JPS63295122A - Electrolytic polsihing device - Google Patents

Abstract

PURPOSE:To control an electrode performing its good follow-up motion and to easily polish a three-dimensional curved surface, by supporting a polishing unit tiltably moving by a universal joint and providing an insulating material made spacer, which comes into slide contact with surfaces of a workpiece, pressing the polishing unit to the workpiece. CONSTITUTION:A polishing unit 12, which is vertically movably supported with a corner drill 13 and pressed to surfaces of a workpiece by the gravity, supports a holder 17 tiltably moving by a universal joint 16 to be automatically tilted in accordance with a curve, and a ceramics made spacer 18 comes into contact with the surface of the workpiece. The polishing unit 12 is driven reciprocating by a robot arm and rotating by the corner drill 13, and the spacer 18, coming into contact with the surface of the workpiece, rotates with a rotary shaft 15 serving as the center. The polishing unit, which removes a passive state film in a protrusive part of the surface by polishing to be melted by electrolytic action, flatly smooths the surface by exposing the metallic surface of the workpiece in an electrolyte and opposing a negative electrode 19 to the metal exposed part of a positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrolytic polishing device for efficiently smoothing a metal surface after machining or electrical discharge machining.

(Prior art) Press molding molds, plastic injection molding molds, die-casting molds, etc. are formed by machining or electric discharge machining because the smoothness of their surfaces greatly affects the quality of the product. It is necessary to even out the minute irregularities on the surface of the mold to give it a mirror-like finish. This type of mold chiseling work is difficult to automate because the molds are produced individually and their shapes are complex three-dimensional curved surfaces. They relied on manual polishing using a whetstone. However, this hand-polishing work not only requires man-hours, which accounts for 20% to 30% of the entire mold manufacturing process, but it is also manual labor that requires skill and perseverance, making it difficult to train successor workers, and making it difficult to develop new workers. Automation of polishing work was strongly desired in the mold industry.

Against this background, metal surface polishing devices have been proposed that use the principles of electrolytic machining, grinding/polishing, and electrolytic grinding that combines these.

Electrolytic processing is a processing method in which the workpiece is used as an anode and electrolysis is carried out in an electrolytic solution at a high current density to rapidly dissolve the surface of the workpiece, especially the convex parts, and obtain a smooth surface. It can be machined regardless of the hardness of the workpiece, and the machining speed and finished surface roughness are good. However, since the electrolytic action extends to a position relatively far from the cathode electrode, the machining accuracy is slightly inferior. There is. On the other hand, the grinding/polishing method is a method of smoothing the surface of the workpiece by attaching a tool equipped with a grindstone to an NC machine tool, robot, etc., and the accuracy is very good as long as the grindstone does not wear out. However, it has the disadvantage that the processing force required for grinding and polishing is large and the processing time is long.

The electrolytic grinding method is a combination of the electrolytic processing method and the grinding/polishing method, in which the protrusions of the passive film that are generated on the surface of the workpiece during electrolytic processing are removed by mechanical polishing. This method exposes the metal surface of the convex part of the workpiece and selectively promotes elution of this part to obtain a smooth finished surface. Devices using this principle can be roughly divided into those that remove the passive film using a conductive grindstone containing abrasive grains that acts as a cathode, and those that use a graphite cathode that is rotated at high speed near the surface of the workpiece. It is known that the passive film is removed by generating a liquid flow.

Such an electrolytic grinding device combines the advantages of both electrolytic machining and grinding/polishing, and is currently considered to be the most suitable for automatic polishing of metal surfaces.

(Problems to be solved by the invention) However, in the conventional electrolytic grinding device as described above,
Since the distance between the workpiece and the electrode is only the size of the abrasive grain or the thickness of the laminar flow of the electrolyte, not only is it inevitable to deteriorate the finished surface roughness due to short circuits and discharges, but also the electrode Due to insufficient tracking ability to the workpiece surface,
The problem is that it is difficult to polish complex three-dimensional curved surfaces.

The present invention was made in view of these problems, and its purpose is to improve the ability of a polishing tool to trace the surface of a workpiece in an electrolytic polishing device, and to improve the ability of the polishing tool to imitate the surface of an electrode. By keeping the distance between the surface of the workpiece and the surface of the workpiece constant, automatic polishing can be performed even on three-dimensional curved surfaces.

(Means for solving the problem) In order to achieve this object, in the present invention, a polishing unit having an electrode is tiltably supported by a universal joint, and is biased against a workpiece. In addition, this polishing unit is provided with a spacer made of an insulating material that slides into contact with the surface of the workpiece. The spacer is supposed to mechanically polish the surface of the workpiece and maintain a constant distance between the surface and the electrode.

