Internal expansion type drawing die for special-shaped pipe and forming method

Abstract

The invention belongs to the technical field of metal processing, and particularly relates to a special-shaped pipe inner expansion type drawing die and a forming method.The special-shaped pipe inner expansion type drawing die comprises a die body in a polygon frustum shape, the die body sequentially comprises an inlet section, a forming section and an outlet section, and the maximum radial size of the inlet section is smaller than the inner diameter of a pipe blank; the maximum radial size of the outlet section is smaller than the inner diameter of a target pipe; at least one edge of the forming section is provided with spherical grooves, the spherical grooves are at least formed in the head end and the tail end of the edge, detachable steel balls are arranged in the spherical grooves, the steel balls are in rolling contact with the inner wall of the pipe blank in the drawing process, and the other edges of the forming section are chamfered; the problems that an existing mold is serious in abrasion, frequent in replacement and high in replacement cost in use, the pipe wall at the corner of a special-shaped pipe manufactured through the existing mold is insufficiently filled, and the quality of the formed pipe is poor are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal processing, and in particular relates to an internal expansion drawing die for a special-shaped tube and a forming method. Background Art

[0002] Titanium alloy has the advantages of high strength, low density and corrosion resistance. More and more fields choose to use titanium alloy materials instead of steel when selecting materials. With the continuous updating of market demand, the requirements for the types and specifications of titanium alloy parts have increased relatively, and the titanium alloy manufacturing process has also developed rapidly, from traditional hot process forging extrusion and cold process machining to emerging material manufacturing spinning and cold rolling. However, this series of processing methods cannot be used for the processing of titanium alloy special-shaped pipes.

[0003] like Figure 1 As shown, Figure a is the cross-sectional dimensions of the tube blank; Figure b is a target tube with a triangular cross-sectional shape, the radius of the fillet at the top of the inner wall is R1, the length of the top arc is l1, the radius of the fillet at the bottom is R2, the length of the bottom arc is l2, the waist length is L1, and the bottom side length is L2; ​​Figure c is a target tube with a quadrilateral cross-sectional shape, the radius of the top fillet is R, the radius of the bottom fillet is r, the top side length is d1, the waist length is d2, and the bottom side length is d3. Currently, the processes for manufacturing the above-mentioned special-shaped tubes include drawing and rolling. Such process methods are mostly used in the aluminum alloy and steel alloy industries, while the titanium alloy industry currently uses this process method less, and it is only partially applied to titanium wire and low-strength high-plasticity titanium alloys.

[0004] Drawing dies are mostly external extrusion molding, which are the most commonly used drawing dies on the market. This type of die applies external pressure to draw a round tube into a special-shaped tube once or several times. During the drawing process, the round tube gradually deforms; however, during the drawing process, the corners of the special-shaped tube are not completely filled with the special-shaped tube wall, and the smaller the corner angle, the more incomplete the filling. At the same time, as the corner angle becomes smaller, the stress at the corner gradually increases, and the tube wall is prone to extrusion cracks in the stress concentration area, and even worse, it will cause the tube wall to break. In addition, the drawing die is an external extrusion molding die. In order to ensure the rigidity of the die, the die volume is usually large; at the same time, during the processing, the die contacts the workpiece surface, the friction is large, and the die wear is serious, resulting in frequent die replacement and high cost.

[0005] Rolling dies mainly include reciprocating surface contact dies and roller dies. The reciprocating surface contact die adopts surface contact forming. Through the cooperation of the internal mandrel and the external sleeve, the tube wall is changed from round to special-shaped tube. During the rolling process, the tube wall and the tube are in full surface contact, the contact area is large, and the processing wear is more serious. In addition, this type of rolling method requires special modification of the rolling mill to adapt to the rolling process. The modification cost is high. At the same time, the modified rolling mill can no longer roll other tubes and lacks flexibility. The roller die supports the tube by the mandrel, and then the roller rotates and rolls on the surface of the tube to plasticize the outer surface of the tube. This type of die is also used as a set. Generally, a mandrel is used in conjunction with one or several groups of rollers. The die is large in size and requires the use of a mandrel and a roller. When the roller is worn, the complete set of rollers needs to be replaced, and the replacement cost is also high. Summary of the invention

[0006] At least in view of the technical problems mentioned in the background technology, the present invention aims to provide a special-shaped tube internal expansion drawing die and a forming method.

