CN111822553A

CN111822553A - Novel process for laser thermoforming, stretch bending and production of metal sheet

Info

Publication number: CN111822553A
Application number: CN201910314292.9A
Authority: CN
Inventors: 石永军; 郭延阔; 孙瑞; 李县法
Original assignee: China University of Petroleum East China
Current assignee: China University of Petroleum East China
Priority date: 2019-04-18
Filing date: 2019-04-18
Publication date: 2020-10-27

Abstract

The invention relates to a method for realizing laser bending metal plate forming by using a pre-stretch bending method, which can reduce springback to a greater extent and further improve the bending angle of a plate. Firstly, a forming workpiece is fixed on a three-dimensional numerical control platform, one end of the workpiece is fixed by a clamp, and the other free end of the workpiece is firstly applied with longitudinal tension by using a stretch bending device and then applied with transverse pressure. And then scanning and heating the upper surface of the plate by using laser, finally completely cooling a heating area of the plate, removing the stretch bending device and removing the transverse longitudinal force. According to a large number of documents, the stress state in the plate can be changed under the bending force, so that more tangential compressive stress generated on the inner side of the neutral layer of the laser heating area is converted into tensile stress, the whole section of the plate is under the action of the tensile stress in the tangential direction, and after the plate is unloaded, the rebounds of the inner layer fiber and the outer layer fiber are mutually offset, and the rebounds can be greatly reduced, so that the bending angle of the plate is improved. The method is suitable for forming high-hardness, brittle and hard-to-deform medium plate materials, and has a wide application prospect in the fields of aerospace, medical treatment and automobile manufacturing.

Description

Novel process for laser thermoforming, stretch bending and production of metal sheet

Technical Field

The invention relates to a method for realizing laser bending metal plate forming by utilizing a pre-stretch bending method, belongs to the technical field of mechanical manufacturing, and can be applied to rapid bending and shape-righting processing of metal plates made of small-batch or difficult-to-form materials.

Technical Field

The laser bending forming under the pre-pressure is a novel processing technology based on the original laser bending, a certain elastic deformation of a workpiece is applied through a die, and then the elastic deformation concentrated area is scanned by laser. This region has a reduced yield strength due to the high temperature of the laser, thereby increasing its ability to plastically deform, converting more elastic deformation toward plastic deformation. Under the condition of utilizing a simple die, laser bending forming under precompression has four better advantages besides having the traditional excellent characteristics: (1) the sheet material bending forming device has good forming capability, has larger single forming amount due to laser bending forming under the pre-pressure, and realizes the control of the bending forming direction of the sheet material by controlling the pre-pressure loading direction; (2) the laser has high energy density, small heat affected zone and less influence on the performance of the formed part material, and is not easy to wrinkle during forming. (3) The sheet material has good repeatability, the deformation of the sheet material is elastic deformation conversion, and the defects of microcracks, sliding lines and the like caused by plastic loading can be effectively avoided. (4) And the bending angle is accurately controlled by controlling the magnitude of the pre-pressure. The laser bending forming under the pre-pressure provides a new method for bending processing, and has important research significance on the bending processing of parts with complicated and changeable structures and difficult application of conventional forming

At present, in laser bending forming under pre-pressure, because laser scanning only adopts an upper surface scanning mode, a heat source can only form a small plastic deformation area on the upper surface of a plate, and the bending deformation is small due to the fact that the rebound quantity is large after the pressure is removed. Especially for medium and thick plates which are applied more in actual production, the plate thickness is larger, and the inside of the plate has larger elastic internal energy, so that the conventional pre-pressure laser bending forming is difficult to effectively convert. Therefore, a simple and effective process scheme is needed to further reduce the springback and improve the single forming amount of the laser bending medium plate under the pre-pressure, so that a larger bending angle is obtained.

Disclosure of Invention

In order to overcome the problems of large resilience and small bending angle in laser thermoforming of a metal plate under pre-pressure, a new method, namely a stretch bending method, is provided: that is, in the conventional laser plate bending process under pre-pressure, transverse pre-pressure is generally applied, and in the stretch bending method, longitudinal tension is applied while transverse pre-pressure is applied, so that the stress distribution in a deformation area is changed, and thus, the springback is reduced, and the bending angle of the plate is increased.

