Low-frequency vibration assisted electric discharge machining device and method

Abstract

This invention discloses a low-frequency vibration-assisted electrical discharge machining (EDM) device and method, belonging to the field of EDM technology. The device includes an electrode rod with an EDM electrode mounted at its front end and connected to a machine tool drive shaft at its rear end. The device also includes a cam assembly disposed within the front end of the electrode rod. The cam assembly includes an electrode drive cam and a balancing cam, both capable of rotation. The balancing cam balances the rotational inertia of the electrode drive cam. The EDM electrode is equipped with a cam ejector shaft. One end of the cam ejector shaft is fixed to the EDM electrode, and the other end extends into the electrode rod, always in contact with the cam surface of the electrode drive cam. The electrode drive cam drives the cam ejector shaft to reciprocate along its axial direction through rotation, and the EDM electrode reciprocates accordingly. This invention has advantages such as stability and controllability.

Description

Technical Field

[0001] This invention belongs to the field of electrical discharge machining technology, and relates to a machining device and a machining method, particularly to a low-frequency vibration-assisted electrical discharge machining device and a machining method. Background Technology

[0002] Electrical discharge machining (EDM) is a material removal process that utilizes the electro-erosion principle of pulsed discharge. Due to its low processing stress and copy-like processing characteristics, it is widely used in machining special structures such as thin walls and deep cavities, as well as difficult-to-machine materials. Timely and effective removal of EDM products is a prerequisite for ensuring the stability of the EDM process. Therefore, industrial applications commonly use methods such as oil flushing and periodic electrode vibration lifting to enhance oil flow in the machining area, promote product removal, and improve machining stability. For example, patent application CN1013353B proposes a method to optimize machining by adaptively changing electrical parameters by monitoring oil pressure. Patent application US9707637B2 improves upon HSEDM by flushing the machining area with high-pressure oil when the electrode is slightly lifted, replacing high retraction with small-volume, periodic retraction, and monitoring retraction with electrical parameters, thereby improving machining efficiency under specific conditions.

[0003] Currently, the most common method for periodic electrode lifting is the servo-driven lifting method controlled by the motion axis of the EDM machine tool. This method uses the machine tool's servo axis to drive the electrode, causing periodic vibration lifting motion. This method is simple in structure and easy to implement. However, the electrode rods used in deep cavity EDM are long and thin, causing uncontrollable chattering during the periodic vibration lifting motion, affecting the stability of the EDM process. Therefore, there is an urgent need for a device and method to achieve relative stationarity of the electrode rod during the periodic vibration lifting motion. Summary of the Invention

[0004] This invention provides a low-frequency vibration-assisted electrical discharge machining device and machining method to overcome the defects of the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a low-frequency vibration-assisted electrical discharge machining (EDM) device, comprising an electrode rod with an EDM electrode mounted at its front end and a machine tool drive shaft connected at its rear end; and a cam assembly disposed within the front end of the electrode rod; the cam assembly includes an electrode drive cam and a balance cam, both of which are rotatable; the balance cam is used to balance the rotational inertia of the electrode drive cam; the EDM electrode is equipped with a cam ejector shaft; one end of the cam ejector shaft is fixed to the EDM electrode, and the other end extends into the electrode rod, always in contact with the cam surface of the electrode drive cam; the electrode drive cam drives the cam ejector shaft to reciprocate along its axial direction by rotation, and the EDM electrode reciprocates accordingly.

[0007] Furthermore, it also includes an electromagnetic coil; the cam ejector shaft is made of magnetic material; the electromagnetic coil is fixed on the electrode rod and surrounds the cam ejector shaft; when the electromagnetic coil is energized, it generates a magnetic field, the direction of which is parallel to the axis of the cam ejector shaft.

[0008] Furthermore, the end of the cam pin shaft has an outer edge structure protruding from its side; an elastic element is provided between the outer edge structure and the rod wall of the electrode rod, and the elastic element ensures that the end of the cam pin shaft is always in contact with the cam surface of the electrode driving cam.

[0009] Furthermore, the elastic element is a spring; the spring is sleeved on the cam pin shaft.

[0010] Furthermore, the electrode drive cam and the balance cam are coaxially arranged and rotate synchronously.

[0011] Furthermore, a drive motor is provided inside the electrode rod; both the electrode drive cam and the balance cam are mounted on the output shaft of the drive motor.

[0012] Furthermore, the profile curve of the electrode-driven cam is a modified sine curve, a trapezoidal curve, or a polynomial curve.