[0007] The present invention adopts the following technical solution:

[0008] A special-shaped tube internal expansion drawing die comprises a multi-sided cone-shaped die body, which comprises an inlet section, a forming section and an outlet section in sequence, wherein the maximum radial dimension of the inlet section is smaller than the inner diameter of the tube blank, and the maximum radial dimension of the outlet section is smaller than the inner diameter of the target tube; a spherical groove is provided on at least one edge of the forming section, and the spherical groove is provided at least at the head end and the tail end of the edge, and a detachable steel ball is provided in the spherical groove, and the steel ball is in rolling contact with the inner wall of the tube blank during the drawing process, and the other edges of the forming section are rounded.

[0009] Furthermore, at least one side of the mold body is provided with a groove and a cover body, the spherical groove is located on the side of the groove, the cover body is detachably connected to the mold body, and the cover body and the mold body cooperate to embed the steel ball in the spherical groove, and the steel ball part protrudes out of the cover body.

[0010] Furthermore, the mold body is in the shape of a triangular prism, one edge of the forming section is chamfered to a fillet with a radius of R1, and the other two edges of the forming section are provided with steel balls with a radius of R2.

[0011] Furthermore, the mold body is in the shape of a triangular prism, one edge of the forming section is provided with a steel ball with a radius of R1, and the other two edges of the forming section are chamfered to a fillet of R2.

[0012] Furthermore, the mold body is in the shape of a triangular prism, one edge of the forming section is provided with a steel ball with a radius of R1, and the other two edges of the forming section are provided with steel balls with a radius of R2.

[0013] Furthermore, the mold body is in the shape of a quadrangular pyramid, two adjacent edges of the forming section are provided with steel balls with a radius of R, and the other two edges of the forming section are provided with steel balls with a radius of r.

[0014] Furthermore, the height of the portion of the steel ball protruding from the cover body is H, H is greater than 1 / 3 times the radius of the steel ball, and H is less than 1 / 2 times the radius of the steel ball.

[0015] Furthermore, the steel balls of the forming section are arranged in four rows, and the four rows of steel balls are evenly distributed along the edges of the forming section.

[0016] A method for forming a special-shaped tube by internal expansion, comprising the following steps:

[0017] Step 1: Heat the tube to 400-500°C and keep it warm for 30 minutes;

[0018] Step 2: Place the heated tube blank into the feeding section of the drawing machine, feed the inlet section of the above-mentioned special-shaped tube inner expansion drawing die into the tube blank, and use the drawing chuck of the drawing machine to clamp the head of the tube blank;

[0019] Step 3: Use the feeding push rod of the drawing machine to push the tail of the tube blank, and the drawing chuck pulls the head of the tube blank. At the same time, the push rod is used to fix the special-shaped tube inner expansion drawing die until the tube blank is completely pulled through the special-shaped tube inner expansion drawing die, and the special-shaped tube is formed;

[0020] Step 4: Place the special-shaped tube into a heat treatment furnace for stress relief heat treatment;

[0021] Step 5: Pickling to remove oxide scale.

[0022] Compared with the prior art, the present invention has the following technical effects:

[0023] 1. The drawing die of the present invention is an internal expansion type forming die. Compared with the external extrusion forming method in the prior art, the corners and sharp corners of the special-shaped pipe formed by the present invention are filled more fully, which effectively improves the forming quality of the special-shaped pipe.

[0024] 2. The drawing die of the present invention is integral and has a small overall size, which is easy to design and manufacture. In the process of forming special-shaped pipes, the stress concentration point of the pipe deformation is contacted by the steel ball, and the line friction pair is converted into a rolling pair, which can effectively reduce the friction in the drawing process, reduce the wear on the mold, reduce the replacement frequency of the mold, and have a smaller drawing power. The wear parts of the mold are mainly steel balls. When the steel balls are completely worn, the mold can be updated by replacing the steel balls. The replacement operation is simple and convenient, which effectively improves the economy of the mold and reduces the replacement cost of the mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1It is a schematic cross-sectional view of the tube blank and the target tube;

[0026] Figure 2 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0027] Figure 3 is a schematic cross-sectional view of a target pipe manufactured using Example 1;

[0028] Figure 4 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0029] Figure 5 This is a schematic diagram of the structure of Embodiment 3 of the present invention;

[0030] Figure 6 This is a schematic diagram of the structure of Embodiment 3 of the present invention;

[0031] Figure 7 This is a schematic diagram of the structure of Embodiment 3 of the present invention;

[0032] Figure 8 This is a schematic diagram of the structure of Embodiment 4 of the present invention;

[0033] Fig. 9 Schematic diagram of the cross section of the target pipe manufactured using Example 4.

