阅读说明：本技术 一种偏焊缝薄壁高强度方形冷弯钢管的成型方法 (Forming method of bias-weld-joint thin-wall high-strength square cold-bent steel pipe ) 是由 朱成松 盛珍剑 阮建刚 万业成 张尧 魏鹏 雷浩 段军科 梁诚 于 2021-08-06 设计创作，主要内容包括：本发明涉及冷弯成型技术领域,尤其涉及一种偏焊缝薄壁高强度方形冷弯钢管的成型方法,粗成型阶段,先进行边缘成型,再进行中间部位反弯成型,中间部位成型过程中,边缘圆弧R值保持不变,采用两辊式挤压辊,解决了变型不均匀问题、边缘变型易产生浪形等难题,提高了焊接稳定性及焊接时钢管变型的均匀性；采用两架次可拆卸式弧形刀片对焊接两侧边外毛刺进行刨除,解决了更换刀杆较麻烦、生产效率不高难题,刨削后焊接面平整、光滑；采用定径扭偏成型方法解决了焊缝无法偏移及偏移量无法精整控制难题；采用定径精成型(包弧成型、平面度精整成型),解决了外圆弧R值不匀称,尤其是焊缝偏移处因焊接边过短,外圆弧易变椭、平面不平整问题。(The invention relates to the technical field of cold roll forming, in particular to a forming method of a bias-weld thin-wall high-strength square cold roll steel pipe, which comprises the following steps of performing edge forming at the rough forming stage, then performing middle part reverse roll forming, wherein the R value of an edge arc is kept unchanged in the middle part forming process, and two roll type extrusion rolls are adopted, so that the problems of uneven deformation, easy wavy generation of edge deformation and the like are solved, and the welding stability and the uniformity of steel pipe deformation during welding are improved; two sets of detachable arc-shaped blades are adopted to remove burrs on the outer sides of two sides of the welding, the problems that cutter bar replacement is troublesome and production efficiency is not high are solved, and the welding surface is smooth after planing; the difficult problems that the welding line cannot be deviated and the deviation cannot be finished and controlled are solved by adopting a sizing twist deviation forming method; by adopting sizing finish forming (arc wrapping forming and flatness finish forming), the problems that the R value of the outer arc is not uniform, particularly the outer arc is easy to deform and the plane is not flat due to the fact that the welding edge of the welding line offset position is too short are solved.)

1. The forming method is characterized by comprising the steps of rough forming, extruding, welding forming, outer weld joint planing, weld joint twisting forming, round squaring forming, sizing finish forming, straightening shaping and sawing, wherein the rough forming stage comprises edge bending forming, middle bending forming and closed forming, the rough forming stage is carried out by adopting a double-radius forming method, edge forming is carried out firstly, then middle part reverse bending forming is carried out, and the R value of an edge arc is kept unchanged in the middle part reverse bending forming process.

2. The molding method according to claim 1, wherein the rough molding comprises the following specific steps:

firstly, performing edge forming for one frame in a rough forming frame until the radius of the edge forming is consistent with that of a circular pipe during welding, then performing reverse bending forming at the middle part for 3 frames, wherein the reverse bending forming and the edge forming are performed at the middle part for 1 st frame simultaneously, and simultaneously ensuring that the edge parameters are unchanged during the reverse bending forming of the 2 nd and 3 rd frames;

then, carrying out cold-bending forming on the middle part of the 4 th to 7 th frames by adopting a flat roll and vertical roll alternating mode, wherein the 4 th frame vertical roll adopts a 3-frame continuous vertical roll group mode;

finally, carrying out closed forming for 8 th to 10 th frames by adopting a flat roller and vertical roller alternating mode;

the flat rollers comprise two upper rollers (21), two lower side rollers (22) and a lower flat roller (23).

