CN115069801B - Multi-pass drawing forming process for cladding tube with straight ribs and cladding tube - Google Patents
Multi-pass drawing forming process for cladding tube with straight ribs and cladding tube Download PDFInfo
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- CN115069801B CN115069801B CN202210669397.8A CN202210669397A CN115069801B CN 115069801 B CN115069801 B CN 115069801B CN 202210669397 A CN202210669397 A CN 202210669397A CN 115069801 B CN115069801 B CN 115069801B
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- 238000005253 cladding Methods 0.000 title claims abstract description 48
- 238000000034 method Methods 0.000 title claims abstract description 36
- 230000008569 process Effects 0.000 title claims abstract description 35
- 238000000137 annealing Methods 0.000 claims abstract description 4
- 238000004513 sizing Methods 0.000 claims description 38
- 230000007704 transition Effects 0.000 claims description 11
- 230000009467 reduction Effects 0.000 claims description 7
- 230000009471 action Effects 0.000 claims description 6
- 230000007547 defect Effects 0.000 abstract description 19
- 229910052751 metal Inorganic materials 0.000 abstract description 4
- 239000002184 metal Substances 0.000 abstract description 4
- 238000005429 filling process Methods 0.000 abstract description 3
- 238000005482 strain hardening Methods 0.000 abstract description 3
- 239000000047 product Substances 0.000 description 19
- 239000003758 nuclear fuel Substances 0.000 description 6
- 238000007493 shaping process Methods 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000002826 coolant Substances 0.000 description 2
- 230000001627 detrimental effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 239000010687 lubricating oil Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 229910001093 Zr alloy Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 230000001050 lubricating effect Effects 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 229910001256 stainless steel alloy Inorganic materials 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C1/00—Manufacture of metal sheets, metal wire, metal rods, metal tubes by drawing
- B21C1/16—Metal drawing by machines or apparatus in which the drawing action is effected by other means than drums, e.g. by a longitudinally-moved carriage pulling or pushing the work or stock for making metal sheets, bars, or tubes
- B21C1/22—Metal drawing by machines or apparatus in which the drawing action is effected by other means than drums, e.g. by a longitudinally-moved carriage pulling or pushing the work or stock for making metal sheets, bars, or tubes specially adapted for making tubular articles
- B21C1/24—Metal drawing by machines or apparatus in which the drawing action is effected by other means than drums, e.g. by a longitudinally-moved carriage pulling or pushing the work or stock for making metal sheets, bars, or tubes specially adapted for making tubular articles by means of mandrels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C3/00—Profiling tools for metal drawing; Combinations of dies and mandrels
- B21C3/02—Dies; Selection of material therefor; Cleaning thereof
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- Metal Extraction Processes (AREA)
Abstract
The invention relates to the technical field of metal plastic forming process and equipment, and provides a multi-pass drawing forming process for a cladding tube with a straight rib. Bright annealing is used between the different forming stages to relieve residual stresses, improve work hardening and further restore its plasticity. The invention reduces the problems of limited rib filling height in single-pass drawing forming and defects generated by concave inner surface at the corresponding position of the rib in the rib groove filling process, and the section of the pipe between each pass formed by adopting the process is gradually transited, so that the ribbed pipe with the wall thickness larger than that of the finished pipe can be formed, and the formed pipe has high section precision, small error and higher strength and rigidity.
Description
Technical Field
The invention relates to the technical field of metal plastic forming technology and equipment, in particular to a multi-pass drawing forming technology for a cladding tube with a straight rib and the cladding tube.