[0034] In the figure, there are inlet section 1, forming section 2, outlet section 3, steel balls 4, cover body 5, and screws 6. DETAILED DESCRIPTION

[0035] The following is further described in detail through specific implementation methods:

[0036] Example 1

[0037] like Figure 2 As shown, a special-shaped tube internal expansion drawing die includes a triangular prism-shaped die body, which includes an inlet section 1, a forming section 2 and an outlet section 3 from top to bottom. The inlet section 1, the forming section 2 and the outlet section 3 are integrally formed. The maximum radial dimension of the inlet section 1 is smaller than the inner diameter of the tube blank, and the maximum radial dimension of the outlet section 3 is smaller than the inner diameter of the target tube.

[0038] like Figure 2As shown, one edge of the die body is chamfered to a fillet with a radius of R1, and a plurality of spherical grooves are respectively opened on the other two edges of the die body, and a steel ball 4 with a radius of R2 is installed in each spherical groove; a groove and a cover body 5 are provided on the front side of the die body, and the spherical groove is located on two opposite sides of the groove, and the cover body 5 is detachably connected to the die body by screws 6, and the cover body 5 cooperates with the die body to embed the steel ball 4 in the spherical groove, and the steel ball 4 partially protrudes from the cover body 5, and the steel ball 4 rolls in contact with the inner wall of the tube blank during the drawing process; the drawing die of this embodiment is used to manufacture a target tube with a triangular cross-section, R1>R2, R1>2R2, (R2+R2)×1.5≥L2 (such as Figure 3 As shown in the figure, since the arc radius R1 of the top of the target tube is large and the strain of this part of the tube is small, one edge of the mold body is chamfered so that the top arc of the target tube can retain the arc surface expansion shape during the forming process.

[0039] In this embodiment, in order to consider the economy and the stability of the steel balls 4, the forming process of the tube blank is set to three-stage stretching, and the steel balls 4 are arranged in four rows, and the four rows of steel balls 4 are evenly distributed along the edges of the forming section 2. The head end and the tail end of the forming section 2 are each provided with a row of steel balls 4, and each row includes two steel balls 4. In order to ensure the continuity of stretching and the safety margin of stretching, and to prevent the steel balls 4 from falling off during the drawing process, the height of the protruding part of the steel balls 4 is H,

[0040] The four rows of steel balls 4 are evenly distributed on the edges of the forming section 2, which can ensure that the force points of the steel balls 4 remain unchanged during the drawing and forming process of the tube blank. When the tube blank passes through the four rows of steel balls 4 in sequence, the connection is smooth and the large strain area is always on the steel balls 4.

[0041] The diameter of the circumscribed circle of the cross section where the top steel ball 4 of the forming section 2 is located is D=C / π. In order to ensure that the deformation vertex does not slip during the expansion process, resulting in multiple expansion marks on the inner wall of the finally formed special-shaped tube, it is necessary to ensure that the position of the inlet expansion point and the position of the outlet expansion point remain basically unchanged. The tangent point angle α of the expansion point of the inlet section 1 is calculated by formula (1).

[0042]

[0043] The drawing die of the present invention is integral and has a small overall size, and is easy to design and manufacture. During the forming process of special-shaped pipes, the stress concentration point of the deformation of the pipe is contacted by the steel ball 4, and the line friction pair is converted into a rolling pair, which can effectively reduce the friction during the drawing process, reduce the wear on the mold, reduce the replacement frequency of the mold, and have a smaller drawing power. The wear parts of the mold are mainly the steel ball 4. When the steel ball 4 is completely worn, the mold can be updated by replacing the steel ball 4. The replacement operation is simple and convenient, which effectively improves the economy of the mold and reduces the replacement cost of the mold.

