Low-frequency vibration auxiliary electric spark machining device and machining method

Abstract

The invention discloses a low-frequency vibration auxiliary electric spark machining device and method, and belongs to the technical field of electric spark machining. The device comprises an electrode rod with the front end provided with an electric spark machining electrode and the rear end connected with a machine tool driving shaft; the device further comprises a cam assembly arranged in the front end of the electrode rod. The cam assembly comprises an electrode driving cam and a balance cam which can rotate; the balance cam is used for balancing the rotation inertia of the electrode driving cam; the electric spark machining electrode is provided with a cam ejector pin shaft; one end of the cam ejector pin shaft is fixed to the electric spark machining electrode, and the other end of the cam ejector pin shaft extends into the electrode rod and is attached to the cam surface of the electrode driving cam all the time. The electrode driving cam rotates to drive the cam ejector pin shaft to reciprocate in the axial direction of the cam ejector pin shaft, and the electric spark machining electrode reciprocates along with the cam ejector pin shaft. The method has the advantages of stability, controllability and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electric spark machining, and relates to a machining device and a machining method, in particular to a low-frequency vibration assisted electric spark machining device and a machining method. BACKGROUND

[0002] Electric spark machining technology is a machining process that removes materials by using the principle of electric corrosion of pulse discharge. It is widely used in the machining of special structures such as thin-walled and deep-cavity structures and difficult-to-machine materials due to its low machining stress and copy machining characteristics. Timely and effective removal of the products of electric spark machining is a prerequisite for ensuring the stability of the electric spark machining process. Therefore, methods such as oil flushing and periodic electrode vibration lifting are commonly used in industry to strengthen the flow of oil in the machining area, promote the removal of products, and improve machining stability. For example, patent application CN1013353B proposes a method of changing electric parameters adaptively by monitoring oil pressure to optimize machining, and patent application US9707637B2 improves the HSEDM by using high-pressure oil to flush the machining area when the electrode is slightly lifted, replacing the high amount of back-off with a small amount of periodic back-off, and monitoring the back-off of electric parameters to improve machining efficiency in certain cases.

[0003] Currently, the most common method of periodic electrode lifting is the servo lifting method driven by the motion axis of the electric spark machining machine tool. The electrode is driven by the servo axis of the machine tool to perform periodic vibration lifting movement. This method is simple in structure and easy to implement. However, the electrode rod used in deep-cavity structure electric spark machining is long and thin, so the electrode rod will experience uncontrollable flutter during periodic vibration lifting movement, affecting the stability of the electric spark discharge process. Therefore, there is an urgent need for a device and method that can achieve relative stability of the electrode rod during periodic vibration lifting movement of the electrode. SUMMARY

[0004] The present application provides a low-frequency vibration assisted electric spark machining device and a machining method to overcome the defects of the prior art.

[0005] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0006] In a first aspect, the present application provides a low-frequency vibration assisted electric discharge machining device, comprising an electrode at the front end and an electrode rod connected to the driving shaft of a machine tool at the rear end; further comprising a cam assembly arranged in the front end of the electrode rod; the cam assembly comprises an electrode driving cam and a balance cam, both of which can rotate; the balance cam is used to balance the rotational inertia of the electrode driving cam; the electrode is provided with a cam plunger shaft; one end of the cam plunger shaft is fixed with the electrode, and the other end extends into the electrode rod and is always in contact with the cam surface of the electrode driving cam; the electrode driving cam drives the cam plunger shaft to reciprocate along its axial direction by rotating, and the electrode reciprocates with it.

[0007] Further, it further comprises an electromagnetic coil; the cam plunger shaft is made of magnetic material; the electromagnetic coil is fixed on the electrode rod and surrounds the cam plunger shaft; when the electromagnetic coil is energized, a magnetic field is generated, and the direction of action of the magnetic field is parallel to the axis of the cam plunger shaft.

[0008] Further, the end of the cam plunger shaft has an outer edge structure protruding from the side surface; an elastic member is arranged between the outer edge structure and the wall of the electrode rod, which makes the end of the cam plunger shaft always in contact with the cam surface of the electrode driving cam.

[0009] Further, the elastic member is a spring; the spring is sleeved on the cam plunger shaft.

[0010] Further, the electrode driving cam and the balance cam are coaxially arranged and synchronously rotate.

[0011] Further, a driving motor is arranged in the electrode rod; the electrode driving cam and the balance cam are arranged on the output shaft of the driving motor.

[0012] Further, the profile curve of the electrode driving cam is a modified sine curve, a trapezoidal curve or a polynomial curve.

[0013] Further, it further comprises a vibration sensor; the vibration sensor is arranged on the electrode rod to detect the vibration amplitude of the electrode rod.

