Machining process of piston rod

Abstract

The invention belongs to the field of piston rod machining, and particularly relates to a piston rod machining technology which comprises the steps that according to the rod diameter, length and mechanical property requirements of a piston rod finished product, a wire of a corresponding specification is selected, the wire is cut into a blank of a preset length through cutting-off equipment, and the machining allowance of follow-up procedures is reserved for the length of the blank; and a pre-punching forming die is adopted for punching the upper end of the blank, so that the upper end of the blank forms a preliminary outline matched with the preset appearance of the head of the piston rod, meanwhile, the lower end of the blank is extruded through a lower die with a chamfer forming groove, and an annular bottom chamfer is formed at the lower end of the blank. Therefore, independent operation by working procedures is not needed, the time cost of working procedure switching and the frequency of equipment adjustment are reduced, and the problems that in an existing cold extrusion process, the working procedures of rod part machining and threaded hole machining are dispersed, and the production efficiency is low due to the fact that blanks need to be transferred for multiple times are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of piston rod processing, and particularly relates to a processing technology of a piston rod. BACKGROUND

[0002] In the field of piston rod processing, for the production of piston rods used in electric vehicles, motorcycles and other scenarios, the existing technology mostly adopts a cold extrusion processing technology. The specific process is as follows: first, according to the size requirements of the finished piston rod, cut the wire rod to complete the blanking, after blanking, the billet needs to be phosphating annealed to improve the material performance, then the billet is extruded by a hydraulic machine in a branch-by-branch processing manner, and after extrusion forming, a separate hexagonal upsetting process is carried out, so as to complete the processing of key structures such as the head of the piston rod, and realize the preliminary forming of the piston rod.

[0003] The above-mentioned existing cold extrusion processing technology has obvious low production efficiency problem. The process includes blanking, phosphating annealing, branch-by-branch extrusion, separate hexagonal upsetting and other independent processes, and additional manual intervention or equipment adjustment is required for the connection between each process, and the branch-by-branch extrusion and separate hexagonal upsetting processing mode of the hydraulic machine cannot realize continuous production, resulting in a long processing cycle of a single piston rod, limited product output per unit of time, and difficulty in adapting to the efficiency requirements of large-scale production, and also increasing the waiting time in the production process due to the dispersion of processes, further restricting the improvement of the overall processing efficiency. SUMMARY

[0004] The purpose of the present application is to solve the problem of low production efficiency in the existing cold extrusion processing technology in the background technology. The process includes blanking, phosphating annealing, branch-by-branch extrusion, separate hexagonal upsetting and other independent processes, and additional manual intervention or equipment adjustment is required for the connection between each process, and the branch-by-branch extrusion and separate hexagonal upsetting processing mode of the hydraulic machine cannot realize continuous production, resulting in a long processing cycle of a single piston rod, limited product output per unit of time, and difficulty in adapting to the efficiency requirements of large-scale production, and also increasing the waiting time in the production process due to the dispersion of processes, further restricting the improvement of the overall processing efficiency.

[0005] To achieve the above-mentioned purpose, the following technical scheme is adopted: a processing technology of a piston rod, comprising the following steps:

[0006] S1. blanking, according to the rod diameter, length and mechanical property requirements of the finished piston rod, select the corresponding specification wire rod; cut the wire rod into billets of a predetermined length by cutting equipment, and the billet length needs to reserve the processing allowance of subsequent processes.

[0007] S2. The head preliminary profile is formed with a bottom chamfer, and a die is used to stamp the upper end of the blank to form a preliminary profile matching the preset shape of the head of the piston rod. Meanwhile, the lower end of the blank is extruded by a lower die with a chamfer forming groove to form a ring-shaped bottom chamfer.

[0008] S3. Head cold heading, the head of the blank is cold heading extruded by a matched upper die and lower die; the lower end surface of the upper die is provided with a regular hexagonal positioning hole matched with the internal hexagonal head, and the end surface or the inner wall of the positioning hole is engraved with a letter mark for subsequent positioning and calibration, and the upper end surface of the lower die is provided with a conical port (coaxial with the positioning hole axis); the head is extruded to form an internal hexagonal sketch and an external conical surface matched with the conical port through the cooperation of the upper and lower dies.

[0009] S4. First stretching and positioning, the upper die assembly with stretching needles is axially stamped along the axis of the blank (from the head to the rod) to stretch the rod to a first preset length; meanwhile, the lower die assembly with positioning guide holes positions the lower end of the rod, the axis of the positioning guide hole is coaxial with the axis of the blank, and the hole diameter is matched with the outer diameter of the stretching needle.

[0010] S5. Second stretching and positioning, the upper die assembly with stretching needles is continuously axially stamped in the same direction to further stretch the rod to a second preset length; the lower die assembly keeps the positioning effect of the positioning guide hole on the rod, and if the rod diameter is reduced due to the first stretching, the positioning guide hole matched with the current rod diameter needs to be replaced.

[0011] S6. Collaborative stamping sizing, the blank is finally stamped by a composite die composed of an upper die punch and a lower die punch; the upper die punch finishes stretching the rod to reach the finished product size; the lower die punch is positioned according to the positioning guide hole of S4 and S5 to process a threaded hole inside the rod, and the feeding depth of the lower die punch is controlled during processing to keep a preset unbroken thickness at the bottom of the threaded hole, avoiding rod diameter deformation or punch damage.

[0012] S7. Punching hole, according to the requirement of the finished product through hole, the upper die with head positioning structure (the lower end surface is engraved with a hexagonal groove matched with the outer hexagonal head and an outer circle height line for controlling the height of the head) is matched with the lower die with built-in buffer assembly (containing spring, punch, push tube and elastic cushion, the push tube covers the outside of the punch, the spring abuts against the lower end of the push tube and the die seat, and the elastic cushion is arranged between the upper end of the push tube and the lower end of the blank) to perform the punching operation on the bottom of the threaded hole; the spring provides elastic support through the push tube to avoid accuracy exceeding the tolerance or rod length shortening until the threaded hole is completely punched and the outer circle height line of the upper die is flush with the upper end surface of the head, completing the processing.

