JPH11216642A - Turning method in nc lathe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the turning with excellent dimensional accuracy by moving a tool tip along the section of a work after displacement taking into consideration the elastic displacement of the work accompanied by the rotation. SOLUTION: In a turning method, when a work W is turned using an NC lathe, the elastic displacement accompanied by the rotation of the work W is calculated, the moving route of a tool tip taking into consideration the elastic displacement is obtained, a working program including the obtained moving route in the command is prepared, and inputted in a numerical control device of the NC lathe to turn the work W. As an example, in a figure to show the displacement condition of the work W, the work W before the displacement is indicated by a two-dot chain line, while the displacement of the work W after the displacement is expanded and indicated by a solid line. The working error generated by the elastic displacement accompanied by the rotation of the work W can be extremely small, and the work can be turned with excellent dimensional accuracy even when the work W is easy to displace by the rotation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for turning a workpiece using an NC lathe, and more particularly to a turning method in which elastic displacement accompanying rotation of a workpiece is taken into consideration.

[0002]

2. Description of the Related Art Turning in an NC lathe is based on a machining program instructing a moving path of a tool edge in a machining coordinate system and the like, so that the tool edge passes along a path instructed by the machining program. This is performed by numerically controlling the feed drive unit.

FIG. 2 shows an example of a simple turning process. Specifically, a workpiece (hereinafter, referred to as a "work") W held by a nail C of a spindle chuck (not shown). Is turned, and the dimension of the outer diameter is changed from φX'b to φXb.
This is an example of turning work to finish the work. As shown in the figure, in this example, the cutting edge Ta of the tool T
After passing through the points b, Pc, and Pd in this order, the point is returned to the Pa point again.

In this case, a coordinate value of each movement target point in a machining coordinate system (XZ coordinate system) is commanded to the machining program. For example, when the point G shown in FIG. 2 is set as the origin of the machining coordinate system, the coordinates of the point Pa are (Xa, Z
a), assuming that the coordinates of point Pb are (Xb, Zb), the coordinates of point Pc are (Xc, Zc), and the coordinates of point Pd are (Xd, Zd), the respective coordinate values (Xa, Za), (Xb , Zb),
(Xc, Zc), (Xd, Zd), (Xa, Za) are sequentially instructed in the machining program. The X coordinate value is a value corresponding to the diameter of the work W.

The numerical control device of the NC lathe sequentially executes a machining program in which coordinate values of the movement target point are instructed,
The feed drive unit is numerically controlled so that the tool edge Ta sequentially passes through the moving target points. Thereby, the tool edge Ta actually moves through the same part in the order of Pa point, Pb point, Pc point, Pd point, and Pa point, and moves from the Pb point to the Pc point while the outer diameter portion of the workpiece W is being moved. Is cut and its size is φ
Finished from X'b to φXb.

[0006]

When the work W is rotated, the work W generates an internal stress in the radial direction due to centrifugal force, and generates a displacement (distortion) due to the stress. Some of the workpieces W that are usually processed have low rigidity, and some of the workpieces W are largely displaced by the centrifugal force.

FIG. 3 shows an example of this, and the work W (before turning) in FIG.
5 shows a state of displacement of the workpiece W when the workpiece W is rotated. The work W is made of an aluminum alloy (AC4CH) having a Poisson's ratio of 0.33 and a Young's modulus of 71.5 kN / mm ² , and its outer diameter φX′b
Is 360.2 mm, length D is 80 mm, and bottom thickness t _1.
Was set to 10 mm, and the outer diameter portion thickness t ₂ was set to 5 mm. In FIG. 3, the work W before the displacement is shown by a two-dot chain line, and the work W after the displacement is shown by a solid line with its displacement amount enlarged.

As shown in FIG. 3, when the above-described work W is rotated at a rotation speed as high as 3000 rpm, the work W is elastically displaced by centrifugal force, and the outer diameter portion of the work W expands outward in the radial direction. It becomes drum-shaped. Incidentally, when the displacement amount of the work W was measured under the above conditions, the maximum displacement amount ΔX in the radial direction (X-axis direction) at the outer diameter portion was 22 μm, and the displacement amount ΔZ in the Z-axis direction was 6 μm. Was.

