Composite structure cold heading extrusion die

Abstract

The present application relates to a kind of composite structure cold heading extrusion die, including upper die and lower die.The upper die is the overall flat bottom angle convex die, and the shaped end face is provided with the profile contour of twelve-angle and flange composite.The lower die adopts transverse segmentation type three-layer concave die structure, and is sequentially from inside to outside working die core and insert, inner layer and outer layer prestressed ring, press sleeve;Working die core and / or insert adopt Cr12MoV and are quenched by vacuum tempering, and press sleeve adopts 45 steel.The lower die is provided with the unloading rod of stepped inner cavity, and is matched with the lower end of convex die when die is closed, and metal flow is constrained, and is independently pushed up when die is opened Demoulding.The present application is dispersed by prestressed ring layering constraint load, and stress concentration is slowed down, and metal flow is improved by unloading rod and the risk of sticking die is reduced, with the advantages of high forming precision, smooth unloading, long service life, suitable for the cold heading forming of complex special-shaped head workpiece.

Description

Technical Field

[0001] This invention relates to the field of cold heading dies, and more particularly to a composite structure cold heading die. Background Technology

[0002] Upsetting and extrusion is a volume forming technology that combines upsetting and extrusion. It has core advantages such as high material utilization, high forming efficiency and excellent mechanical properties of workpieces. It is widely used in the processing of complex structural parts in fields such as machinery manufacturing, aerospace, rail transportation and high-end fasteners.

[0003] However, as the requirements for workpiece forming accuracy, structural complexity, and performance stability continue to rise in high-end equipment, traditional upsetting dies have revealed the following technical problems in application:

[0004] When forming complex structural parts such as dodecagonal heads and flanges, traditional integrated molds are prone to damage such as mold cavity collapse and cracks due to concentrated stress in the cavity and poor stress transmission. They may also cause forming defects such as uneven wall thickness and folding in the workpiece, which seriously affect the quality of the workpiece and the life of the mold.

[0005] If the metal flow control process during forming is not designed properly, it will not only increase forming resistance and reduce forming efficiency, but also aggravate friction and wear between the mold and the workpiece, further shortening the mold's service life. Especially in the upsetting and extrusion composite process, metal flows in both the radial and axial directions at the same time, which places higher demands on the mold cavity's constraint ability.

[0006] Third, existing molds often experience problems such as sticking and tearing during the demolding process, which affects the smoothness and repeatability of demolding and makes it difficult to meet the stability requirements of mass production.

[0007] Therefore, there is an urgent need for a composite structure cold heading die with reasonable stress distribution, stable forming, long service life and smooth unloading, in order to break through the existing technical bottlenecks. Summary of the Invention

[0008] To solve the above-mentioned technical problems, the present invention provides a composite structure cold heading extrusion die.

[0009] According to one objective of the present invention, the present invention provides a composite structure cold heading extrusion die, including an upper die and a lower die; the upper die is an integral flat-bottomed conical punch, and the lower die adopts a transversely segmented three-layer concave die structure. The die is mainly composed of four parts: the inner layer is a working die core and insert, the middle layer is an inner prestressing ring and an outer prestressing ring, and the outermost layer is a pressure sleeve structure.

[0010] Specifically, the upper die is a flat-bottomed conical punch, and its forming end face has a profile that matches the shape of the workpiece head, used to complete the precision forming of complex heads such as dodecagonal heads and flanges; the lower die adopts a transversely segmented three-layer die structure, consisting of a core assembly, a prestressing assembly and a pressure sleeve arranged sequentially from the inside out, wherein the core assembly includes a working core and an insert, the prestressing assembly includes an inner prestressing ring and an outer prestressing ring, and the pressure sleeve is the outermost support structure.

[0011] The upper mold is a flat-bottomed tapered punch, which has a cavity profile adapted to the head of the workpiece as a forming mold; the unloading rod is located below the die pad, and its inner cavity has a stepped structure, which is used to provide a self-locking function during the forming process, prevent the mold core from axially displacing under pressure, and provide guidance for unloading the workpiece after the mold is opened.

[0012] The working mold core and / or the insert are made of Cr12MoV mold steel, which has been vacuum quenched and tempered to improve the mold's hardness, wear resistance and fatigue resistance.

[0013] The mold core is provided with an insert below it. The insert is concentric with the working mold core to help the working mold core achieve precise matching of the cavity contour and improve the forming accuracy.

[0014] The lower mold adopts a transversely segmented three-layer concave mold structure. Through the layered constraint of the prestressed ring and the pressure sleeve, the overall crack resistance and fatigue life of the mold are improved.

[0015] To better meet the precision forming requirements of irregularly shaped workpieces, the forming end face of the flat-bottomed conical punch is provided with a profile that matches the shape of the workpiece head. This profile is a composite structure of a dodecagon and a flange, which has high shape retention and positioning function.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] This invention constructs an optimized forming path by designing the upper mold as an integral flat-bottomed conical punch, combined with the lower mold's transversely segmented three-layer concave mold structure. The lower mold, through the layered constraints of the inner and outer prestressed rings and the pressure sleeve, effectively disperses the load and reduces stress concentration, thus solving the problems of collapse and cracking caused by stress concentration and poor stress transmission in traditional mold cavities. This significantly improves the structural stability and fatigue life of the mold.

