A pipe making process for thermoformed material

Abstract

The present application belongs to the field of material processing, and particularly relates to a pipe manufacturing process of hot forming material. The present application adopts preheating before welding and high-frequency resistance welding as the welding method of hot forming pipe welding into steel pipe. For the pipe of hot forming material, preheating at 80-120 DEG C is carried out before welding, so as to reduce welding stress, reduce the risk of crack and deformation in the forming process, and improve the overall forming quality; auxiliary pulse magnetic field is helpful to uniform heating, reduction of welding stress, and improvement of steel pipe formability. High-frequency resistance welding adopts inductive power of 2kW / 100kHz for welding, so as to realize rapid heating, reduce welding time and heat affected zone, and maintain the mechanical properties and forming precision of the steel pipe. 10% Ar+0.3% SF6 gas protection in the welding process effectively avoids the melting or peeling of the plating layer in the welding process, and improves the formability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of material processing, and particularly relates to a pipe-making process method of hot forming material. BACKGROUND

[0002] With the rapid development of new energy vehicles, higher requirements are put forward for the lightweight and high strength of the vehicle body. As the blank of the automobile body, the hot forming pipe has 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 process for producing automobile blanks, which can produce hot forming material pipes to provide high-quality lightweight structural materials for automobile manufacturing. At present, more and more vehicle bodies begin to use hot forming pipes as blanks, so the demand for hot forming pipe-making process is increasing.

[0003] However, the hot forming material has differences in strength and performance with other pipe materials, and the traditional pipe-making process has difficulties such as poor formability and complex process when producing hot forming pipes.

[0004] CN 116060892A discloses a process production method of hot-dip galvanized steel pipe. The hot-rolled coil is opened, phosphorus is removed, heat treated, galvanized, welded and cut to obtain a galvanized steel pipe for urban pipelines. Although this process has a certain universality, it still has certain limitations for the pipe-making of hot forming materials due to the difference in use environment. SUMMARY

[0005] The existing pipe-making process is aimed at material coils meeting the GB700-88 or GB1591-88 standards, and the uncoiling, flattening and welding process does not fully consider the material properties of the coating. The traditional metal roller will cause significant wear to the coating during uncoiling and flattening, affecting the surface quality of the material. In addition, during the welding process, the existing pipe-making process lacks effective protection of the coating, resulting in oxidation, peeling or damage of the coating surface at high temperature. To repair the damaged coating, subsequent large-area re-plating treatment is required, which increases the process cost.

[0006] Compared with the traditional pipe-making process, the present application adopts a low-speed, multi-roller flattening process, and uncoils and flattens 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, the welding process is preceded by preheating and then high-frequency welding, which significantly reduces the risk of coating damage while improving the forming performance of the hot forming material.

[0007] The pipe-making of hot forming material is a process that forms hot forming material at a slightly higher temperature in multiple steps and generates pipe material by high-frequency welding. The production process flow consists of four modules: raw material processing - heating and forming - welding and finishing - post-processing (such asFigure 1 Raw material processing is to prepare for subsequent processes by low-speed unwinding and small deformation flattening. The heating forming includes three-stage induction heating, multi-step forming and gradient cooling, which can make the material gradually form a shape close to the pipe and optimize the internal organization at a suitable temperature. Post-processing covers quality testing and identification packaging to ensure product quality meets standards and is traceable. In the entire pipe manufacturing process, the high-frequency welding process in the welding finishing is particularly critical, which has a significant impact on pipe forming.

[0008] To solve the pipe forming problem, the application provides the following technical solutions:

[0009] The application provides a pipe manufacturing process method of a hot forming material, including heating forming and welding finishing.

[0010] The method of heating forming includes the following steps:

[0011] S11: Three-stage heating of the hot forming material containing a plating layer;

[0012] S12: Multi-step forming of the hot forming material after three-stage heating in step S11 at a holding temperature;

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

[0014] The method of welding finishing includes the following steps:

[0015] S21: Preheating of the part needing welding in the hot forming material after gradient cooling in step S13; the preheating uses pulse magnetic field assistance, and the temperature is 80-120℃;

[0016] S22: High-frequency resistance welding of the hot forming material after preheating in step S21 to obtain a pipe; during high-frequency resistance welding, the top forging 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: Weld seam finishing and slitting treatment of the pipe.

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

[0019] Preferably, in step S11, the three-stage heating is: in the first stage, the temperature is raised to 150-250℃ at a temperature rising rate of 2.5℃ / s; in the second stage, the temperature is raised to 250-300℃ at a temperature rising rate of 3℃ / s; and in the third stage, the temperature is held at 300℃ for 3 min.

