Electrospark combined machining method for long and narrow slit structure

Abstract

This invention discloses a combined electro-discharge machining (EDM) method for long, narrow slit structures, specifically relating to the field of EDM technology. The steps are as follows: The workpiece is mounted on the EDM electrode wire; the EDM electrode wire moves in the XY plane; the machined workpiece is then aligned with the electrolytic machining wire electrode; the power supply and electrolytic control system are turned on for secondary machining; the electrolytic machining wire electrode moves along a predetermined trajectory in the XY plane; after secondary machining, the power supply is disconnected, the electrolyte circulation system is shut off, the electrolytic machining wire electrode and workpiece are removed, and both are cleaned, thus completing the machining process. This invention solves the problem of existing machining methods struggling to achieve high-quality machining of ultra-thin sheet-like long, narrow slit structures, improving the machining quality and efficiency of such structures.

Description

Technical Field

[0001] This invention relates to the field of electrical discharge machining (EDM) technology, and particularly to an EDM combined machining method with a long narrow slit structure. Background Technology

[0002] With the continuous advancement of industrial modernization, the requirements for the performance of metallic materials in various high-end manufacturing technologies are becoming increasingly stringent. In aerospace, automotive manufacturing, and weaponry, difficult-to-machine materials such as high-temperature alloys, titanium alloys, and aluminum-based composites are finding wider application. In the aerospace field, thin-walled parts refer to parts with a wall thickness to height ratio between 1 / 5 and 1 / 8; those smaller are considered ultra-thin-walled parts. A large number of ultra-thin sheet parts exist in aero-engine rotors, flexible pendulum accelerometers, laser gyroscopes, and platform inertial navigation systems. Examples include contact fingertip seals in engine rotors, pendulum plates in accelerometers, and gaskets in gyroscopes. The assembly accuracy of many micro-precision devices needs to be better than 25–30 μm. Taking fingertip seals as an example, their wall thickness to height ratio can even reach 1 / 50 or less, making them more difficult to machine than typical thin-walled parts, especially in the finishing stage where the rigidity of the workpiece or structure is already very poor. High-precision, rapid manufacturing of such parts is highly beneficial for improving product quality and production capacity.

[0003] Currently, existing machining technologies for various difficult-to-machine ultrathin sheet structures of metal materials mainly include precision forging, CNC precision milling, and sectional cyclic layer-by-layer cutting. However, common problems easily arise during the finishing stage: ultrathin workpieces experience elastic tool deflection under clamping and cutting forces, leading to significant dimensional and shape errors; poor workpiece machining stability results in elastic chatter under cutting forces, making normal machining impossible and causing the workpiece surface quality to fail to meet design requirements. Current optimization methods include optimizing toolpaths, tool position compensation, designing dedicated vibration-suppressing fixtures, and optimizing CNC system programming. However, based on industry consensus, there is still no non-contact special machining method for ultrathin sheet structures with long, narrow slits. Achieving precise, high-quality, efficient, and low-cost machining of ultrathin sheet structures with long, narrow slits has become a challenge for the industry. Therefore, it is necessary to propose an innovative machining method for ultrathin sheet structures with long, narrow slits in difficult-to-machine metal materials to promote the further application of special machining technologies. Summary of the Invention

[0004] The present invention aims to provide an electrical discharge electrolytic combined processing method for long narrow slit structures, which solves the problem that existing processing methods are difficult to achieve high-quality processing of ultra-thin sheet-like long narrow slit structures.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: a method for combined electrical discharge machining (EDM) of a long narrow slit structure, comprising the following steps:

[0006] S1. Load the workpiece to be processed into the electrical discharge machining system and complete the tool setting between the workpiece and the electrical discharge machining electrode wire;

[0007] S2. Turn on the coolant circulation system to cool down the workpiece, turn on the power and EDM control system, and the EDM electrode wire will move along the predetermined trajectory in the XY plane to complete the preliminary machining.

[0008] S3. Turn off the power and remove the workpiece that has completed the initial machining from the electrical discharge machining system;

[0009] S4. Turn on the electrolyte circulation system, connect the workpiece that has completed the preliminary processing to the positive terminal of the power supply, connect the electrolytic machining wire electrode to the negative terminal of the power supply, and complete the tool setting between the workpiece and the electrolytic machining wire electrode; turn on the power supply and the electrolytic control system to perform secondary processing; the electrolytic machining wire electrode performs feed motion along the predetermined trajectory in the XY plane.