[0044] A method for forming a special-shaped tube by internal expansion, comprising the following steps:

[0045] Step 1: Heat the tube to 400-500°C and keep it warm for 30 minutes;

[0046] Step 2: Place the heated tube blank into the feeding section of the drawing machine, feed the inlet section 1 of the special-shaped tube inner expansion drawing die of this embodiment into the tube blank, and clamp the head of the tube blank with the drawing chuck of the drawing machine;

[0047] Step 3: Use the feeding push rod of the drawing machine to push the tail of the tube blank, and the drawing chuck pulls the head of the tube blank. At the same time, the push rod is used to fix the special-shaped tube inner expansion drawing die until the tube blank is completely pulled through the special-shaped tube inner expansion drawing die, and the special-shaped tube is formed;

[0048] Step 4: Place the special-shaped tube into a heat treatment furnace for stress relief heat treatment;

[0049] Step 5: Pickling to remove oxide scale.

[0050] This embodiment uses the target pipe with R1=53mm, R2=18mm, L1=118.31mm, L2=167.32mm as an example to perform finite element linear analysis:

[0051] The inner wall circumference of the special-shaped tube is:

[0052] C=118.31*2+167.32+18*2*π*232.07 / 360+53*2*π*127.93 / 360=595.19

[0053] The diameter of the tube is calculated by the cross-sectional area of ​​the tube: (R12-R22)×π=1159.76

[0054] According to the inner surface circumference, the inner wall diameter of the tube can be calculated as: 595.4×0.983 / π=186.38

[0055] The wall thickness of the tube is: 1.96

[0056] In the finite element nonlinear analysis, the material is set to TC4, the material temperature is 500°C, and the material properties are: tensile strength: 583MPa, yield strength: 401MPa, elastic modulus: 75GPa, tangent modulus: 34GPa, Poisson's ratio: 0.37, thermal expansion coefficient: 9.7, and friction coefficient: 0.05.

[0057] After simulation, it is found that the combined force on the pipe is 21144.6N. At the sharp corner arc, the maximum stress is 4608MPa, the maximum strain is 0.096, and the maximum elongation of TC4 titanium alloy is 26.5% at 500℃. It is judged that during the drawing process, the material will not have local defects such as cracks; the maximum stress point of the mold is the 4 steel balls in the last row, where the maximum stress of the steel balls 4 is 586.8MPa. Therefore, the mold material can be selected from common hot working die steels, such as 3CR2W8V, 5Cr4Mo3SiMnVA1, 5Cr4W5Mo2V. The maximum combined force on the mold is 46324.7N, the mold strain is 0.012, and the material elastic strain is 0.06, which does not exceed the elastic strain range of the material.

[0058] In summary, it can be seen that the special-shaped pipe formed by the above method has more sufficient filling at the corners and sharp corners, which can effectively improve the forming quality of the special-shaped pipe.

[0059] Example 2

[0060] The difference between this embodiment and embodiment 1 is that:

[0061] like Figure 4 As shown, a steel ball 4 with a radius of R1 is installed on one edge of the forming section 2 of the mold body, and the other two edges of the mold body are chamfered to be fillets with a radius of R2. The left side or right side of the mold body is provided with a groove and a cover body 5. The drawing die of this embodiment is used to manufacture the target pipe with a triangular cross-section, and R1<R2, R2>2R1, (R1+R2)×1.5≥L1.

[0062] Example 3

[0063] The difference between this embodiment and embodiment 1 is that:

[0064] like Figure 5-7As shown, steel balls 4 are installed on the three edges of the mold body forming section 2, and the radii of the steel balls 4 are R1, R2, and R2 respectively. Grooves and cover bodies 5 are provided on the three sides of the mold body. According to actual production requirements, the steel balls 4 can be arranged in 3 rows or 6 rows; the drawing die of this embodiment is used to manufacture the target pipe with a triangular cross-section, and R1=R2, (R1+R2)×1.5≥L1, (R2+R2)×1.5≥L2, or to manufacture the target pipe with a triangular cross-section, and R2<R1≤2R2, (R1+R2)×1.5≥L1, (R2+R2)×1.5≥L2, or to manufacture the target pipe with a triangular cross-section, and R1<R2≤2R1, (R1+R2)×1.5≥L1, (R2+R2)×1.5≥L2.

