Waterjet guided laser is a hybrid technology of laser technology and water flow technology. In this unique laser cutting process, a thin wire-like water jet is used as an optical waveguide to make a high-power laser fire on the workpiece.
Compared with the traditional laser cutting process, the main advantages of this method are (1) parallel side walls; (2) low heat input of the workpiece, thanks to the cooling of the workpiece between laser pulses just before it is heated (3) The molten metal is discharged in time, thanks to the high momentum of the water jet. Compared with sawing, this technology can cut metal to achieve a burr-free effect, and the mechanical pressure exerted on the workpiece is much smaller.
The diagram of the waterjet-guided laser cutting system is shown in Figure 1. The waterjet used is 5 to 50 MPa pure deionized water and filtered water. The nozzle is made of sapphire or diamond to ensure that it can produce a long and stable water jet. The laser beam is transmitted from the laser through the optical fiber, is collimated, passes through the beam expander, and then passes through a quartz window and enters the nozzle. The coupling unit is similar to the normal fiber coupling unit, except that the light intensity distribution in the nozzle is flat and there is no Gaussian distribution. When the laser enters the waterjet, the light is completely internally reflected at the interface of air and water.
During the cutting process, the workpiece is fixed on a CNC table and moves in one direction under the laser beam guided by the water jet. The bald head moves in a direction perpendicular to it. It is only necessary to change the distance between the worktable and the workpiece in order to adapt to various working distances of different nozzle sizes under different water pressures. Will not change during the cutting process.
For more than five years, this tool has been used in many processing areas. During this period, compared with traditional laser cutting technology, LMJ waterjet-guided lasers showed various advantages in industrial applications.
Generally, LMJ technology uses solid-state Nd: YAG infrared lasers (1064nm, 50-200W). Infrared waterjet-guided lasers have high efficiency when applied to silicon, ceramics and hard metals, cubic boron nitride, manganese-zinc cores, and metal thin films. Using this type of laser can obtain a cutting speed that is 8 times better than the grinding method. The LMJ system has high efficiency on brittle and difficult to machine materials such as GaAs, GaN, and copper.
These materials are not sensitive to contact with deionized water. All semiconductor products are produced through lithography and wet etching processes and are often in contact with deionized water and water-containing methods. So in the cutting process of these materials, the participation of water is completely possible.
Because the absorption coefficient of green light (532nm) is slightly lower than that of infrared light, we did an experiment with a 200W green laser to see if we can get a faster speed while obtaining the same cutting quality as the infrared laser. The result is positive. A 200W green laser can easily get higher speeds. Especially in the semiconductor industry, the advantages of waterjet laser technology can be transformed into no debris, no burrs, and no broken corners, even like a 75-micron chip. It’s okay to be thin.
So far, this technology has only used infrared and green lasers. Therefore, the applicable range of the material is limited to materials with a sufficient absorption rate for these wavelengths. Therefore, cutting transparent materials (glass, diamonds, sapphires, transparent polymers) is difficult, or even impossible. Ultraviolet light has a better absorption rate in transparent materials, so an idea of applying ultraviolet laser is proposed in the field of micro-jet technology.
A device suitable for ultraviolet wavelengths has been established, which uses quartz and CaF2 lenses.
This theory shows that the usable wavelength is limited to a range where the absorptivity is lower than that of water, which means that the absorptivity is lower than 1/cm. Ultraviolet light is contained in this window, but no high-intensity experiments have been done so far.
Microjet equipment can be combined. The laser source is connected to the cutting head through an optical fiber. In order to avoid damage to the optical fiber, a water jet with a diameter of 50 microns uses a core with a diameter of 100 microns. The introduction of ultraviolet lasers should bring new cutting applications, such as transparent materials, and also a smaller water jet diameter.
An infrared multimode laser requires a very small nozzle for the waterjet. This requirement is difficult to meet because of the necessary size for focusing and expanding the laser beam into the waterjet.
Other new processing capabilities, such as cutting or engraving transparent materials, such as polymers, glass, diamonds, and sapphires are very promising applications. For example, UV lasers can cut silicon chips for the semiconductor industry, covered with a layer of glass or diamond, which is often used to produce fast optoelectronic components. It is also promising in the electronics industry, because the presence of glass and Kevlar fibers in PCBs, especially the flexible ones, is difficult to achieve using standard microjet cutting methods.
