By: Hong Q. Chen

Hongqiang Chen, Geoff Shannon
Miyachi Unitek Corporation
1820 S. Myrtle Ave, Monvoria, CA 91016, USA
Overview
Recently developed of pulsed fibre laser marking system is becoming a powerful tool for precision cutting and drilling. It can provide dimensional cut repeatability to sub 10 microns, cut or drill material up to 0.5mm with minimal to no burring, and offer multi axis motion options.
The material removal mechanism of the new process is vaporization cutting. In this process the solid material is vaporized without it passing through a liquid phase. Normally no gas assist is needed except for optics protection. By this means, short pulse lasers with high peak power can cut highly reflective metals such as copper and gold with a very small HAZ and burr.
A fibre laser marking system (LMF2000 marker from Miyachi Unitek) is selected for the study. A unique feature of this marker is the laser pulse shape: a high peak power short (20~30ns) pulse with a long (up to 300ns) flat tail. The high peak power helps achieve good coupling of the laser energy into work piece and the long tail region can provides great advantages for deep material penetration and fast removal rate. By optimizing the laser parameters, material can be removed a thin layer at a time with a high speed scan, the multiple passes helping to improve cut quality. The method uses no direct assist gas, and control of laser parameters allows the cut to be optimized to minimize the heat affected zone (HAZ), underside burr and, on small tubes, backside damage.
Copper and copper alloys have been developed for a wide variety of applications. Figure 1 shows the cutting result on a thin copper sheet. The customer designed butterfly pattern was directly imported to the marker software, to drive the scan head. Using optimized laser parameters clean, sharp edge cuts were achieved and the cycle time for the whole pattern was about 32s.
Laser drilling of micro holes is especially important in medical tool manufacturing. In addition to high speed trepanning a pulsed fibre marker in burst mode can percussion drill both through and blind holes; an attractive alternative to customized pulsed YAG laser drilling systems. Examples of hole drilling with the fibre marker are shown in figure 2.
Pulsed fibre laser markers that offer high peak power and pulse shape features, such as the LMF2000, show great potential for high quality precision cutting and drilling of both ferrous and highly reflective metals. This approach offers an extremely cost effective option to multi axis CNC laser cutting systems. Other benefits include a simple intuitive interface that directly imports files of many graphic formats.
.
Figure 1: Laser cutting customer-designed pattern on 0.25 mm copper sheet
Figure 2: Laser hole drilling on SS304. (a) percussion drilling through 40 μm sheet (b) hole array machined in 0.4s thanks to the fast scan mirror beam control

The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here

Paper 1708