[0010] S5. After completing the secondary processing, disconnect the power supply, shut off the electrolyte circulation system, remove the electrolytic machining wire electrode and workpiece, clean the electrolytic machining wire electrode and workpiece, and the processing is completed.

[0011] Furthermore, in steps S2 and S4, the coolant and electrolyte are supplied by external spraying, sprayed from the spray holes below multiple nozzles.

[0012] With the above settings, the liquid supply methods are mainly divided into two types: external spray and internal spray. Compared with the internal spray method, the external spray method reduces costs. Traditional wire electrode processing requires pre-drilling slots inside the workpiece, which increases processing costs. The external spray method facilitates the discharge of products from the processing area, thereby improving processing localization and processing quality.

[0013] Furthermore, the operating voltage range in steps S2 and S4 is controlled within 20-25V.

[0014] With the above settings, the voltage will affect the width of the processed seam. Through multiple experiments, the influence of processing voltage on electrolytic processing was studied. It was found that increasing the voltage can significantly increase the seam width, and the voltage of 20-25V can meet the requirements for seam processing.

[0015] Furthermore, the feed rate range for step S4 is set to 2.0 mm / min - 20.0 mm / min.

[0016] With the above settings, the slit width decreases as the feed speed increases. If a low-speed feed is used, more material can be removed per unit time, and vice versa. After controlling the voltage, the feed speed within this range can achieve the slit width to be processed. However, in order to improve processing efficiency, a feed speed of 20.0 mm / min can be set.

[0017] Furthermore, in step S4, the initial machining gap between the workpiece and the electrolytic machining wire electrode is 150 μm.

[0018] With the above settings, the initial machining gap is related to the diameter of the wire electrode, and the initial gap is determined according to the electrode diameter; under this gap condition, the corresponding slot width can be machined.

[0019] Furthermore, both the electrical discharge machining electrode wire and the electrolytic machining wire electrode are made of stainless steel, with a wire diameter of 0.3 mm.

[0020] By using the above settings, the cost can be reduced by selecting electrodes of the same material, and stainless steel is not easily corroded when immersed in coolant and electrolyte. Selecting electrodes of this diameter meets the requirements of the slot width design. If the diameter is too large, the processing slot width will be too large; conversely, if the diameter is too small, the slot width will be too small.

[0021] Furthermore, the material of the workpiece to be processed is high-temperature alloy GH536, with a thickness not exceeding 150μm.

[0022] Compared with existing technologies, the beneficial effects of this solution are:

[0023] 1. This solution solves the problem of elastic chatter and residual stress that are easily caused by cutting ultra-thin sheet structures with a thickness of less than 150μm in the existing technology. This solution uses a two-step process. First, it uses electrical discharge machining (EDM) to remove a large amount of material. Then, it uses wire electrode electrolytic machining to perform dimensional finishing and remove the remelted layer. This allows the points on the long and narrow slit structure to obtain a surface with good processing quality after combined processing. Finally, it can produce a multi-long and narrow slit structure with an aspect ratio of more than 100.

[0024] 2. This solution addresses the problem of elastic tool deflection and chatter caused by the simultaneous action of clamping and cutting forces on ultra-thin sheet metal workpieces, which prevents normal machining and results in the workpiece's surface quality failing to meet design requirements. This invention proposes an electrical discharge machining (EDM)-electrolysis combined machining method. In the first process, during preliminary material removal, the electrode wire remains completely in contact with the workpiece, eliminating issues like elastic chatter caused by cutting forces. This allows for rapid preliminary material removal of ultra-thin, difficult-to-machine sheet metal materials. The second process effectively removes the heat-affected zone and remelted layer generated in the first process. Even with coolant flushing, slow wire EDM still leaves a significant heat-affected zone in the machined area. However, the EDM-electrolysis combined machining method, as shown in subsequent embodiments, produces a long, narrow groove structure with consistent crystal structure and elemental composition between the machined and unmachined areas, exhibiting excellent physical properties and eliminating any issues affecting the performance of the machined area after machining.