Background
Cladding tubes are an important structural component of the core and are mainly used for protecting the fuel pellets from coolant corrosion and avoiding the leakage of fissile material in the cladding. The ribbed tube has ribs protruding from the tube material on the outer surface, so that the heat transfer performance of the coolant can be enhanced, the fluid mixing is promoted, and the ribbed tube is a novel nuclear fuel cladding tube applied at present. Because of the small size of the external surface ribs, the traditional ribbed tube production process is to wind iron wires on the external surface of the thin-wall tube and fix the iron wires by means of electric welding. However, the method cannot realize integral molding, has low production efficiency and poor surface size, and leads to the phenomenon of isolation failure of the cladding tube easily caused by rib separation in the subsequent high-temperature high-pressure service process. In order to improve this situation and to improve the safety performance of cladding tubes, it is currently necessary to integrally form ribbed tubes. Meanwhile, the height of the rib on the outer surface of the ribbed pipe is larger than or equal to the wall thickness of the finished pipe, so that the problems of insufficient rib filling height, rib groove defects on the inner surface of the corresponding position caused by filling of the rib on the outer surface of the pipe and the like are generated in the forming process, and the problems of ensuring the height of the rib on the outer surface of the pipe and eliminating the rib groove defects on the inner surface are solved in the integral forming process.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a multi-pass drawing forming process for a cladding tube with a straight rib and the cladding tube, wherein the process reduces the defects that the cross section error of a finished tube is large, defects are easy to generate and the requirements cannot be met in single-pass drawing forming, and the tube formed by the process has high cross section precision, small error, higher strength and rigidity and ensures the requirements of the cladding tube for nuclear fuel for safe service.
The invention adopts the following technical scheme:
in one aspect, the invention provides a multi-pass drawing forming process for a straight ribbed cladding tube, comprising: taking a circular section pipe as an initial pipe blank, and under the combined action of a die and a core rod, sequentially passing through a pre-forming stage corresponding to a first special-shaped die, a transition forming stage corresponding to a second special-shaped die and a finished product forming stage corresponding to a third special-shaped die, and finally forming the final pipe blank into a finished product pipe with a straight rib cladding pipe with a certain characteristic section; the core rod is used for controlling the inner diameter size of the special-shaped section pipe after the corresponding pass forming, and the first special-shaped die, the second special-shaped die and the third special-shaped die are respectively used for controlling the outer diameter size and the straight rib size of the special-shaped section pipe after the corresponding pass forming.
In any of the possible implementations described above, there is further provided an implementation in which bright annealing is used to eliminate residual stress between the various forming stages of the pre-forming stage, the transitional forming stage, and the finish forming stage, to improve work hardening and further restore its plasticity.
In any one of the possible implementation manners described above, there is further provided an implementation manner, wherein the number of the first special-shaped dies and the number of the third special-shaped dies are one, and the number of the second special-shaped dies is one or a plurality of second special-shaped dies;
the first special-shaped die, the second special-shaped die and the third special-shaped die comprise conical inlet sections and cylindrical sizing sections which are connected in sequence;
the taper of the inlet section is alpha, and one or a plurality of inclined slots with taper of beta are arranged on the inlet section; α=5 to 15 °, β=2 to 10 °; too small or too large alpha and beta can lead to poor rib filling and to pipe breakage during drawing;
one or a plurality of special-shaped grooves with certain width, height and filling angle are arranged on the inner wall of the sizing section, the bottoms of the special-shaped grooves are rounded, and the radius of the rounded corners is R;
in any of the possible implementation manners described above, there is further provided an implementation manner, in the preforming stage, the sizing section of the first special-shaped die is provided with a special-shaped groove with a width W1, a height H1, a fillet radius R1 and a filling angle ω1, and the selection range of technological parameters is as follows: w1= (1-1.5) W3, h1= (0.2-0.5) H3, r1= (1-20) R3, ω1=90-150 °; w3, H3, R3, ω3 are the mold parameters of the third shaped mold (the final forming stage), respectively: the width, height, fillet radius and filling angle of the sizing section special-shaped groove are determined by the finished pipe, and the sizing section special-shaped groove is the same as the finished pipe in size.
In any one of the possible implementation manners described above, there is further provided an implementation manner, in the transition forming stage, the sizing section of the second special-shaped die is provided with a special-shaped groove with a width W2, a height H2, a fillet radius R2 and a filling angle ω2, and the selection range of technological parameters is as follows: w2= (1.5-2) W3, h2= (0.7-0.8) H3, r2= (1-5) R3, ω2=90-130 °; w3, H3, R3, ω3 are the mold parameters of the third shaped mold (the final forming stage), respectively: the sizing section is special-shaped groove width, height, fillet radius and filling angle.
In any one of the possible implementations described above, there is further provided an implementation, wherein the process parameter selection range between adjacent pass drawing is: the diameter reduction rate is 10-35%, and the wall thickness reduction rate is 10-25%. A decrease rate below the minimum value of the selected range fails to meet rib filling requirements, while a maximum value above the selected range results in excessive deformation and snap-off.
