JP2002224918A - Method for preventing relative position displacement in electric discharge machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance accuracy of electric discharge machining by preventing displacement of a position of a workpiece relative to a machining origin reference ball. SOLUTION: An electric discharge machine is used to perform the machining by installing a workpiece mounting base and the reference ball on a machine table so as to take the reference ball on the machine table as a machine coordinate origin. A distance between the reference ball and the workpiece fixed onto the workpiece mounting base is measured in advance, a position of a tool is measured with the reference ball when the workpiece is machined with the tool, and the workpiece is moved to a workpiece machining part so as to be machined. This method is characterized by using a low thermal expansion material for the workpiece mounting base and the reference ball.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for maintaining a distance between an origin reference sphere of a machine tool and the origin of a workpiece and reducing a relative position displacement. The present invention relates to a method for preventing displacement of a relative position with respect to a reference ball.

[0002]

2. Description of the Related Art Conventionally, in an electric discharge machine in which a reference sphere on a machine table is machined as an origin of a machine coordinate, a base on which a reference sphere and a work are mounted has different sizes and materials so that the amount of expansion and contraction due to heat is different. In addition, the distance between the reference sphere and the work, that is, the relative position, cannot be kept constant due to a change in room temperature.

For this reason, in the case of performing high-precision machining, conventionally, it has been necessary to suppress the change in room temperature, or to perform correction by re-measuring the distance between the reference sphere and the workpiece origin during machining. The environmental equipment in the constant temperature room and the correction reprocessing were expensive and had economical problems. Also,
Since the conventional work mounting base uses a magnet base, the surface on which the work is placed has a low hardness, and there are scratches due to the work and deformation due to turning the magnet on and off. I needed to. Further, there is a problem that machining dust and machining fluid easily accumulate on the magnet, and it is difficult to clean when replacing the workpiece with the next workpiece.

Further, as a prior example, there is a case where a low thermal expansion alloy material is used for a heat generating portion of a machine tool. For example, in Japanese Patent Application Laid-Open No. Hei 8-257804, a low thermal expansion alloy material is used for a tool mounting portion of a main spindle to suppress the elongation of the main spindle itself, and a surface of the mounting portion is subjected to an abrasion resistance treatment with a composite alloy film layer. I have. In this method, if the entire column holding the main shaft is displaced by a change in room temperature, the column is displaced together with the tool holding portion.

Further, if the table on which the workpiece is placed is also thermally displaced, the relative distance between the workpiece and the tool will not be constant. As described above, the relative displacement between the work and the tool cannot be reduced even if the workpiece is used only for the tool mounting portion of the spindle, and high-precision machining cannot be performed.

In Japanese Patent Publication No. 5-45366, a work mounting base and a machine table which affect heat generation are used. However, this also supports the entire table supporting the base side in the same manner as described above. Is displaced due to a change in room temperature, the displacement of the workpiece is reduced, but the member supporting the processing tool expands and contracts, and the positional accuracy deteriorates. In other words, it is useless to suppress the thermal displacement of only one single point.
It is necessary to suppress more than two points.

[0007] Since the low thermal expansion material has a considerably higher cost than ordinary steel materials and casting materials, it is economically difficult to use it for the entire machine, and therefore, it is partially effective. It would be desirable to use.

[0008]

As described above, in a machine for processing a reference sphere on a machine table as the origin of the machine coordinates, the distance between the reference sphere and the work is measured in advance, and when the work is processed with a tool, In the method of measuring the tool position with the reference sphere and moving it to the workpiece machining part, the displacement between the base on which the workpiece is mounted and the reference sphere is kept small, providing a high-precision base that does not require periodic correction Therefore, it is desired to provide a method for improving the processing accuracy.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems in the prior art by preventing displacement of the relative position between a workpiece and a machining origin reference sphere to improve the accuracy of electric discharge machining. Is to provide.

