Ultrasonic electric pulse composite assisted magnesium alloy thin-walled micro tube longitudinal torsion drawing device and method

Abstract

The application belongs to the technical field of metal material drawing processing, and particularly relates to an ultrasonic electric pulse composite assisted magnesium alloy thin-wall micro-pipe longitudinal torsion drawing device and method. The device is installed on a linear motion platform and comprises an ultrasonic transducer, a horn, a die, a drill chuck and a pulse power source. The ultrasonic transducer comprises a back cover, a piezoelectric wafer and an outer mode ultrasonic transducer. The horn is installed on the outer mode ultrasonic transducer through bolts, and a spiral groove is arranged on the horn. The die is installed on the horn through threads, and the die has a forming cavity. The drill chuck is installed on the linear motion platform. The positive pole of the pulse power source is connected with the drill chuck, and the negative pole is connected with the horn. The back cover, the outer mode ultrasonic transducer, the horn and the die are all provided with coaxial hollow channels for the magnesium alloy thin-wall micro-pipe to pass through. The ultrasonic vibration, the electric pulse and the longitudinal torsion composite motion are integrated in the same device, and the three work together, so that the drawing force can be significantly reduced, the material flow uniformity can be improved, and the single pass deformation amount and the forming quality of the magnesium alloy thin-wall micro-pipe can be improved.

Description

Technical Field

[0001] This invention relates to the field of metal material drawing technology, and in particular to a longitudinal torsion composite drawing device and method for magnesium alloy thin-walled microtubes assisted by ultrasound and electrical pulse. Background Technology

[0002] Magnesium alloys have a wide range of applications in the medical field. As a biodegradable implantable material, they have broad application prospects in medical devices such as cardiovascular stents. The density and elastic modulus of magnesium alloys are close to those of human bone, which can effectively reduce stress shielding effects, and long-term placement in the body will not affect tissue repair or health monitoring. Therefore, research on the fabrication technology of magnesium alloy thin-walled microtubes is of great significance.

[0003] However, magnesium alloys, with their close-packed hexagonal structure, exhibit poor room-temperature plasticity and are difficult to deform, a problem particularly pronounced in the drawing process of thin-walled microtubes. The small cross-sectional dimensions of thin-walled microtubes lead to significant frictional effects, making tensile stress in the principal stresses highly susceptible to necking and even fracture, severely limiting the deformation per pass. Furthermore, magnesium alloy drawing is prone to surface defects such as scratches and microcracks, making dimensional accuracy and stability difficult to control. Residual stress introduced during drawing can also trigger springback deformation. These issues severely restrict the fabrication efficiency and quality of magnesium alloy thin-walled microtubes.

[0004] To address these issues, existing technologies employ ultrasonic vibration-assisted drawing techniques. For instance, thin-walled microtube drawing devices reduce friction by providing a vibration field to the drawing die. Furthermore, research has shown the use of a combined warm drawing and ultrasonic-assisted drawing process to manufacture magnesium alloy microtubes. While these ultrasonic-assisted methods can reduce friction between the metal material and the die to some extent and improve lubrication, their impact on improving the plasticity of the material itself is limited.

[0005] On the other hand, while electro-pulse assisted machining technology has been applied in the field of magnesium alloy processing, it is mostly used for post-drawing annealing or hot drawing processes. There are no reports of combining electro-pulse with ultrasonic vibration in the cold drawing process of thin-walled microtubes in magnesium alloys. An electro-pulse-ultrasonic multi-field coupling assisted progressive forming device exists, but this device is suitable for dieless forming of sheet metal, and belongs to a completely different technical field and product form from thin-walled microtube drawing.

[0006] Furthermore, longitudinal-torsional combined ultrasonic vibration technology has been developed in the processing field. Longitudinal-torsional ultrasonic tensile devices have been developed that utilize threaded grooves at the amplitude transformer to achieve longitudinal-torsional combined ultrasonic vibration; however, this technology is currently applied to general tensile testing and has not yet been introduced into thin-walled microtube drawing processes.

