Electrochemical removal method for graphite coating on surface of molybdenum wire

Abstract

The invention discloses an electrochemical removal method for a graphite coating on the surface of a molybdenum wire. According to the method, an electrolysis procedure is added after a traditional molybdenum wire machining forming process, and a graphite layer attached to the surface of the molybdenum wire is effectively removed. The innovation solves the problem of floating pollution of graphite powder, the cutting fluid is kept clean, the service life of the cutting fluid is prolonged, meanwhile, the production environment is improved, and the risk that operators inhale the graphite powder is reduced. In addition, the electrolytic process can passivate the surface of the molybdenum wire, eliminate burrs and reduce the secondary machining requirement, in the wire cut electrical discharge machining process, the method enables discharge of wire cut electrical discharge machining to be more uniform, and the surface quality of workpiece machining is remarkably improved. Besides, by removing the graphite coating, the problem of uneven stress of the molybdenum wire caused by graphite attachment in the using process of the traditional molybdenum wire is solved, tension change caused by graphite falling in the machining process is avoided, meanwhile, blockage of the guide hole die is effectively prevented, and the success rate of automatic threading is greatly increased.

Description

Technical Field

[0001] The present invention relates to the field of metalworking technology, specifically to a method for electrochemically removing graphite coatings from molybdenum wire surfaces. The method is particularly suitable for efficiently cleaning residual graphite layers on molybdenum wire surfaces after machining. This technology, primarily used in the preparation of molybdenum wire for precision wire-cut electrical discharge machining (EDM), effectively addresses processing contamination and product quality issues associated with residual graphite on the surface of conventional molybdenum wire. Background Art

[0002] With the rapid development of modern manufacturing towards high precision and high efficiency, wire EDM technology, as a key tool for precision machining, has placed unprecedentedly stringent demands on the performance of electrode wires. Molybdenum wire, due to its unique physical and chemical properties, has become the irreplaceable electrode material of choice in wire EDM. This rare metal, with its ultra-high melting point of 2620°C, exhibits exceptional stability in high-temperature discharge environments. Its tensile strength, exceeding 2000 MPa, far exceeds that of ordinary metals, ensuring resistance to breakage during machining. Furthermore, molybdenum wire's excellent electrical and thermal conductivity allows it to quickly conduct heat from discharge, preventing localized overheating and deformation. More notably, molybdenum wire has a low elongation of 1-3% and a low coefficient of thermal expansion. These properties make it particularly suitable for machining high-hardness materials such as titanium alloys for aerospace applications, cemented carbides for molds, and hardened steel, enabling the perfect realization of complex cavities with micron-level precision. In the field of high-speed wire EDM, molybdenum wire, with its excellent cost-effectiveness and stable machining performance, has become an indispensable machining tool for high-end manufacturing applications such as precision molds, medical devices, and electronic components.

[0003] However, the use of graphite emulsion lubricants in traditional molybdenum wire production has become a key bottleneck hindering product quality improvement. Throughout the entire molybdenum wire drawing process, from rough drawing to finishing, graphite emulsion lubrication is essential. While this process effectively reduces die wear, it leaves a residual graphite layer 2 to 5 μm thick on the molybdenum wire surface. As machining precision demands advance into the submicron era, the shortcomings of this traditional process are becoming increasingly prominent. First, during EDM, uneven shedding of the graphite coating causes variations in the discharge gap, resulting in streaky defects on the machined surface. Second, the shed graphite particles contaminate the working fluid, increasing its conductivity and decreasing its dielectric properties. This not only increases the frequency of cutting fluid changes but also accelerates wear on precision machine tool components. More seriously, these ultrafine graphite dust particles can remain suspended in the workshop air for extended periods, and long-term exposure can lead to occupational diseases such as pneumoconiosis. Furthermore, the presence of the surface graphite layer alters the electrical resistance of the molybdenum wire, leading to secondary discharges when machining highly reflective materials, severely impacting machining accuracy and efficiency. The existence of these problems makes it difficult for molybdenum wire produced by traditional technology to meet the multiple standards of modern precision manufacturing for processing quality, environmental protection requirements and production costs.

