An inner core formed by drawing an aluminum alloy tube

Abstract

The invention discloses an inner core for drawing and forming an aluminum alloy tube, relates to the technical field of tube drawing and forming, and aims to solve the problem that the friction resistance between the inner core and the inner wall of the tube blank is large, especially at the working belt, and the inner hole is scratched by the accumulation of sticky aluminum. The invention comprises a drawing part and a connecting part fixedly connected thereto, the drawing part having the largest diameter is provided with a working belt, an internal threaded connection is provided inside one end of the connecting part away from the drawing part, an oil cavity is provided at one end close to the working belt, a supporting part is provided on the outer periphery of the connecting part, and the supporting part is at the largest diameter of the inner core; a truncated cone-shaped pre-lubricating head is fixedly provided at one end of the drawing part away from the connecting part; a through hole is opened along the central axis of the inner core, one end of the through hole is connected to the oil cavity, and the other end passes through the drawing part and the pre-lubricating head; the inner mold deformation cone angle θ1=12±1°; the invention effectively reduces the problem of inner hole scratching caused by the sticky aluminum of the inner core, reduces the friction resistance when the casing is used, and is beneficial to improving product quality.

Description

Technical Field

[0001] The invention relates to the technical field of tube drawing and forming, in particular to an inner core for drawing and forming an aluminum alloy tube. Background Art

[0002] There are several basic methods for drawing aluminum alloy pipes: coreless empty drawing, long core rod drawing, short core head drawing and floating core head drawing; among them, short core head drawing is the most widely used in pipe drawing, and the inner core structure of short core head drawing has been fully disclosed in many existing technologies. For example, the invention patent with publication number CN102186609A and titled Drawing Processing Device for Tubular Workpieces discloses a drawing mandrel with a larger diameter drawing portion; there is also a utility model patent with publication number CN204448883U and titled A Special Die for Manufacturing Aluminum-Based Tubes with Bright and Smooth Surfaces for Photosensitive Drums, which specifically discloses structures such as the inner die sleeve guide angle, the inner die sizing working zone, and the inner die deformation cone angle; for another example, the invention patent with publication number CN102319524A and titled A Lubricating Oil Internal and External Circulation and Filtering Clarification Device for Cold Working Drawing also discloses an inner core with an oil outlet hole, such as Figure 1 As shown, it is a schematic diagram of the internal structure of this inner core;

[0003] The general process of short-core drawing is to fix one end of the draw rod equipped with the short core during drawing, then insert the short core connected to the draw rod into the tube blank, and then realize the diameter reduction and wall reduction deformation processing through the outer die hole; in the existing process, it is generally designed to extrude the blank tube to draw the finished tube, a total of 2-3 passes, each time a small amount of deformation drawing is performed to ensure the dimensional accuracy requirements and appearance quality of the drawn product; but the main disadvantages of multi-pass drawing are many processing passes, long production time, large personnel investment, labor and time-consuming, and energy waste due to multiple equipment operations.

[0004] In order to solve the above problems, the applicant optimized the processing deformation amount and the deformation angle of the drawing die many times during the production process, and tried to adopt one-time drawing forming. However, during the trial production process, the inner hole was often scratched, resulting in unqualified products. The reason was analyzed as follows: during the casing process, the inner core working belt and the inner wall of the tube blank were in direct contact. In the case of insufficient lubrication, friction with the tube wall occurred, resulting in aluminum accumulation on the inner core working belt. Since the inner core moves inside the tube blank during casing, it cannot be discovered in time during the casing process. When aluminum sticking occurs, the inner hole of the entire 6-7m long tube will be scratched and scrapped. After discovery, the inner core must be removed, polished, and then installed on the machine for use, which seriously affects the product production efficiency. If the discovery and treatment are not timely, it will lead to batch scrapping, resulting in a decrease in the overall qualified rate of the product, and stable production cannot be carried out well. Summary of the invention

[0005] The present invention is proposed under the premise mentioned in the above background technology, and its purpose is to solve the problem of large friction resistance between the inner core and the inner wall of the tube blank, especially in the working zone, where sticky aluminum accumulates and scratches the inner hole.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: an inner core formed by drawing of an aluminum alloy tube, comprising a drawing part and a connecting part fixedly connected thereto, a working band being provided at the part with the largest diameter of the drawing part, an internal threaded connection being provided inside an end of the connecting part away from the drawing part, an oil chamber being provided at the end thereof close to the working band, a supporting part being provided on the outer periphery of the connecting part, and the supporting part being at the part with the largest diameter of the inner core.

