Laser cleaning and innovative scanning components - MASM multi-level array scanning system released

Compared to laser cutting, laser welding and other laser processing industries, the development of laser cleaning is significantly slow, mainly due to the low efficiency and cost-effectiveness of laser cleaning. The efficiency of laser cleaning is mainly determined by the laser power and scanning speed. With the rapid development of domestic lasers, pulsed lasers have reached 1KW pulses, and continuous lasers have even reached 50KW. High laser power, large laser spot size, high-power 1000W pulse laser beam diameter ranging from 30mm to 40mm.

The laser cleaning and scanning components mainly consist of a galvanometer motor and a few octahedral rotating mirrors. The galvanometer motor loads the reflector and is used to swing the laser spot back and forth to achieve laser line scanning. The larger the laser spot, the larger the mirror size, and the stronger the yaw inertia, resulting in a slower yaw rate. For the HurryScan series products from Scanlab manufacturer, the scanning speed of 10mm spot galvanometer is about 12m/s, 20mm spot scanning speed is about 6m/s, and 30mm spot scanning speed is about 1.2m/s. The higher the laser power, the larger the laser spot, and the slower the scanning speed. Efficient cleaning requires high laser power and fast scanning speed, and the galvanometer cannot meet the requirements of high-power laser. At the same time, due to the back and forth deflection scanning of the galvanometer motor, the laser scans the edge area and decelerates to zero before accelerating in the opposite direction, resulting in a longer residence time of the laser spot in the edge area and a longer laser thermal action time, leading to serious edge burning phenomenon. Therefore, the galvanometer motor has two obvious defects in high-power laser cleaning applications, namely slow scanning speed and severe edge burning. The galvanometer motor is more used for low-power laser marking than for high-power cleaning applications.

Figure 1 Schematic diagram of octahedral rotating mirror scanning

The technology of octahedral rotating mirror (or other quantity planes such as hexahedral rotating mirror, tetrahedral rotating mirror, etc.) is based on expired foreign patents in the last century, that is, there is a reflector installed on each of the eight sides of the octahedral prism, and the laser is obliquely injected into the side reflector of the prism at a certain incidence angle. The direction of the incident light remains unchanged, and the prism rotates along the center.

When the laser spot cuts across the mirror surface of the side reflector, the incident laser changes relative to the incident angle of the side reflector, and the reflected laser forms a scan. For octahedral mirrors, when the laser scans the edges between adjacent side mirrors, it is necessary to turn off the laser and wait for the laser spot to fully enter the side mirror before turning on the laser. Otherwise, the edge of the side mirror will be damaged, and the entire mirror will be damaged after a long time. The laser spot has a certain size. When the laser spot slides from one edge of the side mirror to the other edge, the track is relative to the Central angle of the octahedral mirror center ɑ For the actual light output angle of the side reflector, rotate it for one cycle and the light output angle is 8 * ɑ， Introducing laser utilization efficiency,

As shown in Figure 1, when the size of the side mirror of the prism is 20 * 18mm and the laser runs from P1 to P2, the utilization rate of the prism is

The innovative scanning component of laser cleaning -- MASM multistage array scanning system was released. The cleaning efficiency of equivalent 100W pulsed eight-sided rotating mirror is the same as that of 63.8W pulsed galvanometer, while the cleaning efficiency of high-power pulsed laser is lower. At the same time, because the laser is turned off in the edge area, the laser is turned on when the edge of the new side mirror is scanned. The first pulse effect will appear immediately after the laser is turned on from off to on, resulting in the problem of laser edge overburning still occurs. The two obvious defects of eight-sided rotating mirror applied in high power laser cleaning are low laser utilization rate and edge overburning. The eight-sided rotating mirror is mainly used for radar scanning, the radar laser power is low, and the laser can not be closed in the intersection area of the edges.

Figure 2 Left: Scanning image of galvanometer system Right: Scanning image of MASM system
In response to the problems of slow scanning speed and edge burning cleaning, the Institute of Surface and Interface Science and Technology of Jiangsu University has successfully developed a high-speed multi array scanning system MASM (Multi Array Scan Mirror) over a period of 5 years. This system uses a unidirectional high-speed DC motor as the power component to compress and shape the incident laser spot in space, and finally scans and emits it in a linear laser manner. The laser scanning line speed can reach 100m/s. As shown in Figure 2, the scanning speed of the galvanometer is set to 15m/s, the speed of the MASM system is set to 50m/s, and the vertical scanning direction of the platform moves at a speed of 90mm/s. The laser is always in the on state, which means the laser utilization rate is 100%. The distance between adjacent rows of the galvanometer is 0.81mm, and the distance between adjacent rows of the MASM system is 0.18mm.

The Edge Deal System (EDS) subsystem within the MASM system can completely solve the problem of edge burning and control the smooth transition of laser from edge to non edge areas. The left side of Figure 3 shows the state of not being extinguished to extinction, indicating that both ends of the red light have been weakened; On the right of Figure 3, there is a comparison between the left and right ends after cleaning, with no extinction and extinction. The extinction area transitions smoothly to the substrate. Tang Faquan, the technical chief engineer responsible for innovative development of cleaning technology, introduced that "the robot applied MASM system can meet the requirements of 30 to 40 spot lasers, and the scanning speed can still reach 50m/s, making it very suitable for high-power pulse laser cleaning applications. The development of MASM array scanning mirror system provides effective solutions for high-power high-speed laser cleaning applications and low-power handheld weld cleaning.

Source: OFweek