JPS63267120A - Finishing method by electrochemical machining - Google Patents

Abstract

PURPOSE:To form a three-dimensional form surface of hard-cut metals into mirror-finishing form by setting current density at the half period to less than 2/3 of that at the latter period, in case of a method for finishing as removing an electrolytic product formed between a workpiece and a tool electrode. CONSTITUTION:At the first period of finishing work, a pulse current of 5A/ cm<2>-20A/cm<2> in current density is fed to a gap between a workpiece 2 and an electrode 4 from a power unit 8 by a control signal out of a working condition control part 10, thus the workpiece is machined. And, after raw material is eluted, an electrolytic product is removed together with dielectric fluid 41 by operation of a solenoid valve 50. Next, the fresh dielectric fluid 41 is fill up, a series of processes is repeated by a signal of a controller 12. Afterward, when machining depth accumulated value becomes within the specified difference to the setting value, it is changed over to the pulse current of more than about 30A/cm<2> in current density. With this constitution, such a three-dimensional metal curved surface that showed a mirror-like gloss of highly accurate and fine surface roughness is securable in a short time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a finishing method using electrolytic machining, and in particular to a method for finishing a three-dimensionally shaped workpiece made of a difficult-to-cut metal in a short time and with high precision. The present invention relates to a finishing method using electrolytic machining that allows for finishing with high precision and obtaining a mirror-like glossy surface.

[Prior Art] As conventional metal processing methods, electrolytic machining methods and electric discharge machining methods are known. The former electrolytic processing method is
The gap between the workpiece and the processing electrode is filled with an electrolytic solution such as sodium nitrate or sodium chloride, and this electrolytic solution is flowed at high speed to remove electrolytic products that inhibit stable electrolytic action, such as eluted metal compounds and metal ions. For example, JP-A-61-71921 and JP-A-60-44228 disclose a method in which a DC current is passed from a workpiece to a processing electrode while removing hydrogen gas and the like.

In the latter electric discharge machining method, the workpiece and the machining electrode are opposed to each other with a small gap in a machining liquid such as water or kerosene, and they are connected to an appropriate power source, and sparks are generated instantaneously in the gap. For example, Japanese Patent Publication No. 60-26646 and Japanese Unexamined Patent Application Publication No. 60-177 disclose methods that generate electrical discharge or transient arc discharge and process a workpiece using the electrical discharge energy.
It is disclosed in Publication No. 819.

[Problems to be Solved by the Invention] However, the former electrolytic machining method has a fatal flaw as a machining means. In other words, especially in bottom machining of three-dimensional shapes (machining of three-dimensional structures formed in the shape of concave holes), the electrolyte is uniformly applied to the gap between the workpiece, which has a complex contour, and the machining electrode. It is impossible to flow the electrolyte at a constant flow rate, resulting in differences in the supply of electrolyte, the concentration of electrolyzed products changes depending on the position, and even if high liquid pressure is applied to the gap, the inlet and outlet of the electrolyte The concentration of electrolyzed products changes. Therefore, even if a current with a uniform density is applied, the machining conditions, especially the machining progress speed, change in each part of the gap, resulting in differences in the gap dimensions, making it difficult to accurately transfer the machining electrode to the workpiece. However, it is difficult to obtain high-precision surface quality.

In addition, if all machining from the shape of the material is done by electrolytic machining, an electrolytic solution containing a large amount of electrolytic products will be generated, which requires time and cost to dispose of the wastewater, which is particularly inconvenient when machining stainless steel containing chromium. In this case, harmful hexavalent chromium was produced, and the above-mentioned disadvantages were even more remarkable.

On the other hand, in the latter electric discharge machining method, the surface roughness is Rma
x: Relatively high efficiency for finishing to about 20 μm, but to achieve a finished surface roughness higher than that, a microcurrent of less than IA is required, especially for workpieces with a large surface area. In addition to being time-consuming and inefficient, if the surface area is large, the capacitance between the surface of the workpiece and the machining electrode becomes large, making it difficult to narrow down the discharge current to a minute level to obtain good surface roughness. There was an inconvenience that it was difficult to use.

