A low-temperature minimum quantity lubrication cooling method in precision machining of aluminum alloy

Abstract

The present invention discloses a cryogenic minimum quantity lubrication cooling method in precision machining of aluminum alloy, which relates to the field of precision machining of aluminum alloy; machining parameters such as cutting speed and feed rate are determined according to the aluminum alloy material, machining requirements and tool performance, and optimized through finite element simulation; a high-purity vegetable oil-based lubricating oil is selected, and a nano anti-wear agent and an antioxidant are added, and the coolant is made by mixing compressed air through a vortex tube refrigeration; it is sprayed onto the machining area through a special multi-channel nozzle, and the flow rate is dynamically adjusted; various sensors are used to monitor the temperature, tool wear and surface quality, and adjustment is made when the threshold is exceeded; the coolant is recovered, and after centrifugation and membrane filtration treatment, it is recycled, and the metal chips are classified and recycled. The cooling and lubrication effect of the present invention is good, which reduces cutting heat and tool wear, improves machining accuracy and tool life; the use of environmentally friendly lubricating oil for recycling reduces pollution and cost; real-time monitoring and adjustment ensure stable machining quality, improve machining efficiency, and meet the needs of high-end manufacturing.

Description

Technical Field

[0001] The present invention relates to the technical field of precision machining of aluminum alloys, and particularly to a low-temperature minimum quantity lubrication cooling method in precision machining of aluminum alloys. Background Art

[0002] In the field of precision machining of aluminum alloys, there are many problems with traditional cooling and lubrication methods. Currently, the commonly used wet machining method with a large amount of cutting fluid has a huge consumption of cutting fluid, which not only increases the processing cost, but also the chemical substances contained in the cutting fluid are difficult to treat after use, causing serious pollution to the environment.

[0003] In addition, the cutting fluid is prone to phenomena such as oil mist and splashing during the machining process, which is harmful to the physical health of the operators. Although dry machining avoids the pollution problems caused by cutting fluid, due to the lack of effective lubrication and cooling, a large amount of cutting heat will be generated during the machining process, resulting in increased tool wear, decreased machining accuracy, and problems such as thermal deformation and increased surface roughness on the aluminum alloy surface, making it difficult to meet the requirements of precision machining.

[0004] The emergence of minimum quantity lubrication technology (MQL) has improved the above problems to a certain extent. It achieves the lubrication effect with a small amount of lubricating oil. However, in the precision machining of aluminum alloys, the cooling effect of ordinary minimum quantity lubrication is limited. Especially in working conditions such as high-speed cutting, it is unable to effectively reduce the temperature in the cutting area. With the wide application of aluminum alloys in high-end fields such as aerospace and automotive manufacturing, higher requirements are put forward for the precision, surface quality, and processing efficiency of its precision machining. The existing cooling and lubrication methods are difficult to meet these requirements simultaneously, and there is an urgent need for a new cooling and lubrication method to solve the problems of cooling, lubrication, and environmental protection in the process of precision machining of aluminum alloys. Summary of the Invention

[0005] The low-temperature minimum quantity lubrication cooling method in precision machining of aluminum alloys proposed by the present invention is to solve the problems mentioned in the above prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: A low-temperature minimum quantity lubrication cooling method in precision machining of aluminum alloys, including:

[0007] Step of determining machining parameters: Determine the cutting speed v, feed rate f, and cutting depth a according to the material properties of the aluminum alloy, machining requirements, and tool performance p , based on the thermal conductivity λ, hardness H, and tool sharpness coefficient k f , through the formula Determine the coolant flow rate Q, where k is a coefficient related to the machining method, simulate the cutting force and temperature through a finite element simulation model, and optimize and adjust the machining parameters;

[0008] Coolant preparation steps: Select a vegetable oil-based base lubricating oil, use vortex tube refrigeration technology to reduce the compressed air temperature to a set threshold, and calculate the vortex tube refrigeration efficiency through the formula where T in is the initial temperature of the compressed air, and T out is the temperature after refrigeration. Control the refrigeration effect by adjusting the inlet pressure and flow rate of the vortex tube;

[0009] Coolant injection steps: Inject the coolant into the processing area through a special multi-channel nozzle. Adjust the injection angle and flow rate according to the processing requirements. The injection angle θ is dynamically adjusted according to the processing technology and tool shape. Use an intelligent flow control valve to adjust the coolant flow rate Q through the formula where F is the cutting force, and F0 is the preset cutting force threshold; adjust

[0010] Monitoring and adjustment steps: Monitor the temperature in the processing area, tool wear condition, and surface quality parameters. Use a fiber Bragg grating temperature sensor to measure the temperature change for temperature monitoring. Use an acoustic emission sensor combined with a vision monitoring system for tool wear monitoring. The former captures the tool wear signal, and the latter observes the tool wear morphology. Use a white light interferometer to measure the microtopography and roughness for processing surface quality monitoring. Optimize the processing surface quality by adjusting the processing parameters and coolant flow rate;

[0011] Post-processing steps after machining: Recycle and process the coolant. Separate large particle impurities and metal chips in the coolant through a centrifugal separation device. Use membrane filtration technology to remove fine particles and colloidal impurities. Detect the performance of the processed coolant and adjust the performance according to the detection results. Collect and process the recycled metal chips and make them into aluminum alloy raw materials through a smelting and refining process.

