A method for rapid machining of wire cut electrical discharge machining based on electromagnetic heat effect

Abstract

The application discloses a kind of based on electromagnetic heat effect's wire cut electrical discharge rapid machining method, when certain length narrow slit (or crack) is formed by wire cut electrical discharge machining in conductive workpiece, the narrow slit in workpiece is continuously pulsed discharge by using high-frequency pulse current, electromagnetic heat effect is generated at the tip of workpiece narrow slit, the sharp rise of temperature around narrow slit makes the hardness of metal material, melting point reduces, so that the material at narrow slit is quickly eroded under the action of spark; Specific steps are that when wire cut electrical discharge machining, the pulse power with adjusted power parameters is used to discharge machining to the conductive workpiece placed on machine tool worktable.The application greatly improves the processing productivity of wire cut electrical discharge, delays the loss of electrode wire, reduces processing cost, ensures processing quality;It also has the characteristics such as simple, reliable and easy to use processing device, and well meets the processing requirements of ordinary conductive materials and various difficult-to-machine materials.

Description

Technical Field

[0001] This invention relates to the field of wire electrical discharge machining technology, specifically to a rapid wire electrical discharge machining method based on the electromagnetic thermal effect. Background Technology

[0002] Wire electrical discharge machining (EDM) is a process that uses a wire electrode (such as copper or molybdenum wire) to cut a workpiece by spark discharge. Wire EDM machines account for over 70% of all EDM machines both domestically and internationally, making it one of the most important and essential special machining technologies. It is based on the electro-corrosion phenomenon during pulsed discharge between electrodes. A thin metal wire is used as the electrode and moves at a certain speed along the wire's axis, continuously entering and leaving the discharge machining zone within the kerf. During machining, the positive terminal of the pulse power supply is connected to the workpiece, and the negative terminal is connected to the electrode wire. An insulating liquid is sprayed between the electrode wire and the workpiece kerf. Simultaneously, a control device on the worktable, which holds the workpiece, controls the motor drive according to a predetermined cutting trajectory, thereby machining the desired parts.

[0003] Wire electrical discharge machining (EDM) can process metal materials of any hardness, strength, toughness, and brittleness, and is particularly adept at machining complex micro-surfaces and low-rigidity parts. It can also perform ultra-precision machining. Since material removal during machining is achieved through the electrical and thermal effects of electrical discharge, the machinability of the material is mainly related to its electrical conductivity and thermal properties, such as resistivity, melting point, boiling point, specific heat capacity, and thermal conductivity, and almost entirely unrelated to its mechanical properties, such as hardness and strength. Therefore, it breaks through the limitation in traditional cutting processes where the hardness of the tool material must be greater than the hardness of the material being machined, enabling the machining of hard and tough workpieces with soft tools.

[0004] The application fields of wire electrical discharge machining (EDM) are expanding rapidly, and it is widely used in manufacturing sectors across various industries, including machinery, aerospace, aviation, electronics, nuclear energy, and instrumentation. It is used to solve the manufacturing problems of various difficult-to-machine materials, complex-shaped parts, and parts with special requirements. The processing range extends from tiny shafts, holes, and slits a few micrometers to ultra-large molds and parts several meters in size. It is an important supplement and extension to conventional cutting processes and has become an indispensable machining method.

[0005] One of the main limitations of wire electrical discharge machining (EDM) is its generally low cutting speed, which cannot compare with traditional machining. Therefore, it is often necessary to first use cutting methods to remove most of the excess material from the part before performing EDM to improve efficiency; alternatively, methods such as selecting appropriate electrical parameters, using suitable working fluids, and maintaining process stability can be used to increase the speed, but these measures cannot significantly improve the wire EDM speed. Electrode wear is also a problem. Since EDM relies on electricity and heat to erode metal, the electrodes also experience wear, which is concentrated at sharp corners or on the bottom surface, affecting forming accuracy. These limitations have greatly hindered the application of wire EDM. To date, there is still no good method to significantly increase the processing speed of wire EDM; therefore, improving the processing speed of wire EDM remains a key research focus and challenge. Summary of the Invention

[0006] The purpose of this invention is to address the main limitation of existing wire electrical discharge machining technology, namely its relatively slow processing speed, by providing a rapid wire electrical discharge machining method based on the electromagnetic thermal effect.

