Method for softening riveting area of hot forming part through laser

Abstract

The invention belongs to the field of metal heat treatment, and particularly relates to a method for softening a riveting area of a hot forming part through laser. The method for softening the riveting area of the hot forming part through the laser comprises the following steps that (1) the hot forming part needing to be softened is fixed to a clamp; and (2) laser beams are used for heating the surface of the riveting area of the hot-formed part according to the set laser parameters and the scanning technology, the hardness of the riveting area is reduced through the tempering principle, the plasticity is improved, and after tempering is completed, the part is taken down and naturally cooled. And (3) the softened hot forming part is subjected to laser trimming, and the hot forming part with the area needing to be riveted softened is obtained. The scanning area is heated and tempered through laser, the hardness of the hot forming part is reduced to 200 HV-450 HV, the problems that in an original riveting process, rivets cannot penetrate through, the rivets deform, a steel plate cracks and the like can be solved, and the riveting process of the hot forming part is qualified.

Description

Technical Field

[0001] The invention belongs to the field of metal heat treatment, and in particular relates to a method for softening a riveted area of ​​a hot-formed part by using laser. Background Art

[0002] In recent years, new energy vehicles have developed rapidly, and the requirements for automobile energy conservation and emission reduction have been continuously improved. Automobile lightweighting has become an important development direction for automobile companies. Using hot-formed steel to replace traditional steel to manufacture the body in white can achieve higher strength while using less material thickness. While achieving weight reduction, it also greatly enhances the collision performance of the car. The hot-formed steel body in white has higher strength and deformation resistance. In the body in white, the proportion of hot-formed parts is increasing year by year, and its proportion has also become the basis for judging the safety of the car.

[0003] With the rapid development of the automobile industry, people are paying more and more attention to reducing the weight of the car body, reducing fuel consumption (economy), and reducing exhaust emissions (environmental protection). At the same time, people's requirements for the safety and comfort of cars are gradually increasing. In order to adapt to this development trend, major steel companies have developed high-strength steel plates for car body parts, which also brings about the problem of forming high-strength steel plates. It is difficult to form high-strength steel plates at room temperature, so hot forming technology came into being.

[0004] Hot forming technology is mainly developed for high-strength steel plates. The process is as follows: first, the boron alloy steel plate with a strength of 500-600MPa at room temperature is heated to 850-950℃ to make it uniformly austenitized, and then it is sent into a mold with an internal cooling system for stamping. Finally, it is quickly cooled to transform the austenite into martensite, so that the stamped parts are hardened and the strength (safety) is greatly improved.

[0005] The use of hot forming technology can greatly improve the rigidity and strength of the overall structure of the vehicle body, and significantly improve the collision safety performance and NVH performance of the vehicle; the extensive use of this technology can effectively reduce the weight of the vehicle and improve the economic performance of the vehicle. According to the requirements of the vehicle body structure strength, hot forming parts are recommended for the following parts of the vehicle body.

[0006] However, as the material strength increases, reaching 1500MPa or even 2000MPa tensile strength, hot-formed steel has high hardness and low plasticity, and it is easy for rivets to fail to penetrate, rivets to deform, and steel plates to crack during riveting. The existing riveting process can no longer meet the connection requirements. In order to solve the above problems, it is necessary to reduce the hardness of the riveted area by softening and improve the plasticity. However, how to soften only the riveted area without losing the strength of other areas of the part and without introducing large deformation of the part becomes a difficulty.

[0007] The hot stamping laser welding inner and outer front door ring system was first used on the Acura RDX model in 2019, which deeply impressed the laser welding hot forming technology into the minds of domestic automotive material engineers. In fact, as early as 2014, the Acura MDX model showed the world the laser welding outer door ring.

[0008] Laser welding hot forming technology refers to the technology of using laser energy to weld and weld plates of different materials, thicknesses and coatings to form an integral plate before hot stamping. The emergence of tailor-welded plate technology solves the problem of ultra-wide plates and different process performance requirements for different parts, and plays an important role in reducing the weight of the vehicle body, reducing the cost of the whole vehicle, and energy conservation and environmental protection. Summary of the invention

[0009] To this end, the technical problem to be solved by the present invention is to overcome the problems in the prior art that hot-formed parts have high hardness and low plasticity, and that rivets are easily unable to pass through, rivets are deformed, and steel plates crack during riveting. The softening technology is used to soften a smaller area while ensuring that the parts do not undergo a large amount of deformation.