[0013] Furthermore, it also includes a vibration sensor; the vibration sensor is disposed on the electrode rod to detect the vibration amplitude of the electrode rod.

[0014] Secondly, the present invention also provides a processing method for the aforementioned low-frequency vibration-assisted electrical discharge machining (EDM) device: First, the electrode drive cam and the balance cam are selected and installed according to the target workpiece; then, the electrode drive cam and the balance cam are driven to rotate and the electrode rod is started for EDM. During the EDM process, the vibration amplitude of the electrode rod is detected in real time; when the vibration amplitude of the electrode rod exceeds a threshold, one or a combination of the following compensation operations are performed: controlling the electromagnetic coil to input a compensation current to generate a magnetic field and applying an axial auxiliary force away from the direction of the electrode drive cam to the cam pin shaft; reducing the rotational speed of the electrode drive cam; replacing the balance cam; and through the compensation operation, making the vibration amplitude of the electrode rod lower than the threshold until the processing is completed.

[0015] Furthermore, the compensation current I is: I = k × Δm; where k is the electromagnetic proportionality coefficient; Δm is the electrode loss, Δm = λ × S × t, where λ is the electrode loss rate, S is the discharge area, and t is the discharge time.

[0016] The beneficial effects of this invention are as follows: First, this invention achieves the reciprocating motion of the EDM electrode through an electrode-driven cam and a cam-ejector shaft, and different retraction distances can be achieved by selecting different electrode-driven cams. Second, this invention balances the initial rotational inertia of the electrode-driven cam by pre-setting a basic compensation amount through a balancing cam. Furthermore, this invention also includes an electromagnetic coil capable of applying an axial auxiliary force to the cam-ejector shaft. When the EDM electrode is worn, the vibration amplitude generated by the electrode rod can be balanced by controlling the input compensation current to the electromagnetic coil, thereby ensuring stability during machining. In addition, this invention provides a compensation operation for the vibration of the balancing electrode rod, including forming an adjusting magnetic field through compensation current, reducing the rotational speed of the electrode-driven cam, and replacing the balancing cam. These compensation operations reduce vibration during EDM and achieve stable machining. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the external structure of a low-frequency vibration-assisted electrical discharge machining device;

[0018] Figure 2 This is a schematic diagram of the internal structure of a low-frequency vibration-assisted electrical discharge machining (EDM) device.

[0019] Figure 3 This is a schematic diagram of the control relationship of a low-frequency vibration-assisted electrical discharge machining device;

[0020] Figure 4 This is a flowchart of the low-frequency vibration-assisted electrical discharge machining (EDM) device.

[0021] The labels in the attached diagram are as follows: 1. Electrode rod; 2. Electrical discharge machining electrode; 21. Cam pin shaft; 22. Elastic element; 3. Machine tool drive shaft; 41. Electrode drive cam; 42. Balance cam; 43. Drive motor; 5. Electromagnetic coil; 6. Vibration sensor; 7. Control module; 8. Human-machine display module. Detailed Implementation

[0022] The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0023] like Figures 1-3 As shown, this embodiment provides a low-frequency vibration-assisted electrical discharge machining (EDM) device, including an electrode rod 1 and a cam assembly. An EDM electrode 2 is mounted at the front end of the electrode rod 1, and the rear end is connected to a machine tool drive shaft 3. The machine tool drive shaft 3 drives the electrode rod 1 to move in the X, Y, and Z directions. The cam assembly is located inside the front end of the electrode rod 1 and includes an electrode drive cam 41 and a balance cam 42, both of which are rotatable. The balance cam 42 is used to balance the rotational inertia of the electrode drive cam 41, i.e., the inertial force generated by the rotation of the electrode drive cam 41. The EDM electrode 2 is equipped with a cam ejector shaft 21. One end of the cam ejector shaft 21 is fixed to the EDM electrode 2, and the other end extends into the electrode rod 1, always in contact with the cam surface of the electrode drive cam 41.

[0024] During machining, the electrode drive cam 41 drives the cam ejector shaft 21 to reciprocate along its axis by rotating, and the EDM electrode 2 reciprocates accordingly, thereby drawing the flow field at the front end of the EDM electrode 2 and improving the chip removal effect in the discharge gap. At the same time, the rotating balance cam 42 balances the inertial force brought about by the rotation of the electrode drive cam 41.