[0013] Further, the cutting device is a numerical control cutting device to ensure the consistency of the cutting length of the blank, the material of the wire rod is carbon structural steel or alloy structural steel, the carbon structural steel is selected from one of Q235 steel and 45# steel, and the alloy structural steel is selected from one of 20Cr steel and 40Cr steel, so as to adapt to the different mechanical property requirements of the piston rod, and the preset length of the blank is determined according to the length of the finished piston rod and the processing requirements of subsequent processes, wherein the processing allowance of the rod part and the processing allowance of the head part are reserved respectively to meet the processing accuracy requirements of different parts.

[0014] Further, a pressure maintaining link is arranged in the stamping process to ensure that the head part of the upper end of the blank is preliminarily profiled full, and the problem of unclear profile is avoided, and after the bottom chamfer is formed, the chamfer surface needs to meet the quality requirements of no burr and no edge collapse to avoid affecting the processing accuracy in subsequent processes due to chamfer defects.

[0015] Further, the distance between opposite sides of the regular hexagon of the upper punch positioning hole is adapted to the distance between opposite sides of the inner hexagon of the head part of the piston rod, and the depth of the positioning hole is determined according to the height of the head part of the piston rod to ensure the forming integrity of the inner hexagon sketch, the letter mark is processed by laser engraving, and the mark character needs to be clear and identifiable, which is used for calibrating the circumferential position of the blank in subsequent processes through the visual detection equipment to ensure the coaxiality of each process, and the size of the lower die conical port is determined according to the diameter of the blank head part after preforming to avoid the blank and the lower die from being stuck during cold heading extrusion, and to ensure the smoothness of the extrusion process.

[0016] Further, the material of the stretching needle of the upper die assembly is selected from high-speed steel or hard alloy, the high-speed steel is W18Cr4V steel, and the hard alloy is WC-Co alloy to ensure the wear resistance and strength of the stretching needle, the surface of the stretching needle is subjected to nitriding treatment to further improve the surface hardness and wear resistance of the stretching needle, the head part of the stretching needle is provided with a guide cone angle to facilitate the stretching needle to smoothly enter the inside of the blank and reduce the resistance in the stretching process, and the stamping speed of the stretching process is determined according to the ductility of the wire rod material to avoid cracks in the rod part of the blank due to too high speed.

[0017] Further, the second preset length is close to the finished rod length of the piston rod to reduce the processing amount of the subsequent final stamping, the stamping speed of the second stretching is lower than that of the first stretching, the gradual stretching mode is adopted to reduce the stress concentration in the blank, and deformation or cracking of the blank due to excessive stress is avoided, if the stretching needle is replaced in S five, the diameter of the new stretching needle is adapted to the diameter of the current blank rod part, and the axis of the new stretching needle is coaxial with the axis of the stretching needle used in S four, so as to ensure the straightness of the rod part of the blank after stretching.

[0018] Further, the size of the threaded hole is matched with the threaded requirement of the piston rod product, the threaded precision meets the assembly requirement of the product, the un-punched thickness is adjusted according to the diameter of the threaded hole, so as to balance the machining depth of the threaded hole and the structural strength of the blank rod, and the cooling lubrication measures are adopted in the punching process of the upper and lower die punches, the cooling lubricant is selected as the water-soluble cutting fluid, so as to reduce the friction heat in the punching process and protect the surface quality of the die and the blank.

[0019] Further, the spring of the lower die buffer assembly needs to have stable elastic supporting capacity, so as to ensure the consistency of the buffering effect, the inner diameter of the push tube is matched with the diameter of the lower die punch, so as to avoid that the too large or too small gap causes the shaking of the punch or the jamming of the push tube, the material of the elastic pad is selected from polyurethane or nitrile rubber, so as to further enhance the buffering effect through the elasticity of the elastic pad, and the pressure monitoring link is arranged in the punching process of the punch hole, the punching force is monitored in real time through the pressure sensor, the machine is automatically stopped when the punching force exceeds the preset threshold, so as to avoid the damage of the equipment overload or the blank processing scrap.

[0020] Compared with the prior art, the machining process of the piston rod has the following advantages:

[0021] 1. The composite die composed of the upper die punch and the lower die punch realizes the integration of the finishing stretching of the blank rod (so that the rod diameter reaches the product size) and the machining of the internal threaded hole of the rod in the same process, so that the separate operation of the processes is not needed, the time cost of process switching and the adjustment frequency of the equipment are reduced, and thus the problem of low production efficiency caused by the dispersion of the rod machining and the threaded hole machining processes and the multiple transfer of the blank in the existing cold extrusion process is solved.

[0022] 2. The combined mechanism of the upper die assembly provided with the stretching needle and the lower die assembly provided with the positioning guide hole which can be replaced and matched according to the change of the rod diameter realizes the progressive axial stretching of the blank rod (stretching twice to approach the product length), and the coaxiality of the blank in the stretching process is ensured through the positioning guide hole, and the progressive stretching can reduce the stress concentration in the blank, and thus the problems that the one-time stretching of the blank easily causes the cracks and fractures of the rod, and the inaccurate positioning easily causes the eccentricity and uneven diameter of the rod in the existing process are solved.

[0023] 3. The lower die buffer assembly including the spring, the push tube and the elastic pad realizes the elastic supporting force applied to the blank to buffer the punching impact force in the punch hole process, the push tube limits the radial shaking of the lower die punch, the elastic pad avoids the hard damage of the lower end of the blank, and the pressure monitoring ensures the stability of the punching force, and thus the problems that the excessive impact force causes the outer circle precision of the blank rod to be out of tolerance and the length of the rod to be shortened, or the direct impact of the punch causes the damage and the blank to be scrapped in the existing process are solved. DETAILED DESCRIPTION

[0024] The following examples are for illustrative purposes only and are not intended to limit the scope of the present application.

[0025] The present application proposes a machining process of a piston rod, comprising the following steps.

[0026] S1. blanking, according to the rod diameter, length and mechanical property requirements of the finished piston rod, select the corresponding specification wire; cut the wire into a blank of a preset length through a cutting device, and the blank length needs to reserve the machining allowance of subsequent processes;

[0027] It should be noted that the selection of the corresponding specification wire described in this embodiment is not only based on the basic size of the finished product, but also needs to consider the requirements of material ductility and strength in subsequent cold heading, stretching and other processes - for example, if there are multiple stretching processes in the subsequent processes, the wire with suitable ductility will be preferred to avoid cracking during stretching; the cutting method of the cutting device needs to match the material of the wire to ensure that the cutting surface is smooth and free of burrs, preventing the burrs from scratching the mold or causing the blank to be positioned off-center during subsequent stamping; and the reserved machining allowance needs to consider the material deformation amount of each process, avoiding both insufficient allowance leading to substandard finished product size and excessive allowance causing material waste, thereby providing a basic guarantee for stable processing of subsequent processes and finished product precision.

