Pipe manufacturing process method of thermal forming material

Abstract

The invention belongs to the field of material processing, and particularly relates to a pipe manufacturing process method of a thermal forming material. According to the welding method, preheating before welding and high-frequency resistance welding are adopted as the welding method for welding the hot-formed pipe into the steel pipe. As for a pipe made of a thermal forming material, preheating is conducted at the temperature of 80-120 DEG C before welding, the welding stress is reduced, the crack and deformation risks in the forming process are reduced, and the overall forming quality is improved; the auxiliary pulsed magnetic field is beneficial to uniform heating, reduction of welding stress and improvement of the formability of the steel pipe. And the high-frequency resistance welding adopts inductance power 2kW / 100kHz welding, rapid heating is realized, the welding time and the heat affected area are reduced, and the mechanical property and the forming precision of the steel pipe are kept. And in the welding process, 10% Ar + 0.3% SF6 gas protection effectively avoids melting or stripping of the plating layer in the welding process, and the formability is improved.

Description

Technical Field

[0001] The invention belongs to the field of material processing, and in particular relates to a pipe making process method of a thermoforming material. Background Art

[0002] With the rapid development of new energy vehicles, higher requirements are put forward for the lightweight and high strength of the car body. As the blank of the car body, the hot-formed pipe fittings have excellent mechanical properties and flexible design, which can improve the safety, comfort and endurance of new energy vehicles, thereby improving the market competitiveness of new energy vehicles. The pipe making process is an efficient and precise method for producing automobile blanks. It can produce hot-formed material pipe fittings and provide high-quality lightweight structural materials for automobile manufacturing. At present, more and more car bodies are beginning to use hot-formed pipe fittings as blanks, which makes the demand for hot-formed pipe making process methods growing.

[0003] However, thermoforming materials differ from other pipe materials in strength and performance. Traditional pipe making processes face difficulties such as poor formability and complex processes when producing thermoforming pipes.

[0004] CN 116060892A discloses a process for producing hot-dip galvanized steel pipes. The galvanized steel pipes for urban pipelines are obtained by unrolling and dephosphorizing the hot-rolled coils, heat treating, galvanizing, welding and slitting. Although the process has certain versatility, it still has certain limitations for the production of hot-formed materials due to different use environments. Summary of the invention

[0005] The existing pipe making process is aimed at coils of materials that meet the GB700-88 or GB1591-88 standards. The unwinding, leveling and welding processes do not fully consider the material characteristics of the coating. Traditional metal rollers will cause significant wear to the coating during the unwinding and leveling process, affecting the surface quality of the material. In addition, during the welding process, the existing pipe making process lacks effective protection for the coating, resulting in oxidation, peeling or damage to the coating surface at high temperatures. In order to repair the damaged coating, a large area of ​​re-plating is required, which increases the process cost.

[0006] Compared with the traditional pipe making process, the present invention adopts a low-speed, multi-roller leveling process, and unwinds and levelles the material at a temperature slightly higher than room temperature, effectively avoiding damage to the coating and the generation of material cracks. At the same time, during the welding process, high-frequency welding is performed after preheating before welding, which significantly reduces the risk of coating damage and improves the forming performance of the thermoforming material.

[0007] Thermoforming tube making is a process of forming thermoforming materials in multiple steps at a slightly higher temperature and using high-frequency welding to produce tubes. The production process consists of four modules: raw material processing - heating forming - welding finishing - post-processing (such asFigure 1 ). Raw material processing is to prepare for subsequent processes by low-speed unwinding and small deformation leveling. Heating and forming includes three-stage induction heating, multi-step forming and gradient cooling. This process enables the material to gradually form a shape close to the tube at a suitable temperature and optimize its internal structure. Post-processing covers quality inspection and labeling packaging to ensure that product quality meets standards and is traceable. In the entire pipe making process, the high-frequency welding process in welding finishing is particularly critical, which has a significant impact on the formability of the pipe.