[0007] Preferably, a truncated cone-shaped pre-lubrication head is fixedly provided at one end of the drawing part away from the connecting part, whose diameter is smaller than the working belt, and the diameter is largest near the working belt; a through hole is opened along the central axis of the inner core, one end of the through hole is connected to the oil chamber, and the other end passes through the drawing part and the pre-lubrication head.

[0008] Preferably in the above solution, a plurality of pre-lubrication holes are provided on the side wall of the pre-lubrication head, and the pre-lubrication holes are connected to the through hole.

[0009] Preferably, an inner mold deformation cone angle θ1 is provided on one side of the working belt of the drawing portion close to the connecting portion, and θ1 = 12±1°.

[0010] Preferably, the support portion is located in the middle of the connecting portion, and a support portion conical surface is provided between the support portion and the drawing portion, on which a plurality of oil outlet holes are opened, and the oil outlet holes are connected to the oil cavity in the connecting portion.

[0011] Preferably in the above solution, the diameters of the conical surface of the supporting portion and the connection portion are equal.

[0012] Preferably, a pull rod is threadedly connected to the internal thread connection of the connection part, and the pull rod is hollow and communicated with the oil chamber.

[0013] Preferably, the support portion has the same cross-sectional shape as the tube blank to be processed, and the tube blank is sleeved on the support portion, and the size matching clearance between the two is 0.1-0.2 mm.

[0014] Preferably, the support portion is made of 45# steel and is integrally formed with the connecting portion.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The inner core of the aluminum alloy tube is drawn and formed with a support part, and the size of this part is the thickest. When the tube blank is sleeved, the inner core working belt does not produce contact friction with the material tube wall. Since the working belt is generally made of high-hardness tungsten alloy and the support part is 45# steel, the problem of inner hole scratching caused by aluminum sticking to the inner core is avoided.

[0017] 2. The inner core of the aluminum alloy tube drawing and forming has optimized the design and improvement of the inner die deformation cone angle. The existing inner die deformation cone angle is 8°, and the improved design is 12±1°. The purpose is to extend the distance difference between the first diameter reduction and the second wall reduction, reduce the friction resistance generated in the process of diameter reduction and wall reduction during drawing, reduce the residual stress of plastic processing deformation retained in the product after drawing, which is beneficial to reduce the stress release rebound coefficient generated during subsequent turning processing, and can effectively reduce the occurrence of abnormalities such as linear bending, run-out, roundness elliptical variation to varying degrees, thereby ensuring the roundness and run-out of the product. Stable, especially the inner die deformation cone angle is suitable for one-time drawing and forming, which can effectively alleviate the problem of greater friction resistance than multiple passes when the diameter and wall reduction are more due to the use of one-time drawing and forming.

[0018] 3. The inner core formed by drawing of the aluminum alloy pipe has also been extended in terms of lubrication. A pre-lubrication head is installed at the front end of the working belt and connected to the oil chamber. The existing inner core cannot lubricate the working belt part and must be manually oiled before each sleeve. However, due to the long tube billet, it is impossible to ensure that the entire tube billet is lubricated inside, so aluminum sticking often occurs. After the pre-lubrication head is set, the lubricating oil can continuously lubricate the front end during the sleeve process, effectively avoiding the situation of insufficient lubrication.

[0019] 4. The inner core of the aluminum alloy tube drawing is suitable for one-time drawing and forming, and the single deformation is large, which can reduce more than 50% of the production time and reduce the production cost. The scratch rate is reduced from 15-20% to 8%, and the severe scratch is reduced from 6% to 0%, which can significantly improve the product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the internal structure of the inner core in the prior art;

[0021] Figure 2 A schematic diagram of the internal structure of an embodiment of the inner core of the present invention;

[0022] Figure 3 for Figure 2 A schematic diagram of a working state of the illustrated embodiment.

[0023] In the figure: 10, working belt; 20, connecting part; 30, pull rod; 40, tube blank; 1, supporting part; 11, conical surface of supporting part; 2, through hole; 3, pre-lubricating head; 31, pre-lubricating hole. DETAILED DESCRIPTION

[0024] Figure 1It is a structural schematic diagram of the inner core in the prior art, including a drawing part and a connecting part fixedly connected thereto, the connecting part is generally a cylinder, the drawing part includes an inner mold sleeve guide cone at the front end, a working belt in the middle, and an inner mold deformation cone connected to the connecting part, wherein the inner mold deformation cone angle θ2 of the inner mold deformation cone is generally 8°, this common inner core has a small deformation amount, is mainly used for 2-3 drawing processes, is not suitable for one-time forming, has a long production time, requires a large amount of manpower, is labor-intensive and time-consuming, and most importantly, when the sleeve blank is formed, the inner core often sticks to aluminum, causing scratches on the inner hole. According to actual production statistics, there are 15-20% inner hole scratches in the product. If the aluminum sticking scratches appear early and are not discovered in time, the scratch rate may even exceed 50%, with the highest batch being as high as 57%, and severe scratches exceeding 6%.