[0028] S2. forming the preliminary profile of the head and the bottom chamfer, stamping the upper end of the blank with a mold to form a preliminary profile matching the preset shape of the piston rod head; at the same time, extruding the lower end of the blank through the lower die with a chamfer forming groove to form a ring-shaped bottom chamfer;

[0029] It should be noted that the shape of the inner wall of the pre-stamping forming mold cavity described in this embodiment needs to be strictly controlled to match the preset shape of the piston rod head, ensuring that the preliminary profile is formed without a large amount of subsequent correction, reducing processing time; at the same time, the pressure during pre-stamping needs to be adapted to the plasticity of the wire material to avoid unclear profile due to insufficient pressure or cracking of the upper end of the blank due to excessive pressure; and the formation of the ring-shaped chamfer at the bottom not only removes the cutting burrs at the lower end of the blank, but also provides stable guidance for the blank during the subsequent stretching process - when the blank enters the positioning guide hole of the lower die, the chamfer can guide the blank to quickly align with the axis of the guide hole, avoiding the eccentric stretching of the rod due to the offset of the blank, and further improving the processing stability of the subsequent process.

[0030] S3. head cold heading, cold heading and extruding the head of the blank with a matched upper punch and lower die; the lower end surface of the upper punch is provided with a regular hexagonal positioning hole matching the inner hexagonal head, and the end surface or the inner wall of the positioning hole is marked with a letter mark for subsequent positioning and calibration, and the upper end surface of the lower die is provided with a conical port (collinear with the axis of the positioning hole); through the cooperation of the upper and lower dies, the head is extruded to form an inner hexagonal outline and an outer conical surface matching the conical port;

[0031] It should be noted that the upper punch hexagonal positioning hole described in the embodiment needs to be smooth processed to reduce the friction with the blank head during cold heading extrusion, avoid scratches on the blank surface, and ensure the clear edges of the hexagonal embryo; the setting position of the letter mark needs to be convenient for subsequent visual inspection equipment to identify, such as being engraved on the inner wall of the positioning hole close to the opening, which will not be covered due to extrusion, and can quickly capture calibration information to ensure the consistent circumferential position of the blank in subsequent processes, and avoid the eccentricity of the hexagonal and the rod part; and the axis of the lower die conical port and the positioning hole of the upper punch is collinear, in order to ensure that the blank head is uniformly stressed during cold heading, and avoid eccentricity or deformation of the head; the formation of the outer conical surface can provide a stable support surface for the axial positioning of the blank in the subsequent stretching process, and reduce the shaking of the head during stretching.

[0032] S4. First stretching and positioning, the upper die assembly with a stretching needle is axially punched along the blank axis (from the head to the rod part) to stretch the rod part to a first preset length; at the same time, the lower die assembly with a positioning guide hole positions the lower end of the rod part, the axis of the positioning guide hole is collinear with the axis of the blank, and the hole diameter is matched with the outer diameter of the stretching needle;

[0033] It should be noted that the connection between the stretching needle and the upper die assembly described in the embodiment needs to be firm to avoid loosening or deviation of the stretching needle during stretching, which may cause uneven stretching of the rod part; the punching direction is arranged along the axis of the blank to ensure that the force acting on the rod part during stretching is distributed along the axial direction, avoiding the problems of bending or uneven diameter of the rod part; the matching of the positioning guide hole and the outer diameter of the stretching needle can not only limit the radial displacement of the rod part of the blank, but also provide axial guidance for the blank during stretching to prevent the blank from deviating due to the stretching force, thereby ensuring the coaxiality of the rod part and laying a good processing foundation for the second stretching process, reducing the workload of the subsequent correction process.

[0034] S5. Second stretching and positioning, the upper die assembly with a stretching needle is continuously axially punched in the same direction to further stretch the rod part to a second preset length; the lower die assembly keeps the positioning effect of the positioning guide hole on the rod part, and if the rod diameter is reduced due to the first stretching, the positioning guide hole matched with the current rod diameter needs to be replaced;

[0035] It should be noted that the continuation of the stamping direction consistent with S4 described in this embodiment can ensure the straightness of the rod stretching, avoid the bending or step of the rod due to the direction deviation; gradually stretching the blank rod to the second preset length by using the "progressive stretching" instead of one-time stretching to the finished product length can effectively reduce the stress concentration inside the blank, reduce the risk of cracks or fractures of the rod; and replacing the appropriate positioning guide hole according to the reduction of the rod diameter can avoid positioning failure caused by too large gap between the positioning guide hole and the rod diameter - if the gap is too large, the blank is prone to radial shaking during stretching, resulting in a decrease in rod diameter accuracy, and the replacement of the appropriate guide hole can continuously ensure the positioning stability and further improve the processing accuracy of the rod.

[0036] S6. Cooperate with sizing, the composite die composed of the upper die punch and the lower die punch is used for final stamping of the blank; the upper die punch is used for finishing stretching of the rod to make the rod diameter reach the finished product size; the lower die punch is positioned according to the positioning guide hole of S4 and S5, and is used for processing the thread hole inside the rod; the feeding depth of the lower die punch is controlled during processing, so that a preset non-punched thickness is reserved at the bottom of the thread hole, and rod diameter deformation or punch damage is avoided;

[0037] It should be noted that the composite die described in this embodiment integrates the finishing stretching of the upper die and the thread hole processing of the lower die in the same process, which can reduce the time cost of process switching and improve the overall processing efficiency; the finishing stretching of the upper die punch not only can make the rod diameter reach the finished product size, but also can correct the slight deviation of the rod diameter that may occur in the previous two stretching processes, so as to ensure the uniformity of the rod diameter; the lower die punch is positioned according to the positioning guide hole in the previous stage, which can ensure the coaxiality of the thread hole and the rod, and avoid the eccentricity of the thread hole affecting the subsequent assembly; in addition to avoiding the direct impact of the punch on the end of the rod, the reserved non-punched thickness can also provide a stable processing reference for the subsequent punch hole process after the thread hole is formed, prevent the hole wall from deforming due to the too thin bottom during the punch, and protect the punch from hard impact, thereby prolonging the service life of the die.