[0007] In summary, existing ultrasonic-assisted drawing devices and electrical pulse-assisted processing devices are all single-energy-field auxiliary methods or applied to different technical fields. No technical solution has yet been found that effectively integrates ultrasonic vibration, electrical pulses, and longitudinal-torsional combined motion into a single magnesium alloy thin-walled microtube drawing device. The aforementioned single-aid methods have limited effect on improving the drawing performance of magnesium alloy thin-walled microtubes, and the deformation per pass is still insufficient to meet the requirements for efficient fabrication. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide an ultrasonic-electric pulse composite-assisted longitudinal torsion drawing device and method for magnesium alloy thin-walled microtubes. This device can reduce the drawing force, improve the material flow uniformity, and effectively improve the single-pass deformation and forming quality of magnesium alloy thin-walled microtubes through the synergistic effect of ultrasonic vibration, electric pulse and longitudinal torsion composite motion.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides an ultrasonic electrical pulse composite-assisted longitudinal torsion drawing device for thin-walled magnesium alloy microtubes, mounted on a linear motion platform, comprising: An ultrasonic transducer includes a rear cover, a piezoelectric crystal, and an outer mold ultrasonic transducer, wherein the rear cover and the outer mold ultrasonic transducer clamp and fix the piezoelectric crystal by hexagonal screws. An amplitude transformer is bolted to the outer ultrasonic transducer. The amplitude transformer is provided with a spiral groove to convert the longitudinal ultrasonic vibration into a composite vibration of longitudinal and torsional forces. A die is threadedly mounted on the amplitude transformer, and the die has a forming cavity for drawing thin-walled magnesium alloy microtubes. A drill chuck, mounted on the linear motion platform, is used to hold the front end of a magnesium alloy thin-walled microtube that is protruding from the die. A pulse power supply, the positive terminal of which is connected to the drill chuck via a positive cable, and the negative terminal of which is connected to the amplitude transformer via a negative cable; The rear cover, outer mold ultrasonic transducer, amplitude transformer, and die are all equipped with coaxial hollow channels to allow magnesium alloy thin-walled microtubes to pass through. By integrating the ultrasonic transducer, the amplitude transformer with spiral grooves, the die, the drill chuck, and the pulse power supply into the same device, ultrasonic vibration energy field, electric pulse energy field, and longitudinal torsional mechanical motion field can be applied simultaneously during the drawing process of magnesium alloy thin-walled microtubes, achieving multi-energy field synergistic assisted drawing. Ultrasonic vibration can effectively reduce the friction between the microtube and the die, electric pulses can reduce the material deformation resistance, and the longitudinal torsional composite motion generated by the spiral grooves can improve the material flow uniformity. The synergistic effect of the three can significantly improve the single-pass deformation amount and forming quality of magnesium alloy thin-walled microtubes.

[0010] In some embodiments, the amplitude transformer has 3 to 6 spiral grooves, a spiral angle of 30° to 60°, a pitch of 5 mm to 20 mm, and a groove depth of 2 mm to 5 mm. By selecting 3 to 6 spiral grooves, a spiral angle of 30° to 60°, a pitch of 5 mm to 20 mm, and a groove depth of 2 mm to 5 mm, ultrasonic longitudinal vibration can be efficiently converted into a composite vibration of longitudinal and torsional forces. This achieves good longitudinal-torsional efficiency while ensuring the structural strength of the amplitude transformer, providing a stable longitudinal-torsional composite motion output for the die, thereby effectively promoting the tangential flow of material within the molding cavity.

[0011] In some embodiments, the amplitude transformer is made of 40Cr steel or titanium alloy, with a total length of 100mm to 300mm. Using 40Cr steel or titanium alloy ensures a good balance between acoustic transmission performance and sufficient mechanical strength and fatigue life. The total length of the amplitude transformer, set to 100mm to 300mm, facilitates resonance within the commonly used ultrasonic frequency range. Combined with the helical groove, it achieves frequency degeneracy, improving the energy conversion efficiency and output stability of the longitudinal-torsional composite vibration.

[0012] In some embodiments, the forming cavity of the die is sequentially divided into a lubrication zone, a reduction zone, and a sizing zone along the drawing direction. The cone angle of the lubrication zone is 20°–40°, the cone angle of the reduction zone is 6°–16°, and the length of the sizing zone is 0.5 mm–2.0 mm. By sequentially arranging the lubrication zone, reduction zone, and sizing zone along the drawing direction, and defining the cone angle of the lubrication zone as 20°–40°, the cone angle of the reduction zone as 6°–16°, and the length of the sizing zone as 0.5 mm–2.0 mm, the microtube can be smoothly introduced, uniformly reduced in diameter, and precisely sizingd sequentially during the drawing process, reducing drawing resistance and ensuring the final dimensional accuracy and surface quality of the microtube.