[0010]

In order to achieve the above-mentioned object, a method for preventing relative displacement of an electric discharge machine according to the present invention comprises providing a work mounting base and a reference sphere on a machine table, and Measure the distance between the reference sphere and the workpiece fixed on the workpiece mounting base in advance using a machine that processes the upper reference sphere as the origin of the machine coordinates, and refer to the tool position when machining the workpiece with the tool. In a method of measuring by using a sphere and moving the workpiece to a workpiece processing portion, a low thermal expansion material is used for the workpiece mounting base and the origin reference sphere.

Further, the method for preventing relative displacement of an electric discharge machine according to the present invention is characterized in that the reference sphere is supported on a support, and a low thermal expansion material is used for the support.

Further, in the method for preventing relative displacement of the electric discharge machine according to the present invention, the work mounting base body and the reference sphere main body are made of a low thermal expansion material, and the work mounting base and the reference sphere have a hard tip ball surface. A chromium carbide alloy is coated.

Still further, in the method for preventing relative displacement of the electric discharge machine according to the present invention, a screw hole may be passed through the work mounting base to the back surface, and the screw hole may be passed through the back surface hole to the end of the work mounting base. The communicating grooves are provided in a lattice shape or a mesh shape.

In the method for preventing relative displacement of the electric discharge machine according to the present invention, a relief hole penetrating in a lateral direction is provided on a side surface of the screw hole of the work mounting base.

[0015]

DETAILED DESCRIPTION OF THE INVENTION In the method for preventing relative displacement of an electric discharge machine according to the present invention, a height adjusting table for a work mounting base and a height adjusting table for a reference ball are fixed on a same machine table with screws. The height adjustment table for the work mounting base and the height adjustment table for the reference sphere are also made of a low thermal expansion material like the work mounting base and the reference sphere. Further, the surface of the work mounting base is coated with a coating to improve the slipperiness and increase the surface hardness of the low thermal expansion material to prevent scratches and rust on the work mounting base. Further, as an example of the coating, a hard chromium plating or a hard chromium carbide alloy having a higher hardness and a lower friction coefficient is coated by about 30 μm.

The work mounting base is provided with a large number of tap holes in a honeycomb or mesh shape so that the work can be fixed.
These tap holes are penetrated to the bottom. On the back surface of these penetrating screw holes such as tap holes, grooves are provided in a grid or mesh pattern, and processing chips and processing liquid during processing accumulate on the work mounting base. It can be naturally discharged together with the working fluid into a lower groove communicating with a screw hole such as a tap hole.

Other objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

(Embodiment 1) Hereinafter, an embodiment of a method for preventing relative displacement of an electric discharge machine according to the present invention will be described with reference to FIG.

FIG. 1 is a schematic diagram of a measurement for obtaining a relative position coordinate value of a processing origin before processing according to the present invention. In the figure, a machine table 1 is made of a casting, a steel material, or the like.
Has been fixed. In order to increase the rigidity of the reference sphere 3 and adjust the height, the mounting base 2 is separately provided from the reference sphere 3.
It is constructed so that only the mounting base 2 can be replaced with screws. If necessary, the mounting table 2 and the reference ball 3 may be integrally manufactured without being separated from each other. A table-side reference sphere 3 having a spherical tip (made of steel in this embodiment) is mounted on the mounting base 2 so that the height can be adjusted.

A work mounting base 5 is installed on the machine base 1 via a work height adjusting table 4.
The work 6 is arranged on the work mounting base 5. The work 6 has a work mounting base 5 mounted on a work height adjusting table 4 capable of adjusting the processing height of the work 6, and is set thereon. The work mounting base 5 on which the work 6 to be processed is mounted is made of a low thermal expansion material, and the work 6 on the work mounting base 5 is processed by the electric discharge machining.

Further, a reference sphere 8 attached to the column side of the machine is provided corresponding to the reference sphere 3 on the machine base 1 side. The reference sphere 8 is formed in a spherical shape in the same manner as the reference sphere 3 on the machine base 1 side, and is detachably or integrally attached to a tip portion of the support base 8a.