[0025] See also Figure 2 The present invention provides an inner core formed by drawing of an aluminum alloy tube, comprising a drawing part and a connecting part 20 fixedly connected thereto, the two are generally formed in one piece, and are distinguished due to different functions of the parts, wherein a working belt 10 is provided at the part with the largest diameter of the drawing part, and is generally made of tungsten alloy, an internal threaded connection is provided inside the end of the connecting part 20 away from the drawing part, and an oil chamber is provided at the end close to the working belt 10, and a supporting part 1 is provided on the periphery of the connecting part 20, and the supporting part 1 is the part with the largest diameter of the inner core. Generally, when processing round tubes, the cross-sectional shapes of the inner core at various places are all circular, but in special cases, such as processing square tubes or other special-shaped tubes, the above-mentioned part with the largest diameter should be understood as the part with the largest area of ​​the shape surrounded by the outermost contour of the cross-section.

[0026] like Figure 1 As shown, the existing inner core cannot lubricate the working belt 10 part, and must be manually oiled before each sleeve of the tube blank 40. However, since the tube blank 40 is relatively long, it is impossible to ensure that the entire tube blank 40 is lubricated inside, so aluminum sticking often occurs. To further solve this problem, a truncated cone-shaped pre-lubrication head 3 is fixed at one end of the drawing portion away from the connecting portion 20, and its diameter is smaller than the working belt 10, and the diameter is largest near the working belt 10; a through hole 2 is opened along the central axis of the inner core, one end of the through hole 2 is connected to the oil cavity, and the other end passes through the drawing portion and the pre-lubrication head 3. After the pre-lubrication head 3 is provided, the lubricating oil can continuously lubricate the front end during the sleeve process, effectively avoiding the situation of insufficient lubrication; more specifically, a plurality of pre-lubrication holes 31 are opened on the side wall of the pre-lubrication head 3, and the pre-lubrication holes 31 are connected to the through hole 2, and the direction of the pre-lubrication holes 31 can be as shown in the figure. Figure 2 As shown, it can also be directed toward the front end of the inner core.

[0027] like Figure 1As shown, the existing inner mold deformation cone angle (sometimes this angle is also referred to as the transition deformation angle or other names in the art) is generally 8°. However, in the process of reducing the diameter and reducing the wall, this angle shortens the distance difference between the first diameter reduction and the second wall reduction, increases the friction resistance in the drawing deformation process, and causes more residual stress of plastic processing deformation to remain in the product after drawing. During the subsequent turning process, stress release rebound will be performed, resulting in different degrees of linear bending, runout, roundness and elliptical variation in the product. Therefore, in one embodiment of the present invention, it is preferred that the side of the working band 10 of the drawing part close to the connecting part 20 is provided with an inner mold deformation cone angle θ1, θ1=12±1°, and the ±1° is the allowable error range, preferably 12°. Although a patent document mentioned in the background technology limits the angle to 5 to 30 degrees, it does not record the influence of different angles, and does not mention the unexpected effect brought by 12±1°.

[0028] Furthermore, the support portion 1 is located in the middle of the connecting portion 20, and a support portion conical surface 11 is provided between the support portion 1 and the drawing portion, on which a plurality of oil outlet holes are opened, and the oil outlet holes are connected to the oil cavity in the connecting portion 20. During the process of sleeve pipe blank 40, lubricating oil is added to the front end of the support portion 1 from the oil outlet holes, so as to ensure that the support portion 1 and the pipe blank 40 are lubricated in place; preferably, the diameter of the connection between the support portion conical surface 11 and the connecting portion 20 is equal, which is more conducive to processing and forming and prevents the accumulation of solidified lubricating oil, debris, etc.

[0029] See also Figure 3 , similar to the prior art, the internal thread connection of the connection part 20 is threadedly connected with a pull rod 30, and the pull rod 30 is hollow and communicated with the oil chamber.