[0025] 3. The structure of the EDM electrode wire and the wire electrolytic cathode in this solution is very simple, with a short manufacturing cycle, low processing cost, and convenient assembly and disassembly. Through arc ablation and electrochemical anodic removal, it is possible to remove any conductive metal material, thereby expanding the applicability of the innovative processing method of this invention.

[0026] 4. During the combined machining process using this scheme, the feed motion of the linear machining electrode and the linear machining cathode is controlled by the CNC system to form the contour generation line. This method features high machining flexibility, high machining efficiency, low tool cost, and high machining stability. Compared with CNC machine tools for machining ultra-thin sheet metal parts, the EDM-electrolysis combined machining technology for long and narrow slits proposed in this invention allows for easier cathode design and replacement, better guarantees the flatness and perpendicularity of the machined structure, and eliminates the influence of remelted layers and heat-affected zones. Furthermore, it avoids issues such as suppressing elastic chatter and elastic tool deflection during machining, thereby improving the machining efficiency of parts made from difficult-to-machine materials, reducing costs, and shortening the machining cycle. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the contact-type fingertip sealing structure mentioned in the background section;

[0028] Figure 2 This is a schematic diagram of workpiece changes in the electric spark electrolytic combined machining method with a long narrow slit structure according to the present invention;

[0029] Figure 3 This is a microscopic morphology image of the workpiece magnified 1000 times using a scanning electron microscope after preliminary processing in the embodiment;

[0030] Figure 4This is a magnified macroscopic image of the long narrow slit structure after preliminary processing in the embodiment, magnified 35 times.

[0031] Figure 5 yes Figure 3 Elemental composition diagrams obtained from elemental energy spectrum analysis at two different locations in the middle;

[0032] Figure 6 This is a microscopic morphology image of the workpiece of the embodiment after secondary processing, magnified 1000 times using a scanning electron microscope;

[0033] Figure 7 This is a magnified macroscopic morphology image of the long narrow slit structure after secondary processing in the embodiment, magnified 35 times.

[0034] Figure 8 This is a schematic diagram of the actual long and narrow slit structure after secondary processing in the embodiment;

[0035] Figure 9 yes Figure 6 The elemental composition diagram obtained by performing elemental energy spectrum analysis at two different locations in the middle. Detailed Implementation

[0036] The present invention will be further described in detail below through specific embodiments:

[0037] Example

[0038] The ultrathin sheet long narrow slit structure targeted in this embodiment is... Figure 1 For example, Figure 1 This is a schematic diagram of a typical ultrathin, sheet-like, long, narrow slit structure—a contact-type fingertip seal structure. Figure 1 It can be seen from the data that the metal part is 0.20mm thick and has multiple long and narrow slit structures with complex shapes. The entrance width of the long and narrow slit structures is 0.40mm, and the width of the curved sections is only 0.16mm.

[0039] This embodiment of the electrical discharge electrolytic combined machining method for a long narrow slit structure includes the following steps:

[0040] S1. Load the workpiece to be processed into the electrical discharge machining system and complete the tool setting between the workpiece and the electrical discharge machining electrode wire. In this embodiment, the material of the electrical discharge machining electrode wire is stainless steel with a wire diameter of 0.3 mm, and the material of the workpiece to be processed is high-temperature alloy GH536 with a thickness not exceeding 150 μm.

[0041] S2. The coolant circulation system is turned on to cool the workpiece. In this embodiment, the coolant is supplied via an external spray nozzle, sprayed from the nozzle holes below multiple coolant nozzles. The purpose of supplying coolant is to fill the space between the EDM electrode wire and the workpiece with coolant through circulating coolant flushing. In special machining fields, using coolant flushing can effectively wash away the workpiece material, improving the quality of the resulting workpiece structure. Then, the power supply and EDM control system are turned on, with the operating voltage controlled within the range of 20-25V. The EDM electrode wire performs a feed motion along a predetermined trajectory in the XY plane, completing the initial machining.

[0042] S3. Turn off the power, remove the workpiece that has completed the initial processing from the EDM system, and clean the workpiece with anhydrous ethanol and an ultrasonic cleaner to remove the coolant from the workpiece surface.