In any of the possible implementations described above, there is further provided an implementation in which the height of the straight ribs of the finished pipe is greater than or equal to the finished pipe wall thickness.
In any one of the possible implementation manners described above, there is further provided an implementation manner, when a plurality of second special-shaped dies are adopted, the deformation amounts of the pipe diameter, the pipe wall thickness, the width of the straight rib, the height of the straight rib and the filling angle of the straight rib in the transitional forming stage are jointly realized by the plurality of second special-shaped dies.
In any of the possible implementations described above, there is further provided an implementation in which the mandrel at the different shaping stages is formed by a conical inlet section with a taper of γ and an outer diameter Φ 2 Length is L 2 Is composed of a cylindrical sizing section. The selection range of the technological parameters is as follows: l (L) 2 =0.1 to 1mm, γ=10 to 30 °; the length L of the sizing section of the first special-shaped die, the second special-shaped die and the third special-shaped die 1 The range of (2) is: l (L) 1 ＝0.5～5mm，L 1 Too small can cause the pipe to rebound, so that the outer diameter of the deformed pipe is larger than the target value, L 1 Too large drawing force can cause the pipe to be broken; l (L) 2 Too small to ensure the dimensional accuracy of the inner surface of the deformed pipe, L 2 Too much will cause the drawing force to be too great, resulting in the tube breaking.
Any one of the possible implementation manners described above further provides an implementation manner, wherein the different forming stages are that the special-shaped die and the core rod are matched for use, and the special-shaped die is used for sizing the section L 1 Is greater than or equal to the sizing section L of the core rod 2 The die sizing section should contain a mandrel sizing section.
In any of the possible implementations described above, there is further provided an implementation, wherein the material of the cladding tube with straight ribs is a stainless steel or zirconium alloy tube for nuclear fuel.
In any of the possible implementations described above, there is further provided an implementation, wherein the specific steps of each pass of drawing are as follows:
(1) fixing the special-shaped die on a frame; (2) the positions of the sizing section of the core rod and the sizing section of the special-shaped die are further adjusted by adjusting nuts at the end part of the core rod, so that the sizing section of the die comprises the sizing section of the core rod; (3) reducing one end of the pipe through a head reducing machine to enable the outer diameter of the pipe blank to be smaller than the inner hole size of the special-shaped die; (4) uniformly smearing drawing lubricating oil on the inner surface and the outer surface of the pipe; (5) passing the pipe at the warp shrinkage end through a die; (6) inserting the adjusted core rod from the other end of the pipe; (7) the drawing force is applied to the pipe passing through the die, and the core rod plugged into the pipe moves along with the drawing force in the direction of the applied force, and the position of the nut at the end part of the core rod is fixed by the baffle plate, so that the core rod can not be changed after moving to the position which is adjusted before; (8) the tube blank is subjected to plastic deformation under the combined action of the special-shaped die and the core rod.
When the ribs are matched between different passes, in order to increase the filling degree of the ribs and prevent the inner surface corresponding to the ribs from flowing into the die cavity due to metal transition, so that groove defects are generated on the inner surface, and the deformation degree of the different passes is different when the process is designed. A minimum value of each parameter below the selected range is detrimental to the next rib filling, while a maximum value above the selected range is subject to rib groove defects, all of which affect the dimensional accuracy of the finished tube.
On the other hand, the invention also provides the cladding tube with the straight rib, which is prepared by the multi-pass drawing forming process of the cladding tube with the straight rib, and the rib height of the cladding tube with the straight rib is more than or equal to the wall thickness of the cladding tube with the straight rib.
The beneficial effects of the invention are as follows:
the invention reduces the problems of limited rib filling height in single-pass drawing forming and defects generated by concave inner surface at the corresponding position of the rib in the rib groove filling process, and the section of the pipe between each pass formed by adopting the process is gradually transited, so that the ribbed pipe with the wall thickness larger than that of the finished pipe can be formed, and the formed pipe has high section precision, small error and higher strength and rigidity.
Drawings
Fig. 1 is a schematic drawing of a drawing forming process of a cladding tube with straight ribs according to an embodiment of the invention.
Figure 2 shows a schematic structural view of a seed-ribbed cladding tube in an embodiment.