In addition, in normal electric discharge machining using insulating oil, a hardened altered layer is created and micro-cracks due to thermal stress penetrate deeply into the machined surface, and in wire electric discharge machining using pure water, a softened layer is created. The surface quality of both types of electrical discharge machining is unfavorable. Therefore, under conditions of use that require high precision and long service life for the surface quality, manual surface polishing is performed, even though the shape accuracy will be compromised. This has the disadvantage that surface finishing requires a lot of time and effort.

[Purpose of the invention] Therefore, this invention eliminates the above-mentioned inconveniences, and provides a method for finishing three-dimensionally shaped surfaces of workpieces, especially by liquid machining of difficult-to-cut metals, in a short period of time and with high precision, to create a mirror-like glossy surface. The objective is to realize a finishing method using electrolytic machining that can obtain the desired results.

[Means for Solving the Problems] In order to achieve this object, the present invention supplies a pulse current between a workpiece and a machining electrode that are disposed opposite to each other via a machining fluid, and In a finishing method that performs finishing while intermittently removing electrolytic products generated between electrodes, the current density of the pulsed current is made different between the first and second stages of finishing, and the current density in the first half of finishing is changed. It is characterized by setting the current density to 2/3 or less of the current density in the latter half of the finishing process.

[Function] According to the configuration of the present invention, surface quality with high precision and micro surface roughness can be obtained by using a pulsed current with a low current density in the early stage of finishing, and surface quality with high current density can be obtained in the latter half of finishing. A mirror-like glossy surface can be obtained without changing the roughness.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail and specifically with reference to the drawings.

1 to 6 show one embodiment of this invention. In FIGS. 1 to 3, reference numeral 1 denotes a finishing device capable of implementing the finishing method according to the present invention, and this device 1 includes a workpiece fixing device 3 for fixing a workpiece 2, and an electrode for fixing an electrode 4. A fixing device 5, a drive conversion section 7 that converts the rotational motion of the electrode drive section 6 into a reciprocating motion, a power supply device 8 that generates a pulse current, a motor drive control section 9, a machining condition control section 10, and a machining fluid flow control section 11. The control device 12 includes a control device 12, an input device 13 for inputting machining conditions, a machining fluid filtration device 14, a machining fluid scattering prevention cover 15, and the like.

The workpiece fixing device 3 is made of highly insulating granite or ceramics, and is, for example,
A table that can be moved in the direction (pol) 16
Fix it by etc. Further, the electrode fixing device 5 has an electrode 4 made of, for example, pure copper or graphite attached to the lower end of a rod 17 provided at its lower part, so that the electrode surface 4a and the processed surface 2a of the workpiece 2 are aligned in a three-dimensional direction. and fix it so that a uniform gap 18 is maintained. The electrode fixing device 5 is moved up and down to set the gap 18 to a predetermined value by the electrode drive section 6 and drive conversion section 7, which constitute electrode drive means. That is, the rotation of the motor 19 is controlled by control signals output from the motor drive control section 9 of the control device 12 based on signals from the rotary encoder 20 and the tacho generator 21 of the electrode drive section 6, and the motor 19 is rotated.
The rotational motion of is converted into a reciprocating motion by the drive converter 7,
The electrode fixing device 5 is moved up and down to set a predetermined gap 18 between the electrode surface 4a and the surface to be processed 2a.

The current density between the workpiece 2 and the electrode 4 is 70A/cm"
The power supply device 8, which serves as a current supply means for supplying the following predetermined pulse current, generates a pulse current with a current density calculated according to the surface area of the workpiece 20 in response to a control signal from the processing condition control unit 10, and is a direct current. It has a power source section 22 and a charge/discharge section 23, and is configured as shown in FIG. 4, for example. In FIG. 4, the charging/discharging section 23 includes a discharging section 24 and a charging section 2.
5, and the discharge section 24 has power storage devices 26-1 to 26-n.
, diodes 27-1 to 27-n, and discharge switch 28-
1 to 28-n, etc., and the charging section 25 includes the voltage detector 2
9, a voltage comparator 31, a charging switch 32, etc. Further, the DC power supply unit 22 includes a transformer 33 and a rectifier 34, and supplies DC current to the capacitors 26-1 to 26-n.

