JPH0122095B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The disclosed technology belongs to the field of technology for manufacturing molds by numerically controlled wire cut electrical discharge machining.

Therefore, the present invention is capable of cutting a workpiece into a predetermined contour shape by a moving wire that is stretched between the arms of a numerically controlled wire-cut electric discharge machining device, or between a column head and an arm, or a bed, and then the workpiece is cut into a predetermined contour shape. Polishing finish machining can be performed under the same numerical control program by simply changing the relative offset between the workpiece and the finishing tool using the same processing equipment without changing the process using the finishing tool attached to the column head or bed. In particular, the arm, column head, or
The polishing finishing tool is set via a polishing finishing setting device provided in the bed so that the output shaft of the rotational drive device is aligned with the axis of the wire electrode during wire cut electrical discharge machining, and the polishing finishing tool is set in a position where the output shaft of the rotational driving device coincides with the axis of the wire electrode during wire cut electrical discharge machining. This relates to a mold manufacturing method in which a corresponding finishing rotary tool is selectively connected to the mounting device of the device output shaft, energized, and the workpiece is moved under NC control to perform finishing machining.

As is well known, numerically controlled wire cut electrical discharge machining is often used in mold machining, etc., but the machined surface has an uneven satin-like surface, and the roughness of the machined surface is inversely proportional to the machining speed. If you try to make the roughness a little smaller, the machining speed will drop dramatically, so wire cut electrical discharge machining is usually performed at a Rmax of about 10 to 20 μm.
Furthermore, due to the machining shape effect, there are variations in the roughness of the machined surface between straight parts and corner parts of the machining contour, and therefore, it is necessary to polish the machined surface after wire cut electrical discharge machining.

Until now, after the wire cut electrical discharge machining process was completed, the workpiece was removed from the machine table, and in a separate process, it was finished by grinding and grinding using a grindstone, buffing, liquid honing, and various other mechanical methods.
Alternatively, electrochemical processing, chemical etching, or the like is used to finish the surface to a surface roughness of 0.5 μm Rmax.

Although the finished surface roughness is smooth when viewed microscopically, in the case of complex shapes, it is not possible to finish the entire cut surface after wire cut electric discharge machining with the specified machining allowance and surface roughness. There was a problem that did not result in the ideal finish.

Furthermore, since a separate finishing step is required after the wire cut is cut by electrical discharge machining, there is a disadvantage that the work is cumbersome and management is complicated.

For this reason, after approximate NC-controlled wire-cut electrical discharge machining, wire-cut electrical discharge machining (commonly known as second cut), which has a finish with less machining stock and a smaller machined surface roughness, is being performed. It is not possible to reduce the roughness to less than a few μmRmax, and since the wire electrode is open on the opposite side to the machined surface, the position of the wire electrode is unstable, resulting in poor accuracy in parts with different machined shapes. There were some drawbacks such as difficulty in coming out.

The purpose of the present invention is to solve the problem of finishing the cut surface of a numerically controlled wire-cut electrical discharge machining workpiece based on the conventional technology, by attaching an abrasive finishing device to a fixed part such as an arm, a column head, or a bed of a wire-cut electrical discharge machining device. It is an object of the present invention to provide an excellent method for manufacturing a die that allows numerically controlled polishing to be performed immediately after cutting with the same wire cut electric discharge machining device by bringing a finishing rotary tool into contact with the cutting surface.

In accordance with the above object, the present invention has a structure in which a numerically controlled wire-cut electrical discharge machining machine performs a predetermined cutting process on a workpiece, and after the cutting process is completed, a polishing finishing machine is provided on a fixed part such as an arm of the wire-cut electrical discharge machine. Attach the finishing rotary tool to the mounting device that extends to the rotary drive device of the setting device, and carry out the work first so that the finishing rotary tool comes into contact with the cutting surface so that finish polishing of a predetermined machining allowance is performed. The program of the NC control device used during the electric discharge machining of the broken wire cut is used to move the workpiece under numerical control using a machining feed signal offset according to the diameter of the rotary tool, and to rotate the finishing tool as necessary. The gist is to perform reciprocating motion in the axial direction with a predetermined stroke or further vibration, etc., and to apply electrolytic machining if desired, so that the polished finish of the cut surface is uniformly and accurately performed.