[0038] S7. Punch hole, according to the finished product hole requirement, the upper die with a head positioning structure (the lower end surface is engraved with a hexagonal groove matched with the outer hexagonal head and an outer circle height line for controlling the height of the head) is used in cooperation with the lower die with a built-in buffer assembly (containing a spring, a punch, a push tube and an elastic pad, the push tube is sleeved outside the punch, the spring abuts against the lower end of the push tube and the die seat, and the elastic pad is arranged between the upper end of the push tube and the lower end of the blank) to perform the punching operation on the bottom of the thread hole; the spring provides elastic support force through the push tube during stamping to avoid accuracy deviation or rod length shortening, until the thread hole is completely punched and the outer circle height line of the upper die is flush with the upper end surface of the head, the processing is completed.

[0039] It needs to be explained that the matching of the upper die hexagonal groove and the outer hexagon of the head in the embodiment described can fix the head of the blank during the punching process, prevent the blank from rotating circumferentially, and ensure the coaxiality of the punched hole and the threaded hole; the outer circle height line is flush with the upper end surface of the head, which can directly judge whether the height of the head meets the requirements of the finished product, and avoid the unqualified finished product caused by the deviation of the height of the head; the spring, push tube and elastic cushion of the lower die buffer assembly form multiple buffering - the elastic support of the spring can absorb part of the stamping impact force, the push tube can limit the radial displacement of the lower die punch rod, and the elastic cushion can avoid the damage caused by the hard contact between the lower end of the blank and the push tube, and the cooperation of the three can effectively relieve the stress during stamping, prevent the deformation of the rod diameter caused by excessive impact force, and shorten the length of the rod, etc., and finally ensure the size accuracy and appearance quality of the finished product piston rod.

[0040] Specifically, taking the wire rod suitable for subsequent cold upsetting and stretching process as raw material, the wire rod is selected according to the finished product parameters and cut into a blank with a reserved machining allowance through S1 blanking process, laying a size foundation for subsequent processing; then S2 forms a head preliminary profile on the upper end of the blank through a pre-punch forming die, and forms a bottom chamfer on the lower end at the same time, which not only removes the burr of the blank but also provides guidance for subsequent stretching; then S3 uses the matched upper and lower dies to upset the head of the blank, forms an internal hexagonal sketch through the regular hexagonal positioning hole of the upper die, and sets letter marks to ensure subsequent positioning and calibration, the coaxial cooperation of the lower die conical port and the positioning hole of the upper die ensures uniform stress on the head and avoids deformation; then S4 and S5 use the upper die assembly with stretching needles to progressively stretch the rod part of the blank in the axial direction to the preset length, and at the same time, the lower die positioning guide hole (replaceable with a suitable guide hole as the rod diameter decreases) is used to ensure the coaxiality and straightness of the rod part and reduce stress concentration; then S6 uses a composite die to integrate the upper die punch rod to finish stretching the rod diameter to the finished product size, and the lower die punch rod processes the threaded hole according to the positioning of the previous guide hole, while reserving the un-punched thickness to avoid the impact between the punch rod and the end of the rod part; finally, S7 uses the upper die with head positioning structure (hexagonal groove to fix the head, outer circle height line to control the height) and the lower die buffer assembly with built-in spring, push tube and elastic cushion to cooperate with each other to perform the punching operation on the bottom of the threaded hole, and multiple buffering avoids the size out-of-tolerance caused by impact force, finally processing qualified piston rods. The process closely connects the processes and integrates the functions, such as S6 integrates finishing stretching and threaded hole processing to reduce process switching, S3 cold upsetting simultaneously completes internal hexagonal forming and positioning mark to save separate hexagonal forming process, S4 and S5 progressive stretching do not need additional phosphating and annealing treatment, and each process realizes continuous processing through positioning guide hole, letter mark, etc., without frequent manual intervention, effectively solving the problem of low production efficiency caused by the dispersion of the existing cold extrusion process, the need for processing one by one, and the inability to produce continuously in the background technology, improving the product output per unit time, and adapting to the needs of large-scale production.

[0041] Further, in S1, the cutting device is a numerical control cutting device to ensure the consistency of the length of the blank, the material of the wire is carbon structural steel or alloy structural steel, the carbon structural steel is selected from one of Q235 steel and 45# steel, and the alloy structural steel is selected from one of 20Cr steel and 40Cr steel to adapt to the different mechanical property requirements of the piston rod, and the preset length of the blank is determined according to the length of the finished piston rod and the processing requirements of subsequent processes, wherein the processing allowance of the rod part and the processing allowance of the head part are reserved respectively to meet the processing accuracy requirements of different parts.

[0042] It should be noted that the numerical control cutting device described in the embodiment is not only used to ensure the consistency of the length, but also to avoid the inclination or burr of the cutting surface caused by manual operation error of the traditional cutting device by precisely controlling the cutting speed and force through the program of the numerical control cutting device. The flatness of the cutting surface directly affects the fit of the blank and the mold in the subsequent S2 preforming process, and reduces the contour deviation of the head part caused by poor fit. The classification selection of the material of the wire is based on the difference in the application scene of the piston rod, for example, the carbon structural steel can be selected for the piston rod used in the low load scene, which takes into account the cost and basic strength, and the alloy structural steel is selected for the piston rod used in the high load and high wear resistance scene, which improves the service life of the finished product by the material properties. The processing allowance of the rod part and the head part is reserved respectively, considering that the multiple stretching of the rod part in subsequent S4-S6 will cause more material deformation, and the cold heading extrusion deformation of the head part in S3 is relatively fixed. Separate reservation can avoid the size shortage or material waste of a part after processing caused by single allowance allocation, and further guarantees the accuracy of each part of the finished product to meet the standard.

[0043] Specifically, the working principle of S1 in the embodiment is as follows: through the program control of the numerical control cutting device, the selected wire is precisely cut according to the preset length, ensuring that the length error of each blank is extremely small, and providing a basis for the standardized processing of subsequent processes; according to the mechanical property requirements of the piston rod, the wire of the corresponding material is selected, so that the blank adapts to the processing strength requirements of the subsequent cold heading, stretching and other processes from the source, avoiding cracking or deformation during processing due to mismatch of the material; the allowances are reserved respectively for the different processing requirements of the rod part and the head part, to ensure that the rod part still has enough material to finish to the finished product size after multiple stretching, and the head part can accurately form an internal hexagonal structure after cold heading. This scheme solves the problems in the background art that the existing process may cause inconsistent length of the blank due to low precision of the cutting device, processing failure due to random selection of the material, and substandard finished product size due to unreasonable allowance reservation, reduces the correction workload of subsequent processes, and indirectly improves the overall processing efficiency, providing stable early-stage guarantee for large-scale production.