[0007] Because the electrode wire in wire electrical discharge machining (EDM) has a thin diameter, ranging from 0.02 to 0.3 mm, the kerf formed during cutting is very narrow, making it suitable for micro-machining. When machining parts, brass or galvanized copper wires are typically used with a diameter of 0.15 to 0.35 mm; fine tungsten wires with a diameter of 0.02 to 0.03 mm are used. For example, using a 0.03 mm diameter tungsten wire as the electrode wire can result in a kerf as small as 0.04 mm and an inner angle radius as small as 0.02 mm. Alternatively, to make the kerf (tip) even narrower, thus making the electromagnetic thermal effect easier, more pronounced, and stronger, a fatigue crack of a certain length can be pre-fabricated (stretched) on top of the narrow kerf using a tensile-compression fatigue testing machine.

[0008] The electromagnetic thermal effect occurs when a pulsed current is passed through a conductor with cracks or slits. Due to the presence of the crack (or slit), a high-density current concentrates around the crack (or slit) tip, instantly generating a large amount of Joule heat around the slit or crack tip—that is, electrical energy is converted into heat energy. This causes the temperature of the surrounding metal material at the tip or slit to rise rapidly and instantly, enough to soften or even melt the material. The electromagnetic thermal effect is a combined effect of the interaction between mechanical, electromagnetic, and temperature fields within and outside an elastic solid.

[0009] The mechanism of pulsed current action differs from continuous steady current; it is a suddenly changing current, characterized by its abrupt change and extremely short duration, ranging from tens to hundreds of microseconds. Its effect on metal structures is impactful and sudden. This invention utilizes a combination of effects generated by high-voltage pulsed discharge, including electric field, magnetic effect, thermal effect, and shock wave effect, with wire EDM to complete the processing. Specifically, it leverages the current concentration phenomenon generated by the pulsed current at the tip of the narrow slit (or crack) in the metal material during the instantaneous energization. The electric field, magnetic field, and thermal effect generated by the strong pulsed discharge instantly create a heat concentration effect at the crack tip, generating high temperatures that soften the surrounding metal material. When the wire EDM electrode wire re-discharges, the metal material is easily electro-eroded away, greatly improving processing speed and production efficiency. This significantly enhances the application value of wire EDM.

[0010] When using high-intensity pulsed discharge (HIFL), there are specific requirements for the voltage and discharge time. If the pulse voltage is too high or the discharge time is too short, the energy will be too concentrated, causing overheating at the tip of the slit (or crack), resulting in an excessively large softened area. This could lead to the metal material vaporizing, resulting in unstable processing and poor processing quality. If the pulse voltage is too low or the discharge time is too long, the heat concentration effect around the slit (or crack) tip will not be significant, and the temperature rise may not be sufficient to soften the metal at the tip, thus failing to achieve rapid cutting. Therefore, the optimal energizing time and voltage should be determined based on factors such as conductivity, size, and material. Only when the discharge voltage and discharge time are appropriate, and the softened area or size at the slit (or crack) tip is suitable, can the best rapid cutting effect be obtained when performing electrical discharge machining (EDM). Because the pulsed discharge process is completed within tens of microseconds, and the heat source is concentrated only in a small area near the slit (or crack) tip, the average temperature can reach over 2000℃, while the temperature of other parts of the metal averages no more than 200℃.

[0011] This invention involves wire electrical discharge machining (EDM) on a metal workpiece to create a narrow slit (or crack) of a certain length, or pre-fabricating a fatigue crack of a certain length using a tensile-compression fatigue testing machine. A dedicated anode connector is then installed at one end of the workpiece, connecting it to the positive terminal of the power supply; a dedicated cathode connector is installed at the other end, connecting it to the cathode, thus forming a current loop. During machining, the slit (or crack) surface is ideally perpendicular to the direction of the incoming pulse current. This is because when the crack surface (or slit surface) is perpendicular to the current direction, the current concentration phenomenon is most pronounced, resulting in the largest temperature change and highest temperature rise in the slit (or crack) area of ​​the workpiece. This softens the metal material, making it easier for the wire EDM to erode it, thereby greatly increasing machining speed and productivity.