The work W which is easily displaced by such centrifugal force
Is turned in such a manner that its outer diameter becomes φXb.
a is moved from the point Pb to the point Pc.
Is rotating, the dimension of the same part is maintained at the dimension φXb after turning due to the displacement accompanying the rotation, but when the rotation of the work W is stopped, the centrifugal force that has been acting up to that time acts on the work W. The displacement that has occurred due to the displacement is eliminated, and the dimension φXb of the outer diameter portion is calculated by the displacement amount (2 · ΔX = 44).
μm). As you know, such 4
The processing error of 4 μm is quite large in ordinary machining.

As described above, in the conventional cutting method in which the tool edge Ta is simply moved so as to follow the finished shape of the work W without considering the displacement of the work W due to the rotation, the work W is displaced by centrifugal force. If it is easy to process, there is a problem that it cannot be processed with high accuracy.

In such a case, a work which is deformed into a relatively simple shape such as the work W shown in FIG. 3 may be able to be dealt with by so-called tool correction, but the shape of the work W is complicated. In some cases, the displacement state is also complicated, and it is not possible to take appropriate measures by merely correcting the tool. That is, such a work W has a different displacement amount in that portion, or displaces so that a portion has a larger allowance for a certain portion, and displaces such that a portion has a reduced allowance for a certain portion. To do
They cannot respond uniformly.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cutting method capable of finishing a workpiece, which is easily displaced by rotation, with high dimensional accuracy.

[0013]

Means for Solving the Problems and Effects The present invention for achieving the above object is to rotate a workpiece gripped by a spindle chuck of an NC lathe so that a tool edge passes through a predetermined path. A turning method for turning the workpiece to a desired cross-sectional shape by numerically controlling the feed drive unit and moving the tool, wherein an elastic displacement amount accompanying rotation of the workpiece is calculated. Based on the calculated amount of elastic displacement, determine the movement path of the tool edge along the cross-sectional shape of the workpiece after the displacement, the feed drive so that the tool edge passes on the determined movement path The workpiece is turned into a desired cross-sectional shape by moving the tool by numerically controlling a part.

As described above, some of the workpieces turned by the NC lathe have low rigidity, and some of them are largely displaced by centrifugal force accompanying rotation. In this case, if the tool is moved so that the tool edge passes along a path along the finished cross-sectional shape of the workpiece, the displacement amount of the workpiece becomes a processing error as it is, and the workpiece becomes high. It cannot be finished with precision.

According to the present invention, the amount of elastic displacement associated with the rotation of the workpiece is calculated, and based on the calculated amount of elastic displacement, the tool edge along the cross-sectional shape of the workpiece after the displacement is calculated. Is determined, and the tool cutting edge is made to pass on the determined moving route. That is, the moving path of the tool cutting edge is changed to a path along the finished sectional shape of the workpiece by the elastic displacement. Because it is assumed that the amount is taken into account,
During the rotation of the workpiece, the cross-sectional dimension of the workpiece after cutting is a dimension obtained by adding the amount of elastic displacement to the desired finished cross-sectional dimension, but when the rotation of the workpiece is stopped. The elastic displacement that has occurred up to that point is eliminated, and the cross-sectional dimension of the workpiece after rotation has stopped is the desired finished cross-sectional dimension.

As described above, according to the present invention, the tool edge is moved along the sectional shape of the workpiece after the displacement in consideration of the elastic displacement of the workpiece due to the rotation. Even a work piece that is easy to perform can be turned with high dimensional accuracy.

In the present invention, the amount of elastic displacement caused by the rotation of the workpiece is calculated when the workpiece is actually rotated and its displacement is measured, and a displacement analysis method such as the finite element method is used. And the case where the displacement amount is calculated by using

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.

First, the outline of the turning method according to the present embodiment will be described. The turning method according to the present example is performed when the above-described work W shown in FIG. 2 is turned using an NC lathe. Calculate the amount of elastic displacement associated with the rotation of W,
Then, a movement path of the tool edge is calculated in consideration of the elastic displacement amount, a machining program including the determined movement path in the command content is created, and the created machining program is input to the numerical control device of the NC lathe. And turning the workpiece W in accordance with the machining program.