[0044] Further, the cavity surface of the pre-punching forming die is smooth processed to reduce the scratches on the head surface of the blank during the punching process, a pressure maintaining link is arranged in the punching process of the pre-punching forming to ensure that the head of the upper end of the blank is preliminarily profiled fully, and the problem of unclear profile is avoided, and after the bottom chamfer is formed, the chamfer surface needs to meet the quality requirements of no burr and no edge collapse to avoid affecting the machining precision due to chamfer defects in the subsequent process.

[0045] It should be noted that the smooth processing of the cavity surface of the pre-punching forming die described in the embodiment not only reduces the scratches on the head of the blank, but also reduces the frictional resistance between the die and the blank during punching, so that the blank is more easily flowed in the cavity, thereby making the details of the head preliminary profile more clear, and reducing the correction pressure in the subsequent S3 cold heading process; the pressure maintaining link in the punching process is to continuously apply a certain pressure to make the blank fully fill in the die cavity, especially for the corner parts of the head profile, to avoid incomplete filling of the corner due to sudden pressure drop, thereby reducing the waste caused by profile defects in subsequent processing; the requirements of no burr and no edge collapse of the bottom chamfer not only avoid scratching the subsequent die or the operator, but more importantly, ensure that the blank can be smoothly introduced into the positioning guide hole of the lower die in the S4 stretching process, if there are burrs or edge collapse on the chamfer, it is easy to cause the blank to be stuck or positioned offset in the guide hole, affecting the coaxiality of the rod stretching.

[0046] Specifically, the working principle of S2 in the embodiment is: the friction between the smooth processed die cavity and the head of the blank is reduced when they are in contact, and the blank can uniformly adhere to the inner wall of the cavity during punching, forming a preliminary profile that matches the preset profile height; the pressure maintaining link ensures that the blank is fully formed in the cavity by continuously applying pressure, avoiding the profile corners from being concave or unclear; after the bottom chamfer is extruded, it is simply trimmed to meet the no burr and no edge collapse standards, providing smooth guidance for subsequent processes. This scheme solves the problems in the background art that the existing process may cause many scratches on the head of the blank due to rough die cavity, unclear profile due to no pressure maintaining, and defects in the chamfer affecting subsequent positioning, reduces the rework or scrap caused by defects in the head processing, and lays a foundation for accurate positioning in the subsequent stretching process, further improving the processing efficiency and the qualified rate of finished products.

[0047] Further, the distance between opposite sides of the regular hexagon of the upper punch positioning hole is adapted to the distance between opposite sides of the inner hexagon of the head of the piston rod, and the depth of the positioning hole is determined according to the height of the head of the piston rod to ensure the forming integrity of the inner hexagon, the letter mark is processed by laser engraving, and the mark character needs to be clear and identifiable, which is used for calibrating the circumferential position of the blank in the subsequent process by the visual detection equipment to ensure the coaxiality of the machining in each process, and the size of the lower die conical port is determined according to the diameter of the head of the blank after pre-forming to avoid the blank from being stuck with the lower die during cold heading extrusion, and to ensure the smoothness of the extrusion process.

[0048] It should be noted that the upper punch positioning hole and the distance between the head internal hexagon in the embodiment described in this embodiment are adapted to the distance between the head internal hexagon, so that the blank head can accurately fill the positioning hole during cold heading extrusion, and the internal hexagonal embryo formed can meet the positioning requirements of the S7 punch hole process without a large amount of subsequent processing. If the degree of adaptation is insufficient, the internal hexagonal embryo size deviation is easy to occur, and the subsequent correction process is increased. The depth of the positioning hole is determined according to the height of the head, which can avoid the insufficient height of the internal hexagonal embryo due to the too shallow hole depth, or the excessive extrusion deformation of the blank head due to the too deep hole depth. The letter mark engraved by laser has the advantages of clear marking, not easy to wear, high processing precision, and can continuously provide accurate positioning reference for visual inspection equipment in subsequent processes, so as to ensure that the circumferential position of the blank is always consistent, and the internal hexagon and the rod are not coaxial due to the circumferential deviation. The size of the lower die conical port is adapted to the diameter of the preformed head, which can provide a stable support surface for the blank head during cold heading, and also reserves a proper gap for the deformation of the blank, so as to avoid the blank and the conical port being stuck due to the too small gap, or the head being deformed unevenly due to the too large gap.

[0049] Specifically, the working principle of S3 in the embodiment is as follows: when the upper punch is pressed down, the positioning hole is accurately fitted with the blank head, the blank head is deformed to form an internal hexagonal embryo by cold heading force, and the depth of the positioning hole ensures that the embryo height meets the standard; the letter mark engraved by laser is retained on the head during the cold heading process, and the visual inspection equipment adjusts the circumferential angle of the blank in the subsequent process by identifying the mark to ensure that the machining axes of each process are consistent; the lower die conical port provides support for the blank head, and the adapted size allows the blank to deform smoothly during extrusion, avoiding being stuck. This scheme solves the problems in the background art, such as incomplete internal hexagonal forming due to poor adaptation of the mold positioning hole, low coaxiality due to the lack of circumferential positioning mark, and extrusion sticking due to improper size of the lower die, reduces internal hexagonal machining defects and process jamming, improves the coaxiality of the finished product, avoids equipment downtime or blank scrap due to sticking, and ensures production continuity.

[0050] Further, the material of the stretching needle of the upper die assembly is selected from high-speed steel or hard alloy, the high-speed steel is W18Cr4V steel, and the hard alloy is WC-Co alloy, so as to ensure the wear resistance and strength of the stretching needle, the surface of the stretching needle is subjected to nitriding treatment, so as to further improve the surface hardness and wear resistance of the stretching needle, the head of the stretching needle is provided with a guide cone angle, which facilitates the smooth entry of the stretching needle into the blank, reduces the resistance in the stretching process, and the stamping speed of the stretching process is determined according to the ductility of the wire material, so as to avoid cracks in the rod part of the blank due to too high speed.