[0010] In order to solve the above technical problems, the present invention provides a method for softening the riveting area of ​​a thermoformed part by laser. The laser beam is moved to irradiate the surface of the thermoformed part to make it reach the required softening temperature, thereby achieving the effect of local tempering. According to the different softening temperatures (100℃-800℃), as well as the design of the laser movement trajectory and speed, different softening effects of the required local areas are achieved, thereby solving the problems in the riveting process of thermoformed parts.

[0011] In order to solve the above-mentioned technical problems, this application provides the following technical solutions:

[0012] The present invention provides a method for softening a riveted area of ​​a hot-formed part by using a laser, comprising the following steps:

[0013] (1) Fix the hot-formed part on the fixture;

[0014] (2) Utilizing a laser beam to heat and soften the riveted area of ​​the thermoformed part according to the set laser parameters and scanning process, the hardness of the riveted area is reduced and the plasticity is increased by tempering, and after laser heating and softening, the thermoformed part is removed and cooled naturally.

[0015] Furthermore, in the step (2), the shape of the heated and softened riveted area is a triangle, a quadrilateral or a circle, such as Figure 1 , area is 20mm 2 -1600 mm 2 .

[0016] Furthermore, in the step (2), the laser beam movement path of the scanning process is a multi-line segment type, a broken line type, a concentric circle type or a center surround type.

[0017] Furthermore, in step (2), the laser beam is vertically irradiated on the surface of the riveting area of ​​the part, and the scanning directions include from front to back, from back to front, from left to right, from right to left, from inside to outside, and from outside to inside, including but not limited to the scanning directions listed above. A suitable laser scanning direction can obtain smaller soft zone deformation.

[0018] Furthermore, in the step (2), during laser heating and softening, the overlap rate of the laser spot moving path is 0-60%.

[0019] Furthermore, in the step (2), the laser focal length of the laser parameters is 40mm-500mm; the temperature of laser heating and softening is set according to the hardness of the laser heating and softening area. When the hardness is 400HV-350HV, the temperature is set to 250℃-400℃; when the hardness is 349HV-300HV, the temperature is set to 400℃-550℃; when the hardness is 299HV-250HV, the temperature is set to 550℃-700℃; when the hardness is 249HV-200HV, the softening temperature is set to 700℃-800℃.

[0020] Furthermore, the thickness of the thermoformed part is 0.6mm-4mm, and the moving speed of the laser beam is 2mm / s-1000mm / s; the greater the thickness of the thermoformed part, the slower the moving speed of the laser beam. If the thickness of the part is too low, the part is easy to deform after laser softening. If the thickness of the part is too high, the temperature difference between the upper and lower surfaces is too high, and it takes a long time of laser irradiation to make the temperature consistent and have a more uniform softening effect. It is not impossible to perform laser softening outside the thickness range.

[0021] Furthermore, in the step (2), the removal method is laser trimming; the laser heating softening can be performed before or after the laser treatment of the thermoformed part to soften the riveted area of ​​the thermoformed part.

[0022] Furthermore, the material of the hot-formed part is one of an uncoated plate and an aluminum-silicon coated or galvanized hot-formed steel.

[0023] Furthermore, in step (1), the hardness of the thermoformed part is 405HV-600HV, and the tensile strength of the thermoformed part is 1300MPa-2000MPa.

[0024] Furthermore, in the step (1), the fixture is a metal fixture that has the function of supporting and fixing the part surface, and has the function of compensating and controlling the deformation of the soft zone of the part.

[0025] Furthermore, in step (2), the laser beam is a Gaussian beam emitted by a semiconductor laser or a solid-state laser; the semiconductor laser or the solid-state laser detects the temperature of the part in real time through a temperature sensor and adjusts the power to reach the set temperature.

