Method for dynamically controlling liquid surface rising speed of titanium alloy vacuum suspension melting and pouring

Abstract

The application discloses a dynamic control method for liquid surface rising speed of titanium alloy vacuum suspension smelting and pouring, belongs to the field of titanium alloy casting and the technical field of casting forming methods, and comprises the following steps: placing titanium alloy raw materials in a vacuum cold crucible suspension smelting furnace, making the raw materials be suspended and smelted in a vacuum water-cooled copper crucible environment through a high-frequency electromagnetic field, making the melt be separated from the contact with the crucible, and obtaining clean high-temperature titanium alloy melt. The application exerts the upward braking force of the stable and constant magnetic field generated by the direct-current electromagnet on the metal liquid, and exerts the downward driving force of the traveling wave magnetic field generated by the alternating current coil on the metal liquid, cooperates with interlocking logic to avoid the simultaneous opening of the two, solves the problem that a single electromagnetic field cannot bidirectionally and accurately regulate and control the flow rate, realizes the continuous adjustable acceleration and deceleration control of the pouring speed, and provides a hardware basis for the dynamic matching of the liquid surface rising speed and the solidification speed.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy casting and the field of casting forming methods, and more specifically, to a method for dynamically controlling the rising speed of the liquid surface in vacuum suspension melting and casting of titanium alloys. Background Technology

[0002] Vacuum suspension melting (cold crucible suspension melting) technology is widely used in the vacuum casting of titanium alloys and active metals. Because it avoids refractory material contamination and achieves pure melting of high-melting-point alloys, it has become one of the mainstream manufacturing technologies for aerospace titanium alloy castings. Bottom-plug casting is a typical melt guiding method in this field. In the production of titanium alloy bar castings, axial shrinkage porosity has always been a core technical challenge restricting product quality and yield. Titanium alloys themselves have poor thermal conductivity, a wide solidification range, and large volume shrinkage, making it easy for dispersed or continuous shrinkage cavities to form along the central axis during solidification, seriously affecting the mechanical properties and subsequent processing performance of the material. Addressing this persistent industry problem, how to achieve real-time matching between the liquid level rise rate and the solidification rate during casting, ensuring the unobstructed flow of the central liquidus compensation channel, is a technical problem urgently needing to be solved in this field.

[0003] However, existing plug-in casting technology has the following drawbacks: First, once the casting is initiated, the flow rate is determined solely by gravity until the melt has completely flowed out. The casting speed is not adjustable, making it impossible to achieve precise bidirectional control of the molten metal flow. It cannot actively decelerate to suppress air entrapment caused by excessively fast initial flow rates, nor can it actively accelerate to compensate for insufficient feeding or undercasting caused by excessively slow flow rates in the later stages. Second, operators can only select the plug diameter based on experience. If the diameter is too large, the initial flow rate will be too fast, and the liquid level rise speed will exceed the solidification speed, causing the feeding channel to close prematurely and resulting in a central shrinkage cavity. If the diameter is too small, the melt flow rate will be too slow, and the liquid level rise speed will not keep up with the solidification speed, leading to defects such as cold shuts and undercasting in the casting, resulting in poor process stability and low yield. Third, existing technology lacks online quantitative characterization methods for the solidification process inside the casting. It cannot obtain the instantaneous solidification speed in real time, nor can it automatically decide to accelerate or decelerate based on the deviation between the liquid level rise speed and the solidification speed, making it difficult to adapt to the production needs of different titanium alloy grades and casting specifications.

[0004] Based on this, the present invention designs a dynamic control method for the liquid level rise speed in vacuum suspension melting and casting of titanium alloys to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for dynamically controlling the liquid level rise speed in vacuum suspension melting and casting of titanium alloys, so as to solve the problems mentioned in the background art.

