Ultra-long nickel-titanium alloy ultrafine wire drawing method

Abstract

The invention discloses a method for drawing an ultra-long nickel-titanium alloy ultrafine wire. The method comprises the following steps: carrying out heat treatment on a nickel-titanium alloy wire to be drawn; continuously drawing the obtained wire in a martensite phase state by using a wire drawing machine; the steps are continuously repeated until the diameter and the length of the wire reach preset targets; according to the method, drawing is carried out in a martensite phase (the elastic modulus is 30-40 GPa), the deformation resistance of the wire is remarkably reduced, the unit pressure on the hole wall of a mold is reduced, the abrasion rate is fundamentally reduced, the continuous drawing length of the single-disc wire is larger than or equal to 10000 m, the size is not out of tolerance and is more than two times that of a traditional method (-5000 m), the production requirement of the super-filament is met, and the production cost is reduced. The service life of the die and the length of a single coiled wire are greatly prolonged.

Description

Technical Field

[0001] This invention belongs to the field of precision metal wire processing, and in particular relates to a method for drawing ultra-long nickel-titanium alloy ultra-fine wires. Background Technology

[0002] With the rapid development of minimally invasive interventional medical devices, the market demand for ultra-fine (diameter ≤0.1mm), ultra-long (single coil length reaches tens of thousands of meters) nickel-titanium alloy wires with strict dimensional tolerances is becoming increasingly urgent. However, existing technologies face severe challenges when drawing such ultra-fine wires: because nickel-titanium alloys are usually in the austenitic phase with a high elastic modulus (70~85 GPa) at room temperature, their deformation resistance is high. During high-speed drawing, this generates enormous pressure and friction on the diamond die hole wall, leading to severe and rapid wear and hole expansion of the die. Typically, after drawing only 2000 to 5000 meters, the wire diameter exceeds the tolerance range of ±0.001mm due to changes in the die hole diameter, necessitating a machine shutdown and die replacement. This not only limits the length of single coil wires to a relatively short range, failing to meet the continuous production needs of downstream weaving industries, but also significantly increases production costs due to the extremely high cost of expensive diamond die consumables. Although the industry has tried to alleviate this problem by optimizing mold materials and lubrication conditions, none of these methods have been able to fundamentally and effectively solve the problem of high wear caused by high-modulus austenitic phases. Summary of the Invention

[0003] The purpose of this invention is to provide a method for drawing ultra-long nickel-titanium alloy ultra-fine wires, which stably maintains the wire in the martensitic phase during drawing, significantly reduces wear on the die, and enables stable production of wires with lengths of over 10,000 meters per disc.

[0004] This invention adopts the following technical solution: a method for drawing ultra-long nickel-titanium alloy ultrafine wires, comprising: The nickel-titanium alloy wire to be drawn is heat-treated; the obtained wire is continuously drawn in the martensitic phase using a wire drawing machine. Repeat the above steps until the wire diameter and length reach the predetermined target. During the drawing process, the temperature of the drawing lubricant in the lubricant storage tank of the drawing machine is 5~30°C below the martensitic phase transformation end temperature of the wire.

[0005] The beneficial effects of this invention are: This invention significantly reduces the deformation resistance of the wire by drawing it through a martensitic phase (elastic modulus 30~40 GPa), thereby reducing the unit pressure on the die hole wall and fundamentally lowering the wear rate. This allows for continuous drawing of single-coil wire lengths ≥10,000 meters without exceeding dimensional tolerances, more than twice that of traditional methods (~5,000 meters). This meets the production requirements for ultra-long wires and greatly extends die life and single-coil wire length. This invention can reduce mold wear, thereby reducing the frequency of mold replacement, directly reducing the consumption cost of expensive diamond molds, enabling large-scale mass production of ultra-fine nickel-titanium wires, and significantly reducing production costs. Detailed Implementation

[0006] The present invention will now be described in detail with reference to specific embodiments.

[0007] This invention discloses a method for drawing ultra-long nickel-titanium alloy ultra-fine wires, comprising: The nickel-titanium alloy wire to be drawn is heat-treated; the obtained wire is continuously drawn in the martensitic phase using a wire drawing machine. Repeat the above steps until the wire diameter and length reach the predetermined target. Before heat treatment, the phase transformation temperature of the nickel-titanium alloy wire blank needs to be tested. First, differential scanning calorimetry (DSC) is used to accurately determine the martensitic phase transformation end temperature M of the nickel-titanium alloy wire blank. f .