3. The molding method according to claim 2, characterized in that the molding method comprises the steps of:

according to the overall dimension of the partial weld thin-wall high-strength cold-bending steel pipe, designing, simulating and optimizing key process parameters such as cold-bending forming passes, forming angles of each pass, arc R values, excessive bending amount and the like of a steel strip by using a copra professional analysis software to obtain optimal forming parameters of the cold-bending forming passes and each pass;

secondly, uncoiling, feeding, shearing and butt welding the steel strip sheared according to the strip width, and conveying the steel strip to a material guiding vertical roll by a pinch roll;

thirdly, carrying out cold bending deformation according to the forming pass and the optimal forming parameter until the optimal parameter value before welding is reached, and finishing rough forming;

(IV) extruding, welding and shaping, and planing outer welding seam

Adopting two roller type extrusion rollers (31) to carry out extrusion welding molding, finally sealing and molding two welding edges, forming a closed hole type steel pipe after finishing high-frequency welding through extrusion, adopting two external welding seam planing cutter bars with arc-shaped detachable edge planing cutters to plane and remove the external burrs on the two welding edges, and ensuring that the welding surface is flat and smooth;

(V) sizing twist deviation forming and sizing flat vertical roller round squaring forming

Carrying out one-frame twisting vertical roll forming by utilizing a rotatable vertical roll (41); then, carrying out five times of sizing flat vertical roller rounding squaring forming;

(VI) sizing and precision forming

Performing arc wrapping flat roll forming for one frame by utilizing the four-corner arc roll (42) to finish arc wrapping finishing, and finally performing drum flat roll forming for one frame by utilizing the drum flat roll (43) and finishing and shaping the surface flatness of the steel pipe by utilizing the drum vertical roll (44) for one frame to ensure that the flatness of the steel pipe meets the standard requirement;

(VII) straightening, shaping, milling, sawing and cutting

In the straightening process, two secondary straightening rollers are adopted for straightening and shaping, a single-saw-blade cold saw is used for fixed-length saw cutting, packaging and collecting, and warehousing, and the straightening rollers are closed straightening rollers consisting of one Turkish head roller 451, a straightening lower roller 452 and two straightening side rollers 453.

4. The forming method as claimed in claim 3, wherein the arc-shaped detachable beveling tool is a detachable blade with an arc shape on four sides, the blade is detachably mounted, and the radian of the arc-shaped blade is matched with that of the closed hole type steel pipe.

5. The molding method according to claim 3, wherein the rough molding comprises the following specific steps:

a) "edge forming": firstly, forming the edge radius to be consistent with the radius of a circular tube during welding, namely forming the edge with a central angle of 48 degrees and an arc R value of R17, and keeping the edge radius unchanged during the middle forming;

b) the 'middle part is molded': in the processes of back bending of 45 degrees, 30 degrees and 15 degrees in the first three-pass flat roll stand, the back bending forming of the first stand is carried out simultaneously with the edge forming in the step a), and in the processes of cold bending of the fourth stand to the seventh stand, the forming center angle and the R value of the circular arc of each stand are respectively 32 degrees (R149), 52 degrees (R90), 62 degrees (R76), 74 degrees (R65), 90 degrees (R52), 116 degrees (R40), 140 degrees (R33), 162 degrees (R29), 182 degrees (R25) and 200 degrees (R23), wherein the 32 degrees (R149) represents the forming center angle of the flat roll of the fourth stand, the R value 149, 52 degrees (R90) represents the forming center angle 52 degrees of the first vertical roll when the vertical roll group of the fourth stand is formed, the R value 90 degrees is kept in the free edge forming state, no angular modification "; in the fourth frame, a three-frame vertical roller group is adopted for modification, and the three-frame vertical roller group comprises a first frame vertical roller 24, a second frame vertical roller 25 and a third frame vertical roller 26;

c) "closed molding": and (3) performing closed forming in an alternate mode of a flat roller and a vertical roller, wherein in the process of cold-bending forming from the eighth pass to the tenth pass, the forming central angle and the arc R value of each frame are as follows in sequence: flat eight 312 ° (R20), upright eight 320 ° (R19), flat nine 330 ° (R18.5), upright nine 340 ° (R18), flat ten 344 ° (R17.5), upright ten 350 ° (R17) to ensure gradual rounding.

6. The forming method of claim 3, wherein the five sizing flat roller round squaring forming comprises the following specific steps: and (3) calculating the formed central angle and the corresponding outer circular arc value of each side dividing section of each frame by using a copra software, and performing five-in-five vertical circle squaring forming on the circular tube subjected to seam deviation by using a sizing flat vertical roller through a gradual circle squaring changing method to form the circular tube into a square with the required specification and size.

Technical Field

The invention relates to the technical field of cold-bending forming, in particular to a forming method of a partial-weld-seam thin-wall high-strength square cold-bending steel pipe.

