High-wear-resistance heavy-load transmission screw heat treatment and processing integrated method

Abstract

The application discloses a high-wear-resistance heavy-load transmission screw rod heat treatment and machining integrated method and relates to the technical field of screw rod machining, and specifically comprises the following steps: rough thread turning pretreatment is carried out on a high-strength alloy structural steel screw rod blank after quenching and tempering treatment, surface oxide layers and oxide skins are removed, and a finishing allowance is reserved; a tooth root plasma synchronous micro-boron infiltration activation process is carried out on a thread tooth root area, so that a boron content gradient is formed on the tooth root surface; the screw rod blank after the micro-boron infiltration activation treatment is transferred to an induction quenching station on line, and integral synchronous induction quenching heat treatment is carried out; and finally, thread tooth forming grinding machining is carried out on line; through the synergistic effect of the tooth root plasma synchronous micro-boron infiltration activation process and the integral synchronous induction quenching, a uniform boron content gradient and a phosphorus content gradient are formed on the thread tooth root, the hardness of the tooth root is ensured to be higher than that of the tooth tip, the hardenability of the tooth root is significantly improved, and the service life of the screw rod is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of lead screw processing technology, specifically a method for integrating heat treatment and processing of high wear-resistant heavy-duty transmission lead screws. Background Technology

[0002] As a core transmission component in high-end equipment, heavy machine tools, and engineering machinery, heavy-duty transmission screws must withstand enormous axial loads, radial loads, and periodic alternating loads during their service life, which places extremely high demands on their wear resistance, hardness uniformity, dimensional accuracy, and long-term stability.

[0003] Currently, the manufacturing process for heavy-duty lead screws has significant technical defects:

[0004] First, as the stress concentration point at the root of the thread, the quenching process makes it difficult to achieve uniform hardening of the root area, resulting in insufficient root hardness. This can easily lead to failures such as root fatigue fracture and excessive wear, which seriously affects the service life of the lead screw.

[0005] Secondly, during the heat treatment process, long heavy-duty lead screws are prone to uneven axial residual stress due to their large axial dimensions and uneven heat distribution. After subsequent precision machining, deformation will still occur, leading to lead screw accuracy failure and failing to meet the high-precision transmission requirements of high-end equipment.

[0006] Third, in the processing flow, each processing step is independent of the others and there is no coordinated control mechanism. The mismatch between the parameters of heat treatment and processing further aggravates the accuracy deviation and performance fluctuation. Summary of the Invention

[0007] In response to the above problems, although the industry has tried to adopt improvement measures such as local quenching and artificial stress relief, it has not fundamentally solved the core bottlenecks of insufficient hardenability of tooth root and uneven axial residual stress. Moreover, the processing efficiency is low and the process stability is poor, making it difficult to adapt to the needs of large-scale and high-precision production of heavy-duty ball screws.

[0008] Therefore, developing an integrated machining method that can simultaneously address tooth root strengthening and residual stress control, while ensuring continuous, stable, and reliable processes, has become an urgent need in the field of heavy-duty transmission screw machining.

[0009] This invention provides an integrated heat treatment and machining method for high wear-resistant heavy-duty transmission lead screws, specifically including the following steps:

[0010] The high-strength alloy structural steel wire rod blank after quenching and tempering is pre-treated by rough thread turning to remove the surface oxide layer and oxide scale and leave a finishing allowance.

[0011] The root region of the threaded tooth is treated with a synchronous micro-boron infiltration process using plasma to create a boron content gradient on the root surface.

[0012] The lead screw blank after micro-boron activation treatment is transferred online to the induction hardening station for overall synchronous induction hardening heat treatment, so that the hardness of the thread root is higher than that of the tooth tip, and at the same time a continuous phosphorus content gradient is formed from the thread root to the tooth tip.

[0013] Both the boron content gradient and the phosphorus content gradient were linearly fitted using the least squares method, and the R-squared of the fitted curve was not less than 0.98.

[0014] Keeping the original fixed state of the lead screw unchanged, online low-temperature stress-relieving tempering treatment is carried out; after tempering, a dynamic pre-tension coupling processing technology with residual stress adaptation is adopted. First, the axial residual stress distribution of the lead screw is detected online by X-ray diffraction. The X-ray beam is perpendicular to the axis of the lead screw. Each detection point is detected three times and the average value is taken. The residual stress data of each detection point is collected once every second. Then, the axial pre-tension loading force distribution is dynamically adjusted, and the temperature of each position is matched synchronously.

[0015] Finally, the thread tooth forming grinding process is performed online.

[0016] Furthermore, the specific steps of the thread roughing pretreatment are as follows;

[0017] During the machining process, the cutting speed is controlled to be uniform, which drives the lead screw blank to rotate synchronously. At the same time, the tool is controlled to feed at a uniform speed along the lead screw axis, and the feed direction is consistent with the screw thread direction. During the machining process, emulsion cutting fluid is continuously sprayed into the cutting area.

[0018] By coordinating the control of cutting speed and tool feed, the oxide layer and scale on the surface of the lead screw blank are gradually removed, and the threaded tooth blank is machined, while reserving a finishing allowance.

[0019] Furthermore, the specific technical solution for the tooth root plasma synchronous micro-boron infiltration activation process is as follows:

[0020] The working gas is a boron-argon-hydrogen mixture as the plasma jet medium. The mixture is composed of argon, high-purity hydrogen and boron source gas in a specific ratio. The boron source gas is a gaseous boride that can achieve local micro-boron infiltration.

[0021] During processing, the rough-machined thread blank is fixed to ensure that the thread root area is fully exposed. The plasma generator is started, and the generated plasma jet is adjusted to be aligned with the thread root area. The root is scanned using a closed-loop scanning method. During the scanning process, the energy of the plasma jet acts on the surface of the thread root, and at the same time, the boron source gas in the mixed gas is dissociated, allowing boron atoms to gradually penetrate into the surface layer of the root.

[0022] During the scanning process, the penetration depth and amount of boron atoms are controlled to ensure that the penetration depth is consistent with the depth of the hardened layer at the tooth root. The amount of boron is controlled between 0.8% and 1.2%, so that the modification and strengthening are achieved only within the hardened layer at the tooth root and do not penetrate into the tooth flank and tooth crest areas.

[0023] Furthermore, the specific implementation steps of the tooth root plasma synchronous micro-boron infiltration activation process are as follows:

[0024] First, the boron-argon-hydrogen mixed working gas is dehydrated and purified by using a dehydration device to remove moisture from the gas and a filtration device to remove solid impurities from the gas.

[0025] Then start the plasma generator and adjust the power of the equipment to five to fifteen kilowatts. The power is calculated and determined according to the tooth root size to generate a plasma jet. Adjust the jet nozzle to maintain a distance of three to five millimeters from the working surface of the thread tooth root. At the same time, adjust the jet axis to form an angle of forty-five to sixty degrees with the bottom surface of the thread tooth root. The angle is determined according to the tooth root angle.

[0026] During scanning, the lead screw blank is controlled to rotate at a constant speed, while the plasma jet is controlled to move at a constant speed along the axial direction of the lead screw thread to achieve closed-loop scanning. During the scanning process, the jet power, scanning speed and mixed gas ratio are adjusted once every second to control the penetration depth and amount of boron atoms.

[0027] During the treatment process, the pH value of the reaction environment is adjusted every fifteen minutes using a 10% (w / w) dilute sulfuric acid or dilute sodium hydroxide solution, with the pH fluctuation of a single adjustment not exceeding 0.1%.

[0028] Furthermore, the specific technical solution for the overall synchronous induction hardening heat treatment is as follows:

[0029] Medium-frequency induction heating equipment is used for heating, and the induction component of the heating equipment is adapted to the shape of the lead screw blank. The heating process adopts a segmented heating method, first gradually raising the heating temperature to a specific preheating temperature, and then maintaining this temperature for heat preservation treatment.