[0030] In a preferred embodiment, the support portion 1 has the same cross-sectional shape as the tube blank 40 to be processed, and the tube blank 40 is sleeved on the support portion 1, and the size matching clearance between the two is 0.1 to 0.2 mm. The clearance should be understood as, when the tube blank 40 to be processed is a round tube, the outer wall cross-sectional diameter of the support portion 1 is 0.1 to 0.2 mm smaller than the inner wall cross-sectional diameter of the tube blank 40. When the tube blank 40 to be processed is of other shapes, the support portion 1 is made to coincide with the center line of the tube blank 40, then the distance from any point of the outer wall of the support portion 1 to the inner wall of the tube blank 40 in the same cross-section is 0.05 to 0.1 mm. The reason for setting it in this gap range is that if the gap is too small, it is difficult to insert the tube blank 40, and if the gap is too large, the support portion 1 may not be able to play a good supporting role because its length is limited and the tube blank 40 is long. It is difficult to ensure that the center line is parallel during the sleeve process, and the inner wall of the tube blank 40 is more or less still in contact with the working belt 10.

[0031] Generally, the support part 1 is made of 45# steel and is integrally formed with the connection part 20. To further reduce friction, the support part 1 and the connection between the support part 1 and the conical surface 11 of the support part may be polished smooth, and the corners of the connection may be rounded.

[0032] When the present invention is in use, the inner core is inserted into the tube blank 40. Since the diameter at the support part 1 is the largest, the tube blank 40 is in direct contact with it. If the axes of the two cannot be kept parallel during the insertion process, there may still be contact points at the position of the working belt 10. However, since the pre-lubrication head 3 can continuously lubricate the front end, there is no dry friction, and the friction resistance is also small, which can effectively avoid scratching and sticking aluminum. At the same time, because the deformation cone angle of the inner mold θ1 is 12±1°, the friction resistance can be effectively reduced, and the roundness and runout of the product are guaranteed to be stable, which is beneficial to improving product quality. The angle of the deformation cone angle θ1 of the inner mold is particularly suitable for one-time drawing and forming, which can effectively alleviate the problem that the friction resistance is greater than that of multiple passes when the diameter and wall are reduced more due to the one-time drawing and forming.

[0033] In the actual test of the present invention, 100 tube blanks were drawn and formed at one time. After inspection, only 8 were slightly scratched and no serious scratches were found. The reason was analyzed to be mainly related to the operating habits of the staff. There was no aluminum sticking to the inner core, and the condition was good, which is suitable for promotion and production.

[0034] The above are only preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope defined by the claims.

[0035] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

Claims

1. An inner core formed by drawing an aluminum alloy tube, comprising a drawing portion and a connecting portion (20) fixedly connected thereto, a working band (10) being provided at the drawing portion having the largest diameter, an internal threaded connection being provided inside the end of the connecting portion (20) away from the drawing portion, and an oil chamber being provided at the end thereof close to the working band (10), characterized in that: A support portion (1) is provided on the outer periphery of the connecting portion (20), the support portion (1) being the part with the largest diameter of the inner core, so that when the tube blank is sleeved, the inner core working belt (10) does not generate contact friction with the wall of the raw tube; an inner mold deformation cone angle θ1 is provided on the side of the working belt (10) of the drawing portion close to the connecting portion (20), θ1=12±1°; A truncated cone-shaped pre-lubricating head (3) is fixedly provided at one end of the drawing portion away from the connecting portion (20), wherein the diameter of the pre-lubricating head (3) is smaller than the working band (10), and the diameter is largest near the working band (10); a through hole (2) is opened along the central axis of the inner core, wherein one end of the through hole (2) is connected to the oil chamber, and the other end passes through the drawing portion and the pre-lubricating head (3).

2. The inner core formed by drawing an aluminum alloy tube according to claim 1, characterized in that: A plurality of pre-lubrication holes (31) are formed on the side wall of the pre-lubrication head (3), and the pre-lubrication holes (31) are connected to the through hole (2).

3. The inner core formed by drawing an aluminum alloy tube according to claim 1, characterized in that: The support portion (1) is located in the middle of the connecting portion (20), and a support portion conical surface (11) is provided between the support portion (1) and the drawing portion, on which a plurality of oil outlet holes are provided, the oil outlet holes being connected to the oil cavity in the connecting portion (20).

4. The inner core formed by drawing an aluminum alloy tube according to claim 1, characterized in that: The internal thread connection of the connection portion (20) is threadedly connected to a pull rod (30), which is hollow and communicates with the oil chamber.

5. The inner core formed by drawing an aluminum alloy tube according to claim 1, characterized in that: The support portion (1) has the same cross-sectional shape as the tube blank (40) to be processed, and the tube blank (40) is sleeved on the support portion (1), and the size matching clearance between the two is 0.1-0.2 mm.

6. The inner core formed by drawing an aluminum alloy tube according to claim 1, characterized in that: The support portion (1) is made of 45# steel and is integrally formed with the connection portion (20).

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