[0012] The specific steps involve installing a high-frequency pulse power supply on an electrical discharge wire cutting machine and adjusting appropriate pulse power supply parameters (voltage, discharge time, frequency, etc.). While performing electrical discharge wire cutting, the pulse power supply is used to perform electrical discharge wire cutting on the metal workpiece placed on the machine tool table, thereby achieving a fast electro-erosion processing speed and correspondingly reducing electrode wire wear and extending electrode wire life.

[0013] To achieve the above objectives, the present invention adopts the following technical solution: a rapid machining method for wire electrical discharge machining based on electromagnetic thermal effect, comprising the following steps:

[0014] (1) Install a pulse power supply device:

[0015] This machining method uses a pulse power supply. The power supply device must be installed in a suitable position on the EDM machine tool beforehand.

[0016] (2) Install conductive workpieces:

[0017] Use a fixture to mount a conductive material workpiece onto the worktable of an electrical discharge wire cutting machine.

[0018] (3) Install the special connector for pulse power supply machining anode:

[0019] Connect the anode connector to the power anode cable, then install the anode connector on one end of the workpiece and make it contact with the workpiece;

[0020] (4) Install the dedicated cathode connector for the pulse power supply:

[0021] Connect the cathode connector to the power cathode cable, then install the cathode connector on the other end of the workpiece and make it contact with the workpiece.

[0022] (5) Start the wire EDM machine:

[0023] Start the machine tool and perform wire electrical discharge machining on the conductive workpiece to form a narrow slit; or use a tensile and compressive fatigue testing machine to pre-fabricate (stretch) a fatigue crack of a certain length on the narrow slit of the workpiece, and then install it on the machine tool worktable.

[0024] (6) Start pulse power supply for machining:

[0025] Beforehand, adjust the positional relationship between the current direction and the cutting slit (or crack) surface, and set the processing parameters of the pulse power supply. Then, turn on the power supply to perform pulse discharge on the workpiece.

[0026] Furthermore, the pulse power supply used in step (1) has adjustable electrical parameters (such as frequency, voltage, etc.) depending on the processing conditions, with an output voltage of 0 to 3KV and an output current of 0 to 500A.

[0027] Furthermore, in step (2), when using a fixture to position and clamp the conductive workpiece, the fixture and the workpiece must be insulated.

[0028] Furthermore, in steps (3) and (4), the connection points between the pulse power processing anode, the anode-specific machine head, and the machine tool must be insulated and connected to the pulse power anode and cathode cables via quick-connect plugs.

[0029] Furthermore, in step (6), the positional relationship between the current direction and the cutting slit (or crack) surface is adjusted, that is, during the processing, the positional relationship between the two is adjusted to be perpendicular as much as possible.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] This processing method utilizes a high-frequency pulsed current to continuously pulse and discharge into narrow slits (or cracks) in a workpiece. This generates an electromagnetic heating effect at the tip of the slit (or crack), causing a softening effect on the metal material there. Specifically, the rapid increase in temperature around the slit (or crack) reduces the hardness or yield strength of the metal, leading to a change in flow stress, which decreases as temperature rises. This softening makes the material at the slit (or crack) easily eroded away by the electrical discharge machining (EDM), significantly increasing the cutting speed. This is especially beneficial when machining difficult-to-machine metals such as hardened steel. The high strength and hardness of the material, combined with the softening effect, greatly enhances the EDM speed. Simultaneously, it reduces and delays electrode wire wear, extends electrode wire life, and improves machining accuracy. Therefore, the advantages of this invention are significantly improved processing efficiency, reduced processing costs, and guaranteed processing quality. Furthermore, the processing device is simple, reliable, and easy to use, all of which effectively meet the processing requirements of difficult-to-machine materials used in national defense, aerospace, and other fields. Attached Figure Description

[0032] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention, but do not constitute a limitation thereof.

[0033] Figure 1 This represents the experimental state of the electromagnetic thermal effect principle of this invention;

[0034] Figure 2 This is a schematic diagram of the experimental state of softening at the tip of a narrow slit (or crack) in the electromagnetic thermal effect of the present invention and the concentration of current flow around it.

[0035] Figure 3This is a diagram illustrating the working state of the wire electrical discharge machining based on the electromagnetic thermal effect of the present invention.