[0065] Example 4

[0066] The difference between this embodiment and embodiment 1 is that:

[0067] like Figure 8 As shown, the die body is in the shape of a quadrangular pyramid, two adjacent edges of the forming section 2 are provided with steel balls 4 with a radius of R, the other two edges of the forming section 2 are provided with steel balls 4 with a radius of r, the steel balls 4 are arranged in four rows, and grooves and a cover body 5 are provided on two opposite sides of the die body; the drawing die of this embodiment is used to manufacture target pipes (such as) with a quadrilateral cross-section, and r≤R≤2R, (R+R)×1.5≥d1=d3, (R+r)×1.5≥d2, Fig. 9 shown).

[0068] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A special-shaped tube internal expansion drawing die, characterized in that: The mold body is in the shape of a polygonal pyramid, and the mold body comprises an inlet section (1), a forming section (2) and an outlet section (3) in sequence. The maximum radial dimension of the inlet section (1) is smaller than the inner diameter of the tube blank, and the maximum radial dimension of the outlet section (3) is smaller than the inner diameter of the target tube. A spherical groove is provided on at least one edge of the forming section (2), and the spherical groove is provided at least at the head end and the tail end of the edge. A detachable steel ball (4) is provided in the spherical groove. The steel ball (4) is in rolling contact with the inner wall of the tube blank during the drawing process. The other edges of the forming section (2) are rounded.

2. The special-shaped tube internal expansion drawing die according to claim 1, characterized in that: At least one side surface of the mold body is provided with a groove and a cover body (5), the spherical groove is located on the side of the groove, the cover body (5) is detachably connected to the mold body, and the cover body (5) cooperates with the mold body to embed the steel ball (4) in the spherical groove, and the steel ball (4) partially protrudes outside the cover body (5).

3. The special-shaped tube internal expansion drawing die according to claim 2, characterized in that: The mold body is in the shape of a triangular prism, one edge of the molding section (2) is chamfered to a rounded corner with a radius of R1, and the other two edges of the molding section (2) are provided with steel balls (4) with a radius of R1.

4. The special-shaped tube internal expansion drawing die according to claim 2, characterized in that: The mold body is in the shape of a triangular prism, one edge of the molding section (2) is provided with a steel ball (4) with a radius of R1, and the other two edges of the molding section (2) are chamfered to a fillet of R2.

5. The special-shaped tube internal expansion drawing die according to claim 2, characterized in that: The mold body is in the shape of a triangular prism, one edge of the molding section (2) is provided with a steel ball (4) with a radius R1, and the other two edges of the molding section (2) are provided with steel balls (4) with a radius R2.

6. The special-shaped tube internal expansion drawing die according to claim 2, characterized in that: The mold body is in the shape of a quadrangular pyramid, two adjacent edges of the molding section (2) are provided with steel balls (4) with a radius of R, and the other two edges of the molding section (2) are provided with steel balls (4) with a radius of r.

7. The special-shaped tube internal expansion drawing die according to any one of claims 3 to 6, characterized in that: The height of the portion of the steel ball (4) protruding from the cover body (5) is H, which is greater than 1 / 3 times the radius of the steel ball (4) and less than 1 / 2 times the radius of the steel ball (4).

8. The special-shaped tube internal expansion drawing die according to claim 3, characterized in that: The steel balls (4) of the forming section (2) are arranged in four rows, and the four rows of steel balls (4) are evenly distributed along the edges of the forming section (2).

9. A method for forming a special-shaped tube by internal expansion, comprising the following steps: Step 1: Heat the tube to 400-500°C and keep it warm for 30 minutes; Step 2: Place the heated tube blank into the feeding section of the drawing machine, feed the inlet section (1) of the special-shaped tube internal expansion drawing die as described in claim 7 into the tube blank, and clamp the head of the tube blank with the drawing chuck of the drawing machine; Step 3: Use the feeding push rod of the drawing machine to push the tail of the tube blank, and the drawing chuck pulls the head of the tube blank. At the same time, the push rod is used to fix the special-shaped tube inner expansion drawing die until the tube blank is completely pulled through the special-shaped tube inner expansion drawing die, and the special-shaped tube is formed; Step 4: Place the special-shaped tube into a heat treatment furnace for stress relief heat treatment; Step 5: Pickling to remove oxide scale.

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