As described above, the work W used in this example
Is the same as the work W shown in FIG. 2 described above, and will be described again. The work W has a Poisson's ratio of 0.33 and a Young's modulus of 71.5 kN / mm ² as a material.
The outer diameter φX′b was φ360.2 mm, the length D was 80 mm, the bottom thickness t ₁ was 10 mm, and the outer diameter portion thickness t ₂ was 5 mm. In this example, the outer diameter portion of the work W is set to φX′b = φ36 at a rotation speed of 3000 rpm.
Turning from 0.2 mm to φXb = φ360 mm shall be performed. Hereinafter, details of the turning method according to this example will be described.

First, a work W having the above-mentioned dimensions is 3,000
The amount of elastic displacement when rotating at rpm was calculated. Specifically, a model in which the work W is divided into small units of elements is created, and displacement analysis is performed by the finite element method based on material constants such as Young's modulus and Poisson's ratio, and boundary conditions between elements set as appropriate. The amount of elastic displacement of the work W was calculated. next,
The displacement state of the work W was obtained based on the calculated elastic displacement amount. FIG. 1 shows the obtained displacement state of the work W.
In FIG. 1, the work W before displacement is shown by a two-dot chain line, and the work W after displacement is shown by a solid line with its displacement amount enlarged.

As shown in FIG. 1, in this embodiment,
Outer diameter portion of the workpiece W becomes inflated barrel shape radially outward, the outer diameter portion corresponding to the finished dimension FaiXb, 11 pieces points at equal intervals along the Z-axis direction Pb ₁ ~Pb ₁₁
, Pb ₁ becomes P′b ₁ , P
b ₂ is the P'b _2, the Pb ₃ is P'b _3, Pb ₄ within P'b _4,
Pb ₅ is to P'b _5, Pb ₆ is to P'b _6, Pb ₇ is P'b
₇ , Pb ₈ is P'b ₈ , Pb ₉ is P'b ₉ , Pb ₁₀ is P '
a b _10, displaced Pb ₁₁ is P'b _11, each displacement amount [Delta] X ₁ is 20μm in the X-axis direction, [Delta] X ₂ is 21 [mu] m,
ΔX ₃ is 21.5 μm, ΔX ₄ is 22 μm, ΔX ₅ is 22
μm, ΔX ₆ is 21 μm, ΔX ₇ is 19.5 μm, ΔX ₈
Is 17 μm, ΔX ₉ is 13.5 μm, ΔX ₁₀ is 8.5 μm
m and ΔX ₁₁ were 3 μm. Incidentally, the displacement amount in the X-axis direction in the Pb ₁₂ is 0 .mu.m, Z axis direction displacement amount ΔZ in Pb ₁ was -3Myuemu.

Next, the tool edge (not shown) is P'b,
_{P'b 1, P'b 2, P'b 3} , P'b 4, P'b 5, P'b 6,
_{P'b 7, P'b 8, P'b 9} , P'b 10, P'b 11, Pb 12,
A machining program was created so that Pc and Pd were sequentially passed through linear interpolation. When the G point is set as the origin of the machining coordinate system, the coordinates of each point are P′b (X) = (Xb + 2Δ
X ₁ ), P′b (Z) = 3, P′b ₁ (X) = (Xb + 2ΔX ₁ ),
P′b ₁ (Z) = 0, P′b ₂ (X) = (Xb + 2ΔX ₂ ), P′b
₂ (Z) = − (D−t ₁ ) / 11, P′b ₃ (X) = (Xb + 2Δ
X ₃ ), P′b ₃ (Z) = − 2 (D−t ₁ ) / 11, P′b ₄ (X)
= (Xb + 2ΔX ₄ ), P′b ₄ (Z) = − 3 (D−t ₁ ) / 1
1, P′b ₅ (X) = (Xb + 2ΔX ₅ ), P′b ₅ (Z) = − 4
(D−t ₁ ) / 11, P′b ₆ (X) = (Xb + 2ΔX ₆ ), P ′
b ₆ (Z) = − 5 (D−t ₁ ) / 11, P′b ₇ (X) = (Xb +
2ΔX ₇ ), P′b ₇ (Z) = − 6 (D−t ₁ ) / 11, P′b
₈ (X) = (Xb + 2ΔX ₈ ), P′b ₈ (Z) = − 7 (D−t ₁ )
/ 11, P'b ₉ (X) = (Xb + 2ΔX ₉ ), P'b ₉ (Z) =
−8 (D−t ₁ ) / 11, P′b ₁₀ (X) = (Xb + 2Δ)
X ₁₀ ), P′b ₁₀ (Z) = − 9 (D−t ₁ ) / 11, P′b
₁₁ (X) = (Xb + 2ΔX ₁₁ ), P′b ₁₁ (Z) = − 10 (D−
t ₁ ) / 11, Pb ₁₂ (X) = Xb, Pb ₁₂ (Z) = − (D−
t ₁ ), Pc (X) = Xb, Pc (Z) = − (D−t ₁ ) −2,
Pd (X) = (Xb + 50), Pd (Z) = − (D−t ₁ ) −
2. Further, the displacement amount ΔZ in the Z-axis direction in this example
Is extremely small and has a negligible effect on the machining accuracy. Therefore, the correction of the tool movement path for the displacement ΔZ in the Z-axis direction is not performed.