Figure 3 shows a cross-sectional view of the tube after forming in different passes of the multi-pass drawing process of the straight ribbed cladding tube in an embodiment.
Fig. 4 shows an enlarged partial cross-section of the tube after forming in different passes during the multi-pass drawing of the straight ribbed cladding tube in an embodiment.
Fig. 5 is a schematic diagram of a drawing forming process special-shaped die structure of a cladding tube with straight ribs in an embodiment.
Fig. 6 is a schematic diagram of a drawing forming process core rod structure of a cladding tube with straight ribs in an embodiment.
Detailed Description
Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be regarded as being isolated, and they may be combined with each other to achieve a better technical effect. In the drawings of the embodiments described below, like reference numerals appearing in the various drawings represent like features or components and are applicable to the various embodiments.
The embodiment of the invention discloses a multipass drawing forming process of a cladding tube with a straight rib, which comprises the following steps: taking a circular section pipe as an initial pipe blank, and under the combined action of a die and a core rod, sequentially passing through a pre-forming stage corresponding to a first special-shaped die, a transition forming stage corresponding to a second special-shaped die and a finished product forming stage corresponding to a third special-shaped die, and finally forming the final pipe blank into a finished product pipe with a straight rib cladding pipe with a certain characteristic section; the core rod is used for controlling the inner diameter size of the special-shaped section pipe after the corresponding pass forming, and the first special-shaped die, the second special-shaped die and the third special-shaped die are respectively used for controlling the outer diameter size and the straight rib size of the special-shaped section pipe after the corresponding pass forming.
In one embodiment, bright annealing is used to eliminate residual stress between the forming stages of the pre-forming stage, the transition forming stage and the finished product forming stage, to improve work hardening and further restore its plasticity.
In a specific embodiment, the number of the first special-shaped mold and the number of the third special-shaped mold are one, and the number of the second special-shaped molds is one or a plurality of second special-shaped molds. When a plurality of second special-shaped dies are adopted, the deformation of the diameter of the pipe, the wall thickness of the pipe, the width of the straight rib, the height of the straight rib and the filling angle of the straight rib in the transition forming stage is commonly realized by the plurality of second special-shaped dies.
As shown in fig. 1, any one drawing step is as follows: (1) fixing the die on a frame; (2) adjusting nuts at the end parts of the core rods to enable the sizing sections of the core rods to coincide with the sizing sections of the die; (3) reducing one end of the pipe through a head reducing machine to enable the outer diameter of the pipe blank to be smaller than the inner hole size of the die; (4) uniformly smearing drawing lubricating oil on the inner surface and the outer surface of the pipe to obtain the pipe; (5) passing the pipe at the warp shrinkage end through a die; (6) the core rod with the adjusted position is plugged in from the other end of the pipe; (7) the drawing force is applied to the pipe passing through the die, and the core rod plugged into the pipe moves along with the drawing force in the direction of the applied force, and the position of the nut at the end part of the core rod is fixed by the baffle plate, so that the core rod can not be changed after moving to the position which is adjusted before; (8) the tube blank is plastically deformed under the combined action of the die and the core rod.
As shown in figure 2, the cladding tube with the straight ribs prepared by the invention is provided with one or more ribs protruding out of the outer surface, wherein the ribs are straight, the height of the ribs is larger than or equal to the wall thickness of the tube, and the cladding tube is a typical special-shaped tube with the special wall which is difficult to integrally form.
In a specific embodiment, as shown in fig. 3, in the sectional view of a tube after being formed in different passes in the multi-pass drawing process of the cladding tube with the straight rib, a circular section tube is taken as an initial blank, sequentially passes through a first special-shaped die, a second special-shaped die and a third special-shaped die, and is drawn into a special-shaped tube with a certain characteristic section under the combined action of a core rod and the special-shaped die, and the corresponding forming stages are respectively called a first-stage pre-forming stage, a second-stage transitional forming stage and a third-stage finished product forming stage. The drawing process of each pass is a forming process with reduced pipe diameter and wall thickness, and the selection range of the process parameters among the rest passes is as follows except that the outer diameter and the wall thickness of the final finished product are determined by the target size: the diameter reduction rate is 10-35%, and the wall thickness reduction rate is 10-25%. A decrease rate below the minimum value of the selected range fails to meet rib filling requirements, while a maximum value above the selected range results in excessive deformation and snap-off.