[0006] A method for dynamically controlling the liquid level rise rate in vacuum suspension melting and casting of titanium alloys includes the following steps: S1. Place the titanium alloy raw material in a vacuum cold crucible suspension melting furnace, and use a high-frequency electromagnetic field to suspend and melt the raw material in a vacuum water-cooled copper crucible environment, so that the melt is separated from the crucible and a clean high-temperature titanium alloy melt is obtained. S2. The obtained high-temperature titanium alloy melt is injected into the mold through a flow guiding system set at the bottom of the crucible. The flow guiding system includes a graphite flow guiding tube, a ceramic heat insulation sleeve and a secondary high-frequency heating coil. The secondary high-frequency heating coil is powered by an independent power supply and is used to assist in heating the melt in the flow guiding tube to maintain its fluidity. S3. During the pouring process, a high-speed camera is used to capture real-time images of the liquid level inside the mold, and the instantaneous liquid level rise speed is obtained through image processing. Simultaneously, by pre-embedding thermocouple arrays at different heights and radial positions within the mold, the solidification process inside the casting is monitored in real time, and the instantaneous solidification rate is obtained. ; The high-speed camera and thermocouple array share a unified hardware trigger clock for synchronous acquisition, and the thermocouple acquisition module has a sampling frequency of no less than 10Hz; based on the factory-calibrated response time constant of the thermocouples. Time offset compensation is performed on the temperature measurement solidification time. Eliminate the calculation deviation of solidification rate caused by the second-level response lag of thermocouples; S4, Based on the preset safety compensation coefficient Calculate speed deviation Among them, the safety compensation coefficient The value range is 1.1 to 1.3, which is used to ensure that the liquid level rise rate is slightly greater than the solidification rate, so as to keep the central liquidus replenishment channel unobstructed. S5, according to The positive or negative sign automatically selects to activate or adjust the electromagnetic acceleration or deceleration device: when When the actual liquid level rises too slowly, the solidification front is about to exceed the liquid level, posing a risk of shrinkage cavities. At this point, the electromagnetic acceleration device is automatically activated or adjusted to increase the downward Lorentz force, accelerating the flow of the molten metal and increasing the rate of liquid level rise. When the actual liquid level rises too fast, it may cause inclusions or surface cold shuts. At this time, the electromagnetic deceleration device is automatically activated or adjusted to increase the upward braking force, slow down the flow of molten metal, and reduce the speed at which the liquid level rises. The acceleration device and the deceleration device are not activated at the same time to avoid mutual interference of magnetic fields. The electromagnetic deceleration device is a DC excitation structure that outputs a steady magnetic field; the electromagnetic acceleration device is an AC excitation coil that outputs a traveling wave magnetic field; the two excitation structures are independent of each other, each with its own independent power supply circuit, and the excitation current and excitation frequency are independently adjustable. S6. Repeat steps S3 to S5, dynamically adjusting the liquid level rise rate in real time to ensure it always meets the requirements. Continue until the pouring is complete.

[0007] Preferably, the electromagnetic deceleration device is a pair of DC electromagnets arranged opposite each other on both sides of the guide tube, generating a steady magnetic field in the horizontal direction passing through the guide tube. When the molten metal flows downward and cuts the magnetic field lines in the horizontal direction perpendicularly, according to Faraday's law of electromagnetic induction, an induced electromotive force is generated in the molten metal, which in turn forms an induced current loop in a plane perpendicular to the magnetic field and the flow direction. This induced current interacts with the steady magnetic field to generate a Lorentz force. According to Lenz's law, the direction of this Lorentz force is opposite to the flow direction of the molten metal, that is, upward, thereby applying a braking force to the molten metal. The magnitude of this braking force is proportional to the square of the magnetic field strength and the flow velocity of the molten metal. By adjusting the excitation current of the DC electromagnets to change the strength of the steady magnetic field, the magnitude of the braking force can be changed, thereby achieving a continuously adjustable deceleration of the molten metal flow velocity.

[0008] Preferably, the electromagnetic acceleration device is an AC coil located below the guide tube. The AC coil generates a traveling wave magnetic field that moves downward along the pouring direction. When the molten metal is in the traveling wave magnetic field, an induced current is generated in the molten metal. The induced current interacts with the traveling wave magnetic field to generate a Lorentz force. The direction of the Lorentz force is the same as the direction of movement of the traveling wave magnetic field, that is, downward, thereby driving the molten metal to flow downward at an accelerated speed. By adjusting the excitation current of the AC coil and the frequency of the traveling wave magnetic field, the magnitude of the downward Lorentz force can be changed, thereby achieving a continuously adjustable acceleration of the molten metal flow rate.

[0009] Preferably, the instantaneous solidification rate Obtained through the following steps: A set of thermocouples is arranged at different heights from bottom to top inside the mold. Each set of thermocouples is arranged radially on the same horizontal plane from the inner wall of the mold to the center line at equal intervals to monitor the process of the solidified layer advancing from the mold wall to the center. Connect each group of thermocouples to a high-speed data acquisition module with a sampling frequency of no less than 10Hz, record the temperature-time curve of each temperature measurement point in real time, and transmit the data synchronously to the control center. Based on the specific grade of the titanium alloy being smelted, its solidus temperature can be obtained through differential thermal analysis or literature references. When the temperature at a certain measuring point drops to At that point, it is determined that the metal has completely solidified, and this moment is recorded. ; use Timing compensation is performed on the solidification time. This is the measured response time constant of the thermocouple; On a plane at a certain height, the radial solidification propulsion velocity is calculated using the solidification time difference between thermocouples at adjacent radial positions: ,in The radial spacing between adjacent thermocouples. This corresponds to the solidification time difference; The axial solidification propulsion velocity is calculated using the solidification time difference of thermocouples at the same radial position on planes of different heights: ,in The distance between adjacent heights; By summarizing data from multiple height and radial positions, the variation of solidification rate with time and space during the entire solidification process of the casting was obtained, and finally, an instantaneous solidification rate curve along the axial direction was fitted. Used for dynamic control.