Next, the created machining program is input to the numerical control device of the NC lathe, and the work W is gripped by the pawl C of the spindle chuck (not shown). W was turned. The workpiece W after turning was rotated at 3000 rpm while the claws C of a spindle chuck (not shown) gripped the workpiece W, and the dimension of the outer diameter was measured along the Z-axis direction. the _{P'b, P'b 1, P'b 2,} P'b 3, P'b 4, P'b 5, P '
_{b 6, P'b 7, P'b 8} , P'b 9, P'b 10, P'b 11, P
A shape similar to the line shape drawn by b ₁₂ and Pc was shown. On the other hand, when the rotation of the work W is stopped, the above Pb, Pb ₁ ,
Pb ₂ , Pb ₃ , Pb ₄ , Pb ₅ , Pb ₆ , Pb ₇ , Pb ₈ ,
Shapes similar to the line shapes drawn by Pb ₉ , Pb ₁₀ , Pb ₁₁ , Pb ₁₂ , and Pc were shown.

As described above, according to the turning method according to the present embodiment, the amount of elastic displacement accompanying the rotation of the work W is calculated in advance, and the path of movement of the tool edge is set in consideration of the calculated amount of elastic displacement. Since the workpiece W is turned by moving the tool edge along the cross-sectional shape after the displacement of the workpiece W, machining errors caused by elastic displacement accompanying rotation of the workpiece W are minimized. Can be,
Even a work W that is easily displaced by rotation can be turned with high dimensional accuracy.

[0026] In the example described above, a plurality of points along the cross-sectional shape of the workpiece W after displacement (P'b ₁ ~P'b ₁₁₎
Are connected by linear interpolation, so that the tool edge (not shown) moves on the straight line. However, the present invention is not limited to this, and the points are connected by circular interpolation.
The tool edge (not shown) may be moved on the arc.

Further, if the above-mentioned plurality of point intervals are shortened to set more points, the movement path of the tool edge (not shown) substantially matches the sectional shape of the workpiece W after further displacement. In addition, machining errors caused by elastic displacement can be almost completely eliminated.

Further, a machining program may be automatically created by an automatic programming device based on the calculated displacement data.

Also, in this example, the work W
Although the displacement amount is calculated, the displacement amount is not limited to this, and the displacement amount may be calculated using another displacement analysis method. Also,
Instead of calculating the displacement amount using the displacement analysis method, the work W may be actually rotated and the displacement amount may be measured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for explaining a turning method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining a conventional turning method using an NC lathe.

FIG. 3 is an explanatory diagram for explaining an elastic displacement of a work caused by rotation.

[Explanation of symbols]

 C Claw T Tool Ta Tool edge W Work G Origin

Claims (1)

[Claims] An object is achieved by rotating a workpiece gripped by a spindle chuck of an NC lathe and moving a tool by numerically controlling a feed drive unit so that a tool edge passes a predetermined path. A turning method of turning the work piece into a cross-sectional shape obtained by calculating an elastic displacement amount accompanying rotation of the work piece, and based on the calculated elastic displacement amount, the work piece after the displacement. By determining the movement path of the tool edge along the cross-sectional shape of, and by moving the tool by numerically controlling the feed drive unit so that the tool edge passes on the determined movement path, the target cross section A turning method in an NC lathe, wherein the workpiece is turned into a shape.