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

[0021] Preferably, in the step S13, the step of gradient cooling is: in the first stage, the temperature is lowered to 200-300 DEG C under the dry nitrogen atmosphere; in the second stage, the temperature is lowered to 100-200 DEG C under the carbon dioxide atmosphere; in the third stage, the temperature is lowered to below 100 DEG C by using the circulating air cooling mode.

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

[0023] Further, in the second stage, the temperature is lowered by using the inner cavity assisted air extraction, and the circumferential temperature difference is not more than 3 DEG C, and the delta P is 50 Pa.

[0024] Further, in the third stage, the temperature lowering speed is 0.5 DEG C / s, and the residual stress is not more than 50 MPa.

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

[0026] Specifically, the method of pre-welding preheating is: the preheating temperature is 80-120 DEG C, the area of 20-30 mm on both sides of the welding bead is uniformly heated, the inductive power of 2 kW / 100 kHz is used in cooperation with infrared monitoring, and at the same time, the pulse magnetic field assistance (magnetic induction intensity 0.5 T) is used, and the multi-technology combination greatly improves the uniformity of the plating to the point.

[0027] The present application adopts pre-welding preheating (80-120 DEG C) and auxiliary pulse magnetic field (0.5 T magnetic induction intensity), so that the welding area is uniformly heated, and the appropriate preheating temperature and magnetic field assistance reduce the welding stress, reduce the risk of cracks and deformation in the forming, and improve the formability of the steel pipe.

[0028] Preferably, in the step S22, the nitrogen gas knife is composed of 10% argon and 0.3% sulfur hexafluoride, and the balance is nitrogen gas in terms of volume fraction.

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

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

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

[0032] Preferably, in the step S23, the weld finishing includes weld trimming, coating repair, and surface treatment; the weld finishing includes weld scraping and slag blowing; the coating repair is selected by the method of plasma spraying; and the surface treatment is oiling or film coating treatment on the pipe surface.

[0033] Further, 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 weld finishing method includes: a, weld trimming: weld scraping and slag blowing; b, coating repair: plasma spraying, AlSi10-Mg alloy (matching the base material coating composition), power 40 kW, powder feeding rate 30 g / min, 0.3 mm transition layer (composition gradient continuously changes from base material to coating); c, surface treatment: oiling or film coating treatment on the pipe surface to prevent damage to the coating during storage and transportation.

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

[0036] Specifically, the slitting process includes: (1) sizing and straightening (finishing): using appropriate lubrication to straighten and size the pipe; (2) cutting and end face treatment: speed measurement, laser cutting to cut the pipe to a reasonable length, and burr treatment on the cut end face.

[0037] The technical scheme of the present application has the following advantages compared with the prior art:

[0038] The welding method of the present application is to adopt preheating before welding and high frequency resistance welding as the welding method of hot forming pipe material welded into steel pipe. For the pipe material of hot forming material, preheating at 80-120℃ is carried out before welding to reduce welding stress, reduce the risk of cracking and deformation in the forming process, and improve the overall forming quality; auxiliary pulse magnetic field is helpful to uniform heating to reduce welding stress and improve the formability of steel pipe. High frequency resistance welding adopts welding frequency of 300-350 kHz, fast heating, reduces welding time and heat affected zone, and maintains the mechanical properties and forming precision of steel pipe. The 10% Ar+0.3% SF6 gas protection in the welding process effectively avoids the melting or peeling of the plating layer during the welding process, and improves the formability. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The production process flow of pipe making of hot forming material.

[0040] Figure 2 The whole process of high frequency welding of pipe making of hot forming material.

[0041] Figure 3 The welds prepared from Example 1 to Example 4.

[0042] Figure 4 The welds prepared from Example 5 to Example 6.

[0043] Figure 5 The welds prepared from Comparative Example 1. DETAILED DESCRIPTION

[0044] The present application will be further described below in conjunction with the drawings and specific examples, so that those skilled in the art can better understand the present application and implement it, but the examples are not as a limitation on the present application.

[0045] Example 1: Material treatment

[0046] The steel material of silicon aluminum plated layer 22MnB5 is used as hot forming material, low speed uncoiling, resistance coil induction heating, heating temperature to 150℃, gradually flattening the material by multiple small deformation.