[0010] Preferably, the safety compensation coefficient The step-rate comparison experiment determined the specific steps, including: setting several different ratios of liquid surface rise rate to solidification rate, including... The instantaneous rise rate of the liquid surface was captured by a high-speed camera. With instantaneous solidification rate The fitted dynamic matching speed curve, combined with the electromagnetic acceleration and deceleration devices, was precisely executed. X-ray non-destructive testing was performed on the castings obtained from each group of experiments to detect shrinkage cavities or porosity along the central axis. The proportion of the titanium alloy grade with no shrinkage cavities, no porosity, and optimal microstructure was selected as the safe feeding coefficient. value.

[0011] Preferably, in step S5, an interlock logic is provided between the acceleration device and the deceleration device: when the control center determines that acceleration is needed, the system software automatically ensures that the deceleration device is in the off state, and only turns on or adjusts the acceleration device; when the control center determines that deceleration is needed, the system software automatically ensures that the acceleration device is in the off state, and only turns on or adjusts the deceleration device. When the speed is within the allowable deviation range, both the acceleration and deceleration devices remain in their current state or are turned off simultaneously to maintain a stable pouring speed.

[0012] Preferably, in step S3, a high-speed camera captures feature points of the liquid surface inside the mold in real time, and an image processing algorithm is used to calculate the displacement of the liquid surface per unit time to obtain the actual liquid surface rise rate. The velocity data is transmitted synchronously to the control center along with the solidification velocity data collected by the thermocouple array, and compared with the preset initial pouring velocity curve, which is determined in advance by the molten metal flow rate and the cross-sectional area of ​​the mold based on the law of conservation of mass.

[0013] Preferably, in step S5, when the control center determines that acceleration is needed, it increases the downward Lorentz force by increasing the excitation current of the AC coil or adjusting the frequency of the traveling wave magnetic field, thereby increasing the flow rate of the molten metal. When the control center determines that deceleration is needed, it increases the excitation current of the DC electromagnet to enhance the magnetic induction intensity of the steady magnetic field, thereby increasing the upward braking force and slowing down the flow rate of the molten metal. Both acceleration and deceleration adjustments are continuously adjustable to achieve precise dynamic control of the rising speed of the liquid surface.

[0014] Compared with the prior art, the advantages of this invention are: 1. This invention applies an upward braking force to the molten metal by setting a steady magnetic field generated by a DC electromagnet and a downward driving force to the molten metal by a traveling wave magnetic field generated by an AC coil, and uses interlocking logic to prevent both from being activated at the same time. This solves the problem that a single electromagnetic field cannot accurately control the flow rate in both directions, and realizes continuous adjustable acceleration and deceleration control of the pouring speed, providing a hardware foundation for the dynamic matching of the liquid surface rise speed and the solidification speed.

[0015] 2. This invention uses pre-embedded thermocouple arrays at different heights and radial positions within the mold to monitor the time difference between each temperature measuring point and the solidus temperature in real time. This allows for precise calculation of the radial and axial solidification propulsion speeds, which are then fitted into an instantaneous solidification speed curve along the axial direction. This enables online quantitative characterization of the solidification process inside castings, providing accurate data support for dynamic control.

[0016] 3. This invention utilizes a high-speed camera to acquire real-time images of the liquid level inside the mold, obtaining the instantaneous liquid level rise speed. And combined with the solidification rate obtained in real time Based on speed deviation The automatic decision-making to activate or adjust the electromagnetic acceleration or deceleration device enables intelligent dynamic control of the solidification-pouring coupling, which can cope with interference factors such as melt superheat fluctuations and mold temperature changes without manual intervention.

[0017] 4. This invention sets a safety compensation coefficient. (1.1–1.3) and ensure This ensures that the liquid level rises at a rate slightly higher than the solidification rate, guaranteeing that the feeding channel at the center liquidus remains unobstructed throughout the solidification process. This fundamentally solves the problems of axial shrinkage and porosity caused by premature closure of the feeding channel in traditional bottom-pouring casting, and significantly improves the density and mechanical properties of the bar stock.

[0018] 5. This invention utilizes a step-speed comparison experiment (such as...) , , By combining X-ray non-destructive testing, the optimal safety feeding coefficient K value is determined for different titanium alloy grades, so that the control method has excellent versatility and adjustability and can be adapted to different alloy properties and casting specifications. Attached Figure Description

[0019] Figure 1 This is a flowchart of the dynamic control method for the liquid level rise speed in the vacuum suspension melting and casting of titanium alloys proposed in this invention. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 (TC4 titanium alloy bar, K=1.2) This embodiment provides a method for dynamically controlling the liquid level rise speed during the vacuum suspension melting and casting process of titanium alloy, which is used to prepare TC4 titanium alloy bars with a diameter of 120 mm and a length of 300 mm.