[0008] During the drawing process, the temperature of the drawing lubricant in the lubricant storage tank of the drawing machine is 5~30°C below the martensitic phase transformation end temperature of the wire.

[0009] The diameter of the nickel-titanium alloy wire to be drawn is ≤0.1mm.

[0010] The pulling deformation is 35-45%.

[0011] The inner wall of the lubricant storage tank of the wire drawing machine is equipped with a cooling pipe. The cooling pipe is used to contain the coolant, which is a mixture of anhydrous ethanol and liquid nitrogen. The coolant is used to exchange heat with the wire drawing lubricant, thereby keeping the wire drawing lubricant 5~30°C below the martensitic phase transformation end temperature.

[0012] The lubricant storage tank of the wire drawing machine is equipped with a stirring device for stirring the wire drawing lubricant.

[0013] The wire drawing lubricant is a lubricant that remains liquid at a temperature of -30 to -80°C.

[0014] The wire drawing lubricant is a perfluoropolyether lubricant.

[0015] The wire drawing speed of the wire drawing machine is 10~100m / min. The operation process of this invention is as follows: Install the wire to be drawn onto the wire feeding device; Pass the wire end through the die of the desired drawing size, fix the die on the wire drawing machine, and finally fix the wire end to the take-up device; Inject sufficient perfluoropolyether lubricant into the water tank of the wire drawing machine to ensure that the mold is completely submerged; Set the target drawing temperature (T) on the control system. set = M f - (5~30)℃; Open the liquid nitrogen valve and add liquid nitrogen into the cooling tank containing ethanol to cool the ethanol to an extremely low temperature. Then start the pump in the cooling tank to pump the low-temperature ethanol into the cooling pipes coiled on the inner wall of the tank, so as to drastically cool the lubricant through heat exchange. Start the stirring device in the water tank to quickly and evenly heat the lubricant; A temperature sensor monitors the lubricant temperature in real time and feeds the data back to the control system. The control system dynamically adjusts the liquid nitrogen injection rate using a PID algorithm to precisely stabilize the lubricant temperature at T. set .

[0016] Once the temperature stabilizes, start the wire drawing machine to begin drawing. Set the drawing speed to 10~100m / min.

[0017] Online monitoring and intelligent control: A laser diameter gauge installed in front of the take-up device measures the diameter of the wire at high frequency and the data is transmitted to the control system in real time. The control system continuously calculates and analyzes the standard deviation or range of the diameter of the most recent 1000 meters of wire. The control logic is as follows: Normal state: If the diameter fluctuation is within ±0.001mm and the trend of change is stable (e.g., change rate <0.5~1%), the system maintains the current drawing speed.

[0018] Warning and Compensation: If the system detects a slow increase in diameter (indicating that the die may be beginning to wear slightly) and the rate of change exceeds 0.5%, it will automatically reduce the drawing speed by 10%. Reducing the speed can decrease the deformation rate, thereby partially offsetting the increase in friction caused by the slight increase in die size and the thinning of the lubricating film, keeping the drawing force stable and slowing down the wear process.

[0019] Abnormal shutdown: If the diameter suddenly changes or exceeds the tolerance range, the control system will immediately alarm and stop the machine, prompting the operator to check or replace the mold.

[0020] Drawing Completion and Post-processing: When a single coil of wire reaches the target length or all wire is drawn, stop drawing. Turn off the cooling system, drain the lubricant, and remove the wire coil. Then perform an intermediate annealing (annealing temperature 550~750℃, annealing time 30~120s) to eliminate work hardening and prepare for the next drawing pass.