In one particular embodiment, shown in FIG. 4, the tube is partially enlarged in cross-section after forming at different passes during the multi-pass drawing of the straight ribbed cladding tube. The preformed sizing section is provided with a special-shaped groove with a width W1, a height H1, a fillet radius R1 and a filling angle omega 1. The selection range of the technological parameters is as follows: w1= (1 to 1.5) W3, h1= (0.2 to 0.5) H3, r1= (1 to 20) R3, ω1=90 to 150 °. The transition forming sizing section is provided with a special-shaped groove with a width W2, a height H2, a fillet radius R2 and a filling angle omega 2. The selection range of the technological parameters is as follows: w2= (1.5-2) W3, h2= (0.7-0.8) H3, r2= (1-5) R3, ω2=90-130 °. The final drawing stage (final product forming stage) third special-shaped die parameters (inner hole diameter phi) 1 Width W3, height H3, fillet radius R3 and filling angle ω3) and mandrel parameters (outer diameter Φ 2 ) The size of the finished pipe is determined by the size of the finished pipe, and the finished pipe is the same as the size of the target product. When the ribs are matched between different passes, in order to increase the filling degree of the ribs and prevent the inner surface corresponding to the ribs from flowing into the die cavity due to metal transition, so that groove defects are generated on the inner surface, and the deformation degree of the rest different passes is different during process design. A minimum value of each parameter below the selected range is detrimental to the next rib filling, while a maximum value above the selected range is subject to rib groove defects, all of which affect the dimensional accuracy of the finished tube.
In one embodiment, as shown in fig. 5, the profile die is schematically structured. The special-shaped dies at different shaping stages are used for controlling the outer diameter size and the rib size of the shaped special-shaped section tube after shaping and consist of a conical inlet section and a cylindrical sizing section. The taper of the inlet section is alpha, and the inlet section is provided with a plurality of inclined grooves with taper beta. The selection range of the technological parameters is as follows: α=5 to 15 °, β=2 to 10 °, and too small or too large α, β may cause poor rib filling effect and cause pipe breakage during drawing. The inlet section is provided with a plurality of special-shaped cross-section inclined grooves which are respectively W, H, R and omega. The length of the sizing section is L 1 The selection range of (2) is as follows: l (L) 1 ＝0.5～5mm。L 1 Too small can cause the pipe to rebound, so that the outer diameter of the deformed pipe is larger than the target value, L 1 Too much will cause the drawing force to be too great, resulting in the tube breaking.
In one embodiment, as shown in FIG. 6, the mandrel is schematically configured. The core rod in different shaping stages is used to control the inner diameter of shaped cross section pipe and consists of conic inlet section with conicity gamma and outer diameter phi 2 Length L 2 Is composed of a cylindrical sizing section. The selection range of the technological parameters is as follows: l (L) 2 ＝0.1～1mm，γ＝10～30°。L 2 Too small to ensure the dimensional accuracy of the inner surface of the deformed pipe, L 2 Too large drawing force can cause the pipe to be broken, and the lubricating effect of lambda in the parameter range is good, so that the drawing force can be reduced. Different shaping stages are that a special-shaped die and a core rod are matched for use, and a sizing section L of the special-shaped die is used 1 Is greater than or equal to the sizing section L of the core rod 2 The die sizing section should include a mandrel sizing section.
The material of the pipe in the following comparative example is 316L stainless steel.
Comparative example 1
And when the diameter of the target product pipe is 6mm and the wall thickness is 0.5mm, comparing the product size and performance obtained by single pass with those obtained by multiple passes (3 passes). The maximum value of the rib height obtained in the single-pass drawing is 0.284mm, and the wall thickness is only 56.8% compared with the wall thickness. The maximum rib height obtained after multi-pass pulling as proposed herein is 0.496mm, up to 99.2% compared to wall thickness filling. Therefore, the multi-pass drawing scheme provided herein is adopted to obtain a product with 42.4% rib height than that of a product obtained by a single-pass scheme, and the rib filling effect is obviously improved. In addition, the increase in the height of the external surface ribs increases the tensile strength of the ribbed tube by 6-12%.