[0012] Furthermore, it also includes:

[0013] Coolant atomization effect optimization steps: Set a turbulence structure inside the nozzle to evenly distribute the oil mist particle size. The average oil mist particle size D is controlled by the formula where P is the compressed air pressure, C and m are constants related to the nozzle structure, ρ air is the density of the compressed air, and ρ oil is the density of the lubricating oil; Use pulse injection technology to inject the coolant through the frequency and pulse width. The pulse frequency f pulse is adjusted according to the processing parameters and coolant flow rate.

[0014] Furthermore, it also includes:

[0015] Processing energy consumption optimization steps: Establish a comprehensive energy consumption model E = α×v + β×f + γ×Q + δ×P according to the processing parameters, coolant flow rate, and power of the refrigeration equipment cool, where \(E\) is the total energy consumption during the processing, \(\alpha\), \(\beta\), and \(\gamma\) are coefficients related to the processing equipment and technology, \(\delta\) is the coefficient related to the refrigeration equipment, and \(P\) cool is the power of the refrigeration equipment. By optimizing the processing parameters and coolant flow rate through the genetic algorithm, the processing parameters and the operating state of the refrigeration equipment are dynamically adjusted according to the energy consumption monitoring data during the processing.

[0016] Furthermore, the vegetable oil-based lubricant is prepared by a multi-stage refining process to remove impurities and moisture. The vacuum distillation technology is adopted during the refining process, and the refined lubricant is hydrogenated. The degree of hydrogenation is adjusted by controlling the hydrogen pressure, temperature, and reaction time.

[0017] Furthermore, the vortex tube refrigeration equipment is insulated with heat-insulating materials. The thermal conductivity of the heat-insulating materials is less than \(0.05\ W / (m\cdot K)\) to maintain the low-temperature environment inside the vortex tube. The structural design of the vortex tube is optimized, the length and spiral angle of the vortex tube are increased, and the structural parameters of the vortex tube are determined through experiments combined with simulation values.

[0018] Furthermore, the multi-channel nozzle uses 3D printing technology to control the internal structural design and dimensions. The nozzle material is selected as a stainless steel alloy, and a micro-nano structure coating is set at the outlet.

[0019] Furthermore, the fiber Bragg grating temperature sensors are distributed in different positions of the processing area to monitor the temperature distribution. By establishing a temperature field model to analyze and process the collected data to feedback the temperature change trend, the temperature sensors are in real-time communication with the control system. When the temperature exceeds the set threshold, the coolant injection parameters are adjusted to control the temperature of the processing area.

[0020] Furthermore, the acoustic emission sensors and the visual monitoring system use a fusion algorithm to process data. The acoustic emission sensors collect signals to reflect the change in tool wear, and the visual monitoring system collects images to display the tool wear morphology. By correlatively analyzing the two types of data through the fusion algorithm, the tool wear degree and wear type are judged.

[0021] Furthermore, the white light interferometer uses a displacement platform and a data acquisition system to measure the processed surface. The measurement results are analyzed through an image processing algorithm to obtain the surface roughness parameters and microscopic profile information of the processed surface. By comparing the measurement results with the preset surface quality standard, when the threshold is exceeded, the processing parameters and coolant flow rate are automatically adjusted.

[0022] Furthermore, during the coolant recycling process, the ultrasonic-assisted cleaning technology is used to preprocess the coolant. The ultrasonic frequency is \(20 - 40\ kHz\) to generate cavitation effects, separating the impurities and metal chips in the coolant. The cross-flow filtration method is adopted during the membrane filtration process, and it is recycled through optimizing the treatment process.

[0023] Compared with the existing technologies, the beneficial effects of the present invention are:

[0024] In terms of cooling and lubrication, by combining cryogenic technology with minimum quantity lubrication (MQL), the cryogenic compressed air can rapidly carry away a large amount of cutting heat generated during the machining process, effectively reducing the temperature in the machining area, minimizing the thermal deformation of the aluminum alloy caused by high temperature, and improving the machining accuracy. At the same time, the specially formulated lubricating oil can still maintain good lubricating performance under low-temperature conditions. With an optimized spraying method, the lubricating oil can be more evenly distributed in the cutting area, greatly reducing the friction between the cutting tool and the workpiece, reducing tool wear, and extending the tool life.

[0025] In terms of environmental protection and energy conservation, this method adopts MQL, significantly reducing the amount of lubricating oil used. Moreover, vegetable oil-based lubricating oil with good biodegradability is selected, reducing environmental pollution. The refrigeration equipment uses highly energy-efficient technologies, such as vortex tube refrigeration technology, which consumes less energy compared to traditional refrigeration methods. The coolant is recycled and deeply treated for reuse, improving resource utilization efficiency, reducing waste liquid discharge, and lowering machining costs.