[0014] In a second aspect, the application also provides a processing method of the low-frequency vibration assisted electric spark machining device: first, the electrode driving cam and the balance cam are selected and installed according to the target processing piece; then, the electrode driving cam and the balance cam are driven to rotate, and the electrode rod is started for electric spark machining, and the vibration amplitude of the electrode rod is detected in real time during the electric spark machining; when the vibration amplitude of the electrode rod exceeds a threshold value, one or a combination of the following compensation operations is performed: a compensation current is input to the electromagnetic coil to generate a magnetic field to exert an axial auxiliary force on the cam pin shaft in a direction away from the electrode driving cam; the rotating speed of the electrode driving cam is reduced; the balance cam is replaced; and the vibration amplitude of the electrode rod is reduced to below the threshold value through the compensation operation until the processing is completed.

[0015] Further, the compensation current I is: I=k x Am; wherein, k is an electromagnetic proportional coefficient; Am is an electrode loss amount, Am= l x S x t, l is an electrode loss rate, S is a discharge area, and t is a discharge time.

[0016] The application has the following beneficial effects: first, the electrode driving cam and the cam pin shaft are used to realize the reciprocating motion of the electric spark machining electrode, and different tool withdrawal distances can be realized by selecting the electrode driving cam; second, the balance cam is used to pre-set a basic compensation amount to balance the rotating inertia of the electrode driving cam in the initial stage; further, the electromagnetic coil is used to exert an axial auxiliary force on the cam pin shaft, and when the electric spark machining electrode is worn out, the vibration amplitude generated by the electrode rod can be balanced by controlling the compensation current input to the electromagnetic coil, so that the stability during processing is ensured. In addition, the application also provides compensation operations for balancing the vibration of the electrode rod, including forming an adjusting magnetic field by a compensation current, reducing the rotating speed of the electrode driving cam, and replacing the balance cam, so that the vibration during electric spark machining is reduced, and stable processing is realized. BRIEF DESCRIPTION OF DRAWINGS

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

[0018] Figure 2 is a schematic diagram of the internal structure of the low-frequency vibration assisted electric spark machining device;

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

[0020] Figure 4 is a processing flow chart of the low-frequency vibration assisted electric spark machining 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 processing device further comprises an electromagnetic coil 5. The cam plunger shaft 21 is made of magnetic material. The electromagnetic coil 5 is fixed on the electrode rod 1 and surrounds the cam plunger shaft 21. When the electromagnetic coil 5 is powered, a magnetic field is generated, and the direction of action of the magnetic field is parallel to the axis of the cam plunger shaft 21. By applying an axial auxiliary force to the cam plunger shaft 21 through the magnetic field, the inertia force of the electrode spark processing electrode 2 during movement is balanced, and the dynamic fine adjustment of the overall inertia of the electrode rod 1 is realized.

[0029] The processing device further comprises a vibration sensor 6. The vibration sensor 6 is arranged on the electrode rod 1 to detect the vibration amplitude of the electrode rod 1.

[0030] The processing device further comprises 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 input to the electromagnetic coil 5 and the rotation speed of the driving motor 43 according to the vibration amplitude of the electrode rod 1.

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

[0032] As shown in Figure 4 The embodiment also provides a processing method of the low-frequency vibration auxiliary electric spark processing device:

[0033] Firstly, the electrode driving cam 41 and the balance cam 42 are selected and installed according to the target workpiece.

[0034] Specifically, the shape of the electric spark processing electrode 2 and the processing parameters are designed according to the workpiece material (such as die steel, titanium alloy) and the processing precision requirement (such as Ra≤0.8μm). The electrode mass, the expected loss amount, the suction back-off amount, etc. are calculated according to the material and shape of the electric spark processing electrode 2, and the shape of the electrode driving cam 41 is designed in combination with the processing parameters. The shape of the balance cam 42 is designed according to the mass and shape of the electric spark processing electrode 2 and the shape of the electrode driving cam 41. The electrode driving cam 41 and the balance cam 42 are installed inside the electrode rod 1.

[0035] Then, the electrode driving cam 41 and the balance cam 42 are driven to rotate, and the electrode rod 1 is started to perform electric spark processing. In the process of electric spark processing, the vibration amplitude of the electrode rod 1 is detected in real time.

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

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

[0038] The compensation current I is:

[0039] I=k*Δm

[0040] In the formula, k is the electromagnetic proportional coefficient; Δm is the electrode loss amount, Δm=λ*S*t, λ is the electrode loss rate, S is the discharge area, and t is the discharge time. The magnetic field strength is adjusted through the change of the compensation current, the axial auxiliary force applied to the cam needle shaft 21 is changed, and the vibration is continuously balanced.