Background

The traditional cold-bending steel pipe is moderate in wall thickness (3-12 mm), centered in welding seams, low in material physical properties such as yield strength (235-600 MPa), and high in elongation (more than or equal to 20%), so that cold-bending forming and welding are facilitated. The partial weld seam thin-wall high-strength cold-bent steel pipe is applied to a bottom support of a carriage of a passenger car, a new energy weight reduction scheme is adopted, 1.5-2 mm thin-wall high-strength steel is adopted for manufacturing (the yield strength is larger than or equal to 700MPa, the elongation is larger than or equal to 12%), an inner die is required to be installed inside the steel pipe, a weld seam must be eccentric, and the sectional views of the traditional cold-bent steel pipe and the partial weld seam thin-wall high-strength cold-bent steel pipe are respectively shown in figures 1.1 and 1.2.

The traditional partial weld thin-wall high-strength cold-bent steel pipe has the following problems: 1) the wave shape of the edge part caused by uneven extension of the edge part in the cold bending forming process due to thin wall thickness and high strength, thereby influencing the stability of welding quality and simultaneously bringing the quality problems of poor forming size precision, welding dislocation, welding missing and the like; 2) after the partial welding seam thin-wall high-strength cold-bent steel pipe is subjected to extrusion welding, the outer welding seam of the outer welding seam is not planed and uneven, and the inner welding seam is not deviated accurately; 3) the outer arc ellipse changing caused by too short welding edge can not meet the standard requirement after the welding line is deviated and the perfect circle becomes square; 4) due to high material strength, large rebound, thin wall thickness, easy flatness unevenness and the like.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a method for forming a partial-weld thin-wall high-strength cold-bent steel pipe.

In order to achieve the purpose, the forming method of the bias-weld thin-wall high-strength square cold-bent steel pipe comprises the steps of rough forming, extruding, welding forming, outer weld planning, weld twisting and bias forming, circle squaring forming, sizing precision forming, straightening and shaping and saw cutting, wherein the rough forming stage comprises edge bending forming, middle bending forming and closed forming, the rough forming stage is carried out by adopting a double-radius forming method, edge forming is carried out firstly, then middle part reverse bending forming is carried out, and the R value of an edge arc is kept unchanged in the middle part reverse bending forming process.

Further, the rough forming comprises the following specific steps:

firstly, performing edge forming for one frame in a rough forming frame until the radius of the edge forming is consistent with that of a circular pipe during welding, then performing reverse bending forming at the middle part for 3 frames, wherein the reverse bending forming and the edge forming are performed at the middle part for 1 st frame simultaneously, and simultaneously ensuring that the edge parameters are unchanged during the reverse bending forming of the 2 nd and 3 rd frames;

then, carrying out cold-bending forming on the middle part of the 4 th to 7 th frames by adopting a flat roll and vertical roll alternating mode, wherein the 4 th frame vertical roll adopts a 3-frame continuous vertical roll group mode;

finally, carrying out closed forming for 8 th to 10 th frames by adopting a flat roller and vertical roller alternating mode;

the flat roller comprises two upper rollers, two lower side rollers and a lower flat roller.

Further, the molding method comprises the following steps:

designing, simulating and optimizing key process parameters of cold bending forming passes, forming angles of each pass, arc R values, excessive bending amounts and the like of a steel strip by using a copra professional analysis software according to the overall dimension of a partial weld thin-wall high-strength cold bending steel pipe to obtain optimal forming parameters of the cold bending forming passes and each pass;

secondly, uncoiling, feeding, shearing and butt welding the steel strip sheared according to the strip width, and conveying the steel strip to a material guiding vertical roll by a pinch roll;

thirdly, carrying out cold bending deformation according to the forming pass and the optimal forming parameter until the optimal parameter value before welding is reached, and finishing rough forming;

fourthly, extruding, welding and shaping, planing outer welding seam

Adopting two roller type extrusion rollers to carry out extrusion welding molding, finally sealing and molding two welding edges, forming a closed hole type steel pipe after finishing high-frequency welding through extrusion, adopting two external welding seam planing cutter bars with arc-shaped detachable edge planing cutters to plane and remove external burrs on two welding side edges, and ensuring that a welding surface is flat and smooth;

fifthly, sizing twist forming and sizing flat vertical roller round squaring forming