[0013] In some embodiments, the piezoelectric wafer is a PZT-8 type piezoelectric ceramic sheet with a diameter of 30mm to 60mm and a thickness of 2mm to 6mm; the die is made of cemented carbide or mold steel. Using a PZT-8 type piezoelectric ceramic sheet provides a high electromechanical coupling coefficient and low dielectric loss, making it suitable for high-power ultrasonic driving applications. The piezoelectric wafer, with a diameter of 30mm to 60mm and a thickness of 2mm to 6mm, can provide the ultrasonic power output required for the drawing process. The die, made of cemented carbide or mold steel, has good wear resistance and dimensional stability, extending the die's service life and ensuring the quality of the drawing process.

[0014] In some embodiments, the ultrasonic transducer, amplitude transformer, and die constitute an ultrasonic vibration system. During drawing, the magnesium alloy thin-walled microtube contacts the inner wall of the die's forming cavity to receive ultrasonic vibration. The ultrasonic transducer, amplitude transformer, and die form a complete ultrasonic vibration system. During drawing, the magnesium alloy thin-walled microtube directly contacts the inner wall of the die's forming cavity, enabling the ultrasonic vibration to effectively act on the contact interface between the microtube and the die, fully utilizing the friction-reducing and load-reducing effects of ultrasonic vibration, and reducing drawing force and the risk of surface damage.

[0015] In some embodiments, the pulse power supply, positive cable, drill chuck, magnesium alloy thin-walled microtube, die, amplitude transformer, and negative cable constitute an electrical pulse circuit, allowing the pulse current to pass through the deformation region along the axial direction of the magnesium alloy thin-walled microtube. The pulse power supply, through the positive cable, drill chuck, magnesium alloy thin-walled microtube, die, amplitude transformer, and negative cable, forms a complete electrical pulse circuit, allowing the pulse current to pass directly through the drawing deformation region along the microtube's axial direction. This circuit has a compact structure and a short current path, ensuring that the electrical pulse acts efficiently on the material in the deformation region, fully utilizing the thermal effect of the electrical pulse and the non-thermal effect of the electron wind, effectively reducing the material's deformation resistance and improving its plasticity.

[0016] This invention also provides a method for longitudinal torsion drawing of thin-walled magnesium alloy microtubes using ultrasonic electrical pulse composite-assisted methods, comprising the following steps: Step S1: Install the drill chuck and ultrasonic transducer onto the linear motion platform, connect the drill chuck to the positive terminal of the pulse power supply using a positive cable, and connect the amplitude transformer to the negative terminal of the pulse power supply using a negative cable. Step S2: Pre-treatment of the magnesium alloy thin-walled microtubes to be drawn: Place the microtubes in acetone solution and ultrasonically clean for 5 min to 15 min to remove surface oil; then uniformly coat the outer surface of the microtubes with graphite emulsion or molybdenum disulfide lubricant, with a coating thickness of 0.01 mm to 0.05 mm; after coating, air dry at room temperature for 10 min to 30 min. Step S3: Flatten the front end of the microtube so that the outer diameter after flattening is smaller than the inlet diameter of the cavity forming cavity. Then, pass the microtube through the back cover, the outer mold ultrasonic transducer, the amplitude transformer and the hollow channel of the cavity in sequence. Hold and fix the front end of the microtube that has passed through with a drill chuck. Step S4: Lock the drill chuck that clamps the microtube onto the linear motion platform and check whether the microtube axis is straight; Step S5: First, turn on the ultrasonic transducer power supply. After the ultrasonic vibration stabilizes for 2 to 5 seconds, turn on the pulse power supply. After the pulse power supply is turned on for 1 to 3 seconds, start the linear motion platform and begin pulling at the set pulling speed. Step S6: When the magnesium alloy thin-walled microtube is completely drawn out of the die, first stop the linear motion platform, then sequentially turn off the pulse power supply and the ultrasonic transducer power supply to complete the drawing process. Through proper wiring and installation in Step S1, cleaning and lubrication pretreatment in Step S2, microtube insertion and clamping in Step S3, alignment check in Step S4, timing control of ultrasonic start-up followed by electrical pulse start-up in Step S5, and standardized shutdown operation in Step S6, it is possible to ensure the orderly activation of each energy field in the device, avoid microtube damage or equipment failure due to improper operation, guarantee the stability and repeatability of the drawing process, and achieve the preparation of high-quality magnesium alloy thin-walled microtubes.

