CN109834143B - Servo following hot roll bending module and method for forming bent pipe with unequal strength structure on line - Google Patents

Abstract

The present invention discloses a servo-following hot roll bending module and a method for online forming a bent pipe with unequal strength structure, wherein the method for online forming a bent pipe with unequal strength structure comprises: a feeding step, guiding a pipe bar to advance along a production line direction; a heating step, performing high-frequency local heating on a first local section of the pipe bar; a hot roll bending step, using a four-roll hot rolling mechanism to roll-bend the first local section to form a curvature; an online servo-following holding step, using an online roller-following holding cooling unit to measure the curvature of the first local section, and multiple groups of multiple follow-up holding corrections and repeated measurement of the curvature of the first local section, so that the curvature accuracy of the first local section meets the product requirements; an online servo cooling step, using a cooling nozzle to perform online cooling on the first local section to form a first strength; the technical solution can control the phase change curve and cooling accuracy variation of the pipe bar online, thereby controlling the different curvatures and the changes of the unequal strength structure of the pipe bar.

Description

Servo-following hot roll bending module and method for forming unequal-strength structural bends online

technical field

The invention relates to a servo-following hot roll bending module and a method for forming an unequal-strength structural bend on-line, in particular to a method that can form an unequal-strength and different-curvature bend that can be servo-followed and cooled on-line for the curvature of the hot roll The servo-following hot roll-bending module and method of forming unequal-strength structural bends online.

Background technique

At present, the forming technologies for frame pipe fittings mainly include hydroforming (cold forming), hot stamping (hot stamping). Forming can only deal with three-dimensional plates; in addition, in terms of manufacturing speed, the manufacturing speed of hydroforming is relatively slow, and the manufacturing speed of hot stamping is relatively faster than that of hydroforming; compared with the strength of machinable materials: materials that can be processed by hydroforming The strength is -980 MPa, and that of hot stamping is 1.2-1.5GPa; in terms of structural strength, the hydroformed product is a three-dimensional closed medium structural strength, and the hot stamping is a three-dimensional shell with high strength. Then compare the equipment volume of the two. The hydroforming equipment is large in size, and the hot stamping equipment is not only large in size, but also in a high temperature state during processing; the process energy consumption of the two processing technologies, the energy consumption of hydroforming is low, and the heat consumption is relatively low. The energy consumption of stamping is high (high temperature dissipation); and for the mold processing cost, hydroforming needs to cooperate with large molds, so the mold processing cost is high, and hot stamping also requires the use of large hot stamping molds, so the mold processing cost is the same is high; finally, for the development process, since both hydroforming and hot stamping are mature technologies, the development process is moderate.

While the weight of the car is light, safety is still an issue that must be considered. Advanced countries in the world have made mandatory requirements for automobile crash safety and established stricter specifications and tests. The trend of lightweight and high safety in the global automotive market has driven the vigorous development of automotive high-strength steel parts. North American countries, India, Mexico and ASEAN countries are the regions with high sales growth for global auto parts and components. The increase in auto sales and ownership has driven the expansion of the demand for auto parts. At present, the problems faced by the auxiliary factory parts industry in the automobile industry: there are many product categories, and it is difficult to produce management. Different auto parts have different specifications. There are hundreds of different models in the market, and each model has many different parts strength requirements. Therefore, manufacturers have difficulties in production, manufacturing and material preparation management. Therefore, it is helpful to develop technologies that show different strengths in different areas of the car body (high-strength protection areas, sub-strength areas, and energy-absorbing areas) for different situations and vehicle models, especially under consideration of small quantities, diversity, light weight, and cost. development of the industry in this field.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a servo-following hot roll bending module, which applies a servo hot roll-bending unit to hot-roll a pipe and bar, and uses an online roller-following and holding cooling unit to measure the roll bending rate accuracy of the pipe and bar. After calibration, in-line cooling with a controllable cooling rate was performed to form curved tube rods with different curvatures of unequal strength.