Next, embodiments of the present invention will be described below based on the drawings.

In the embodiment shown in FIGS. 1 and 2, 1 is a wire-cut electric discharge machining apparatus, and a column head extending from a stand 3 on a base frame 2 containing a machining fluid tank, etc., or a guide 5 of an arm 4 is A lower arm (not shown) from which the wire 6 extends downward, or
The X and Y machining tables 7 and 7 move the workpieces 8 on the X and Y machining tables 7 and 7 under the control of the NC control device by being transported by a lower guide provided on the base frame and a reel provided on the stand 3. The set contour shape is processed by the displacement of .

A setting device 9 for finishing polishing is provided on the arm 4 in the vicinity of the installation position of the guide 5, and the setting device 9 has a configuration as shown in one embodiment in detail in FIG. The setting device 9 is fixed to the arm 4, or can be positioned by moving up and down using hydraulic, pneumatic, or mechanical mechanisms, and can be rotated and fixed to a retractable shaft 10 via a positioning pin 11. A set arm 12 is provided to the set arm 12, and a motor 13 serving as a rotational drive device is provided to the set arm 12 via a bracket.

A chuck 16 as a mounting device is provided on the output shaft 14 of the motor 13 via a dressing device 15 as appropriate.
A current-carrying brush 18 is connected to the output shaft 14 from the casing via the holder 17, and is connected to the negative electrode of a power source 19 electrically connected to the workpiece 8.

20 is a finishing rotary tool for a metal bond grindstone in which diamond abrasive grains or the like are bonded and fixed by plating or other means, or mixed with metal powder and sintered, and the types and dimensions of the work 8 and its cutting surface 21 are The type of tool grindstone, its diameter, length, etc. are determined by the shape and shape, and it can be selectively attached to and removed from the chuck 16 via the attachment handle.

Normally, the machining fluid for wire cut electrical discharge machining is used as it is, but if necessary, an electrolyte is added to the fluid injection nozzle 22 facing the cutting surface, and 23 is an NC control device. In addition, X and Y (not shown) of the processing tables 7, 7
Connected to the shaft drive motor.

For convenience of illustration, FIG. 2 shows the set arm 12 set so as to coincide with the axis of the wire 6.

In the above configuration, the workpiece 8 is set on the processing tables 7, 7 as shown in FIG.
The wire 6 is fed while being displaced to a predetermined value through the wire 3, and a predetermined contour is cut by electrical discharge machining. When the cutting is completed, the wire 6 is reset as in the conventional case, so that the wire 6 is brought into a state where one punching is completed.

Therefore, the setting arm 12 of the setting device 9 is rotated via the positioning pin 11 to position the center of the output shaft 14 so that it substantially coincides with the setting center axis of the wire 6.

At this time, the tables 7, 7 are actually driven by the NC control device 23 so that the side surface of the grinding wheel 20 comes into contact with the electrical discharge machining cutting surface 21 so that polishing with a predetermined machining amount can be performed accurately. Performs offset and performs NC according to the amount of offset.
The tool offset of the machining program in the control device 23 is corrected.

Next, if the corresponding combination grindstone 20 is not installed in advance, the grindstone 20 is installed on the chuck 16 above the cutting hole, and the shaft 10 is extended and driven downward so that the grindstone 20 faces the cutting surface 21. Setting device 9
Then, the negative electrode of the power source 19, which had been connected to the wire 6, is switched to the brush 18 side via a changeover switch (not shown).

When the setting is completed in this way, the machining fluid is fed from the machining fluid nozzle 22 to the cutting surface 21, and
The NC control device 23 and motor 13 are started.

Therefore, since the workpiece 8 is set in the starting state, the machining tables 7, 7 are displaced again according to a predetermined program such as the machining contour shape whose offset has been corrected, and the workpiece 8 is moved during electrical discharge machining by the wire 6. The polishing finishing process is performed by moving along a trajectory in which an offset amount corresponding to the diameter of the grindstone 20 and a predetermined machining allowance are added to the displacement trajectory.