[0051] It should be noted that the stretching needle described in the embodiment is selected from high-speed steel or hard alloy, which is based on the need to repeatedly apply force to the rod part of the blank in the S4 stretching process. The two materials have high strength and high wear resistance, which can avoid the bending or wear of the stretching needle after long-term use, resulting in size deviation of the rod part during stretching. The surface nitriding treatment can form a hard nitriding layer on the surface of the stretching needle, further improving the wear resistance and prolonging the service life, while reducing the friction between the stretching needle and the blank inside, avoiding scratches inside the blank due to excessive friction. The setting of the head guiding cone angle can gradually separate the material when the stretching needle enters the blank, rather than being directly inserted, reducing the damage to the internal structure of the blank and reducing the risk of cracks.

[0052] Specifically, the working principle of S4 in the embodiment is as follows: the high-strength stretching needle can stably apply tension to the rod part of the blank during axial stamping, the nitriding layer reduces friction with the blank, the guiding cone angle helps the stretching needle smoothly enter the blank, and the appropriate stamping speed allows the rod part of the blank to slowly deform during stretching, gradually reaching the first preset length, while the lower die positioning hole cooperates with the stretching needle to ensure the coaxiality of the rod part. This scheme solves the problems in the background art, such as frequent replacement of the stretching needle due to poor material quality, surface wear causing blank defects, lack of guiding structure causing difficulty in insertion, and improper speed causing rod cracks, reducing the frequency of mold replacement and the rejection rate of the blank, improving the stability and efficiency of the stretching process, and laying a good foundation for subsequent second stretching.

[0053] Further, the second preset length is close to the length of the rod part of the finished piston rod, to reduce the processing amount of subsequent final stamping, and the stamping speed of the second stretching is lower than that of the first stretching, using a gradual stretching method to reduce stress concentration inside the blank, avoiding deformation or cracking of the blank due to excessive stress. If the stretching needle is replaced in S5, the diameter of the new stretching needle is adapted to the diameter of the current blank rod part, and the axis of the new stretching needle is coaxial with the axis of the stretching needle used in S4, to ensure the straightness of the blank rod part after stretching.

[0054] It should be noted that the second preset length described in the embodiment is close to the length of the finished rod, which can greatly reduce the finishing workload in the final stamping S6, avoid size deviation or surface quality degradation of the rod due to excessive processing amount in the final stamping, shorten the processing time of the final stamping, and improve the overall efficiency; the second stretching speed is lower than the first stretching speed, because the internal structure of the blank rod has been deformed after the first stretching, and the strength has changed, so reducing the speed can make the blank release internal stress more fully in the second stretching, avoid cracking or deformation caused by stress concentration, and the gradual stretching can better protect the structural integrity of the blank than one-time stretching; the diameter adaptation and axis coaxiality when replacing the stretching needle can ensure that the new stretching needle can accurately act on the rod with a reduced diameter, avoid uneven stress in the rod due to diameter mismatch, and ensure that the stretching direction is consistent to prevent the rod from bending or stepping and ensure that the straightness meets the standard.

[0055] Specifically, the working principle of S5 in the embodiment is as follows: the second preset length close to the length of the finished product reduces the subsequent processing amount, the lower stamping speed allows the blank rod to deform slowly and release stress, and if the stretching needle is replaced, the adapted diameter and coaxial axis ensure the stability of the stretching process, and the positioning hole of the lower die ensures that the rod reaches the preset length after the second stretching and maintains good straightness and integrity. This scheme solves the problems in the background art that the existing process may cause the blank to crack due to excessive one-time stretching processing amount, the rod to bend due to improper replacement of the stretching needle, and low efficiency due to excessive final stamping processing amount, reduces the defects of the blank, improves the efficiency of the final stamping, and ensures the straightness of the rod, providing a precise rod base for subsequent thread hole processing.

[0056] Further, the size of the thread hole is adapted to the thread requirement of the finished piston rod, the thread precision meets the assembly requirements of the finished product, the un-punched thickness is adjusted according to the diameter of the thread hole to balance the processing depth of the thread hole and the structural strength of the blank rod, and cooling and lubricating measures are adopted during the stamping process of the upper and lower die rods, and water-soluble cutting fluid is selected as the cooling and lubricating agent to reduce the friction heat in the stamping process and protect the surface quality of the die and the blank.

[0057] It should be noted that the thread hole size described in the embodiment is adapted to the product demand, which can ensure that the piston rod is directly assembled without additional thread correction after processing, avoid assembly difficulties caused by size deviation, and reduce subsequent rework; the un-punched thickness is adjusted according to the thread hole diameter, because the larger the thread hole diameter, the stronger the required structural support, and the un-punched thickness that is too thin is easy to cause deformation of the bottom of the thread hole during processing, and the thickness that is too thick increases the workload of the subsequent punch hole process, and the adapted thickness can ensure the structural strength of the rod part while providing a suitable processing basis for the punch hole process; the cooling and lubricating measures select water-soluble cutting fluid, which not only effectively removes the heat generated by the friction between the mold and the blank during the punching process, avoids the precision decline or damage of the mold due to overheating, but also forms a lubricating film on the surface of the blank, reduces the friction between the punch rod and the blank, protects the surface quality of the blank, and avoids scratches or oxidation.

[0058] Specifically, the working principle of S6 in the embodiment is as follows: the upper mold punch rod of the composite mold performs finishing stretching on the rod part to reach the finished product size, the lower mold punch rod accurately processes the thread hole of the finished product according to the positioning guide hole in the previous stage, the un-punched thickness ensures the strength of the rod part, the water-soluble cutting fluid removes the friction heat, and the mold and the blank surface are protected. This scheme solves the problems in the background art, such as assembly problems caused by the non-adapted thread hole size, rod deformation or processing difficulty caused by improper un-punched thickness, and mold damage or blank defects caused by no cooling and lubrication, reduces the assembly rework and mold replacement cost, improves the thread hole processing precision and the blank surface quality, and at the same time, through the integrated process of the composite mold, the process switching time is reduced, and the processing efficiency is further improved.

