Production process of elbow expansion bolt

Abstract

The invention provides a production process of an elbow expansion bolt, which relates to the technical field of bolt production and realizes efficient production and quality improvement of the elbow expansion bolt through the steps of multi-station cold heading forming, high-precision thread rolling, gradient heat treatment, environment-friendly electroplating, intelligent detection and the like. An ML08 material wire is adopted to synchronously complete head pre-forming, bent part forming and rib position pressing through a three-station cold header, the key size is controlled in cooperation with a Cr12MoV alloy steel mold, stress is eliminated through gradient heat treatment staged heating, the rod strength is improved to 8.8 grade, a zinc-nickel alloy coating is adopted for environment-friendly electroplating in combination with ultrasonic pickling, the coating thickness is larger than or equal to 8 micrometers, and the thickness of the coating is larger than or equal to 8 micrometers. No white rust exists in 72 hours of salt spray test, no red rust exists in 120 hours of salt spray test, and intelligent tail cutting is combined with visual positioning and magnetic powder inspection, so that the tail precision and no crack defect are ensured. Gradient heat treatment realizes mechanical property optimization, environment-friendly electroplating enhances corrosion resistance, and intelligent detection guarantees product consistency.

Description

Technical Field

[0001] The invention belongs to the technical field of bolt production, and more specifically, relates to a production process of an elbow expansion bolt. Background Art

[0002] In the fields of construction, machinery, equipment installation, etc., elbow expansion bolts are key connectors and are widely used to fix structures such as walls and ceilings. Their quality directly affects the safety and reliability of the project. The existing production process of elbow expansion bolts mainly has the following technical bottlenecks:

[0003] Traditional production processes mostly use single-station cold heading, which makes it difficult to simultaneously complete complex structural processing such as elbow bending and head rib pressing. This results in low production efficiency (long single-station forming time) and insufficient dimensional accuracy (such as large bending angle deviation and uneven rib distribution). At the same time, mold materials have poor wear resistance (such as ordinary carbon steel molds) and need to be replaced frequently, increasing production costs. In addition, traditional processes have high requirements for the cold heading adaptability of wire materials and lack a systematic solution for the forming control of low-carbon steels such as ML08, which is prone to defects such as head cracking and rod deformation.

[0004] Existing heat treatments often rely on a single temperature hold, which simply eliminates cold heading stresses and fails to specifically improve shank strength and head toughness. For example, conventional processes only achieve a 4.8-grade strength for bolt shanks, failing to meet the high-strength requirements of heavy equipment installation. Furthermore, the lack of differentiated hardness control for the head, bend, and threaded section results in uneven overall mechanical properties, making the bend susceptible to fracture due to stress concentration.

[0005] Traditional electroplating processes generally use pure zinc coatings, resulting in uneven coating thickness. Red rust appears after 48 hours of salt spray testing, and the coating is susceptible to corrosion and failure in humid, acidic, and alkaline environments. Furthermore, pre-plating treatment relies on manual pickling, which incompletely removes scale and lacks efficient cleaning techniques such as ultrasonic waves. This results in poor coating adhesion and easy peeling. Furthermore, traditional processes lack the addition of brighteners, resulting in a rough coating surface. Both the appearance quality and corrosion resistance require improvement.

[0006] In traditional production, tail cutting relies on manual positioning, resulting in large errors in verticality and incomplete removal of tail burrs, which affects installation accuracy and safety. Dimensional inspection often uses tools such as vernier calipers, but the accuracy of key parameters such as the head bend angle and thread pitch diameter is insufficient, making it difficult to ensure product consistency. The packaging process lacks moisture-proofing measures and a quality traceability system, making bolts prone to rusting during storage. When quality issues arise, it is difficult to trace production batches and process parameters.

[0007] Traditional cold heading dies consume large quantities of material, and the disposal of used dies results in a waste of resources. The electroplating process uses highly polluting hexavalent chromium and other plating solutions, which do not meet the requirements of modern green manufacturing. Furthermore, low yield rates and high testing costs result in poor overall production costs.