[0036] Explanation of reference numerals in the attached diagram: 1. Pulse power supply; 2. Wire EDM machine tool; 3. Fixture; 4. Workpiece; 5. Worktable; 6. Anode cable; 7. Anode connector; 8. Cathode cable; 9. Cathode connector; 10. Cutting narrow slit (or crack) surface. Detailed Implementation

[0037] The following will be combined with the appendix Figure 1-3 This invention will be described in detail, and the technical solutions in the embodiments of this invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] (1) Install a pulse power supply device:

[0039] This processing method uses an adjustable pulse power supply 1. The power supply device should be installed in a suitable position on the wire EDM machine tool 2 beforehand.

[0040] (2) Install conductive workpieces:

[0041] Use clamp 3 to mount the conductive material workpiece 4 onto the worktable 5 of the wire EDM machine.

[0042] (3) Install the special connector for pulse power supply machining anode:

[0043] Connect the anode cable 6 to the anode connector 7, then install the anode connector 7 on one end of the workpiece 4 and make it contact with the workpiece 4;

[0044] (4) Install the dedicated cathode connector for the pulse power supply:

[0045] Connect the cathode cable 8 to the cathode connector 9, and then install the cathode connector 9 on the other end of the workpiece 4 and make it contact with the workpiece 4.

[0046] (5) Start the wire EDM machine:

[0047] Start machine tool 2 and perform wire electrical discharge machining on conductive workpiece 4 to form a narrow slit; or use a tensile and compressive fatigue testing machine to pre-fabricate (stretch) a fatigue crack of a certain length on the narrow slit of the workpiece, and then install it on the machine tool worktable 5.

[0048] (6) Start pulse power supply for machining:

[0049] Beforehand, adjust the positional relationship between the current direction and the cutting slit (or crack) surface 10, and set the processing parameters of the pulse power supply 1. Then, turn on the power supply to perform pulse discharge on the workpiece 4. The pulse power supply device 1 is adjustable. With an input of 220V, 50Hz power, the output current can be selected between 0-3000A depending on the processing conditions.

[0050] The pulse power supply used in step (1) has adjustable electrical parameters (such as frequency and voltage) depending on the processing conditions. Its output voltage is 0 to 3KV and its output current is 0 to 500A.

[0051] In step (2), when using a fixture to position and clamp the conductive workpiece, the fixture and the workpiece must be insulated.

[0052] In steps (3) and (4), the connection points between the pulse power processing anode, the anode-specific machine head, and the machine tool must be insulated and connected to the pulse power anode and cathode cables via quick-connect plugs.

[0053] In step (6), the positional relationship between the current direction and the cutting slit (or crack) surface is adjusted, that is, during the processing, the positional relationship between the two is adjusted to be perpendicular as much as possible.

[0054] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A rapid machining method for wire electrical discharge machining based on electromagnetic thermal effect, characterized in that, Includes the following steps: (1) Install pulse power supply: Install the adjustable pulse power supply in a suitable position on the wire EDM machine tool. The pulse power supply outputs voltage 0-3KV and outputs current 0-500A. (2) Installing conductive workpieces: Use a fixture to mount the workpieces on the worktable of the wire EDM machine tool, and insulate the fixtures from the workpieces. (3) Install the anode special connector: Connect the anode cable to the anode special connector, and then install the anode special connector on one end of the workpiece. The connection between the anode special connector and the wire EDM machine tool is insulated and connected to the anode cable through a quick connector. (4) Install the cathode special connector: Connect the cathode cable to the cathode special connector, and then install the cathode special connector on one end of the workpiece. The cathode special connector is insulated from the connection point of the wire EDM machine tool and is connected to the cathode cable through a quick connector. (5) Start the wire EDM machine and perform wire EDM on the workpiece to form a narrow slit; or use a tensile and compressive fatigue testing machine to pre-stretch fatigue cracks in the narrow slit, and then mount the workpiece on the worktable of the wire EDM machine. (6) Turn on the pulse power supply: Adjust the current direction to be perpendicular to the narrow slit or fatigue crack surface, set the pulse power supply processing parameters and discharge to generate an electromagnetic thermal effect at the tip of the narrow slit or fatigue crack to soften the metal, and then erode it by discharge through the wire cutting electrode wire.

2. The method according to claim 1, characterized in that, In step (6), the temperature rise at the tip of the narrow slot is highest when the current direction is perpendicular to the narrow slot surface or fatigue crack surface.

Images