[0059] Further, the spring of the lower mold buffer assembly needs to have stable elastic support ability to ensure the consistency of the buffering effect, the inner diameter of the push tube cooperates with the diameter of the lower mold punch rod to avoid excessive clearance between the punch rod and the push tube, which causes the punch rod to shake or too small clearance which causes the push tube to jam, the material of the elastic pad is selected from polyurethane or nitrile rubber to further enhance the buffering effect through its elasticity, and a pressure monitoring link is arranged in the punching process of the punch hole, the punching force is monitored in real time through the pressure sensor, and the equipment is automatically stopped when the punching force exceeds the preset threshold, which avoids damage of the equipment due to overload or scrap of the blank processing.

[0060] It should be noted that the spring described in the embodiment has stable elastic support capability, which can ensure the consistency of the buffering degree each time the hole is punched, avoid the deformation of the blank due to insufficient buffering or incomplete punching of the hole due to excessive buffering caused by unstable spring elasticity; the diameter cooperation of the push tube and the lower die punch rod can limit the radial displacement of the punch rod, avoid the deviation of the punch hole from the axis caused by the shaking of the punch rod, and the appropriate gap ensures that the push tube can smoothly follow the movement of the punch rod, avoiding interruption of the process caused by jamming; the elastic pad made of polyurethane or nitrile rubber material has good elasticity and wear resistance, which can further absorb the stamping impact force on the basis of spring buffering, and avoid hard contact between the lower end of the blank and the push tube to protect the surface of the blank; the setting of the pressure monitoring link can monitor the change of the stamping force in real time, and when an abnormality occurs (such as an increase in resistance caused by impurities in the blank), it can automatically stop in time to avoid damage to the equipment due to overload, or scrap of the blank due to excessive stamping.

[0061] Specifically, the working principle of S7 in the embodiment is as follows: the upper die hexagonal groove fixes the head of the blank, and the height line of the outer circle ensures that the head height meets the standard; the spring, push tube and elastic pad of the lower die buffering assembly work together to absorb the stamping impact force and avoid deformation of the blank; the pressure sensor monitors the stamping force in real time and automatically stops when an abnormality occurs; the lower die punch rod punches the bottom of the threaded hole under the protection of the buffer, and the processing of the piston rod is completed. This scheme solves the problems in the background art that the existing process may cause deformation of the blank due to lack of buffering, deviation of the hole position due to shaking of the punch rod, damage to the equipment or scrap of the blank due to lack of pressure monitoring, etc., greatly improves the dimensional accuracy and appearance quality of the finished piston rod, reduces the equipment maintenance cost and blank scrap rate, ensures the stability and safety of the punching process, and provides a guarantee for the efficient implementation of the entire processing process.

[0062] In summary, the wire rod with material properties (such as ductility and strength) suitable for subsequent cold heading and drawing processes is used as the raw material. First, in the S1 blanking process, the corresponding specification wire rod is selected according to the piston rod product parameters, and the blank is cut into a pre-rod part and a head part with a separate processing allowance using a numerical control cutting equipment, laying the size and material foundation for subsequent standardized processing. Then, in the S2, the pre-punching forming die with smooth cavity surface is used to punch the blank to form the head part with a preliminary profile on the upper end, and the profile is ensured to be full by cooperating with the pressure holding link, while the bottom chamfer without burrs and collapse is formed by extruding the lower end, which not only removes the burrs but also provides guidance for the subsequent drawing. Subsequently, in the S3, the upper punch (with a smooth positioning hole matched with the inner hexagonal head part and a laser-engraved letter mark) and the lower die (with a conical port matched with the pre-formed diameter of the head part, and coaxial with the positioning hole of the upper punch) are used to cold heading the blank head part to form the inner hexagonal outline and the outer conical surface. The letter mark provides a circumferential positioning reference for the subsequent process to avoid head eccentricity. Then, in the S4 and S5, the upper die assembly with high-strength nitriding treatment drawing needle (with a guide cone angle) is used to gradually stretch the blank rod part along the axial direction at a speed suitable for the ductility of the wire rod to a second preset length close to the product length, while the lower die assembly changes the matching positioning guide hole according to the change of the rod diameter to ensure the coaxiality and straightness of the rod part and reduce stress concentration. After that, in the S6, the composite die integrates the upper punch rod finishing stretching (correcting the rod diameter deviation to the product size) and the lower punch rod (processing the thread hole according to the positioning of the previous guide hole), and retains the unbroken thickness of the thread hole diameter matched with the thread hole, which is cooled and lubricated with water-soluble cutting fluid to avoid punch impact and die overheating. Finally, in the S7, the upper die with a hexagonal groove (to fix the head part to prevent circumferential rotation) and an outer circle height line (to control the height of the head part), and the lower die buffer assembly with an embedded spring (to provide stable elastic support), a gap push tube (to limit the swing of the punch rod), and an elastic cushion (to enhance the cushioning protection of the blank) are used to punch the bottom of the thread hole, while the pressure sensor is used to monitor the punching force in real time, and the machine stops automatically when an abnormality occurs to ensure that the punched hole and the thread hole are coaxial and the blank is not deformed, and finally a qualified piston rod is processed. The process reduces the process switching time through multi-process function integration (such as the S6 composite die integrating finishing and thread processing, and the S3 cold heading simultaneously completing the inner hexagonal outline and the positioning mark), realizes continuous processing without frequent manual intervention with the help of numerical control equipment, positioning guide hole, and letter mark, and reduces the problems of blank cracking, die damage, and size deviation through progressive stretching, multiple buffering, and cooling and lubrication, effectively solving the problems of low production efficiency caused by the dispersion of the existing cold extrusion process, the need for processing one by one, and the inability to produce continuously, and the problems of size not meeting the standards, blank scrap, and large die wear, improving the product output per unit time and the product qualification rate, and adapting to the needs of large-scale production.