[0021] For online monitoring and intelligent control, a non-contact laser diameter gauge can be used to monitor the wire diameter in real time and transmit the data to the control system. The control system is connected to the transmission system of the wire drawing machine and adjusts the machine's operating status based on the analysis results. Specifically, for wires of different diameters, the control system analyzes the diameter value of the first 1000 meters of wire (if the length of wire already drawn is less than 1000 meters at the beginning of drawing, the diameter of the already drawn length is analyzed first): When the wire diameter is greater than 0.5mm: if the diameter change rate is less than 0.5%, the current speed is maintained; if the change rate is greater than 0.5%, the drawing speed is automatically reduced by 10%~15% to compensate for the increased friction due to slight wear of the die and to maintain stable drawing force. When the wire diameter is less than or equal to 0.5 mm: if the diameter change rate is less than 1%, the current speed is maintained; if the change rate is greater than 1%, the drawing speed is automatically reduced by 10% to 15% to compensate for the increased friction caused by slight wear of the die and to maintain stable drawing force. By reducing the strain rate, the rheological stress is reduced, thereby balancing the increased friction caused by mold wear; if the diameter exceeds the tolerance, an alarm will sound and the machine will stop.

[0022] For the selection of wire drawing machines, commercially available water tank tower wheel wire drawing machines can be selected, and the water tank can be used as the lubricant storage tank of the wire drawing machine. Metal cooling pipes are designed on the four walls and bottom of the water tank of the wire drawing machine. The cooling pipes have inlets and outlets, and stirring blades are installed at the bottom of the wire drawing machine to uniformly stir the lubricant during the cooling process, so as to achieve the effect of rapid cooling and overall uniform cooling.

[0023] In practical use, anhydrous ethanol must be added to the water tank beforehand. During use, liquid nitrogen is piped from the liquid nitrogen tank to the coolant tank. A control system is located above the coolant tank, connected to the liquid nitrogen tank and a temperature-measuring thermocouple / sensor. The control system compares the thermocouple / sensor data with the actual input drawing temperature. If the temperature is higher than the set value, the liquid nitrogen content in the coolant is increased; if it is lower than the set value, the amount of liquid nitrogen added is reduced, thus regulating the lubricant temperature in real time. The control system is also connected to the mechanical pump in the lubricant storage tank of the drawing machine, controlling its on / off state, and can also control the drawing parameters and the machine's on / off state.

[0024] The lubrication cone angle β of the wire drawing machine's die is 30~50°, and the die angle α is 5~8°. This angle range can better establish hydrodynamic lubrication and reduce contact stress under low martensitic modulus conditions.

[0025] Based on the above conditions, the continuous drawing length of a single filament of the present invention can be ≥10,000 meters, and the diameter tolerance fluctuation of the filament during the drawing process can be controlled within ±0.001 mm.

[0026] Example 1: Preparation of Φ0.03mm ultralong nickel-titanium ultrafine wire Raw material: A 0.3 kg, 0.111 mm Φ Ni-50.8 at.%Ti alloy wire was used as the raw material, with a wire length of 5008 m. The phase transformation temperature M of the wire in the fully annealed state was measured by DSC. f = -16℃.

[0027] Pulling parameters: Target size: Φ0.03mm.

[0028] Mold: Polycrystalline diamond mold.

[0029] Lubricant: Perfluoropolyether low-temperature lubricating oil.

[0030] Operation process: First drawing pass: Φ0.111mm - Φ0.093mm (35% deformation). Lubricant temperature: -46℃. Speed: 10 m / min. Die: α=8°, β=50°. Annealing: 750℃ / 120s. The system operated stably during the drawing process, and the laser diameter gauge showed that the wire diameter was stable at 0.093mm±0.0004mm, and the wire length was 6794m.

[0031] Second drawing pass: Φ0.093mm - Φ0.078mm (deformation 45%). Lubricant temperature: -46℃. Speed: 50 m / min. Die: α=8°, β=40°. Annealing: 650℃ / 100s. The system operated stably during the drawing process, and the laser diameter gauge showed that the wire diameter was stable at 0.078mm±0.0004mm, and the wire length was 9658m.

[0032] Third drawing pass: Φ0.078mm - Φ0.065mm (deformation 45%). Lubricant temperature: -21℃. Speed: 80 m / min. Die: α=8°, β=40°. Annealing: 600℃ / 60s. The system operated stably during the drawing process, and the laser diameter gauge showed that the wire diameter was stable at 0.065mm±0.0003mm, and the wire length was 13908m.

[0033] Fourth drawing pass: Φ0.065mm - Φ0.03mm (deformation 45%). Lubricant temperature: -21℃. Speed: 100 m / min. Die: α=5°, β=30°. Annealing: 550℃ / 30s. The system operated stably during the drawing process, and the laser diameter gauge showed that the wire diameter was stable at 0.030mm±0.0003mm, and the wire length was 65294m.