A processing condition control unit 10 that controls the power supply device 8 includes a charging voltage setting device 30 that sets charging voltages of the V electric appliances 26-1 to 26-n, and a charging voltage setting device 30 that sets charging voltages of the V electric devices 26-1 to 26-n, and a charging voltage setting device 30 that discharges electricity into the gap 18 between the workpiece 2 and the electrode 4. A current waveform setting device 35 that sets the current waveform of the charge to be discharged, a pulse generator 36 that generates a pulse of a predetermined time width of the charge to be discharged, and a gate that outputs an opening/closing signal to the discharge switches 28-1 to 28-n. It consists of circuit 37 etc.

The human power device 13 inputs the material and surface area of the workpiece, the finishing margin and dimensional accuracy grade, the finished surface roughness, the initial electrode gap, etc., and sends these signals to the motor drive control section 9 of the control device 12. and output to the processing condition control section 10.

The machining fluid filtration device 14 filters the machining fluid 41 containing electrolytic products generated during machining, and is configured as shown in FIG. 6, for example. That is, the machining fluid filtration device 14 includes a dirty tank 42 that stores the returned machining fluid containing a large amount of electrolytic products from the machining fluid tank 40, and the machining fluid in the dirty tank 42 is pumped up by an electromagnetic pump 43, passed through a filter 44, and then centrifuged. Centrifuge ja45 to separate and this centrifuge 4
A clean tank 46 that stores the machining fluid that does not contain electrolytic products separated in step 5, an electromagnetic pump 47 that pumps up the machining fluid from the clean tank 46, and a throttle valve 48 that adjusts the fluid pressure to the machining fluid tank 40. .49, a solenoid valve 50 that discharges electrolysis products generated in the gap by jetting the machining fluid from the clean tank 46 into the gap between the workpiece 2 and the electrode 4, and supplying the machining fluid to the machining fluid tank 40. It consists of a liquid/pressure gauge 51 etc. that measures and instructs the liquid pressure of the machining liquid. In addition, 52 in the figure
．． 53 is an upper limit float switch and a lower limit float switch that detect the liquid level of the dirty tank 42; 54 is a motor that drives the centrifugal separator 45;

Processing fluid flow control section 11 that controls this processing fluid filtration device 14
supplies machining fluid at a constant pressure to the machining fluid tank 40 based on a control signal from the machining condition control unit 10,
In order to eliminate electrolytic products generated between the workpiece surface 2a and the electrode surface 4a during machining, the electrode 4 moves upward every pulse or several pulses, and in synchronization with the workpiece 2 and the electrode 4. The electromagnetic pumps 43, 47, throttle valves 48, 49, electromagnetic valves 50, etc. are controlled so as to spout fresh machining fluid.

Next, a finishing method using this apparatus will be explained.

During finishing, the electrode 4 is attached to the lower end of the rod 17 of the electrode fixing device 50, and the electrode 4 is lowered and its electrode surface 4a is machined into a desired shape by electrolytic machining or electrical discharge machining, and then the workpiece fixing device 3 A workpiece surface 2 of a workpiece 2 made of, for example, heat-treated special steel, fixed to the
a, and the electrode 4 and the workpiece 2 are immersed in the machining liquid 41 of the machining liquid tank 40. Then, taking this position as the origin A, raise the electrode 4 to a position that maintains the initial electrode gap,
When the machining liquid fills between the surface to be machined 2a and the electrode surface 4a, finishing machining is started using this as the machining origin.

During the first half of finishing machining (from the start of finishing machining until the cumulative value of machining depth, which will be described later, reaches a predetermined value), the machining condition control unit 10
0 control signal, the current density from the power supply 8 is 5A/c.
m2 to 20A/cm2 (e.g. 17A/cm2), two-thirds (2/3) of the current density in the later stage of finishing, which will be described later.
A pulsed current with a pulse on time (ton in FIG. 5) of about 5 msec (1 msec is 1/1000 second) (however, 10 msec or less) is supplied between the workpiece 2 and the electrode 4.

