JPH0116605B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an electric discharge machining method in which a discharge mark is formed into an elliptical shape by performing pulse discharge while supplying machining fluid to a facing machining gap between a vibrating electrode and a workpiece. [Prior art] The principle of machining using electrical discharge is that when electrical discharge occurs due to dielectric breakdown between electrodes, the electrical discharge current flows in a concentrated manner at one point of discharge, rapidly raising the temperature in the vicinity and damaging the metal on the electrode surface. The metal gas and the decomposed gas of the machining fluid generated at the same time generate a discharge pressure, and this discharge pressure causes the molten metal on the electrode surface to be ejected and scattered as fine particles, causing an eruption on the electrode surface. Discharge marks resembling mouths are formed, and by applying a discharge pulse voltage, the discharge points are moved over the entire machined surface and generated, forming machined holes, machined grooves, etc. as accumulations of discharge marks. The discharge point is generated by moving sequentially to the closest part between the electrodes,
Therefore, the opposite electrode (workpiece)
A hole is formed in the electrode, the electrode is formed into a desired shape, and the desired shape can be processed by moving and feeding the electrode into the desired shape. [Problems to be Solved by the Invention] The shape of the discharge trace is approximately circular, as shown in FIG. Fountain B that rose to the top
is formed. The amount of machining is determined by the depth H of the hollow of the spout A, the height h of the spout A, and the diameter Dx of the spout A. This size is proportional to the energy of a single discharge, so if the discharge energy is increased, the discharge marks will become larger and the amount of machining will increase, but on the other hand, if the discharge marks become larger, the machined surface roughness will increase (deteriorate).
Normally, when the discharge energy is increased, both the depth H of the nozzle and the height h of the spout increase, and the machined surface roughness determined by H+h increases. Therefore, the ratio of machining speed (machining amount per unit time) to machined surface roughness is not improved even if the pulse discharge energy is increased. There is usually a relationship between the machined surface roughness Rmax and the machined amount W as Rmax ³ ∝W (1). However, even with the same discharge energy and the same amount of machining, if the shape of the discharge mark can be formed by decreasing H+h and increasing Dx, the exponent of Rmax can be decreased and the machined surface roughness Rmax can be decreased. An object of the present invention is to provide an electric discharge machining method that reduces the machined surface roughness Rmax so that the relational expression between the machining amount and the machined surface roughness becomes Rmax ^{1.5 to} 2 ∝W (2) It is something. [Means for Solving the Problems] In order to achieve the above object, the present invention provides a workpiece fixed to a table whose X-axis and Y-axis drive is controlled by a motor and whose NC feed control is performed to provide machining feed of a desired shape. A workpiece, an electrode that faces the workpiece to form a machining gap, a chuck that fixedly supports the electrode, a drive device that rotates the chuck, and a machining pulse that applies machining pulses between the electrode and the workpiece. A processing pulse power supply capable of switching the processing pulse width to be applied, a control circuit for switching and controlling the rotation speed of a drive device such as a motor in accordance with switching control of the processing pulse width of the processing pulse power supply, and a processing fluid supply nozzle, While applying machining feed of the required shape to the workpiece and supplying machining fluid from the machining fluid supply nozzle to the machining gap where the workpiece and electrode face each other, a machining pulse power source is applied between the workpiece and the electrode. By applying a machining pulse and changing the rotation speed of the electrode by switching the control circuit according to the switching of the machining pulse width of the machining pulse power source, the discharge point melting part of the pulse discharge is moved and the long diameter of the discharge scar is changed. is made to be more than twice the short axis. [Function] That is, by rotating the electrode that forms the machining gap, relative movement is made between the workpieces, and the present invention makes the relative movement speed correspond to the pulse width of the machining pulse. By controlling the speed to match the melting time of the discharge point, the control circuit makes the pulse width faster when the pulse width is short and slower when the pulse width is long. The discharge marks formed on the workpiece are
The front view is made to be elliptical as shown in Fig. 3 and Fig. 3, and the ratio of machined surface roughness is improved by reducing H+h of the nozzle spout. [Example] An example of the drawings will be explained below. In FIG. 4, 1 is a workpiece, and 2 is an electrode, which face each other to form a machining gap. The electrode 2 is fixedly supported by a chuck 4 at the end of a rotating shaft 3, and is rotated at high speed by a motor 5. The workpiece 1 is fixed to a table 6 where NC feed control is performed, and X is moved by motors 7 and 8.
Axis and Y-axis drives are controlled, and machining feed of the desired shape is given. 9 is an NC control device that applies a drive signal;
10 is a processing pulse power source whose processing pulse width can be changed to apply a processing pulse between the electrode 2 and the workpiece 1;
Reference numeral 1 designates a control circuit that switches and controls the rotational speed of the motor 5 in accordance with switching control of the processing pulse width of the processing pulse power source 10, 12 a processing fluid supply nozzle, 13 a pump, and 14 a processing fluid storage tank. The processing fluid supplied from the nozzle 12 is water, for example, treated with an ion exchange resin to have a specific resistance on the order of 10 ³ to ^{10 5} Ωcm. Of course, this does not preclude the use of conventionally used oils and other processing fluids other than water. Electric discharge is generated in the machining gap between the electrode 2 to which the machining fluid is supplied and the workpiece 1 by machining pulses supplied from the pulse power source 10, and machining is performed by repeated discharge. During machining, a relative machining feed is applied to the workpiece 1 side with respect to the electrode 2. The X-axis motor 7 and Y-axis motor 8 are driven by distributed pulses from the NC control electrode 9 to give a numerically controlled feed to the table 6, and electrical discharge machining progresses according to the shape of the workpiece 1 moving and the required feed is performed. Shape processing is performed. During processing, the electrode 2 is rotated at high speed by a motor 5. After cutting the outer periphery by rotating a 130 mm diameter disc at 20,000 rpm, apply grease and adjust the current and voltage.
When a single discharge is performed using a power supply of 300V and a capacitor capacity of 300μF, the total length of the eruption is 5.1mm, width d is 1.7mm, and the depth is approximately 3mm as shown in Figure 5c, as shown in Figure 5b. A small amount of water erupted. Figure a shows a graph of the changes in the discharge voltage, discharge current, and discharge power at this time. Although the time of the deepest eruption and the time of the maximum discharge power almost coincide, the cross section of the depth The power waveforms are not similar, and the ejection side is flat. It is known that this is because consumption efficiency decreases above a certain level of power. Therefore, due to the high-speed rotation of the electrode 2, a relative movement is performed between the electrode 2 and the workpiece 1, and the discharge point melting of the pulsed discharge occurs on the machined surface of the workpiece 1 parallel to the rotation axis of the electrode 2. The part is stretched in the direction of relative movement,
As described in FIGS. 2 and 3, the nozzle is formed in an oval shape. The rotational speed of the electrode 2 is determined by controlling the motor 5, which is a drive device, by the control circuit 11 in response to a switching signal from the processing pulse power source 10, and rotates the electrode 2 at a speed corresponding to the processing pulse.
That is, when the pulse width is short corresponding to the pulse width that controls the discharge melting time of the machining pulse supplied from the pulse power source 10, the melting time at the discharge point is short, so the rotation speed of the electrode 2 is increased and the pulse width is increased. When the melting time at the discharge point is long, electrode 2 is adjusted accordingly.
The rotational speed of the discharge point may be slowed down, and by giving a relative movement speed that matches the melting time of this discharge point, it is possible to stretch the discharge melting point in the relative movement direction and form a discharge mark in an elliptical shape. , the machined surface roughness can be reduced by making the nozzle spout smaller. That is, this will be explained using an example as follows. When processing iron materials using a Cu electrode with a diameter of 3 mmφ,
The machining results were obtained under machining conditions in which the machining pulse had a peak value Ip = 27 A and a pulse width τon that were varied.The results were compared with the conventional case where the electrode was not rotated, and when the electrode of the present invention was rotated and the rotation speed corresponded to the machining pulse width. The table below shows a comparison of the machined surface roughness results with those controlled by The machining gap is automatically determined when the required roughness Rmax is determined, and the machining speed g/min (machining amount per unit time) is also determined in relation to the surface roughness Rmax. The machining gap and machining speed are set based on the conventional surface roughness, and the surface roughness obtained when the present invention is also machined under the same conditions is tabulated and compared. The relative movement speed between the electrode and the workpiece is approximately 3
mm/sec.