[0030] After preheating and heat preservation, the heating temperature is gradually increased to the target quenching temperature so that the entire thread area of ​​the lead screw is synchronously within the target quenching temperature range, and this temperature is maintained for heat preservation treatment. Nitrogen gas is continuously introduced into the heating area during the heat preservation process.

[0031] After the heat preservation is completed, the lead screw is immediately subjected to quenching and cooling treatment. Cooling water is evenly sprayed onto the entire surface of the lead screw through a ring-shaped spray structure. The cooling rate is controlled by adjusting the spray pressure and flow rate of the cooling water, so that the hardness of the thread root is higher than that of the tooth tip.

[0032] Furthermore, the specific technical solution for the online low-temperature stress-relieving tempering treatment is as follows:

[0033] After induction hardening, the lead screw blank is kept in its original fixed state, without disassembly or movement, and directly transferred to the tempering furnace for tempering treatment;

[0034] The tempering furnace uses a programmable temperature control method to control the heating rate to rise slowly;

[0035] Once the furnace temperature reaches the target tempering temperature, maintain that temperature for constant temperature insulation treatment, and continuously introduce nitrogen into the tempering furnace during the insulation process.

[0036] After the constant temperature holding is completed, a slow cooling method is adopted in the furnace to control the cooling rate and gradually reduce the temperature inside the furnace, so that the lead screw is slowly cooled to below a specific temperature, and then the lead screw is removed to complete the heat treatment closed loop.

[0037] Furthermore, the specific technical solution for the dynamic pre-tension coupling processing technology for residual stress adaptation is as follows:

[0038] After the lead screw is tempered online, keep it in its original fixed state and keep the X-ray diffraction instrument consistent with the lead screw fixed reference. Use X-ray diffraction to detect residual stress. During the test, the X-ray beam is perpendicular to the lead screw axis. Perform three tests on each test point and take the average value of the three test results as the residual stress value at that point.

[0039] Inspection points are arranged along the axis of the lead screw. The inspection points are denser at both ends and evenly distributed in the middle section. The length of the dense area at both ends is one-fifth of the total length of the lead screw, and an inspection point is arranged every 10 millimeters in this area. The length of the middle section is three-fifths of the total length of the lead screw, and an inspection point is arranged every 20 millimeters in this area.

[0040] Start the X-ray diffraction instrument and perform residual stress detection at each detection point using the method described above. Collect residual stress data at each detection point once per second, establish the correspondence between axial position and residual stress value, and form a complete residual stress distribution database.

[0041] Furthermore, based on the collected axial residual stress distribution data, the specific technical solution for implementing residual stress-adaptive dynamic axial preload loading is as follows:

[0042] Pre-tension loading is performed using a pre-tension loading process. The pre-tension loading device is connected to the fixed parts at both ends of the lead screw to ensure a firm connection without slippage.

[0043] The loading process follows the principle of complementary stress control. First, an initial preload is applied to the lead screw. The initial loading force is controlled within the range that causes slight elastic deformation of the lead screw. The initial loading force is calculated and determined based on the yield strength of high-strength alloy structural steel and the cross-sectional area of ​​the lead screw.

[0044] Then, based on the data in the residual stress distribution database, the preload force at each axial position of the screw is dynamically adjusted. For the middle section where the residual stress is greater than 300 MPa, the preload force is gradually increased so that the preload stress and the residual stress cancel each other out.

[0045] For the two ends where the residual stress does not exceed 300 MPa, adjust the preload force to match the residual stress range, which is 1.0 to 1.1 times the residual stress.

[0046] During the loading process, force sensing devices are used to monitor the loading force at each location. The force sensing devices are connected to the data acquisition system and collect loading force data once per second. The loading parameters are adjusted in a timely manner based on the feedback data.

[0047] Furthermore, the specific technical solution for the simultaneous implementation of dynamic preload and axial zone temperature coordinated control is as follows:

[0048] Along the screw axis, corresponding residual stress detection points are arranged with zoned temperature control units evenly spaced according to the detection point spacing. Each temperature control unit corresponds to one detection point. The temperature control unit adopts an independent electric heating module, and each module is equipped with an independent temperature controller, which can adjust its own temperature independently.

[0049] The temperature control unit is connected to the temperature control system, and collects temperature data from each temperature control unit every second. Based on the residual stress distribution and preload, the temperature at each point is adjusted accordingly. The adjustment standard is as follows:

[0050] For the intermediate section where the residual stress is greater than 300 MPa and the pretension is greater than the initial pretension, the temperature of the temperature control unit is adjusted to 40 to 60 degrees Celsius.

[0051] For the two ends where the residual stress does not exceed 300 MPa, the temperature of the temperature control unit is adjusted to 25 to 40 degrees Celsius;

[0052] During the control process, the temperature change along the entire length of the lead screw is monitored in real time, and the temperature fluctuation along the entire length of the lead screw is controlled within ±2 degrees Celsius.

[0053] Furthermore, the specific technical solution for online thread forming grinding under stress-temperature coupling conditions is as follows:

[0054] Keep the lead screw in its original fixed state, adjust the grinding mechanism to match the lead screw thread, and select a diamond grinding wheel suitable for heavy-duty lead screw grinding;

[0055] The grinding process adopts a multi-pass progressive grinding method. The first pass removes 60% to 70% of the total finishing allowance, the second pass removes 20% to 30% of the total finishing allowance, and the third pass removes 5% to 10% of the total finishing allowance. It is mainly used to correct thread tooth profile error and pitch error.

[0056] The grinding process is cooled and lubricated by constant temperature cutting fluid.

[0057] After grinding, maintain the coupling state until the lead screw cools to room temperature.

[0058] The technical solutions provided by the embodiments of this disclosure have at least the following beneficial effects:

[0059] By combining the synchronous micro-boron infiltration activation process of tooth root plasma with the overall synchronous induction hardening, a uniform boron content gradient and phosphorus content gradient are formed at the root of the thread, ensuring that the hardness of the tooth root is higher than that of the tooth tip, significantly improving the hardenability of the tooth root, avoiding failure problems such as tooth root fatigue fracture and excessive wear, and extending the service life of the screw.

[0060] Precise control of axial residual stress to ensure dimensional accuracy: The dynamic pre-tension coupling machining process with residual stress adaptation is adopted, combined with online detection and real-time parameter control by X-ray diffraction, to achieve uniform distribution of axial residual stress, effectively suppress screw deformation during heat treatment and finishing, and ensure that the screw pitch accuracy and tooth profile accuracy meet the requirements of high-end equipment.

[0061] Achieving continuous processing and improving machining efficiency and stability: The steps of rough thread turning, micro-boron diffusion activation of tooth roots, induction hardening, low temperature tempering, dynamic pre-stretching, and grinding are performed online continuously without the need to disassemble the lead screw, avoiding accuracy deviations caused by multiple clamping, and reducing process intervals. Attached Figure Description

[0062] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0063] 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0064] Please see Figure 1 This application provides an integrated heat treatment and machining method for high wear-resistant heavy-duty transmission screws, specifically including the following steps:

[0065] The high-strength alloy structural steel wire rod blank after quenching and tempering is pre-treated by rough thread turning to remove the surface oxide layer and oxide scale and leave a finishing allowance.

[0066] The root region of the threaded tooth is treated with a synchronous micro-boron infiltration process using plasma to create a boron content gradient on the root surface.

[0067] The lead screw blank after micro-boron activation treatment is transferred online to the induction hardening station for overall synchronous induction hardening heat treatment, so that the hardness of the thread root is higher than that of the tooth tip, and at the same time a continuous phosphorus content gradient is formed from the thread root to the tooth tip.

[0068] Both the boron content gradient and the phosphorus content gradient were linearly fitted using the least squares method, and the R-squared of the fitted curve was not less than 0.98.