(Function) With this configuration, the polishing unit equipped with the electrodes can be tilted freely, so that even a workpiece with a three-dimensional curved surface can be polished by simply applying pressure. can be easily opposed. therefore,
When the polishing unit is moved along the surface of the workpiece, it can easily follow even surfaces with complex shapes.
The movement will follow the surface.

Since this polishing unit is equipped with a spacer that slides into contact with the surface of the workpiece, the protrusions of the passive film formed on the surface of the workpiece immersed in the electrolyte are removed by contact with the spacer. The exposed convex portions of the metal surface face the electrode at a predetermined distance and are eluted, smoothing the metal surface.

(Example) Hereinafter, the present invention will be explained in detail based on the drawings.

In the drawings, FIGS. 1 and 2 show an embodiment of the electrolytic polishing apparatus according to the present invention. FIG. 1 is a schematic overall view thereof, and FIG. 2 is an enlarged view of the polishing unit. Also, the third
The figure is a diagram showing the processing principle.

As is clear from FIG. 1, a workpiece 1 having a three-dimensional surface to be polished is placed in a processing tank 3 filled with an electrolyte 2 consisting of an aqueous sodium nitrate solution. This electrolytic solution 2 is injected into the processing tank 3 from an electrolytic solution tank 6 by a metering pump 5 provided in an injection conduit 4a. At that time, the sludge contained in the electrolyte 2 is
It is removed by filter 7.

The electrolyte 2 overflowing from the processing tank 3 is
The electrolyte is returned to the electrolyte tank 6 through the discharge pipe 4b.

A nut 10 is attached to the tip of the arm 9 of the two-axis robot 8, and a ball spline shaft 11 is fitted into the nut 10. A corner drill 13 that supports the polishing unit 12 and rotates it is attached to the lower end of the shaft 11. In this way, the polishing unit 12 is controlled to move in a horizontal plane by the robot 8, and the ball spline shaft 11
It is supported in a vertically movable manner by a ball spline mechanism consisting of a nut lO and a nut lO.

As shown in detail in FIG. 2(A), the polishing unit 12 has a rotating shaft 15 made of an insulating material and fixed to the chuck 14 of the corner drill 13. This rotating shaft 1
A disk-shaped first holder 17 made of aluminum alloy is attached to the tip of the holder 5 via a universal joint 16. This first holder 17 constitutes the main part of the polishing unit 12. The universal joint 16 supports the first holder 17 so as to be tiltable in any direction, and is capable of transmitting the rotation of the rotating shaft 15 to the first holder 17.

A spacer 18 made of ceramic, which is an insulating material, and an electrode 19 made of copper are attached to the first holder 17 so as to be adjacent to each other. The tip of the spacer 18 slightly protrudes from the tip of the electrode 19, and when the polishing unit 12 is positioned on the workpiece 1, the spacer 18
is brought into contact with the surface of the workpiece 1. At that time, there is a distance of 1 mm between the surface of the workpiece 1 and the electrode 19.
A certain degree of spacing is formed. Second
As shown in Figure (B), three sets of these spacers 18 and electrodes 19 are provided on the same circumference, and each set is arranged around the rotating shaft 15 at intervals of 120°.

A second holder 20 made of copper is fixed to an intermediate portion of the rotating shaft 15. This second holder 20 is cylindrical and has a flange 21 at its upper end. The tip of a brush 23 attached to the frame of the corner drill 13 via an insulating material 22 comes into sliding contact with the flange 21. Second holder 20 and first holder 1
7 is electrically connected by a flexible lead wire 24. In this way, the polishing unit 12 is insulated from the corner drill 13, and moreover, the polishing unit 12 is insulated from the corner drill 13.
Electrical conduction between the electrode 19 of the first holder 17, which rotates with respect to the first holder 17 and tilts about the universal joint 16, and the brush 23 on the fixed side is always maintained.

As shown in FIG. 1, the brush 23 is connected to the processing tank 3.
The terminal is connected to the negative pole of a power supply 25 installed outside the terminal. The positive pole of the power supply 25 is connected to the workpiece l. Therefore, the workpiece 1 immersed in the electrolyte 2
serves as an anode, and the electrode 19 of the polishing unit 12 serves as a cathode.

Next, the operation of the electrolytic polishing apparatus configured as described above will be explained.