A method for obtaining the relative position coordinate value between the workpiece and the machining origin from the electric discharge machine according to the present invention configured as described above will be described below.

First, in the X direction, both sides of the side of the reference sphere 3 on the table side are measured by the reference sphere 8 on the column side and sorted to determine the center position of the sphere. The measurement is performed by touch sensing with a minute current. This contact point is defined as the zero origin of the machine. Next, measurement is similarly performed for the Y direction. In the Z direction, Z is measured from the previously measured X and Y center points, and the tip of the reference sphere 3 on the table side is set to zero as the mechanical origin. From the above, X, Y and Z are (0, 0, 0)
And

Next, the reference sphere 8 on the column side is moved toward the work 6, and the reference end face of the work 6 in the Z direction is measured.
Let the coordinates be Z1. Therefore, Z1 is the distance between the reference sphere origin and the workpiece origin.

Thus, the distance between the reference sphere 3 on the table side and the work 6 is determined. Next, the X and Y directions of the work 6 are measured in the same manner, and the distances X1 and Y in the X and Y directions are measured.
1 is obtained (not shown).

Next, the reference sphere 8 and the support 8a on the column side are removed from the machine and replaced with the electrode 9 as a working tool. Next, a measurement diagram of the electrode processing position before processing will be described with reference to FIG.

As shown in FIG. 2, the electrode 9 is moved so that the Z-direction reference is brought into contact with the tip of the reference sphere 3 on the table side, and the position Z0 is rewritten to zero.

Next, the X and Y references of the electrode 9 are similarly measured by contacting the reference sphere 3 on the table side to obtain X0 and Y0, and the position is rewritten to zero of X and Y.

Next, the electrode 9 is moved to the processing position of the workpiece 6, and the electrode 9 is moved based on the following calculated values.
Send.

In the Z direction, the machining end position coordinate Z2 of the machine is the sum of the previously obtained Z1 and the machining depth Z from the Z origin of the work end face, and is given by the following equation.

Z2 = Z1 ± Z (1) (where Z
Is the designated machining depth given in the drawing) The machining position coordinates of X2 and Y2 are similarly: X2 = X1 ± X ----- (2) (X is the position of X designated in the drawing) Y2 = Y1 ± Y (3) (Y is the position of Y specified in the drawing).

The above-mentioned reference numerals may be plus or minus depending on how the position of the workpiece is set with respect to the origin reference sphere.

Thus, it is understood that when Z1, X1, and Y1 change due to thermal displacement, the processing position shifts and the processing accuracy deteriorates.

There is no problem if the amount of change in expansion and contraction between the measurement in FIG. 1 and the measurement in FIG. 2 is the same, but matching the size of the workpiece mounting base and the reference sphere reduces the processing range. There is difficulty. Therefore, as a method that does not cause a change, the work height adjustment table 4, the work mounting base 5,
The mounting base 2 is made of a low thermal expansion material so that the relative displacement is suppressed. However, since the low thermal expansion material has a low hardness, it cannot be used as it is.

Next, the work mounting base of the present invention will be described in detail with reference to FIG.

FIG. 3 (a) is a plan view of the work mounting base 5, and FIG. 3 (b) is a sectional view of a screw hole of a work mounting set screw and a part of the work mounting base mounting screw hole.
FIG. 3C is a partial plan view of a groove on the back surface side of the work mounting base, and FIG. 3D is an enlarged sectional partial view of the groove. The work mounting screw hole 10 is a tapped hole that penetrates to the back surface of the work mounting base 5 and is provided in a large number in a honeycomb shape so that the work 6 can be mounted on the work mounting base 5 from any position. It has become. The screw hole 11 is
A screw hole for fixing the work mounting base 5 on the work height adjusting table 4 by a set screw, which is provided as a stepped hole penetrating the work mounting base 5, and a side surface of the screw hole 11. An escape hole 12 for a machining fluid is formed in the work mounting base 5 and penetrates laterally to the side surface. Furthermore, a groove 13 as an escape groove for machining fluid
A screw hole 10 such as a tap hole or the like, all of which has been penetrated, in a grid or mesh shape on the back side of the work mounting base 5;
It is provided so as to pass through the center of the screw hole 11 of the set screw, respectively, and is connected to the end of the work mounting base 5. Also, on the surface side of such a work mounting base 5,
The coating 14 is formed by coating the surface of the work mounting base 5 with a hard chromium carbide alloy to a thickness of about 30 μm on which the work 6 is placed.