On the other hand, the side surface of the grinding wheel 20 is substantially connected to the wire 6.
Since the cutting surface 21 is brought into contact with the cutting surface 21 in the same posture as the cutting surface 21, the cutting surface 21 is completely automatically finished according to the cutting shape in a type of copy polishing process.

In normal cases, the polishing finish is completed when the workpiece 8 has made one or more revolutions in which the depth of cut has been sequentially increased.

In addition, the mechanical polishing action by the grindstone 20 alone cannot
Although it varies depending on the type of whetstone, the material of the workpiece, the rotational speed of the whetstone, the processing feed rate for contour tracing, and the removal amount per polishing, the polishing surface should be approximately 4.
It is difficult to achieve a finish of ~5μmRmax or higher.

However, if electricity is supplied through the brush 18 from the power supply for wire cut electrical discharge machining or a separately provided power supply, and the electrolytic machining action is added with the machining fluid for wire cut electrical discharge machining, for example, 2 to 0.2 μmRmax
A finished surface can be obtained relatively easily.

Of course, for this purpose, it is necessary to use a conductive grindstone as described later as the grindstone 20.

In the explanation of the above embodiment, the grinding wheel 20 only rotates, but in the embodiment shown in FIG. A magnet 25 is provided on the output shaft 14', and an electromagnetic coil 26 is provided on the holder 17 extending downward from the casing of the motor 13, which is connected to an AC power source 19' of a predetermined frequency to rotate the grinding wheel 20 and generate high frequency, low frequency, or , it may be made to vibrate up and down at a varying frequency, and the above-mentioned first to second
In the illustrated embodiment, the entire setting device 9 can be vibrated up and down with a predetermined stroke by the vertical movement mechanism of the shaft 10, and in this way, the finished surface roughness of the polished surface can be improved. It is desirable to do so.

Furthermore, as in the embodiment shown in FIG. 4, the set arm 12', the motor 13', and the sleeve 27 are fixedly installed, and a slide 29 is provided in the guide slit 28 of the sleeve 27 so as to be movable up and down. The motor 13 may be fixed to the grinding wheel 20, and its upper cam follower 30 may be engaged with a cam plate 31 provided on the motor 13' to rotate the grindstone 20 and raise and lower it at a predetermined frequency. .

However, it goes without saying that the embodiments of this invention are not limited to the above-mentioned embodiments; for example,
By mixing abrasive grains into the machining fluid, or by using an electrolyte solution to which an electrolyte has been added as the machining fluid, the grinding wheel 20
In addition to the X and Y control of the NC control device, longitudinal vibration in the axial direction may be performed under NC control as Z direction vibration of the axis 10 drive. Various embodiments can be adopted, such as using a porous grindstone treated to make it conductive, or using a synthetic resin or a metal wire mass with abrasive grains attached.

The outline of the present invention has been explained above, but to explain in more detail, various conventionally known conductive grindstones can be used as the grindstone 20, but diamond, CBN,
It is preferable to use abrasive grains such as SiC and TiC hardened with metal or alloy, preferably sintered.
A whetstone shaft is attached and fixed to such a cylindrical whetstone during or after the above-mentioned sintering process, but it is normal for such a whetstone and its shaft to not have a sufficiently protruding core. Even if a core with a predetermined accuracy comes out, when the motor 13 output shaft is fixed to the mounting device 16, the core does not necessarily come out as the motor shaft or setting device, and the accuracy and processing within a few μm are not guaranteed. Difficult to finish with surface roughness.

Therefore, in carrying out the present invention, after attaching the grinding wheel 20 to the mounting device 16, an electric discharge machining electrode with surface accuracy on the vertical side surface is placed on the workpiece 8 or the table 7, The side surface of the grinding wheel 20 is brought into contact with the side surface of this electrode, and a power source for wire cut electrical discharge machining is connected between the electrode and the grinding wheel, and while the grinding wheel is rotated and vibrated or reciprocated in the vertical axis direction, the wire cut electrical discharge is performed. Spray the machining fluid and remove the grinding wheel 2.
Performs 0 centering, blur removal, and dress processing.