[0017] In some embodiments, in step S5, the vibration frequency of the ultrasonic transducer is 20kHz to 40kHz, and the amplitude is 5μm to 20μm; the current density of the pulse power supply is 10A / mm² to 50A / mm², the pulse frequency is 100Hz to 1000Hz, and the duty cycle is 10% to 50%; the drawing speed of the linear motion platform is 1mm / min to 20mm / min. An ultrasonic vibration frequency of 20kHz to 40kHz and an amplitude of 5μm to 20μm provide sufficient vibration energy to reduce friction while avoiding damage to the microtube surface from excessive amplitude; a current density of 10A / mm² to 50A / mm², a pulse frequency of 100Hz to 1000Hz, and a duty cycle of 10% to 50% ensure the softening effect of the electrical pulse while preventing overheating of the microtube; and a drawing speed of 1mm / min to 20mm / min balances drawing efficiency and forming quality. The combination of the above parameter ranges provides an adjustable optimization space for the drawing process of thin-walled microtubes of different grades of magnesium alloy.

[0018] In some embodiments, when the magnesium alloy thin-walled microtube is made of AZ31B material with an initial outer diameter of 3.0 mm and a wall thickness of 0.3 mm, the ultrasonic frequency is 28 kHz, the amplitude is 10 μm, the current density is 30 A / mm², the pulse frequency is 500 Hz, the duty cycle is 30%, and the drawing speed is 5 mm / min. When the microtube has an initial outer diameter of 3.0 mm and a wall thickness of 0.3 mm, using a specific parameter combination of 28 kHz ultrasonic frequency, 10 μm amplitude, 30 A / mm² current density, 500 Hz pulse frequency, 30% duty cycle, and 5 mm / min drawing speed can achieve the best composite auxiliary effect, significantly reducing the drawing force and increasing the single-pass diameter reduction rate. This provides a directly applicable preferred process solution for the efficient and high-quality drawing of AZ31B magnesium alloy thin-walled microtubes.

[0019] The beneficial effects of this invention are: First, by using the synergistic effect of the ultrasonic transducer and the amplitude transformer, high-frequency ultrasonic vibration is provided to the die, which can effectively reduce the friction and drawing force between the magnesium alloy thin-walled microtube and the die forming cavity, reduce the contact stress, and thus significantly suppress the initiation of surface scratches and microcracks caused by friction, thereby improving the surface quality of the microtube.

[0020] Secondly, by directly applying an axial pulsed current to the magnesium alloy thin-walled microtube in the drawing deformation zone using a pulsed power supply, the thermal effect of the electric pulse is used to reduce the energy barrier for dislocation movement. At the same time, the non-thermal effect of the electron wind is used to promote dislocation slip, which can reduce the yield strength and deformation resistance of the material, alleviate work hardening, improve the plasticity of magnesium alloy at room temperature, and reduce the risk of necking and fracture during the drawing process.

[0021] Third, a spiral groove is set on the amplitude transformer to convert the longitudinal vibration into a composite high-frequency vibration of longitudinal and torsional forces under ultrasonic vibration, causing the die to generate a composite longitudinal-torsional motion. This motion causes periodic compression and relaxation between the microtube and the die, promoting microscopic plastic flow on the surface of the microtube, facilitating tangential flow of material in the molding cavity, effectively improving the uniformity of wall thickness reduction, and reducing the risk of tearing and breakage.

[0022] Fourth, by integrating the ultrasonic vibration energy field, the electric pulse energy field, and the longitudinal torsional mechanical motion field into the drawing process, the three elements work together from different dimensions to produce a significant synergistic effect: ultrasonic vibration mainly improves the interfacial friction between the microtube and the mold, reducing the drawing force; electric pulse mainly improves the plasticity of the material itself, reducing the deformation resistance; and the longitudinal torsional composite motion optimizes the flow state of the material in the forming cavity, improving the wall thickness uniformity. The synergistic cooperation of these three elements can significantly increase the single-pass deformation of magnesium alloy thin-walled microtubes, achieving efficient fabrication while obtaining high-quality thin-walled microtubes with smooth surfaces and uniform wall thickness. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0024] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present invention; Figure 2 for Figure 1 Enlarged view of section A in the middle; Figure 3 This is a schematic diagram of the electrical pulse circuit according to an embodiment of the present invention; Figure 4This is a flowchart illustrating the longitudinal torsion drawing method for thin-walled magnesium alloy microtubes according to an embodiment of the present invention.

