Two embodiments of the present invention will be described below using the block diagram of FIG. 1 and the flowcharts of FIGS. 4 to 6.

As shown in FIG. 1, the NC device 24 for carrying out the machining method according to the present invention is an NC device 24 equipped with NC command data such as the operation mode, movement position, and feed rate of the tool.
An input section 32 for inputting the program 26, an arithmetic control section 34 for performing calculations such as positioning and interpolation based on NC command data input from the input section 32, and a storage section for recording calculation results and control programs. 36, and a servo control unit 38 that controls the feed drive motor and main shaft motor of each axis based on the calculation results. In carrying out the present invention, the amount of displacement in the machining part of the work clamped by the jig on the work table is calculated, and the amount of displacement is used as a correction value to modify the NC program 26 recorded in the storage section 36. The apparatus further includes a correction calculation section 40 that corrects the specified processing part coordinate value data. According to a preferred embodiment of the present invention, the data for calculating the above-mentioned workpiece displacement amount is obtained by using a touch probe 28 attached to the machining spindle to calculate coordinate values of the machining part of the workpiece before and after clamping, that is, the displacement. Obtained by measuring before and after displacement. Hereinafter, a series of processes of a processing method according to an embodiment of the present invention will be described with reference to FIGS. 4 and 5.

In FIGS. 4 and 5, first, as a preliminary preparation, the NC program 26 is input to the NC device 24 of the drilling machine 10, the workpiece W is placed at a predetermined position on the work table 22 in the machining attitude, and the NC device Press the start button on 24. This starts machining work on the drilling machine 10, but in the present invention, first in step 41, the touch probe 2 is attached to the machining spindle 18 by an automatic tool changer.
Install 8. Here, the jig 30 on the work table 22
is released (step 42), and the workpiece W is brought into a state without deformation (see FIG. 3(a)). Next, in step 43, the touch probe 28 attached to the machining spindle 18 is moved using the machining part coordinate value data (XP, YP,
ZP ), first approach the processing area on the workpiece W from the
=XP) and determine whether the processing position can be reached (the direction of movement can be positive or negative).
. Here, in this example, since drilling is assumed to be performed using an NC drilling machine, the machining position is not on the end face of the workpiece W, and the machining surface is generally on the X-Y plane perpendicular to the feed direction of the machining spindle, that is, the Z-axis direction. . Therefore, with the above method, it is virtually impossible to accurately make the touch probe 28 reach the workpiece W. Therefore, by setting a predetermined intersection 2α, the coordinates of the position where the touch probe 28 contacts the workpiece W are determined. If it is within the intersection range (that is, in step 43, Xp - α≦X≦Xp + α), it is determined that the processing site has been reached. If it is determined that the machining site can be approached from the X-axis direction in this manner, the feed movement of the machining spindle 18 is stopped at the position where the touch probe 28 contacts the workpiece W (switch is turned on) in step 44. On the other hand, if it is determined that the machined part cannot be accessed from the X-axis direction,
In step 45, the touch probe 28 is slightly shifted in the Y-axis direction and similarly approached to the workpiece W from the X-axis direction, and the feed movement of the machining spindle 18 is stopped at the position where it contacts the workpiece W (switch ON) near the machining area. let When the touch probe 28 is turned on and stops moving in this way, the X coordinate value X1 at this time is recorded in the storage section 36 of the NC device 24 in step 46. Similarly, in steps 47 to 50, the Y coordinate value Y at the machining site or one point near the machining site is determined.
1 and record Z in steps 51-54.
Measure and record the coordinate value Z1.

In each step up to this point, the position coordinate values (X1, Y1, Z1) of one point at or near the machining area on the undeformed work W before being clamped by the jig 30 on the work table 22 are measured. and recorded. Next, the work W is firmly clamped by the jig 30 at the same position and in the same posture on the work table 22 (step 55). Subsequently, in step 56, the machining part coordinate values (X1,
Y1, Z1), the touch probe 28 is first approached from the X-axis direction to this measurement position (that is, the X-axis and Y-axis feed drive motors are activated to move the machining spindle 18 on the line of Y=Y1 (move towards the point)
, the touch probe 28 comes into contact with the workpiece W (switch ON)
), the feed movement of the machining spindle 18 is stopped. Then, in step 57, the X coordinate value X2 at this time is recorded in the storage section 36 of the NC device 24. Similarly, in steps 58 and 59, the Y coordinate value Y2 of the clamped workpiece or at one point near the workpiece part is measured and recorded, and in steps 60 and 61, the Z coordinate value Z2 is similarly measured and recorded.

In this way, the position coordinate value (X
1, Y1, Z1) and (X2, Y2, Z2)
Once measured and recorded, in step 62, the automatic tool changer replaces the touch probe 28 with the desired tool for machining. Then, in step 63, the correction calculation unit 40 of the NC device 24 calculates the amount of displacement of the workpiece W at the machining site or its vicinity from the difference in the position coordinate values before and after the clamp, and uses this as a correction value in the NC program 28.
The machining part coordinate values specified in (XP, YP, ZP
) is corrected. Processing part coordinate value after correction (Xc,
Yc, Zc) are therefore determined by the following formulas.

[0018]

[Math 1]

In this way, the corrected processing part coordinate values (Xc, Y
c, Zc) is calculated and recorded in the storage unit 36,
In step 64, the arithmetic control unit 34 performs calculations such as tool positioning and interpolation based on the corrected machining part coordinate values (Xc, Yc, Zc), and via the servo control unit 38, calculates the positions of the X, Y, and Z axes. The respective feed drive motors and the drive motor MS of the machining spindle 18 are operated to carry out machining. After the machining is completed, when the jig 30 is opened and the workpiece W is taken out, a product having the desired machining accuracy is obtained despite the deformation caused by the clamping of the jig 30.

