Forming process of short half-tooth flange face hexagonal bolt

Abstract

This invention discloses a forming process for short-tooth flange hexagonal bolts, comprising six steps: blanking, primary pre-deformation, secondary pre-deformation, shrinkage extrusion, nut forming, and single-diameter reduction. The primary pre-deformation processes the end of the blank into a conical truncated cone, the secondary pre-deformation processes the end into a spherical cylinder, followed by shrinkage extrusion and nut forming, and finally, bolt forming. Compared with traditional processes, this method separates nut forming from bolt forming, significantly reducing the overall external stress and internal stress concentration of the mold, thereby reducing the requirements for mold materials and structure, effectively improving mold lifespan, reducing the risk of mold bulging during operation, and saving production costs.

Description

Technical Field

[0001] This invention relates to the field of fastener manufacturing, and in particular to a forming process for short half-thread flange face hexagonal bolts. Background Technology

[0002] The production of short-thread flange hexagonal bolts has always been a challenge for fastener manufacturers. The traditional production process involves a four-station cold heading process, including head conical stamping, head cylindrical stamping, hexagonal reduction, and integrated forming of the nut and screw. In the final step, nut forming and screw diameter reduction are performed simultaneously in a single mold. This results in significant stress on the mold, leading to irreversible deformation damage, affecting performance and lifespan, and frequently causing mold cracking during cold heading, severely impacting product quality and increasing production costs. Current solutions involve modifying existing molds to improve precision, reduce clearance between stations, increase preload, add vents, improve wire lubrication, and reduce wire hardness. However, these methods fail to fundamentally solve the mold cracking problem, and adding vents can further affect the mold structure. Therefore, a comprehensive process optimization approach is needed to improve product quality and extend mold lifespan. Summary of the Invention

[0003] The main technical problem solved by this invention is to provide a short half-thread flange face hexagonal bolt forming process, which can reduce the requirements for molds, increase the service life of molds, and improve product quality.

[0004] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: to provide a short half-thread flange face hexagonal bolt forming process, characterized in that the short half-thread flange face hexagonal bolt forming process includes the following:

[0005] Step 1: Cutting: Select the corresponding diameter of the coil material according to the bolt specifications and cut it into blanks;

[0006] The second step is pre-deformation: According to the processing requirements, the end of the billet is punched using a conical heading die to pre-process the end face into a conical truncated body. At the same time, the billet rod is upset once.

[0007] The third step is secondary pre-deformation: According to the processing requirements, the head of the billet is further stamped using a ball-forming die to form a head cylinder, and the end face of the cylinder is squeezed into a spherical surface by upsetting. At the same time, the billet rod is subjected to secondary upsetting.

[0008] Step 4: Extrusion: According to the processing requirements, the upper part of the cylindrical head of the billet is extruded into a hexagonal prism using an extrusion die. A conical transition slope is formed between the remaining part of the cylindrical head and the hexagonal prism. At the same time as extrusion, the billet rod is upset three times.

[0009] Step 5: According to the processing requirements, use a stamping die to stamp the hexagonal prism and the lower part of the head cylinder at the same time. While extruding the remaining part of the head cylinder into a flange surface, the top surface of the hexagonal prism is corrected. At the same time, the billet rod is upset four times, and the bottom end of the rod is upset and chamfered.

[0010] Step 6: Diameter reduction: According to the processing requirements, the semi-finished blank obtained in step 4 is added to a special single diameter reduction mold and upset to obtain the finished short half-thread flange face hexagonal bolt.

[0011] In a preferred embodiment of the present invention, the diameter of the coil selected in the first step is smaller than the diameter of the smooth part of the finished short half-thread flange hexagonal bolt, and larger than the diameter of the threaded part of the finished short half-thread flange hexagonal bolt.

[0012] In a preferred embodiment of the present invention, the total deformation of the billet rod during the first and second upsetting processes is no greater than 0.05 mm.

[0013] In a preferred embodiment of the present invention, the deformation of the billet rod diameter during both the third and fourth upsetting processes does not exceed 0.03 mm.

[0014] In a preferred embodiment of the present invention, the single-diameter reduction die includes an upper die and a lower die, wherein the upper die and the lower die do not directly contact each other during cold heading. The upper die includes an upper die sleeve and an upper die core, the upper die sleeve being fitted outside the upper die core. The upper die core has a nut cavity matching the nut profile of the workpiece to be processed, the height of the nut cavity being greater than the height of the workpiece nut. A flange pushing surface matching the profile of the workpiece to be processed is provided at the opening of the nut cavity. The lower die includes a lower die sleeve and a lower die core, the lower die sleeve being fitted outside the lower die core. A forming cavity is provided in the middle of the lower die core, and a diameter reduction section is provided within the forming cavity, dividing the forming cavity into an upper screw guiding area and a lower screw forming area. The minimum distance between the bottom surface of the upper die and the top surface of the lower die during upsetting is 0.5~0.9mm. An alloy washer is installed between the upper surface of the upper die core and the upper die sleeve.