[0022] S1, Smelting Preparation Take 8 kg of TC4 titanium alloy raw material (Ti-6Al-4V) and place it in a water-cooled copper crucible of a vacuum cold crucible suspension melting furnace. Evacuate to 5 × 10⁻⁶ mm. -2 After Pa, argon gas is backfilled to 0.5 atm. The first power supply is turned on, and a high-frequency electromagnetic field (65kW power, 200kHz frequency) is applied to completely melt the raw material and suspend it from the crucible wall under the action of Lorentz force, thus obtaining a high-temperature titanium alloy melt at 1700±10℃.

[0023] S2, Flow Guiding System Configuration A flow guiding system is installed at the bottom opening of the crucible. A graphite flow guide tube (15mm inner diameter) is placed inside a ceramic heat insulation sleeve, and a two-stage high-frequency heating coil (powered by a second power source, with a preheating power of 4kW) is installed on the outside to preheat the flow guide tube to 850℃ to prevent the melt from condensing and blocking it.

[0024] S3, Thermocouple Array Arrangement Five monitoring planes are set along the axial direction (height) within the mold (casting mold), located at distances of 20mm, 80mm, 140mm, 200mm, and 260mm from the bottom, respectively. On each plane, five thermocouples are arranged radially from the center to the wall at equal intervals: r=0 (center), r=0.25R, r=0.5R, r=0.75R, and r=0.95R (R=60mm). All thermocouples are connected to a high-speed data acquisition module with a sampling frequency of 20Hz, recording the temperature-time curve in real time and synchronously transmitting it to the control system.

[0025] S4, Preset control parameters Based on the differential thermal analysis (DSC) data of TC4 titanium alloy, its solidus temperature Set the safety compensation factor. (The optimal value was determined through a step-rate comparison experiment). An initial pouring rate curve based on mass conservation was pre-set, with the target liquid level rise rate being... The speed gradually increased from 8 mm / s in the early stage to 12 mm / s in the middle stage, and then smoothly transitioned to the final stage.

[0026] The thermocouple model used in this embodiment is calibrated for response time constant. =0.4s, the control system has a built-in timing compensation algorithm In the control experiment without the added compensation algorithm, the calculation deviation of the solidification rate reached as high as 1.2 mm / s, which is prone to causing... The judgment was incorrect; after adding time-series compensation, the calculation deviation of the solidification rate was controlled within 0.1 mm / s, which met the requirements of real-time dynamic control.

[0027] S5, Dynamic Casting Control Process Pouring Start-up and Initial Monitoring The pouring process begins, and the high-temperature molten metal is injected into the mold (casting mold) through a guide pipe. A high-speed camera (sampling frequency 100Hz) captures real-time feature points of the liquid surface inside the mold (casting mold) and calculates the instantaneous rise rate of the liquid surface. Meanwhile, the control system adjusts the temperature of each thermocouple as it decreases. Time difference, real-time calculation of instantaneous solidification rate .

[0028] Phase 1 (t=3s, deceleration requirement appears) Monitoring data: .

[0029] Calculate the deviation: .

[0030] Control decision: The actual speed is too fast, which poses a risk of air entrapment.

[0031] Action: The control system automatically activates the DC electromagnet (reduction gear), with an initial excitation current of 5A, generating a steady horizontal magnetic field of 0.2T, applying an upward braking force to the molten metal. Real-time monitoring. It gradually decreased to 9.6 mm / s, meeting the requirements. .

[0032] The second stage (t=15s, an acceleration requirement appears) Monitoring data: .

[0033] Calculate the deviation: .

[0034] Control decision: The actual speed is too slow, and the solidification front is about to exceed the liquid surface, which poses a risk of shrinkage cavities.

[0035] Action: The control system automatically shuts off the DC electromagnet and turns on the AC coil (acceleration device). The excitation current gradually increases from 0 to 8A, and the traveling wave magnetic field frequency is 40Hz, generating a downward Lorentz force that accelerates the molten metal. It gradually recovered to 10.2 mm / s.

[0036] Phase 3 (t=25s until the end) The system enters steady-state fine-tuning. Maintain at The acceleration and deceleration devices follow an interlocking logic and are never activated simultaneously.

[0037] S6, Final Result After casting, the casting underwent X-ray non-destructive testing, and no shrinkage cavities or porosity defects were found along the central axis. After dissection, samples were taken and tested according to ASTM E8 standard, and the tensile strength reached 965MPa (standard requirement ≥895MPa), the elongation was 12% (standard requirement ≥10%), and the microstructure was significantly denser than that of traditional processes.

[0038] Example 2 (TA15 titanium alloy large-size bar stock) =1.25) This embodiment is basically the same as Embodiment 1, except for the following parameters: I. Alloys and Specifications Large-diameter bars with a diameter of 160 mm and a length of 400 mm were prepared using TA15 titanium alloy (Ti-6.5Al-2Zr-1Mo-1V).

[0039] II. Adjustment of Safety Compensation Coefficient Based on the wider solidification range of TA15, the optimal solidification velocity was determined through a step-rate comparison experiment. =1.25.

