A short stubby rod bolt cold heading die and process

Abstract

The application relates to the field of new energy automobile accessory production, and discloses a short-thick rod bolt cold heading die and process. Through improvement of the process and the die, the one-end of a rod material is first shortened, the other end is thickened into a conical surface structure, the thin rod is kept from being stressed in the second process, the conical surface structure is further upset, the thin rod is kept from being stressed again in the third process, the conical surface structure is further thickened and a hexagonal head initial blank is formed, and the conical surface structure is thickened into a stepped thick rod in the fourth process, and the thin rod and the hexagonal head are formed by upsetting. The short-thick rod bolt product with a stepped thick rod in the middle section can be directly obtained through the cold heading process, and the problems that the short-thick rod bolt cold heading die is easily damaged due to large stress and the service life of the die is short in the prior art can be solved.

Description

Technical Field

[0001] This invention relates to the field of new energy vehicle parts manufacturing, specifically to a cold heading mold and process for short, thick rod bolts. Background Technology

[0002] New energy vehicles represent the future development direction of the automotive industry. They not only help reduce environmental pollution and improve energy efficiency, but also bring a more economical and intelligent driving experience. With continuous technological advancements, the market share of new energy vehicles will continue to grow, becoming one of the mainstream modes of transportation. A type of short, thick bolt is required in various applications of new energy vehicles, including battery packs, motors, reducers, suspension systems, transmission systems, and body connections.

[0003] This type of short, thick-rod bolt has a disc-shaped head formed by a pressure plate at one end, and a large-diameter cylindrical thick rod at the root of the other end. The thick rod is relatively short, and the tail is a small-diameter cylindrical thin rod. Finally, threads are machined on the thin rod at the tail. In the existing technology, during the cold-forging process of cap bolts, one end is first reduced to form a thin rod section, and the other end is upset to form a stepped thick rod. Then, in the second, third, and fourth stages, the thin rod section and the stepped thick rod section are gradually upset to the final size. The reduction of the thick rod section and the thin rod section, as well as the pressure plate at the head, are all formed in one step in the fourth stage. Furthermore, the radial structure of the mold needs to have a stepped change. The combination of these three factors results in the mold being subjected to high stress, easily damaged, and having a short service life. Summary of the Invention

[0004] The present invention aims to provide a cold heading die for short and thick bolts to solve the problems of high stress and easy damage to the die and short service life in the cold heading process of short and thick bolts in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a cold heading process for short, thick bolts, comprising the following steps: A. Cutting: Cut the coiled steel into rods of a fixed length. The diameter of the rod is 1.15 times the outer diameter of the short, thick bolt or thin rod. B. First step: On a multi-station cold heading machine, the lower end of the rod is shortened to 0.9 times the outer diameter of the short, thick rod bolt. The middle section of the rod is upset to form a frustum. The minor diameter of the frustum is the same as the lower end diameter. The major diameter of the frustum is 0.94 times the outer diameter of the short, thick rod bolt step. The height of the frustum is 1.42 times the length of the short, thick rod bolt step. The upper end of the rod is upset to form a frustum. C. Second step: Use a multi-station cold heading machine to upset the upper frustum of the rod material into a cylinder with a spherical top surface, upset the middle frustum of the rod material to a height 1.15 times the length of the short, thick rod bolt step, upset the middle frustum of the rod material to a minor diameter 0.94 times the outer diameter of the short, thick rod bolt step, upset the middle frustum of the rod material to a major diameter 0.97 times the outer diameter of the short, thick rod bolt step, keeping the diameter of the lower end of the rod material unchanged; D. In the third step, a multi-station cold heading machine is used to upset the upper cylindrical part of the rod into a hexagonal head. A pressure plate is formed at the root of the hexagonal head. A chamfer is formed between the pressure plate and the middle section frustum of the rod. The middle section frustum is upset to a minor diameter that is 0.96 times the outer diameter of the short, thick rod bolt step. The middle section frustum is upset to a major diameter that is 0.98 times the outer diameter of the short, thick rod bolt step. A chamfer is formed between the minor diameter end of the middle section frustum and the lower end of the rod. E. Fourth step: Use a multi-station cold heading machine to further upset the hexagonal head at the top of the rod and form an inner hexagonal hole in the middle. The pressure plate at the root of the hexagonal head is upset to the forming size. The middle section of the truncated cone is upset to the forming size as a cylindrical step rod of equal diameter. The lower end of the thin rod is shortened to the forming size.