Carrying out one-frame twisting vertical roll forming by utilizing a rotatable vertical roll; then, carrying out five times of sizing flat vertical roller rounding squaring forming;

sixthly, sizing and fine forming

Performing one-frame arc-wrapping flat roll forming by utilizing the four-corner arc-shaped rolls to finish arc wrapping finishing, and finally performing one-frame drum-shaped flat roll and one-frame drum-shaped vertical roll to finish and shape the surface flatness of the steel pipe so as to ensure that the flatness of the steel pipe meets the standard requirement;

seventhly, straightening, shaping, milling, sawing and cutting

And in the straightening process, two secondary straightening rollers are adopted for straightening and shaping, a single-saw-blade cold saw is utilized for fixed-length saw cutting, packaging and collecting, and warehousing, wherein the straightening roller is a closed straightening roller consisting of a Turkish head roller, a straightening lower roller and two straightening side rollers.

Further, the edge planer sword can be dismantled to arc is the detachable blade of arc in four sides area, and the blade is demountable installation, and the radian of arc blade etc. and closed pass steel pipe phase-match.

Furthermore, the rough forming comprises the following specific steps:

a) "edge forming": firstly, forming the edge radius to be consistent with the radius of a circular tube during welding, namely forming the edge with a central angle of 48 degrees and an arc R value of R17, and keeping the edge radius unchanged during the middle forming;

b) the 'middle part is molded': in the processes of back bending of 45 degrees, 30 degrees and 15 degrees in the first three-pass flat roll stand, the back bending forming of the first stand is carried out simultaneously with the edge forming in the step a), and in the processes of cold bending of the fourth stand to the seventh stand, the forming center angle and the R value of the circular arc of each stand are respectively 32 degrees (R149), 52 degrees (R90), 62 degrees (R76), 74 degrees (R65), 90 degrees (R52), 116 degrees (R40), 140 degrees (R33), 162 degrees (R29), 182 degrees (R25) and 200 degrees (R23), wherein the 32 degrees (R149) represents the forming center angle of the flat roll of the fourth stand, the R value 149, 52 degrees (R90) represents the forming center angle 52 degrees of the first vertical roll when the vertical roll group of the fourth stand is formed, the R value 90 degrees is kept in the free edge forming state, no angular modification "; the third-frame vertical roll group is adopted for modification in the fourth frame, and comprises a first-frame vertical roll, a second-frame vertical roll and a third-frame vertical roll;

c) "closed molding": and (3) performing closed forming in an alternate mode of a flat roller and a vertical roller, wherein in the process of cold-bending forming from the eighth pass to the tenth pass, the forming central angle and the arc R value of each frame are as follows in sequence: flat eight 312 ° (R20), upright eight 320 ° (R19), flat nine 330 ° (R18.5), upright nine 340 ° (R18), flat ten 344 ° (R17.5), upright ten 350 ° (R17) to ensure gradual rounding.

Further, the five sizing flat roller rounds are formed in a square mode through the specific steps of: and (3) calculating the formed central angle and the corresponding outer circular arc value of each side dividing section of each frame by using a copra software, and performing five-in-five vertical circle squaring forming on the circular tube subjected to seam deviation by using a sizing flat vertical roller through a gradual circle squaring changing method to form the circular tube into a square with the required specification and size.

Compared with the prior art, the invention has the following advantages and beneficial effects:

a) double-radius molding is adopted: the method of forming the edge and then forming the middle part (in the middle part forming process, the R value of the edge arc is kept unchanged, and the method of combining the reverse bending forming and the vertical roll group forming is adopted) solves the problems of uneven deformation, insufficient deformation stability, easy wave shape generation of edge deformation and the like, the production process is stable, and the welding quality stability of the product is also ensured;

b) by adopting the two-roller type extrusion rollers, the problems of high yield strength, large rebound and thin wall thickness of the steel pipe material and uneven deformation easily caused are solved, and the welding stability and the uniformity of the deformation of the steel pipe during welding are improved;

c) the outer burrs on two sides of the welding are planed by adopting two outer welding seam planing cutter bars with detachable arc-shaped planing edge cutters, the problems that cutter bar replacement is troublesome and production efficiency is not high are solved, a welding surface is flat and smooth after planing, and the problem that a planing surface is a groove after planing by a traditional straight cutter bar is solved; the arc-shaped detachable edge planer is a detachable blade with four arc-shaped surfaces, so that not only can the planing quality be ensured, but also the blade can be used by replacing the surface through a detachable screw immediately after being worn, and the efficiency is higher;

