Laser precision welding device and method for collimator grid structure
Technical Field
The invention relates to a laser precision welding device and method for a collimator grid structure, and belongs to the field of laser welding processing.
Background
The high-precision collimator is a key component in the fields of deep space exploration, pulsar navigation, medical instruments and the like. The collimator consists of a collimator metal frame body and a metal foil grid unit inserted on the body. The overall structure of the collimator is of the order of meters, while the grid size is of the order of millimeters and the foil thickness is of the order of micrometers. The collimator grid structure is a typical cross-scale precision component, the number of welding points is large, and the number of welding points of a single part is nearly ten thousand. The orthogonal metal foils which are mutually inserted form a grid unit structure, the materials are usually metals such as tungsten, tantalum and the like, the thickness of the foils is dozens of micrometers, the requirements on the parallelism and verticality precision of the grid are strict, and the processing difficulty is very high. The collimator grid structure is manufactured by a mechanical method in foreign countries, a grid frame with thicker inner part and the outer wall are made of the same material and are quickly formed into a whole by casting or laser, then microgrooves are processed on the grid plate, and tungsten plates or tantalum plates are vertically inserted to form the collimator body. The concept of manufacturing the high-precision collimator by adopting the laser welding after the tantalum sheets are alternately inserted is put forward by domestic units, and related patents are applied.
The structural characteristics of the high-precision collimator determine the great manufacturing difficulty. Due to the extremely high requirements for welding high melting point metal foils, it is difficult to prepare a qualified collimator grid using conventional laser welding equipment. Firstly, the whole structure of the collimator is meter-level, the size of a single grid of the grid structure is millimeter-level, the thickness of a metal foil is micrometer-level, the parallelism and verticality precision requirements of grid plate foils which are orthogonally inserted are high, and the large-size collimator body is manufactured step by laser welding of microfine foils, which is a cross-scale ultra-precise welding technology; secondly, the high melting point of metals such as tantalum and the like requires larger welding energy, and the foils with the thickness of micron order are very easy to deform under the action of welding heat, so that the heat input is required to be accurately controlled to control the thermal stress and the thermal deformation, and the dimensional accuracy is ensured; thirdly, the number of welding spots of a single grid structure is hundreds or thousands, and the requirements on the positioning accuracy, the redundancy rate and the stability of the welding process are very high, which requires the accurate control of the laser energy input. These provide challenges to welding equipment and welding technology, and no ultra-precise laser welding device capable of meeting the manufacturing requirements of a high-precision collimator is available at present, and the development of a device and technology for precise laser welding is urgently needed.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a laser welding apparatus and method for a grid structure of a collimator, which can achieve high-precision and automatic welding of the grid structure and meet the requirements for manufacturing a high-precision collimator.
In order to achieve the purpose, the invention adopts the following technical scheme:
in one aspect, the present invention provides a laser welding apparatus for a collimator grid, including: laser instrument, beam shaping system, dynamic focus scanning system, visual detection system, XY numerical control work platform, Z to motion axis, welding clean system, supplementary welding equipment and control system, its characterized in that:
the dynamic focusing scanning system is fixed on the Z-direction movement axis; the collimator grid is fixed on the XY numerical control working platform;
the vision detection system can detect the welding position of the collimator grid, and the XY numerical control platform can calibrate and adjust the position; the control system can drive and control the laser beams, realize scanning movement and dynamic focusing and weld the grid structure.
Preferably, the laser is a pulse laser, the laser power is 50-200W, and the minimum focusing spot is less than or equal to 30 μm.
Preferably, the dynamic focusing scanning system comprises a dynamic focusing lens group, a two-axis reflecting galvanometer and a galvanometer control unit.
Preferably, the scanning range of the dynamic focusing scanning system is more than or equal to 50mm multiplied by 50mm, the scanning linearity is less than or equal to 3.5mrad, and the repetition precision of the dynamic focusing scanning system is less than or equal to 8 mu mad.
Preferably, the vision inspection system comprises two CCD image sensors and an imaging objective lens, which are respectively located at two sides of the light outlet of the dynamic focusing scanning system.
Preferably, the detection precision error of the characteristic structure dimension of the visual detection system is less than or equal to 2 μm; the error of the feature structure size positioning precision is less than or equal to 5 mu m.