[0043] S4. Connect the workpiece that has undergone preliminary processing to the positive terminal of the power supply, and connect the electrolytic machining wire electrode to the negative terminal of the power supply. Set the workpiece and the electrolytic machining wire electrode together. In this embodiment, the initial processing gap between the workpiece and the electrolytic machining wire electrode is 150 μm. The electrolytic machining wire electrode is made of stainless steel with a wire diameter of 0.3 mm. Turn on the electrolyte circulation system and use an external spray-type electrolyte supply method to fill the space between the wire electrolytic machining cathode and the workpiece to be processed with electrolyte. Then turn on the power supply and the electrolytic control system for secondary processing. The operating voltage range is controlled between 20-25V. The electrolytic machining wire electrode moves along a predetermined trajectory in the XY plane, with a feed speed range of 2.0 mm / min-20.0 mm / min. Secondary processing is used to remove the remelted layer and perform finishing on the long, narrow slit.

[0044] S5. After completing the secondary processing, disconnect the power supply, shut down the electrolyte circulation system, remove the electrolytically processed wire electrode and workpiece, and clean the electrolytically processed wire electrode and workpiece using anhydrous ethanol and an ultrasonic cleaner. The processing is completed. The purpose of cleaning is to remove the electrolyte and residual electrolytic products from the workpiece and cathode surface for subsequent storage and use, and for further research.

[0045] Figure 2 This diagram illustrates the changes to the workpiece resulting from the processing method described in this embodiment. The electrical discharge machining (EDM) electrode wire used in this embodiment has a diameter of 0.3 mm and is made of 316L stainless steel. The ultra-thin sheet workpiece to be processed in this embodiment has a thickness of 0.30 mm and is made of GH536 high-temperature alloy. The EDM electrode wire feeds along a given trajectory in the XY direction on the ultra-thin sheet workpiece. As the processing progresses, due to the large amount of arc and heat generated during EDM, remelted layers and ablation pits appear on both sides of the long, narrow groove, such as... Figure 3 The part marked with a dashed line is shown in the image.

[0046] By observing the remelted layer at 1000x magnification using a scanning electron microscope (Hitachi Regulus 8100, Tokyo, Japan), it can be seen that the area marked by the yellow dashed line lacks obvious grain structure and intergranular boundaries. Based on the general consensus in the field, this is a remelted layer formed by the arc and heat action on the GH536 matrix material. Figure 5 As shown, two sampling points, A (in the remelted layer) and B (outside the remelted layer), were selected for elemental energy dispersive spectroscopy (EDS). At point A, the mass fraction of carbon (C) was 53.05%, and the mass fraction of oxygen (O) was 8.25%. The mass fractions of Ni, Fe, and Cr, which belong to the GH536 matrix, were all less than 25%. At point B, the mass fraction of C was 21.44%, O was not detected, and the mass fractions of Ni, Fe, and Cr, which belong to the GH536 matrix, were 52.24%, 17.70%, and 18.23%. It can be seen that the closer to the remelted layer, the higher the proportion of C and O, while the lower the proportion of metal elements belonging to the matrix. This leads to a decrease in the physical properties of the remelted layer region, a looser structure, and affects the final processing quality of the long, narrow slit structure. Figure 4 This is a 35x magnified macroscopic morphology image of the long, narrow slit structure after preliminary processing; such as... Figure 4 As shown, the long and narrow slit structure after preliminary processing is affected by the remelted layer and ablation pits, and there is a need to further improve the processing quality.

[0047] pass Figure 2 Step 4 of the machining process further refines the workpiece to be processed in this embodiment. The electrolytic salt solution used in this embodiment is a 20% sodium chloride electrolytic salt solution by mass; the wire electrode used in the electrolytic machining has a diameter of 0.2 mm and is made of 316L stainless steel; the wire electrode used in the electrolytic machining continues to feed along a given trajectory in the XY direction on the workpiece that has completed the preliminary machining.