[0008] In order to solve the problem of tube forming, the present application provides the following technical solutions:

[0009] The present invention provides a method for making a tube of a thermoforming material, including heating forming and welding finishing;

[0010] The heating forming method comprises the following steps:

[0011] S11: heating the thermoforming material containing the coating in three stages;

[0012] S12: performing multi-step forming on the thermoforming material after the three-stage heating in step S11 at a heat preservation temperature;

[0013] S13: Gradual cooling of the thermoformed material after multi-step forming in step S12;

[0014] The welding finishing method comprises the following steps:

[0015] S21: preheating the part to be welded of the thermoforming material after gradient cooling in step S13; the preheating is assisted by a pulsed magnetic field at a temperature of 80-120° C.;

[0016] S22: performing high-frequency resistance welding on the hot-formed material preheated in step S21 to obtain a pipe; during the high-frequency resistance welding, the upsetting pressure is 1.2-1.8 MPa, the welding frequency is 300-350 kHz, and a nitrogen knife is used for welding; the nitrogen knife is composed of argon, sulfur hexafluoride and nitrogen;

[0017] S23: performing weld finishing and slitting processing on the pipe.

[0018] Preferably, the hot forming material is steel containing a silicon-aluminum coating.

[0019] Preferably, in step S11, the three-stage heating is as follows: the first stage, heating to 150-250°C at a heating rate of 2.5°C / s; the second stage, heating to 250-300°C at a heating rate of 3°C / s; the third stage, keeping warm at 300°C for 3 minutes.

[0020] Preferably, in step S12, the multi-step forming includes the steps of pre-bending, progressive deformation and curling, and closed forming.

[0021] Preferably, in step S13, the gradient cooling steps are: in the first stage, cooling to 200-300°C in a dry nitrogen atmosphere; in the second stage, cooling to 100-200°C in a carbon dioxide atmosphere; in the third stage, cooling to below 100°C by circulating air cooling.

[0022] Furthermore, in the first stage, the dew point of the nitrogen atmosphere is not greater than -70°C, and the oxygen content is not greater than 20 ppm.

[0023] Furthermore, in the second stage, inner cavity assisted air extraction is used for cooling, the circumferential temperature difference is no more than 3°C, and ΔP is 50Pa.

[0024] Furthermore, in the third stage, the cooling rate is 0.5°C / s and the residual stress is not greater than 50MPa.

[0025] Preferably, in step S21, the intensity of the pulsed magnetic field assistance is 0.5T.

[0026] Specifically, the preheating method before welding is: preheating temperature 80-120℃, uniform heating of 20-30mm area on both sides of the weld, using inductive power 2kW / 100kHz with infrared monitoring, and pulsed magnetic field assistance (magnetic induction intensity 0.5T). This combination of multiple technologies greatly improves the uniformity of the coating to the point.

[0027] The present invention adopts preheating before welding (80-120°C) and auxiliary pulse magnetic field (magnetic induction intensity of 0.5T) to uniformly heat the welding area. Appropriate preheating temperature and magnetic field assist in reducing welding stress, reducing the risk of cracks and deformation during forming, and improving the formability of the steel pipe.

[0028] Preferably, in step S22, the nitrogen knife is composed of 10% argon and 0.3% sulfur hexafluoride, with the remainder being nitrogen, by volume fraction.

[0029] Preferably, in step S22, the flow rate of the nitrogen knife is not less than 20 m / s.

[0030] Specifically, during the welding process: high-frequency resistance welding, the nitrogen knife is mixed with 10% Ar + 0.3% SF6 gas, and the flow rate is ≥ 20m / s to isolate the Al-Si phase change zone, improve the arc stability, and ensure the continuity and stability of the welding process. At the same time, the top forging pressure is increased to 1.2-1.8MPa. The precise adjustment of this pressure well compensates for the plasticity difference of the Al-Si layer, making the weld more firmly bonded. And the frequency is adjusted to 300-350kHz. The high-frequency welding operation realizes fast and efficient heat transfer, reduces welding time, thereby reducing the size of the heat-affected zone and minimizing the impact on the formability of the pipe.

[0031] During the welding process, the protective gas (10% Ar + 0.3% SF6) is added, the top forging pressure (1.2-1.8MPa) is increased, and high-frequency resistance welding (300-350kHz) is used to reduce the porosity and inclusions in the weld, reduce welding deformation, and help maintain the forming accuracy of the steel pipe.

[0032] Preferably, in step S23, weld finishing includes weld trimming, coating repair and surface treatment; the weld finishing includes weld scraping and slag purging; the coating repair adopts plasma spraying method; the surface treatment method is to oil or coat the pipe surface.

[0033] Furthermore, the plasma spraying power is 40 kW, the powder feeding rate is 30 g / min, and a 0.3 mm transition layer is formed.

[0034] Specifically, the method for finishing the weld includes: a. Weld finishing: weld scraping and slag blowing; b. Coating repair: plasma spraying, AlSi10-Mg alloy (matching the composition of the substrate coating), power 40kW, powder feeding rate 30g / min, 0.3mm transition layer (the composition gradient changes continuously from the substrate to the coating); c. Surface treatment: oiling or coating the surface of the pipe to prevent the coating from being damaged during storage and transportation.