[0025] The meanings of the markings in the diagram are as follows: 1—Back cover; 2—Hex socket screw; 3—Piezoelectric crystal; 4—Outer mold ultrasonic transducer; 5—Bolt; 6—Amplitude rod; 7—Die; 8—Magnesium alloy thin-walled microtube; 9—Drill chuck; 10—Linear motion platform; 11—Pulse power supply; 12—Positive cable; 13—Negative cable; 14—Helical groove; 15—Forming cavity; 151—Lubrication area; 152—Reduction area; 153—Sizing area. Detailed Implementation

[0026] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings, are intended to cover non-exclusive inclusion.

[0028] The directional and positional terms used in this invention, such as up, down, front, back, left, right, inside, outside, top, bottom, side, etc., are merely for reference to the accompanying drawings. Therefore, the directional and positional terms used are for illustrating and understanding this invention, and not for limiting the scope of protection of this invention.

[0029] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments: Example 1 like Figure 1 As shown, this embodiment provides an ultrasonic-electric pulse composite-assisted longitudinal torsion drawing device for magnesium alloy thin-walled microtubes, which is mounted on a linear motion platform 10. The device includes an ultrasonic transducer, an amplitude transformer 6, a die 7, a drill chuck 9, and a pulse power supply 11.

[0030] The ultrasonic transducer consists of a rear cover 1, a piezoelectric crystal 3, and an outer mold ultrasonic transducer 4. The piezoelectric crystal 3 is a PZT-8 type piezoelectric ceramic sheet with a diameter of 30mm to 60mm and a thickness of 2mm to 6mm. The rear cover 1 and the outer mold ultrasonic transducer 4 are clamped and fixed to the piezoelectric crystal 3 by hexagonal screws 2, forming a stable ultrasonic excitation source.

[0031] The amplitude transformer 6 is mounted on the outer mold ultrasonic transducer 4 via bolts 5. The amplitude transformer 6 is made of 40Cr steel or titanium alloy, with a total length of 100mm to 300mm. The amplitude transformer 6 is provided with helical grooves 14, the number of which is 3 to 6, with a helix angle of 30° to 60°, a pitch of 5mm to 20mm, and a groove depth of 2mm to 5mm. These helical grooves 14 are used to convert the longitudinal vibration generated by the ultrasonic transducer into a composite vibration of longitudinal and torsional forces, thereby providing the concave mold 7 with a combined longitudinal and torsional motion.

[0032] The die 7 is threaded onto the luffing rod 6. The die 7 is made of cemented carbide (preferably YG8) or mold steel and has a forming cavity 15 inside. Figure 2 As shown, the forming cavity 15 is divided into a lubrication zone 151, a reduction zone 152, and a sizing zone 153 along the drawing direction. The cone angle of the lubrication zone 151 is 20° to 40°, the cone angle of the reduction zone 152 is 6° to 16°, and the length of the sizing zone 153 is 0.5 mm to 2.0 mm. The inlet diameter of the forming cavity 15 is 3 mm to 8 mm, and the outlet diameter is 1 mm to 5 mm.

[0033] The drill chuck 9 is mounted on the linear motion platform 10 and is used to clamp the front end of the magnesium alloy thin-walled microtube 8 that passes through the die 7. The rear cover 1, the outer mold ultrasonic transducer 4, the amplitude transformer 6, and the die 7 are all provided with coaxial hollow channels, the inner diameter of which is larger than the outer diameter of the magnesium alloy thin-walled microtube 8, to ensure that the microtube can pass through freely. During the pulling process, the magnesium alloy thin-walled microtube 8 passes through the hollow channels from left to right, and the front end is flattened and clamped and fixed by the drill chuck 9.

[0034] The positive terminal of the pulse power supply 11 is connected to the drill chuck 9 via the positive cable 12, and the negative terminal is connected to the amplitude transformer 6 via the negative cable 13. Thus, as... Figure 3 As shown, a complete electrical pulse circuit is formed: pulse power supply 11 → positive cable 12 → drill chuck 9 → magnesium alloy thin-walled microtube 8 → die 7 → amplitude transformer 6 → negative cable 13 → pulse power supply 11. During drawing, the pulse current flows along the axial direction of the magnesium alloy thin-walled microtube 8 through the deformation area.

[0035] In this embodiment, the ultrasonic transducer, the amplitude transformer 6, and the die 7 constitute an ultrasonic vibration system. During the drawing process, the magnesium alloy thin-walled microtube 8 contacts the inner wall of the die 7 within the forming cavity 15, thereby receiving ultrasonic vibrations.