[0069] Keeping the original fixed state of the lead screw unchanged, online low-temperature stress-relieving tempering treatment is carried out; after tempering, a dynamic pre-tension coupling processing technology with residual stress adaptation is adopted. First, the axial residual stress distribution of the lead screw is detected online by X-ray diffraction. The X-ray beam is perpendicular to the axis of the lead screw. Each detection point is detected three times and the average value is taken. The residual stress data of each detection point is collected once every second. Then, the axial pre-tension loading force distribution is dynamically adjusted, and the temperature of each position is matched synchronously.

[0070] Finally, the thread tooth forming grinding process is performed online.

[0071] It should be noted that the high-strength alloy structural steel lead screw blank refers to the initial blank made of high-strength alloy structural steel. This steel has high strength, high toughness, and good hardenability, making it suitable for heavy-duty lead screw service requirements. Thread roughing pretreatment refers to the preliminary thread machining of the blank through cutting processes to remove the surface oxide layer and scale. The formula for calculating the pre-reserved finishing allowance is: finishing allowance equals heat treatment deformation plus grinding allowance. The heat treatment deformation is calculated based on the lead screw length, specifically ΔL equal to 0.0005 multiplied by L (L is the total length of the lead screw, in millimeters). The grinding allowance is determined based on the thread accuracy grade. Tooth root plasma synchronous... The micro-boron infiltration activation process refers to a process that uses a boron-containing argon-hydrogen mixed gas as the plasma jet medium to scan the thread root turn by turn, simultaneously achieving root activation and local boron atom infiltration. The boron content gradient refers to a continuous and gradual distribution of boron atom content from the root surface to the interior, while the phosphorus content gradient refers to a continuous and gradual distribution of phosphorus content from the thread root to the tip. The specific calculation steps for the least squares linear fitting are as follows: select n detection points (n not less than five) on the gradient distribution, record the position coordinates xi and the corresponding element content yi of each detection point; assume the fitted straight line equation is y equal to a multiplied by x plus b, and calculate the average value x of xi, which is equal to the sum of all xi divided by n and yi. The average value y is equal to the sum of all yi divided by n; the regression coefficient a is equal to the sum of all (xi minus x-mean) multiplied by (yi minus y-mean) divided by the sum of all (xi minus x-mean) squares; the regression constant b is equal to y-mean minus a multiplied by x-mean; the determination coefficient R-squared of the fitted curve is equal to one minus the sum of all (yi minus (a multiplied by xi plus b)) squares divided by the sum of all (yi minus y-mean) squares, ensuring that R-squared is not less than 0.98; online low-temperature stress-relieving tempering treatment refers to the low-temperature heating and heat preservation of the quenched screw in a tempering furnace without disassembly and fixation; dynamic residual stress adaptation The pre-tension coupling machining process refers to a collaborative machining process in which the axial residual stress of the lead screw is first detected by X-ray diffraction, and then the pre-tension force and corresponding temperature are dynamically adjusted. The thread forming grinding process refers to the machining steps of high-precision machining of the thread through grinding to ensure the accuracy of the tooth shape and pitch. The sampling frequency of once per second, determined by the lead screw machining accuracy requirements and the performance of the data acquisition equipment, can ensure real-time capture of residual stress changes and meet the dynamic adjustment requirements. X-ray diffraction is a mature residual stress detection method in the industry, with a detection accuracy of ±5 MPa, which can obtain the axial residual stress distribution of the lead screw, providing core data support for subsequent dynamic pre-tensioning and temperature control.

[0072] As an optional embodiment, the specific steps of the thread roughing pretreatment are as follows;

[0073] During the machining process, the cutting speed is controlled to be uniform, which drives the lead screw blank to rotate synchronously. At the same time, the tool is controlled to feed at a uniform speed along the lead screw axis, and the feed direction is consistent with the screw thread direction. During the machining process, emulsion cutting fluid is continuously sprayed into the cutting area.

[0074] By coordinating the control of cutting speed and tool feed, the oxide layer and scale on the surface of the lead screw blank are gradually removed, and the threaded tooth blank is machined, while reserving a finishing allowance.

[0075] It should be noted that the carbide cutting tools adapted for high-strength alloy structural steel refer to the YW2 model carbide cutting tools, which can withstand the cutting hardness of high-strength alloy structural steel; the cutting edge grinding treatment refers to polishing the cutting edge of the tool with a grinding wheel to ensure that the cutting edge is sharp and free from chipping; the cutting speed is determined according to the lead screw diameter, and the calculation formula is v equal to π multiplied by d multiplied by n and then divided by 1000 (v is the cutting speed, in meters per minute, d is the diameter of the lead screw blank, in millimeters, and n is the rotational speed, in revolutions per minute); the axial uniform feed rate of the tool is determined according to the thread lead, and the feed rate f is equal to the lead multiplied by the rotational speed n to ensure the roughing accuracy of the thread; the emulsion cutting fluid refers to the cutting fluid made by mixing water, emulsifier and rust inhibitor in a mass ratio of 95:4:1, and its function is to reduce the cutting temperature, reduce tool wear and remove cutting chips; the thread tooth blank refers to the lead screw semi-finished product that has a preliminary thread profile after rough machining but has not yet reached the final accuracy requirements.

[0076] As an optional embodiment, the specific technical solution for the tooth root plasma synchronous micro-boron infiltration activation process is as follows:

[0077] The working gas is a boron-argon-hydrogen mixture as the plasma jet medium. The mixture is composed of argon, high-purity hydrogen and boron source gas in a specific ratio. The boron source gas is a gaseous boride that can achieve local micro-boron infiltration.

[0078] During processing, the rough-machined thread blank is fixed to ensure that the thread root area is fully exposed. The plasma generator is started, and the generated plasma jet is adjusted to be aligned with the thread root area. The root is scanned using a closed-loop scanning method. During the scanning process, the energy of the plasma jet acts on the surface of the thread root, and at the same time, the boron source gas in the mixed gas is dissociated, allowing boron atoms to gradually penetrate into the surface layer of the root.

[0079] During the scanning process, the penetration depth and amount of boron atoms are controlled to ensure that the penetration depth is consistent with the depth of the hardened layer at the tooth root. The amount of boron is controlled between 0.8% and 1.2%, so that the modification and strengthening are achieved only within the hardened layer at the tooth root and do not penetrate into the tooth flank and tooth crest areas.

[0080] It should be noted that the mixing ratio calculation steps for the boron-argon-hydrogen mixed working gas are as follows: argon accounts for 85% to 90%, high-purity hydrogen accounts for 5% to 10%, and boron source gas accounts for 1% to 5%. The specific ratio is calculated based on the screw tooth root size. The gaseous boride used is boron trifluoride (BF3). The plasma generating equipment refers to a plasma generating device with adjustable output power, ranging from 5 to 15 kilowatts. Closed-loop scanning refers to the plasma jet scanning along the screw tooth root circle by circle, with the scanning trajectory completely matching the screw tooth root contour, leaving no missed areas. Boron atom penetration depth refers to the depth of boron atom penetration from the tooth... The distance the penetrating from the root surface into the interior, and the depth of the hardened layer at the tooth root are calculated based on the screw diameter. Specifically, the hardened layer depth is equal to 0.05 times the screw diameter (in millimeters), and the difference between the penetration depth and the hardened layer depth does not exceed ±0.02 millimeters. The boron penetration amount refers to the mass fraction of boron atoms on the tooth root surface. The calculation steps are: the boron penetration amount equals (the mass of boron on the tooth root surface after boron penetration minus the mass of boron on the tooth root surface before boron penetration) divided by the total mass of the tooth root surface before boron penetration, and then multiplied by 100. The range of boron penetration amount from 0.8% to 1.2% has been verified through multiple experiments to improve the hardenability of the tooth root while avoiding an increase in tooth root brittleness, which is the optimal and reasonable range.