In the electric discharge machine configured as described above, electric discharge machining is performed as follows.

First, the machining fluid is filled until the workpiece 6 on the workpiece mounting base 5 installed in the machining fluid tank sinks, and electric discharge machining is performed in the circulating machining fluid. When the workpiece 6 is machined, the machining chips fall on the work mounting base 5, and the dropped machining chips flow together with the machining fluid into the threaded holes 10, 11 of the work mounting base 5, and the machine chips 1 Fall up to the top. The portion closed by the work height adjusting table 4 passes through the groove 13 and the screw hole 11.
And flows out onto the machine table 1. by this,
The processing chips are discharged well, and the amount of processing chips accumulated on the machine table 1 is reduced. Furthermore, when air or the like is blown after the processing is completed, the remaining processing chips on the work mounting base 5 can be easily discharged through the screw holes 11 in the same manner.

In the case of the large work mounting base 5, there is no through hole even when cleaning with conventional air, and the work mounting base 5
It was necessary to move the swarf to the end face of the workpiece, it took a long time to clean, and it was easy to scratch when placing or removing the work. Can be prevented. In particular, when work pieces are removed from the work mounting base 5 when the work is removed, the work pieces are often entrained by the work, and the work mounting base 5 is often scratched. The improvement makes it harder to scratch. Further, the use of the hard chromium carbide alloy having a coefficient of friction of the coating 14 which is about 5 times lower than that of the hard chromium plating facilitates the cleaning work for discharging the processing debris and brings about a double effect. ing. Further, the working fluid itself accumulated on the work mounting base 5 is also easily discharged, and further, in order to prevent the working fluid from accumulating in the screw hole 11 of the set screw, the side surface of the screw hole 11 extends to the end face of the work mounting base 5. By providing the communication escape hole 12, the work for cleaning the processing waste is further facilitated, and the screw holes for mounting the work and the base for mounting the work can be suitably used, and the simple means can be used. Good effects can be obtained.

Embodiment 2 Next, Embodiment 2 of the present invention will be described with reference to FIG.

As shown in FIG. 4, Embodiment 2 of the present invention
In the above, the work height adjustment table 4
A work mounting base 5 of a low thermal expansion material is installed through
A table reference ball 3 of the same low thermal expansion material is placed on the work mounting base 5 and a work 6 is installed.

As described above, the present embodiment is a method in which the reference ball 3 of the low thermal expansion material is placed on the work mounting base 5 of the low thermal expansion material.

By placing the work 6 and the reference sphere 3 on the work mounting base 5 made of the same low thermal expansion material, even if the machine table 1 itself expands and contracts because the machine table 1 is not a low thermal expansion material, the effect is not affected. In contrast, the displacement is further reduced and the accuracy is improved as compared with the case where the reference sphere 3 is placed on the machine table 1 in FIG. If the machine table 1 is made of a low thermal expansion material or a ceramic material corresponding thereto, the same effects as described above can be obtained.

Next, the effect of the present invention will be described with reference to FIGS. 5 (a) and 5 (b) in comparison with the prior art. FIG. 5 (a) shows the relative displacement when the low thermal expansion material of the present invention is used. FIG. 5B is a graph showing the amount of relative displacement in the conventional example.