In order to achieve the purpose of the above-mentioned servo-following hot roll-bending module, the technical means provided by the present invention is to provide a servo-following hot roll-bending module, comprising: a guiding and conveying unit, which includes a feeding roller and a fixed roller for pushing The tube and bar advance along the production line; a servo hot rolling unit includes a four-roll hot rolling mechanism that enables each roller to move independently and telescopically to change the pressure applied to the tube and bar, and an electrical coupling. Connected to the servo controller of the four-roll hot-rolling mechanism, the four-roll hot-rolling mechanism accepts the pipe and bar pushed out of the guiding and conveying unit, and performs roll bending; a high-frequency local heating unit is arranged in the The feeding front section of the four-roll hot rolling mechanism is used to heat the pipe and bar; and an in-line roller tracking and holding cooling unit includes a programmable controller, a programmable controller electrically coupled to the A first position sensor for measuring the curvature of the tube and bar output by the hot rolling unit of the servo hot rolling unit is electrically coupled to the programmable controller, and for the tube and bar advancing in the direction of the production line A servo following and holding roller set for carrying out multiple sets of following and holding, and an electrical coupling to the programmable controller for measuring the output of the pipe and bar after being held by the servo following and holding the roller set. a second position sensor for curvature, and a plurality of cooling nozzles electrically coupled to the programmable controller for online cooling of the tube and bar output after being held by the servo following the holding roller set and conforming to the standard of curvature .

In one embodiment, the pipe rod is a hollow pipe body, and the servo-following hot roll bending module further includes a composite through-core inner mold unit, which sequentially includes a flexible mandrel segment and a ceramic mandrel segment. and a metal mandrel section, which penetrates the inner diameter of the hollow tube body from the feeding end of the tube bar, and makes the flexible mandrel section correspond to the rolling position of the tube bar by the four-roll hot rolling mechanism , The ceramic mandrel segment corresponds to the heating position of the high-frequency local heating unit for the pipe rod, and the metal mandrel segment corresponds to the pushing position of the feeding roller and the fixing roller to the pipe rod.

In one embodiment, the pipe and bar rolled by the servo hot roll bending unit have different curvatures, and the pipe and bar hot rolled and output by the servo hot roll bending unit is a first partial section, and the first A partial section includes a first section, a second section and a third section in sequence, and the servo-following holding roller set includes a first roller set, A second roller set, a third roller set and a fourth roller set, the second position sensor is arranged on the output section of the first roller set, the cooling nozzles are arranged on the second roller Between the wheel set, the third roller set and the fourth roller set.

Another object of the present invention is to apply the servo to follow the method of forming the bending tube with the structure of unequal strength on-line of the hot roll bending module.

In order to achieve the purpose of the above method, the technical means provided by the present invention is to provide a method for forming an on-line bending pipe with an unequal strength structure, the steps of which include: providing the aforementioned servo-following hot roll bending module; The unit guides a high-rigidity pipe and bar along the direction of the production line; a heating step is performed, and a first partial section of the pipe and bar is heated to a better formability with a high-frequency local heating unit; hot roll bending is performed step, the first partial section is rolled with a four-roll hot rolling mechanism, and a curvature is formed in the first partial section; the online servo tracking and holding step is performed, and the online roller tracking and holding cooling unit is used to measure the warp The curvature of the first partial section that is rolled and passed along the direction of the production line, and the curvature of the first partial section is repeatedly measured by following and holding in multiple groups for multiple times to make the curvature of the first partial section. The precision meets the product requirements; and the online servo cooling step is performed, and the first partial section is cooled online at a first cooling rate by the cooling nozzle, so that the first partial section forms a first strength.

In an implementation aspect of the above-mentioned method, the method further comprises: at the rear section of the first partial section of the pipe rod, applying the high-frequency partial heating unit to heat a second partial section of the pipe rod to a relatively high frequency Good formability; rolling the second partial section with the four-roll hot rolling mechanism, and forming a curvature in the second partial section; and measuring the roll bending and The curvature of the second partial section advancing along the direction of the production line is followed by multiple groups to hold and repeatedly measure the curvature of the second partial section to make the curvature accuracy meet the product requirements. The second partial segment is cooled in-line at a second cooling rate different from the value of the first cooling rate so that the second partial segment develops a second intensity.

In one embodiment, the second partial segment is adjacent to the first partial segment or separated from the first partial segment by a distance.

In one embodiment, the material crystal phase of the pipe and rod of the first partial section when heated to the better formability is Vostian iron, and the tube of the first partial section is The material crystal phase of the rod cooled to the first strength is Matian loose iron.

In one embodiment, the material crystal phase of the pipe and rod of the second partial section when heated to the better formability is Vostian iron, and the tube of the second partial section is The material crystal phase of the rod cooled to the second strength is Matian loose iron.