As a result, the material of the processed surface 2a is eluted. After supplying a predetermined pulse current once or several times, the motor 19 is driven by a signal from the motor drive control section 9 to raise the electrode 4 and separate the electrode surface 4a from the surface to be processed 2a. Due to this separation, the electrolytic products between the processed surface 2a and the electrode surface 4a are removed together with the processing fluid by the electromagnetic valve 50 of the processing fluid filtration device 14, which will be described later.
Eliminate by such actions.

After removing the electrolytic products, the electrode 4 is lowered and the electrode surface 4
a contacts the processed surface 2a. As a result, the origin A
and the current position are compared by the control device 12 to measure the machining depth per machining (machining every one pulse or several pulses). Thereafter, the electrode 4 is raised again so that a predetermined gap is maintained between the surface to be processed 2a and the electrode surface 4a, and the machining fluid that does not contain electrolytic products in the machining liquid layer 40 is transferred between the surface to be machined 2a and the electrode surface 4a.
Fill in between. In this case, the machining fluid N40 is applied only once.

Fresh machining fluid is supplied from the clean tank 46 of the machining fluid filtration device 14 to supplement the machining fluid that is removed together with the electrolytic products generated in several electrolytic machining cycles.

In this way, a machining fluid containing no electrolytic products is filled between the workpiece surface 2a and the electrode surface 4a, which face each other with a predetermined gap 18, and a predetermined pulse is applied between the workpiece 2 and the electrode 4. A current is supplied to dissolve the material of the processed surface 2a into the processing liquid 41, eliminate the electrolytic products generated between the processed surface 2a and the electrode surface 4a, and bring the electrode surface 4a into contact with the processed surface 2a again. By doing so, a series of steps of measuring the machining depth per machining and accumulating the values is repeated according to a signal from the control device 12.

The cumulative value of the machining depth is compared with the set value of the machining depth calculated by the machining condition control unit IO based on the input data inputted by the input device 13, and the cumulative value of the machining depth is determined as the set value of the machining depth. , when the difference is within a predetermined value (for example, 1 μm), the current density of the pulse current of the power supply device 8 is set to 30 A/cm2 or more (for example, 4 O
A/cm”) and the pulse on-time ton is 5 msec.
(10 msec or less) pulse current. In this case, the on-time ton of the pulse current in the first half and the second half of the finishing process can be switched within 10 m5eC if necessary.

Then, electrolytic machining is performed once or several times using this pulsed current. At that time, it is preferable that the pulse waveform of the pulsed current be close to a rectangular wave. Especially in machining that produces gloss on the finished surface, As shown in A), it is necessary to maintain a current density of 30 A/cm2 or more at the end of the pulse waveform, and as shown in Figure 5 (B), it is necessary to maintain a current density of 30 A/cm2 or more at the end of the pulse waveform. It has been confirmed through experiments that even if this is achieved, gloss cannot be obtained with a pulse waveform of 30 A/cm2 or less at the terminal end A.

After this finishing process is completed one or more times, the electrolytic products between the processed surface 2a and the electrode surface 4a are removed by the processing fluid filtering device 14, as described above. In this case, the cycle for eliminating electrolysis products is determined by the on-time of the applied pulse (
However, if several pulses are added to the second machining process (including the off-time of the pulses), it depends on the magnitude of the current density, provided that the pulse off time is the same as in the first half of finishing. Note that the detection of the timing to switch the pulse current is not limited to detection by comparing the cumulative value of the machining depth and the machining depth set value as described above, but also by calculating the coulomb amount from the machining allowance to the end of machining, and detecting this value. Detection can also be controlled by

Here, the operation of the machining fluid filtration device 14 will be explained.

The machining fluid containing electrolytic products returned from the machining fluid tank 40 is stored in a dirty tank 42, and its liquid level is above and below.
It is detected by the lower float switches 52 and 53 and input to the machining fluid flow control section 11. The processing liquid flow control unit 11 outputs a drive signal to the electromagnetic pump 43 when the liquid level in the dirty tank 42 reaches a predetermined value, that is, when the liquid level is between the upper and lower float switches 52 and 53. Then, the processing fluid in the dirty tank 42 is pumped up and sent to the centrifuge 45 through the filter 44.