〔Effect of the invention〕

As described above, the present invention allows relative movement between the electrode and the workpiece, and the relative movement speed is made to correspond to the pulse width of the machining pulse, so that when the pulse width is short, it is fast and when the pulse width is long, it is slow. Since the speed is controlled according to the melting time of the discharge point, the melt at the discharge point is stretched by relative movement, especially the part of the volcano where the melt swells, in the direction of relative movement during melting to create discharge traces. It can be formed into an elliptical shape, which significantly reduces the roughness of the machined surface.
Therefore, the relationship between the machining speed and the machined surface roughness can be significantly improved, which has the effect of enabling high-precision, high-performance electrical discharge machining.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the conventional discharge trace shape, Figs. 2 and 3 are explanatory diagrams of the discharge trace shape of the present invention, Fig. 4 is an explanatory diagram of the configuration of an embodiment of the device of the present invention, and Figs. 5 a and b. ，
FIG. 1c is a diagram illustrating the state of a nozzle formed when a single electric discharge is conventionally applied to a moving workpiece. 1... Workpiece, 2... Electrode, 5... Rotating motor, 6... Table, 10... Processing pulse power supply,
11... Control circuit, 12... Machining liquid nozzle.

Claims (1)

[Scope of Claims] 1. A workpiece fixed to a table whose X-axis and Y-axis drive is controlled by a motor and subjected to NC feed control to provide machining feed of a desired shape; An electrode that forms a machining gap, a chuck that fixedly supports this electrode, a drive device that rotates this chuck, and a machining pulse power supply that can switch the machining pulse width that applies machining pulses between the electrode and the workpiece. It is equipped with a control circuit that switches and controls the rotation speed of a drive device such as a motor in accordance with switching control of the processing pulse width of the processing pulse power supply, and a processing fluid supply nozzle, and provides processing feed of a desired shape to the workpiece,
While supplying machining fluid from the machining fluid supply nozzle to the machining gap where the workpiece and the electrode face each other, machining pulses are applied from the machining pulse power source between the workpiece and the electrode, and the machining pulses of the machining pulse power source are applied between the workpiece and the electrode. An electric discharge machining method in which a control circuit is switched in accordance with the width change to change the number of revolutions of the electrode, thereby moving the melting point of the discharge point of the pulsed discharge so that the discharge mark becomes elliptical. 2. The electrical discharge machining method according to claim 1, wherein the control circuit is switched and controlled so that the major axis of the elliptical discharge trace is at least twice the minor axis.