As shown, to see the effect on the relative displacement according to the invention, one side on the same machine
The work was placed on a work mounting base using the same low thermal expansion material as the reference sphere using the low thermal expansion material, and the relative displacement was measured. On the other side, the workpiece was placed on a standard sphere made of a general steel material and a commercially available magnet base made of a general steel material and a magnet material, and the relative displacement was measured.

The above measurements were taken on the same day, at the same time, alternately at approximately 30 minute intervals, and the measurement time was not different from several minutes. The work material placed on each was a general steel material, and was the same size of about 100 mm square dice. Further, the distances X, Y, and Z between the workpiece and the reference sphere were set to the same distance.

Since the measurement accuracy is deteriorated in the state of being immersed in the working fluid, the working fluid was put under the work mounting base and the upper part was left in the air.

As a result, when the room temperature changes by about 4 ° C., the displacement amount which had been Max 12 μ in the past was changed to Max 4 μ.
And decreased. Further, when the distance in the Y direction is 200 mm and X,
The displacement is large because the lens is placed at a position longer than Z. In addition, when it was considered that the variation accuracy of the measurement itself had an error of 2 μ, the displacement was further reduced and showed a value close to approximately 1/8 of the target. The coefficient of linear expansion of the low thermal expansion material used in the test was 1 × 10 ⁻⁶ / K · 2
0-100 degrees, about 1/8 of ordinary steel material.

In actual machining, the machining fluid temperature rises due to the electric discharge machining heat (approximately 3000 ° C., which is higher than the temperature at which iron dissolves), so that not only room temperature but also machining fluid temperature changes. Also, the relative displacement increases. Further, the processing heat also changes under processing conditions (finish processing conditions with low current and rough processing conditions with high current). Further, the machining fluid has a purpose of cooling the electric discharge machining heat, but a machining fluid temperature difference also occurs near the base near the machining and near the reference sphere far from the machining, which affects the change in the relative distance.

However, with the work mounting base and the reference sphere of the present invention, regardless of the working fluid temperature or room temperature change,
Processing can be performed with high accuracy without any problems.

The ball at the tip of the reference ball 3 of the present invention was not made of a low thermal expansion material, but it may be used. In this case, the wear resistance is increased by improving the hardness to extend the life and to improve rust. It is more preferable to perform the same coating treatment on the surface as that of the work mounting base in order to prevent the above. Although the present invention has been carried out by the electric discharge machine, the present invention is not limited to the electric discharge machine but also to other machine tools, in which the work mounting base and the origin reference sphere are installed and the relative positional displacement between the work and the tool is required. Can be valid. For example, a cutting machine sometimes measures the surface position in the Z direction of a tool such as a cutter or an end mill via a reference sphere in the same manner as in the present invention. In such a case, the thermal displacement prevention method of the present invention is effective. It is.

[0052]

As described above, in the method for preventing relative displacement of the electric discharge machine according to the first aspect of the present invention, the work mounting base and the reference sphere are set on the machine table, and the reference sphere on the machine table is set. With the machine that is processed as the origin of the machine coordinates,
In the method of measuring the distance between the reference sphere and the workpiece fixed on the workpiece mounting base in advance, measuring the tool position with the reference sphere when processing the workpiece with the tool, and moving the workpiece to the workpiece processing unit for processing. Since the low thermal expansion material is used for the work mounting base and the reference sphere, the reference sphere and the work mounting base are changed by changing the reference sphere and the work mounting base on the machine table to a material having a small linear expansion coefficient. The low thermal expansion material has low hardness, so it is easily scratched as it is and cannot be used as a work mounting base. The thin coating of the chromium alloy makes scratches less likely to occur and reduces the need for polishing correction.

According to a second aspect of the present invention, in the method for preventing relative displacement of the electric discharge machine, the reference sphere is supported on a support base and a low thermal expansion material is used for the support base. The displacement of the relative position between the workpiece and the work mounting base can be suitably reduced.