[0015] The beneficial effects of this invention are as follows: Through process optimization, this invention decomposes the last step of the traditional four-station cold heading forming process for short half-thread flange hexagonal bolt forming mold into two steps: nut and flange forming and rod diameter reduction, transforming it into a five-station cold heading forming process. From a stress analysis perspective, the tonnage force on each station is significantly reduced. In particular, the single forming stress of the last two stations is reduced by more than 30% compared to the traditional one-station forming process, as measured by actual tests. The internal stress of the mold is significantly reduced, and the requirements for the material and structural strength of the mold used in the last two stations are also significantly reduced. This not only effectively reduces the risk of cold heading mold cracking but also improves the service life of the mold and saves production costs. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the step-by-step bolt forming process in a preferred embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram of the single diameter reduction mold structure used in the diameter reduction process of this invention;

[0018] The components in the attached diagram are labeled as follows:

[0019] 1. Workpiece; 2. Upper mold; 3. Lower mold;

[0020] 201. Upper mold sleeve; 202. Upper mold core; 203. Alloy washer; 204. Nut cavity;

[0021] 301. Lower mold sleeve, 302. Lower mold core, 303. Reduction section, 304. Guide area, 305. Forming area. Detailed Implementation

[0022] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0023] Please see Figure 1 The embodiments of the present invention include:

[0024] A forming process for short-thread flange face hexagonal bolts, the forming method of which includes the following:

[0025] Step 1: Cutting: Select the corresponding diameter of the coil material according to the bolt specifications and cut it into blanks;

[0026] The second step is pre-deformation: According to the processing requirements, the end of the billet is punched using a conical heading die to pre-process the end face into a conical truncated body. At the same time, the billet rod is upset once.

[0027] The third step is secondary pre-deformation: According to the processing requirements, the head of the billet is further stamped using a ball-forming die to form a head cylinder, and the end face of the cylinder is squeezed into a spherical surface by upsetting. At the same time, the billet rod is subjected to secondary upsetting.

[0028] Step 4: Extrusion: According to the processing requirements, the upper part of the cylindrical head of the billet is extruded into a hexagonal prism using an extrusion die. A conical transition slope is formed between the remaining part of the cylindrical head and the hexagonal prism. At the same time as extrusion, the billet rod is upset.

[0029] Step 5: According to the processing requirements, use a stamping die to stamp the hexagonal prism and the lower part of the head cylinder at the same time. While extruding the remaining part of the head cylinder into a flange surface, the top surface of the hexagonal prism is corrected. At the same time, the billet rod is upset and the bottom end of the rod is upset and chamfered.

[0030] Step 6: Diameter reduction: According to the processing requirements, the semi-finished blank obtained in step 4 is added to a special single diameter reduction mold and upset to obtain the finished short half-thread flange face hexagonal bolt.

[0031] In the above process steps, the short half-thread flange hexagonal bolts undergo a total of 5 upsetting processes from blank to final forming. In the first step of blanking, a coil of material with a diameter between the diameter of the smooth shank and the diameter of the threaded section is selected according to the bolt specifications and cut into blanks to reduce the difficulty of subsequent processing.

[0032] According to the above process, for a short-threaded flange hexagonal bolt with a shank diameter of 6mm and a threaded section diameter of 5.24mm, a 5.8mm diameter coil is selected for the first blanking step. In the second step, the blank diameter deformation is selected as 0.01mm during the first upsetting, 0.03mm during the second upsetting, 0.02mm during the third upsetting, and 0.02mm during the fourth upsetting. The final diameter reaches 5.88mm after four upsetting steps, and finally, a diameter reduction process achieves the required 5.24mm. This processing method results in minimal overall deformation, ensuring the final strength of the bolt shank while minimizing the working pressure during the final diameter reduction process, thereby extending the mold's service life.