[0006] The principle and advantages of this scheme are as follows: In practical application, the diameter of the rod material is controlled from the beginning of the blanking process. Then, in the first process, the upper and middle sections of the rod material are upset into a frustum. In this way, the radial pressure on the middle forming die is small, and the lower end is shortened. The blanking diameter at the lower end is close to the forming diameter, and the deformation during the shortening process is small. Most of the deformation control can be completed in the first process. Then, in the second process, the upper end of the rod material in the first process is continued to be upset to form a cylinder. In the subsequent hexagonal head forming process, the deformation is reduced and it is easier to form. The frustum in the middle section is further upset and shortened but still maintains the taper. The deformation in the single process is small, and the pressure on the die is small. The shortened part at the lower end remains unchanged, that is, the shortened part at the lower end is not stressed. In this way, the die in the second process only bears the radial deformation pressure at the upper end. The overall force on the die is small, and it is not easy to cause damage to the die in the second process. Then, in the third stage, the lower end of the shrinkage rod remains stress-free. The upper hexagonal head is first upset, and the middle frustum is further upset and shortened while maintaining a taper. The deformation in the third stage is relatively smaller, allowing for smooth forming during cold forging without applying excessive pressure to the mold, thus avoiding mold damage. Finally, in the fourth stage, the hexagonal head, pressure plate, stepped thick rod, and thin rod are upset in one step. The deformation in the fourth stage is significantly reduced compared to existing technologies. In particular, the stepped thick rod is formed through four deformation upsets, while the thin rod remains stress-free. This allows for effective forming while ensuring mold lifespan and effectively avoids mold damage caused by excessive forging pressure required for large deformations.

[0007] A cold heading die for short and thick bolts is used to complete the cold heading process of short and thick bolts. It includes a four-stage lower die, which includes a die sleeve. A shrinking die is installed inside the die sleeve. A C-shaped sleeve is provided inside the die sleeve at the upper end of the shrinking die. A top die is provided inside the C-shaped sleeve. A die plate is provided at the upper end of the top die. A threaded sleeve connects the bottom end of the shrinking die to the die sleeve.

[0008] Preferably, as an improvement, the shrinking die, the top die, and the die plate are all made of cemented carbide.

[0009] Preferably, as an improvement, the C-type sleeve is tapered in shape, and the inner hole at the upper end of the mold sleeve is an inner tapered hole that matches the shape of the C-type sleeve. The C-type sleeve is pressed into the inner tapered hole by the threaded sleeve and the shrinking rod mold.

[0010] The principle and advantages of this scheme are as follows: In practical application, the four-stage molding process is the main process. In the four-stage mold, the mold sleeve serves as an external support. The mold cavity inside the shrinking rod mold, the top mold, and the mold plate forms the molding cavity for the short and thick rod bolt. The shrinking rod mold is used to form the thin rod at the bottom, while the top mold and the mold plate are used to form the stepped thick rod in the middle and the hexagonal head and pressure plate at the top. The C-shaped sleeve is used to fix and guide the rod material, ensuring the correct position of the rod material during cold heading and stable and reliable molding quality. The tapered fit between the C-shaped sleeve and the mold sleeve, as well as the threaded sleeve at the bottom, press and fix the shrinking rod mold, the top mold, and the mold plate, further ensuring the molding quality of the short and thick rod bolt. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the deformation of the rod material during the processing in Embodiment 1 of the present invention.

[0012] Figure 2 This is a schematic diagram of the structure of the fourth-order lower mold in Embodiment 2 of the present invention. Detailed Implementation

[0013] The following detailed description illustrates the specific implementation method: The reference numerals in the accompanying drawings include: mold sleeve 1, C-type sleeve 2, mold piece 3, top mold 4, shrink rod mold 5, and threaded sleeve 6.

[0014] Example 1: A cold heading process for short, thick bolts, combined with... Figure 1 As shown, it includes the following steps: A. Cutting: Cut the coiled steel into rods of a fixed length. The diameter of the rod is 1.15 times the outer diameter of the short, thick bolt or thin rod. B. First step: On a multi-station cold heading machine, the lower end of the rod is shortened to 0.9 times the outer diameter of the short, thick rod bolt. The middle section of the rod is upset to form a frustum. The minor diameter of the frustum is the same as the lower end diameter. The major diameter of the frustum is 0.94 times the outer diameter of the short, thick rod bolt step. The height of the frustum is 1.42 times the length of the short, thick rod bolt step. The upper end of the rod is upset to form a frustum. C. Second step: Use a multi-station cold heading machine to upset the upper frustum of the rod material into a cylinder with a spherical top surface, upset the middle frustum of the rod material to a height 1.15 times the length of the short, thick rod bolt step, upset the middle frustum of the rod material to a minor diameter 0.94 times the outer diameter of the short, thick rod bolt step, upset the middle frustum of the rod material to a major diameter 0.97 times the outer diameter of the short, thick rod bolt step, keeping the diameter of the lower end of the rod material unchanged, and the lower end of the rod material is not subjected to force; D. In the third step, a multi-station cold heading machine is used to upset the upper cylindrical part of the rod into a hexagonal head. A pressure plate is formed at the root of the hexagonal head. A chamfer is formed between the pressure plate and the middle section frustum of the rod. The middle section frustum is upset to a minor diameter that is 0.96 times the outer diameter of the short, thick rod bolt step. The middle section frustum is upset to a major diameter that is 0.98 times the outer diameter of the short, thick rod bolt step. A chamfer is formed between the minor diameter end of the middle section frustum and the lower end of the rod, keeping the diameter of the lower end of the rod unchanged. The lower end of the rod is not subjected to force. E. Fourth step: Use a multi-station cold heading machine to further upset the hexagonal head at the top of the rod and form an inner hexagonal hole in the middle. The pressure plate at the root of the hexagonal head is upset to the forming size. The middle section of the truncated cone is upset to the forming size as a cylindrical step rod of equal diameter. The lower end of the thin rod is shortened to the forming size.

