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Compared with amorphous materials such as PC and PMMA, semi-crystalline materials such as nylon and PBT have lower laser penetration rates. If it is a black laser-penetrable PA, PBT and other materials containing glass fiber, the laser penetration rate is lower. Sufficient and stable laser penetration of plastic materials is crucial for mass production of plastic laser welding processes.
In the process of plastic laser welding, when the laser hits the surface of the upper penetrating plastic, part of the laser will be reflected off, and another part of the laser will be refracted into the interior of the plastic material; part of the laser entering the interior of the plastic material will penetrate the plastic material Reach the laser absorption layer, while the other part of the laser undergoes complex optical path changes inside the plastic material: some will be diffusely reflected by the semi-crystalline particles, some will be absorbed by the material, and some will return to the air after various reflections or enter to the absorbent layer material. In actual production, the laser is generally incident on the upper plastic, so we can briefly divide the above into: a part of the laser is reflected (R), a part of the laser is absorbed (A), and a part of the laser penetrates the upper plastic to reach the absorption layer ( T). The above T+A+R=1.
Detection method of laser penetration rate
1Direct detection with a laser power meter
For customers who already have plastic laser welding equipment, the laser power meter can be used directly to test the laser penetration rate of plastic materials. First use a laser power setting to trigger the laser and read the reading P0 of the laser power meter. Then let the laser with the same setting penetrate the plastic material to be detected, and the power meter obtains the second value PP. Laser penetration rate T=Pp/P0. This detection method is relatively simple, but the disadvantage is that it can only detect workpieces whose laser-penetrating parts are flat sheets.
2Detection using a photometer
The determination of the transmittance T with the aid of a photometric instrument is achieved by the formation of the ratio of two electrical signals generated by different radiant fluxes, simply using an 800-1000nm light-emitting diode radiating a very low laser wattage (5mW). ), after the mW-level laser penetrates the plastic sheet to be detected, it is detected by the photometric detector on the other side. The photometric detector generates an electrical signal proportional to the amount of radiated laser light from the light-emitting diode. Measured laser penetration. This test method is widely used in the market, and the disadvantages of this method are obvious: on the one hand, because the laser power emitted by the radiation end is very small, after it penetrates the detection material, it is received by the sensor at the other end. The amount of radiation is smaller, so the detection value is very inaccurate or the laser penetration rate cannot be detected at all. On the other hand, this detection method can only detect a single point, which is not enough to explain the laser penetration rate of the welding area of the plastic part.
3Using a full spectrum detector
Using a full spectrum detector can test the penetration rate of light in all wavelength bands to plastic materials, because the equipment is expensive and it is not necessary to detect the penetration rate of light in all wavelength bands for plastic materials. This detection method is rarely used in actual production. Generally used in scientific research institutes or plastic material manufacturers.
Full Spectral Transmittance Detects the spectral transmittance of PMMA, PA6, PP and PC, 2mm thick.
4Full Weld Scanning Plastic Laser Penetration Tester
The equipment uses a laser light source of the same wavelength band as the laser plastic welding, which can accurately measure the laser penetration rate of the plastic products to be inspected. At the same time, the plastic laser penetration rate detector can take pictures and scan the entire weld to obtain the laser penetration rate and injection defects of the entire welding area. In some applications, it is even possible to check the quality of the welded seam after plastic laser welding, as one of the means of quality monitoring.