[0035] Preferably, in step S23, the slitting process includes sizing, straightening, cutting and end face processing.

[0036] Specifically, the slitting method includes: (1) sizing and straightening (finishing): using appropriate lubrication to straighten and size the pipe; (2) cutting and end face processing: measuring the speed, using laser cutting to cut the pipe of a reasonable length as required, and performing burr treatment on the end face after cutting.

[0037] The technical solution of the present invention has the following advantages over the prior art:

[0038] Preheating before welding and high-frequency resistance welding are used as welding methods for hot-formed pipes into steel pipes. For pipes made of hot-formed materials, preheating at 80-120°C before welding can reduce welding stress, reduce the risk of cracks and deformation during the forming process, and improve the overall forming quality; auxiliary pulse magnetic field helps to uniformly heat and reduce welding stress, and improve the formability of steel pipes. High-frequency resistance welding uses an inductive power of 2kW / 100kHz welding, which heats quickly, reduces welding time and heat-affected area, and maintains the mechanical properties and forming accuracy of the steel pipe. During the welding process, 10% Ar+0.3% SF6 gas protection effectively prevents the melting or peeling of the coating during the welding process and improves the formability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The production process of making tubes from thermoforming materials.

[0040] Figure 2 The whole process of high frequency welding for making tubes of thermoforming materials.

[0041] Figure 3 These are the welds prepared in Examples 1 to 4.

[0042] Figure 4 This is the weld prepared in Examples 5 and 6.

[0043] Figure 5 This is the weld prepared in Comparative Example 1. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0045] Example 1 Raw material processing

[0046] The steel with silicon-aluminum coating 22MnB5 is used as the hot forming material, unrolled at a low speed, and induction heated by a resistance coil. The heating temperature is heated to 150℃ and the material is gradually flattened through multiple small deformations.

[0047] Example 2 Heating and forming

[0048] 2.1 The raw materials treated in Example 1 were subjected to three-stage coil induction heating.

[0049] (1) 150℃-250℃: heating rate 2.5℃ / s, slow speed in phase change sensitive area;

[0050] (2) 250-300℃: 3.0℃ / s, quickly passing through the brittle range;

[0051] (3) 300℃ insulation: 3min, shortening the high temperature exposure time.

[0052] 2.2 Multi-step forming at insulation temperature

[0053] (1) Pre-bending: The first set of rollers pre-bends the edge of the steel strip to form an initial curvature with a bending radius ≥ 5 times the thickness of the plate (to prevent the coating from falling off);

[0054] (2) Progressive deformation bending: formed in 8 steps, the first 3 steps: 0.5-0.8% / step (coating adaptation stage); the middle 3 steps: 0.8-1.2% / step; the last two steps: 1.2% / step (total cumulative strain ≤10%); after the 6th step, add martensite content detection to ensure that the substrate has not triggered phase transformation and the α' phase is ≤5%;

[0055] (3) Closed forming: The last set of rollers closes the edge of the steel strip to form a complete tubular structure, and an appropriate amount of lubricant is added to reduce friction to ≤ 0.08.

[0056] 2.3 Gradient cooling

[0057] (1) The first stage (300-200°C): ultra-dry N2 mist (dew point ≤ -70°C) oxygen content ≤ 20ppm;

[0058] (2) The second stage (200-100°C): CO2 mist annular injection + inner cavity auxiliary exhaust (ΔP = 50Pa) circumferential temperature difference ≤ ±3°C;

[0059] (3) The third stage (<100℃): gradient cycle air cooling (rapid drop of 0.5℃ / s) residual stress ≤50MPa.

[0060] Example 3 Welding finishing

[0061] 3.1 High frequency welding

[0062] (1) Preheating before welding: The material after gradient cooling in Example 2 was preheated at a temperature of 120° C. The 30 mm area on both sides of the weld was evenly heated. An inductive power of 2 kW / 100 kHz was used in combination with infrared monitoring and pulsed magnetic field assistance with a magnetic induction intensity of 0.5 T.

[0063] (2) Welding process: high-frequency resistance welding, nitrogen knife mixed with 10% Ar + 0.3% SF6 gas, with a flow rate of ≥ 20m / s to isolate the Al-Si phase change zone, improve arc stability, and ensure the continuity and stability of the welding process. At the same time, the top forging pressure is increased to 1.6MPa. The precise adjustment of this pressure well compensates for the plasticity difference of the Al-Si layer, making the weld more firmly bonded, and the frequency is adjusted to 300kHz.