[0033] Appendix Figure 2The diagram shows a special single-diameter reduction die structure redesigned based on the above process optimization. The single-diameter reduction die includes an upper die 2 and a lower die 3. During cold heading, the upper die 2 and the lower die 3 do not directly contact each other. The minimum distance between the bottom surface of the upper die 2 and the top surface of the lower die 3 during heading is 0.5~0.9mm. The upper die 2 includes an upper die sleeve 201 and an upper die core 202. The upper die sleeve 201 is fitted on the outside of the upper die core 202. An alloy washer 203 is installed between the upper surface of the upper die core 202 and the upper die sleeve 201. The upper mold core 202 is provided with a nut cavity 204 that matches the nut contour of the workpiece 1 to be processed. The height of the nut cavity 204 is greater than the nut height of the workpiece 1. The opening of the nut cavity 204 is provided with a flange pushing surface that matches the contour of the workpiece 1 to be processed. The lower mold 3 includes a lower mold sleeve 301 and a lower mold core 302. The lower mold sleeve 301 is sleeved on the outside of the lower mold core 302. A forming cavity is provided in the middle of the lower mold core 302. A reducing section 303 is provided in the forming cavity. The reducing section 303 divides the forming cavity into an upper screw guide area 304 and a lower screw forming area 305.

[0034] Since the nut forming and diameter reduction are divided into two steps, the dedicated single diameter reduction die can be designed as the aforementioned split upper and lower parts. This way, during the downward extrusion of the diameter reduction die by the upper die 2, the naturally occurring air gap solves the venting problem in traditional dies. It avoids the impact on structural strength caused by vent holes and also prevents vent blockage, effectively improving the die's durability. Furthermore, due to the step-by-step process design, the overall stress is smaller compared to traditional methods; the overall stress is reduced by approximately 30% during single diameter reduction. Therefore, during upsetting, the entire die can be extruded through the flange extrusion surface. When workpiece 1 is placed, the support surface does not directly contact the top surface of the die, reducing stress concentration points and thus preventing stress concentration from damaging the internal structure of the die, further reducing the risk of die cracking.

[0035] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A forming process for short-tooth flange face hexagonal bolts, characterized in that, The forming process for the short-tooth flange face hexagonal bolts includes the following: Step 1: Cutting: Select the corresponding diameter of the coil material according to the bolt specifications and cut it into blanks; The second step is pre-deformation: According to the processing requirements, the end of the billet is punched using a conical heading die to pre-process the end face into a conical truncated body. At the same time, the billet rod is upset once. The third step is secondary pre-deformation: According to the processing requirements, the head of the billet is further stamped using a ball-forming die to form a head cylinder, and the end face of the cylinder is squeezed into a spherical surface by upsetting. At the same time, the billet rod is subjected to secondary upsetting. Step 4: Extrusion: According to the processing requirements, the upper part of the cylindrical head of the billet is extruded into a hexagonal prism using an extrusion die. A conical transition slope is formed between the remaining part of the cylindrical head and the hexagonal prism. At the same time as extrusion, the billet rod is upset three times. Step 5: According to the processing requirements, use a stamping die to stamp the hexagonal prism and the lower part of the head cylinder at the same time. While extruding the remaining part of the head cylinder into a flange surface, the top surface of the hexagonal prism is corrected. At the same time, the billet rod is upset four times, and the bottom end of the rod is upset and chamfered. Step 6: Drilling: According to the processing requirements, the semi-finished blank obtained in step 5 is added to a special single-drilling die and upset to obtain the finished short half-thread flange face hexagonal bolt; The single-diameter reduction die includes an upper die and a lower die. During cold heading, the upper die and the lower die do not directly contact each other. The minimum distance between the bottom surface of the upper die and the top surface of the lower die during heading is 0.5 to 0.9 mm. The upper die includes an upper die sleeve and an upper die core. The upper die sleeve is fitted outside the upper die core. The upper die core has a nut cavity that matches the nut profile of the workpiece to be processed. The height of the nut cavity is greater than the height of the workpiece nut. The opening of the nut cavity has a flange pushing surface that matches the profile of the workpiece to be processed. An alloy washer is installed between the upper surface of the upper die core and the upper die sleeve. The lower die includes a lower die sleeve and a lower die core. The lower die sleeve is fitted outside the lower die core. The lower die core has a forming cavity in the middle. The forming cavity has a diameter reduction section that divides the forming cavity into an upper screw guiding area and a lower screw forming area.

2. The short half-thread flange face hexagonal bolt forming process according to claim 1, characterized in that, In the first step, the diameter of the selected coil is smaller than the diameter of the smooth shank of the finished short half-thread flange hexagonal bolt, while the diameter of the threaded portion of the finished short half-thread flange hexagonal bolt is larger.

3. The short half-thread flange face hexagonal bolt forming process according to claim 2, characterized in that, The total deformation of the billet rod during the first and second upsetting processes shall not exceed 0.05 mm.

4. The short half-thread flange face hexagonal bolt forming process according to claim 1, characterized in that, The deformation of the billet rod diameter during both the third and fourth upsetting processes does not exceed 0.03 mm.

Images