[0025] Specifically, the end of the cam ejector shaft 21 has an outer edge structure protruding from its side. An elastic element 22 is provided between the outer edge structure and the rod wall of the electrode rod 1, and the elastic element 22 ensures that the end of the cam ejector shaft 21 is always in contact with the cam surface of the electrode drive cam 41. In this embodiment, the elastic element 22 is a spring. The spring is sleeved on the cam ejector shaft 21.

[0026] The electrode drive cam 41 and the balancing cam 42 are coaxially arranged and rotate synchronously. More specifically, a drive motor 43 is installed inside the electrode rod 1. Both the electrode drive cam 41 and the balancing cam 42 are mounted on the output shaft of the drive motor 43. Both the electrode drive cam 41 and the balancing cam 42 are detachable structures, and can be disassembled and installed by removing the bottom end cap of the electrode rod 1, thereby balancing the large rotational inertia.

[0027] The profile curve of the electrode-driven cam 41 is a modified sine curve, a trapezoidal curve, or a polynomial curve.

[0028] The machining apparatus also includes an electromagnetic coil 5. The cam ejector shaft 21 is made of magnetic material. The electromagnetic coil 5 is fixed to the electrode rod 1 and surrounds the cam ejector shaft 21. When the electromagnetic coil 5 is energized, it generates a magnetic field, the direction of which is parallel to the axis of the cam ejector shaft 21. By applying an axial auxiliary force to the cam ejector shaft 21 through the magnetic field, the inertial force of the EDM electrode 2 during its movement is balanced, thereby achieving dynamic fine-tuning of the overall inertia of the electrode rod 1.

[0029] The processing device also includes a vibration sensor 6. The vibration sensor 6 is mounted on the electrode rod 1 and detects the vibration amplitude of the electrode rod 1.

[0030] The processing device also includes a control module 7. The control module 7 is used to receive the vibration amplitude of the electrode rod 1 detected by the vibration sensor 6, and control the compensation current of the input electromagnetic coil 5 and the rotation speed of the drive motor 43 according to the vibration amplitude of the electrode rod 1.

[0031] The processing device also includes a human-machine interface module 8. The human-machine interface module 8 is used to input processing parameters (such as workpiece material, processing accuracy, etc.) and to display the vibration amplitude curve of the electrode rod 1 in real time.

[0032] like Figure 4 As shown, this embodiment also provides a processing method using a low-frequency vibration-assisted electrical discharge machining (EDM) device:

[0033] First, select and install the electrode drive cam 41 and the balance cam 42 according to the target workpiece.

[0034] Specifically, based on the workpiece material (e.g., mold steel, titanium alloy) and machining accuracy requirements (e.g., Ra≤0.8μm), the shape and machining process parameters of the EDM electrode 2 are designed. The electrode mass, expected wear, and suction / retraction amount are calculated based on the material and shape of the EDM electrode 2, and the shape of the electrode drive cam 41 is designed in conjunction with the machining process parameters. Based on the mass and shape of the EDM electrode 2 and the shape of the electrode drive cam 41, the shape of the balancing cam 42 is designed. The electrode drive cam 41 and the balancing cam 42 are then installed inside the electrode rod 1.

[0035] Then, the drive electrode drives the cam 41 and the balance cam 42 to rotate and start the electrode rod 1 to perform electrical discharge machining. During the electrical discharge machining process, the vibration amplitude of the electrode rod 1 is detected in real time.

[0036] When the vibration amplitude of electrode rod 1 exceeds the threshold, one or a combination of the following compensation operations are performed:

[0037] a. The control module 7 controls the electromagnetic coil 5 to input compensation current, generate a magnetic field, and apply an axial auxiliary force to the cam pin shaft 21 away from the direction of the electrode driving cam 41.

[0038] The compensation current I is:

[0039] I = k × Δm;

[0040] In the formula, k is the electromagnetic proportionality coefficient; Δm is the electrode loss, Δm=λ×S×t, where λ is the electrode loss rate, S is the discharge area, and t is the discharge time. By adjusting the magnetic field strength through changes in the compensation current, the axial auxiliary force applied to the cam pin shaft 21 is changed, thereby continuously balancing and compensating for vibration.

[0041] b. The control module 7 reduces the rotational speed of the electrode drive cam 41, that is, reduces the rotational speed of the drive motor 43, thereby reducing the moving frequency of the EDM electrode 2, and thus reducing the vibration amplitude of the electrode rod 1.

[0042] c. Suspend processing and replace balance cam 42.