[0026] In terms of machining quality and efficiency, the real-time monitoring and intelligent adjustment system can timely adjust the cooling and lubrication strategy according to various parameters during the machining process, ensuring the stability of the machining surface quality and reducing the scrap rate. The optimized machining parameters and cooling and lubrication methods improve machining efficiency, enabling precision machining of aluminum alloy to better meet the requirements for product quality and production efficiency in high-end fields such as aerospace and automotive manufacturing. Description of the Drawings

[0027] Figure 1 It is a schematic block diagram of a cryogenic minimum quantity lubrication cooling method in precision machining of aluminum alloy proposed by the present invention;

[0028] Figure 2 It is a schematic diagram comparing the tool wear amounts of different machining methods;

[0029] Figure 3 It is a schematic diagram comparing the surface roughness of machined surfaces of different machining methods;

[0030] Figure 4 It is a schematic diagram showing the change of coolant usage with machining time;

[0031] Figure 5 It is a schematic diagram showing the proportion of machining energy consumption of different machining methods. Detailed Embodiments

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0033] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0034] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, the meaning of "a plurality" is two or more unless otherwise specifically defined. In addition, the terms "mounted", "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The present invention will be further described in detail below with reference to the drawings.

[0035] Refer to Figures 1 to 5 : A cryogenic minimum quantity lubrication cooling method in precision machining of aluminum alloy, comprising:

[0036] Processing parameter determination step: According to the material properties of the aluminum alloy, processing requirements and the performance of the cutting tool, determine the appropriate cutting speed v (unit: m / min), feed rate f (unit: mm / r) and cutting depth a p (unit: mm). The cutting speed v can be calculated by the formula v = πdn / 1000, where d is the tool diameter (unit: mm) and n is the tool speed (unit: r / min). At the same time, based on the thermal conductivity λ (unit: W / (m・K)), hardness H (unit: HB) of the aluminum alloy and the sharpness coefficient k f of the cutting tool, the flow rate Q (unit: ml / h) of the lubricating coolant is preliminarily determined through an empirical formula , where k is a coefficient related to the aluminum alloy material and processing method. In addition, by establishing a finite element simulation model for aluminum alloy processing, simulating the cutting force, temperature distribution, etc. under different processing parameters, the preliminarily determined processing parameters are optimized and adjusted.

[0037] Coolant Preparation Steps: A high-purity vegetable oil-based base lubricant, such as soybean oil that has undergone multi-stage refining and hydrogenation, is used in the preparation of the coolant. The multi-stage refining process includes degumming, deacidification, decolorization, and deodorization to remove impurities, moisture, and free fatty acids, thereby improving the purity and stability of the lubricant. During the hydrogenation process, the hydrogen pressure is controlled at 0.5 MPa, the temperature is 180°C, and the reaction time is 2 hours. This converts some unsaturated fatty acids into saturated fatty acids, maintaining the iodine value of the lubricant at approximately 100 g / 100 g. Testing indicates that the unsaturated fatty acid content of this vegetable oil-based lubricant reaches 91%. Nano-molybdenum disulfide (MoS2), a nano-scale anti-wear additive, is added to the base lubricant. Its particle size is carefully selected to approximately 70 nanometers, and the addition level is 1.8% of the lubricant's mass. Nano-MoS2 has a well-defined layered structure, forming a lubricating film on the friction surface, effectively reducing the coefficient of friction. At the same time, an organic borate antioxidant is added in an amount of 1.2% of the mass of the lubricating oil to enhance the antioxidant capacity of the lubricating oil and extend its service life. The prepared lubricating oil is mixed with compressed air that has undergone multi-stage filtration and drying. The compressed air first passes through a primary filter with an accuracy of 5μm to remove larger particle impurities, and then passes through a secondary filter with an accuracy of 1μm and a high-level filter with an accuracy of 0.3μm for further purification. Then, the moisture in the compressed air is removed by a freeze dryer to reduce its dew point to below -40°C. Vortex tube refrigeration technology is used to reduce the temperature of the compressed air to the set low temperature range. The inlet pressure of the vortex tube is set to 0.7MPa and the flow rate is 1.8m³ / h. Through the formula To calculate and control the refrigeration efficiency, where Tin is the initial temperature of the compressed air.

[0038] Coolant injection steps: spray low-temperature minimal lubrication coolant into the aluminum alloy processing area through a special multi-channel nozzle. The multi-channel nozzle is manufactured using 3D printing technology, and the material selected is high-strength, corrosion-resistant 316L stainless steel alloy. The nozzle consists of a main channel and 6 auxiliary channels. The main channel has a diameter of 1.5mm, and the auxiliary channel has a diameter of 0.8mm. The auxiliary channels are evenly distributed in a ring around the main channel. In actual processing, the nozzle injection angle θ is adjusted to 50° according to the tool shape (such as the spiral angle of the drill bit, the shape of the cutting edge, etc.) and the processing technology (such as the depth of the drilling, the size of the aperture, etc.). In order to ensure that the coolant can be accurately sprayed into the cutting area, the nozzle is fine-tuned through a high-precision angle adjustment device, and the adjustment accuracy can reach ±0.5°. At the same time, an intelligent flow control valve is used to adjust the flow of the coolant in real time. The intelligent flow control valve has a built-in pressure sensor and flow sensor, which can monitor the pressure and flow of the coolant in real time. When the real-time cutting force F changes during the processing, the formula Perform flow adjustment.