[0081] As an optional embodiment, the specific implementation steps of the tooth root plasma synchronous micro-boron infiltration activation process are as follows:

[0082] First, the boron-argon-hydrogen mixed working gas is dehydrated and purified by using a dehydration device to remove moisture from the gas and a filtration device to remove solid impurities from the gas.

[0083] Then start the plasma generator and adjust the power of the equipment to five to fifteen kilowatts. The power is calculated and determined according to the tooth root size to generate a plasma jet. Adjust the jet nozzle to maintain a distance of three to five millimeters from the working surface of the thread tooth root. At the same time, adjust the jet axis to form an angle of forty-five to sixty degrees with the bottom surface of the thread tooth root. The angle is determined according to the tooth root angle.

[0084] During scanning, the lead screw blank is controlled to rotate at a constant speed, while the plasma jet is controlled to move at a constant speed along the axial direction of the lead screw thread to achieve closed-loop scanning. During the scanning process, the jet power, scanning speed and mixed gas ratio are adjusted once every second to control the penetration depth and amount of boron atoms.

[0085] During the treatment process, the pH value of the reaction environment is adjusted every fifteen minutes using a 10% (w / w) dilute sulfuric acid or dilute sodium hydroxide solution, with the pH fluctuation of a single adjustment not exceeding 0.1%.

[0086] It should be noted that the dehydration device uses a molecular sieve dehydrator, which can remove moisture from the gas to no more than 10 ppm; the filtration device uses a filter to remove solid impurities from the gas; the calculation steps for the power of the plasma generator are: power P equals 0.5 times the tooth root circumference (in millimeters), and a power range of 5 to 15 kilowatts is suitable for micro-boroning requirements of different tooth root sizes; the calculation steps for the distance between the jet nozzle and the working surface of the thread tooth root are: distance equals 0.8 times the jet nozzle diameter (in millimeters); the selection standard for the angle between the jet axis and the bottom surface of the thread tooth root is: when the tooth root angle is 30 degrees, the angle is taken as 60 degrees; when the tooth root angle is 45 degrees, the angle is taken as 45 degrees; the uniform rotation speed of the lead screw blank is matched with the scanning speed, and the calculation formula is: rotation speed n equals scanning speed v divided by thread lead p (n is the rotation speed, in revolutions per minute). (Minutes, v is the scanning speed in millimeters per minute, p is the thread lead in millimeters); 10% concentration dilute sulfuric acid refers to a mixture of 10 grams of concentrated sulfuric acid and 90 grams of deionized water; 10% concentration dilute sodium hydroxide solution refers to a mixture of 10 grams of sodium hydroxide and 90 grams of deionized water. The specific calculation steps for pH adjustment are as follows: First, detect the current pH value of the reaction environment. If the pH is less than 4.8, add dilute sodium hydroxide solution. The amount added, V, is equal to (4.8 minus the current pH value) multiplied by the volume of the reaction system and then multiplied by 0.01 (in milliliters). If the pH is greater than 5.2, add dilute sulfuric acid solution. The amount added, V, is equal to (current pH value minus 5.2) multiplied by the volume of the reaction system and then multiplied by 0.01 (in milliliters). The frequency of adjustment once per second ensures that the parameters match the boronizing requirements in real time, avoiding deviations between the penetration depth and the amount of boron.

[0087] As an optional embodiment, the specific technical solution for the overall synchronous induction hardening heat treatment is as follows:

[0088] Medium-frequency induction heating equipment is used for heating, and the induction component of the heating equipment is adapted to the shape of the lead screw blank. The heating process adopts a segmented heating method, first gradually raising the heating temperature to a specific preheating temperature, and then maintaining this temperature for heat preservation treatment.

[0089] After preheating and heat preservation, the heating temperature is gradually increased to the target quenching temperature so that the entire thread area of ​​the lead screw is synchronously within the target quenching temperature range, and this temperature is maintained for heat preservation treatment. Nitrogen gas is continuously introduced into the heating area during the heat preservation process.

[0090] After the heat preservation is completed, the lead screw is immediately subjected to quenching and cooling treatment. Cooling water is evenly sprayed onto the entire surface of the lead screw through a ring-shaped spray structure. The cooling rate is controlled by adjusting the spray pressure and flow rate of the cooling water, so that the hardness of the thread root is higher than that of the tooth tip.

[0091] It should be noted that medium-frequency induction heating equipment refers to induction heating equipment with an output frequency of one to ten kilohertz. The output power is calculated based on the lead screw diameter, specifically, the power P equals two times the lead screw diameter (in millimeters) (in kilowatts). The matching of the induction component and the lead screw blank shape means that the inner diameter of the induction component is two to three millimeters larger than the diameter of the lead screw blank, ensuring uniform heating. The segmented heating method refers to a preheating stage and a quenching heating stage. The specific preheating temperature is determined based on the phase transformation temperature of the high-strength alloy structural steel. The calculation steps for the preheating holding time are: holding time t equals 0.5 times the lead screw diameter (in millimeters) (in minutes). The target quenching temperature is 850 to 800 kilohertz. Eighty degrees Celsius, quenching and holding time t equals 0.3 times the lead screw diameter (in millimeters) (in minutes); nitrogen flow rate is calculated based on the volume of the heating area, its function is to isolate air and prevent oxidation of the lead screw surface; uniform spray water cooling method refers to the spray structure being uniformly arranged in a ring, with the spray range covering the entire surface of the lead screw; cooling water spray pressure range is 0.2 to 0.4 MPa, flow rate range is 10 to 20 liters per minute, and the cooling rate calculation steps are: cooling rate v equals (quenching temperature minus 200 degrees Celsius) divided by cooling time (in degrees Celsius per minute), controlling the cooling rate to 50 to 80 degrees Celsius per minute to ensure that the hardness of the tooth root is higher than that of the tooth tip.

[0092] As an optional embodiment, the specific technical solution for the online low-temperature stress-relieving tempering treatment is as follows:

[0093] After induction hardening, the lead screw blank is kept in its original fixed state, without disassembly or movement, and directly transferred to the tempering furnace for tempering treatment;

[0094] The tempering furnace uses a programmable temperature control method to control the heating rate to rise slowly;

[0095] Once the furnace temperature reaches the target tempering temperature, maintain that temperature for constant temperature insulation treatment, and continuously introduce nitrogen into the tempering furnace during the insulation process.

[0096] After the constant temperature holding is completed, a slow cooling method is adopted in the furnace to control the cooling rate and gradually reduce the temperature inside the furnace, so that the lead screw is slowly cooled to below a specific temperature, and then the lead screw is removed to complete the heat treatment closed loop.

[0097] It should be noted that the original fixed state refers to the screw maintaining its fixed position and method during induction hardening, avoiding changes in the fixed position that could generate new residual stress; the programmable temperature control method refers to the automatic heating, holding, and cooling achieved by presetting a temperature curve through the tempering furnace control system; the heating rate is controlled at 5 to 10 degrees Celsius per minute, calculated as follows: heating rate v equals (target tempering temperature minus room temperature) divided by heating time (in degrees Celsius per minute); the target tempering temperature is 180 to 220 degrees Celsius, determined based on the magnitude of residual stress in the screw; the constant temperature holding time is calculated as follows: holding time t equals 1.5 times the screw diameter (in millimeters) (in minutes); the nitrogen flow rate is 1 to 2 liters per minute, used to prevent oxidation of the screw surface; the slow cooling method refers to the tempering furnace cooling device not being turned on during the cooling process, allowing the furnace temperature to drop naturally, with the cooling rate controlled at 2 to 5 degrees Celsius per minute, and the specific temperature referring to room temperature, ensuring that no new residual stress is generated after the screw cools.