[0026] Furthermore, in step (2), the power of laser heating and softening is 0kW-8kW, the wavelength is 600nm-1200nm, and the spot diameter is 1mm-20mm.

[0027] The technical solution of the present invention has the following advantages over the prior art:

[0028] (1) The method of using laser to soften the riveted area of ​​a hot-formed part described in the present invention uses laser as a heat source, has low energy consumption, high energy utilization rate, and is green and pollution-free.

[0029] (2) The method of using laser to soften the riveted area of ​​a hot-formed part described in the present invention uses a laser to heat the riveted area according to a predetermined trajectory, and can flexibly prepare a soft area of ​​any shape and size.

[0030] (3) The method of using laser to soften the riveted area of ​​a hot-formed part described in the present invention heats and tempers the scanned area through laser, thereby reducing the hardness of the hot-formed part to 200HV-450HV. This can solve the problems of rivets being unable to pass through, rivets being deformed, and steel plates being cracked in the original riveting process, thereby making the riveting process of the hot-formed part qualified.

[0031] (4) After the hardness of the riveted area is reduced by the method of using laser to soften the riveted area of ​​the thermoformed part described in the present invention, the difficulty of the riveting process can be reduced, the requirements for rivet materials can be reduced, and costs can be saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of different moving paths of the laser beam of the present invention;

[0033] Figure 2 This is an appearance diagram of the riveted area after laser softening in Example 4 of the present invention;

[0034] Figure 3 is a cross-sectional view of a rivet according to embodiment 4 of the present invention;

[0035] Figure 4 Softening zone hardness curves of various embodiments of the present invention and comparative examples. DETAILED DESCRIPTION

[0036] 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. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0037] In the present invention, unless otherwise explained, technical and scientific terms used in the present invention have the same meanings as commonly understood by those skilled in the art to which the present invention belongs.

[0038] In the present invention, unless otherwise stated, the term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0039] In the present invention, unless otherwise stated, when the terms "comprise" and / or "include" are used in the specification of the present invention, it indicates the existence of the described features, wholes, steps, operations, elements or components, but does not exclude the existence or addition of one or more other features, wholes, steps, operations, elements, components or combinations thereof.

[0040] In the present invention, unless otherwise stated, the ranges and alternatives of the parameters of the heat treatment process can be combined with each other to form a new heat treatment process.

[0041] In the present invention, unless otherwise specified, if no specific conditions are specified in the examples, the experiments were carried out according to conventional conditions or conditions recommended by the manufacturer.

[0042] In the present invention, unless otherwise specified, all reagents or instruments used without indicating the manufacturer are conventional products that can be purchased from the market.

[0043] Example 1

[0044] A method for softening the riveted area of ​​a hot-formed part by laser, comprising the following steps:

[0045] (1) Select an aluminum-silicon coated plate part with a thickness of 1.6 mm and fix it on the fixture;

[0046] (2) Set the laser softening parameters: the soft zone size is a 20*20 rectangle, the focal length is 300 mm, the laser spot diameter is 4 mm, the laser scanning path is a: multi-segment type, the overlap rate of the laser spot moving path is 50%, the laser beam moving speed is 72 mm / s, and the heating temperature is 400°C.

[0047] The surface of the riveted area of ​​the thermoformed part is heated in sequence, and the hardness of the riveted area is reduced and the plasticity is increased through the tempering principle. After completion, the part is removed and allowed to cool naturally.

[0048] Example 2

[0049] A method for softening the riveted area of ​​a hot-formed part by laser, comprising the following steps:

[0050] (1) Select an aluminum-silicon coated plate part with a thickness of 1.6 mm and fix it on the fixture;

[0051] (2) Set the laser softening parameters: the soft zone size is a 20*20 rectangle, the focal length is 300 mm, the laser spot diameter is 4 mm, the laser scanning path is a: multi-segment type, the overlap rate of the laser spot moving path is 50%, the laser beam moving speed is 72 mm / s, and the heating temperature is 550°C.

[0052] The surface of the riveted area of ​​the thermoformed part is heated in sequence, and the hardness of the riveted area is reduced and the plasticity is increased through the tempering principle. After completion, the part is removed and allowed to cool naturally.