[0039] Monitoring and adjustment steps: During the precision machining of aluminum alloy, parameters such as the temperature in the machining area, the wear condition of the cutting tool, and the surface quality of the machining are monitored in real time. For temperature monitoring, fiber Bragg grating temperature sensors with a distributed layout are used. At different positions in the machining area, such as near the cutting edge of the tool and on the workpiece surface, 3 fiber Bragg grating temperature sensors are arranged, and the distance between the sensors is 15 mm. The fiber Bragg grating temperature sensors have the advantages of high precision (the measurement accuracy can reach ±0.5 °C) and strong anti-interference ability, and can accurately measure the temperature change in the machining area in real time. The data collected by the sensors is transmitted to the data acquisition system, and through the establishment of a temperature field model, the data is analyzed and processed to accurately grasp the temperature distribution in the machining area. When a certain sensor monitors that the temperature T exceeds the set threshold T0 = 70 °C, the control system immediately issues an instruction to enhance the cooling effect by increasing the flow rate Q of the coolant adjust , reducing the temperature of the compressed air or adjusting the spraying angle of the nozzle. Tool wear monitoring adopts a combination of acoustic emission sensors and visual monitoring systems. The acoustic emission sensor is installed on the tool shank and can capture the acoustic emission signals generated during the tool wear process in real time. The visual monitoring system consists of a high-definition camera and image processing software. The high-definition camera is installed near the machining area and can observe the wear morphology of the tool in real time. Through a fusion algorithm, the signals collected by the acoustic emission sensor and the images collected by the visual monitoring system are correlated and analyzed. When the characteristic frequency of the acoustic emission signal changes and the visual monitoring shows that there are wear marks on the cutting edge of the tool, it is judged that the tool is in the initial wear stage; when the energy of the acoustic emission signal increases sharply and the visual monitoring shows that the tool is severely damaged, it is judged that the tool needs to be replaced in time. Machining surface quality monitoring uses a white light interferometer. The white light interferometer has a high-precision displacement platform and a fast data acquisition system, and can complete high-precision measurement of the machining surface in a short time. The measurement results are analyzed through image processing algorithms, and not only the roughness parameters of the machining surface can be obtained, but also the microscopic profile information of the surface can be obtained. The measurement results are compared with the preset surface quality standards (such as the surface roughness Ra is required to reach 0.8 μm). When the surface quality does not meet the requirements, the system automatically adjusts the machining parameters (such as cutting speed, feed rate, etc.) and the flow rate of the coolant to achieve closed-loop control of the machining surface quality.

[0040] Post - processing steps: After the machining is completed, the coolant is recycled and deeply processed. First, the used coolant is collected in a recycling container and preliminarily separated by a centrifugal separation device. The rotational speed of the centrifuge is set at 3500 r / min, and the large - particle impurities and metal chips in the coolant are separated by centrifugal force. The separated metal chips are classified and collected for subsequent smelting and refining processes. Then, membrane filtration technology is used to further process the coolant. A polyethersulfone membrane with a pore size of 0.1 μm is selected for filtration. The cross - flow filtration method is adopted, with a filtration pressure of 0.3 MPa and a filtration speed of 10 L / h. The cross - flow filtration method can reduce membrane fouling and blockage, improving the service life and filtration efficiency of the membrane. During the filtration process, ultrasonic - assisted cleaning technology is utilized. The ultrasonic frequency is set at 30 kHz, which can produce cavitation effects, making it easier for the tiny particles and colloidal impurities in the coolant to be separated from the liquid. Performance tests are conducted on the processed coolant, including indicators such as viscosity, flash point, and acid value. A viscometer is used to measure the viscosity of the coolant to ensure that its viscosity is within a suitable range (assuming the required viscosity is 20 - 30 mPa・s); a flash point tester is used to measure the flash point to ensure that the flash point of the coolant meets the safety requirements (assuming the flash point requirement is not lower than 180 °C); an acid - base titration method is used to measure the acid value to ensure that the acid value is within a reasonable range (assuming the acid value requirement does not exceed 0.5 mgKOH / g). According to the test results, appropriate additives (such as anti - wear agents, antioxidants, etc.) are added for performance adjustment so that the coolant can be recycled.

[0041] In the present invention, the following steps are further included:

[0042] Steps for optimizing the atomization effect of the coolant: By setting a special turbulence structure inside the nozzle, strong turbulence is generated during the mixing process of the lubricating oil and compressed air, thereby making the oil mist particle size distribution more uniform. The average particle size D (unit: μm) of the oil mist can be precisely controlled by the formula , where P is the pressure of the compressed air (unit: MPa), C and m are constants related to the nozzle structure, ρ air is the density of the compressed air, and ρ oil is the density of the lubricating oil. At the same time, pulse injection technology is adopted to inject the coolant at a certain frequency and pulse width, so that the oil mist forms a periodic distribution in the machining area, improving the lubrication and cooling efficiency. The pulse frequency f pulse (unit: Hz) can be adjusted according to the machining parameters and the flow rate of the coolant, generally between 10 - 100 Hz.