[0034] When the wire was drawn to approximately 43,012 meters, the control system detected a slow increase in diameter (average diameter change of approximately 1.2%) and automatically reduced the drawing speed to 85 m / min. After the speed reduction, the diameter fluctuation returned to the normal range. The machine was stopped after successfully drawing 65,294 meters continuously. The diameter of the entire spool of wire was controlled within 0.100 mm ± 0.001 mm, fully meeting the technical requirements. Inspection revealed minimal wear on the die.

[0035] Comparative Example 1 (Drawing of Traditional Austenitic Wire) Using the same blank and mold as in Example 1, at room temperature (25°C, above A) f Under the condition that the wire material is in austenitic state, the wire is drawn at the same speed and the intermediate annealing process is the same.

[0036] Results: During the drawing process from Φ0.093mm to Φ0.078mm, when the wire was drawn to approximately 5232 meters, the wire diameter exceeded 0.0784mm (the wire diameter change rate reached 0.5%) and continued to increase. When the wire was drawn to 9658 meters, the wire size reached 0.0789mm, which is close to the upper tolerance.

[0037] During the drawing process from Φ0.078mm to Φ0.065mm, when the wire diameter was drawn to 6492 meters, the change rate of the wire diameter reached 0.5%. After drawing 13908 meters, the wire diameter reached 0.0663mm, which exceeded the upper tolerance by 0.066mm.

[0038] During the Φ0.065mm - Φ0.03mm drawing process, when the wire diameter reached 5642 meters, the change rate of the wire diameter reached 1%. After drawing 16285 meters, the wire diameter had reached 0.031mm, reaching the upper limit of the tolerance, and the machine was forced to stop. The mold showed obvious enlargement after measurement.

[0039] Therefore, this embodiment successfully extended the length of a single wire coil from approximately 16,285 meters in the conventional method to over 65,294 meters, and significantly reduced mold wear, demonstrating the superior effectiveness of the method of the present invention.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for drawing ultra-long nickel-titanium alloy ultrafine wires, characterized in that, include: The nickel-titanium alloy wire to be drawn is heat-treated. The obtained filament is continuously drawn in the martensitic phase using a wire drawing machine; Repeat the above steps until the wire diameter and length reach the predetermined target. During the drawing process, the temperature of the drawing lubricant in the lubricant storage tank of the drawing machine is 5~30°C below the end temperature of the martensitic phase transformation of the wire in its fully annealed state.

2. The method for drawing ultra-long nickel-titanium alloy ultrafine wires according to claim 1, characterized in that, The diameter of the nickel-titanium alloy wire to be drawn is ≤0.1mm.

3. The method for drawing ultra-long nickel-titanium alloy ultrafine wires according to claim 1, characterized in that, The drawing deformation is 35-45%.

4. The method for drawing ultra-long nickel-titanium alloy ultrafine wires according to claim 1, characterized in that, The inner wall of the lubricant storage tank of the wire drawing machine is equipped with a cooling pipe. The cooling pipe is used to contain the coolant, which is a mixture of anhydrous ethanol and liquid nitrogen. The coolant is used to exchange heat with the wire drawing lubricant, thereby keeping the wire drawing lubricant 5~30°C below the martensitic phase transformation end temperature.

5. The method for drawing ultra-long nickel-titanium alloy ultrafine wires according to claim 1, characterized in that, The lubricant storage tank of the wire drawing machine is equipped with a stirring device for stirring the wire drawing lubricant.

6. The method for drawing ultra-long nickel-titanium alloy ultrafine wires according to claim 1, characterized in that, The wire drawing lubricant is a lubricant that remains liquid at a temperature of -30 to -80°C.

7. The method for drawing ultra-long nickel-titanium alloy ultrafine wires according to claim 6, characterized in that, The wire drawing lubricant is a perfluoropolyether lubricant.

8. The method for drawing ultra-long nickel-titanium alloy ultrafine wires according to claim 1, characterized in that, The wire drawing speed of the wire drawing machine is 10~100m / min.

9. The method for drawing ultra-long nickel-titanium alloy ultrafine wires according to claim 1, characterized in that, Annealing is performed after each drawing process at a temperature of 550~750℃ for 30~120s.