[0048] The example workpiece was observed at 1000x magnification using a scanning electron microscope (Hitachi Regulus 8100, Tokyo, Japan). The results are as follows: Figure 6 As shown. Figure 6 and Figure 3 In contrast, there is no longer a remelted layer with a distinct grain structure and intergranular boundary regions. Similarly, in Figure 6 Two sampling points, C (close to the machined surface) and B (far from the machined surface), were selected for elemental energy dispersive spectroscopy (EDS) analysis. The results are as follows: Figure 9As shown in the figure. At point C, the mass fraction of C is 2.95%, the mass fraction of O is 0.32%, the mass fraction of Ni (belonging to the GH536 matrix) is 53.73%, the mass fraction of Fe is 18.23%, and the mass fraction of Cr is 22.06%. At point D, C and O were not detected, the mass fraction of Ni (belonging to the GH536 matrix) is 52.34%, the mass fraction of Fe is 18.12%, and the mass fraction of Cr is 19.23%. The elemental energy dispersive spectroscopy (EDS) results show that after secondary processing, the original remelted layer structure has been completely removed. The resulting long-narrow slit structure has the same elemental composition and crystal structure in both the processed and unprocessed areas, and there are no issues affecting physical properties or structural strength. Figure 7 This is a 35x magnified macroscopic morphology image of the long, narrow slit structure after secondary processing; such as... Figure 7 and Figure 8 As shown, the long narrow slit structure processed by the method proposed in this invention exhibits high surface quality and good dimensional control, meeting the processing requirements for long narrow slit structures of ultra-thin sheet-like, difficult-to-machine metal materials. Compared to traditional laser cutting and ultra-precision wire cutting methods, the method proposed in this invention overcomes their shortcomings and improves product quality. Traditional laser cutting is costly, limited in material selection, and generates heat in the cutting area, resulting in slow cutting speeds and reduced processing efficiency. Ultra-precision wire cutting, on the other hand, suffers from slow processing speeds, leading to low processing efficiency and poor surface quality.

[0049] The present invention proposes an electro-discharge and electrolytic combined machining method for long and narrow slit structures of ultrathin sheet-like difficult-to-machine metal materials. This method enables non-contact machining of long and narrow slit structures of ultrathin sheet-like difficult-to-machine materials through special machining combined machining methods. On ultrathin sheet-like metal parts, the final result is a long and narrow slit structure that meets the design requirements and is not affected by cutting stress, elastic deformation, remelting layer, etc., thereby increasing the processing flexibility and operability.

[0050] The above description is merely an embodiment of the present invention, and common knowledge such as specific structures and / or characteristics in the solutions are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for combined electrical discharge machining (EDM) with a long narrow slit structure, characterized in that: Includes the following steps: S1. Load the workpiece to be processed into the electrical discharge machining system and complete the tool setting between the workpiece and the electrical discharge machining electrode wire; S2. Turn on the coolant circulation system to cool down the workpiece, turn on the power and EDM control system, and the EDM electrode wire will move along the predetermined trajectory in the XY plane to complete the preliminary machining. S3. Turn off the power and remove the workpiece that has completed the initial machining from the electrical discharge machining system; S4. Turn on the electrolyte circulation system, connect the workpiece that has completed the preliminary processing to the positive terminal of the power supply, connect the electrolytic machining wire electrode to the negative terminal of the power supply, and complete the tool setting between the workpiece and the electrolytic machining wire electrode; turn on the power supply and the electrolytic control system to perform secondary processing; the electrolytic machining wire electrode performs feed motion along the predetermined trajectory in the XY plane. S5. After completing the secondary processing, disconnect the power supply, shut off the electrolyte circulation system, remove the electrolytic machining wire electrode and workpiece, clean the electrolytic machining wire electrode and workpiece, and the processing is completed. In steps S2 and S4, the operating voltage range is controlled between 20-25V. The feed rate range for step S4 is set to 2.0 mm / min - 20.0 mm / min; In step S4, the initial machining gap between the workpiece and the electrolytic machining wire electrode is 150 μm; In steps S2 and S4, the coolant and electrolyte are supplied by external spraying, sprayed from the spray holes below multiple nozzles; Both the electrical discharge machining electrode wire and the electrolytic machining wire electrode are made of stainless steel, and the wire diameter is 0.3 mm. The material of the workpiece to be processed is high-temperature alloy GH536, with a thickness not exceeding 150μm.

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