[0063] The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A processing method for a piston rod, characterized in that, Includes the following steps: S1. Material preparation: Select wire of the corresponding specification according to the diameter, length and mechanical performance requirements of the finished piston rod; cut the wire into blanks of the preset length using a cutting device, and the length of the blanks should be reserved for processing allowances in subsequent processes. S2. Initial head contour and bottom chamfering: The upper end of the blank is stamped with a mold to form an initial contour that matches the preset shape of the piston rod head; at the same time, the lower end of the blank is squeezed by a lower mold with a chamfering groove to form an annular bottom chamfer. S3. Head cold heading: The head of the blank is cold-headed using matching upper and lower dies. The lower end face of the upper die is provided with a regular hexagonal positioning hole that matches the internal hexagon of the head, and the end face or the inner wall of the positioning hole is engraved with letter markings for subsequent positioning calibration. The upper end face of the lower die is provided with a conical opening (collinear with the axis of the positioning hole). Through the cooperation of the upper and lower dies, the head is extruded to form an internal hexagonal prototype and an outer conical surface that matches the conical opening. S4. First stretching and positioning: The upper die assembly with stretching needles is used to axially press along the blank axis (from the head to the rod) to stretch the rod to the first preset length; at the same time, the lower die assembly with positioning guide holes is used to position the lower end of the rod. The axis of the positioning guide holes is collinear with the axis of the blank, and the hole diameter is adapted to the outer diameter of the stretching needles. S5. Second stretching and positioning: Continue to use the upper die assembly with stretching needles to axially press in the same direction to further stretch the rod to the second preset length; the lower die assembly maintains the positioning effect of the positioning guide hole on the rod. If the rod diameter is reduced due to the first stretching, the positioning guide hole that matches the current rod diameter needs to be replaced. S6. Collaborative stamping to determine dimensions: A composite die consisting of an upper die punch and a lower die punch is used to perform final stamping on the blank. The upper die punch finishes and stretches the rod to achieve the finished rod diameter. The lower die punch is positioned according to the positioning holes in S4 and S5, and a threaded hole is formed inside the rod. During processing, the feed depth of the lower die punch is controlled to ensure that the bottom of the threaded hole retains a preset un-penetrated thickness, thus avoiding rod diameter deformation or punch damage. S7. Punching through hole: According to the requirements of the finished through hole, use an upper die with a head positioning structure (the lower end face is engraved with a hexagonal groove that matches the outer hexagon of the head and an outer circle height line that controls the height of the head) to cooperate with a lower die with built-in buffer components (including spring, punch, push tube and elastic pad, the push tube sleeves the outside of the punch, the spring abuts against the lower end of the push tube and the die base, and the elastic pad is placed between the upper end of the push tube and the lower end of the blank) to punch through the bottom of the threaded hole; during punching, the spring applies elastic support force through the push tube to buffer and avoid precision deviation or rod length shortening, until the threaded hole is completely punched through and the outer circle height line of the upper die is flush with the upper end face of the head, completing the processing.

2. The processing technology for a piston rod according to claim 1, characterized in that, In S1, the cutting equipment is a CNC cutting equipment to ensure the consistency of the cutting length of the blank. The material of the wire is carbon structural steel or alloy structural steel. The carbon structural steel is selected from Q235 steel and 45# steel, and the alloy structural steel is selected from 20Cr steel and 40Cr steel to adapt to the different mechanical performance requirements of the piston rod. The preset length of the blank is determined according to the finished length of the piston rod and the processing requirements of subsequent processes. The machining allowance of the rod and the machining allowance of the head are reserved respectively to meet the processing accuracy requirements of different parts.

3. The processing technology for a piston rod according to claim 1, characterized in that, In S2, a pressure holding step is set during the stamping process to ensure that the initial outline of the upper end of the blank is fully formed and to avoid the problem of unclear outline. After the bottom chamfer is formed, the chamfer surface must meet the quality requirements of no burrs and no collapsed edges to avoid the impact of chamfer defects on the processing accuracy in subsequent processes.

4. The processing technology for a piston rod according to claim 1, characterized in that, In S3, the distance between opposite sides of the regular hexagon of the upper punch positioning hole is adapted to the distance between opposite sides of the inner hexagon of the piston rod head. The depth of the positioning hole is determined according to the height of the piston rod head to ensure the integrity of the inner hexagonal prototype. The letter markings are processed by laser engraving, and the marking characters must be clearly distinguishable. They are used in subsequent processes to calibrate the circumferential position of the blank through visual inspection equipment to ensure the coaxiality of each process. The size of the lower die conical opening is determined according to the diameter of the pre-formed blank head to avoid the blank from jamming with the lower die during cold heading and to ensure the smoothness of the extrusion process.

5. The processing technology for a piston rod according to claim 1, characterized in that, In S4, the drawing pin of the upper die assembly is made of high-speed steel or cemented carbide. The high-speed steel is W18Cr4V steel, and the cemented carbide is WC-Co alloy to ensure the wear resistance and strength of the drawing pin. The surface of the drawing pin is nitrided to further improve its surface hardness and wear resistance. The head of the drawing pin is provided with a guide cone to facilitate the smooth entry of the drawing pin into the blank and reduce the resistance during the drawing process. The stamping speed of the drawing process is determined according to the ductility of the wire material to avoid cracks in the blank rod due to excessive speed.

6. The processing technology for a piston rod according to claim 1, characterized in that, In S5, the second preset length is close to the length of the finished piston rod to reduce the amount of processing required for the final stamping. The stamping speed of the second stretching is lower than that of the first stretching. The progressive stretching method reduces stress concentration inside the blank and avoids deformation or cracking of the blank due to excessive stress. If the stretching needle is replaced in S5, the diameter of the new stretching needle is matched with the diameter of the current blank rod, and the axis of the new stretching needle is kept coaxial with the axis of the stretching needle used in S4 to ensure the straightness of the blank rod after stretching.

7. The processing technology for a piston rod according to claim 1, characterized in that, In S6, the size of the threaded hole is adapted to the thread requirements of the finished piston rod, and the thread accuracy meets the assembly requirements of the finished product. The unpierced thickness is adjusted according to the diameter of the threaded hole to balance the machining depth of the threaded hole and the structural strength of the blank rod. Cooling and lubrication measures are adopted during the stamping process of the upper and lower die punches. Water-soluble cutting fluid is selected as the cooling and lubricating agent to reduce the frictional heat during the stamping process and protect the surface quality of the die and the blank.

8. The processing technology for a piston rod according to claim 1, characterized in that, In S7, the spring of the lower die buffer assembly must have stable elastic support capacity to ensure consistent buffering effect. The inner diameter of the push tube matches the diameter of the lower die punch to avoid excessive gap causing punch to shake or excessive gap causing push tube to jam. The material of the elastic pad is selected from polyurethane or nitrile rubber to further enhance the buffering effect through its own elasticity. A pressure monitoring link is set in the punching process of the punching hole. The punching pressure is monitored in real time by a pressure sensor. When the punching pressure exceeds the preset threshold, the machine will automatically stop to avoid equipment overload damage or scrap of the blank processing.