d) the difficult problems that the welding line cannot be deviated and the deviation cannot be finished and controlled are solved by adopting a sizing twist deviation forming method;

e) by adopting sizing finish forming (arc wrapping forming and flatness finish forming), the problems of asymmetric R value of the outer arc (particularly, the outer arc is easy to deform due to too short welding edge at the offset part of a welding line) and uneven plane are solved;

f) after the method is implemented, the product quality and the yield are ensured and are approved by customers, and the production and sales volume of the thin-wall high-strength bias-weld square cold-bent steel pipe is increased.

Drawings

FIG. 1.1 is a cross-sectional view of a traditional cold-bent steel pipe with a centered weld;

FIG. 1.2 is a cross-sectional view of a bias-welded thin-walled high-strength cold-bent steel pipe.

FIG. 2.1 is a roller flower diagram of rough forming of a partial weld seam thin-wall high-strength cold-bent steel pipe.

FIG. 2.2 is a schematic view of an edge forming process;

FIG. 2.3 is a schematic view of a reverse bending process in the middle forming process;

FIG. 2.4 is a schematic view of a general vertical and horizontal forming process;

FIG. 2.5 is a schematic view of a vertical roller group forming process during a middle forming process;

FIG. 2.6 is a schematic view of a horizontal and vertical forming process of a sealing roller in the middle forming process.

FIG. 3.1 is a schematic view of an extrusion welding process of a partial weld seam thin-wall high-strength cold-bent steel pipe;

FIG. 3.2 is a schematic diagram of a process for planing off the outer burrs of a partial-weld thin-wall high-strength cold-bent steel pipe.

FIG. 4.1 is a schematic view of a process of a weld-seam-biased thin-wall high-strength cold-bent steel pipe weld-seam-twisting vertical roll;

FIG. 4.2 is a schematic diagram of a sizing-circle squaring modification process of a bias-weld thin-wall high-strength cold-bent steel pipe;

FIG. 4.3 is a schematic view of a process of a weld arc wrapping roller for a bias weld thin-wall high-strength cold-bent steel pipe;

FIG. 4.4 is a schematic view of a weld seam bulging roll process of a bias weld seam thin-wall high-strength cold-bent steel pipe;

FIG. 4.5 is a schematic view of the weld straightening and shaping process of the partial-weld thin-wall high-strength cold-bent steel pipe.

The components in the figures are numbered as follows: the device comprises an upper roll 21, a lower roll 22, a lower flat roll 23, a first vertical roll 24, a second vertical roll 25, a third vertical roll 26, a two-roll extrusion roll 31, a rotatable vertical roll 41, a four-corner arc roll 42, a drum flat roll 43, a drum vertical roll 44, 451-Turkish head rolls, 452-straightening lower rolls and 453-straightening side rolls.

Detailed Description

For a better understanding of the present invention, reference will now be made in detail to the present invention, examples of which are illustrated in the accompanying drawings.

A forming method of a bias welding seam thin-wall high-strength square cold-bent steel pipe comprises the steps of uncoiling, feeding, shearing and butt welding, pinch roll clamping to a material leading vertical roll → rough forming (edge bending forming, middle bending forming and closed forming) → extrusion, welding forming → external welding seam planing → welding seam twisting and bias forming → round square forming → sizing and fine forming → straightening and shaping → sawing and collecting → warehousing.

Firstly, calculating widening, forming central angle, arc value and forming pass:

according to the overall dimension of the offset welding seam thin-wall high-strength cold-bent steel pipe, designing, simulating and optimizing key process parameters such as cold-bending forming passes, forming center angles of each pass, arc R values, springback angles and the like of the steel strip by using a copra analysis software to obtain the cold-bending forming passes, the optimal forming center angles of each pass, the arc R values and the forming passes; forming process loading rollers, arranging rollers for each frame, ensuring the proper position of the rollers for each frame in the transverse and height directions, and ensuring that the roll gap value, the central position and the like meet the requirements;

secondly, uncoiling, feeding, shearing and butt welding the steel strip sheared according to the bandwidth, and conveying the steel strip to a material guiding vertical roll for rough forming by a pinch roll;