[0004] To address these issues, the present invention uses an electrochemical method to deeply clean the molybdenum wire surface. This not only thoroughly removes surface graphite residue, ensuring clean processing, but also forms a dense oxide passivation layer during the electrolysis process, significantly improving corrosion resistance. It also eliminates microscopic burrs, reduces surface roughness of the electrode wire, and ensures uniform and stable EDM. This process fully complies with green manufacturing standards, meeting the stringent performance requirements of modern high-precision wire EDM processes while providing an innovative solution for the sustainable development of molybdenum wire production, achieving a win-win situation in both economic and environmental benefits. Summary of the Invention

[0005] The purpose of the present invention is to address the defects in the current traditional molybdenum wire processing process with graphite attached to the surface, and to invent an electrochemical removal method for the graphite coating on the surface of the molybdenum wire. First, molybdenum powder is pressed into a molybdenum rod through a traditional process method, and then subjected to high-temperature rolling, multiple annealing and drawing to 0.182-0.183 mm. Then, according to the diameter of the wire, appropriate current, voltage, speed and electrolyte concentration are selected to perform electrolytic processing to remove the graphite coating on the surface of the molybdenum wire, thereby improving the surface quality of the molybdenum wire and reducing the stress of the molybdenum wire.

[0006] The specific technical solutions adopted in the present invention are as follows:

[0007] A method for electrochemically removing graphite coating from the surface of a molybdenum wire is characterized in that, after a multi-mode stretching process, the diameter of the molybdenum wire is retained at 0.182 to 0.183 mm, an electrolysis process is added after a traditional molybdenum wire processing and forming process, and corresponding parameters such as current, voltage, and electrolyte concentration are selected according to the wire diameter. Finally, after cleaning and drying and testing of indicators such as tensile strength and stress, a finished molybdenum wire that meets the requirements is obtained. This method effectively removes the graphite coating attached to the surface of the molybdenum wire, passivates the surface of the molybdenum wire, and reduces the stress of the molybdenum wire while ensuring that the diameter and various indicators of the molybdenum wire meet the requirements.

[0008] The electrolyte is an alkaline solution or an acidic solution, preferably sodium chloride, sodium hydroxide or sodium sulfate solution.

[0009] The electrolysis parameters of the electrolysis treatment are selected according to the diameter of the wire, the current is controlled within 10 to 80A, and the voltage is controlled within 10 to 15V.

[0010] The take-up speed is adjusted according to the diameter of the molybdenum wire and is controlled at 10 to 60 m / min.

[0011] The concentration of the electrolyte is selected according to the diameter of the wire and is controlled within a range of 5% to 20%.

[0012] The drying temperature is controlled at 600-800°C.

[0013] Compared with the prior art, the present invention has the following specific beneficial effects:

[0014] The present invention solves the problem of floating graphite powder pollution by removing the graphite coating on the surface of the molybdenum wire through an electrochemical method, keeps the cutting fluid clean and extends its service life, while improving the production environment and reducing the risk of operators inhaling graphite dust. The electrolysis process can also passivate the surface of the molybdenum wire, eliminate burrs, and reduce the need for secondary processing. During the electric spark wire cutting process, this method makes the discharge of the electric spark wire cutting more uniform, significantly improving the surface quality of the workpiece processing. In addition, by removing the graphite layer, the problem of uneven stress on the molybdenum wire caused by graphite adhesion during the use of traditional molybdenum wire is solved, and the tension change caused by graphite shedding during the processing is avoided. At the same time, it effectively prevents the clogging of the guide eye mold, greatly improving the success rate of automatic wire threading. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Molybdenum wire structure after drawing

[0016] FIG2 is a flow chart of the processing process of the present invention

[0017] Figure 2(a) shows the process of ammonium molybdate being calcined and reduced to molybdenum powder.

[0018] Figure 2(b) shows the process of pressing molybdenum powder into molybdenum rods

[0019] Figure 2(c) shows the process of rolling and drawing molybdenum rod into molybdenum wire

[0020] Figure 2(d) shows the process of electrolytic decomposition of graphite coating by molybdenum wire DETAILED DESCRIPTION

[0021] The first step is to calcine ammonium molybdate at 450-550°C to decompose it into molybdenum trioxide and generate ammonia and water vapor. The heating rate during the calcination process needs to be strictly controlled to avoid the volatilization loss of molybdenum trioxide. Then, a primary reduction is carried out, and hydrogen is introduced at 450-650°C to reduce the molybdenum trioxide to molybdenum dioxide. Then, a secondary reduction is further carried out at 900-1100°C to reduce the molybdenum dioxide to metallic molybdenum powder.

