3 Application comparisons and differences between continuous and pulsed laser cleaning Machine

3 Application comparisons and differences between continuous and pulsed laser cleaning Machine

In the field of laser cleaning, fiber lasers have become the best choice for laser cleaning light sources with higher reliability, stability and flexibility. As the two major components of fiber lasers, continuous fiber lasers and pulsed fiber lasers occupy the market-leading positions in macro-material processing and precision material processing, respectively.

For emerging laser cleaning applications, different voices have emerged on whether to use continuous or pulsed lasers, and two types of laser cleaning equipment using pulsed and continuous lasers have also appeared on the market. Many industrial end users do not know how to choose when choosing. JPT Laser conducted a comparative test on the laser cleaning application of continuous and pulsed lasers, and analyzed their respective characteristics and applicable application scenarios, hoping to provide a useful reference for industrial users when choosing the corresponding laser cleaning technology.

experiment material

Laser model YDFLP-CL-200-12-A is a pulsed laser, and Continious Way-RB-W-2000 is a continuous laser. The detailed parameters of the two lasers are compared in Table 1. The first sample used in the experiment is an aluminum alloy plate, and the dimensions of the aluminum alloy plate are 400 mm × 400 mm × 4 mm in length, width and height. The second sample is a carbon steel flat plate, and the dimensions of the carbon steel are 400mm × 400mm × 10mm in length, width and height. The surface of the sample is sprayed with white paint, the thickness of the paint on the first surface of the sample is about 20 μm, and the thickness of the paint on the second surface of the sample is about 40 μm.

Two lasers were used to remove paint on the surfaces of two materials, and the laser cleaning parameters were optimized to obtain the best pulse width, frequency, scanning speed and other parameters, and the cleaning effect and efficiency under the optimized experimental conditions were compared.

1.Pulse laser cleaning experiment of paint layer

In the pulsed light paint removal experiment, the power of the laser is 200W, the focal length of the field lens used is 163mm, and the diameter of the laser focusing spot is about 0.32mm. The cleaning area of a single block is 13mm × 13mm, and the filling distance is 0.16mm. The laser scanning and cleaning are repeated 2 times when the aluminum alloy surface is depainted, and the laser scanning and cleaning are repeated 4 times when the carbon steel surface is depainted.

Table 1: Comparison of pulsed laser and continuous laser parameters

Under the condition that the vertical and horizontal superposition rates of the light spot are both 50%, the influence of the parameters of laser pulse width, frequency and laser scanning speed (as shown in Table 2) on the cleaning effect is tested. The experimental effect of paint removal on the aluminum alloy surface is shown in Figure 1. The results of the paint removal experiment on the carbon steel surface are shown in Figure 2.

Table 2: Experimental parameters of pulsed laser cleaning of aluminum alloy and carbon steel surface paint

The experimental results show that under the same frequency, the short pulse width is easier to remove the surface paint layer of aluminum alloy and carbon steel than the long pulse width. Under the same pulse width, the lower the frequency, the easier it is to cause damage to the substrate. When the frequency is higher, the paint removal effect is worse. The preferred parameters for pulse laser cleaning of aluminum alloy surface paint layer are 15# (laser power 200W, pulse width 100ns, frequency 60kHz, scanning speed 9600mm/s), and the preferred parameters for cleaning carbon steel surface paint layer are 13# (laser power 200W, The pulse width is 100ns, the frequency is 40kHz, and the scanning speed is 6400mm/s), both of which can remove the paint layer completely, and basically damage the base of the sample.

Figure 1: Comparison of pulsed laser cleaning of aluminum alloy surface paint layers under different laser parameters

2.Continuous laser cleaning paint layer experiment

In the experiment of continuous light paint removal, the power of the laser is 50%, the duty cycle is 20% (equivalent to an average power of 200W), and the frequency is 30kHz. The focal length of the field lens used is 220mm, and the diameter of the laser focusing spot is about 0.2mm. The cleaning area of a single block is 13mm×13mm, and the filling spacing is 0.1mm. The laser scans twice when cleaning the aluminum alloy surface paint layer, and the laser scans four times when cleaning the carbon steel surface paint layer. Under the condition of constant laser power, duty cycle and frequency, the influence of laser scanning speed on cleaning effect was tested.