thirdly, coarse forming: adopting double-radius molding: a method of forming the edge first and then forming the middle (in the middle forming process, the R value of the edge arc is kept unchanged, and a method combining reverse bending forming and vertical roll group forming is adopted):

firstly, performing edge forming for one frame in a rough forming frame, then performing reverse bending forming for the middle part of 3 frames, and performing the reverse bending forming in a flat roll mode (wherein the reverse bending forming for the middle part of the 1 st frame and the edge forming are performed simultaneously, and meanwhile, edge parameters are ensured to be unchanged when the reverse bending forming for the 2 nd and 3 rd frames is performed);

then, continuously carrying out cold bending forming on the middle part of the 4 th to 7 th frames, and carrying out cold bending forming by adopting a flat roller and vertical roller alternating mode, wherein the 4 th frame vertical roller adopts 3 continuous vertical roller groups;

finally, carrying out closed forming for 8 th to 10 th frames by adopting a flat roller and vertical roller alternating mode; adopt flat roll and vertical roll alternating mode, guide and reduce the marginal wave shape problem that the limit portion extends and bring to the steel pipe that does not take shape.

The roll flower pattern of the rough forming of the offset welding seam thin-wall high-strength cold-bent steel tube is shown in figure 2.1;

fourthly, extruding, welding and forming, and then planing the outer welding seam: adopting two-roller extrusion, high-frequency welding and planing an outer welding seam to be flat and smooth; rolling liquid is sprayed in the extrusion and welding forming processes, so that the welded seam 0 is ensured to be cooled in time after welding, and the welded seam is prevented from cracking;

fifthly, one-frame twisting vertical roll forming, five-frame sizing horizontal vertical roll round squaring forming, one-frame arc wrapping flat roll forming and one-frame horizontal flatness shaping are carried out. Rolling liquid is sprayed between the rollers to ensure cooling and lubrication;

sixthly, straightening and shaping, milling, sawing, packaging, collecting and warehousing;

the third step comprises the following specific operations:

a) "edge forming": the process schematic diagram of the 'edge forming' is shown in fig. 2.2, wherein the flat roller comprises two upper rollers 21, two lower rollers 22 and a lower flat roller 23, the edge radius is firstly formed to be consistent with the radius of a circular tube during welding, namely the edge forming center angle is 48 degrees, the circular arc R value is R17, the edge radius is always kept unchanged during the middle forming frame, the welding is directly carried out during the welding frame, the problem of uneven extension of the edge caused by multiple times of middle deformation is avoided, and the stability of the welding quality is ensured;

b) the 'middle part is molded': the schematic diagram of the reverse bending forming process is shown in fig. 2.3, the reverse bending forming is carried out for 45 degrees, 30 degrees and 15 degrees in sequence in the first three times of flat roll stands, the reverse bending forming of the first stand and the edge forming of the step a) are carried out simultaneously, the deformation amount of the edge part of the steel strip along the longitudinal direction in the forming process can be reduced, and meanwhile, the stability of the steel tube in the forming process is ensured. In the cold roll forming processes of the fourth to seventh stands, the forming center angle and the arc R value of each stand are flat four 32 degrees (R149), vertical four one 52 degrees (R90), vertical four two 62 degrees (R76), vertical four three 74 degrees (R65), flat five 90 degrees (R52), vertical five 116 degrees (R40), flat six 140 degrees (R33), vertical six 162 degrees (R29), flat seven 182 degrees (R25), vertical seven 200 degrees (R23) in sequence, wherein the flat four 32 degrees (R149) represents the forming center angle 32 degrees of the flat roll of the fourth stand, the arc R value 149, and the vertical four 52 degrees (R90) represent the forming center angle 52 degrees of the first vertical roll during the forming of the stand roll group of the fourth stand, the arc R value 90, and so on, two sides of the edge forming are kept in a free state in the middle forming process, and no angle modification is carried out; with reference to fig. 2.4, in the fourth frame, a three-frame vertical roll group is adopted for modification, and the three-frame vertical roll group comprises a first frame vertical roll 24, a second frame vertical roll 25 and a third frame vertical roll 26, so that the problems of surface scratch and the like caused by uneven modification and insufficient stability due to 'flat vertical and flat' molding can be solved;

c) "closed molding": and (3) performing closed forming by using the flat vertical rollers in an alternating mode, wherein in the process of cold-bending forming from the eighth pass to the tenth pass, the forming central angle and the arc R value of each pass are as follows in sequence: flat eight 312 ° (R20), upright eight 320 ° (R19), flat nine 330 ° (R18.5), upright nine 340 ° (R18), flat ten 344 ° (R17.5), upright ten 350 ° (R17) to ensure gradual rounding.