In the above embodiment, the touch probe 28 for measuring the position of the workpiece surface included in the NC drilling machine is used to measure the data for calculating the workpiece displacement amount, that is, the coordinate values of the machining area before and after clamping or a point in its vicinity. Although the configuration was configured to calculate the corrected machining part coordinate values based on the workpiece, the shape of the workpiece was complex and the touch probe 28 could not approach the machining part.
Even if a point near the machined part is measured, if it is predicted that the error between the obtained displacement amount and the actual displacement of the machined part is large, the above method can also be used to obtain the desired machining accuracy. I can't. In order to eliminate this problem, for example, a protrusion having a shape that can be contacted by the touch probe 28 is attached to the processing surface of the processing part of the workpiece W using a magnet or the like, and the protrusion is placed as close to the processing part as possible. One possible method is to measure the However, this method requires manual work when attaching and detaching the protrusion to the workpiece, which hinders complete automation. Therefore, as explained below with reference to FIG. 6, we propose another embodiment in which various data for clamping the workpiece are input and the workpiece displacement amount is calculated by a predetermined calculation (for example, the finite element method). can do.

The finite element method is known as an effective means of stress/strain analysis at a desired part of a structure. The finite element method is an analysis method that divides the structure into a large number (finite number) of elements.If this analysis method is applied to the present invention, data such as workpiece dimensions, jig clamping positions, and clamping forces can be obtained. Using this method, the displacement of a desired region can be determined only by calculation. In this case, as shown in FIG. 6, first, as a preliminary preparation, the NC program 26 is input to the NC device 24, and various data necessary for structural analysis using the finite element method are input.
For example, data such as the shape and dimensions of the workpiece, physical property values of the workpiece material, jig shape, clamp position, and clamping force are input. Then, the work W is placed on the work table 22 and clamped by the jig 30. First, in step 65, the NC device 24 models the workpiece structure based on the above-mentioned workpiece shape and dimension data and performs element division. Next, in step 66, the deformation state of the entire workpiece or a desired portion is calculated based on data such as the material property values of the workpiece, the restraint conditions by the jig clamp, and the pressing force of the clamp. From the deformation state obtained by calculation, in step 67, the machining part coordinate values (XP, YP,
Displacement amount (Xe, Ye
, Ze). Then, in step 68, the machining part coordinate values (XP, YP, ZP) of the NC program 28 are corrected using this displacement amount as a correction value. The corrected machining part coordinate values (Xc, Yc, Zc) are therefore determined by the following equations.

[0022]

[Math 2]

The above operations (including finite element analysis) are N
The corrected machining part coordinate values (Xc, Yc
, Zc) in step 69, which is the same as in the embodiment using the touch probe 28 described above. In this way, by simply performing predetermined calculations, it is possible to correct the displacement of the machined part due to the deformation of the workpiece, and to obtain a product with desired processing accuracy.

[0024]

Effects of the Invention As described above, according to the processing method of the present invention, the deformation of the workpiece clamped by a jig on the work table due to the clamping is taken into account, and the processing part on the workpiece or its vicinity is fixed. Calculate the displacement amount due to the clamping force at a predetermined position, use this displacement amount as a correction value to correct the machining part coordinate value specified in the NC program, and perform NC machining based on the corrected machining part coordinate value. Therefore, the desired product shape and processing accuracy can be obtained even when the workpiece is deformed. Therefore, regardless of the material or shape of the workpiece, it can be firmly clamped with a force that can withstand the cutting force, expanding the machining capacity of NC machine tools, that is, the range of workpieces that can be machined, and increasing work efficiency. improves.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the relationship between components for implementing a processing method according to the present invention.

FIG. 2 is a schematic diagram of a vertical NC drilling machine that can be used to implement the present invention.

FIG. 3 is a diagram showing a deformed state of a workpiece clamped on a work table.

FIG. 4 is a flowchart illustrating the first half of a process according to one embodiment of the invention.

FIG. 5 is a flowchart showing the second half of the process following FIG. 4;

FIG. 6 is a flowchart illustrating a process according to another embodiment of the invention.

[Explanation of symbols]

18...Machining spindle 22...Work table 24...NC device 26...NC program 28...Touch probe 30...Jig 34... Arithmetic control unit 40...Correction calculation section

Claims (2)

[Claims] 1. A workpiece to be machined by an NC machine tool according to a predetermined NC program is clamped on a work table in a predetermined machining posture by a jig, and a machining part of the clamped workpiece and the vicinity of the machining part are Detect and calculate the amount of displacement at any of the predetermined positions as each axial component amount in the same coordinate system as the orthogonal three-axis coordinate system of the NC machine tool, and each axial component amount of the calculated displacement amount, The coordinate value data of the designated machining part in each block of the NC program is incorporated into each axis coordinate value, the coordinate value data of the designated machining part is corrected in advance, and the NC machining is performed based on the corrected coordinate value data of the machining part. A machining method that corrects workpiece deformation due to clamping, characterized in that: is performed for each program block. 2. The step of detecting and calculating the amount of displacement at either the machining part of the clamped workpiece or a predetermined position near the machining part is performed using a touch mounted on the tip of the machining spindle of the NC machine tool. The coordinate values of the machined part of the workpiece or a predetermined position near the machined part are measured in advance by a probe before the workpiece is clamped by the jig, and then the coordinate values of the same part are measured after the workpiece is clamped by the jig. 2. The machining method according to claim 1, wherein the coordinate values are measured and the difference between the two coordinate values is determined within an NC controller.