When the arm 9 of the robot 8 is reciprocated in a horizontal plane, the polishing unit 12 moves over the surface of the workpiece 1 accordingly. At this time, since the polishing unit 12 and the corner drill 13 are supported by a ball spline mechanism so as to be able to move up and down, the polishing unit 12 and the corner drill 13 are pressed against the surface of the workpiece 1 by gravity, and automatically follow the surface. move up and down. This shows that the polishing unit 12 can always be biased against the workpiece 1 with a constant force by gravity without controlling the arm 9 of the robot 8 in the vertical direction. Further, since no reaction force is applied to the arm 9, there is no need to require the robot 8 to have great rigidity.

Since the first holder 17 of the polishing unit 12 is supported by the universal joint 16 so as to be tiltable with respect to the rotating shaft 15, when moving over the surface of the workpiece 1, it follows the curvature of the surface. Tilt automatically. Moreover, since the first holder 17 is provided with spacers 18 at three points, these spacers 18 are always attached to the workpiece.
will be in contact with the surface of

In this way, by simply reciprocating the arm 9 of the robot 8 in a horizontal plane, the spacer 18 of the polishing unit 12 can be
And the electrode 19 starts to move along the surface of the workpiece 1.

Therefore, while reciprocating the arm 9 of the robot 8, the corner drill 13 is used to polish the polishing unit 1.
2 to rotate. Then, the three spacers 18 of the polishing unit 12 rotate around the rotating shaft 15 while always being in contact with the surface of the workpiece 1. Therefore, these spacers 18 come into sliding contact with the surface of the workpiece 1.

A passive film 26 is formed on the surface of the workpiece 1 immersed in the electrolytic solution 2, as shown in FIG. Therefore, the surface is in a state where metal elution is less likely to occur. However, when the spacer 18 slides into contact with the surface of the workpiece 1, the passive film 2 on the convex portion of the surface
6 is removed by mechanical polishing. As a result, the metal surface of the workpiece l is exposed in the electrolyte 2 in that part, and the electrode 1 moving following the spacer 18
9 will face the exposed metal part. Since the workpiece 1 is used as an anode and the electrode 19 is used as a cathode, metal is eluted from the exposed portion by electrolytic action.

In this way, the spacers 18 and the electrodes 19 alternately pass over the workpiece 1, and mechanical polishing and electrolytic action are performed alternately, so that the surface of the workpiece 1 is rapidly smoothed. Since this action is performed only at the location where the spacer 18 passes, selective finishing is possible. Moreover, since the electrolyte 2 is a sodium nitrate aqueous solution whose current efficiency decreases as the gap between the electrode 19 and the workpiece 1 increases, elution of areas away from the area where the electrode 19 passes is prevented. Ru. Further, by using the sodium nitrate aqueous solution, the passive film 26 is easily formed, so the concave portions on the surface of the workpiece 1 are protected by the passive film 26, and only the convex portions are eluted.

During this time, the distance between the electrode 19 and the workpiece 1 is
It is kept constant by the spacer 18. Therefore, the most efficient electrolytic action is performed, and deterioration of the finished surface due to short circuits and discharges is also prevented. Since the spacer 18 is made of ceramic, it is less likely to be worn out by mechanical polishing.

As the polishing unit 12 rotates, a liquid flow is generated in the processing gap between the electrode 19 and the workpiece 1. Therefore, sludge and air bubbles generated by polishing are discharged from the processing gap by the liquid flow. Furthermore, the temperature rise in the processed portion is also suppressed by the liquid flow.

Next, experimental results using such an electrolytic polishing device will be explained.

FIG. 4 shows a flat plate of carbon steel 545C subjected to electrolytic polishing in a 20% aqueous sodium nitrate solution, and changes in the finished surface roughness at the center of the streaks were investigated over time.

The processing conditions are: polishing unit rotation speed 3oorpm, reciprocating feed stroke 35mm, and feed speed 0.5m/min.
, the machining gap was 1 mm, and the machining current was 20 A.

As is clear from this figure, the finished surface roughness Rmax is
After processing for 15 minutes, the thickness was reduced from 2°0 μm to 0.2 μm. In this way, it was confirmed that this electrolytic polishing can perform everything from removing cutter marks after machining to mirror finishing.

Furthermore, the experiment confirmed that only the convex and convex portions of the surface of the workpiece were selectively removed and smoothed.

By the way, in such an electrolytic polishing device, when the polishing unit 12 is moved back and forth in one direction, the cross-sectional shape of the streaks formed thereby is often not flat in the direction perpendicular to the direction of movement. This is thought to be due to the fact that the frequency with which the electrode 19 passes is different between both sides and the center of the streak when the polishing unit 12 moves back and forth. As a result, the amount of processing is uneven, and both sides of the groove are deeper than the center.

In order to solve this problem, three sets of spacers 1
It is conceivable to make the radial positions of the electrodes 8 and 19 different from each other.