In an embodiment, the first partial section of the pipe rod includes adjacent first to third sections, respectively, and the preset ideal curvatures of the first to third sections are a first to a third section, respectively. Three ideal curvatures, the first position sensor measures the curvatures of the first to third sections of the pipe bar rolled by the four-roll hot rolling mechanism as the first to third original curvatures, respectively, and calculates these quantities The measured curvature is input to the programmable controller; the online rollers follow the programmable controller holding the cooling unit to control the first roller set to the first section according to the difference between the first ideal curvature and the first original curvature Carry out adjustment and hold, adjust and hold the second section according to the difference value of the second ideal curvature and the second original curvature, and adjust the hold of the third section according to the difference value of the third ideal curvature and the third original curvature Sections are adjusted and held; the second position sensor respectively measures the curvature of the pipes and rods in the first to third sections after they are adjusted and held by the servo tracking and holding rollers, and the measured The curvature is input to the programmable controller; the programmable controller is used to respectively control the holding curvature positions of the first to third sections of the pipe and bar pushed by the second roller set to follow the first roller set, Controlling the holding curvature position of the first to third sections of the pipe rod pushed by the third roller set to follow the second roller set and controlling the pipe rod pushed by the fourth roller set The holding curvature positions of the first to third sections follow the third roller set; and repeatedly measure the pipe rods of the first to third sections adjusted by the servo following the holding roll set and the corresponding first to third ideal curvatures are compared until the comparison value conforms to a tolerance.

The characteristics of the present invention are: the present invention follows the hot roll bending module through the servo, controls the phase transition curve and the variation of the cooling accuracy of the pipe and bar on-line, and can directly achieve the display of unequal strength on the production line (the material strength of the finished product is 900 -1500MPa). Part of the tube and bar or the whole tube and bar can be subjected to thermomechanical treatment, and the servo tracking and holding roller set of the online roller follows the holding and cooling unit to control the change of different curvature radii to meet the requirements of different curvature changes of parts and components. The advantages of short development time and fast manufacturing process. The present invention can be aimed at different situations and vehicle models, under consideration of a small amount of variety, light weight and cost, using a material (manganese boron steel) and the on-line servo tracking hot roll bending module key process technology of the present invention to form different curvatures and irregularities online. The method of equal-strength structural bending to achieve different structural strength and size specifications in different areas of the car body (high-strength protection zone, sub-strength zone, energy-absorbing zone) will have a breakthrough in the production form of the auto parts industry.

Description of drawings

FIG. 1 is a schematic plan view of a guide and conveying unit of a servo-following hot-rolling module and a servo hot-rolling unit for hot-rolling according to an embodiment of the present invention;

FIG. 2 is a schematic plan view of the actuation of the guide conveying unit, the servo hot roll bending unit, the high-frequency local heating unit and the online roller tracking and holding cooling unit of the servo following hot roll bending module of FIG. 1;

FIG. 3 is a flow chart of the steps of a method for online forming bends with different curvatures and unequal strength structures according to an embodiment of the present invention;

FIG. 4 is a schematic plan view of the servo-following hot roll bending module in accordance with an embodiment of the present invention forming a second partial section of a different strength after processing a first partial section of a pipe and bar to form a second partial section of a different strength;

FIG. 5 is a flow chart of the steps of a method for online forming two structural bends with different curvatures and unequal strengths according to an embodiment of the present invention.

Description of symbols in the attached drawings:

1 Servo following hot roll bending module; 11 Guide transfer unit; 111 Feed roll; 112 Fixed roll; 12 Servo hot roll bending unit; 121 Four-roll hot rolling mechanism; 122 Servo controller; 13 High frequency local heating unit; 14 Online Roller following and holding cooling unit; 141 Programmable controller; 142 1st position sensor; 143 Servo following and holding roll set; 1431 1st roll set; 14311 Output section; 1432 2nd roll set; 1433 3rd roll Wheel Set; 1434 Fourth Roller Set; 144 Second Position Sensor; 145 Cooling Nozzle; 15 Composite Feedthrough Unit; 151 Flexible Mandrel Section; Bar; 20 Inner Diameter; 21 First Partial Section; 211 First Section; 212 Second Section; 213 Third Section; 221 First Ideal Curvature; 222 Second Ideal Curvature; 223 Third Ideal Curvature; 231 Section 1. Original curvature; 232. Second original curvature; 233. Third original curvature; Method steps for bending pipes of unequal strength structures.