[0064] (3) Weld finishing: a. Weld finishing: weld scraping and slag blowing; b. Coating repair: plasma spraying, AlSi10-Mg alloy (matching the coating composition of the substrate), power 40kW, powder feeding rate 30g / min, 0.3mm transition layer (the composition gradient changes continuously from the substrate to the coating); c. Surface treatment: oil or film coating the surface of the pipe to prevent the coating from being damaged during storage and transportation (the whole process of high-frequency welding is as follows: Figure 2 shown).

[0065] 3.2 Cutting process

[0066] (1) Sizing and straightening (finishing): Use appropriate lubrication to straighten and size the pipe.

[0067] (2) Cutting and end face processing: Measure the speed and use laser cutting to cut the tube to a reasonable length according to customer requirements, and perform burr treatment on the end face after cutting.

[0068] Example 4 Post-treatment

[0069] 4.1 Quality Inspection

[0070] (1) Testing the coating integrity of the product obtained in Example 3:

[0071] a. Use a coating thickness gauge to detect the integrity and thickness of the coating to ensure that the coating is not damaged;

[0072] b. 60° cross peeling method to test the bonding strength of the coating;

[0073] c. ISO 9223 corrosion rating checks the total area of ​​oxidation.

[0074] (2) Weld inspection: Perform non-destructive testing (such as ultrasonic testing or X-ray testing) on ​​the weld to ensure welding quality; (3) Mechanical property testing: Perform tensile, bending and impact tests on the pipe to ensure that its mechanical properties meet the requirements.

[0075] 4.2 Labeling and packaging

[0076] (1) Marking: Mark on the surface or end of the pipe, taking care to avoid damage to the coating;

[0077] (2) Packaging: Use moisture-proof and scratch-resistant packaging materials (such as foam pads or plastic film) to protect the coating from damage during transportation.

[0078] Example 5 Welding Finishing

[0079] 3.1 High frequency welding

[0080] (1) Preheating before welding: The material after gradient cooling in Example 2 was preheated at a temperature of 120° C. The 30 mm area on both sides of the weld was evenly heated. An inductive power of 2 kW / 100 kHz was used in combination with infrared monitoring and pulsed magnetic field assistance with a magnetic induction intensity of 0.5 T.

[0081] (2) Welding process: high-frequency resistance welding, nitrogen knife mixed with 10% Ar + 0.3% SF6 gas, with a flow rate of ≥ 20m / s to isolate the Al-Si phase change zone, improve arc stability, and ensure the continuity and stability of the welding process. At the same time, the top forging pressure is increased to 1.6MPa. The precise adjustment of this pressure well compensates for the plasticity difference of the Al-Si layer, making the weld more firmly bonded, and the frequency is adjusted to 350kHz.

[0082] (3) Weld finishing: a. Weld finishing: weld scraping and slag blowing; b. Coating repair: plasma spraying, AlSi10-Mg alloy (matching the coating composition of the substrate), power 40kW, powder feeding rate 30g / min, 0.3mm transition layer (the composition gradient changes continuously from the substrate to the coating); c. Surface treatment: oil or film coating the surface of the pipe to prevent the coating from being damaged during storage and transportation (the whole process of high-frequency welding is as follows: Figure 2 shown).

[0083] 3.2 Cutting process

[0084] (1) Sizing and straightening (finishing): Use appropriate lubrication to straighten and size the pipe.

[0085] (2) Cutting and end face processing: Measure the speed and use laser cutting to cut the tube to a reasonable length according to customer requirements, and perform burr treatment on the end face after cutting.

[0086] Example 6 Post-treatment

[0087] 4.1 Quality Inspection

[0088] (1) The coating integrity of the product obtained in Example 5 was tested:

[0089] a. Use a coating thickness gauge to detect the integrity and thickness of the coating to ensure that the coating is not damaged;

[0090] b. 60° cross peeling method to test the bonding strength of the coating;

[0091] c. ISO 9223 corrosion rating checks the total area of ​​oxidation.

[0092] (2) Weld inspection: Perform non-destructive testing (such as ultrasonic testing or X-ray testing) on ​​the weld to ensure welding quality; (3) Mechanical property testing: Perform tensile, bending and impact tests on the pipe to ensure that its mechanical properties meet the requirements.