Further, as shown in FIG. 5, an electrode 27 other than the three electrodes 19 arranged on the circumference may be attached to the center of the first holder 17. When such an electrode 27 is provided, the amount of machining at the center portion of the striation is increased by the electrode 27, so the amount of machining at both sides and the center portion is equalized, and the cross section thereof is flattened.

When using such an electrode 27, its size is appropriately determined so that the amount of machining is uniform in each part when the polishing unit 12 moves, and its height is determined so that the three spacers 18 It is necessary to set the electrode 27 so that it does not come into contact with the workpiece 1 even when it is in sliding contact with the curved surface of the workpiece 1.

In addition, in the above embodiment, the polishing unit 12 is
It is assumed that the robot 8 moves the robot 8 back and forth and the corner drill 13 rotates the robot 8, but when drilling very narrow grooves or deep holes, it is also possible to have only the reciprocating movement or vibration movement. .

Further, in the above embodiment, the polishing unit 12 is supported by a ball spline mechanism so as to be able to move up and down, and is pressed against the workpiece 1 by gravity, but a spring, an air cylinder, etc. may also be used as the pressing force means. can. If the corner drill 13 is attached to the piston of a low-pressure air cylinder, the polishing unit 12
is pressed against the workpiece 1 by air pressure, and its vertical movement is absorbed by the air cylinder.

The material of the spacer 18 may be any insulating material that has the hardness necessary to remove the passive film 26. However, if it wears out, the distance between the electrode 19 and the workpiece 1 will no longer be maintained, so it is desirable to use a material that is resistant to wear.

(Effects of the Invention) As is clear from the above description, according to the present invention, the polishing unit is tiltably supported and is biased against the workpiece, so that Just by moving the polishing unit along the surface of the workpiece, the polishing unit will automatically follow the surface of the workpiece. Therefore, complicated control to accurately move the polishing unit following the surface of the workpiece is unnecessary. Moreover, since the polishing unit is pressed against the workpiece with a constant force, the processing force necessary for mechanical polishing can also be obtained.

The polishing unit is equipped with a spacer and an electrode, so that after the passive film on the surface of the workpiece is mechanically removed by the spacer, electrolysis occurs between the workpiece and the electrode. become. Therefore, finishing of the workpiece surface can be performed efficiently. Furthermore, since the processing force required to mechanically remove the passive film is small, a processing machine with low rigidity, such as a robot, can be used.

Furthermore, since a constant distance is always maintained between the workpiece and the electrode by the spacer, the finish of the workpiece surface will not deteriorate due to short circuits or electric discharges.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of an electrolytic polishing device according to the present invention, and FIGS. 2 (A) and (B) are longitudinal sectional side views and enlarged views of the polishing unit portion of the electrolytic polishing device. Fig. 3 is an explanatory diagram for explaining the processing principle of the electrolytic polishing device, Fig. 4 is a graph showing the results of processing experiments using the electrolytic polishing device, and Fig. 5 is the polishing unit and other parts. It is a bottom view showing an example of this. 1... Workpiece 2... Electrolyte 3...
Processing tank 8... Robot 10... Nut 11... Ball spline shaft 12... Polishing unit 13... Corner drill 15... Rotating shaft 16... Universal joint 17... First Holder 18...Spacer 19
... Electrode 25 ... Power supply 26 ... Passive film

Claims (6)

[Claims] (1) A workpiece forming an anode and a polishing unit equipped with an electrode forming a cathode are immersed in a tank filled with electrolyte, and the polishing unit is moved along the surface of the workpiece. In an electrolytic polishing apparatus for electrolytically grinding the surface of a workpiece, the present invention includes: a universal joint that tiltably supports the polishing unit; and a pressing force that presses the polishing unit against the surface of the workpiece; , bringing the polishing unit into sliding contact with the surface of the workpiece,
An electrolytic polishing device comprising an insulating spacer that mechanically polishes the surface and maintains a predetermined distance between the surface and the electrode. (2) The electrolytic polishing device according to claim 1, wherein the polishing unit is rotationally driven via the universal joint. (3) The electrolytic polishing device according to claim 2, wherein the polishing unit is provided with three sets of the electrodes and spacers. (4) The pressing and urging means of the polishing unit is constituted by a ball spline mechanism that supports the polishing unit in a vertically movable manner, so that the polishing unit is pressed against the surface of the workpiece by gravity. , An electrolytic polishing apparatus according to any one of claims 1 to 3. (5) The electrolytic polishing device according to claim 1, wherein the electrolytic solution is an aqueous sodium nitrate solution. (6) The electrolytic polishing device according to claim 1, wherein the spacer is made of ceramics.