In the centrifugal separator 45, a motor 54 rotates in response to a control signal from the machining fluid flow control section 11 to separate the machining fluid. The separated machining fluid that does not contain electrolytic products is stored in a clean tank 46 , and the machining fluid flow control section 11 controls the electromagnetic pump 47 , the throttle valve 48 .
49. Send a control signal to the solenoid valve 50, and the machining fluid is pumped up from the clean tank and flows into the machining fluid tank 40.

In this case, between the clean tank 46 and the machining liquid tank 40, a hydraulic pressure gauge 51 for instructing to measure the hydraulic pressure and a crest valve 48, 49 are provided, and the hydraulic pressure of the hydraulic pressure gauge is set to the setting value of the machining fluid flow control unit 11. If it is lower than that, increase the opening/closing degree of the throttle valve 48 on the processing liquid tank 40 side, and
The degree of opening and closing of the throttle valve 49 is decreased to allow more machining fluid to flow into the machining liquid tank 40, and when the hydraulic pressure of the hydraulic pressure gauge 51 is higher than the set value, the degree of opening and closing of the throttle valve 49 is increased. The opening/closing degree of the stop valve 48 is made small so that more of the machining fluid returns to the clean tank 46. Moreover, the solenoid valve 50 provided between the clean tank 46 and the processing liquid tank 40 is
In response to a control signal from the machining fluid flow control unit 11 synchronized with the upward movement of the electrode 4, the machining fluid from the clean tank 46 is spouted into the gap between the workpiece 2 and the electrode 40, and the machining fluid containing electrolytic products in the gap is It works to eliminate.

In this way, the machining fluid flow control section 11 controls the clean tank 4
The pressure of the machining fluid flowing into the machining fluid tank 40 from the workpiece 2 is controlled to be constant at all times, and the machining fluid containing electrolytic products between the workpiece 2 and the electrode 4 is controlled in synchronization with the upward movement of the electrode 4. Next, an example of processing using the finishing apparatus in electrolytic processing according to the present invention will be described.

Electrode Pure copper Workpiece material Tool steel (surface roughness 20μm) Electrolyte Sodium nitrate solution (concentration 40%) Pulse-on time in the first half of finishing process 5msec Current density 17A/Cm2 Pulse-on time in the second half of finishing process 5msec Current density 40A/cm2 Finishing Surface roughness Rmax: 3μm or less finished surface
Mirror-like glossy surface Note that the current density of the ttn pulse current before finishing is
Although it can be changed to some extent depending on the material of the workpiece, if the finished surface roughness does not require Rmax: 3 μm, it is recommended to use a pulsed current with a longer pulse on time and higher current density in terms of work efficiency. is preferred.

In addition, the cycle of separating the electrode from the surface to be machined and eliminating electrolytic products between the electrode surface and the surface to be machined is performed every pulse, which is most stable over the entire surface to be machined.
For example, the pulse on time in the first half of finishing processing is 1mse.
In the case of a short pulse c, there are few electrolytic products generated by one pulse of processing, so it is possible to remove them every few times.

In the above embodiment, the current density of the pulse current is set to a predetermined value of 5 A/cm2 to 20 A/am2 (e.g. 17 A/cm2) in the first half of the finishing process, and 30 A/cm" or more in the latter half of the finishing process. predetermined value (for example, 40A/
cm2), but the present invention is not limited thereto, and can be used in the first or second half of finishing. The current density of the H pulse current may be set to multiple types. That is, for example, in the first half of finishing machining, a pulse current of 17 A/cm2 is supplied, and in the latter half, a pulse current of 30 A/cm2 is supplied for a predetermined period of time, and then a pulse current of 40 A/cm2 is supplied; Pulse currents of 15A/cm2 and 20A/+:m were supplied in the first half of the period, and 30
Processing may be performed by appropriately supplying pulse currents of A/cm2, 40 A/cm2, and 60 A/cm2 depending on the finishing state. Furthermore, the on-time ton of the pulse current can also be set in the same manner.