[0008] To address these challenges, the existing technology urgently needs a high-precision, high-strength, long-life, and environmentally friendly production process for elbow expansion bolts. This invention systematically addresses the shortcomings of traditional processes in forming accuracy, mechanical properties, corrosion resistance, and production efficiency through multi-station cold heading, gradient heat treatment, environmentally friendly electroplating, and intelligent detection technology. This meets the stringent fastener requirements of high-end engineering and promotes the industry's development towards intelligent and green manufacturing. Summary of the Invention

[0009] In order to solve the above technical problems, the present invention provides a production process of an elbow expansion bolt to solve the above problems.

[0010] A production process for an elbow expansion bolt comprises the following steps:

[0011] S1: Multi-station cold heading: Using ML08 material φ8.30 wire, a three-station cold heading machine is used to complete the head pre-forming, bending part forming and rib pressing in sequence. During the head forming, four evenly distributed small ribs are pressed simultaneously (single rib height 0.15±0.05mm, width 0.3±0.05mm), the straight length of the bending part is controlled to 32.00±0.20mm, the head bending angle is 65°±1.5°, and the bend radius is R3.00±0.50mm;

[0012] S2: High-precision thread rolling process: Use high-precision tungsten carbide dies (accuracy ±0.03mm) to roll the rod to form an M8×1.25 external thread with a thread surface roughness of Ra≤1.6μm and a thread length of 118.00±2.00mm. At the same time, a guide chamfer R0.50±0.10mm is processed at the starting end of the thread.

[0013] S3: Gradient heat treatment: Heat treatment is carried out in a box-type resistance furnace, with two stages of heating (the first stage is 500-600℃ for 20 minutes, and the second stage is 850-900℃ for 40 minutes). The steel is then cooled to 200℃ in the furnace and then air-cooled to eliminate cold heading stress and improve the strength of the rod to level 8.8.

[0014] S4: Environmentally friendly electroplating process: Ultrasonic pickling (oxalic acid solution concentration 5-8%, temperature 50-60°C) is used to remove surface oxide scale before electroplating. Zinc-nickel alloy plating (zinc content 85-90%) is used for electroplating. The coating thickness is ≥8μm. Salt spray test shows no white rust for 72 hours and no red rust for 120 hours.

[0015] S5: Intelligent tail cutting and inspection: The tail cutting position is located by the visual inspection system. The verticality error between the tail cutting end face and the bolt axis is ≤0.3°, and the tail length is 25.00±1.00mm. At the same time, magnetic particle inspection is performed on each bolt to eliminate products with surface cracks.

[0016] Preferably, in the multi-station cold heading forming step, the mold is made of Cr12MoV alloy steel (hardness HRC58-62), the first station forming pressure is 60-70 tons, and the bending station pressure is 80-90 tons, ensuring the dimensional accuracy of the head thickness of 9.00±0.20mm and the rod diameter of 7.00±0.20mm.

[0017] Preferably, in the high-precision thread rolling process, the thread plate speed is controlled at 150-200 r / min, the thread rolling feed is 0.5-0.8 mm / revolution, and the pressure is adjusted in real time by the servo motor to avoid thread profile distortion.

[0018] Preferably, after the gradient heat treatment step, the bolt is subjected to Rockwell hardness testing (testing points: head, bend, thread section), and the hardness value must meet HRC28-32 for the head and HRC32-36 for the shank.

[0019] Preferably, in the environmentally friendly electroplating process, 0.1-0.3 g / L of polyethylene glycol is added to the electroplating solution as a brightener, and uniform zinc flowers are formed on the surface of the coating, thereby improving the corrosion resistance and appearance quality.

[0020] Preferably, in the intelligent tail cutting step, a high-speed rotary cutting knife (rotation speed 3000-4000 r / min) is used, and the tail is deburred after cutting to ensure that the surface roughness Ra ≤ 3.2 μm.

[0021] Preferably, a double R chamfer (R3.63±0.50mm and R1.25±0.20mm) is provided in the transition area between the head and the stem of the elbow expansion bolt, and the bolt is formed in one step by a cold heading die to reduce stress concentration.

[0022] Preferably, during the rib pressing process, four anti-slip ribs are formed synchronously through the protruding structure of the mold cavity, and the ribs are evenly distributed along the circumference of the head to enhance the tightness of the fit between the bolt and the expansion sleeve.

[0023] Preferably, in the packaging step, a moisture-proof aluminum film bag is used for packaging, a humidity indicator is built in (changes color when humidity is greater than 20%), and a unique traceability code is attached. By scanning the code, the salt spray test data and heat treatment curve of the batch of bolts can be queried.

