An integral internal mold for tube drawing

Abstract

This utility model relates to the field of pipe processing technology and discloses an integral inner mold for pipe drawing, including a mold body. The mold body is a solid structure without a hollow inner cavity. Along its axial direction, the mold body sequentially includes a sizing section, a transition section, a cylindrical section, and a threaded section for connection. A replaceable head assembly for performance zoning is provided on the side of the sizing section away from the transition section. A mechanical locking assembly for anti-loosening is provided on the side of the threaded section away from the cylindrical section. This utility model employs an integral solid structure, which significantly improves the structural rigidity, bending resistance, and compression resistance of the inner mold when subjected to enormous drawing forces. Furthermore, by using a differentiated heat treatment process of integral quenching and segmented tempering, the mold becomes both wear-resistant and less prone to breakage, fundamentally solving the problem of deformation and breakage of small-diameter inner molds in existing technologies due to insufficient support.

Description

Technical Field

[0001] This utility model relates to the field of pipe processing technology, and in particular to an integral inner mold for pipe drawing. Background Technology

[0002] In the drawing process of tubing, especially small-diameter tubing, the inner die (also known as the mandrel) is a key tool for determining the inner diameter and surface quality of the tubing. During high-speed drawing, a large amount of heat is generated between the die and the tubing due to intense friction and plastic deformation of the metal. To dissipate this heat promptly and control the process temperature, existing inner dies are typically designed with a hollow structure. This hollow channel allows coolant or lubricant to be delivered from the tail of the inner die to its working end, thus carrying away heat and reducing the drawing force.

[0003] However, in existing technologies, the hollow design significantly weakens the overall structural strength of the inner mold, especially when producing small-diameter, thin-walled pipes. The inner mold's diameter is already very small, and to retain necessary cooling channels, its wall thickness must be extremely thin. This results in an excessively small effective load-bearing cross-sectional area and severely insufficient support. Under enormous axial pulling forces, this fragile inner mold is highly susceptible to bending deformation (commonly known in the industry as "mold softening") or even direct breakage. This not only leads to frequent production line downtime and reduced yield but also significantly increases production costs due to frequent mold replacements. Therefore, an integral inner mold for pipe drawing is proposed to address these issues. Utility Model Content

[0004] To overcome the above deficiencies, this utility model provides an integral inner mold for pipe drawing, aiming to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: An integral inner mold for drawing tubes includes a mold body, which is a solid structure without a hollow inner cavity. The mold body includes, along its axial direction, a sizing section, a transition section, a cylindrical section, and a threaded section for connection. A replaceable head assembly for performance zoning is provided on the side of the sizing section away from the transition section. A mechanical locking assembly for providing anti-loosening locking is provided on the side of the threaded section away from the cylindrical section. As a further description of the above technical solution: The mold body is a one-piece molded structure, and at least two regions with different hardness values ​​are formed on the one-piece molded structure through a heat treatment process, wherein the hardness of the region where the sizing section is located is higher than the hardness of the region where the thread section is located. As a further description of the above technical solution: The transition section and the sizing section form a transition angle of 7° at their connection. As a further description of the above technical solution: The replaceable head assembly includes an insert head connected to the sizing section via a connecting structure, wherein the insert head has a 3mm chamfer at one end away from the sizing section; As a further description of the above technical solution: The threaded section has a 5mm chamfer at the end away from the cylindrical section, and a connection port is provided at the end of the threaded section away from the cylindrical section. As a further description of the above technical solution: The total length of the mold body is in the range of 240mm to 250mm; As a further description of the above technical solution: The outer contour of the transition section is a smoothly transitioning arc surface; As a further description of the above technical solution: The outer diameter of the sizing section and the inner diameter of the mating external mold are configured to form an annular gap for accommodating the cooling medium. As a further description of the above technical solution: The connecting structure includes a threaded rod integrally formed with the insert head and extending from its left end, and the sizing section is provided with an internal threaded hole for screwing into the threaded rod. As a further description of the above technical solution: The mechanical locking assembly includes a locking groove formed on the inner wall of the connection port, the locking groove being used to engage with a locking structure on a pull rod screwed into the connection port.

[0006] This utility model has the following beneficial effects: 1. In this utility model, an integral solid structure is adopted, which makes the structural rigidity and resistance to bending and compression of the inner mold a qualitative leap when subjected to huge tensile forces, fundamentally solving the problem that small-diameter inner molds in the prior art are prone to deformation and breakage due to insufficient support.

[0007] 2. In this utility model, by adopting a differentiated heat treatment process of overall quenching and segmented tempering, the sizing section that works directly has an ultra-high hardness of HRC58-62, ensuring excellent wear resistance; while the threaded section that bears tensile stress has excellent toughness of HRC34-38, effectively preventing brittle fracture, making the mold both wear-resistant and not easy to break, and its comprehensive service life far exceeds that of traditional single-hardness inner molds.

[0008] 3. In this utility model, the 7° transition angle and the 3mm chamfer at the sizing section inlet work together to provide an extremely smooth deformation path for the pipe blank, effectively avoiding stress concentration during the drawing process and improving the surface quality, dimensional accuracy and yield of the final pipe.

