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CN-122007827-A - Processing technology for gentle ending of root of thread of piston rod

CN122007827ACN 122007827 ACN122007827 ACN 122007827ACN-122007827-A

Abstract

The invention relates to the technical field of flat ending processing of a threaded root of a piston rod, and discloses a flat ending processing technology of the threaded root of the piston rod, which comprises blank pretreatment, threaded pretreatment, flat ending parameter setting, threaded forming processing, transition curve optimization, rolling strengthening, surface strengthening processing and multidimensional quality detection; the processing technology can enable the thread at the root of the piston rod to be in smooth transition, avoids sharp stress concentration points caused by traditional right-angle tail withdrawal, improves the fatigue strength of the thread, and prolongs the service life of the piston rod.

Inventors

  • SUN XINGXIN
  • DING XINCHENG

Assignees

  • 江苏聚源电气有限公司

Dates

Publication Date
20260512
Application Date
20260408

Claims (9)

  1. 1. The processing technology for the smooth ending of the root of the thread of the piston rod is characterized by comprising the following steps: S1, pre-treating a blank, namely selecting No. 45 steel as a base material, carrying out blanking and quenching and tempering, roughly turning the outer circle of a piston rod by adopting a high-precision numerical control lathe, controlling the dimensional tolerance of the outer circle to be +/-0.05 mm, positioning by adopting two center holes, and controlling the coaxiality error to be less than or equal to 0.02mm ‌ ‌; S2, thread pre-processing, namely turning thread profile by adopting a numerical control lathe, wherein the thread precision reaches 6H level, the thread root is reserved with a machining allowance of 0.5-1.0mm, a follower rest is used for supporting in the turning process, and the straightness error is less than or equal to 0.03mm/m; S3, setting a gentle tail withdrawal parameter, inputting basic parameters of threads in a control system of the numerical control lathe, including a nominal diameter, a thread pitch and a tooth angle, and setting the gentle tail withdrawal parameter; S4, thread forming processing, starting a numerical control lathe, performing thread processing according to set parameters, and performing gentle tool withdrawal action in a final stage to enable the thread root to form a final structure with smooth transition; S5, optimizing a transition curve, namely processing a cubic spline transition curve of the thread root by a numerical control milling machine, wherein the starting point of the curve is tangent to the thread root, the end point of the curve is smoothly connected with the outer circle of the piston rod, the length of the transition section is 1.5-2.0 times of the thread pitch, and the radius of the circular arc is 0.8-1.2 times of the thread pitch; s6, rolling and strengthening, namely adopting a thread rolling machine tool to roll and machine the transition area of the thread and the root, controlling the rolling pressure to be 20-30MPa and the rolling speed to be 10-15m/min; s7, carrying out surface strengthening treatment, nitriding the transition areas of the thread and the root, wherein the depth of the nitriding layer is 0.2-0.3mm; And S8, multi-dimensional quality detection, namely detecting pitch diameter, top diameter and bottom diameter of the thread by adopting a thread gauge, ensuring to meet the 6H-level precision requirement, detecting the outer diameter of the thread by adopting a laser calliper, observing whether defects such as scratches and cracks exist on the surface of the thread, detecting whether crack defects exist on the root of the thread by adopting magnetic powder flaw detection, and returning to a rolling procedure for correction if the defects exist.
  2. 2. A process for smoothly ending the root of a piston rod thread according to claim 1, wherein the quenching and tempering temperature is controlled to be 820-850 ℃ in the blank pretreatment, the blank is subjected to oil cooling after 2-3 hours of heat preservation, and the blank is subjected to low-temperature tempering at 200-220 ℃ to eliminate residual stress ‌ ‌.
  3. 3. The process for smoothly ending the root of the thread of the piston rod according to claim 1, wherein in the thread pre-processing, a numerical control lathe needs to perform accuracy calibration in advance, and the process comprises spindle runout detection and guide rail parallelism adjustment, so that the concentricity error of a tailstock center and a spindle is ensured to be less than or equal to 0.01mm ‌.
  4. 4. A process for smoothly ending the root of the thread of a piston rod according to claim 1, wherein in the rolling strengthening treatment, a rolling tool is made of hard alloy, the angle of the tool is matched with the thread form angle, and cooling lubricating liquid is continuously sprayed in the rolling process, so that the processing temperature is reduced.
  5. 5. A process for smoothly ending the root of a thread of a piston rod according to claim 1, wherein in the setting of the smoothly ending parameter, when the nominal diameter of the thread is greater than 30mm, the ending angle is selected to be 30-45 degrees, the ending distance is selected to be 2-3 times of the thread pitch, and when the nominal diameter of the thread is less than or equal to 30mm, the ending angle is selected to be 15-30 degrees, and the ending distance is selected to be 1-2 times of the thread pitch.
  6. 6. A process for smoothly ending the root of the thread of a piston rod according to claim 1, wherein in the optimization of the transition curve, a ball end milling cutter is adopted when a numerical control milling machine is used for processing a cubic spline transition curve, the milling feeding speed is controlled to be 500-800mm/min, and the milling depth is 0.1-0.2mm each time.
  7. 7. A process for smoothly ending the root of the thread of a piston rod according to claim 1, wherein in the rolling strengthening, a roller of a thread rolling machine tool is made of Cr12MoV, the roller is quenched to have the hardness of 58-62HRC, and the surface of the roller is polished ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ before rolling.
  8. 8. A process for gradually ending the root of the thread of a piston rod according to claim 1, wherein in the surface strengthening treatment, ammonia gas is introduced at 520-560 ℃ for gas nitriding, the nitriding time is 15-20 hours, cooling is performed after nitriding, and the cooling speed is controlled at 10-15 ℃ per minute ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌.
  9. 9. The gentle ending processing technology of the threaded root of the piston rod according to claim 1, wherein in the magnetic powder flaw detection, magnetizing current is 1000-2000A, magnetizing time is 2-3 seconds, and a 20-40-time magnifying glass is adopted to observe whether crack defects ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ exist at the threaded root after flaw detection.