[0093] 4.2 Labeling and packaging

[0094] (1) Marking: Mark on the surface or end of the pipe, taking care to avoid damage to the coating;

[0095] (2) Packaging: Use moisture-proof and scratch-resistant packaging materials (such as foam pads or plastic film) to protect the coating from damage during transportation.

[0096] Comparative Example 1

[0097] In this comparative example, a preheating temperature of 120°C is used to uniformly heat both sides of the weld, a 0.5T magnetic induction intensity pulse magnetic field is used as an auxiliary, high-frequency resistance welding is adopted, the frequency is adjusted to 250kHz, the top forging pressure is increased to 1.6MPa, and a nitrogen knife is mixed with 10% Ar+0.3% SF6 gas to isolate the Al-Si phase change zone at a flow rate ≥20m / s.

[0098] The difference from Examples 1 to 4 is that the frequency of high-frequency resistance welding is adjusted to 250 kHz.

[0099] Effect evaluation 1

[0100] Table 1 Description of welding conditions of the embodiments and comparative examples

[0101]

[0102] The welding method proposed by the present invention can achieve good welding conditions and fast welding speed while protecting the coating as much as possible through preheating before welding and high-frequency resistance welding. Taking silicon-aluminum-coated 22MnB5 steel as a hot forming material as an example, 120°C preheating and high-frequency resistance welding are used, and the welding frequency is within the range of 300-350kHz, and the welding formability of silicon-aluminum-coated 22MnB5 steel is relatively intact.

[0103] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for making a tube of a thermoforming material, characterized in that: Includes heat forming and welding finishing; The heating forming method comprises the following steps: S11: heating the thermoforming material containing the coating in three stages; S12: performing multi-step forming on the thermoforming material after the three-stage heating in step S11 at a heat preservation temperature; S13: Gradual cooling of the thermoformed material after multi-step forming in step S12; The welding finishing method comprises the following steps: S21: preheating the part to be welded of the thermoforming material after gradient cooling in step S13; the preheating is assisted by a pulsed magnetic field at a temperature of 80-120° C.; S22: performing high-frequency resistance welding on the hot-formed material preheated in step S21 to obtain a pipe; during the high-frequency resistance welding, the upsetting pressure is 1.2-1.8 MPa, the welding frequency is 300-350 kHz, and a nitrogen knife is used for welding; the nitrogen knife is composed of argon, sulfur hexafluoride and nitrogen; S23: performing weld finishing and slitting processing on the pipe.

2. The method for making a tube from a thermoforming material according to claim 1, characterized in that: In step S11, the three-stage heating is as follows: the first stage, heating to 150-250°C at a heating rate of 2.5°C / s; the second stage, heating to 250-300°C at a heating rate of 3°C / s; the third stage, keeping at 300°C for 3 minutes.

3. The method for making a tube from a thermoforming material according to claim 1, characterized in that: In step S12, the multi-step forming includes the steps of pre-bending, progressive deformation and curling, and closed forming.

4. The method for making a tube from a thermoforming material according to claim 1, characterized in that: In step S13, the gradient cooling steps are as follows: in the first stage, the temperature is lowered to 200-300° C. in a dry nitrogen atmosphere; in the second stage, the temperature is lowered to 100-200° C. in a carbon dioxide atmosphere; in the third stage, the temperature is lowered to below 100° C. by circulating air cooling.

5. The method for making a tube from a thermoforming material according to claim 1, characterized in that: In step S21, the intensity of the pulsed magnetic field assistance is 0.5T.

6. The method for making a tube from a thermoforming material according to claim 1, characterized in that: In the step S22, the nitrogen knife is composed of 10% argon and 0.3% sulfur hexafluoride, and the remainder is nitrogen, by volume fraction.

7. The method for making a tube from a thermoforming material according to claim 1, characterized in that: In step S22, the flow rate of the nitrogen knife is not less than 20 m / s.

8. The method for making a tube from a thermoforming material according to claim 1, characterized in that: In step S23, weld finishing includes weld trimming, coating repair and surface treatment; the weld finishing includes weld scraping and slag purging; the coating repair adopts plasma spraying method; the surface treatment method is to oil or coat the pipe surface.

9. The process for making a tube from a thermoforming material according to claim 8, characterized in that: The plasma spraying power is 40 kW, the powder feeding rate is 30 g / min, and a 0.3 mm transition layer is formed.

10. The method for making a tube from a thermoforming material according to claim 1, characterized in that: In step S23, the slitting process includes sizing, straightening, cutting and end surface processing.

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