The specific operation of the step four is as follows:

a) the method comprises the following steps of extrusion and welding molding: the central angle and the arc R value of the two edge forming of the edge forming are 48 degrees (R17) degrees, the central angle and the arc R value of the middle part of the final closed forming are 350 degrees (R17), the steel tube has high yield strength, large rebound and thin wall thickness, so that the deformation is not uniform, and in order to avoid the stability during welding and the uniformity of the steel tube deformation during welding, the design adopts two roller type extrusion rollers 31 to carry out extrusion forming, the two welding edges are finally closed forming, and the closed hole type steel tube is formed after the high-frequency welding is completed through extrusion.

b) "outer weld planing": for a high-strength thin-wall steel pipe, the welded outer welding seam is thin, if a traditional straight planer tool is adopted, the welding seam is prone to being planed deeply, and a groove is formed in the welding seam after the welding seam is squared; moreover, as the material is hard and the blades are easy to consume, the traditional welding type planing tool is adopted, the tool bar is troublesome to replace, and the production efficiency is influenced, and in combination with the figure 3.2, the outer welding seam planing tool bar with the arc-shaped detachable planing edge tool is adopted for two times in the embodiment to plane the outer burrs on the two sides of the welding, so that the welding surface is smooth and flat; and the production efficiency is also ensured. The arc can be dismantled and the edge planer sword is four sides area arc, detachable blade, and the radian of arc blade etc. and closed pass steel pipe phase-match not only can guarantee the planing quality, can change the face through dismantling the screw immediately after the blade wearing and tearing moreover and use, and efficiency is higher.

The concrete operation of the step five is as follows:

a) sizing and twisting and forming: before sizing, because of the symmetry of the round pipe forming, the welding seam is positioned in the middle of the steel pipe and can not meet the requirement of welding seam deviation, so that the welding seam deviation is needed; with reference to fig. 4.1, in this embodiment, a round pipe is twisted by a certain angle by using a single rotatable vertical roller 41, the twisting angle is performed according to the requirement of weld joint deviation, and the weld joint is deviated to a certain value by twisting, so as to meet the design requirement;

b) and (3) five-frame sizing flat roller round squaring forming: and (3) calculating the formed central angle and the corresponding outer circular arc value of each side dividing section of each frame by using copra software, performing five-horizontal five-vertical-circle square-changing forming on the circular tube subjected to seam deviation by using a sizing flat vertical roller through a gradual circle-changing square-changing deformation method, and forming the circular tube into a square with a required specification and size, wherein a process schematic diagram is shown in fig. 4.2.

c) The sizing and fine forming method comprises the following steps: the steel pipe after the sizing circle becomes square is subjected to outer circular arc wrapping shaping and flatness finishing shaping, and by combining the drawing with 4.3 and 4.4, the steel pipe is subjected to one-time flat roll shaping by adopting the four-corner circular arc rollers 42 to finish the arc shaping, so that the problem that the R value of the outer circular arc of the steel pipe becomes elliptical due to the eccentricity of a welding line and cannot meet the standard requirement is solved; and then, finishing and shaping the surface flatness of the steel pipe by adopting a primary drum-shaped flat roller 43 and a primary drum-shaped vertical roller 44 to ensure that the flatness of the steel pipe meets the standard requirement.

The concrete operation of the step six is as follows:

straightening and shaping: straightening and shaping the steel pipe subjected to sizing finish forming to ensure that the longitudinal straightness of the steel pipe meets the requirements of customer standards, and straightening and shaping by adopting two straightening rollers for two times in the straightening process as shown in a figure 4.5, wherein the straightening roller is a closed straightening roller consisting of a Turkish head roller 451, a lower straightening roller 452 and two straightening side rollers 453; and then, carrying out fixed-length sawing by adopting a single-saw-blade cold saw, automatically packaging, lifting and warehousing.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.