Description

Processing technology for gentle ending of root of thread of piston rod Technical Field The invention belongs to the technical field of smooth ending processing of a threaded root of a piston rod, and particularly relates to a smooth ending processing technology of the threaded root of the piston rod. Background The reliability of the hydraulic mechanism serving as a core power component in the fields of engineering machinery, aerospace, ship manufacturing and the like directly influences the operation safety and the service life of the whole system. The piston rod is used as a key force transmission element of the hydraulic mechanism, and is connected with the execution part through locking threads, so that frequent alternating load, impact stress and corrosion environment test are required to be born. The traditional numerical control turning piston rod thread machining, and the program and parameters are set to be quick tool withdrawal and ending by default. The rapid tool withdrawal ending forms a sharp right angle transition structure at the thread root, which becomes a sensitive point for stress concentration. Under the action of alternating load, stress can be accumulated sharply at sharp corners, local stress peaks are far higher than average stress can exceed the fatigue limit of materials, and the fatigue fracture of the thread root at the initial position of the fatigue fracture of the thread root is easily caused after the thread root is subjected to long-term motion stress, so that the service life of a piston rod is influenced. Therefore, a gentle ending processing technology for the root of the thread of the piston rod is provided. Disclosure of Invention The invention aims to provide a smooth ending processing technology of the root part of the thread of the piston rod, which aims to ensure that the thread ending of the root part of the piston rod forms smooth transition, avoid sharp stress concentration points caused by traditional right-angle ending, improve the fatigue strength of the thread and prolong the service life of the piston rod. The technical scheme adopted by the invention is as follows: a processing technology for gentle ending of the root of a piston rod thread comprises the following steps: S1, pre-treating a blank, namely selecting No. 45 steel as a base material, carrying out blanking and quenching and tempering, roughly turning the outer circle of a piston rod by adopting a high-precision numerical control lathe, controlling the dimensional tolerance of the outer circle to be +/-0.05 mm, positioning by adopting two center holes, and controlling the coaxiality error to be less than or equal to 0.02mm ‌ ‌; S2, thread pre-processing, namely turning thread profile by adopting a numerical control lathe, wherein the thread precision reaches 6H level, the thread root is reserved with a machining allowance of 0.5-1.0mm, a follower rest is used for supporting in the turning process, and the straightness error is less than or equal to 0.03mm/m; S3, setting a gentle tail withdrawal parameter, inputting basic parameters of threads in a control system of the numerical control lathe, including a nominal diameter, a thread pitch and a tooth angle, and setting the gentle tail withdrawal parameter; S4, thread forming processing, starting a numerical control lathe, performing thread processing according to set parameters, and performing gentle tool withdrawal action in a final stage to enable the thread root to form a final structure with smooth transition; S5, optimizing a transition curve, namely processing a cubic spline transition curve of the thread root by a numerical control milling machine, wherein the starting point of the curve is tangent to the thread root, the end point of the curve is smoothly connected with the outer circle of the piston rod, the length of the transition section is 1.5-2.0 times of the thread pitch, and the radius of the circular arc is 0.8-1.2 times of the thread pitch; s6, rolling and strengthening, namely adopting a thread rolling machine tool to roll and machine the transition area of the thread and the root, controlling the rolling pressure to be 20-30MPa and the rolling speed to be 10-15m/min; s7, carrying out surface strengthening treatment, nitriding the transition areas of the thread and the root, wherein the depth of the nitriding layer is 0.2-0.3mm; And S8, multi-dimensional quality detection, namely detecting pitch diameter, top diameter and bottom diameter of the thread by adopting a thread gauge, ensuring to meet the 6H-level precision requirement, detecting the outer diameter of the thread by adopting a laser calliper, observing whether defects such as scratches and cracks exist on the surface of the thread, detecting whether crack defects exist on the root of the thread by adopting magnetic powder flaw detection, and returning to a rolling procedure for correction if the defects exist. In a preferred mode of the invention, the tempering temper