[0040] III. Thermocouple Arrangement Optimization Considering the larger radial temperature gradient of large-size castings, a sixth thermocouple is added at r=0.9R to more accurately capture the advancing speed of the solidification front near the wall.

[0041] IV. Typical Data of Control Process During the middle stage of pouring (t=22s), the low mold temperature led to... It surged to 7.2 mm / s: Calculate the deviation: Control decisions: need to be accelerated.

[0042] Action executed: The control system quickly increased the excitation current of the AC coil to 12A and adjusted the frequency to 60Hz, successfully preventing the compensation channel from being blocked.

[0043] V. Final Results X-ray inspection showed no shrinkage porosity along the central axis of the large-diameter bars, and ultrasonic testing achieved grade AA. The tensile strength reached 925 MPa (standard requirement ≥890 MPa), and the elongation was 10.5%.

[0044] Comparative Example Comparative Example 1 (Traditional plug-type casting, without electromagnetic control) This comparative example uses a traditional bottom-plug casting process and is compared with Example 1.

[0045] Process parameters Alloy and Specifications: TC4 titanium alloy, 120mm diameter bar (identical to Example 1) Plug diameter: 15mm (empirical value) There are no electromagnetic acceleration / deceleration devices; the pouring speed is entirely determined by gravity and cannot be adjusted. Phenomena during the pouring process In the initial stage of pouring: the melt flow rate is extremely high, and the peak liquid surface rise velocity reaches 22 mm / s, which is much higher than the solidification velocity (about 8 mm / s), causing violent fluctuations in the liquid surface, entraining gas, and forming porosity defects in the casting.

[0046] In the later stages of casting: as the melt level drops, the static pressure decreases, the flow rate decreases to below 5 mm / s, and the solidification rate (approximately 7 mm / s) surpasses the rate of rise of the melt level. The shrinkage channel gradually closes.

[0047] Test results X-ray non-destructive testing revealed that there was a clear continuous shrinkage cavity (approximately 120 mm in length) along the central axis of the bar, and multiple scattered shrinkage cavities appeared in the area 80-200 mm from the bottom, with a small number of random scattered pores at the top of the casting.

[0048] Mechanical properties: The tensile strength is only 782MPa and the elongation is 5.8%, both of which do not meet the requirements of aviation standards (tensile strength ≥895MPa, elongation ≥10%).

[0049] Yield: Of the 10 castings in this batch, only 2 barely passed the test, resulting in a yield of 20%.

[0050] in conclusion Traditional slab casting cannot dynamically adjust the flow rate according to the solidification process, thus failing to meet the requirements. Due to the feeding conditions, shrinkage cavities / shrinkage porosity defects are a systemic and persistent problem.

[0051] Comparative Example 2 (only deceleration device, no dynamic acceleration capability) This comparative example is used to verify the necessity of bidirectional adjustment of acceleration and deceleration.

[0052] Process settings The same melting and diversion system and thermocouple monitoring were used as in Example 1.

[0053] Only DC electromagnets (speed reducers) are installed; AC coils (speed reducers) are not installed.

[0054] The control system still calculates in real time. But when When acceleration is required, since there is no acceleration device, the system can only shut down the deceleration device or sound an alarm, and cannot actively increase the flow rate.

[0055] Pouring process and results In the initial stage of pouring (t=0-8s): the liquid level rises relatively quickly. The speed reduction device is working normally. It was effectively controlled within a reasonable range.

[0056] In the later stages of pouring (after t=15s): due to factors such as the natural cooling of the melt and the rise in mold temperature... Gradually increase.

[0057] Example of monitoring data: at t=18s, , , Calculated At this time, no acceleration device is available. consistently below The shrinkage channel gradually closes.

[0058] Test results X-ray inspection: Obvious central shrinkage porosity is found in the lower part of the bar (100-200mm from the bottom), and the shrinkage porosity rating reaches level 3 (GB / T 11346).

[0059] Mechanical properties: tensile strength 812MPa, elongation 7.2%, still does not meet aviation standard requirements.

[0060] in conclusion Having only deceleration capabilities without acceleration is insufficient to handle the increased solidification rate in the later stages of casting, and shrinkage defects will still occur. This invention incorporates both acceleration and deceleration devices with interlocking logic, ensuring that the entire process meets requirements. The key to dynamic matching.

[0061] The results of a comprehensive comparison between Examples 1-2 and Comparative Examples 1-2 are as follows: I. Comparison of Process Control Capabilities Both Examples 1 and 2 employ the dynamic control method of the present invention, using a high-speed camera to monitor the liquid level rise rate in real time. The solidification rate is obtained in real time through a pre-embedded thermocouple array. The control system is based on The calculation results automatically determine whether to activate the acceleration or deceleration device. In Example 1, during the initial stage of pouring (t=3s), an excessively rapid rise in the liquid level was detected. The control system automatically activated the DC electromagnet to apply upward braking force, causing the speed to drop back to a reasonable range; during the middle stage of pouring (t=15s), it was detected that the liquid level rise rate was too slow. The control system automatically switches to applying a downward driving force through the AC coil, causing the speed to recover. Example 2 also achieves precise control of the large-diameter bar casting process. When an acceleration demand arises at t=22s, the control system responds quickly, preventing the feeding channel from closing.