[0024] Preferably, the key dimensions of the elbow expansion bolts are detected using a three-coordinate measuring machine, and the detection accuracy of parameters such as the head bending angle, thread diameter, and rod straightness is ≤0.05mm to ensure product consistency.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] In the present invention, a multi-station cold heading machine is used to simultaneously complete the head preforming, bending part forming and rib pressing. Combined with high-precision molds and pressure control, the forming efficiency and dimensional accuracy are significantly improved, solving the problems of low efficiency and poor accuracy of traditional single-station forming, and ensuring the consistency of key parameters such as elbow angle and rib size.

[0027] In the present invention, a gradient heat treatment process is adopted to increase the temperature in stages to eliminate cold heading stress and improve the strength of the rod to level 8.8. At the same time, the hardness distribution of the head and the rod is controlled to enhance the overall fatigue resistance and load capacity of the bolt to meet the needs of high-strength engineering applications.

[0028] In the present invention, the environmentally friendly electroplating process uses zinc-nickel alloy plating instead of traditional pure zinc, combined with ultrasonic pickling pre-treatment, the plating layer is uniform and dense, the rust-free time in the salt spray test is greatly extended, and the service life of the bolts in humid and highly corrosive environments is effectively improved, which is in line with the green manufacturing trend.

[0029] In the present invention, through intelligent detection technologies such as visual positioning, magnetic particle inspection and three-coordinate measuring instrument, high-precision control of tail cutting and elimination of surface defects are achieved, ensuring the accuracy of key dimensions and the absence of crack defects, greatly reducing the defective rate, and improving product reliability and consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0031] Figure 2 It is a schematic diagram of the multi-station cold heading forming step in the present invention;

[0032] Figure 3 It is a schematic diagram of the high-precision thread rolling process of the present invention;

[0033] Figure 4 is a schematic diagram of the gradient heat treatment in the present invention;

[0034] Figure 5 It is a schematic diagram of the process of intelligent tail cutting and detection in the present invention. DETAILED DESCRIPTION

[0035] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0036] See also Figure 1-Figure 5The present invention provides a production process for elbow expansion bolts. The process primarily includes multi-station cold heading, high-precision thread rolling, gradient heat treatment, environmentally friendly electroplating, intelligent tail cutting and testing, and packaging. These interrelated steps collectively ensure the high quality and performance of the elbow expansion bolts.

[0037] Specific implementation steps:

[0038] (1) Multi-station cold heading forming:

[0039] 1. Raw material selection:

[0040] ML08 φ8.30 wire rod is selected as the raw material. ML08 is a high-quality carbon structural steel with good cold heading and processing properties, which can meet the production requirements of elbow expansion bolts. Its chemical composition and mechanical properties are shown in the following table:

[0041] Chemical composition (%) C Si Mn S P content ≤0.10 ≤0.03 0.25-0.50 ≤0.035 ≤0.035

[0042] Mechanical properties Tensile strength (MPa) Yield strength (MPa) Elongation (%) Sectional shrinkage (%) Numerical ≥325 ≥195 ≥33 ≥60

[0043] 2. Multi-station cold heading machine operation:

[0044] A three-station cold heading machine is used to sequentially complete the head preforming, bending part forming and rib pressing. The main parameters of the cold heading machine are set as follows:

[0045] First-stage forming: A Cr12MoV alloy steel mold (hardness HRC 58-62) is used, with a forming pressure controlled at 60-70 tons. This mold's high hardness, strength, and excellent wear resistance ensure precision and quality in head forming. At this first stage, the wire is initially machined into the approximate shape of the bolt head, preparing for subsequent forming steps.

[0046] Bending: This station also utilizes Cr12MoV alloy steel dies, with pressure increased to 80-90 tons. By precisely controlling the die shape and pressure, the bent portion of the bolt is formed, with a straight length of 32.00 ± 0.20 mm. The bending angle is controlled at 65° ± 1.5°, with a corner radius of 3.00 ± 0.50 mm. To ensure these dimensional accuracies, the cold heading machine is equipped with high-precision sensors and control systems to monitor and adjust parameters during the forming process in real time.