[0098] As an optional embodiment, the specific technical solution of the dynamic pre-tension coupling processing technology for residual stress adaptation is as follows:

[0099] After the lead screw is tempered online, keep it in its original fixed state and keep the X-ray diffraction instrument consistent with the lead screw fixed reference. Use X-ray diffraction to detect residual stress. During the test, the X-ray beam is perpendicular to the lead screw axis. Perform three tests on each test point and take the average value of the three test results as the residual stress value at that point.

[0100] Inspection points are arranged along the axis of the lead screw. The inspection points are denser at both ends and evenly distributed in the middle section. The length of the dense area at both ends is one-fifth of the total length of the lead screw, and an inspection point is arranged every 10 millimeters in this area. The length of the middle section is three-fifths of the total length of the lead screw, and an inspection point is arranged every 20 millimeters in this area.

[0101] Start the X-ray diffraction detector and perform residual stress detection at each detection point using the method described above. Collect residual stress data at each detection point once per second, establish the correspondence between axial position and residual stress value, and form a complete residual stress distribution database.

[0102] It should be noted that the X-ray diffraction detector refers to the equipment that uses X-ray diffraction to detect residual stress, with a detection accuracy of ±5 MPa. This detection method is a mature residual stress detection method in the industry, with high accuracy and convenient operation. The lead screw fixing datum refers to the positioning datum during lead screw machining, usually the center holes at both ends of the lead screw, ensuring that the detection datum is consistent with the machining datum. The calculation steps for the layout of detection points are as follows: the total length of the lead screw is L (in millimeters), the length of the densely reinforced area at both ends is L divided by five, and a detection point is placed every 10 millimeters in this area; the length of the middle section is three times L divided by five, and a detection point is placed every 20 millimeters in this area. The specific operating standards for residual stress detection are: X The X-ray beam is perpendicular to the screw axis, the detection voltage is 30 to 40 kilovolts, and the detection current is 20 to 30 milliamps. Each detection point is tested three times consecutively, and the average value is taken after removing outliers as the residual stress value at that point. The residual stress distribution database refers to a tabular data set that maps the axial position coordinates of each detection point to the corresponding residual stress value, which is used as the basis for subsequent dynamic pre-tensioning parameter adjustment. The X-ray diffraction method has the advantages of being non-destructive, having high detection accuracy, and being suitable for full axial detection of long screws. It can obtain the axial residual stress distribution of the screw, providing core data support for subsequent dynamic pre-tensioning and temperature control, and ensuring the reproducibility of the technical solution.

[0103] As an optional embodiment, based on the collected axial residual stress distribution data, the specific technical solution for implementing residual stress-adaptive dynamic axial preload is as follows:

[0104] Pre-tension loading is performed using a pre-tension loading process. The pre-tension loading device is connected to the fixed parts at both ends of the lead screw to ensure a firm connection without slippage.

[0105] The loading process follows the principle of complementary stress control. First, an initial preload is applied to the lead screw. The initial loading force is controlled within the range that causes slight elastic deformation of the lead screw. The initial loading force is calculated and determined based on the yield strength of high-strength alloy structural steel and the cross-sectional area of ​​the lead screw.

[0106] Then, based on the data in the residual stress distribution database, the preload force at each axial position of the screw is dynamically adjusted. For the middle section where the residual stress is greater than 300 MPa, the preload force is gradually increased so that the preload stress and the residual stress cancel each other out.

[0107] For the two ends where the residual stress does not exceed 300 MPa, adjust the preload force to match the residual stress range, which is 1.0 to 1.1 times the residual stress.

[0108] During the loading process, force sensing devices are used to monitor the loading force at each location. The force sensing devices are connected to the data acquisition system and collect loading force data once per second. The loading parameters are adjusted in a timely manner based on the feedback data.

[0109] It should be noted that the pre-tension loading process refers to a loading method that can achieve load force control, with a loading accuracy of ±1 kN; the stress complementary control principle means that the pre-tension stress and residual stress are opposite in direction and matched in magnitude, so that the total stress at all positions of the screw tends to be uniform; the calculation steps of the initial pre-tension loading force are as follows: the initial pre-tension force F0 is equal to σs multiplied by A and then multiplied by 0.05, where σs is the yield strength of high-strength alloy structural steel, A is the cross-sectional area of ​​the screw (A is equal to π multiplied by the square of d and then divided by four, where d is the diameter of the screw, in millimeters), and 0.05 here is the elastic deformation coefficient, which is of the same origin as the temperature compensation coefficient of 0.05. Its determination basis, verification process and reasonable range are as follows: Through multiple sets of comparative tests, high-strength alloy structural steel screw samples were selected, and elastic deformation control and temperature control tests were carried out using five coefficients: 0.04, 0.045, 0.05, 0.055, and 0.06. The test results show that the coefficient is within the range of 0.05. Within the range of 4 to 0.06, elastic deformation control and temperature-preload matching can be achieved. The optimal effect is achieved with a coefficient of 0.05, therefore 0.05 is determined as the optimal value, and the reasonable range is 0.04 to 0.06. The calculation steps for the preload force in the middle section are: F1 equals σres1 multiplied by A and then multiplied by k, where σres1 is the residual stress in the middle section (in MPa), and k is the stress adaptation coefficient. The calculation steps for the preload force in both end sections are: F2 equals σres2 multiplied by A and then multiplied by k, where σres2 is the residual stress in both end sections (in MPa), and k is the stress adaptation coefficient. The force sensing device refers to a tension sensing device with an accuracy level of 0.1, and the frequency of sampling once per second ensures timely capture of loading force fluctuations, guaranteeing the loading process. Residual stress greater than 300 MPa is defined as a high stress state, determined in conjunction with the service stress threshold of high-strength alloy structural steel wire rods, which can effectively avoid deformation of the wire rod due to excessive residual stress.

[0110] As an optional embodiment, the specific technical solution for the simultaneous implementation of dynamic preload and axial zone temperature coordinated control is as follows:

[0111] Along the screw axis, corresponding residual stress detection points are arranged with zoned temperature control units evenly spaced according to the detection point spacing. Each temperature control unit corresponds to one detection point. The temperature control unit adopts an independent electric heating module, and each module is equipped with an independent temperature controller, which can adjust its own temperature independently.

[0112] The temperature control unit is connected to the temperature control system, and collects temperature data from each temperature control unit every second. Based on the residual stress distribution and preload, the temperature at each point is adjusted accordingly. The adjustment standard is as follows:

[0113] For the intermediate section where the residual stress is greater than 300 MPa and the pretension is greater than the initial pretension, the temperature of the temperature control unit is adjusted to 40 to 60 degrees Celsius.

[0114] For the two ends where the residual stress does not exceed 300 MPa, the temperature of the temperature control unit is adjusted to 25 to 40 degrees Celsius;

[0115] During the control process, the temperature change along the entire length of the lead screw is monitored in real time, and the temperature fluctuation along the entire length of the lead screw is controlled within ±2 degrees Celsius.

[0116] It should be noted that the zoned temperature control unit refers to a small temperature control module made of electric heating elements, with a power of 50 to 100 watts, and an independent temperature controller to achieve temperature adjustment; the temperature control system refers to a system that can collect temperature data in real time and adjust the temperature of the temperature control unit, with a temperature control accuracy of ±1 degree Celsius; the actual service temperature range of the lead screw is determined according to the application scenario, with the middle section temperature of 40 to 60 degrees Celsius and the two end section temperatures of 25 to 40 degrees Celsius both suitable for the actual service conditions of heavy-duty lead screws; the calculation steps for targeted temperature control are as follows: the middle section temperature T1 is equal to the service temperature plus (F1 minus F0) multiplied by 0.05, and the two end section temperature T2 is equal to the service temperature plus (F2 minus F0) multiplied by 0.05, where 0.05 is the temperature compensation coefficient. The basis, verification process, and reasonable range of this coefficient are as follows: through multiple sets of comparative tests, high-strength alloy structural steel lead screw samples were selected, and 0.04, 0.045, and 0.05 were used respectively. Temperature control experiments were conducted using five coefficients: 0.05, 0.055, and 0.06. The coefficient values ​​were the experimental variables, while residual stress and preload parameters were fixed. The accuracy of temperature control and stress-temperature coupling under different coefficients were tested. The results showed that when the coefficients were within the range of 0.04 to 0.06, the temperature control accuracy error was less than ±1 degree Celsius, indicating a stable stress-temperature coupling state. The optimal coefficient was 0.05, therefore 0.05 was determined as the optimal value, with a reasonable range of 0.04 to 0.06. This avoids problems such as inappropriate generalization of single-point parameters and overly narrow protection ranges, while also ensuring that those skilled in the art can reproduce the temperature control process. Temperature data was collected every second to ensure timely temperature control, and a temperature fluctuation range of ±2 degrees Celsius ensured the stability of the stress-temperature coupling state. A one-to-one correspondence meant that one temperature control unit corresponded to one residual stress detection point, with the spacing between the control units matching the spacing of the detection points, ensuring that temperature control and residual stress detection points were well-matched.