[0062] In contrast, Comparative Example 1 uses a traditional plug-type casting process without any electromagnetic control devices; the casting speed is entirely determined by gravity. In the initial stage of casting, the peak liquid level rise speed reaches 22 mm / s, far exceeding the reasonable range, causing violent fluctuations in the liquid level. In the middle and later stages of casting, the flow rate decreases to below 5 mm / s, overtaken by the solidification speed. No intervention or adjustment can be made throughout the process, and the speed curve exhibits an uncontrolled "fast at first, slow later" state.

[0063] Comparative Example 2, while equipped with a deceleration device, lacked an acceleration device. In the initial stages of pouring, the deceleration device functioned normally, controlling the excessively rapid rise in liquid level within a reasonable range. However, in the later stages of pouring, when the solidification rate increased and acceleration was required, the system was unable to respond due to the lack of an acceleration device, leading to the gradual closure of the feeding channel. This demonstrates that unidirectional adjustment capability cannot meet the dynamic changes required throughout the entire process.

[0064] II. Comparison of the effects of shrinkage cavity / shrinkage porosity defect control The casting in Example 1, after X-ray non-destructive testing, showed no shrinkage cavities or porosity defects along its central axis. The large-diameter bar stock in Example 2 also achieved the goal of no shrinkage porosity, and ultrasonic testing reached grade AA. This is due to the invention's consistent adherence to... The feeding conditions ensure that the feeding channel of the central liquidus line remains unobstructed throughout the solidification process, thus achieving the goal of liquid feeding.

[0065] The casting in Comparative Example 1 exhibits a noticeable continuous shrinkage cavity along its central axis, approximately 120 mm in length, and scattered shrinkage porosity in multiple areas. This is due to the excessively high flow rate during the initial pouring stage, which caused violent fluctuations in the liquid surface and entrainment of gas. In the later stages of pouring, the excessively slow flow rate caused the feeding channels to close prematurely, preventing the solidification shrinkage from being compensated and ultimately resulting in the shrinkage cavity defect.

[0066] The casting in Comparative Example 2 exhibited significant central shrinkage porosity in the lower part of the bar (100-200mm from the bottom), achieving a shrinkage porosity rating of 3. Although the deceleration device resolved the issue of excessively high initial flow rate, it lacked acceleration capability in the middle and later stages, failing to cope with the increased solidification rate, and the shrinkage porosity defect persisted.

[0067] III. Comparison of Mechanical Properties and Yield The casting of Example 1 achieved a tensile strength of 965 MPa and an elongation of 12%, both exceeding the aerospace standard requirements (tensile strength ≥ 895 MPa, elongation ≥ 10%). The casting of Example 2 achieved a tensile strength of 925 MPa and an elongation of 10.5%, also meeting the standard requirements. This indicates that the castings prepared by this invention have a dense microstructure and stable and reliable mechanical properties.

[0068] Comparative Example 1 showed a tensile strength of only 782 MPa and an elongation of 5.8%, both of which failed to meet aerospace standards. Of the 10 castings in this batch, only 2 barely passed the test, resulting in a yield rate of only 20%, and extremely poor production efficiency and economy.

[0069] Comparative Example 2, with a tensile strength of 812 MPa and an elongation of 7.2%, is superior to Comparative Example 1, but still fails to meet aerospace standards. This verifies that deceleration capability alone is insufficient to completely eliminate shrinkage porosity; bidirectional adjustment is the key to solving the problem.

[0070] IV. Comparison of adaptability to different working conditions Examples 1 and 2 were validated for different titanium alloy grades (TC4 and TA15) and different sizes (120mm and 160mm in diameter), respectively, and both achieved good results. Example 2 further adjusted the safety feeding factor to K=1.25 based on the wider solidification range of the TA15 alloy, and optimized the thermocouple arrangement according to the temperature gradient characteristics of large-size castings. This demonstrates that the method of the present invention has good versatility and adjustability, and can be adapted to different alloy properties and casting specifications.

[0071] The traditional plugging process in Comparative Example 1 relies entirely on the operator's experience to select the plugging hole diameter, which cannot be changed once selected, resulting in extremely poor adaptability to different alloys and specifications. Although Comparative Example 2 added a speed reduction device, it still could not adapt to working conditions with large variations in solidification rate, limiting its applicability.

[0072] V. Overall Conclusion Based on the above comparative evaluation, the following conclusions can be drawn: 1. The acceleration + deceleration bidirectional adjustment strategy proposed in this invention, combined with... The dynamic criteria enable real-time matching of pouring speed and solidification speed, fundamentally solving the problem of shrinkage porosity caused by premature closure of the feeding channel in traditional processes.