In this case, the electrode is fed little by little toward the axis of the rotary grindstone.

Such dressing processing by electrical discharge machining of a grinding wheel is described in, for example, Japanese Patent Publication No. 1983-31276. Even with sintered whetstones, it is possible to finish with high precision in a relatively short time.

Once the centering and dressing processing as described above is completed, the main subject, the finish polishing of the workpiece 8, is started. Position of,
Alternatively, using the position where the tool has been offset according to the dressed grinding wheel diameter from this starting origin as the starting origin, the NC controller can use a signal that takes into account the tool offset amount and machining allowance into the program for the wire cut electrical discharge machining. Then, the table 7 moves and polishing finishing is performed. At this time, in wire cut electrical discharge machining, the machining from the machining start origin (prepared hole) to the machining contour line is, so to speak, redundant machining, so the process proceeds straight along the shortest distance and turns at almost a right angle when it reaches the machining contour line. Normally, the machining path from the start (prepared hole) to the contour line is programmed so that it follows the machining contour line, but it depends on the final grinding allowance (cut) with the grindstone, etc. If the rotary grindstone 20 is attempted to bite into the grinding surface in the wire cut electric discharge machining mode, there is a high possibility that the grindstone 20 or the grinding surface 21 will be damaged, and therefore the machining contour will be The NC control program for the start part of the grinding process should be changed so that the line draws as large an arc (R) as possible up to the grinding surface 21 and cuts in as parallel to the grinding surface 21 as possible, thus smoothly. is required,
If it is not possible to obtain a circular arc radius of a desired size, it is desirable to appropriately displace the starting point from the starting point (prepared hole) of wire cut electrical discharge machining.

The cut or bite into the ground surface 21 is approximately 15 to 20 μm, assuming that the surface roughness of the surface 21 due to wire cut electric discharge machining is approximately 13 μm Rmax.
Approximately 1.5 m in diameter will be removed by polishing, but it is best to make the cut as shallow as possible in the range of 1 μm to 20 μm, and then perform the final polishing by dividing the cut into multiple steps and changing the depth one after another.

Depending on the type of the grindstone 20 and the workpiece 8, it may be necessary to correct the tool diameter due to tool wear, but if the grindstone is made of cemented carbide powder as described above and diamond abrasive grains are sintered, As long as the workpiece is not made of a special material or has special dimensions (large), the above correction is hardly necessary.On the other hand, with something like an elastic bonded grindstone, for example, a finished surface of about 0.5μmRmax is required. Even if it is easy to obtain, if you grind the machining contour part of wire cut electric discharge machining once,
Since the diameter of the grinding wheel tends to be off by several tens of micrometers, it is necessary to correct the tool diameter one after another as the polishing process is fed, and there is a high possibility that a highly accurate finish cannot be achieved after all.

Although the machining fluid used in wire cut electrical discharge machining is pure water, it is approximately 10 ^-4 Ωcm and can exhibit electrolytic machining action when energized, so even if a separate DC or other machining power source is installed. However, the power supply for wire cut electric discharge machining should be a pulse power supply with a voltage of about 200V and an average current of about 0.3 to 3A (or 0.1 to 5A/cm ² ), and the width of the voltage pulse is relatively long. Mechanical cutting alone eliminates the occurrence of burrs that tend to appear when the depth of cut is large (for example, around 15 to 30 μm), and
m → 0.2 μm).

It seems that the faster the 20 rotations of the whetstone, the better. For example, 10 ⁴
~4×10 ⁴ RPM, about 2×10 ⁴ RPM was optimal for a grindstone with a shaft diameter of about 2.4 mmφ.

In order to maintain such high-speed rotation stably for a long period of time, fluid bearings that use fluid pressure such as gas or liquid, non-contact magnetic bearings that use magnetic force, or other low-speed bearings are needed. It is believed that it will be necessary to employ friction bearings as bearings for the rotary tool shaft and rotary drive motor shaft.