Preferably, the X/Y axis positioning precision of the XY numerical control working platform is less than or equal to 2 μm, and the X/Y axis repeated positioning precision is less than or equal to 2 μm.
Another aspect of the present invention provides a method for welding a collimator grid using the laser welding apparatus according to any one of the above technical solutions, comprising the steps of:
step 1, arranging a collimator grid on a special fixture and then fixing the collimator grid on an XY numerical control working platform;
step 2, importing the three-dimensional model of the collimator grid into a control system, determining the origin of a coordinate system of the collimator grid, and determining a scanning welding pattern through welding path planning;
step 3, positioning the welding initial position by using a visual detection system, driving the XY numerical control working platform to carry out motion calibration by using a control system, and determining a welding initial point;
step 4, the laser dynamic focusing scanning system plans according to the scanning path to carry out scanning welding;
and 5, after welding one grid unit of the collimator grid, controlling the XY numerical control working platform to move into an unwelded unit, and repeating the step 3 and the step 4 until all the grid units are welded.
Preferably, the collimator grids are formed by mutually intersecting metal foils made of materials selected from tungsten, molybdenum, tantalum and lead, and the thickness of the foils is 20-100 μm; and the intersection of every two orthogonal metal foils is the welding position of the laser beam.
Preferably, in step 4, the dynamic focusing scanning system is driven according to the scanning welding pattern to realize the scanning movement of the laser beam, so that the laser beam is switched on for welding at each welding position, and the light skip is closed between different welding positions.
The invention has the advantages that:
the invention provides an optical-mechanical-electrical cooperative control welding device integrating dynamic fine focusing of a pulse laser beam, high-speed galvanometer scanning welding, high-precision visual sensing detection and linkage of a precise numerical control platform, so that multi-welding-point high-precision rapid scanning machining of large-size workpieces/parts is realized, and automatic welding is implemented more flexibly and efficiently.
Aiming at the welding requirement of manufacturing a collimator grid structure, the laser dynamic focusing scanning system realizes real-time dynamic focusing and high-speed scanning movement, obtains fine ideal light spot diameter in a large-size range of the surface of a workpiece, and can eliminate defocusing error caused by optical path change caused by rotation of a scanning galvanometer and pincushion error and barrel error during scanning of the galvanometer by performing error correction compensation through a control system, thereby ensuring accurate control of a welding position; based on a dynamic focusing galvanometer scanning system, high-speed accurate scanning of laser beams based on graphic driving is achieved, the laser beams are turned on at each welding joint for welding, light is closed and air jumps among different welding beads, welding heat input is reduced to the maximum extent, meanwhile, aiming at a collimator grid structure, a scanning welding path can be optimized, residual stress in components is dispersed and reduced, buckling deformation is prevented, and accurate welding of devices is achieved. Under the control of the precise movement of the numerical control motion platform and the CCD visual sensing detection, the one-by-one welding of a plurality of grid single units can be rapidly realized, and finally the manufacture of the collimator is completed. The laser welding technology based on dynamic focusing galvanometer scanning can meet the requirements of high-performance and light-weight device precision manufacturing in high-end fields such as aerospace, medical instruments, micro-photoelectrons and the like, and has great development potential.
Drawings
Fig. 1 is a schematic view of the structure of a collimator grid to be welded according to the present invention.
Fig. 2 is a schematic view of a cross-over position of a laser welded metal foil.
Fig. 3 is a schematic view of the configuration of the laser welding apparatus of the present invention.
Fig. 4 is a perspective view of a main body portion of the laser welding apparatus.
Fig. 5 is a schematic diagram of the dual CCD image sensor vision inspection.
FIG. 6 is a schematic diagram of dynamic focusing scanning of the laser over the weld spots.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Fig. 1 is a schematic view of a grid structure 1 of a collimator requiring welding according to the present invention, which is mainly composed of a plurality of grid structure units 2, wherein the interior of each grid structure unit 2 is composed of a plurality of transverse metal foils 21 and longitudinal metal foils 22 which are orthogonally inserted into each other, and the crossing positions of the transverse metal foils and the longitudinal metal foils are welding positions 23. The length and width dimensions of the individual grid structures are in the order of millimeters, and the material of the metal foil is usually selected from metals such as tungsten, tantalum and the like, and the thickness is in the order of tens of micrometers. The number of welding points of each grid structure is about ten thousand, and the parallelism and the perpendicularity must be guaranteed to be within 1 angle. In a preferred embodiment, the material of the metal foil is tantalum, the melting point of which is up to 2996 ℃, and the thickness of the foil is 40 μm.