[0036] Example 2 like Figure 4 As shown, this embodiment of the invention provides a method for drawing magnesium alloy thin-walled microtubes using the above-described device, comprising the following steps: Step S1: Install the drill chuck 9 and the ultrasonic transducer onto the linear motion platform 10 as a whole, ensuring that the installation is firm and the position is aligned; connect the drill chuck 9 to the positive terminal of the pulse power supply 11 using the positive cable 12, and connect the amplitude transformer 6 to the negative terminal of the pulse power supply 11 using the negative cable 13, ensuring that the electrical connection is reliable.

[0037] Step S2: Pre-treat the magnesium alloy thin-walled microtube 8 to be drawn: place it in acetone solution and ultrasonically clean for 5 min to 15 min to remove surface oil; then uniformly coat the outer surface with graphite emulsion or molybdenum disulfide lubricant, with a coating thickness of 0.01 mm to 0.05 mm; after coating, air dry at room temperature for 10 min to 30 min.

[0038] Step S3: Flatten the front end of the pretreated magnesium alloy thin-walled microtube 8 so that the outer diameter after flattening is smaller than the inlet diameter of the forming cavity 15 of the die 7; then pass the microtube through the back cover 1, the outer mold ultrasonic transducer 4, the amplitude transformer 6 and the hollow channel of the die 7 in sequence, and clamp and fix the front end of the microtube that has passed through with the drill chuck 9, controlling the clamping force to prevent damage or slippage.

[0039] Step S4: Lock the drill chuck 9 onto the linear motion platform 10 and check whether the microtube axis is straight to avoid loosening or displacement affecting the pulling quality.

[0040] Step S5: After confirming that there are no abnormalities in the equipment, first turn on the ultrasonic transducer power supply. After the ultrasonic vibration stabilizes for 2 to 5 seconds, turn on the pulse power supply 11. After the pulse power supply 11 is turned on for 1 to 3 seconds, start the linear motion platform 10 and start pulling at the set pulling speed.

[0041] Step S6: Observe the drawing state. When the magnesium alloy thin-walled microtube 8 is completely drawn out of the die 7 without defects, first stop the linear motion platform 10, and then turn off the pulse power supply 11 and the ultrasonic transducer power supply in sequence to complete the drawing.

[0042] Example 3 In the above drawing method, the vibration frequency of the ultrasonic transducer can be set to 20kHz~40kHz, and the amplitude to 5μm~20μm; the current density of the pulse power supply 11 is 10A / mm²~50A / mm², the pulse frequency is 100Hz~1000Hz, and the duty cycle is 10%~50%; the drawing speed of the linear motion platform 10 is 1mm / min~20mm / min. These parameters are optimized based on the material, wall thickness, and diameter reduction of the magnesium alloy thin-walled microtube.

[0043] As preferred examples, for AZ31B magnesium alloy thin-walled microtubes (initial outer diameter 3.0 mm, wall thickness 0.3 mm), the ultrasonic frequency is 28 kHz, the amplitude is 10 μm, the current density is 30 A / mm², the pulse frequency is 500 Hz, the duty cycle is 30%, and the drawing speed is 5 mm / min. For WE43 magnesium alloy thin-walled microtubes (initial outer diameter 2.5 mm, wall thickness 0.2 mm), the ultrasonic frequency is 35 kHz, the amplitude is 8 μm, the current density is 25 A / mm², the pulse frequency is 800 Hz, the duty cycle is 20%, and the drawing speed is 3 mm / min.

[0044] like Figures 1 to 3 As shown, the working principle of this invention is as follows: During drawing, the ultrasonic transducer is activated, and the piezoelectric crystal 3 generates mechanical vibration under high-frequency electric field excitation. This vibration is transmitted to the die 7 through the outer mold ultrasonic transducer 4 and the amplitude transformer 6. The spiral groove 14 on the amplitude transformer 6 converts the longitudinal vibration into a combined longitudinal-torsional vibration, causing the die 7 to simultaneously generate axial high-frequency vibration and tangential high-frequency torsion. At the same time, the pulse power supply 11 applies a pulsed current to the microtube through a circuit consisting of the positive electrode cable 12, the drill chuck 9, the magnesium alloy thin-walled microtube 8, the die 7, the amplitude transformer 6, and the negative electrode cable 13. The current passes axially through the deformation zone, generating Joule heating effect and electron wind non-thermal effect, reducing the material yield strength and alleviating work hardening. Driven by the linear motion platform 10, the magnesium alloy thin-walled microtube 8 sequentially passes through the lubrication zone 151, the reduction zone 152, and the sizing zone 153 within the forming cavity 15 to complete the reduction drawing. Ultrasonic vibration reduces the friction and forming force between the microtube and the die 7, electrical pulses reduce the deformation resistance, and longitudinal torsional composite motion promotes tangential material flow and improves wall thickness uniformity. The three work together to effectively improve the deformation amount and forming quality per pass.