[0047] Rib Forming: Simultaneously with head molding, four evenly spaced small ribs are formed. Each rib is 0.15 ± 0.05 mm high and 0.3 ± 0.05 mm wide. These ribs are formed in one step through the raised structure of the mold cavity, enhancing the tightness of the bolt and expansion sleeve.

[0048] 3. Dimensional accuracy control:

[0049] By strictly controlling the cold heading machine parameters and die precision, we ensure that the head thickness is 9.00 ± 0.20 mm and the shaft diameter is 7.00 ± 0.20 mm. During the production process, dimensional inspections are performed every certain number of products, using measuring tools such as vernier calipers and micrometers to ensure that dimensional deviations are within the allowable range. If dimensional deviations are found to be outside the specified range, the cold heading machine parameters are adjusted or the die is replaced.

[0050] (2) High-precision thread rolling process:

[0051] 1. Tooth plate selection:

[0052] Use high-precision tungsten carbide dies (accuracy ±0.03mm) to roll the rod. Tungsten carbide dies have high hardness, high wear resistance and good corrosion resistance, which can ensure the accuracy and surface quality of the rolled threads. The main technical parameters of the dies are as follows:

[0053]

[0054] 2. Setting of thread rolling process parameters:

[0055] Die plate speed: Controlled between 150-200 rpm. A suitable speed ensures thread forming quality and production efficiency. Too fast a speed may increase thread surface roughness and even cause tooth profile distortion; too slow a speed may reduce production efficiency.

[0056] Thread rolling feed: Set to 0.5-0.8mm / revolution. The feed rate directly affects the thread pitch and profile height. By precisely controlling the feed rate, the threaded end is guaranteed to be an M8×1.25 external thread with a surface roughness of Ra ≤ 1.6μm and a thread length of 118.00±2.00mm.

[0057] Pressure Adjustment: A servo motor adjusts pressure in real time to prevent thread profile distortion. During the thread rolling process, pressure can vary due to factors such as material deformation and friction. The servo motor adjusts pressure based on actual conditions to ensure thread quality.

[0058] 3. Guide chamfering processing:

[0059] A guide chamfer of R0.50±0.10mm is machined at the thread start. This chamfer facilitates bolt installation and removal, reducing resistance during installation. A dedicated chamfering tool is used to ensure dimensional accuracy and surface quality.

[0060] (3) Gradient heat treatment:

[0061] 1. Heat treatment equipment:

[0062] A box-type resistance furnace is used for heat treatment. The box-type resistance furnace has the characteristics of uniform temperature and high temperature control accuracy, which can meet the requirements of gradient heat treatment. Its main technical parameters are as follows:

[0063]

[0064] 2. Gradient heating process:

[0065] The first stage of heating: The bolts are placed in a box-type resistance furnace and heated to 500-600°C at a certain heating rate (for example, 10°C / min) and kept at this temperature for 20 minutes. The purpose of this stage is to eliminate the internal stress generated during the cold heading process and prepare for the subsequent high-temperature treatment.

[0066] The second stage of heating: continue to heat up to 850-900℃ and keep it at this temperature for 40 minutes. In this temperature range, the structure of the bolt changes, which can improve the strength and hardness of the rod.

[0067] 3. Cooling process:

[0068] The bolts are then cooled in the furnace to 200°C and then air-cooled. This cooling method ensures uniform bolt structure and avoids defects such as cracks caused by excessive cooling. Through gradient heat treatment, the bolt shank strength can be increased to grade 8.8, meeting the requirements of most projects.

[0069] 4. Hardness test:

[0070] After heat treatment, the bolts are tested for Rockwell hardness. Test points include the head, bend, and threaded section. Hardness values ​​must meet HRC 28-32 for the head and HRC 32-36 for the shank. Testing is performed using a Rockwell hardness tester. Each test point is measured at least three times, and the average result is taken as the final result. If the hardness value does not meet the requirements, the heat treatment process parameters must be readjusted.

[0071] (4) Environmentally friendly electroplating process:

[0072] 1. Electroplating pre-treatment:

[0073] Ultrasonic pickling: Ultrasonic pickling is used to remove surface scale before electroplating. Place the bolt in an oxalic acid solution (5-8% concentration, 50-60°C) while turning on the ultrasonic generator. The cavitation effect of ultrasound accelerates scale removal and improves the pickling effect. The pickling time depends on the thickness of the bolt's surface scale and is generally 5-10 minutes.