It seems suitable for the machining feed rate for polishing finishing machining to be about 1 to 10 mm/min, which is about the same as or slightly faster than the machining feed rate for wire cut electric discharge machining.
The axial vibration or reciprocating motion is approximately 5 to 5 strokes
50 mm and a reciprocating speed of approximately 50 to 200 mm/s, the final polishing process is performed to achieve the desired purpose.

As described above, according to the present application, a wire cut electrical discharge machining apparatus is equipped with a polishing finishing device capable of setting the rotational center axis of a rotary polishing tool at a position that coincides with the axis of a wire electrode, and cutting of a predetermined contour shape by wire cut electrical discharge machining is performed. After finishing, without removing the workpiece from the wire-cut electric discharge machining equipment, while it remains on the machining table, run the NC program used for the previous wire-cut electric discharge machining according to the diameter of the rotary abrasive tool to be used. By repeatedly increasing the depth of cut by simply offsetting the material and polishing it, the polishing process follows the cutting surface itself in a kind of copy machining state. The entire surface can be finished with high precision with a predetermined machining allowance and uniform surface roughness, and there is no need to remove and move the workpiece until the finishing process is completed, which not only improves work efficiency, but also allows for easy processing of the workpiece. There is no need for troublesome repositioning or deterioration of accuracy due to removal and movement of the workpiece, and there is no risk of damage to the workpiece. Furthermore, since it is not necessary to install the polishing and finishing device separately from the wire-cut electric discharge machining device, there is an advantage that it occupies less space, does not increase costs, and requires less maintenance.

In addition, when finish machining is conventionally performed by the so-called second cut of wire cut electrical discharge machining, the wire electrode is open on the side opposite to the machined surface, which tends to cause vibration and curvature of the wire electrode. However, it had the drawbacks of being unstable, difficult to achieve accuracy, and requiring a long time for finishing.
According to the present invention, the finishing process is performed by polishing using a rotary abrasive tool such as a grindstone, so that the entire cut surface can be finished with high precision with a predetermined machining allowance and uniform surface roughness. Finishing can be completed in a shorter time than when using a second cut.

In addition, it is possible to perform finishing by adding electrolytic action to mechanical polishing, and the power source and machining fluid of the wire cut electrical discharge machining device can be used as the power source and machining fluid for electrolysis. This can be easily done without increasing the size or complexity.

[Brief explanation of drawings]

The drawings are explanatory diagrams of embodiments of this invention, and the first
The figure is an overall schematic explanatory diagram of one embodiment, FIG. 2 is an enlarged explanatory diagram of the same part, and FIGS. 3 and 4 are explanatory diagrams of other embodiments corresponding to FIG. 2. 6...Wire, 1...Numerically controlled wire cut electric discharge machining device, 4...Arm, 21...Cutting surface, 1
3... Rotation drive device, 14, 14'... Output shaft,
9... Setting device, 20... Finishing tool, 16...
...Mounting device.

Claims (1)

[Claims] 1. Voltage pulses are repeatedly applied with machining fluid interposed between the wire electrode and the workpiece, which are arranged to face each other, and an NC control device creates a relative position between the two in a plane direction perpendicular to the axial direction of the wire electrode. A wire-cut electrical discharge machining device that performs cutting into a desired contour shape by giving a machining feed of a certain amount is provided with a polishing tool that is detachably attached to the tip of a shaft that is rotated by a rotation drive device, and the center axis of rotation of the polishing tool is aligned with the wire. A polishing finishing device is provided which has a setting device capable of setting the polishing tool at a position coinciding with the axis of the electrode and moving the polishing tool in the direction of the rotation center axis at the position, and after the desired wire cut is electrically discharged. , removing the wire electrode from the machining section, moving it in the direction of the rotation center axis of the polishing tool by the setting device so as to face the cutting surface of the workpiece, and performing the desired wire cut electrical discharge machining while rotating the polishing tool. The program of the NC control device used when performing the wire cut electric discharge machining is moved relative to the polishing tool in the plane direction using a machining feed signal offset according to the diameter of the polishing tool. A mold manufacturing method characterized by polishing and finishing.