[0043] In the present invention, the following steps are further included:

[0044] Processing energy consumption optimization steps: Based on the processing parameters, the flow rate of the coolant, and the power of the refrigeration equipment, establish a comprehensive energy consumption model \(E = \alpha\times v+\beta\times f+\gamma\times Q+\delta\times P\). cool , where \(E\) is the total energy consumption during the processing (unit: \(kW\cdot h\)), \(\alpha\), \(\beta\), and \(\gamma\) are coefficients related to the processing equipment and technology, \(\delta\) is the coefficient related to the refrigeration equipment, and \(P\). cool is the power of the refrigeration equipment (unit: \(kW\)). Optimize the processing parameters and the flow rate of the coolant through the genetic algorithm, with the minimization of the energy consumption \(E\) as the objective function, while satisfying the constraint conditions of the processing quality. During the processing, according to the real-time energy consumption monitoring data, dynamically adjust the processing parameters and the operating state of the refrigeration equipment to keep the energy consumption at a relatively low level all the time.

[0045] In the present invention, the vegetable oil-based lubricant is prepared by a multi-stage refining process to remove impurities and moisture therein, and improve the purity and stability of the lubricant. In the initial stage, preliminary separation means such as sedimentation and filtration are adopted to separate large-particle impurities and free water. Subsequently, it enters a more critical refining step, and chemical and physical methods are used for further purification. Among them, the caustic refining process can effectively remove acidic substances in the lubricant and improve its chemical stability; while in the adsorption decolorization link, adsorbents such as activated clay are used to adsorb and remove pigments and other organic impurities to improve the purity of the lubricant. In the refining process, vacuum distillation technology plays a key role. The distillation operation is carried out under the conditions of low temperature and low pressure, because traditional high-temperature distillation is likely to cause oxidation and decomposition reactions of unsaturated components in the lubricant, thereby reducing the quality of the lubricant. And the mild environment created by vacuum distillation greatly avoids such problems. In the vacuum state, low-boiling impurities in the lubricant are effectively separated, and its own chemical structure is completely retained, ensuring the purity and stability of the lubricant. Then comes the hydrogenation treatment link. This step aims to improve the antioxidant performance and thermal stability of the lubricant. By introducing hydrogen into the refined lubricant, under specific catalytic conditions, some unsaturated fatty acids undergo hydrogenation reactions to be converted into saturated fatty acids. In this process, it is crucial to precisely control the pressure, temperature, and reaction time of hydrogen. By adjusting the hydrogen pressure, the rate and depth of the hydrogenation reaction can be controlled; a suitable temperature can activate the catalyst activity and ensure the efficient progress of the reaction; and the control of the reaction time determines the degree of hydrogenation. By strictly regulating these parameters, the iodine value of the lubricant is controlled within a reasonable range of 80 - 120 \(gl_2 / 100g\), enabling the lubricant to have better antioxidant and thermal stability characteristics, and during the low-temperature minimum quantity lubrication cooling process of precision machining of aluminum alloys, it can continuously and stably play a lubricating role, reduce wear, and improve the processing quality and the service life of the cutting tool.

[0046] In the present invention, the vortex tube refrigeration device is insulated with a new type of thermal insulation material. This thermal insulation material is carefully selected and has an extremely low thermal conductivity, less than 0.05 W / (m·K), and has excellent heat insulation performance. During the refrigeration process, it acts like a solid "heat insulation barrier", tightly wrapping the vortex tube and greatly preventing the intrusion of external heat. By reducing heat transfer, the low-temperature environment inside the vortex tube is effectively maintained, the energy loss during the refrigeration process is reduced, and the refrigeration system can operate more efficiently. Secondly, the structure of the vortex tube is deeply optimized. In terms of length, through multiple experiments and theoretical analyses, the length of the vortex tube is moderately increased, providing more sufficient space and time for the energy conversion and heat exchange of compressed air in the tube. At the same time, the spiral angle of the vortex tube is adjusted so that it can guide the compressed air to rotate in a more reasonable trajectory. In this way, the rotation speed of the compressed air in the vortex tube is significantly increased, and the residence time is also extended. The high-speed rotating compressed air can more fully separate energy in the vortex tube, the heat at the hot end is more effectively discharged, and a lower temperature is generated at the cold end, thereby improving the refrigeration efficiency. In order to determine the optimal structural parameters of the vortex tube, a scientific method combining experiments and numerical simulations is adopted. By building a high-precision experimental platform, the operation of the vortex tube under different working conditions is simulated to obtain a large amount of actual data. At the same time, using advanced numerical simulation software, a three-dimensional physical model of the vortex tube is established, and methods such as computational fluid dynamics (CFD) are used to accurately simulate the flow and heat transfer processes of compressed air in the vortex tube. After repeatedly comparing and analyzing the experimental data and simulation results, the structural parameters of the vortex tube are continuously optimized. Finally, the refrigeration efficiency is increased by 15%-25% compared with the traditional vortex tube, providing a more stable and efficient low-temperature cooling guarantee for precision machining of aluminum alloys, and effectively improving the machining quality and precision.

