How is the penetration rate calculated during plastic laser welding?

Plastic laser welding technology is a combination of plastic transmittance and light absorption to melt plastic. In this connection process, the transmittance and absorbance of plastic materials are important links in determining whether plastic products adopt laser welding technology. So how to check the transmittance of plastic materials? Take plastic materials such as PA and PBT as an example to see how to detect the laser transmittance in the laser plastic welding process of PA, PBT, etc.

The laser transmittance of semi-crystalline materials such as nylon and PBT is lower than that of amorphous materials such as PC and PMMA. If it is a material containing glass fiber such as black PA and PBT, the laser transmittance is low. Mass production of plastic laser welding process Mass production of laser welding process is crucial.

Laser penetration rate

During the plastic laser welding process, when the laser irradiates the upper layer and penetrates the plastic surface, part of the laser will be reflected, and part of the laser will be reflected into the plastic material; some of the laser in the plastic material will penetrate the plastic material to reach the laser absorption layer, while some of the laser will undergo complex optical path changes in the plastic material: some will be diffusely reflected by semi-crystalline particles, some will be absorbed by the material, and some will be absorbed by the material. After various reflections, it will return to the air or enter the absorption layer material. In actual production, the laser usually enters the upper layer of plastic, so we can simply divide it into: part of the laser is reflected (R), part of the laser is absorbed (A), and part of the laser is absorbed (A). The laser penetrates the upper plastic to the absorption layer (T). Above T+A+R=1.

Laser transmittance detection method

1. Direct test with a laser power meter

For customers who already have plastic laser welding equipment, they can directly use a laser power meter to test the laser transmittance of plastic materials. First, use the laser power setting reading P0 to trigger the laser and read the laser power meter. Then, the laser with the same setting penetrates the plastic material to be tested, and the power meter obtains the second value PP. Laser penetration T=PP/P0. This detection method is relatively simple, but the disadvantage is that the laser penetration part can only detect flat workpieces.

2. Detection with a photometer

With the help of a photometer, the transmittance T is determined by the ratio of two electrical signals generated by different radiant fluxes. Simply put, it uses an 800-1000nm light emitting diode to radiate extremely low laser watts (5mw), and the MW laser penetrates the object being detected by the laser. After removing the plastic sheet, it is detected by the photometric detector on the other side. The electrical signal generated by the photometric detector is proportional to the amount of radiated laser from the light emitting diode. This proportional value is the measured laser penetration. This test method is widely used in the market, and its shortcomings are also obvious: on the one hand, because the laser power emitted from the radiation end is very small, the sensor receives the other end after penetrating the test material. The radiation amount is small, 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 one point, which is not enough to explain the laser penetration rate in the plastic welding area.

3. Use a full spectrum detector

Due to the expensive equipment, it is not necessary to test the penetration rate of all wavelengths of light on plastic materials. This detection method is rarely used in actual production and is generally widely used in scientific research institutions or plastic material manufacturers.

4.Full weld scanning plastic laser penetration tester

The recommended laser penetration detection method is to use a scanning camera device for laser penetration detection. The device uses a laser source with the same wavelength as laser plastic welding, which can accurately measure the laser penetration of the plastic product to be inspected. At the same time, the plastic laser penetration detector can take a picture and scan the entire weld to obtain the laser penetration and injection defects of the entire welding area. In some applications, the quality of the weld can even be checked after plastic laser welding as one of the means of quality monitoring.