Detailed ways

The embodiments of the present invention will now be described in detail with the accompanying drawings. The accompanying drawings are mainly simplified schematic diagrams, and only illustrate the basic structure of the present invention in a schematic manner. Therefore, only the components related to the present invention are indicated in these drawings. , and the displayed components are not drawn according to the number, shape, size ratio, etc. of the actual implementation. The size of the actual implementation is actually a selective design, and the layout of the components may be more complicated.

First, please refer to FIG. 1 and FIG. 2 . The servo-following hot roll bending module 1 of this embodiment adopts a multi-station structure, so that the metal pipes and rods 2 are conveyed and processed in sequence along a production line direction. The servo-following hot roll bending module 1 includes: a guide The conveying unit 11 , the servo hot rolling unit 12 , the high-frequency local heating unit 13 and the in-line rollers follow the holding cooling unit 14 . The guiding and conveying unit 11 includes a feeding roller 111 and a fixing roller 112. The feeding roller 111 clamps and pushes the pipe rod 2, and the fixed roller 112 maintains and pushes the pipe rod 2 along the production line. The line direction advances; the servo hot rolling unit 12 includes a four-roll hot-rolling mechanism 121 that enables each roller to move independently and telescopically to change the pressure applied to the pipe and bar 2, and a four-roller electrically coupled to the four-roller The servo controller 122 of the type hot rolling mechanism 121, the four-roll type hot rolling mechanism 121 accepts the pipe and bar 2 pushed out of the guiding and conveying unit 11, and rolls with a preset ideal curvature (the same can be done in the same way). The high-frequency local heating unit 13 is arranged in the feeding front section of the four-roll hot rolling mechanism 121 (the preferred position is located between the four-roll hot rolling mechanism 121 and the guiding and conveying unit 11). In the direction of the production line between the two sides), it is used to rapidly heat the pipe and bar 2; the online rollers follow the holding cooling unit 14, and include a programmable controller 141, a programmable controller 141 electrically coupled to the programmable controller 141 for A first position sensor 142 for measuring the curvature of the pipe and bar 2 outputted after hot rolling by the servo hot rolling unit 12, and a first position sensor 142 electrically coupled to the programmable controller 141, and a A servo tracking and holding roller set 143 for the pipe and bar 2 to follow and hold multiple times is electrically coupled to the programmable controller 141 for measuring the holding by the servo tracking and holding roller set 143 The second position sensor 144 for the curvature of the pipe and rod 2 outputted afterward, and a plurality of electrically coupled to the programmable controller 141, respectively, are held by the servo following the holding roller set 143 and conform to the curvature standard ( That is, the cooling nozzle 145 for on-line cooling of the pipe and rod 2 output after approaching the ideal curvature). The above-mentioned servo-following holding roller set 143 can also be applied to the four-roll hot rolling mechanism 121 , but it is not limited to single-axis or multi-axis.

Referring to FIG. 2 again, in an embodiment in which the pipe and rod 2 is a hollow pipe body, the servo-following hot roll bending module 1 further includes a composite through-core inner mold unit 15, which is viewed from the end. It includes a flexible mandrel section 151 that can flexibly support the tube wall, a ceramic mandrel section 152 that can withstand high heat and support the tube wall, and a metal mandrel section 153 that can withstand high-strength external forces to support the tube wall, The composite through-core inner die unit 15 penetrates the inner diameter 20 of the tube and bar 2 of the hollow tube body from the feeding end of the tube and bar 2, and makes the flexible mandrel section 151 correspond to the four-roll hot rolling The rolling position of the pipe rod 2 by the mechanism 121, the ceramic mandrel section 152 corresponding to the heating position of the high frequency local heating unit 13 to the pipe rod 2, and the metal mandrel section 153 corresponding to the feeding roller 111 and the The fixed roller 112 clamps and pushes the pipe rod 2 .