[0117] As an optional embodiment, the specific technical solution for online thread forming grinding under stress-temperature coupling conditions is as follows:

[0118] Keep the lead screw in its original fixed state, adjust the grinding mechanism to match the lead screw thread, and select a diamond grinding wheel suitable for heavy-duty lead screw grinding;

[0119] The grinding process adopts a multi-pass progressive grinding method. The first pass removes 60% to 70% of the total finishing allowance, the second pass removes 20% to 30% of the total finishing allowance, and the third pass removes 5% to 10% of the total finishing allowance. It is mainly used to correct thread tooth profile error and pitch error.

[0120] The grinding process is cooled and lubricated by constant temperature cutting fluid.

[0121] After grinding, maintain the coupling state until the lead screw cools to room temperature.

[0122] It should be noted that the grinding mechanism refers to the machining mechanism capable of thread grinding, with a grinding accuracy of ±0.001 mm; the diamond grinding wheel is made of diamond abrasive, suitable for the high-precision grinding requirements of heavy-duty lead screws; the allowance distribution of multi-pass progressive grinding is to avoid excessive grinding amount in a single pass, which could cause lead screw deformation, while balancing grinding efficiency and accuracy; the allowable range for thread tooth profile error is no more than 0.002 mm, and the allowable range for pitch error is no more than 0.001 mm; the constant temperature cutting fluid is a synthetic cutting fluid, whose cooling and lubrication performance is suitable for grinding requirements; the special spray structure refers to the structure that can spray cutting fluid onto the grinding area; maintaining coupled cooling after grinding means continuing to maintain pre-load and temperature control until the lead screw temperature drops to room temperature, avoiding deformation during the cooling process.

[0123] The technical effects of the present invention are further illustrated below through specific embodiments and comparative examples. The materials and equipment used in the embodiments are all conventional commercially available products, and the process parameters not specifically described are all set in accordance with the scope of the claims of the present invention.

[0124] Example 1

[0125] The heavy-duty transmission lead screw manufactured in this embodiment has the following specifications: diameter 50mm, total length 1500mm, thread lead 10mm, accuracy grade C5, and is made of high-strength alloy structural steel.

[0126] The processing steps are strictly performed according to the method described in the claims of this invention, and the key parameters are as follows:

[0127] Thread roughing pretreatment: Select YW2 carbide cutting tool, cutting speed 90m / min, feed rate 100mm / min, leave finishing allowance of 0.12mm (heat treatment deformation 0.75mm×0.0005=0.00075mm, grinding allowance 0.119mm), continuously spray emulsion cutting fluid.

[0128] Tooth root plasma synchronous micro-boron infiltration activation: the ratio of boron-argon-hydrogen mixed gas is 88% argon, 8% high-purity hydrogen, and 4% boron trifluoride. The plasma generator power is 10kW, the distance between the jet nozzle and the tooth root working surface is 4mm, the angle between the jet axis and the bottom surface of the tooth root is 50°, the scanning speed is 15mm / min, the boron infiltration amount is 1.0%, and the infiltration depth is 2.5mm (consistent with the depth of the tooth root hardened layer).

[0129] Overall synchronous induction hardening: Medium frequency induction heating equipment with frequency of 5kHz, power of 100kW, preheating temperature of 680℃, preheating holding time of 25min, target quenching temperature of 860℃, quenching holding time of 15min, nitrogen flow rate of 10L / min, cooling water spray pressure of 0.3MPa, flow rate of 15L / min, and cooling rate of 65℃ / min.

[0130] Online low-temperature stress-relief tempering: target tempering temperature 200℃, heating rate 8℃ / min, constant temperature holding time 75min, nitrogen flow rate 1.5L / min, cooling rate 3℃ / min, and removed after cooling to room temperature.

[0131] Dynamic pre-tension coupling processing: Residual stress was detected by X-ray diffraction. The detection points were densely packed at both ends of the section, with one point every 10 mm and one point every 20 mm in the middle section. The initial pre-tension force F0 = 835MPa × (π × 50² / 4) × 0.05 ≈ 8200N. The residual stress in the middle section was 320MPa. The pre-tension loading force F1 = 320MPa × (π × 50² / 4) × 1.2 ≈ 75400N. The residual stress at both ends of the section was 280MPa. The pre-tension loading force F2 = 280MPa × (π × 50² / 4) × 1.05 ≈ 57700N. The temperature was controlled at 50℃ in the middle section and 35℃ in the two ends of the section.

[0132] Grinding: Diamond grinding wheel with a grit size of 100 mesh and a hardness of HV1100, ground in three passes with a filler weight distribution of 65%, 25%, and 10%, constant temperature cutting fluid temperature of 20℃, and spray flow rate of 8L / min.

[0133] Example 2

[0134] The heavy-duty transmission screw processed in this embodiment has the following specifications: diameter 80mm, total length 2000mm, thread lead 16mm, accuracy grade C3, and is made of high-strength alloy structural steel.

[0135] The processing steps are strictly performed according to the method described in the claims of this invention, and the key parameters are as follows:

[0136] Thread roughing pretreatment: Select YW2 carbide cutting tool, cutting speed 85m / min, feed rate 128mm / min, leave finishing allowance of 0.18mm (heat treatment deformation 2000mm×0.0005=0.001mm, grinding allowance 0.179mm), continuously spray emulsion cutting fluid.

[0137] Tooth root plasma synchronous micro-boron infiltration activation: the ratio of boron-argon-hydrogen mixed gas is 85% argon, 10% high-purity hydrogen, and 5% boron trifluoride. The plasma generator power is 15kW, the distance between the jet nozzle and the tooth root working surface is 5mm, the angle between the jet axis and the bottom surface of the tooth root is 60°, the scanning speed is 12mm / min, the boron infiltration amount is 1.2%, and the infiltration depth is 4.0mm (consistent with the depth of the tooth root hardened layer).

[0138] Overall synchronous induction hardening: Medium frequency induction heating equipment with frequency of 3kHz, power of 160kW, preheating temperature of 670℃, preheating holding time of 40min, target quenching temperature of 870℃, quenching holding time of 24min, nitrogen flow rate of 15L / min, cooling water spray pressure of 0.4MPa, flow rate of 20L / min, and cooling rate of 75℃ / min.

[0139] Online low-temperature stress-relief tempering: target tempering temperature 220℃, heating rate 10℃ / min, constant temperature holding time 120min, nitrogen flow rate 2L / min, cooling rate 4℃ / min, and removed after cooling to room temperature.

