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Positioning method of focus position of laser cutting machine


There are nine factors that affect the cutting quality: cutting surface roughness, cutting edge perpendicularity, cutting width, lines, burrs, material deposition, depression and corrosion, heat-affected area, and deformation.Laser cutting is to use a focusing mirror to focus a high-power laser beam to form a small focus, and then use the high energy of the focus to melt and vaporize the steel plate to achieve cutting. The positioning of the laser focus is a very critical step. Only when the focus is aligned can a good quality of steel plate cutting be ensured. Because the CO2 laser beam is infrared invisible light, it is impossible to find the focus of the laser beam by relying on human observation.




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In the field of laser processing, there are usually three methods for positioning the laser focus position: numerically controlled positioning and spotting, bevel focus burning and straight burning.

Numerical control positioning method:

Use a piece of flat and clean white cardboard, spread it on the worktable, and set the laser cutting head above it. The height of the focusing lens from the cardboard is 10mm smaller than the focal length of the focusing lens. For example, the focal length of the focusing lens is 127mm. Then set the focusing lens to approximately 117mm from the cardboard. The numerical control system sets the cutting head to move once every 10mm along the x-axis or y-axis, and the z-axis rises by 1mm at the same time each time it moves, and the distance of 20 consecutive moves can be set. Each time it moves into place, use a laser to emit a 200W pulsed laser to divide, and punch a hole in the cardboard. A total of 20 holes were punched in 20 movements, and the z-axis height increased by 20mm. Observing these 20 holes, we can find that the diameter of the holes gradually changes from large to small, and then from small to large. Find the position where the hole diameter is the smallest is the focus position, and record this point. Measuring the distance between the cardboard and the lens at this position is the actual focus position of the laser beam.

Inclined focus burning method:

Place a straight wooden board diagonally on the workbench, with an inclination of about 10 degrees. Set the cutting head at point A. The height from point A to the focusing lens is 20mm smaller than the focal length of the focusing lens. The numerical control system sets the cutting head to continuously move horizontally along the x-axis or y-axis by 230mm, and the laser output 200W at the beginning of the movement. Continuous laser, the cutting head stops at the same time the laser stops. This is when Ke saw a burnt trace of a laser beam that changed from wide to narrow and from narrow to wide on the wooden board. Take the narrowest part of the trace as the focal position, record this point, and measure the distance between the plank at this position and the lens is the actual focal position of the laser beam.




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Direct burning method:

Hold a flat wooden board, stand on the cutting table at an angle of 85 degrees, raise the cutting head to the position where the focusing lens is about 1.5 times the focal length from the surface of the table, open the laser shutter, continuously output a 200W laser beam, and move it horizontally quickly. From the wood below the focusing lens, you can see that there is a burn mark on the wood surface before and after the laser beam is focused from wide to narrow, and from narrow to wide. This trace is very close to the change in the focusing process of the laser beam. Take the narrowest part of the trace as the focal position, record this point, and measure the distance between the plank at this position and the lens is the actual focal position of the laser beam. Because this method requires manual operation, special attention should be paid to safety to avoid human body harm.

Of course, in addition to the above three methods, the metal probe method is used to directly measure the focal beam. The spot size and energy distribution at the focal point are also directly measured, but the cost is relatively higher.

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