[0073] 2. Comparative Example 1 demonstrates that the traditional plug-in casting process cannot meet the requirements. The shrinkage conditions are such that shrinkage defects are a systemic problem; Comparative Example 2 proves that unidirectional adjustment capability alone cannot meet the dynamic changes required throughout the entire process.

[0074] 3. The successful application of Examples 1 and 2 on castings of different alloy grades and specifications verifies the versatility and reliability of the method of the present invention. The prepared castings are free from shrinkage cavities and porosity defects, and their mechanical properties meet the requirements of aviation standards, resulting in a significant improvement in yield.

[0075] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for dynamically controlling the liquid surface rise rate in vacuum suspension melting and casting of titanium alloys, characterized in that, Includes the following steps: S1. Place the titanium alloy raw material in a vacuum cold crucible suspension melting furnace, and use a high-frequency electromagnetic field to suspend and melt the raw material in a vacuum water-cooled copper crucible environment, so that the melt is separated from the crucible and a clean high-temperature titanium alloy melt is obtained. S2. The obtained high-temperature titanium alloy melt is injected into the mold through a flow guiding system set at the bottom of the crucible. The flow guiding system includes a graphite flow guiding tube, a ceramic heat insulation sleeve and a secondary high-frequency heating coil. The secondary high-frequency heating coil is powered by an independent power supply and is used to assist in heating the melt in the flow guiding tube to maintain its fluidity. S3. During the pouring process, a high-speed camera is used to capture real-time images of the liquid level inside the mold, and the instantaneous liquid level rise speed is obtained through image processing. Simultaneously, by pre-embedding thermocouple arrays at different heights and radial positions within the mold, the solidification process inside the casting is monitored in real time, and the instantaneous solidification rate is obtained. ; The high-speed camera and thermocouple array share a unified hardware trigger clock for synchronous acquisition, and the thermocouple acquisition module has a sampling frequency of no less than 10Hz; based on the factory-calibrated response time constant of the thermocouples. Time offset compensation is performed on the temperature measurement solidification time. Eliminate the calculation deviation of solidification rate caused by the second-level response lag of thermocouples; S4, Based on the preset safety compensation coefficient Calculate speed deviation Among them, the safety compensation coefficient The value range is 1.1 to 1.3, which is used to ensure that the liquid level rise rate is slightly greater than the solidification rate, so as to keep the central liquidus replenishment channel unobstructed. S5, according to The positive or negative sign automatically selects to activate or adjust the electromagnetic acceleration or deceleration device: when When the actual liquid level rises too slowly, the solidification front is about to exceed the liquid level, posing a risk of shrinkage cavities. At this point, the electromagnetic acceleration device is automatically activated or adjusted to increase the downward Lorentz force, accelerating the flow of the molten metal and increasing the rate of liquid level rise. When the actual liquid level rises too fast, it may cause inclusions or surface cold shuts. At this time, the electromagnetic deceleration device is automatically activated or adjusted to increase the upward braking force, slow down the flow of molten metal, and reduce the speed at which the liquid level rises. The acceleration device and the deceleration device are not activated at the same time to avoid mutual interference of magnetic fields. The electromagnetic deceleration device is a DC excitation structure that outputs a steady magnetic field; the electromagnetic acceleration device is an AC excitation coil that outputs a traveling wave magnetic field; the two excitation structures are independent of each other, each with its own independent power supply circuit, and the excitation current and excitation frequency are independently adjustable. S6. Repeat steps S3 to S5, dynamically adjusting the liquid level rise rate in real time to ensure it always meets the requirements. Continue until the pouring is complete.

2. The method for dynamically controlling the liquid level rise speed in vacuum suspension melting and casting of titanium alloys according to claim 1, characterized in that, The electromagnetic deceleration device consists of a pair of DC electromagnets arranged opposite each other on both sides of the guide tube, generating a steady magnetic field that passes through the guide tube in a horizontal direction. When the molten metal flows downward and cuts the magnetic field lines in the horizontal direction perpendicularly, an induced electromotive force is generated in the molten metal according to Faraday's law of electromagnetic induction. This induces a current loop in a plane perpendicular to the magnetic field and the flow direction. The induced current interacts with the steady magnetic field to generate a Lorentz force. According to Lenz's law, the direction of the Lorentz force is opposite to the flow direction of the molten metal, i.e., upward, thus applying a braking force to the molten metal. The magnitude of this braking force is proportional to the square of the magnetic field strength and the flow velocity of the molten metal. By adjusting the excitation current of the DC electromagnets, the strength of the steady magnetic field is changed, thereby changing the magnitude of the braking force, achieving a continuously adjustable deceleration of the molten metal flow velocity.