[0047] Example 2: Heating forming

[0048] 2.1 Three-stage coil induction heating of the material treated in Example 1

[0049] (1) 150-250℃: 2.5℃ / s, slow speed in the phase transition sensitive zone;

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

[0051] (3) 300 °C holding: 3 min, shorten the high temperature exposure time.

[0052] 2.2 Multi-step forming at holding temperature

[0053] (1) Pre-bending: the first group of rollers pre-bends the edges of the steel strip to form an initial curvature with a bending radius ≥ 5 times the plate thickness (to prevent coating detachment);

[0054] (2) Progressive deformation bending: 8-step forming, first 3 steps: 0.5-0.8% / step (coating adaptation stage); middle 3 steps: 0.8-1.2% / step; last two steps: 1.2% / step (total cumulative strain ≤ 10%); after the 6th step, add martensite content detection to ensure that the base material does not trigger phase change, a' phase ≤ 5%;

[0055] (3) Closed forming: the last group of rollers closes the edges of the steel strip to form a complete tubular structure, adding an appropriate amount of lubricant to reduce friction ≤ 0.08.

[0056] 2.3 Gradient cooling

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

[0058] (2) Second stage (200-100 °C): CO2 gas mist ring spray + inner cavity auxiliary air extraction (ΔP = 50 Pa) with ≤ ± 3 °C circumferential temperature difference;

[0059] (3) Third stage (< 100 °C): gradient circulating air cooling (speed drop 0.5 °C / s) with residual stress ≤ 50 MPa.

[0060] Example 3 Welding finishing

[0061] 3.1 High-frequency welding

[0062] (1) Pre-welding preheating: preheat the material after gradient cooling in Example 2, preheating temperature 120 °C, uniformly heat the 30 mm area on both sides of the weld, use inductive power 2 kW / 100 kHz with infrared monitoring, and at the same time, pulse magnetic field assistance, magnetic induction intensity 0.5 T.

[0063] (2) Welding process: high-frequency resistance welding, nitrogen knife incorporates 10% Ar + 0.3% SF6 gas to isolate the Al-Si phase change area with a flow rate ≥ 20 m / s, improve the stability of the arc, ensure the continuity and stability of the welding process. At the same time, the upset pressure is increased to 1.6 MPa, which precisely compensates for the plasticity difference of the Al-Si layer, making the joint at the weld more secure, and the frequency is adjusted to 300 kHz.

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

[0065] 3.2 Slitting process

[0066] (1) Sizing and straightening (finishing): use appropriate lubrication for pipe straightening and sizing.

[0067] (2) Cutting and end face treatment: speed measurement, laser cutting to the required length, and deburring the cut end face.

[0068] Example 4 Post-processing

[0069] 4.1 Quality inspection

[0070] (1) Coating integrity inspection of the product obtained in Example 3:

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

[0072] b. Test the coating adhesion by 60° cross-cut peeling method;

[0073] c. Check the total oxidation area according to ISO 9223 corrosion rating.

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

[0075] 4.2 Marking and packaging

[0076] (1) Marking: mark on the pipe surface or end, taking care not to damage 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 Weld finishing

[0079] 3.1 High-frequency welding

[0080] ​(1) Pre-weld preheating: The material after gradient cooling in Example 2 was preheated at a temperature of 120°C, with uniform heating of the area 30 mm on both sides of the weld bead, using an inductive power of 2 kW / 100 kHz in combination with infrared monitoring, while being assisted by a pulsed magnetic field with a magnetic induction intensity of 0.5 T.

[0081] (2) Welding process: High-frequency resistance welding, with a nitrogen knife incorporating 10% Ar + 0.3% SF6 gas at a flow rate of > 20 m / s to isolate the Al-Si phase transition zone, improving arc stability and ensuring continuity and stability during the welding process. At the same time, the upset pressure was increased to 1.6 MPa, which precisely compensated for the plasticity difference between the Al-Si layers, making the joint at the weld more secure, and the frequency was adjusted to 350 kHz.

[0082] (3) Weld seam finishing: a, weld seam finishing: weld seam scraping and slag blowing; b, coating repair: plasma spraying, AlSi10-Mg alloy (matching the composition of the base material coating), power 40 kW, powder feed rate 30 g / min, 0.3 mm transition layer (composition gradient continuously changes from base material to coating); c, surface treatment: oiling or film coating treatment of the pipe surface to prevent damage to the coating during storage and transportation (the entire high-frequency welding process is shown in FIG. 1). Figure 2

[0083] 3.2 Slitting treatment

[0084] (1) Sizing and straightening (finishing): The pipe is straightened and sized with appropriate lubrication.