[0140] Dynamic pre-tension coupling processing: Residual stress was detected by X-ray diffraction. The detection points were densely packed at both ends of the section, with one point every 10 mm and one point every 20 mm in the middle section. The initial pre-tension force F0 = 835MPa × (π × 80² / 4) × 0.05 ≈ 26200N. The residual stress in the middle section was 350MPa. The pre-tension loading force F1 = 350MPa × (π × 80² / 4) × 1.3 ≈ 228700N. The residual stress at both ends of the section was 290MPa. The pre-tension loading force F2 = 290MPa × (π × 80² / 4) × 1.1 ≈ 160500N. The temperature was controlled at 60℃ in the middle section and 40℃ in the two ends of the section.

[0141] Grinding: Diamond grinding wheel with a grit size of 80 mesh and a hardness of HV1200, ground in three passes with a filler weight distribution of 60%, 30%, and 10%, constant temperature cutting fluid temperature of 22℃, and spray flow rate of 10L / min.

[0142] Example 3

[0143] The heavy-duty transmission screw processed in this embodiment has the following specifications: diameter 30mm, total length 1000mm, thread lead 8mm, accuracy grade C5, and is made of high-strength alloy structural steel.

[0144] The processing steps are strictly performed according to the method described in the claims of this invention, and the key parameters are as follows:

[0145] Thread roughing pretreatment: Select YW2 carbide cutting tool, cutting speed 95m / min, feed rate 80mm / min, leave finishing allowance of 0.10mm (heat treatment deformation 1000mm×0.0005=0.0005mm, grinding allowance 0.0995mm), continuously spray emulsion cutting fluid.

[0146] Tooth root plasma synchronous micro-boron infiltration activation: the ratio of boron-argon-hydrogen mixed gas is 90% argon, 9% high-purity hydrogen, and 1% boron trifluoride. The plasma generator power is 5kW, the distance between the jet nozzle and the tooth root working surface is 3mm, the angle between the jet axis and the bottom surface of the tooth root is 45°, the scanning speed is 20mm / min, the boron infiltration amount is 0.8%, and the infiltration depth is 1.5mm (consistent with the depth of the tooth root hardened layer).

[0147] Overall synchronous induction hardening: Medium frequency induction heating equipment with frequency of 8kHz, power of 60kW, preheating temperature of 690℃, preheating holding time of 15min, target quenching temperature of 850℃, quenching holding time of 9min, nitrogen flow rate of 8L / min, cooling water spray pressure of 0.2MPa, flow rate of 10L / min, and cooling rate of 55℃ / min.

[0148] Online low-temperature stress-relief tempering: target tempering temperature 180℃, heating rate 5℃ / min, constant temperature holding time 45min, nitrogen flow rate 1L / min, cooling rate 2℃ / min, and removed after cooling to room temperature.

[0149] Dynamic pre-tension coupling processing: Residual stress was detected by X-ray diffraction. The detection points were densely packed at both ends of the section, with one point every 10 mm and one point every 20 mm in the middle section. The initial pre-tension force F0 = 835MPa × (π × 30² / 4) × 0.05 ≈ 2920N. The residual stress in the middle section was 310MPa. The pre-tension loading force F1 = 310MPa × (π × 30² / 4) × 1.1 ≈ 24900N. The residual stress at both ends of the section was 270MPa. The pre-tension loading force F2 = 270MPa × (π × 30² / 4) × 1.0 ≈ 23000N. The temperature was controlled at 40℃ in the middle section and 25℃ in the two ends of the section.

[0150] Grinding: Diamond grinding wheel with a grit size of 120 mesh and a hardness of HV1000, ground in three passes with a filler weight distribution of 70%, 20%, and 10%, constant temperature cutting fluid temperature of 18℃, and spray flow rate of 5L / min.

[0151] Comparative Example

[0152] The heavy-duty transmission lead screw (50mm diameter, 1500mm total length, 10mm thread lead, C5 precision grade, high-strength alloy structural steel) is manufactured with specifications completely identical to those in Example 1. The process steps are: quenching and tempering – rough thread turning – overall quenching – manual stress relief – thread fine grinding. The key parameters are as follows:

[0153] Rough thread turning: Same as in Example 1, with a finishing allowance of 0.12mm.

[0154] Overall quenching: Conventional medium-frequency induction quenching is adopted at a temperature of 860℃ for 15 minutes, followed by cooling water spraying and activation treatment without tooth root micro-boron diffusion.

[0155] Stress relief treatment: Stress relief is achieved by manual hammering, without online low-temperature tempering or dynamic pre-tension control.

[0156] Grinding: Same as in Example 1, without temperature-controlled adjustment.

[0157] Performance comparison results between the examples and the comparative examples

[0158] For the lead screws processed in Examples 1-3 and the comparative example, the tooth root hardness, axial residual stress uniformity, pitch accuracy, wear resistance (wear amount), and service life were tested respectively. The testing methods all adopted industry standards. The comparison results are shown in the table below:

[0159]

[0160] As can be seen from the above comparison results, the integrated machining method of the present invention has significant improvements in key performance indicators such as tooth root hardness, uniformity of axial residual stress, pitch accuracy, wear resistance and service life compared with the machining process.

[0161] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for integrating heat treatment and machining of a high wear-resistant heavy-duty transmission lead screw, characterized in that, Specifically, the following steps are included: The high-strength alloy structural steel wire rod blank after quenching and tempering is pre-treated by rough thread turning to remove the surface oxide layer and oxide scale and leave a finishing allowance. The root region of the threaded tooth is treated with a synchronous micro-boron infiltration process using plasma to create a boron content gradient on the root surface. The lead screw blank after micro-boron activation treatment is transferred online to the induction hardening station for overall synchronous induction hardening heat treatment, so that the hardness of the thread root is higher than that of the tooth tip, and at the same time a continuous phosphorus content gradient is formed from the thread root to the tooth tip. Both the boron content gradient and the phosphorus content gradient were linearly fitted using the least squares method, and the R-squared of the fitted curve was not less than 0.

98. Keeping the original fixed state of the lead screw unchanged, online low-temperature stress-relieving tempering treatment is carried out; after tempering, a dynamic pre-tension coupling processing technology with residual stress adaptation is adopted. First, the axial residual stress distribution of the lead screw is detected online by X-ray diffraction. The X-ray beam is perpendicular to the axis of the lead screw. Each detection point is detected three times and the average value is taken. The residual stress data of each detection point is collected once every second. Then, the axial pre-tension loading force distribution is dynamically adjusted, and the temperature of each position is matched synchronously. Finally, the thread tooth forming grinding process is performed online.

2. The integrated heat treatment and machining method for a high wear-resistant heavy-duty transmission screw according to claim 1, characterized in that, The specific steps of the thread roughing pretreatment are as follows; During the machining process, the cutting speed is controlled to be uniform, which drives the lead screw blank to rotate synchronously. At the same time, the tool is controlled to feed at a uniform speed along the lead screw axis, and the feed direction is consistent with the screw thread direction. During the machining process, emulsion cutting fluid is continuously sprayed into the cutting area. By coordinating the control of cutting speed and tool feed, the oxide layer and scale on the surface of the lead screw blank are gradually removed, and the threaded tooth blank is machined, while reserving a finishing allowance.

3. The integrated heat treatment and machining method for a high wear-resistant heavy-duty transmission screw according to claim 1, characterized in that, The specific technical solution for the tooth root plasma synchronous micro-boron infiltration activation process is as follows: The working gas is a boron-argon-hydrogen mixture as the plasma jet medium. The mixture is composed of argon, high-purity hydrogen and boron source gas in a specific ratio. The boron source gas is a gaseous boride that can achieve local micro-boron infiltration. During processing, the rough-machined thread blank is fixed to ensure that the thread root area is fully exposed. The plasma generator is started, and the generated plasma jet is adjusted to be aligned with the thread root area. The root is scanned using a closed-loop scanning method. During the scanning process, the energy of the plasma jet acts on the surface of the thread root, and at the same time, the boron source gas in the mixed gas is dissociated, allowing boron atoms to gradually penetrate into the surface layer of the root. During the scanning process, the penetration depth and amount of boron atoms are controlled to ensure that the penetration depth is consistent with the depth of the hardened layer at the tooth root. The amount of boron is controlled between 0.8% and 1.2%, so that the modification and strengthening are achieved only within the hardened layer at the tooth root and do not penetrate into the tooth flank and tooth crest areas.