[0045] Example 4: A comparative drawing test was conducted using AZ31B magnesium alloy thin-walled microtubes (initial outer diameter 3.0 mm, wall thickness 0.3 mm) under room temperature and graphite emulsion lubrication conditions. Three tests were performed for each group, and the average value was taken. The target diameter reduction was to 2.5 mm. Control group 1 (conventional cold drawing): peak drawing force 520N±15N, obvious necking and surface scratches, wall thickness non-uniformity ±0.03mm, maximum reduction rate per pass approximately 12%.

[0046] Control group 2 (ultrasound-assisted only, 28kHz, 10μm): peak drawing force 380N±10N, reduced surface scratches, wall thickness non-uniformity ±0.018mm, maximum diameter reduction per pass approximately 18%.

[0047] Control group 3 (electric pulse only, 30A / mm², 500Hz, 30%): peak drawing force 410N±12N, elongation improved, slight scratches still present, wall thickness non-uniformity ±0.025mm.

[0048] Control group 4 (ultrasound + electrical pulse combined assistance, no longitudinal torsion): peak drawing force 320N±10N, good surface quality, wall thickness non-uniformity ±0.015mm, maximum reduction rate per pass approximately 22%.

[0049] Example 4 of the present invention (ultrasound + electrical pulse + longitudinal torsion composite, spiral groove parameters as in Example 1): peak drawing force 290N±8N, reduced by about 44%; smooth surface with no visible defects, wall thickness non-uniformity ±0.010mm; maximum diameter reduction rate per pass is more than 25%, and the material is free from cracking and necking.

[0050] The results show that the combined effect of ultrasonic vibration, electrical pulse and longitudinal torsional motion is significantly better than any single auxiliary method or a simple combination of the two.

[0051] The device of this invention has a compact structure and is easy to operate. It is suitable for drawing thin-walled microtubes of magnesium alloys such as AZ31B, WE43, and ZK60, as well as other difficult-to-deform metals, and has good prospects for industrial application.

[0052] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this invention; the scope of protection of this invention is defined by the claims in the claims, and all equivalent changes and modifications made in accordance with this invention are within the scope of protection of this patent.

Claims

1. An ultrasonic electrical pulse composite-assisted longitudinal torsion drawing device for magnesium alloy thin-walled microtubes, mounted on a linear motion platform, characterized in that: include: An ultrasonic transducer includes a rear cover, a piezoelectric crystal, and an outer mold ultrasonic transducer, wherein the rear cover and the outer mold ultrasonic transducer clamp and fix the piezoelectric crystal by hexagonal screws. An amplitude transformer is bolted to the outer ultrasonic transducer. The amplitude transformer is provided with a spiral groove to convert the longitudinal ultrasonic vibration into a composite vibration of longitudinal and torsional forces. A die is threadedly mounted on the amplitude transformer, and the die has a forming cavity for drawing thin-walled magnesium alloy microtubes. A drill chuck, mounted on the linear motion platform, is used to hold the front end of a magnesium alloy thin-walled microtube that is protruding from the die. A pulse power supply, the positive terminal of which is connected to the drill chuck via a positive cable, and the negative terminal of which is connected to the amplitude transformer via a negative cable; The rear cover, outer mold ultrasonic transducer, amplitude transformer, and concave mold are all provided with coaxial hollow channels for magnesium alloy thin-walled microtubes to pass through.

2. The ultrasonic electrical pulse composite-assisted longitudinal torsion drawing device for thin-walled magnesium alloy microtubes according to claim 1, characterized in that: The number of helical grooves on the amplitude transformer is 3 to 6, the helical angle is 30° to 60°, the pitch is 5mm to 20mm, and the groove depth is 2mm to 5mm.

3. The ultrasonic electrical pulse composite-assisted longitudinal torsion drawing device for thin-walled magnesium alloy microtubes according to claim 1, characterized in that: The amplitude transformer is made of 40Cr steel or titanium alloy, and its total length is 100mm to 300mm.