The technical scheme adopted for solving the technical problems of the invention is as follows:

(1) the metal plate is arranged on the three-dimensional numerical control platform, and one end of the metal plate is fixed. In order to prevent the oil dirt on the surface of the metal plate from influencing heat transfer, the metal plate is cleaned by acetone. Because the absorption rate of the plate to the laser is very low, in order to improve the absorption coefficient of the laser, a layer of coating is uniformly coated on the surface of the metal for blackening;

(2) fixing the free end of the other end of the metal plate by using a stretch bending device, wherein the stretch bending device firstly applies longitudinal tension and then applies transverse pressure;

(3) and (5) after the stretch bending device is set, scanning and heating the upper surface of the plate by using laser. After the laser scanning is finished, waiting for the complete cooling of the heating area of the plate, removing the stretch bending device and removing the transverse and longitudinal force;

the greatest advantage of stretch-bending processes compared to conventional bending methods is the reduction in spring-back, which is proven in a large number of documents. In the common process without pre-stretching force, the outer side of the bent section is in a tensile stress state, the inner side of the bent section is in a compressive stress state, and after unloading, the elastic parts in the two stress states need to recover to generate a moment which is a reason for generating rebound. When pre-longitudinal tensile force exists, the stress central layer with zero stress at the junction of longitudinal tensile stress and pre-compressive stress can move inwards, namely, the pulled part of the section becomes more, the pressed part becomes less, even when the pre-compressive stress is large to a certain degree, the whole section is in a tensile stress state, and the elastic recovery after unloading generates a rebound moment which is much smaller than that when the pre-compressive stress is not added, so that the rebound can be reduced. Compared with the conventional metal plate hot forming under the pre-pressure, the method is simple and easy to implement without increasing equipment, and can greatly reduce the resilience and improve the bending angle of the plate. The method is not only suitable for conventional metal materials, but also can be applied to the forming of high-hardness and brittle materials difficult to deform, and has a wide application prospect in the fields of aerospace, medical machinery, microelectronics and the like.

Drawings

FIG. 1 is a schematic view of a novel process apparatus for laser thermoforming of a metal plate

FIG. 2 is a schematic view of a new process for laser thermoforming and stretch bending of a metal plate

1 laser, 2 reflecting mirrors, 3 focusing mirrors, 4 metal workpieces, 5 three-dimensional control tables, 6 clamps, 7 laser beams and 8 stretch bending devices

Detailed Description

The following describes embodiments of the present invention with reference to the drawings. The novel process device for the laser thermoforming stretch bending of the metal plate consists of a laser (1), a reflector (2), a focusing mirror (3), a three-dimensional control table (5), a clamp table (6) and a stretch bending device (8). As shown in fig. 1, the forming steps are as follows:

1. cleaning the surface of the metal workpiece (4) by using acetone;

2. uniformly coating a layer of laser adsorption coating on the surface of the metal workpiece (4) for blackening;

3. the metal workpiece (4) is placed on a three-dimensional control table (5), and one end of the metal workpiece (4) is fixed by a clamp (6). Longitudinal tension is firstly applied to the other free end of the workpiece (4) by a stretch bending device (8), then transverse pressure is applied, and the positions of the laser beam (7) and the stretch bending device (8) are fixed;

4. the laser beam (7) is emitted by the laser (1), and forms a beam with a certain spot diameter through the reflecting mirror (2) and the focusing mirror (3) to be radiated on the surface of the formed workpiece (4);

5. the three-dimensional control platform (5) drives the formed workpiece (4) to move, so that the continuous laser beam (7) can heat the surface of the formed workpiece (4) along a given motion track b at a certain scanning speed v, as shown in figure 2;

6. and after heating is finished, cooling the heating area of the metal plate by natural cooling, forced convection air cooling or forced convection water cooling. After cooling is finished, removing the stretch bending device;

7. and establishing a basic relation database of workpiece bending angles, bending tension and laser process parameters, and reversely calculating the required bending tension and laser process parameters according to the basic relation database and the plate bending deformation requirement, thereby improving the efficiency.

Claims

1. A method for realizing laser bending metal plate forming by using a pre-stretch bending method comprises the following steps:

1) fixing the free end of the other end of the metal plate by using a stretch bending device, wherein the stretch bending device firstly applies longitudinal tension and then applies transverse pressure;

2) and (5) after the stretch bending device is set, scanning and heating the upper surface of the plate by using laser. After the laser scanning is finished, waiting for the complete cooling of the heating area of the plate, removing the stretch bending device and removing the transverse and longitudinal force;

3) and establishing a basic relation database of workpiece bending angles, bending tension and laser process parameters, and reversely calculating the required bending tension and laser process parameters according to the basic relation database and the plate bending deformation requirement, thereby improving the efficiency.