Comparative example 2
When the diameter of the target product pipe is 6mm and the wall thickness is 0.5mm, the size and the performance of the product obtained by the common multi-pass scheme (3 passes) and the scheme proposed herein are compared. With a common multipass drawing scheme, i.e. with the rib groove width W and the rib groove height H of each pass being the same (w1=w2=w3, h1=h2=h3), a maximum rib height of 0.418mm can be obtained, the inner surface of the tube, which was filled by 83.6% as compared to the wall thickness and was located in the position corresponding to the rib, had a depth of 0.298mm, which was more than half of the wall thickness as compared to 59.6% as compared to the wall thickness. When the multi-pass drawing scheme proposed herein, i.e. different rib groove widths W and rib groove heights H (w1= 1.5W3, w2= 1.3W3, h1= 0.4H3, h2= 0.8H3) are used, a maximum of 0.496mm rib height can be obtained, up to 99.2% compared to wall thickness filling, and a defect depth of 0.076mm, up to 15.2% compared to wall thickness. In summary, compared with the product obtained by the traditional scheme, the multi-pass drawing scheme provided by the invention has the advantages that the rib height is improved by 15.6%, the defect depth is reduced by 44.4%, the rib filling effect is obviously improved, and the rib groove defects are further eliminated. In addition, the increase of the height of the rib on the outer surface improves the tensile strength of the ribbed pipe by 6-8%, the reduction of the rib grooves on the inner surface greatly improves the stability and strength of the combination of the rib and the pipe, and the service life of the cladding pipe in the extreme environment of nuclear fuel is prolonged.
Comparative example 3
When the diameter of the target product pipe is 6mm and the wall thickness is 0.5mm, the size and the performance of the product obtained by comparing the common multi-pass scheme (4 passes are adopted correspondingly by the invention) with the multi-pass scheme proposed herein. A common multi-pass drawing scheme is adopted, i.e. the rib groove width W and the rib groove height H of each pass are set to be the same (w1=w21=w22=w3, h1=h21=h22=h3). At this time, the maximum height of the rib was 0.478mm, which was 95.6% higher than the wall thickness, and the depth of the inner surface of the pipe at the position corresponding to the rib was 0.364mm, which was 72.8% higher than the wall thickness, which was half the wall thickness. When the multi-pass drawing scheme proposed herein is adopted, namely, different rib groove widths W and rib groove heights H (w1= 1.6W3, w21= 1.4W3, w22= 1.2W3, h1= 0.35H3, h21= 0.7H3, h22= 0.85H3) are set, wherein W21 and W22 are the widths of the two second special-shaped die sizing section special-shaped grooves respectively, H21 and H22 are the heights of the two second special-shaped die sizing section special-shaped grooves respectively, the maximum value of the rib heights can be obtained to be 0.734mm, 146.8% compared with wall thickness filling is achieved, the depth of the defect is 0.136mm, and the ratio of the defect to the wall thickness is 27.2%. In summary, compared with the product obtained by the traditional scheme, the multi-pass drawing scheme provided by the invention has the advantages that the rib height is improved by 51.2%, the defect depth is reduced by 45.6%, the pipe with the rib filling height larger than the wall thickness is obtained, and the defects of the rib grooves are further eliminated. The increase of the height of the external surface rib improves the tensile strength of the ribbed pipe by 7-9%, and greatly increases the height of the external surface rib of the ribbed pipe. In addition, tubes with ribs greater than the wall thickness may further increase the positioning spacing of the ribbed cladding tubes relative to each other in nuclear fuel applications. The scheme is expanded to different passes, so that various ribbed tubes with different rib heights can be manufactured, and diversified selection of products with different rib heights in the nuclear fuel cladding tube is realized.
It should be noted that the preformed shape, the transitional shape and the finished shape, and even the number of drawing passes selected in the above examples are only one of a plurality of choices, and those skilled in the art can extend to a variety of other multi-pass forming processes for cladding tubes according to the teachings of the present invention.
The invention reduces the problems of limited rib filling height in single-pass drawing forming and defects generated by concave inner surface at the corresponding position of the rib in the rib groove filling process, and the section of the pipe between each pass formed by adopting the process is gradually transited, so that the ribbed pipe with the wall thickness larger than that of the finished pipe can be formed, and the formed pipe has high section precision, small error and higher strength and rigidity.