[0009] 4. In this utility model, by cleverly setting an annular cooling gap between the sizing section and the external mold, the cooling medium is allowed to continuously carry away the huge heat generated by friction and deformation, which effectively prevents the mold from becoming less hard and aggravating wear due to high temperature, and also ensures that the final pipe is formed at a stable process temperature, thus ensuring the uniformity of its mechanical properties and microstructure.

[0010] 5. In this utility model, an independently replaceable ultra-hard material insert head is used, which multiplies the wear resistance life while minimizing maintenance costs, achieving a balance between high performance and economy. Furthermore, the locking groove of the connection port can prevent the risk of connection loosening under impact and vibration, providing the most stable guarantee for high-precision machining and production safety. Attached Figure Description

[0011] Figure 1 This is a perspective view of an integral inner mold for pipe drawing proposed in this utility model; Figure 2 This is a schematic diagram of the threaded section of an integral inner mold for pipe drawing proposed in this utility model; Figure 3 This is a cross-sectional view of an integral inner mold for pipe drawing proposed in this utility model.

[0012] Legend: 1. Mold body; 2. Threaded section; 3. Cylindrical section; 4. Transition section; 5. Sizing section; 6. Connection port; 7. Transition angle; 8. Insert head; 9. Threaded rod; 10. Locking groove. Detailed Implementation

[0013] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0014] Reference Figure 1 , Figure 2 and Figure 3The present invention provides an embodiment of an integral inner mold for drawing pipes, comprising a mold body 1. The mold body 1 is a solid structure without a hollow inner cavity. The solid design fundamentally solves the problem that traditional inner molds are prone to breakage and deformation when drawing small-diameter pipes due to insufficient support. The mold body 1 includes, along its axial direction, a sizing section 5, a transition section 4, a cylindrical section 3, and a threaded section 2 for connection. A replaceable head assembly for performance zoning is provided on the side of the sizing section 5 away from the transition section 4. A mechanical locking assembly for providing anti-loosening locking is provided on the side of the threaded section 2 away from the cylindrical section 3. The total length of the mold body 1 is in the range of 240mm to 250mm. The mold body 1 is a single, seamless, one-piece molded structure. The mold body 1 adopts an advanced heat treatment process of overall quenching and segmented tempering, thereby achieving differentiated hardness control for different functional areas. Specifically, the sizing section 5, which is in direct contact with the pipe and is ultimately formed, has its hardness precisely controlled at HRC58-62 to ensure extremely high wear resistance and dimensional stability; while the thread 2, which is used for installation and withstands huge tensile stress, has its hardness controlled at HRC34-38, giving it excellent toughness and effectively preventing brittle fracture under high stress. The transition section 4 and the sizing section 5 form a transition angle of 7°. The outer contour of the transition section 4 is a smooth arc surface. When the pipe blank enters, it will first pass through this 7° transition angle and smoothly enter the transition section 4 to undergo gentle shrinkage deformation, in preparation for subsequent precise forming. The replaceable head assembly includes an insert head 8 connected to the sizing section 5 via a connecting structure. The insert head 8 has a 3mm chamfer at the end furthest from the sizing section 5. This chamfer plays a crucial guiding role, allowing the pre-deformed pipe from the transition section 4 to enter the sizing section 5, which serves as the core working area, more smoothly and without obstruction. This effectively reduces entry resistance and prevents the pipe inlet end from being scratched by the edge of the sizing section 5. During operation, after the pipe blank undergoes gentle contraction in the transition section 4, it will be within the ultra-high hardness sizing section 5. The threaded section 2 is precisely shaped to the final inner diameter; the end of the threaded section 2 away from the cylindrical section 3 is provided with a 5mm chamfer, and the end of the threaded section 2 away from the cylindrical section 3 is provided with a connection port 6. The solid cylindrical section 3 provides stable support for the inner mold, and the chamfer provides guidance for the screwing operation of the connection port 6, protecting the starting end of the thread and making the installation process more convenient. The connection port 6 is used to fix the mold body 1 on the pull rod head during cold drawing. The sizing section 5 matches the outer mold to form a gap. The tube achieves the effect of controlling the outer diameter and inner diameter of the product through the gap. The outer diameter of the sizing section 5 and the inner diameter of the mating external mold are configured to form an annular gap for accommodating the cooling medium. This annular gap is a highly efficient cooling channel that allows the cooling medium to circulate. The cooling medium can directly and efficiently cool the inner wall of the external mold and the outer surface of the sizing section 5, ensuring that the sizing section 5, as the core working area, always operates within its optimal hardness range (HRC58-62), maintaining its excellent wear resistance and dimensional stability, thereby greatly extending the overall service life of the mold.