[0022] The second step is to load the molybdenum powder into a rubber mold and use a cold isostatic pressing process to press the molybdenum powder into a molybdenum rod blank. The molybdenum rod blank is then sintered at 1800-2200°C for 2-6 hours to densify the molybdenum rod.

[0023] The third step is to heat the molybdenum rod to 1200-1500℃, roll it to the required size through multiple passes, and draw it using a multi-die drawing process. First, eight-die drawing is performed to draw the molybdenum rod to a diameter of 1.0-0.5mm. The furnace temperature is controlled at 750-850℃, the die temperature at 410-430℃, the drawing speed at 14-16m / min, and the specific gravity of the graphite emulsion at 1.05-1.07g / cm 3 Then, ten-die stretching is performed to draw the molybdenum rod to a diameter of 0.5-0.24 mm. The furnace temperature is controlled at 700-800°C, the die temperature at 360-390°C, the drawing speed at 30-35 m / min, and the specific gravity of the graphite emulsion at 1.03-1.05 g / cm 3 Finally, four-die cold drawing is performed to gradually draw the molybdenum wire to a diameter of 0.182-0.183 mm, and the drawing speed is controlled at 60-90 m / min.

[0024] The fourth step is to electrolyze the molybdenum wire with alkaline or acidic electrolyte at 40-60°C, control the electrolysis parameters to 10-80A current, 10-15V voltage and 10-60m / min winding speed, dissolve the graphite coating and form a molybdenum oxide passivation layer on the surface of the molybdenum wire. Finally, clean it and dry it at 600-800°C, test the performance indicators such as tensile strength and stress, and finally obtain a high-clean molybdenum wire with a diameter of 0.180.

Claims

1. The present invention provides a method for electrochemically removing graphite coating on the surface of molybdenum wire, characterized in that: After the molybdenum wire is drawn and formed, it is fed into an electrolytic cell with a graphite coating on its surface. Using a specific electrolyte, controlled current and voltage parameters are applied, while the wire's processing time in the cell is controlled by adjusting the take-up speed. By precisely controlling the electrolysis parameters and electrolyte concentration, the graphite coating on the molybdenum wire is removed while simultaneously achieving surface passivation and eliminating burrs. After the electrolysis, the molybdenum wire is cleaned and dried, and its tensile strength and stress are tested to obtain a finished molybdenum wire with a clean surface and no graphite residue.

2. The electrochemical removal method of graphite coating on the surface of molybdenum wire according to claim 1, characterized in that: The final diameter of the molybdenum wire after drawing is 0.182-0.183 mm.

3. The electrochemical removal method of graphite coating on the surface of molybdenum wire according to claim 1, characterized in that: The electrolyte is an alkaline solution or an acidic solution, preferably a sodium chloride, sodium hydroxide or sodium sulfate solution.

4. The electrochemical removal method of graphite coating on the surface of molybdenum wire according to claim 1, characterized in that: The electrolysis parameters of the electrolysis treatment are selected according to the diameter of the wire, the current is controlled within the range of 10 to 80A, and the voltage is controlled within the range of 10 to 15V.

5. The electrochemical removal method of graphite coating on the surface of molybdenum wire according to claim 1, characterized in that: The take-up speed is adjusted according to the diameter of the molybdenum wire and is controlled at 10 to 60 m / min to ensure that the graphite coating is completely removed and the diameter of the molybdenum wire meets the requirements after the electrolysis is completed.

6. The electrochemical removal method of graphite coating on the surface of molybdenum wire according to claim 1, characterized in that: The concentration of the electrolyte is selected according to the diameter of the wire and is controlled within a range of 5% to 20%.

7. The electrochemical removal method of graphite coating on the surface of molybdenum wire according to claim 1, characterized in that: The drying temperature is controlled at 600-800°C.

8. The electrochemical removal method of graphite coating on the surface of molybdenum wire according to claim 1, characterized in that: The method effectively reduces graphite powder pollution, prolongs the service life of the cutting fluid, and reduces the dust concentration in the production environment.

9. The electrochemical removal method of graphite coating on the surface of molybdenum wire according to claim 1, characterized in that: The method effectively reduces the stress of the molybdenum wire and reduces surface burrs. After the graphite layer is removed, the molybdenum wire discharges more evenly during electric spark wire cutting, improves the surface quality of the workpiece, and is more suitable for high-precision electric spark wire cutting processing.

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