[0047] In the present invention, the special multi-channel nozzle is manufactured by 3D printing technology. Through 3D printing, materials can be stacked layer by layer according to a precise design model to achieve extremely complex internal structure designs. For example, a flow channel structure with a specific turbulence effect can be precisely constructed, enabling the lubricating oil and compressed air to mix more fully inside the nozzle to form a uniform and stable oil mist. At the same time, 3D printing technology can also achieve precise dimension control, with a dimensional accuracy of up to ±0.05 mm, ensuring that the specifications of each nozzle are highly consistent and guaranteeing the quality stability of mass production. In terms of material selection, the nozzle is made of a high-strength and corrosion-resistant stainless steel alloy. This alloy has excellent mechanical properties, can withstand the high-frequency vibrations and impact forces generated during the processing, and is not prone to deformation or damage. Moreover, its good corrosion resistance can effectively resist the erosion of coolant, machining debris, etc. on the nozzle. Even in a harsh machining environment full of cutting fluid splashing and metal chip abrasion, it can maintain a long service life, reduce the replacement frequency, and lower the maintenance cost. At the outlet of the nozzle, a coating with micro-nano structure is provided, typically a diamond-like carbon (DLC) coating. This coating is prepared by advanced processes such as physical vapor deposition (PVD). Its surface roughness is extremely low, reaching the nanometer level. At the same time, it has excellent self-lubricating properties and a very small friction coefficient. When the oil mist sprays out from the nozzle, the extremely low surface roughness reduces the contact area between the oil mist particles and the nozzle outlet wall surface, while the good self-lubricating properties reduce the adhesion force of the oil mist particles, effectively avoiding the adhesion and blockage of the oil mist at the nozzle outlet, ensuring that the oil mist can be smoothly sprayed out in a stable form and with a suitable particle size distribution, accurately covering the machining area, greatly improving the spraying effect of the oil mist, and providing better lubrication and cooling guarantee for the precision machining of aluminum alloy.

[0048] In this invention, fiber Bragg grating (FBG) temperature sensors are distributed, with multiple sensors strategically placed at key locations within the processing area, such as near the contact point between the tool and the workpiece and around the coolant spray area. These sensors operate based on the temperature-sensitive properties of fiber Bragg gratings (FBGs) and the principle of light reflection. When the temperature changes, the FBG pitch shifts accordingly, causing the wavelength of the reflected light to shift. The sensors can accurately detect these extremely small wavelength changes with a measurement accuracy of ±0.1°C, enabling highly sensitive temperature monitoring. By establishing a precise temperature field model, the data collected by each sensor is deeply analyzed and processed. This model comprehensively considers multiple factors, including the geometry of the processing area, the thermophysical properties of the material, and processing parameters. Using advanced algorithms such as finite element analysis, the collected discrete temperature data is spatially interpolated and fitted, accurately capturing the three-dimensional temperature distribution within the processing area and its temporal trends. More importantly, these temperature sensors communicate in real time with the control system, which incorporates a high-performance microprocessor and advanced control algorithms. When the temperature in a specific area exceeds a preset threshold, the sensors rapidly transmit abnormal temperature data to the control system. After receiving the signal, the control system can analyze and make decisions in a very short time (response time is less than 1 second). Based on the size and location of the temperature deviation, it can quickly adjust the coolant injection parameters corresponding to the area, including the coolant flow rate, injection angle, and injection pressure. For example, if the temperature near the tool cutting edge is found to be too high, the control system will increase the coolant flow rate in this area and adjust the injection angle to more accurately cover the high-temperature area. In this way, the temperature of the processing area can be precisely controlled, effectively avoiding problems such as increased tool wear and workpiece deformation caused by excessive temperatures, and ensuring the quality and accuracy of aluminum alloy precision machining.

[0049] In the present invention, the acoustic emission sensor and the vision monitoring system adopt a fusion algorithm for data processing. As a key component, the acoustic emission sensor is made of a highly sensitive piezoelectric material, which can acutely capture the extremely weak acoustic emission signals generated during the tool wear process. These signals originate from the changes in the internal microstructure of the tool, such as crystal dislocation, crack initiation and propagation, etc. The sensor converts these mechanical vibration signals into electrical signals and collects them at a high sampling frequency to ensure that no detail information reflecting the tool wear state is missed. The vision monitoring system is equipped with a high-resolution industrial camera, which can perform real-time shooting of the tool working area at a frame rate of dozens of frames per second or even higher. Its lens is specially optically designed with high depth of field and high clarity, and can clearly present the wear patterns of key parts such as the tool edge, rake face, and flank face. Whether it is a tiny wear mark or a more obvious damage situation, it can be accurately captured. The fusion algorithm is the core of the entire monitoring system. Based on advanced machine learning and pattern recognition technologies, it first performs spectral analysis on the signals collected by the acoustic emission sensor to extract key parameters such as characteristic frequencies and energies; at the same time, it performs edge detection, feature extraction, etc. on the images collected by the vision monitoring system. Then, through complex association rules and data analysis models, the acoustic emission signal data and the vision image data are deeply fused. For example, in the initial wear stage of the tool, the characteristic frequency of the acoustic emission signal will change slightly, which represents the beginning of instability in the internal microstructure of the tool. At this time, the vision monitoring system can also capture some minor wear marks on the tool edge, such as tiny scratches or wear spots. The fusion algorithm comprehensively analyzes these two types of data and can accurately judge that the tool is in the initial wear stage, and timely remind the operator to take corresponding measures. When the tool wear intensifies, the energy of the acoustic emission signal increases sharply, indicating rapid crack propagation or severe plastic deformation inside the tool. At the same time, the vision monitoring shows serious damage situations such as chipping and large-area wear of the tool. The fusion algorithm will clearly judge that the tool needs to be replaced in time to avoid affecting the machining quality and efficiency due to excessive tool wear, and ensure the stability and reliability of the precision machining process of aluminum alloy.