According to a third aspect of the present invention, in the method for preventing relative displacement of the electric discharge machine, the work mounting base body and the reference sphere main body are made of a low thermal expansion material, and the work mounting base and the reference sphere tip ball are provided. Since the surface is coated with a hard chromium carbide alloy, the low thermal expansion material has low hardness, so it is easily scratched as it is and could not be used as a work mounting base. By coating thinly, it becomes hard to be scratched and can be used, and the number of times of performing the polishing correction can be reduced.

According to a fourth aspect of the present invention, there is provided a method for preventing relative displacement of an electric discharge machine, wherein a plurality of screw holes are formed in the work mounting base in a honeycomb shape, and the screw holes are penetrated to the back surface. Since grooves are formed in a grid or mesh shape so as to pass through the surface holes and communicate with the end of the work mounting base, the structure is such that machining fluid and machining debris are unlikely to collect on the base upper surface, and cleaning of the work mounting surface is performed. It can be performed efficiently.

In the method for preventing relative displacement of the electric discharge machine according to the fifth aspect of the present invention, a relief hole penetrating in the lateral direction is provided on the side surface of the screw hole of the work mounting base, so that the machining liquid or the machining is provided. By adopting a configuration in which debris hardly accumulates on the upper surface of the work mounting base, the work mounting surface can be efficiently cleaned, and there is less thermal displacement and no deformation as compared with the conventional magnet base, thereby improving the processing position accuracy. At the same time, the manufacturing cost can be reduced to the minimum necessary part and the displacement of the relative position between the magnet reference sphere and the work mounting base can be reduced to the same level as a base capable of reducing the displacement.

[Brief description of the drawings]

FIG. 1 is a measurement diagram of a relative position of a machining origin in a first embodiment of a method for preventing relative displacement of an electric discharge machine according to the present invention.

FIG. 2 is a measurement diagram of an electrode processing position in FIG. 1 of the present invention.

FIG. 3 is a view showing a work mounting base according to the present invention;
(A) is a plan view, (b) is a sectional view of a tapped hole and a screw hole portion of a set screw, (c) is a plan partial view of a relief groove, and (d) is an enlarged sectional partial view of the relief groove.

FIG. 4 is a measurement diagram of a relative position of a machining origin in Embodiment 2 of the method for preventing relative displacement of an electric discharge machine according to the present invention.

FIG. 5 is a comparison graph of the relative displacement between the present invention and a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Machine table 2 Mounting stand 3 Reference ball 4 Work height adjustment stand 5 Work mounting base 6 Work 7 Processing part 8 Reference ball 9 Electrode 10 Screw hole 11 Screw hole 12 Escape hole 13 Groove 14 Coating

Claims (5)

[Claims] 1. A machine for setting a workpiece mounting base and a reference sphere on a machine table and processing the reference sphere on the machine table as an origin of machine coordinates, and fixing the workpiece to the reference sphere and the workpiece mounting base. In the method of measuring the distance of the work in advance, measuring the tool position with the reference sphere when processing the work with the tool, and moving the work to the work processing part, the work mounting base and the reference sphere have low thermal expansion. A method for preventing relative displacement of an electric discharge machine, characterized by using a material. 2. The method according to claim 1, wherein the reference sphere is supported on a support, and a low thermal expansion material is used for the support. 3. The work mounting base body and the reference sphere main body are made of a low thermal expansion material, and the surface of the tip sphere of the work mounting base and the reference sphere is coated with a hard chromium carbide alloy. A method for preventing relative displacement of an electric discharge machine according to the above. 4. A plurality of screw holes are formed in the work mounting base in a honeycomb shape, the screw holes are penetrated to the back surface, and a groove is formed to pass through the back surface hole and communicate with the end of the work mounting base. 2. The method according to claim 1, wherein the electric discharge machine is provided in a lattice shape or a mesh shape. 5. The method according to claim 1, wherein a relief hole penetrating in a lateral direction is provided on a side surface of the screw hole of the work mounting base.