[0015] In the specific implementation process, the diameter of the rod material is controlled from the beginning of the blanking process. Then, in the first process, the upper and middle sections of the rod material are upset into a frustum. In this way, the radial pressure on the middle forming die is small, and the lower end is shortened. The blanking diameter at the lower end is close to the forming diameter, and the deformation during the shortening process is small. Most of the deformation control can be completed in the first process. Then, in the second process, the upper end of the rod material in the first process is continued to be upset to form a cylinder. In the subsequent hexagonal head forming process, the deformation is reduced and it is easier to form. The frustum in the middle section is further upset and shortened but still maintains the taper. The deformation in the single process is small, and the pressure on the die is small. The shortened part at the lower end remains unchanged, that is, the shortened part at the lower end is not stressed. In this way, the die in the second process only bears the radial deformation pressure at the upper end. The overall force on the die is small, and it is not easy to cause damage to the die in the second process. Then, in the third stage, the lower end of the shrinkage rod remains stress-free. The upper hexagonal head is first upset, and the middle frustum is further upset and shortened while maintaining a taper. The deformation in the third stage is relatively smaller, allowing for smooth forming during cold forging without applying excessive pressure to the mold, thus avoiding mold damage. Finally, in the fourth stage, the hexagonal head, pressure plate, stepped thick rod, and thin rod are upset in one step. The deformation in the fourth stage is significantly reduced compared to existing technologies. In particular, the stepped thick rod is formed through four deformation upsets, while the thin rod remains stress-free. This allows for effective forming while ensuring mold lifespan and effectively avoids mold damage caused by excessive forging pressure required for large deformations.

[0016] Example 2: Cold heading die for short, thick bolts, used to complete the cold heading process of short, thick bolts. It includes a first-stage die, a second-stage die, a third-stage die, and a fourth-stage die. The first-stage die includes a first-stage lower die, which includes a first-stage rod-shrinking die. The first-stage rod-shrinking die's cavity includes a conical rod cavity and a straight rod cavity. The conical rod cavity is used to form the frustum of the middle section of the bolt, and the straight rod cavity is used to complete the rod-shrinking at the lower end. The second-stage die includes a second-stage lower die, whose cavity includes a second-stage conical rod cavity and a second-stage straight rod cavity. The second-stage conical rod cavity is used to further upset the frustum of the middle section of the bolt. The second-stage straight rod cavity has the same inner diameter as the straight rod cavity of the first-stage lower die, used to keep the thinner end of the bolt from being stressed during the second-stage cold heading process. The lower die of the third-stage die has a similar structure to the second-stage lower die, but with dimensional changes, allowing for further upseting of the frustum of the middle section, while the thinner end of the bolt remains stress-free through the straight rod cavity. The four-stage mold includes a four-stage upper mold and a four-stage lower mold, such as Figure 2 As shown, the fourth-order lower mold includes a mold sleeve 1, a shrinking rod mold 5 installed inside the mold sleeve 1, a C-shaped sleeve 2 inside the mold sleeve 1 at the upper end of the shrinking rod mold 5, a top mold 4 inside the C-shaped sleeve 2, a mold plate 3 at the upper end of the top mold 4, and a threaded sleeve 6 connecting the bottom end of the shrinking rod mold 5 to the mold sleeve 1. The shrinking rod mold 5, the top mold 4, and the mold plate 3 of the fourth order are all made of cemented carbide. The C-shaped sleeve 2 is conical in shape, and the inner hole at the upper end of the mold sleeve 1 is an inner conical hole that matches the shape of the C-shaped sleeve 2. The C-shaped sleeve 2 is pressed into the inner conical hole by the threaded sleeve 6 and the shrinking rod mold 5.