[0074] Cleaning: After pickling, rinse the bolts with clean water to remove surface acid and impurities. Then, perform a neutralization treatment by placing the bolts in a weak alkaline solution to neutralize any residual acid. Finally, rinse again with clean water to ensure the bolt surface is clean and free of impurities.

[0075] 2. Electroplating process:

[0076] Electroplating solution formula: A zinc-nickel alloy coating is used, with a zinc content of 85-90%. Polyethylene glycol (0.1-0.3 g / L) is added to the plating solution as a brightener. Polyethylene glycol creates a uniform zinc spangle on the surface of the coating, improving corrosion resistance and appearance.

[0077] Electroplating parameter setting: electroplating current density is 1-2A / dm 2 , the electroplating time is 30-60 minutes. By precisely controlling the electroplating parameters, the coating thickness is ensured to be ≥8μm.

[0078] 3. Salt spray test:

[0079] Electroplated bolts undergo a salt spray test to verify their corrosion resistance. The bolts are placed in a salt spray test chamber and sprayed with a 5% sodium chloride solution at a controlled temperature of 35°C. The salt spray test requires no white rust for 72 hours and no red rust for 120 hours. If the test results do not meet the requirements, the electroplating process parameters must be adjusted or the electroplating process must be repeated.

[0080] (5) Intelligent tail cutting and detection:

[0081] 1. Visual inspection system positioning:

[0082] The tail cutting position is determined by a visual inspection system. This system uses a high-resolution camera and advanced image processing algorithms to accurately identify the position and shape of the bolt tail. Before cutting, the bolts are placed on a conveyor belt, and the visual inspection system captures the tail position information and transmits it to the cutting equipment.

[0083] 2. High-speed rotary cutting knife operation:

[0084] Cutting is performed using a high-speed rotary cutter (3000-4000 rpm). The cutter's high hardness and sharp edge enable quick and accurate cutting of the bolt tail. During the cutting process, the cutter's feed rate and cutting depth are controlled to ensure a perpendicularity error of ≤0.3° between the cut tail end and the bolt axis, and a tail length of 25.00 ± 1.00 mm.

[0085] 3. Deburring:

[0086] After cutting, the tail is deburred. Using abrasive belt grinding and polishing, burrs and sharp edges are removed to ensure a surface roughness of Ra ≤ 3.2 μm. Deburring not only improves the bolt's appearance but also prevents scratches on operators and other components during installation.

[0087] 4. Magnetic particle inspection:

[0088] Each bolt undergoes magnetic particle inspection to eliminate products with surface cracks. Magnetic particle inspection is a nondestructive testing method that applies a magnetic field and magnetic particles to the bolt surface to detect surface and subsurface cracks. Any cracked bolts are immediately removed to prevent unqualified products from entering the next process.

[0089] (6) Packaging:

[0090] 1. Moisture-proof aluminum film bag packaging:

[0091] Package the bolts in moisture-proof aluminum film bags. These bags offer excellent moisture-proof properties and effectively prevent rust during storage and transportation. Ensure the bolt surface is dry and free of oil and dirt before packaging.

[0092] 2. Humidity indicator:

[0093] A humidity indicator (which changes color when humidity is greater than 20%) is placed inside the aluminum film bag. The humidity indicator can monitor the humidity inside the bag in real time. Once the humidity exceeds 20%, the indicator will change color to remind the user to pay attention to moisture protection.

[0094] 3. Traceability code:

[0095] Each package is labeled with a unique traceability code. Scanning the code provides access to the salt spray test data and heat treatment curve for that batch of bolts. This code facilitates product quality traceability and management, allowing users to understand the production process and quality of the product.

[0096] 4. Key dimension detection:

[0097] Critical dimensions of elbow expansion bolts are inspected using a three-dimensional coordinate measuring machine (CMM). Highly precise and reliable, CMMs accurately measure parameters such as the head bend angle, thread pitch diameter, and shank straightness. Testing accuracy is ≤ 0.05mm, ensuring product consistency. Regular spot checks are conducted throughout the production process to ensure product quality meets requirements.