[0050] In the present invention, the white light interferometer is equipped with a high-precision displacement platform. Based on advanced nanoscale positioning technology, it can achieve precise movement with extremely small step sizes, and its positioning accuracy can reach the nanometer level. At the same time, it is equipped with a fast data acquisition system, which uses high-speed sensors and advanced data transmission technology to rapidly collect interference signal data at an extremely high frequency. With its efficient data processing ability, it can complete a comprehensive measurement of the machined surface in an extremely short time, greatly shortening the detection cycle and improving the machining efficiency. The measured data will be transmitted to the image processing algorithm module for in-depth analysis. This algorithm integrates advanced edge detection, gray-scale analysis and other technologies. Through these algorithms, not only can the roughness parameters of the machined surface be accurately calculated, such as the arithmetic mean deviation of the profile Ra, the ten-point height of the micro-irregularities Rz, etc., but also the microscopic profile information of the machined surface can be obtained through the fine analysis of the interference fringes, such as the small undulations and gully shapes on the surface. More importantly, the system will compare the measurement results with the preset surface quality standards in real time. These preset standards cover the parameter thresholds under different machining accuracy requirements. Once the surface quality does not meet the requirements, the system will quickly respond. Based on the intelligent control algorithm, it will automatically adjust the machining parameters, such as cutting speed, feed rate, etc., and at the same time, it will also accurately control the flow rate of the coolant. Through this closed-loop control mechanism, it ensures that the surface quality of the precision machining of aluminum alloy always remains at a high quality level, effectively improving the overall quality of the product and the stability of the machining.

[0051] In the present invention, during the coolant recovery and treatment process, an ultrasonic-assisted cleaning technique is adopted to pre-treat the recovered coolant. The frequency of the ultrasonic wave is set within a specific range of 20 - 40 kHz, and this frequency range can trigger a strong cavitation effect. When the ultrasonic wave acts on the coolant, numerous tiny cavitation bubbles will instantaneously form in the liquid. These cavitation bubbles rapidly collapse within an extremely short time, generating powerful shock waves and microjets. Under such a powerful force, impurities mixed in the coolant, such as fine dust particles, undissolved chemical substances, and metal chips, whether they are aluminum chips or other metal debris generated during the processing, can be more easily separated from the main body of the coolant. Subsequently, it enters the membrane filtration stage, adopting the cross-flow filtration method. During the cross-flow filtration process, the coolant does not flow directly perpendicular to the filter membrane as in traditional filtration, but flows parallel along the membrane surface. This flow pattern enables most of the impurities not to directly accumulate on the membrane surface but to be carried away with the flowing coolant, thus greatly reducing the blockage and contamination of the membrane. Compared with traditional dead-end filtration, cross-flow filtration can keep the membrane in a relatively clean working state all the time, significantly increasing the service life of the membrane. At the same time, due to the membrane being less likely to be blocked, the filtration efficiency is also greatly improved, and the coolant can be purified more quickly and stably. By optimizing the entire recovered coolant treatment process, including the ultrasonic pre-treatment in the early stage and the cross-flow membrane filtration in the later stage, the recycling rate of the coolant can reach over 90%. This achievement not only effectively reduces the supplementary cost of the coolant during the processing but also reduces the pollution caused by the coolant discharge to the environment, achieving a win-win situation for economic and environmental benefits.

[0052] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention.

Claims

1. A cryogenic minimum quantity lubrication cooling method in precision machining of aluminum alloy, characterized in that, It includes the following steps: Processing parameter determination steps: Determine the cutting speed v, feed rate f, and cutting depth a according to the material properties of aluminum alloy, processing requirements, and tool performance p , based on the thermal conductivity λ, hardness H, and tool sharpness coefficient k f , through the formula Determine the coolant flow rate Q, where k is a coefficient related to the processing method. Simulate the cutting force and temperature through a finite element simulation model, and optimize and adjust the processing parameters; Coolant preparation steps: Select a vegetable oil-based base lubricating oil, use vortex tube refrigeration technology to reduce the compressed air temperature to a set threshold, and calculate the vortex tube refrigeration efficiency through the formula Calculate the vortex tube refrigeration efficiency, T in is the initial temperature of the compressed air, T out is the temperature after refrigeration, and control the refrigeration effect by adjusting the inlet pressure and flow rate of the vortex tube; Coolant injection steps: Inject coolant into the machining area through a special multi-channel nozzle, adjust the injection angle and flow rate according to the machining requirements. The injection angle θ is dynamically adjusted according to the machining process and tool shape, and an intelligent flow control valve is used to adjust the coolant flow rate Q according to the cutting force F through the formula where adjust , F0 is the preset cutting force threshold; Monitoring and adjustment step: Monitor the temperature of the processing area, tool wear condition and surface quality parameters. For temperature monitoring, a fiber Bragg grating temperature sensor is used to measure temperature changes. For tool wear monitoring, an acoustic emission sensor is combined with a vision monitoring system. The former captures tool wear signals, and the latter observes the tool wear morphology. For processing surface quality monitoring, a white light interferometer is used to measure the microtopography and roughness, and the processing surface quality is optimized by adjusting the processing parameters and coolant flow rate; Post-processing step after machining: Recycle and process the coolant. Separate large particle impurities and metal chips in the coolant through a centrifugal separation device, use membrane filtration technology to remove fine particles and colloidal impurities, detect the performance of the processed coolant, adjust the performance according to the detection results, collect and process the recycled metal chips, and make aluminum alloy raw materials through a melting and refining process.