[0017] In the specific implementation process, the traditional first-stage mold directly forms a frustum at the top of the rod, then forms a cylindrical section in the middle, and a thin rod at the bottom. The second stage then upsets the top frustum into a spherical cylinder, and upsets the middle cylinder to shorten it. The third and fourth stages continue to upset in the same way. In this way, the middle section is always upset as a cylinder, and the middle and bottom of the rod are always under stress. Especially in the fourth stage, the deformation is large, so the mold from the second to the fourth stage is under great stress. In particular, the step transition between the middle section and the bottom thin rod has a large and concentrated stress, which can easily cause mold damage. In the schemes of Examples 1 and 2, in the first process, the lower end of the rod is shortened into a thinner rod, and the middle section is upset into a frustum shape. This reduces the stress on the mold between the frustum and the thinner rod. In the second process, the thinner rod is kept stress-free, and the frustum in the middle section is continued to be upset, increasing the diameter and shortening the length of the frustum. A chamfer is used between the frustum and the thinner rod to reduce pressure concentration. In the third process, the same method as the second process is used, keeping the thinner rod stress-free, further upsetting the frustum in the middle section, maintaining the chamfer transition between the frustum and the thinner rod, and completing the initial shaping of the hexagonal head at the top. After the third process, The middle section frustum and the top hexagonal structure are close to the forming dimensions. In the fourth process, the middle section frustum is directly upset into a stepped thick rod. After the third process, the frustum is flattened at the chamfered transition part during the fourth process to form a stepped surface. This makes the mold more reasonably stressed and less prone to damage during cold heading, thus extending the mold's service life. This mold combination, combined with the corresponding cold heading forming process, can directly cold-head short and thick rod bolts. The mold structure is reasonably designed and is not prone to damage during use, enabling long-term production of short and thick rod bolts to meet production needs.

[0018] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A cold heading process for short, thick bolts, characterized in that: Includes the following steps: A. Cutting: Cut the coiled steel into rods of a fixed length. The diameter of the rod is 1.15 times the outer diameter of the short, thick bolt or thin rod. B. First step: On a multi-station cold heading machine, the lower end of the rod is shortened to 0.9 times the outer diameter of the short, thick rod bolt. The middle section of the rod is upset to form a frustum. The minor diameter of the frustum is the same as the lower end diameter. The major diameter of the frustum is 0.94 times the outer diameter of the short, thick rod bolt step. The height of the frustum is 1.42 times the length of the short, thick rod bolt step. The upper end of the rod is upset to form a frustum. C. Second step: Use a multi-station cold heading machine to upset the upper frustum of the rod material into a cylinder with a spherical top surface, upset the middle frustum of the rod material to a height 1.15 times the length of the short, thick rod bolt step, upset the middle frustum of the rod material to a minor diameter 0.94 times the outer diameter of the short, thick rod bolt step, upset the middle frustum of the rod material to a major diameter 0.97 times the outer diameter of the short, thick rod bolt step, keeping the diameter of the lower end of the rod material unchanged; D. In the third step, a multi-station cold heading machine is used to upset the upper cylindrical part of the rod into a hexagonal head. A pressure plate is formed at the root of the hexagonal head. A chamfer is formed between the pressure plate and the middle section frustum of the rod. The middle section frustum is upset to a minor diameter that is 0.96 times the outer diameter of the short, thick rod bolt step. The middle section frustum is upset to a major diameter that is 0.98 times the outer diameter of the short, thick rod bolt step. A chamfer is formed between the minor diameter end of the middle section frustum and the lower end of the rod. E. Fourth step: Use a multi-station cold heading machine to further upset the hexagonal head at the top of the rod and form an inner hexagonal hole in the middle. The pressure plate at the root of the hexagonal head is upset to the forming size. The middle section of the truncated cone is upset to the forming size as a cylindrical step rod of equal diameter. The lower end of the thin rod is upset to the forming size.

2. A cold heading die for short, thick bolts, characterized in that: The process for cold heading of a short, thick bolt as claimed in claim 1 includes a four-stage lower die, which includes a die sleeve, a shrinking die installed inside the die sleeve, a C-shaped sleeve inside the die sleeve at the upper end of the shrinking die, a top die inside the C-shaped sleeve, a die plate at the upper end of the top die, and a threaded sleeve connecting the bottom end of the shrinking die to the die sleeve.

3. The cold heading die for short, thick bolts according to claim 2, characterized in that: The shrinking rod mold, top mold, and mold plate are all made of cemented carbide.

4. The cold heading die for short, thick bolts according to claim 3, characterized in that: The C-shaped sleeve has a conical shape, and the inner hole at the upper end of the mold sleeve is an inner conical hole that matches the shape of the C-shaped sleeve. The C-shaped sleeve is pressed into the inner conical hole by the threaded sleeve and the shrinking rod mold.

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