As described above, in the finishing method by electrolytic machining according to the present invention, a workpiece made of heat-treated special steel or the like that has been processed into a desired shape and an electrode are attached to the finishing device, and the finishing process is carried out by If you input the conditions etc. using the input device and start it up, the current density in the first half of finishing processing will be 5A/cm.
High precision and surface quality with minute surface roughness can be obtained with a pulse current of 2 to 20 A/cm2, and the current density in the latter stage of finishing is 3.
A three-dimensional metal curved surface exhibiting mirror-like luster can be obtained unattended and in a short time without impairing surface roughness using a pulse current of 0 A/cm2 or more. In addition, the surface is susceptible to internal stress accumulation and metal M
There is no change in the weave, no deterioration such as the penetration of mechanical cracks, and the quality of heat treatment before processing is not impaired, making it suitable for finishing in the field of finishing, where labor savings are the slowest in current mold processing. , a great effect can be obtained on quality improvement and v1 mechanization. Furthermore, the machining fluid filtration device allows processing fluid containing a large amount of electrolytic products to be treated simply and inexpensively.

This invention is applicable not only to the field of mold processing, but also to mechanical applications such as the finishing of silicon single crystals and gallium histobase materials in semiconductor production, and the mirror finishing of aluminum disks in magnetic storage devices using single crystal diamond. It can also be applied to finishing machining in fields where slight internal stress on the surface due to machining is a problem. In addition, it is of course possible to use it in combination with an automatic conveyance device for finishing processing of mass-produced hypoid gears and the like after heat treatment.

[Effects of the Invention] As explained in detail above, in the finishing method by electrolytic machining according to the present invention, a pulse current is supplied between the workpiece and the machining electrode disposed opposite to each other via the machining fluid, and , when performing finishing machining while intermittently removing electrolytic products generated between the workpiece and the machining electrode, the current density of the pulse current is made different between the early and late stages of finishing machining, and Since the current density in the first stage is set to 273 (two-thirds) or less of the latter stage of finishing, a three-dimensional metal curved surface with high precision and mirror-like luster with minute surface roughness can be obtained in a short time. , it is possible to obtain a surface that does not accumulate internal stress or change the metal Mi weave, shows no deterioration such as penetration of mechanical cracks, and does not impair the quality of heat treatment before processing, making it possible to create molds that have been slow to save labor. It is possible to achieve quality improvement and mechanization in the processing field. Further, it has the advantage that wastewater containing a large amount of electrolyzed products can be treated easily and inexpensively.

[Brief explanation of drawings]

FIG. 1 is a front view showing a finishing device for implementing the present invention, FIG. 2 is a side view of the device, FIG. 3 is a schematic configuration diagram of the device, and FIG. 4 is a block diagram showing a current supply means. FIG. 5 is a waveform diagram of a pulse current, and FIG. 6 is a schematic diagram of a machining fluid filtration device. 1... Finishing device, 2... Workpiece, 2a...
- Work surface, 3... Workpiece fixing device, 4... Electrode, 5... Electrode fixing device, 6... Electrode drive unit, 7...
- Drive conversion unit, 8... Power supply device, 9... Motor drive control unit, lO... Machining condition control unit, 11... Machining liquid flow control unit, 12... Control device, 13...・Input device,
14... Processing liquid filtration device. Patent applicant Shizuoka Seiki Co., Ltd. 111.2゜Representative Shige Suzuki, Fu) 5 Figure 1 Figure 2

Claims (3)

[Claims] (1) Finishing is performed by supplying a pulse current between the workpiece and the machining electrode that are placed opposite each other via the machining fluid, and intermittently removing electrolytic products generated between the workpiece and the machining electrode. The finishing method is characterized in that the current density of the pulsed current is made different between the first and second stages of finishing, and the current density in the first half of finishing is set to 2/3 or less of the current density in the latter half of finishing. , a finishing method using electrolytic processing. (2) The finishing method by electrolytic machining according to claim 1, wherein the current density of the pulse current in the first half of the finishing process is 5 A/cm^2 or more and 20 A/cm^2 or less. (3) The finishing method by electrolytic machining according to claim 1 or 2, wherein the on-time of the pulse current in the first half of the finishing step is 10 msec or less.