[0098] Five, embodiment:

[0099] (1) Produce a batch of 1,000 elbow expansion bolts.

[0100] 1. Multi-station cold heading forming:

[0101] According to the above multi-station cold heading forming process parameters, 1000 bolts were formed. After forming, 10 pieces were randomly selected for dimensional inspection. The test results are shown in the following table:

[0102]

[0103]

[0104] It can be seen from the test results that the dimensional deviations are all within the allowable range, indicating that the multi-station cold heading forming process can ensure the dimensional accuracy of the product.

[0105] 2. High-precision thread rolling process:

[0106] 1000 bolts were thread-rolled using the above thread-rolling process parameters. After thread rolling, 10 bolts were sampled for thread testing. The results are as follows:

[0107] Test items Standard value Detection value range average value Thread pitch diameter (mm) According to M8×1.25 standard Comply with standards Thread surface roughness Ra(um) ≤1.6 0.8-1.4 1.1 Thread length (mm) 118.00±2.00 117.2-·118.8 118.1 Guide chamfer (mm) 0.50±0.10 0.42-0.58 0.5

[0108] The test results show that the thread rolling process can ensure the accuracy and surface quality of the thread.

[0109] 3. Gradient heat treatment:

[0110] 1000 bolts were subjected to gradient heat treatment according to the above heat treatment process parameters. After heat treatment, 10 bolts were sampled for hardness testing. The results are as follows:

[0111]

[0112] The hardness value meets the requirements, indicating that the gradient heat treatment process can effectively improve the strength and hardness of the bolts.

[0113] 4. Environmentally friendly electroplating process:

[0114] 1,000 bolts were electroplated using the above electroplating process parameters. After electroplating, 10 bolts were sampled for salt spray testing and coating thickness testing. The results are as follows:

[0115]

[0116] The test results show that the environmentally friendly electroplating process can ensure the corrosion resistance of the bolts.

[0117] 5. Intelligent tail cutting and detection:

[0118] 1,000 bolts were trimmed and inspected using the intelligent trimming and inspection process parameters described above. After trimming, 10 bolts were sampled for dimensional and flaw detection testing. The results are as follows:

[0119] Test items Standard value Detection value range average value Perpendicularity error between the cut end face and the bolt axis (°) ≤0.3 0.1-0.25 0.18 Tail length (mm) 25.00±1.00 24.2-25.8 25.1 Magnetic particle inspection No cracks No cracks

[0120] The test results show that the intelligent tail cutting and detection process can ensure the accuracy of tail cutting and product quality.

[0121] 6. Packaging:

[0122] 1,000 bolts were packaged according to the above packaging process. After packaging, the moisture-proof performance of the packaging and the validity of the traceability code were checked, and the results were found to meet the requirements.

[0123] (2) Comparison with traditional technology:

[0124] 100 elbow expansion bolts produced by conventional technology and 100 elbow expansion bolts produced by the present invention were selected for performance comparison testing. The test items included tensile strength, corrosion resistance, and installation ease. The results are shown in the following table:

[0125] Test items Traditional craft products Process products of the present invention Tensile strength (MPa) Average 600 Average 800 Salt spray test (no red rust after 24 hours) 48 120 Ease of installation generally Good (guide chamfer design)

[0126] From the comparison results, it can be seen that the elbow expansion bolts produced by the production process of the present invention have obvious improvements in tensile strength, corrosion resistance and installation convenience.

[0127] The elbow expansion bolt production process of the present invention achieves high-precision, high-strength, high-corrosion resistance and high-efficiency production of elbow expansion bolts through the steps of multi-station cold heading, high-precision thread rolling, gradient heat treatment, environmentally friendly electroplating process, intelligent tail cutting and detection, and packaging. The quality and consistency of the product are ensured by strictly controlling the process parameters of each step and performing key dimension detection. The results of the embodiments and comparative tests show that the production process of the present invention has significant advantages and can meet the market demand for high-quality elbow expansion bolts. At the same time, the process adopts environmentally friendly electroplating technology and intelligent detection technology, which is in line with the development trend of green manufacturing and intelligent manufacturing.

[0128] The embodiments of the present invention are presented for purposes of illustration and description and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments are chosen and described in order to better illustrate the principles of the invention and its practical application and to enable those skilled in the art to understand the invention and design various embodiments with various modifications as suited for specific applications.