[0085] (2) Cutting and end face treatment: speed measurement, laser cutting to cut the pipe to a reasonable length according to customer requirements, and burr treatment of the cut end face.

[0086] Example 6 Post-treatment

[0087] 4.1 Quality testing

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

[0089] a, use a coating thickness gauge to test the integrity and thickness of the coating to ensure that the coating has not been damaged;

[0090] b, test the coating adhesion by 60° cross-cut peeling method;

[0091] c, check the total area of oxidation according to ISO 9223 corrosion rating.

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

[0093] 4.2 Identification and packaging

[0094] (1) Identification: Marking on the surface or end of the pipe, pay attention 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] The preheating temperature of this comparative example is 120℃, the 0.5T magnetic induction intensity pulse magnetic field is assisted, high frequency resistance welding is used, the frequency is adjusted to 250 kHz, the top forging pressure is increased to 1.6 MPa, the nitrogen gas knife is mixed with 10% Ar+0.3% SF6 gas, and the Al-Si phase change area is isolated at a flow rate of ≥20m / s.

[0098] The difference between this example and 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: Welding condition explanation of examples and comparative examples

[0101]

[0102] The welding method proposed in the present application can make the welding condition good and the welding speed faster while protecting the coating as much as possible through preheating before welding and high frequency resistance welding. Taking the silicon-aluminum coated 22MnB5 steel material as a hot forming material as an example, using 120℃ preheating and high frequency resistance welding, the welding frequency is in the range of 300-350 kHz, and the silicon-aluminum coated 22MnB5 steel material has good weldability.

[0103] Obviously, the above examples are only examples for clarity and do not limit the embodiments. For ordinary skilled persons in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to exhaust all embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A pipe-making process of thermoforming a material, characterized in that, The heating forming and welding finishing are included; The heating forming method comprises the following steps: S11: three-stage heating of the hot forming material containing the plating layer; S12: multi-step forming of the hot forming material after three-stage heating in step S11 at a holding temperature; S13: gradient cooling of the hot forming material after multi-step forming in step S12; The welding finishing method comprises the following steps: S21: preheating of the part to be welded in the hot forming material after gradient cooling in step S13; the preheating method is: the preheating temperature is 80-120℃, the area of 20-30mm on both sides of the welding bead is uniformly heated, an inductive power of 2kW / 100kHz is used in cooperation with infrared monitoring, and a pulse magnetic field is assisted at the same time; S22: high-frequency resistance welding of the hot forming material after preheating in step S21 to obtain a pipe; during the high-frequency resistance welding, the top forging 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; during the high-frequency resistance welding, 10% Ar+0.3% SF6 gas is mixed into the nitrogen knife at a flow rate of ≥20m / s to isolate the Al-Si phase change area; S23: weld finishing and slitting treatment of the pipe.

2. The method of claim 1, wherein the thermoformed material is a pipe. 2 In step S11, the three-stage heating is: in the first stage, the temperature is raised to 150-250℃ at a rate of 2.5℃ / s; in the second stage, the temperature is raised to 250-300℃ at a rate of 3℃ / s; and in the third stage, the temperature is held at 300℃ for 3 minutes.

3. The tube manufacturing process of the thermoforming material as described in claim 1, characterized in that, In step S12, the multi-step forming includes the steps of pre-bending, progressive deformation bending and closing forming.

4. The tube manufacturing process of the thermoforming material as described in claim 1, characterized in that, In step S13, the gradient cooling step is: in the first stage, the temperature is lowered to 200-300℃ in a dry nitrogen atmosphere; in the second stage, the temperature is lowered to 100-200℃ in a carbon dioxide atmosphere; and in the third stage, the temperature is lowered to below 100℃ by circulating air cooling.

5. The method of claim 1, wherein the thermoformed material is a pipe. 5 In step S21, the intensity of the pulse magnetic field assistance is 0.5T.

6. The method of claim 1, wherein the thermoformed material is a pipe. 5 In step S23, the weld finishing includes weld trimming, plating repair and surface treatment; the weld finishing includes weld scraping and slag blowing; the plating repair is selected by the method of plasma spraying; and the surface treatment method is oiling or film coating treatment on the surface of the pipe.

7. The method of claim 6, wherein the thermoformed material is a pipe. 7 The plasma spraying power is 40kW, the powder feeding rate is 30g / min, and a 0.3mm transition layer is formed.

8. The method of claim 1, wherein the thermoformed material is a pipe. In step S23, the slitting treatment method includes sizing, straightening, cutting and end face treatment. ​

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