In one embodiment, the pipe bar 2 that is hot rolled and output by the servo hot rolling unit 12 is a first partial section 21, and the first partial section 21 includes a first section 211, a first section 211 in sequence The second section 212 and the third section 213, the servo tracking and holding roller set 143 includes a first roll set 1431, a second roll set 1432, a first roll set 1432, a first roll set 1432, and a The third roller set 1433 and a fourth roller set 1434, the second position sensor 144 is arranged on the output section 14311 of the first roller set 1431, the cooling nozzles 145 are arranged on the second roller set 1432 , between the third roller set 1433 and the fourth roller set 1434 .

Please refer to Figure 3. The method for forming an unequal-strength structural bend on-line in the present embodiment includes the following steps:

Step S10, providing the servo-following hot roll-bending module 1 of the aforementioned embodiment;

Carrying out a feeding step (step S20), using the guiding and conveying unit 11 to guide a high-rigidity pipe and bar 2 to advance along the direction of the production line;

A first partial segment heating step (step S30 ) is performed to heat a first partial segment 21 of the pipe rod 2 with the high-frequency partial heating unit 13 to a better formability (for example, to make the pipe rod 2 The crystal phase of the material is Vostian iron);

In the first partial segment hot roll bending step (step S40 ), the four-roll hot rolling mechanism 121 is used to perform roll bending on the first partial segment 21 according to a preset ideal curvature, and form the first partial segment 21 a curvature; (step S50 ) the first partial segment in-line servo tracking and holding step, the online roller tracking and holding cooling unit 14 is used to measure the first partial segment 21 that has been rolled and passed along the direction of the production line The curvature of the first partial section 21 is measured repeatedly, and the curvature of the first partial section 21 is repeatedly measured to make the first partial section 21 Curvature accuracy meets product requirements;

In the step of online servo cooling of the first partial section (step S60 ), the first partial section 21 that meets the product curvature accuracy requirements is cooled online by the cooling nozzle 145 at a first cooling rate, so that the first partial section 21 is cooled online at a first cooling rate. The first partial section 21 forms a first strength (for example, the material crystal phase of the pipe rod 2 is Matian loose iron). Through this, the pipe rod 2 has two different strengths of the original pipe strength and the first strength.

In one embodiment, as shown in FIG. 4 and FIG. 5 . After completing the above-mentioned first partial section 21 of the pipe rod 2 to form the first strength, the following steps can be further carried out:

In the second partial section heating step (step S70 ), in the latter section of the first partial section 21 of the pipe rod 2 , the high frequency partial heating unit 13 is applied to heat a second partial section 24 of the pipe rod 2 . To a better formability (for example, the material crystal phase of the pipe rod 2 is Vostian iron);

In the second partial section hot rolling step (step S80 ), the four-roll hot rolling mechanism 121 is used to roll the second partial section 24 to form a curvature in the second partial section 24 ;

In the second partial segment online servo following and holding step (step S90 ), the online roller following and holding cooling unit 14 is used to measure the curvature of the second partial segment 24 that has been rolled and moved along the production line direction, And multiple groups follow and hold and repeatedly measure the curvature of the second partial segment 24, so that the curvature accuracy can meet the product requirements;

In the second partial section online servo cooling step (step S100 ), the second partial section 24 , which meets the product curvature accuracy requirement, is sent to the second partial section 24 by the cooling nozzle 145 at a second value different from the first cooling rate value. On-line cooling is performed at two cooling rates, so that the second partial segment 24 forms a second strength (for example, the material crystal phase of the pipe rod 2 is Matian loose iron). Of course, the second intensity may be different from the second intensity.

In addition, in one embodiment, the second partial segment 24 may be adjacent to the first partial segment 21 or spaced apart from the first partial segment 21 by a distance.

2 and FIG. 3, further, the first partial section 21 of the pipe rod 2 includes adjacent first sections 211, second sections 212 and third sections 213, respectively. The preset ideal curvatures of the first to third sections ( 211 , 212 , 213 ) are a first ideal curvature 221 , a second ideal curvature 222 and a third ideal curvature 223 respectively. The first position sensor 142 measures the four-roller type The curvatures of the first to third sections ( 211 , 212 , 213 ) of the pipe and bar 2 rolled by the hot rolling mechanism 121 are respectively a first original curvature 231 , a second original curvature 232 and a third original curvature 233 . The position sensor 142 inputs the measured curvatures into the programmable controller 141;