[0041] b. The control module 7 reduces the rotation speed of the electrode driving cam 41, that is, reduces the rotation speed of the driving motor 43, thereby reducing the moving frequency of the electrode spark machining electrode 2, and further reducing the vibration amplitude of the electrode rod 1.

[0042] c. The machining is paused to replace the balancing cam 42.

[0043] Specifically, when the vibration amplitude of the electrode rod 1 exceeds the threshold value, the compensation current is first controlled to be input into the electromagnetic coil 5, and the balance is adjusted through the magnetic field. If the magnetic field formed by the compensation current is not enough to reduce the vibration amplitude of the electrode rod 1, the balance is adjusted by reducing the rotation speed of the driving motor 43. If the vibration amplitude of the electrode rod 1 cannot be reduced by reducing the rotation speed of the driving motor 43, the balance is adjusted by replacing the balancing cam 42.

[0044] The vibration amplitude of the electrode rod 1 is reduced to below the threshold value through the compensation operation until the machining is completed. If the compensation operation cannot reduce the vibration amplitude of the electrode rod 1 to below the threshold value, the machining is ended.

[0045] In the present application, unless otherwise specified, the 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", "back" and the like cited in the application are only for the convenience of clear description, and are not used to limit the scope of the application. The change or adjustment of the relative relationship without substantial change of the technical content is also regarded as the implementable scope of the application.

[0047] Finally, it should be noted that: the above is only the preferred embodiment of the present application and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacement for part of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A low-frequency vibration assisted electro-discharge machining device, comprising a front-end mounted electro-discharge machining electrode and a rear-end connected electrode rod of a machine tool driving shaft, characterized in that: a cam assembly is arranged in the front end of the electrode rod; the cam assembly comprises an electrode driving cam and a balance cam, both of which are rotatable; the balance cam is used to balance the rotational inertia of the electrode driving cam; the electro-discharge machining electrode is provided with a cam plunger shaft; one end of the cam plunger shaft is fixed with the electro-discharge machining electrode, and the other end extends into the electrode rod and is always in contact with the cam surface of the electrode driving cam; the electrode driving cam drives the cam plunger shaft to reciprocate along its axial direction by rotating, and the electro-discharge machining electrode reciprocates with it.

2. The low-frequency vibration assisted electro-discharge machining device according to claim 1, characterized in that: an electromagnetic coil is further included; the cam plunger shaft is made of magnetic material; the electromagnetic coil is fixed on the electrode rod and surrounds the cam plunger shaft; when the electromagnetic coil is energized, a magnetic field is generated, and the direction of action of the magnetic field is parallel to the axis of the cam plunger shaft.

3. The low-frequency vibration assisted electro-discharge machining device according to claim 1, characterized in that: the end of the cam plunger shaft has an outer edge structure protruding from the side surface thereof; an elastic element is arranged between the outer edge structure and the rod wall of the electrode rod, and the elastic element always makes the end of the cam plunger shaft in contact with the cam surface of the electrode driving cam.

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

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

6. The low-frequency vibration assisted electro-discharge machining device according to claim 5, characterized in that: a driving motor is arranged in the electrode rod; and the electrode driving cam and the balance cam are arranged on the output shaft of the driving motor.

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

8. The low-frequency vibration assisted electro-discharge machining device according to claim 1, characterized in that: a vibration sensor is further included; and the vibration sensor is arranged on the electrode rod to detect the vibration amplitude of the electrode rod.

9. A machining method of the low-frequency vibration assisted electro-discharge machining device according to claim 2, characterized in that: first, the electrode driving cam and the balance cam are selected and installed according to the target workpiece; then, the electrode driving cam and the balance cam are driven to rotate, and the electrode rod is started to perform electro-discharge machining; in the process of electro-discharge machining, the vibration amplitude of the electrode rod is detected in real time; when the vibration amplitude of the electrode rod exceeds a threshold value, one or a combination of the following compensation operations is performed: a compensation current is input to the electromagnetic coil to generate a magnetic field, and the magnetic field exerts an axial auxiliary force on the cam plunger shaft in a direction away from the electrode driving cam; the rotating speed of the electrode driving cam is reduced; the balance cam is replaced; ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The amplitude of the electrode rod is made lower than a threshold value by a compensation operation until the machining is completed.

10. The machining method of the low-frequency vibration assisted electric discharge machining device according to claim 9, characterized in that: The compensation current I is: I = k x Δm; In the formula, k is an electromagnetic proportional coefficient; Δm is an electrode loss amount, Δm = λ x S x t, λ is an electrode loss rate, S is a discharge area, and t is a discharge time.

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