[0015] The connecting structure includes a threaded rod 9 integrally formed with the insert head 8 and extending from its left end. The sizing section 5 has a corresponding internal threaded hole for screwing into the threaded rod 9. The insert head 8 is made of high-grade materials such as hard alloys (e.g., tungsten carbide), ceramics, or cermets, which have higher hardness and wear resistance. The larger mold body 1 continues to use tool steel, which combines strength and high toughness. This ensures the structural toughness of the mold body 1 and gives the working end an extremely long service life. The design of the threaded rod 9 allows the insert head 8 to be easily screwed back after wear. The replacement of the mold body significantly reduces maintenance costs and production downtime, achieving high performance and long service life at low cost. The mechanical locking assembly includes a locking groove 10 formed on the inner wall of the connection port 6. The locking groove 10 is used to engage with the locking structure on the pull rod screwed into the connection port 6. When the pull rod head is tightened by the thread, that is, after the inner mold is installed in place, a locking flat key can be inserted into the locking groove 10. This physical engagement completely prevents any relative rotation between the mold body 1 and the pull rod, keeping the mold and the drawing center line coaxial and firmly connected.

[0016] Working Principle: By employing a single, solid mold body 1 without an internal cavity, the problem of traditional internal molds being prone to breakage and deformation during the drawing of small-diameter pipes due to insufficient support is fundamentally solved. Furthermore, the mold body 1 utilizes an advanced heat treatment process of integral quenching and segmented tempering, achieving differentiated hardness control for different functional areas: the sizing section 5, which directly contacts the pipe and undergoes final forming, has its hardness precisely controlled at HRC58-62 to ensure extremely high wear resistance and dimensional stability; while the threaded section 2, used for installation and bearing enormous drawing stress, has its hardness controlled at HRC34-38, giving it excellent toughness and effectively preventing brittle fracture under high stress. The deep integration of this structure and material properties allows the solid cylindrical section 3 to provide stable support during the operation of the inner mold. When the tube blank enters, it first passes through a 7° transition angle and smoothly enters the transition section 4 for gentle shrinkage deformation. Then, it is precisely shaped to the final inner diameter in the ultra-high hardness sizing section 5. The annular gap formed between the sizing section 5 and the externally mating drawing die allows the cooling medium to circulate and efficiently force-cool the mold and the tube. Therefore, this utility model organically combines and synergistically works the high-strength solid structure, differentiated hardness material process, design of each functional section, and efficient cooling mechanism to ultimately achieve stable, efficient, and high-precision tube drawing operations. The insert head 8 is made of materials such as hard alloy and is connected to the main body through an integrated threaded rod 9. This gives the mold strong overall fracture resistance and the working surface that directly contacts the pipe with extreme wear resistance. It can also be replaced independently after wear, perfectly balancing high performance and economy. The locking groove 10 in the connection port 6 and the screwed-in pull rod structure interlock with each other, forming a second physical safety in addition to the threaded fastening. It can resist vibration and impact during the drawing process, eliminate the major safety hazard of loose connection, and thus ensure the stability and coaxial accuracy of the entire drawing operation.

[0017] Finally, it should be noted that the above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. An integral inner mold for drawing tubes, comprising a mold body (1), characterized in that: The mold body (1) is a solid structure without a hollow inner cavity. The mold body (1) includes, along its axial direction, a sizing section (5), a transition section (4), a cylindrical section (3), and a threaded section (2) for connection. The sizing section (5) is provided with a replaceable head assembly for performance partitioning on the side away from the transition section (4). The threaded section (2) is provided with a mechanical locking assembly for providing anti-loosening locking on the side away from the cylindrical section (3).

2. The integral inner mold for tube drawing according to claim 1, characterized in that: The mold body (1) is an integral molding structure, and at least two regions with different hardness values ​​are formed on the integral molding structure by heat treatment process, wherein the hardness of the region where the sizing section (5) is located is higher than the hardness of the region where the thread section (2) is located.

3. The integral inner mold for tube drawing according to claim 1, characterized in that: The transition section (4) and the sizing section (5) form a transition angle (7) of 7° at the connection.

4. The integral inner mold for tube drawing according to claim 1, characterized in that: The replaceable head assembly includes an insert head (8) connected to the sizing section (5) via a connecting structure, wherein the insert head (8) has a 3mm chamfer at one end away from the sizing section (5).

5. The integral inner mold for tube drawing according to claim 1, characterized in that: The threaded section (2) has a 5mm chamfer at one end away from the cylindrical section (3), and a connection port (6) is provided at the other end of the threaded section (2) away from the cylindrical section (3).

6. The integral inner mold for tube drawing according to claim 1, characterized in that: The total length of the mold body (1) is in the range of 240mm to 250mm.

7. The integral inner mold for tube drawing according to claim 1, characterized in that: The outer contour of the transition segment (4) is a smoothly transitioning arc surface.

8. The integral inner mold for tube drawing according to claim 1, characterized in that: The outer diameter of the sizing section (5) and the inner diameter of the mating external mold are configured to form an annular gap for accommodating the cooling medium.

9. An integral inner mold for tube drawing according to claim 4, characterized in that: The connection structure includes a threaded rod (9) integrally formed with the insert head (8) and extending from its left end, and the sizing section (5) is provided with an internal threaded hole for screwing into the threaded rod (9).

10. An integral inner mold for tube drawing according to claim 5, characterized in that: The mechanical locking assembly includes a locking groove (10) formed on the inner wall of the connection port (6), the locking groove (10) being used to engage with a locking structure on a pull rod screwed into the connection port (6).

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