Deep-space exploration is important to innovate space technology and explore space resources. A collimator is a key component of a deep-space probe; however, producing a high spatial resolution collimator is challenging. Currently, the deep-space exploration collimator grid is mostly composed of frames. Casting or laser additive manufacturing is used to build the inner grid structure, which is quite thick, as well as the entire outside wall. The grid frame is then used to create the microgrooves. Finally, the collimator grid is formed by inserting tungsten or tantalum foils into the microgrooves. Furthermore, collimator grid manufacturing technologies include LIGA and electrical discharge wire-cutting. These approaches may result in thick walls, limiting the collimator’s duty ratio and efficiency, or result in a longer manufacturing period, higher cost, and a smaller grid height. The hard X-ray modulation telescope satellite (HXMT), which China developed independently, is used as an example to present our research progress on laser microwelding technology and equipment development for the cross-scale collimator grid, which is funded by the National Key Research and Development Program.
The laser spot welding experiment was conducted first to identify the welding parameters based on the structural features of the HXMT collimator. The grid deformation finite element analysis was then performed to provide laser welding guidance. Finally, laser welding equipment was designed and validated to meet the grid cell laser welding requirements.
The HXMT collimator is composed of an aluminum alloy frame with many tantalum grid cells placed into it. Laser spot welding junction points formed by two orthogonal arrays of tantalum foils are used to create the grid cell. The fabrication of tantalum foils, grid cell assembly and welding, and grid cell insertion into the collimator frame are all part of the manufacturing process (Fig. 3). For laser welding grid cells, an IPG YLM-150/1500-QCW quasicontinuous fiber laser and a self-developed three-dimensional (3D) dynamic focusing galvanometer are employed. With a beam diameter of 40 μm, laser power of 180-220 W, and pulse width of 6-10 ms, a well-formed welding spot is created (Fig. 4). The results of the finite element analysis show that instability deformation is common during the laser welding of the collimator grid cell (Fig. 5). To address this issue, an integrated set combining tantalum foil assembly and collimator grid welding/insertion is developed (Fig. 6). The assembly error and welding deformation are well-controlled, resulting in the collimating hole’s dimensions accuracy being within ±20 μm. The self-designed laser microwelding equipment consists primarily of a quasicontinuous fiber laser, a self-developed 3D dynamic focusing galvanometer, an X/Y motion platform with a Z support frame and motion axis, a CCD vision inspection system, and a computer control system, among other components (Fig. 7). Before welding, the stage moves to the CCD field of view to locate the welding point; next, the stage moves to the galvanometer, which can quickly and accurately regulate the movement of the laser beam, allowing for the rapid and precise welding of each grid cell’s welding spot. After welding, the stage returns to the CCD field of view to detect and evaluate welding quality (Fig. 8).
High-efficiency laser microwelding and detection of large depth and high spatial resolution collimator grid have been realized using linkage technology of online visual inspection, dynamic focusing galvanometer, and CNC machine as well as the development of an integrated set to combine tantalum foil assembly and collimator grid welding/insertion, as along with the development of laser microwelding equipment and welding process. The accuracy of collimating hole size can be controlled within ±20 μm for the tantalum collimator grid with 70 μm wall thickness, 1.17 mm×4.68 mm collimating hole size, and 67 mm depth.