2. The cryogenic minimum quantity lubrication cooling method in the precision machining of aluminum alloy according to claim 1, characterized in that, It also includes: Optimization steps for the coolant atomization effect: By setting a flow disturbance structure inside the nozzle to evenly distribute the oil mist particle size, the average oil mist particle size D is controlled by the formula , where P is the compressed air pressure, C and m are constants related to the nozzle structure, ρ air is the compressed air density, and ρ oil is the lubricating oil density; The pulse injection technology is adopted to inject the coolant through the frequency and pulse width. The pulse frequency f pulse is adjusted according to the processing parameters and the coolant flow rate.

3. The cryogenic minimum quantity lubrication cooling method in the precision machining of aluminum alloy according to claim 1, wherein It also includes: Processing energy consumption optimization steps: Based on processing parameters, coolant flow rate, and refrigeration equipment power, establish a comprehensive energy consumption model E = α×v + β×f + γ×Q + δ×P cool , where E is the total energy consumption during the processing, α, β, and γ are coefficients related to the processing equipment and process, δ is the coefficient related to the refrigeration equipment, and P cool is the power of the refrigeration equipment. Optimize the processing parameters and coolant flow rate through the genetic algorithm, and dynamically adjust the processing parameters and the operating state of the refrigeration equipment according to the energy consumption monitoring data during the processing.

4. The cryogenic minimum quantity lubrication cooling method in the precision machining of aluminum alloy according to claim 1, characterized in that, The vegetable oil-based lubricating oil is prepared by a multi-stage refining process to remove impurities and moisture. The vacuum distillation technology is used in the refining process, and the refined lubricating oil is hydrogenated. The degree of hydrogenation is adjusted by controlling the hydrogen pressure, temperature and reaction time.

5. The cryogenic minimum quantity lubrication cooling method in the precision machining of aluminum alloy according to claim 1, wherein The vortex tube refrigeration equipment is insulated with thermal insulation materials. The thermal conductivity of the thermal insulation materials is less than 0.05 W / (m·K) to maintain a low-temperature environment inside the vortex tube. Optimize the structural design of the vortex tube, increase the length and spiral angle of the vortex tube, and determine the structural parameters of the vortex tube through experiments combined with simulation values.

6. The cryogenic minimum quantity lubrication cooling method in the precision machining of aluminum alloy according to claim 1, characterized in that The multi-channel nozzle uses 3D printing technology to control the internal structure design and dimensions. The nozzle material is selected as a stainless steel alloy, and a micro-nano structure coating is set at the outlet.

7. The cryogenic minimum quantity lubrication cooling method in the precision machining of aluminum alloy according to claim 1, characterized in that, The fiber Bragg grating temperature sensors are distributed in different positions of the processing area to monitor the temperature distribution. The collected data is analyzed by establishing a temperature field model to feedback the temperature change trend. The temperature sensors are in real-time communication with the control system. When the temperature exceeds the set threshold, the coolant injection parameters are adjusted to control the temperature of the processing area.

8. The cryogenic minimum quantity lubrication cooling method in the precision machining of aluminum alloy according to claim 1, characterized in that, The acoustic emission sensor and the vision monitoring system use a fusion algorithm to process data. The acoustic emission sensor collects signals to reflect tool wear changes, and the vision monitoring system collects images to show the tool wear morphology. The two types of data are analyzed by correlation through the fusion algorithm to judge the tool wear degree and wear type.

9. The cryogenic minimum quantity lubrication cooling method in precision machining of aluminum alloy according to claim 1, characterized in that, The white light interferometer uses a displacement platform and a data acquisition system to measure the processing surface. The measurement results are analyzed by an image processing algorithm to obtain the surface roughness parameters and micro-profile information of the processing surface. The measurement results are compared with the preset surface quality standard. When the threshold is exceeded, the processing parameters and coolant flow rate are automatically adjusted.

10. The cryogenic minimum quantity lubrication cooling method in the precision machining of aluminum alloy according to claim 1, characterized in that, The ultrasonic-assisted cleaning technology is used for pretreatment of the coolant in the coolant recycling process. The ultrasonic frequency is 20 - 40 kHz to generate cavitation effects to separate impurities and metal chips in the coolant. The cross-flow filtration method is used in the membrane filtration process, and the process is recycled by optimizing the treatment process.

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