4. The ultrasonic electrical pulse composite-assisted longitudinal torsion drawing device for thin-walled magnesium alloy microtubes according to claim 1, characterized in that: The forming cavity of the die is divided into a lubrication zone, a reduction zone, and a sizing zone along the drawing direction. The cone angle of the lubrication zone is 20° to 40°, the cone angle of the reduction zone is 6° to 16°, and the length of the sizing zone is 0.5 mm to 2.0 mm.

5. The ultrasonic electrical pulse composite-assisted longitudinal torsion drawing device for thin-walled magnesium alloy microtubes according to claim 1, characterized in that: The piezoelectric wafer is a PZT-8 type piezoelectric ceramic sheet with a diameter of 30mm to 60mm and a thickness of 2mm to 6mm; the die is made of cemented carbide or mold steel.

6. The ultrasonic electrical pulse composite-assisted longitudinal torsion drawing device for thin-walled magnesium alloy microtubes according to claim 1, characterized in that: The ultrasonic transducer, amplitude transformer, and die constitute an ultrasonic vibration system. During drawing, the magnesium alloy thin-walled microtube contacts the inner wall of the forming cavity of the die to receive ultrasonic vibration.

7. The ultrasonic electrical pulse composite-assisted longitudinal torsion drawing device for thin-walled magnesium alloy microtubes according to claim 1, characterized in that: The pulse power supply, positive cable, drill chuck, magnesium alloy thin-walled microtube, die, amplitude transformer, and negative cable constitute an electrical pulse circuit, causing the pulse current to pass through the deformation region along the axial direction of the magnesium alloy thin-walled microtube.

8. A method for longitudinal torsion drawing of magnesium alloy thin-walled microtubes assisted by ultrasonic electrical pulses, using the ultrasonic electrical pulse assisted longitudinal torsion drawing device for magnesium alloy thin-walled microtubes as described in any one of claims 1 to 7, characterized in that: Includes the following steps: Step S1: Install the drill chuck and ultrasonic transducer onto the linear motion platform, connect the drill chuck to the positive terminal of the pulse power supply using a positive cable, and connect the amplitude transformer to the negative terminal of the pulse power supply using a negative cable. Step S2: Pre-treatment of the magnesium alloy thin-walled microtubes to be drawn: Place the microtubes in acetone solution and ultrasonically clean for 5 min to 15 min to remove surface oil; then uniformly coat the outer surface of the microtubes with graphite emulsion or molybdenum disulfide lubricant, with a coating thickness of 0.01 mm to 0.05 mm; after coating, air dry at room temperature for 10 min to 30 min. Step S3: Flatten the front end of the microtube so that the outer diameter after flattening is smaller than the inlet diameter of the cavity forming cavity. Then, pass the microtube through the back cover, the outer mold ultrasonic transducer, the amplitude transformer and the hollow channel of the cavity in sequence. Hold and fix the front end of the microtube that has passed through with a drill chuck. Step S4: Lock the drill chuck that clamps the microtube onto the linear motion platform and check whether the microtube axis is straight; Step S5: First, turn on the ultrasonic transducer power supply. After the ultrasonic vibration stabilizes for 2 to 5 seconds, turn on the pulse power supply. After the pulse power supply is turned on for 1 to 3 seconds, start the linear motion platform and begin pulling at the set pulling speed. Step S6: When the magnesium alloy thin-walled microtube is completely pulled out of the die, first stop the linear motion platform, then turn off the pulse power supply and the ultrasonic transducer power supply in sequence to complete the pulling process.

9. The ultrasonic-electric pulse composite-assisted longitudinal torsion drawing method for thin-walled magnesium alloy microtubes according to claim 8, characterized in that: In step S5, the vibration frequency of the ultrasonic transducer is 20kHz to 40kHz, and the amplitude is 5μm to 20μm; the current density of the pulse power supply is 10A / mm² to 50A / mm², the pulse frequency is 100Hz to 1000Hz, and the duty cycle is 10% to 50%; the pulling speed of the linear motion platform is 1mm / min to 20mm / min.

10. The ultrasonic-electric pulse composite-assisted longitudinal torsion drawing method for thin-walled magnesium alloy microtubes according to claim 9, characterized in that: When the magnesium alloy thin-walled microtube is made of AZ31B material, with an initial outer diameter of 3.0 mm and a wall thickness of 0.3 mm, the ultrasonic frequency is 28 kHz, the amplitude is 10 μm, the current density is 30 A / mm², the pulse frequency is 500 Hz, the duty cycle is 30%, and the drawing speed is 5 mm / min.

Images