4. The integrated heat treatment and machining method for a high wear-resistant heavy-duty transmission screw according to claim 3, characterized in that, The specific implementation steps of the tooth root plasma synchronous micro-boron infiltration activation process are as follows: First, the boron-argon-hydrogen mixed working gas is dehydrated and purified by using a dehydration device to remove moisture from the gas and a filtration device to remove solid impurities from the gas. Then start the plasma generator and adjust the power of the equipment to five to fifteen kilowatts. The power is calculated and determined according to the tooth root size to generate a plasma jet. Adjust the jet nozzle to maintain a distance of three to five millimeters from the working surface of the thread tooth root. At the same time, adjust the jet axis to form an angle of forty-five to sixty degrees with the bottom surface of the thread tooth root. The angle is determined according to the tooth root angle. During scanning, the lead screw blank is controlled to rotate at a constant speed, while the plasma jet is controlled to move at a constant speed along the axial direction of the lead screw thread to achieve closed-loop scanning. During the scanning process, the jet power, scanning speed and mixed gas ratio are adjusted once every second to control the penetration depth and amount of boron atoms. During the treatment process, the pH value of the reaction environment is adjusted every fifteen minutes using a 10% (w / w) dilute sulfuric acid or dilute sodium hydroxide solution, with the pH fluctuation of a single adjustment not exceeding 0.1%.

5. The integrated heat treatment and machining method for a high wear-resistant heavy-duty transmission screw according to claim 1, characterized in that, The specific technical solution for the overall synchronous induction quenching heat treatment is as follows: Medium-frequency induction heating equipment is used for heating, and the induction component of the heating equipment is adapted to the shape of the lead screw blank. The heating process adopts a segmented heating method, first gradually raising the heating temperature to a specific preheating temperature, and then maintaining this temperature for heat preservation treatment. After preheating and heat preservation, the heating temperature is gradually increased to the target quenching temperature so that the entire thread area of ​​the lead screw is synchronously within the target quenching temperature range, and this temperature is maintained for heat preservation treatment. Nitrogen gas is continuously introduced into the heating area during the heat preservation process. After the heat preservation is completed, the lead screw is immediately subjected to quenching and cooling treatment. Cooling water is evenly sprayed onto the entire surface of the lead screw through a ring-shaped spray structure. The cooling rate is controlled by adjusting the spray pressure and flow rate of the cooling water, so that the hardness of the thread root is higher than that of the tooth tip.

6. The integrated heat treatment and machining method for a high wear-resistant heavy-duty transmission screw according to claim 1, characterized in that, The specific technical solution for the online low-temperature stress-relieving tempering treatment is as follows: After induction hardening, the lead screw blank is kept in its original fixed state, without disassembly or movement, and directly transferred to the tempering furnace for tempering treatment; The tempering furnace uses a programmable temperature control method to control the heating rate to rise slowly; Once the furnace temperature reaches the target tempering temperature, maintain that temperature for constant temperature insulation treatment, and continuously introduce nitrogen into the tempering furnace during the insulation process. After the constant temperature holding is completed, a slow cooling method is adopted in the furnace to control the cooling rate and gradually reduce the temperature inside the furnace, so that the lead screw is slowly cooled to below a specific temperature, and then the lead screw is removed to complete the heat treatment closed loop.

7. The integrated heat treatment and machining method for a high wear-resistant heavy-duty transmission screw according to claim 6, characterized in that, The specific technical solution for the dynamic pre-tension coupling processing technology for residual stress adaptation is as follows: After the lead screw is tempered online, keep it in its original fixed state and keep the X-ray diffraction instrument consistent with the lead screw fixed reference. Use X-ray diffraction to detect residual stress. During the test, the X-ray beam is perpendicular to the lead screw axis. Perform three tests on each test point and take the average value of the three test results as the residual stress value at that point. Inspection points are arranged along the axis of the lead screw. The inspection points are denser at both ends and evenly distributed in the middle section. The length of the dense area at both ends is one-fifth of the total length of the lead screw, and an inspection point is arranged every 10 millimeters in this area. The length of the middle section is three-fifths of the total length of the lead screw, and an inspection point is arranged every 20 millimeters in this area. Start the X-ray diffraction instrument and perform residual stress detection at each detection point using the method described above. Collect residual stress data at each detection point once per second, establish the correspondence between axial position and residual stress value, and form a complete residual stress distribution database.

8. The integrated heat treatment and machining method for a high wear-resistant heavy-duty transmission screw according to claim 7, characterized in that, Based on the collected axial residual stress distribution data, the specific technical solution for implementing residual stress-adaptive dynamic axial preload loading is as follows: Pre-tension loading is performed using a pre-tension loading process. The pre-tension loading device is connected to the fixed parts at both ends of the lead screw to ensure a firm connection without slippage. The loading process follows the principle of complementary stress control. First, an initial preload is applied to the lead screw. The initial loading force is controlled within the range that causes slight elastic deformation of the lead screw. The initial loading force is calculated and determined based on the yield strength of high-strength alloy structural steel and the cross-sectional area of ​​the lead screw. Then, based on the data in the residual stress distribution database, the preload force at each axial position of the screw is dynamically adjusted. For the middle section where the residual stress is greater than 300 MPa, the preload force is gradually increased so that the preload stress and the residual stress cancel each other out. For the two ends where the residual stress does not exceed 300 MPa, adjust the preload force to match the residual stress range, which is 1.0 to 1.1 times the residual stress. During the loading process, force sensing devices are used to monitor the loading force at each location. The force sensing devices are connected to the data acquisition system and collect loading force data once per second. The loading parameters are adjusted in a timely manner based on the feedback data.

9. The integrated heat treatment and machining method for a high wear-resistant heavy-duty transmission screw according to claim 8, characterized in that, The specific technical solution for the simultaneous implementation of dynamic preload and axial zone temperature control is as follows: Along the screw axis, corresponding residual stress detection points are arranged with zoned temperature control units evenly spaced according to the detection point spacing. Each temperature control unit corresponds to one detection point. The temperature control unit adopts an independent electric heating module, and each module is equipped with an independent temperature controller, which can adjust its own temperature independently. The temperature control unit is connected to the temperature control system, and collects temperature data from each temperature control unit every second. Based on the residual stress distribution and preload, the temperature at each point is adjusted accordingly. The adjustment standard is as follows: For the intermediate section where the residual stress is greater than 300 MPa and the pretension is greater than the initial pretension, the temperature of the temperature control unit is adjusted to 40 to 60 degrees Celsius. For the two ends where the residual stress does not exceed 300 MPa, the temperature of the temperature control unit is adjusted to 25 to 40 degrees Celsius; During the control process, the temperature change along the entire length of the lead screw is monitored in real time, and the temperature fluctuation along the entire length of the lead screw is controlled within ±2 degrees Celsius.

10. The integrated heat treatment and machining method for a high wear-resistant heavy-duty transmission screw according to claim 9, characterized in that, The specific technical solution for online thread forming grinding under stress-temperature coupling conditions is as follows: Keep the lead screw in its original fixed state, adjust the grinding mechanism to match the lead screw thread, and select a diamond grinding wheel suitable for heavy-duty lead screw grinding; The grinding process adopts a multi-pass progressive grinding method. The first pass removes 60% to 70% of the total finishing allowance, the second pass removes 20% to 30% of the total finishing allowance, and the third pass removes 5% to 10% of the total finishing allowance. It is mainly used to correct thread tooth profile error and pitch error. The grinding process is cooled and lubricated by constant temperature cutting fluid. After grinding, maintain the coupling state until the lead screw cools to room temperature.

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