The hottest laser welding application in medical e

Laser welding applied in medical equipment manufacturing

Author: Dr. JRG neukum, dILAS diodenlaser company

polymer welding in medical equipment manufacturing is closely related to the material and color of weldments, as well as the control of welding process and parameter setting. Compared with the traditional ultrasonic and heating plastic connection method, laser plastic welding has the following special advantages:

● good welding quality

● the damage degree of the welding area is small (inside the welding)

● the welding part is clean and beautiful (no particles)

● welds with high visual quality

● the thermal load of the weldment is the lowest

● the design process is simple and fast (for example, the surface is flat)

● adopt non-contact welding process (which will not affect the welding quality at all)

● at present, the substation has built documentation under closed-loop process control with an area of about 10000 square meters

using a high-power semiconductor laser system with a wavelength range of 640 nm to 2 m, closed-loop process control and parameter documentation can be achieved synchronously. In the laser based plastic welding process, the optimal wavelengths are 810 nm, 940 nm, 980 nm, 1470 nm and 1940 nm. Based on the nature of the semiconductor laser system, the optical output power can be directly modulated by modulating the driving current. The welding process is simple and fast

the color of the weldment determines the complexity of the welding process. In addition to directly welding two transparent materials, the connection of all other material combinations uses a "laser transparent" interlayer - which is located at the top of the "laser absorption" area. The laser will create a molten pool between the contact surfaces. Due to a series of factors such as the absorption of laser by the weldment, the formation of molten pool, and the wet treatment of molten pool on transparent plastic, the welding process takes a certain time (Fig. 1)

various methods used by laser welding plastics are:

● sequential circumferential welding

● synchronous welding

● mask welding

● quasi synchronous welding

the speed of sequential circumferential welding is very low, but the heat applied to the workpiece can be controlled. Synchronous welding is suitable for rapid and mass production, but it has disadvantages such as poor flexibility and uneven heating around. The flexibility of mask welding method is not high, because for each contour, a new mask is required, and the laser energy consumed is higher than that required, so the process efficiency is relatively low. Quasi synchronous welding method combines sequential circumferential welding and rapid galvanometer scanning process, and is equipped with a pyrometer. Quasi synchronous mode can carry out welding quickly and accurately, control heat, and store relevant process data for quality control and tracking

process control

closed loop process control is based on preset welding temperature, measuring welding temperature, and adjusting laser power (such as deviation between set temperature and measured temperature). In the comparison between the open-loop process and the closed-loop process, it can be seen that if the optical power is constant, the temperature of the solder joint will continue to rise. If the processing is not stopped, the weldments will eventually be burned. For the closed-loop process, the solder joint temperature can be close to the set temperature under the closed-loop control by adjusting the laser power. If this process is used, the laser power can be reduced to the extent that only the molten pool needs to be maintained to prevent the solder joint temperature from overheating. By optimizing the welding temperature, the processing can be further carried out

the example above can also reflect other advantages of closed-loop welding process. As mentioned earlier, the signal ripple is generated by the glass reinforced PCB material used (Fig. 2). When the laser power is constant, close to the temperature distribution shape of a single ring, it can be seen that although the weld is symmetrical square, the welding temperature is different on different sides of the square. Detailed inspection shows that this is due to the different orientation of glass fibers in the polymer matrix. According to these different orientations, part of the laser light is transmitted to the deeper part of the matrix by the glass fiber. In this case, the solder joint temperature will be lower than the temperature of the fiber perpendicular to the optical path

obviously, this kind of material can only be welded under the optimized welding temperature, and the laser power needs to be adjusted; Therefore, it is absolutely necessary to use the semiconductor laser system in combination with a pyrometer and a scanning galvanometer. For materials with such uneven surface absorption, it is difficult to achieve excellent welding effect with a fixed power laser source. The burst pressure test shows that using optimized welding temperature can achieve more combinations of process parameters and higher burst pressure

in addition, the pyrometer signal not only helps to optimize the process, but also can be used for failure detection. In one case, there is a gap between two parts due to the existence of bubbles during the molding process. This non-contact area causes overheating and is detected at the peak of the temperature signal. Therefore, such parts can be rejected or sent to the quality inspection department for further inspection