3. The method for dynamically controlling the liquid level rise speed in vacuum suspension melting and casting of titanium alloys according to claim 1, characterized in that, The electromagnetic acceleration device is an AC coil located below the guide tube. The AC coil generates a traveling wave magnetic field that moves downward along the pouring direction. When the molten metal is in the traveling wave magnetic field, an induced current is generated in the molten metal. The induced current interacts with the traveling wave magnetic field to generate a Lorentz force. The direction of the Lorentz force is the same as the direction of the traveling wave magnetic field, that is, downward, thereby driving the molten metal to flow downward at an accelerated speed. By adjusting the excitation current of the AC coil and the frequency of the traveling wave magnetic field, the magnitude of the downward Lorentz force can be changed, thereby achieving a continuously adjustable acceleration of the molten metal flow rate.

4. The method for dynamically controlling the liquid level rise speed in vacuum suspension melting and casting of titanium alloys according to claim 1, characterized in that, The instantaneous solidification rate Obtained through the following steps: A set of thermocouples is arranged at different heights from bottom to top inside the mold. Each set of thermocouples is arranged radially on the same horizontal plane from the inner wall of the mold to the center line at equal intervals to monitor the process of the solidified layer advancing from the mold wall to the center. Connect each group of thermocouples to a high-speed data acquisition module with a sampling frequency of no less than 10Hz, record the temperature-time curve of each temperature measurement point in real time, and transmit the data synchronously to the control center. Based on the specific grade of the titanium alloy being smelted, its solidus temperature can be obtained through differential thermal analysis or literature references. When the temperature at a certain measuring point drops to At that point, it is determined that the metal has completely solidified, and this moment is recorded. ; use Timing compensation is performed on the solidification time. This is the measured response time constant of the thermocouple; On a plane at a certain height, the radial solidification propulsion velocity is calculated using the solidification time difference between thermocouples at adjacent radial positions: ,in The radial spacing between adjacent thermocouples. This corresponds to the solidification time difference; The axial solidification propulsion velocity is calculated using the solidification time difference of thermocouples at the same radial position on planes of different heights: ,in The distance between adjacent heights; By summarizing data from multiple height and radial positions, the variation of solidification rate with time and space during the entire solidification process of the casting was obtained, and finally, an instantaneous solidification rate curve along the axial direction was fitted. Used for dynamic control.

5. The method for dynamically controlling the liquid level rise speed in vacuum suspension melting and casting of titanium alloys according to claim 1, characterized in that, The safety compensation coefficient The step-rate comparison experiment determined the specific steps, including: setting several different ratios of liquid surface rise rate to solidification rate, including... The instantaneous rise rate of the liquid surface was captured by a high-speed camera. With instantaneous solidification rate The fitted dynamic matching speed curve, combined with the electromagnetic acceleration and deceleration devices, was precisely executed. The castings obtained from each group of experiments were subjected to X-ray non-destructive testing to detect the presence of shrinkage cavities or porosity along the central axis. The proportion of the titanium alloy grade with no shrinkage cavities, porosity, and optimal microstructure was selected as the safe feeding coefficient. value.

6. The method for dynamically controlling the liquid level rise speed in vacuum suspension melting and casting of titanium alloys according to claim 1, characterized in that, In step S5, an interlock logic is set between the acceleration device and the deceleration device: when the control center determines that acceleration is needed, the system software automatically ensures that the deceleration device is in the off state, only turning on or adjusting the acceleration device; when the control center determines that deceleration is needed, the system software automatically ensures that the acceleration device is in the off state, only turning on or adjusting the deceleration device. When the speed is within the allowable deviation range, both the acceleration and deceleration devices remain in their current state or are turned off simultaneously to maintain a stable pouring speed.

7. The method for dynamically controlling the liquid level rise speed in vacuum suspension melting and casting of titanium alloys according to claim 1, characterized in that, In step S3, a high-speed camera captures feature points of the liquid surface inside the mold in real time, and an image processing algorithm calculates the displacement of the liquid surface per unit time to obtain the actual liquid surface rise rate. The velocity data is transmitted synchronously to the control center along with the solidification velocity data collected by the thermocouple array, and compared with the preset initial pouring velocity curve, which is determined in advance by the molten metal flow rate and the cross-sectional area of ​​the mold based on the law of conservation of mass.

8. The method for dynamically controlling the liquid level rise speed in vacuum suspension melting and casting of titanium alloys according to claim 1, characterized in that, In step S5, when the control center determines that acceleration is needed, it increases the downward Lorentz force by increasing the excitation current of the AC coil or adjusting the frequency of the traveling wave magnetic field, thereby increasing the flow rate of the molten metal. When the control center determines that deceleration is needed, it increases the excitation current of the DC electromagnet to enhance the magnetic induction intensity of the steady magnetic field, thereby increasing the upward braking force and slowing down the flow rate of the molten metal. Both acceleration and deceleration adjustments are continuously adjustable to achieve precise dynamic control of the rising speed of the liquid surface.

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