[0018] This invention utilizes the stepped internal cavity structure of the unloading rod to cooperate with the lower end of the flat-bottomed conical punch during mold closing and forming, thereby assisting in constraining the radial flow of the workpiece metal, improving the metal flow state, reducing forming resistance and frictional wear, and thus reducing forming defects such as uneven workpiece wall thickness and folds, and improving forming accuracy.

[0019] This invention uses an ejector rod that pushes upward independently during mold opening and demolding to actively eject the workpiece, replacing the traditional ejection method that relies on the upper mold core or lower mold top plate. This effectively reduces the risks of sticking, tearing, and displacement, and improves the smoothness and repeatability of the demolding process.

[0020] As a further improvement of this invention, the working die core and inserts, as well as the prestressed components and pressure sleeves of each layer, are detachably connected, facilitating the rapid replacement and maintenance of locally worn parts, reducing operating costs and improving the reusability of the die. The working die core and / or inserts are made of Cr12MoV die steel and have undergone vacuum quenching and tempering treatment, further improving the die's hardness, wear resistance, and fatigue resistance. The forming end face of the flat-bottomed conical punch has a dodecagonal profile combined with a flange, which can meet the precision forming requirements of complex irregular-shaped head parts.

[0021] In summary, this invention combines the advantages of high forming accuracy, smooth unloading, long service life, and convenient maintenance, and has broad engineering application prospects in the fields of aerospace, automotive, and high-strength fastener manufacturing.

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the closed state of a composite structure cold heading extrusion die according to the present invention;

[0024] Figure 2 This is a schematic diagram of the open state of a composite structure cold heading extrusion die according to the present invention;

[0025] Figure 3 This is a cross-sectional schematic diagram of the closed state of a composite structure cold heading extrusion die according to the present invention. Detailed Implementation

[0026] The following description is intended to provide a detailed account of the invention so that those skilled in the art can implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0027] Please see Figure 1-3 The present invention provides a technical solution: a composite structure cold heading extrusion die, including an upper die and a lower die, the die further including a sample 5, the sample 5 being a workpiece blank to be formed, which is set in the forming cavity of the lower die;

[0028] The upper mold is an integral flat-bottomed conical punch 1, and its forming end face is provided with a profile that matches the shape of the workpiece head. The profile is a composite structure of a dodecagon and a flange, which is used to achieve precision forming of the workpiece head.

[0029] The lower mold adopts a horizontally segmented three-layer concave mold structure, including a mold core assembly, a prestressing assembly, and a pressure sleeve 2 arranged sequentially from the inside out. The mold core assembly includes a working mold core 6 and an insert 7. The working mold core 6 has a forming cavity and is set inside the lower mold body. The insert 7 is set below the working mold core 6 and is concentric with the working mold core 6 to assist the working mold core 6 in achieving precise matching of the cavity contour. The working mold core 6 and / or the insert 7 are made of Cr12MoV mold steel and are vacuum quenched and tempered to obtain high hardness and excellent wear resistance. The mold core structure adopts a replaceable modular design, which is convenient for later maintenance and component replacement.

[0030] The prestressed component includes an inner prestressed ring 4 and an outer prestressed ring 3. The inner prestressed ring 4 is fitted around the outer periphery of the mold core component and fixed by interference fit. The outer prestressed ring 3 is fitted around the outer periphery of the inner prestressed ring 4. The pressure sleeve 2 is fitted around the outer periphery of the outer prestressed ring 3. The pressure sleeve 2 is made of 45 steel. The layered constraint between the prestressed ring and the pressure sleeve improves the overall crack resistance and fatigue life of the mold.

[0031] The lower mold also includes a cavity mold pad 8 located below the mold core assembly, and an ejector rod 9. The ejector rod 9 passes through the cavity mold pad 8 and can slide axially. The ejector rod 9 is located on the lower end face of the cavity mold pad 8 and contacts the bottom of the workpiece. The ejector rod 9 has a stepped internal cavity structure and is located below the mold core assembly. During mold closing and forming, the ejector rod 9 cooperates with the lower end of the flat-bottomed tapered punch 1 to help constrain the metal flow of the workpiece. During mold opening and demolding, the ejector rod 9 pushes upward independently and is driven by a spring or guide post mechanism to eject the workpiece and complete the demolding.

[0032] The working mold core 6 and the insert 7, the working mold core 6 and the prestressing component, and the prestressing component and the pressure sleeve 2 are all detachably connected. These detachable connections are either clearance fits or achieved through locating pins. This detachable design facilitates the rapid replacement and maintenance of locally worn parts, reduces operating costs, and improves the reusability of the mold.