The programmable controller 141 controls the first roller set 1431 to adjust and hold the first section 211 according to the difference between the first ideal curvature 221 and the first original curvature 231 and hold the first section 211 according to the second ideal curvature 222 The second section 212 is adjusted and held by the difference value from the second original curvature 232 and the third section 213 is adjusted and held according to the difference value between the third ideal curvature 223 and the control of the third original curvature 233 hold;

The second position sensor 144 respectively measures the curvature of the output after adjusting and holding the first to third sections ( 211 , 212 , 213 ) of the pipe and rod 2 through the servo tracking and holding roller set 143 , and will measure curvature input to the programmable controller 141;

The programmable controller 141 respectively controls the second roller set 1432 to follow the first roller set 1431, control The third roller set 1433 follows the second roller set 1432 to hold the curvature position of the first to third sections (211, 212, 213) of the pushed pipe bar 2, and controls the fourth roller set 1434 follow the third roller set 1433 to the holding curvature positions of the first to third sections (211, 212, 213) of the pushed pipe and bar 2;

Repeatedly measure the curvature of the pipe rod 2 in the first to third sections ( 211 , 212 , 213 ) adjusted by the servo tracking roller set 143 and match the corresponding first to third ideal curvatures ( 221 , 222 , 223 ) The comparison is performed until the compared difference value conforms to a tolerance, and the processing of the first partial section 21 can be completed. Otherwise, the steps of the tracking and holding adjustment of the online roller tracking and holding cooling unit 14 are repeated.

The above-mentioned embodiments are only illustrative of the principles, features and effects of the present invention, and are not intended to limit the applicable scope of the present invention. Modifications and changes are made to the implementation form. Any equivalent changes and modifications made by using the contents disclosed in the present invention should still be covered by the appended claims. Therefore, the scope of protection of the right of the present invention should be listed in the scope of the patent application.

Claims (10)

1. A servo-tracking hot roll bending module for sequentially processing a metal tube and bar along a production line direction in a multi-station structure, the servo-tracking hot roll bending module comprising:

the guiding and conveying unit comprises a feeding roller and a fixed roller and is used for pushing the pipe rod materials to advance along the production line direction;

a servo hot rolling unit, wherein the servo hot rolling unit comprises a four-roller hot rolling mechanism and a servo controller, the four-roller hot rolling mechanism enables each roller to independently stretch and move so as to change the pressure applied to the pipe and the bar, the servo controller is electrically coupled with the four-roller hot rolling mechanism, and the four-roller hot rolling mechanism receives the pipe and the bar pushed out of the guide conveying unit and performs roll bending;

the high-frequency local heating unit is arranged at the feeding front section of the four-roller hot rolling mechanism and is used for heating the pipe and the bar; and

the online roller following and holding cooling unit comprises a programmable controller, a first position sensor electrically coupled with the programmable controller and used for measuring the curvature of the tube and bar which is output by the servo hot roll bending unit in a hot rolling mode, a servo following and holding roller set which is electrically coupled with the programmable controller and used for carrying out multi-group multi-following and holding on the tube and bar advancing along the production line direction, a second position sensor electrically coupled with the programmable controller and used for measuring the curvature of the tube and bar which is output after being held by the servo following and holding roller set, and a plurality of cooling nozzles which are electrically coupled with the programmable controller and respectively carry out online cooling on the tube and bar which is output after being held by the servo following and holding roller set and meeting the curvature standard.

2. The servo follow-up hot roll bending module of claim 1, wherein the tube or bar is a hollow tube, the servo follow-up hot roll bending module further comprises a composite through-core inner die unit, the composite through-core inner die unit comprises a flexible mandrel section, a ceramic mandrel section and a metal mandrel section in sequence, the flexible mandrel section penetrates into the inner diameter of the hollow tube from the feeding end of the tube or bar, and the flexible mandrel section corresponds to the roll bending position of the four-roll hot rolling mechanism on the tube or bar, the ceramic mandrel section corresponds to the heating position of the high-frequency local heating unit on the tube or bar, and the metal mandrel section corresponds to the pushing position of the feed roll and the fixed roll on the tube or bar.

3. A servo-actuated follow-up hot roll bending module as claimed in claim 1 or 2, wherein the tube rod material being roll-bent by the servo hot roll bending unit is of a different curvature.