[0043] Specifically, when the vibration amplitude of electrode rod 1 exceeds the threshold, the electromagnetic coil 5 is first controlled to input a compensation current to adjust the balance through a magnetic field. If the magnetic field formed by the compensation current is insufficient to reduce the vibration amplitude of electrode rod 1, the balance is adjusted by reducing the speed of drive motor 43. If reducing the speed of drive motor 43 still cannot reduce the vibration amplitude of electrode rod 1, the balance is adjusted by replacing the balance cam 42.

[0044] The vibration amplitude of electrode rod 1 is kept below the threshold by compensation operation until the machining is completed. If the compensation operation fails to reduce the vibration amplitude of electrode rod 1 below the threshold, the machining is terminated.

[0045] In this invention, unless otherwise stated, scientific and technical terms used herein have the meanings commonly understood by those skilled in the art.

[0046] It should be noted that the terms such as "upper", "lower", "left", "right", "front", and "back" used in the invention are only for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0047] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-frequency vibration-assisted electrical discharge machining (EDM) device, comprising an electrode rod with an EDM electrode mounted at its front end and connected to a machine tool drive shaft at its rear end, characterized in that: It also includes a cam assembly disposed within the front end of the electrode rod; the cam assembly includes an electrode drive cam and a balance cam, both of which are rotatable; the balance cam is used to balance the rotational inertia of the electrode drive cam. The electrical discharge machining electrode is equipped with a cam pin shaft; one end of the cam pin shaft is fixed to the electrical discharge machining electrode, and the other end extends into the electrode rod, always in contact with the cam surface of the electrode drive cam; the electrode drive cam drives the cam pin shaft to reciprocate along its axis by rotation, and the electrical discharge machining electrode reciprocates with it. It also includes an electromagnetic coil; the cam ejector shaft is made of magnetic material; the electromagnetic coil is fixed on the electrode rod and surrounds the cam ejector shaft; when the electromagnetic coil is energized, it generates a magnetic field, and the direction of the magnetic field is parallel to the axis of the cam ejector shaft.

2. The low-frequency vibration-assisted electrical discharge machining device according to claim 1, characterized in that: The end of the cam pin shaft has an outer edge structure protruding from its side; an elastic element is provided between the outer edge structure and the rod wall of the electrode rod, and the elastic element ensures that the end of the cam pin shaft is always in contact with the cam surface of the electrode driving cam.

3. The low-frequency vibration-assisted electrical discharge machining device according to claim 2, characterized in that: The elastic element is a spring; The spring is sleeved on the cam pin shaft.

4. The low-frequency vibration-assisted electrical discharge machining device according to claim 1, characterized in that: The electrode drive cam and the balance cam are coaxially arranged and rotate synchronously.

5. The low-frequency vibration-assisted electrical discharge machining device according to claim 4, characterized in that: The electrode rod is equipped with a drive motor; the electrode drive cam and the balance cam are both mounted on the output shaft of the drive motor.

6. The low-frequency vibration-assisted electrical discharge machining device according to claim 1, characterized in that: The profile curve of the electrode-driven cam is a modified sine curve, a trapezoidal curve, or a polynomial curve.

7. The low-frequency vibration-assisted electrical discharge machining device according to claim 1, characterized in that: It also includes vibration sensors; The vibration sensor is mounted on the electrode rod to detect the vibration amplitude of the electrode rod.

8. The processing method of the low-frequency vibration-assisted electrical discharge machining device as described in claim 1, characterized in that: First, select and install the electrode drive cam and balance cam according to the target workpiece; Then, the drive electrode drives the cam and the balance cam to rotate and start the electrode rod to perform electrical discharge machining. During the electrical discharge machining process, the vibration amplitude of the electrode rod is detected in real time. When the vibration amplitude of the electrode rod exceeds the threshold, perform one or a combination of the following compensation operations: The electromagnetic coil is controlled to input a compensation current to generate a magnetic field, which applies an axial auxiliary force to the cam pin shaft away from the direction of the electrode driving cam. Reduce the rotational speed of the electrode-driven cam; Replace the balance cam; The vibration amplitude of the electrode rod is kept below the threshold by compensation operation until the processing is completed.

9. The processing method of the low-frequency vibration assisted electro-discharge processing device according to claim 8, characterized in that: The compensation current I for: ； In the formula, k This is the electromagnetic proportionality coefficient; This refers to electrode loss. , Electrode loss rate, S For the discharge area, t This refers to the discharge time.

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