As shown in fig. 2, in the process of welding the collimator grid, the laser beam 3 is irradiated to the welding position 23, and it is required that the weld joint is reliable and the welding is less deformed as a whole.
Fig. 3 is a general structural view of a laser welding apparatus according to the present invention. Wherein welding set includes: the device comprises a laser, a beam shaping and transmitting system, a dynamic focusing and scanning system, a visual detection system, an XY numerical control working platform, a Z-direction motion axis, a welding purification system, auxiliary welding equipment including a special welding fixture and a related control system.
Fig. 4 shows a perspective view of the body part of the welding device. The QCW pulse fiber laser with the power of 100W is selected as the laser, and the laser can achieve fine focusing of light beams. The laser beam from the laser is transmitted through an optical fiber 31 and through a beam shaper 32 to the dynamic focus scanning system.
The dynamic focusing scanning system mainly comprises a dynamic focusing mirror group 41, a two-axis high-speed scanning reflecting galvanometer 42 and a galvanometer control unit. In order to meet the welding range of the grid structure unit of the collimator, on a welding working plane, the dynamic focusing scanning range of a laser beam is more than or equal to 50mm multiplied by 50mm, the scanning linearity is less than or equal to 3.5mrad, and the repetition precision of a laser dynamic focusing scanning system is less than or equal to 8 mu mad. The dynamic focus scanning system is fixed on the Z-axis of motion 6, which is adjustable up and down in the vertical direction relative to the welding position 23.
The visual detection system comprises two high-resolution CCD image sensors and an imaging objective lens corresponding to each CCD image sensor, and the imaging objective lenses are respectively positioned at two sides of a light outlet of the dynamic focusing scanning system. The detection precision error of the characteristic structure dimension of the visual detection system is less than or equal to 2 mu m; the error of the feature structure size positioning precision is less than or equal to 5 mu m.
The X/Y axis positioning precision of the XY numerical control working platform 7 is less than or equal to 2 mu m; the repeated positioning precision of the X/Y axis is less than or equal to 2 mu m. The collimator grid 1 is fixed on an XY numerically controlled working table 7, all of which are mounted on a table (8). The control system utilizes the visual detection system to automatically detect the welding position of the grid, so as to drive the XY numerical control working platform 7 to automatically calibrate and adjust the position, and the control system can also drive and control the laser beam, realize scanning movement and dynamic focusing and weld the grid structure.
In addition, the whole welding system requires equipment to continuously and stably work on laser, the system must comprehensively consider several factors such as heat dissipation, stability and safety of the system, and the box structure of the system is designed according to the principles of attractive appearance, reliable structure and simple installation. The integral structure is compact and simple, firm and dustproof, and convenient and accurate to install, and is suitable for industrial occasions.
The method for adopting the grid structure of the laser collimator of the welding device comprises the following steps:
firstly, a collimator grid 1 is arranged on a special fixture (not shown in the figure) and then fixed on an XY numerical control working platform 7; the three-dimensional model of the collimator grid is led into a welding computer system serving as a control system, the origin of a coordinate system of a weldment is determined, a thermal-force coupling model of the collimator grid structure in the scanning welding process is established based on the existing welding experience and numerical calculation, the optimized design of a scanning process path is realized by researching the welding deformation rules in different scanning modes, the welding path planning is carried out, and finally the optimal scanning welding pattern is determined in the welding computer system.