Figure 2: Comparison of the surface paint layer of carbon steel cleaned by pulsed laser under different laser parameters

The experimental results show that the lower the scanning speed under the same laser power and frequency, the greater the damage to the substrate. When the scan speed is greater than a certain value, the faster the scan speed, the worse the paint removal effect. The preferred parameters for continuous laser cleaning of aluminum alloy surface paint layer are 21# (laser power 200W, frequency 30kHz, scanning speed 2000mm/s), and the preferred parameters for cleaning carbon steel surface paint layer are 37# (laser power 200W, frequency 30kHz, scanning speed 3400mm) /s). These two parameters not only remove the carbon steel surface paint layer cleanly, but also cause relatively less damage to the sample substrate.

3.Optimal parameter results and analysis

1.Comparison of macro cleaning conditions

Figure 3a shows the results of the optimal parameters for pulsed light cleaning of the aluminum alloy surface paint layer, and Figure 3b shows the results of the optimal parameters for continuous light cleaning of the aluminum alloy surface paint layer. After cleaning with pulsed light, the paint layer on the surface of the sample is completely removed, the surface of the sample appears metallic white, and there is almost no damage to the substrate of the sample. After using continuous light cleaning, the paint layer on the surface of the sample was completely removed, but the surface of the sample appeared gray-black, and the substrate of the sample also appeared micro-melting. Therefore, the use of continuous light is more likely to cause damage to the substrate than pulsed light.

Figure 3 (1): Comparison of macroscopic effects of pulsed light and continuous light paint removal: left (3a), right (3b)

Figure 3 (2): Comparison of macroscopic effects of pulsed light and continuous light paint removal: left (3c), right (3d)

The results of the optimal parameters for the pulsed light cleaning of the carbon steel surface paint layer are shown in Figure 3c, and the results of the optimal parameters for the continuous light cleaning of the carbon steel surface paint layer are shown in Figure 3d. After cleaning with pulsed light, the paint layer on the surface of the sample is completely removed, the surface of the sample appears gray-black, and the damage to the substrate of the sample is small. After using continuous light cleaning, the paint layer on the surface of the sample is also completely removed, but the surface of the sample appears dark black, and it can be intuitively seen that there is a large remelting phenomenon on the surface of the sample. Therefore, the use of continuous light is more likely to cause damage to the substrate than pulsed light.

2. Microscopic morphology comparison

It can be seen from Figure 4(a) that after using pulsed light to clean the paint layer on the surface of the aluminum alloy, the paint on the surface of the sample has been completely removed, and the surface of the sample has little damage and no laser lines. When using continuous light to clean the sample table, the paint is also completely removed as shown in Figure 4(b), but the surface of the sample has serious remelting phenomenon and laser lines.

Figure 4(1): Comparison of the surface micro-morphologies of the sample after pulsed light and continuous light paint removal, the left picture is (4a), the right picture is (4b)

Figure 4(2): Comparison of the surface micro-morphology of the sample after pulsed light and continuous light paint removal, the left picture is (4c), the right picture is (4d)

It can be seen from Figure 4(c) that after using pulsed light to clean the carbon steel surface paint layer, the paint on the surface of the sample has been completely removed, and the surface of the sample is relatively smooth after cleaning with little damage. The paint was also completely removed using continuous light cleaning as shown in Figure 4(d), but the surface of the sample was severely remelted, and the surface of the sample was uneven.

in conclusion

Experiments show that both continuous lasers and pulsed lasers can remove the paint on the surface of the material and achieve the effect of cleaning. Under the same power conditions, the cleaning efficiency of pulsed lasers is much higher than that of continuous lasers. At the same time, pulsed lasers can better control the heat input to prevent the substrate temperature from being too high or micro-melting.

Continuous Way lasers have an advantage in price, and can make up for the gap in efficiency with pulsed lasers by using high-power lasers, but high-power Continuous Way lasers have greater heat input and increased damage to the substrate. Therefore, there are fundamental differences between the two in application scenarios. High precision, the need to strictly control the heating of the substrate, and the application scenarios that require the substrate to be non-destructive, such as molds, it is recommended to choose a pulsed laser. For some large steel structures, pipes, etc., due to the large volume and fast heat dissipation, the requirements for damage to the substrate are not high, and continuous lasers can be selected.