Although a few embodiments of the present invention have been described herein, those skilled in the art will appreciate that changes can be made to the embodiments herein without departing from the spirit of the invention. The above-described embodiments are exemplary only, and should not be taken as limiting the scope of the claims herein.
Claims (6)
1. A multi-pass drawing forming process for a straight ribbed cladding tube, the forming process comprising: taking the prepared circular section pipe as an initial pipe blank, and under the combined action of a die and a core rod, sequentially passing through a pre-forming stage corresponding to a first special-shaped die, a transition forming stage corresponding to a second special-shaped die and a finished product forming stage corresponding to a third special-shaped die, and finally forming the finished product pipe with the straight rib cladding pipe with a certain characteristic section; the first special-shaped die, the second special-shaped die and the third special-shaped die are respectively used for controlling the outer diameter size and the straight rib size of the special-shaped section tube after the corresponding pass forming;
the number of the first special-shaped dies and the number of the third special-shaped dies are one, and the number of the second special-shaped dies is one or a plurality of the second special-shaped dies;
the first special-shaped die, the second special-shaped die and the third special-shaped die comprise conical inlet sections and cylindrical sizing sections which are connected in sequence; the width of the inlet section chute is linearly narrowed along the movement direction of the tube blank, and the tail end of the inlet section chute is connected with the starting end of the sizing section chute;
the taper of the inlet section is alpha, and one or a plurality of inclined slots with taper of beta are arranged on the inlet section; α=5 to 15 °, β=2 to 10 °;
one or a plurality of special-shaped grooves with certain width, height and filling angle are arranged on the inner wall of the sizing section, the bottoms of the special-shaped grooves are rounded, and the radius of the rounded corners is R;
in the pre-forming stage, the sizing section of the first special-shaped die is provided with a special-shaped groove with a width W1, a height H1, a fillet radius R1 and a filling angle omega 1, and the selection range of technological parameters is as follows: w1= (1-1.5) W3, h1= (0.2-0.5) H3, r1= (1-20) R3, ω1=90-150 °; w3, H3, R3 and omega 3 are respectively the width, the height, the fillet radius and the filling angle of the special-shaped groove of the sizing section of the third special-shaped die;
in the transition forming stage, the sizing section of the second special-shaped die is provided with a special-shaped groove with a width W2, a height H2, a fillet radius R2 and a filling angle omega 2, and the selection range of technological parameters is as follows: w2= (1.5-2) W3, h2= (0.7-0.8) H3, r2= (1-5) R3, ω2=90-130 °; w3, H3, R3 and omega 3 are respectively the width, the height, the fillet radius and the filling angle of the special-shaped groove of the sizing section of the third special-shaped die;
the selection range of technological parameters between adjacent pass drawing is as follows: the diameter reduction rate is 10-35%, and the wall thickness reduction rate is 10-25%.
2. The multi-pass drawing forming process for the straight ribbed cladding tube according to claim 1, wherein the residual stress is eliminated by adopting bright annealing among the forming stages of the pre-forming stage, the transition forming stage and the finished product forming stage, and the plasticity is recovered.
3. The multi-pass drawing forming process of a straight ribbed cladding tube of claim 1, wherein the height of the straight ribs of the finished tube is greater than or equal to the wall thickness of the finished tube.
4. The multi-pass drawing forming process for the cladding tube with the straight rib according to claim 1, wherein when a plurality of second special-shaped dies are adopted, the deformation of the diameter of the tube, the wall thickness of the tube, the width of the straight rib, the height of the straight rib and the filling angle of the straight rib in the transitional forming stage is jointly realized by the plurality of second special-shaped dies.
5. A multi-pass drawing forming process for a straight ribbed cladding tube as in claim 1, wherein said mandrel is formed by a conical inlet section with a taper γ and an outer diameter Φ 2 Length is L 2 The selection range of the technological parameters is as follows: l (L) 2 =0.1 to 1mm, γ=10 to 30 °; the length L of the sizing section of the first special-shaped die, the second special-shaped die and the third special-shaped die 1 The range of (2) is: l (L) 1 ＝0.5～5mm。
6. A straight ribbed cladding tube produced by a multi-pass drawing forming process of the straight ribbed cladding tube according to any one of claims 1-5, wherein the rib height of the straight ribbed cladding tube is equal to or greater than the wall thickness of the straight ribbed cladding tube.
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