As shown in fig. 5, the vision inspection system includes two high-resolution CCD image sensors 51 and an imaging objective lens 52, which are respectively located at two sides of the light outlet of the dynamic focus scanning system. And (3) selecting a high-resolution CCD image sensor with more than 1000 ten thousand pixels to visually detect the welding position, wherein each CCD image sensor 51 is provided with a corresponding detection range 53. In a preferred embodiment, the vision detection system adopts double CCD image sensor photogrammetry to realize real-time shadow correction, and can acquire images with clear edges, good sharpening degree and uniform gray distribution, thereby performing image distortion correction and camera internal parameter calibration, realizing high-precision edge extraction for welding positions by using an optimized image processing algorithm, and automatically identifying the positions of reference points or characteristic contours. Therefore, the welding computer system can drive the XY numerical control working platform to carry out motion calibration and determine a welding starting point. After the preparation work is finished, scanning welding is started, and laser emitted by the laser passes through the shaping optical lens group, the dynamic focusing optical lens group and the two-axis scanning galvanometer in sequence and then is emitted to a welding position. The fine laser focusing energy is uniformly focused on the welding surface through the control of the control system. The coordination polarization of the scanning galvanometer realizes that the laser beam is driven by the scanning welding pattern to complete complex scanning movement, error correction compensation is carried out by the control system in a scanning range, and defocusing errors caused by the change of the optical path when the scanning galvanometer rotates to cause and pincushion errors and barrel errors during scanning of the galvanometer can be eliminated, so that the accuracy of a welding position is ensured.
As shown in fig. 5, the laser scanning range on the working plane 20 of the present embodiment is 80mm × 100 mm.
As shown in fig. 6, the welding focal spot diameter can reach 30 μm for each welding position. At each welding position 23, the laser beam is switched on for welding and the light jumps between different welding positions 23 are closed. The dynamic focusing scanning system realizes real-time dynamic focusing and high-speed scanning movement, and error correction compensation is carried out through the control system, so that accurate control of the welding position 23 is ensured.
When the scanning welding of one collimator grid unit is completed, the XY numerical control working platform 7 moves the welding unit out and moves the welding unit into a new non-welding unit. At this time, the vision detection system carries out image detection and analysis on the new grid structure unit again, automatically carries out welding positioning, carries out new scanning welding again, and the operation is circulated until all the grid units are welded.
In the welding process, the welding fume, the welding oxidation and the like are considered, the fume in the welding process can be timely discharged by using a welding purification system, and meanwhile, auxiliary means such as inert gas protection and the like are adopted.
By utilizing the welding device, residual stress in the components can be dispersed and reduced through welding experiments and dimensional precision tests, buckling deformation is prevented, and precision welding of the collimator grid structure is realized. Analysis of the final collimator grid structure confirmed that all weld spots were reliable, with maximum weld distortion not exceeding 30 μm.
Those skilled in the art will appreciate that the dynamic focus scanning system of the present invention may be employed with any of the techniques known in the art of laser three-dimensional machining. The dynamic focusing scanning system is a system capable of dynamically adjusting X, Y, Z axial galvanometer positions according to position parameters to realize laser processing at different positions on the surface of an object, and distortion error correction processing belongs to a common technical means in the field of laser galvanometer scanning.
Those skilled in the art will appreciate that the visual inspection system of the present invention employs associated hardware devices and image processing software algorithms to enable determination of the starting point edge detection method, and that any suitable prior art technique may be used.
According to the technical requirements of the collimator on precision manufacturing process and the technical requirements of aspects of overall dimension, position, precision and the like, in order to realize reliable connection of the collimator grid structure and ensure the high-precision dimension of the collimator grid structure, the laser precision welding device and the laser precision welding technology for the collimator grid structure provided by the invention integrate a dynamic focusing scanning technology, a visual detection and automatic positioning technology and a multi-axis linkage precision motion control technology. Detecting and acquiring images in real time through electro-optical sensing, processing the images in real time, and judging and positioning geometric characteristics of the aligner structure; based on a dynamic focusing galvanometer scanning system, high-speed accurate scanning of laser beams based on graphic driving is realized, the laser beams are switched on at each welding joint for welding, and the light is closed and the air jump is carried out between different welding passes, so that the welding heat input is reduced to the maximum extent; aiming at numerous micro-connections of the collimator grid structure, efficient and full-automatic welding is realized. The device and the method provided by the invention can meet the requirements on precise manufacturing of high-performance and light-weight devices in the high-end manufacturing fields of aerospace, medical instruments, micro-photoelectrons and the like, and have great development potential.
The above description is of the preferred embodiment of the present invention and the technical principles applied thereto, and it will be apparent to those skilled in the art that any changes and modifications based on the equivalent changes and simple substitutions of the technical solution of the present invention are within the protection scope of the present invention without departing from the spirit and scope of the present invention.