[0053] Example 3

[0054] A method for softening the riveted area of ​​a hot-formed part by laser, comprising the following steps:

[0055] (1) Select an aluminum-silicon coated plate part with a thickness of 1.6 mm and fix it on the fixture;

[0056] (2) Set the laser softening parameters: the soft zone size is a 20*20 rectangle, the focal length is 300 mm, the laser spot diameter is 4 mm, the laser scanning path is a: multi-segment type, the overlap rate of the laser spot moving path is 50%, the laser beam moving speed is 72 mm / s, and the heating temperature is 700°C.

[0057] The surface of the riveted area of ​​the thermoformed part is heated in sequence, and the hardness of the riveted area is reduced and the plasticity is increased through the tempering principle. After completion, the part is removed and allowed to cool naturally.

[0058] Example 4

[0059] A method for softening the riveted area of ​​a hot-formed part by laser, comprising the following steps:

[0060] (1) Select an aluminum-silicon coated plate part with a thickness of 1.6 mm and fix it on the fixture;

[0061] (2) Set the laser softening parameters: the soft zone size is a 20*20 rectangle, the focal length is 300 mm, the laser spot diameter is 4 mm, the laser scanning path is a: multi-segment type, the overlap rate of the laser spot moving path is 50%, the laser beam moving speed is 72 mm / s, and the heating temperature is 800°C.

[0062] The surface of the riveted area of ​​the thermoformed part is heated in sequence, and the hardness of the riveted area is reduced and the plasticity is increased through the tempering principle. After completion, the part is removed and allowed to cool naturally.

[0063] Samples were taken from the softened parts with a thickness of 1.6 mm and 1.0 mm, and riveting tests were carried out on the softened riveted areas. The results showed that the riveted areas could be formed smoothly. Figure 2 As shown, the riveted joints have a regular appearance, no cracks, and the sheets are tightly bonded. Figure 3 This is a cross-sectional view of the rivet. The results show that the rivet interlocking value meets the use requirements.

[0064] Example 5

[0065] A method for softening the riveted area of ​​a hot-formed part by laser, comprising the following steps:

[0066] (1) Select an aluminum-silicon coated plate part with a thickness of 1.6 mm and fix it on the fixture;

[0067] (2) Set the laser softening parameters: the soft zone size is a 20*20 rectangle, the focal length is 300 mm, the laser spot diameter is 4 mm, the laser scanning path is c: concentric circle, the overlap rate of the laser spot moving path is 50%, the laser beam moving speed is 72 mm / s, and the heating temperature is 700°C.

[0068] The surface of the riveted area of ​​the thermoformed part is heated in sequence, and the hardness of the riveted area is reduced and the plasticity is increased through the tempering principle. After completion, the part is removed and allowed to cool naturally.

[0069] Comparative Example 1

[0070] A method for softening the riveted area of ​​a hot-formed part by laser, comprising the following steps:

[0071] (1) Select an aluminum-silicon coated plate part with a thickness of 1.6 mm and fix it on the fixture;

[0072] (2) Set the laser softening parameters: the soft zone size is a 20*20 rectangle, the focal length is 300 mm, the laser spot diameter is 4 mm, the laser scanning path is a: multi-segment type, the overlap rate of the laser spot moving path is 50%, the laser beam moving speed is 1200 mm / s, and the heating temperature is 700°C.

[0073] The surface of the riveted area of ​​the thermoformed part is heated in sequence, and the hardness of the riveted area is reduced and the plasticity is increased through the tempering principle. After completion, the part is removed and allowed to cool naturally.

[0074] Comparative Example 2

[0075] A method for softening the riveted area of ​​a hot-formed part by laser, comprising the following steps:

[0076] (1) Select an aluminum-silicon coated plate part with a thickness of 1.6 mm and fix it on the fixture;

[0077] (2) Set the laser softening parameters: the soft zone size is a 20*20 rectangle, the focal length is 300 mm, the laser spot diameter is 4 mm, the laser scanning path is a: multi-segment type, the overlap rate of the laser spot moving path is 50%, the laser beam moving speed is 72 mm / s, and the heating temperature is 900°C.