Claims

1. A production process for elbow expansion bolts, characterized in that: The following steps are involved: S1: Multi-station cold heading: Using ML08 material and φ8.30 wire, a three-station cold heading machine is used to complete the head pre-forming, bending part forming and rib pressing in sequence. During the head forming, four evenly distributed small ribs are pressed simultaneously. The straight length of the bending part is controlled to 32.00±0.20mm, the head bending angle is 65°±1.5°, and the bend radius is R3.00±0.50mm. S2: High-precision thread rolling process: Use high-precision tungsten carbide dies to roll the rod to form an M8×1.25 external thread with a thread surface roughness of Ra≤1.6μm and a thread length of 118.00±2.00mm. At the same time, a guide chamfer R0.50±0.10mm is processed at the starting end of the thread. S3: Gradient heat treatment: Heat treatment is carried out in a box-type resistance furnace, with the temperature rising in two stages, cooling to 200°C with the furnace, and then air cooling, which eliminates cold heading stress and improves the strength of the rod to 8.8 grade; S4: Environmentally friendly electroplating process: Ultrasonic pickling is used to remove surface oxide scale before electroplating. Zinc-nickel alloy plating is used for electroplating with a coating thickness of ≥8μm. Salt spray test shows no white rust for 72 hours and no red rust for 120 hours. S5: Intelligent tail cutting and inspection: The tail cutting position is located by the visual inspection system. The verticality error between the tail cutting end face and the bolt axis is ≤0.3°, and the tail length is 25.00±1.00mm. At the same time, magnetic particle inspection is performed on each bolt to eliminate products with surface cracks.

2. A production process for an elbow expansion bolt as claimed in claim 1, characterized in that: In the multi-station cold heading forming step, the mold is made of Cr12MoV alloy steel, the forming pressure of the first station is 60-70 tons, and the pressure of the bending station is 80-90 tons, ensuring the dimensional accuracy of the head thickness of 9.00±0.20mm and the rod diameter of 7.00±0.20mm.

3. A production process for an elbow expansion bolt as claimed in claim 1, characterized in that: In the high-precision thread rolling process, the thread plate speed is controlled at 150-200 r / min, the thread rolling feed is 0.5-0.8 mm / revolution, and the pressure is adjusted in real time by the servo motor to avoid thread profile distortion.

4. A production process for an elbow expansion bolt as claimed in claim 1, characterized in that: After the gradient heat treatment step, the bolts are subjected to Rockwell hardness testing, and the hardness values ​​must meet HRC28-32 for the head and HRC32-36 for the shank.

5. The production process of an elbow expansion bolt according to claim 1, characterized in that: In the environmentally friendly electroplating process, 0.1-0.3 g / L of polyethylene glycol is added to the electroplating solution as a brightener, and uniform zinc flowers are formed on the surface of the coating, thereby improving the corrosion resistance and appearance quality.

6. A production process for an elbow expansion bolt as claimed in claim 1, characterized in that: In the intelligent tail cutting step, a high-speed rotating cutting knife is used, and the tail is deburred after cutting to ensure that the surface roughness Ra is less than or equal to 3.2 μm.

7. A production process for an elbow expansion bolt as claimed in claim 1, characterized in that: The transition area between the head and the stem of the elbow expansion bolt is provided with double R chamfers, and is formed in one step by a cold heading die to reduce stress concentration.

8. The production process of an elbow expansion bolt according to claim 1, characterized in that: During the rib pressing process, four anti-slip ribs are formed synchronously through the protruding structure of the mold cavity. The ribs are evenly distributed along the circumference of the head to enhance the tightness of the fit between the bolt and the expansion sleeve.

9. A production process for an elbow expansion bolt as claimed in claim 1, characterized in that: In the packaging step, moisture-proof aluminum film bags are used for packaging, with built-in humidity indicators and unique traceability codes attached. By scanning the code, the salt spray test data and heat treatment curve of the batch of bolts can be queried.

10. The production process of an elbow expansion bolt according to claim 1, characterized in that: The key dimensions of the elbow expansion bolts are detected using a three-coordinate measuring machine, and the detection accuracy of parameters such as the head bending angle, thread diameter, and rod straightness is ≤0.05mm to ensure product consistency.

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