4. The servo-actuated follow-up hot roll bending module of claim 3, wherein the tube material hot rolled by the servo hot roll bending unit is a first partial section comprising a first segment, a second segment and a third segment in sequence, the servo follow-up pinch roller set comprises a first roller set, a second roller set, a third roller set and a fourth roller set in sequence along the production line direction, the second position sensor is disposed at the output segment of the first roller set, and the plurality of cooling nozzles are disposed between the second roller set, the third roller set and the fourth roller set.

5. A method for forming a bend pipe with unequal strength structure on line, comprising the steps of:

providing a servo-follow hot roll bending module according to claim 4;

a feeding step, guiding a rigid pipe bar to move forward along the production line direction by a guide conveying unit;

a first partial section heating step of heating a first partial section of the pipe bar to formability by a high-frequency partial heating unit;

a first partial section hot roll bending step of roll bending the first partial section with a four-roll hot rolling mechanism and forming a curvature in the first partial section;

a first partial paragraph online servo following holding step, measuring the curvature of the first partial paragraph passing through the roll bending and advancing along the production line direction by an online roller following holding cooling unit, correcting the curvature by a plurality of groups of times of following holding and repeatedly measuring the curvature of the first partial paragraph, and enabling the curvature precision of the first partial paragraph to reach the product requirement; and

the first partial section on-line servo cooling step is used for cooling the first partial section which meets the requirement of the product curvature precision on line by a cooling nozzle at a first cooling rate, so that the first partial section is formed into a first strength.

6. The method of forming an unequal strength structural bend in-line according to claim 5 further comprising:

a second partial section heating step of heating a second partial section of the pipe bar to formability by using the high-frequency local heating unit at a rear section of the first partial section of the pipe bar;

a second partial section hot roll bending step of roll bending the second partial section with the four-roll hot rolling mechanism and forming a curvature in the second partial section;

a second local paragraph online servo following holding step, measuring the curvature of the second local paragraph which is bent by the roller and passes through along the production line direction by using the online roller following holding cooling unit, and repeatedly carrying out a plurality of groups of times of following holding and measuring the curvature of the second local paragraph to ensure that the curvature precision of the second local paragraph meets the product requirement; and

and a second partial section online servo cooling step, in which the second partial section meeting the product curvature accuracy requirement is cooled online by the cooling nozzle at a second cooling rate different from the first cooling rate value, so that the second partial section is formed with a second intensity.

7. The method of forming an isostrength structural bend in-line of claim 6 wherein the second partial segment is adjacent to or spaced a distance from the first partial segment.

8. The method of forming an isopipe according to claim 5, wherein the material phase of the pipe or rod material being heated to the formability in the first partial section is austenite, and wherein the material phase of the pipe or rod material being cooled to the first strength in the first partial section is martensite.

9. The method of forming an isopipe of claim 6 wherein the material phase of the pipe and rod material during the heating to the formability in the second partial section is austenite, and wherein the material phase of the pipe and rod material during the cooling to the second strength in the second partial section is martensite.

10. The method of forming an unequal strength structural bend according to claim 5 wherein the first partial section of the pipe bar comprises first to third adjacent sections, respectively, the first to third sections having a predetermined desired curvature, respectively, first to third desired curvatures, the first position sensor measuring the first to third sections of the pipe bar rolled by the four high rolling mechanism as first to third original curvatures, respectively, and inputting the measured first to third original curvatures into the programmer;

the programmable controller controls a first roller set to adjust and hold the first section according to the difference value of the first ideal curvature and the first original curvature, adjust and hold the second section according to the difference value of the second ideal curvature and the second original curvature, and adjust and hold the third section according to the difference value of the third ideal curvature and the third original curvature;

the second position sensor respectively measures the curvatures output by the servo following holding roller group after the pipe bars in the first to third sections are adjusted and held, and inputs the measured curvatures to the programmable controller;

respectively controlling the holding curvature positions of the first to third sections of the pipe rod pushed by a second roller set pair to follow the first roller set, controlling the holding curvature positions of the first to third sections of the pipe rod pushed by a third roller set pair to follow the second roller set, and controlling the holding curvature positions of the first to third sections of the pipe rod pushed by a fourth roller set pair to follow the third roller set by the programmable controller; and

and repeatedly measuring the curvatures of the tube and bar materials of the first section, the second section and the third section which are adjusted by the servo following holding roller set, and comparing the curvatures with the corresponding first ideal curvature, the second ideal curvature and the third ideal curvature until the difference value of the comparison accords with an allowable error.

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