[0078] The surface of the riveted area of ​​the thermoformed part is heated in sequence, and the hardness of the riveted area is reduced and the plasticity is increased through the tempering principle. After completion, the part is removed and allowed to cool naturally.

[0079] The soft zone hardness of the above cases was tested, and the results are shown in Table 1. Figure 4 Hardness curve of soft zone in each case.

[0080] Table 1 Soft zone hardness test of each embodiment and comparative example

[0081] Case <![CDATA[Soft zone hardness (HV 10 )]]> Example 1 380 Example 2 313 Example 3 253 Example 4 231 Example 5 267 Comparative Example 1 Upper shallow 1 / 3 softened Comparative Example 2 268

[0082] 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 softening the riveted area of ​​a thermoformed part using a laser, characterized in that: The following steps are involved: (1) Fix the hot-formed part on the fixture; (2) Utilizing a laser beam to heat and soften the riveted area of ​​the thermoformed part according to the set laser parameters and scanning process, the hardness of the riveted area is reduced and the plasticity is increased by tempering, and after laser heating and softening, the thermoformed part is removed and cooled naturally.

2. A method for softening the riveted area of ​​a hot-formed part by laser according to claim 1, characterized in that: In the step (2), the laser beam movement path of the scanning process is a multi-line segment type, a broken line type, a concentric circle type or a center surround type; during laser heating and softening, the laser beam movement path overlap rate is 0-60%.

3. The method of using laser to soften the riveted area of ​​a hot-formed part according to claim 1, characterized in that: In the step (2), the laser focal length of the laser parameters is 40mm-500mm; the temperature of laser heating and softening is set according to the hardness of the laser heating and softening area. When the hardness is 400HV-350HV, the temperature is set to 250℃-400℃; when the hardness is 349HV-300HV, the temperature is set to 400℃-550℃; when the hardness is 299HV-250HV, the temperature is set to 550℃-700℃; when the hardness is 249HV-200HV, the softening temperature is set to 700℃-800℃.

4. The method of using laser to soften the riveted area of ​​a hot-formed part according to claim 1, characterized in that: The thickness of the thermoformed part is 0.6 mm-4 mm, and the moving speed of the laser beam is 2 mm / s-1000 mm / s; the greater the thickness of the thermoformed part, the slower the moving speed of the laser beam.

5. The method of using laser to soften the riveted area of ​​a hot-formed part according to claim 1, characterized in that: The material of the hot-formed parts is one of uncoated plate and aluminum-silicon coated or galvanized hot-formed steel.

6. The method of using laser to soften the riveted area of ​​a hot-formed part according to claim 1, characterized in that: In step (1), the hardness of the thermoformed part is 405HV-600HV, and the tensile strength of the thermoformed part is 1300MPa-2000MPa.

7. The method of using laser to soften the riveted area of ​​a hot-formed part according to claim 1, characterized in that: In the step (2), the laser beam is a Gaussian beam emitted by a semiconductor laser or a solid-state laser; the semiconductor laser or the solid-state laser detects the temperature of the part in real time through a temperature sensor and adjusts the power to reach the set temperature.

8. The method of using laser to soften the riveted area of ​​a hot-formed part according to claim 1, characterized in that: In the step (1), the fixture is a metal fixture that has the function of supporting and fixing the part surface, and has the function of compensating and controlling the deformation of the soft zone of the part.

9. The method of using laser to soften the riveted area of ​​a hot-formed part according to claim 1, characterized in that: In the step (2), the laser beam is vertically irradiated on the riveting area of ​​the thermoformed part, and the scanning direction includes from front to back, from back to front, from left to right, from right to left, from inside to outside or from outside to inside. The appropriate laser scanning direction can obtain smaller soft zone deformation.

10. The method of using laser to soften the riveted area of ​​a hot-formed part according to claim 1, characterized in that: In the step (2), the power of laser heating and softening is 0 kW-8 kW, the wavelength is 600 nm-1200 nm, and the spot diameter is 1 mm-20 mm.

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