[0033] To ensure proper assembly of the mold structure, the working mold core 6 is first installed within the inner prestressed ring 4 and fixed using an interference fit. An insert 7 is located below the working mold core 6, with both fitting concentrically. Then, the outer prestressed ring 3 is fitted onto the outer layer to enhance structural strength. Next, the pressure sleeve 2 is fitted around the outer periphery of the outer prestressed ring 3, and the entire assembly is placed within the lower mold. A cavity mold pad 8 is placed at the bottom to provide structural support and pressure stability. The ejector rod 9 is located on the lower end face of the cavity mold pad 8, contacting the bottom of the workpiece. During the mold opening phase, it is driven by a spring or guide post mechanism to push the workpiece upwards for demolding.

[0034] When the mold is closed, the upper and lower molds are accurately aligned by the flat-bottomed tapered punch 1, the mold core, and the mold core guide sleeve to avoid damage to the mold core or forming deviation caused by stamping misalignment. During the cold heading extrusion process, the workpiece material is placed in the lower mold cavity, and the upper mold closes along the mold core. The impact load is transmitted to the die pad 8 by the external pressure driven by the flat-bottomed tapered punch 1, so as to realize the cold heading of the twelve-corner flange head. After the forming is completed, during the mold opening stage, the upper mold core provides the demolding gap when the mold is opened, guides the workpiece to move axially, and the lower mold ejector rod 9 simultaneously ejects the workpiece to complete one forming-demolding cycle.

[0035] In summary, this cold heading extrusion die, through its integrated forming and unloading design, effectively improves forming accuracy and unloading efficiency, avoiding core deformation and sticking. The stepped internal cavity structure of the core provides a limiting function while forming an unloading channel, ensuring smooth demolding of the workpiece. The die adopts a composite core structure, combined with high-strength materials and heat treatment processes, significantly improving the die's structural strength, service life, and processing stability. The upper and lower dies are aligned and positioned through a core guide sleeve, improving closing accuracy and forming consistency. The unloading rod is located at the lower end of the die pad, ejecting the workpiece mechanically or through an elastic structure, further ensuring smooth demolding and continuous operation capability. This die has a simple structure, clear functions, and convenient assembly, making it suitable for the precision forming of high-strength, high-complexity, multi-batch cold heading extrusion of irregularly shaped fasteners. It is particularly suitable for applications in the aerospace, automotive, or high-strength fastener industries where high precision is required for complex head structures, and has significant potential for widespread application.

[0036] The embodiments described above are only used to illustrate the technical ideas and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The scope of patent application of the present invention should not be limited by these embodiments. That is, any equivalent changes or modifications made in accordance with the spirit disclosed in the present invention still fall within the patent scope of the present invention.

Claims

1. A composite structure cold heading extrusion die, characterized in that, Includes upper mold and lower mold; The upper mold is a single flat-bottomed tapered punch (1); The lower mold includes a mold core assembly, a prestressed assembly and a pressure sleeve (2) arranged sequentially from the inside to the outside. The mold core assembly includes a working mold core (6) and an insert (7). The working mold core (6) has a forming cavity inside. The lower mold also includes an ejector rod (9), which has a stepped internal cavity structure and is located below the mold core assembly. The ejector rod (9) is configured to cooperate with the lower end of the flat-bottomed conical punch (1) during mold closing and forming to assist in constraining the flow of metal in the workpiece, and to push upward independently during mold opening and demolding to eject the workpiece.

2. The cold heading extrusion die according to claim 1, characterized in that, The prestressed component includes an inner prestressed ring (4) and an outer prestressed ring (3). The inner prestressed ring (4) is fitted around the outer periphery of the core component, the outer prestressed ring (3) is fitted around the outer periphery of the inner prestressed ring (4), and the pressure sleeve (2) is fitted around the outer periphery of the outer prestressed ring (3).

3. The cold heading die according to claim 1, characterized in that, The working mold core (6) and / or the insert (7) are made of Cr12MoV mold steel and are subjected to vacuum quenching and tempering.

4. The cold heading die according to claim 1, characterized in that, The working mold core (6) and the insert (7), the working mold core (6) and the prestressing component, and the prestressing component and the pressure sleeve (2) are all detachably connected.

5. The cold heading die according to claim 4, characterized in that, The detachable connection is achieved through clearance fit or by using locating pins.

6. The cold heading die according to claim 1, characterized in that, The forming end face of the flat-bottomed conical punch (1) is provided with a profile that matches the shape of the workpiece head. The profile is a composite structure of a dodecagon and a flange.

7. The cold heading die according to claim 1, characterized in that, The lower mold also includes a concave mold pad (8) located below the mold core assembly. The unloading rod (9) passes through the concave mold pad (8) and can slide axially.

8. The cold heading die according to claim 1, characterized in that, The stepped inner cavity of the unloading rod (9) includes at least two levels of holes with different diameters, wherein the hole diameter is smaller at the end closer to the workpiece and larger at the end farther from the workpiece.

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