beam shaping

in addition to being used with scanners and pyrometers, laser based plastic welding can also make full use of laser beam shaping. In the device shown in Figure 3, a uniform linear laser source is used to weld the microchannel structure, similar to biochip applications. Since the uniformity level of the beam reaches 95%, the welding is also very uniform - even on a large area. Fiber coupled semiconductor laser systems provide such a uniform beam and can be tailored to suit a variety of geometric shapes. The extremely uniform laser beam with a size of 600mm can be realized by a direct beam semiconductor laser module without fiber coupling

white materials and transparent materials

white polymers and transparent polymers are widely used in the manufacturing of medical equipment, and they are more inclined to use semiconductor laser systems for welding. These colors bring high visual quality, gap appearance and particle free process advantages, which make the plastic welding of semiconductor laser system have high application potential and value in the manufacturing of medical equipment. In the special field of medical treatment, special additives are not recommended for plastic welding, because the national approval procedure is cumbersome. Plastic welding is carried out by using the semi conducting full digital amplification and collective laser system. The combination of materials approved and used by the state is adopted, and it can work without additives, which is simple, efficient and fast

it is worth mentioning that when welding white polymers, using a longer wavelength (such as 1470 nm range) can get a better white look. For example, comparing two white polymers can achieve a white look. One polymer adopts 808 nm wavelength welding, and the other adopts 1470 nm wavelength welding. The advantage of welding at 1470 nm is that the approved material for white appearance has variable concentration, so it can play the characteristics of "laser transparency" and "laser absorption" at 1470 nm wavelength without affecting the visible white appearance

for transparent plastics, the welding principle is completely different. Without additives, such plastics usually cannot absorb light in the visible range, even at 1550 nm. This is why we call it transparency. However, there are still opportunities to use the intrinsic absorption properties of polymers for laser welding, starting at a wavelength of about 1800 nm. The polymer chain vibrates under the influence of light wavelength greater than 1800 nm, which leads to this intrinsic absorption. Because a large number of materials themselves, rather than the surface, have this effect, it is extremely suitable for film welding or pipe welding, forming a penetration weld with a strong smell of the future. There is no pressure during film welding; Due to static electricity, the two films have been in contact. After filling the bottle bag, seal the bag mouth with the same laser with a wavelength of 1940 nm

Figure 4. Cross sectional view of laser welded Makrolon components

(using 1940nm wavelength)

as mentioned above, when the wavelength is greater than 1800nm, the absorption processing characteristics of transparent polymers have a volume effect. Therefore, attention should be paid to the internal welding of two transparent parts at their contact surface. The extremely large aperture optical equipment with short working distance has achieved excellent results. In this setting, the energy is focused on the contact surface; At the same time, because the power density outside the focus is lower, the brightness and volume absorption of the material are lower

conclusion of this paper

in view of the process advantages already mentioned, the dILAS semiconductor laser system and its direct and fast modulation characteristics, as well as the fact that it can provide a full range of wavelengths (640 nm to 2000 nm) for different applications, it shows that the semiconductor laser system is an ideal laser source for the weld width of nano meter in plastic welding applications. The combination of pyrometer and galvanometer scanner in semiconductor laser system can optimize the welding effect and meet the requirements of high quality control and process archiving required by medical equipment manufacturing

it has been proved that under optimized welding temperature, semiconductor lasers can be used to weld materials with uneven surface absorption (such as glass reinforced polymers). In addition, the combination of pyrometer and galvanometer scanner, combined with the semiconductor laser system, can compensate for surface absorption changes, such as color changes

the diode laser system also has the advantages of beam shaping and homogenization, allowing the beam geometry to be adjusted according to the application, such as large weld width or mask welding

white and transparent plastics are very important materials in the manufacture of medical equipment. Due to the expansion of the wavelength of semiconductor lasers, laser welding of white and transparent polymers is possible, and this technology has been demonstrated on NPE. Using semiconductor lasers to weld white and transparent plastics in medical equipment will benefit customers a lot

the author of this paper, Dr. JRG neukum, once studied physics at Darmstadt University of science and technology in Germany, and received a doctorate in rare earth spectroscopy. After serving as the product manager of a Japanese laser diode manufacturer and the European sales manager of coherent semiconductor, he joined dILAS diodenlaser company (address:) in 2004 and is now responsible for the global market and sales of dILAS and the industrial laser system Department of dILAS

Dr. JRG neukum would like to thank Wolfgang horn (dILAS diodenlaser), Dr. Chul S. Lee (BASF), Rick Davis (rofin Sinar) and Dr. Alexander savitski (Baxter group) for their help. Therefore, the conclusions mentioned in this article are reached