Thin metal foil with a thickness of less than 100 μm and a micro-scale structure is used for shielding, electrical contact strips, medical equipment and other applications. The production process of such a structure requires a structure that causes minimal mechanical and thermal stress, while providing economic feasibility.
Laser micro-cutting is a non-contact, cost-saving method, if laser heat accumulation and auxiliary gas can be controlled. For economic efficiency, no burrs or debris are necessary in the execution process, which can save subsequent processing costs.
The above process needs to be in the range of femtosecond laser pulse width. The new quality of femtosecond pulse processing is derived from the non-thermal ablation effect. In the femtosecond time range, the melting process of the material is similar to the breaking of chemical bonds, but it does not melt. Because of the heat penetration depth, the surrounding melting area has little effect, depending on the pulse duration being less than 10 nanoseconds. This gives an excellent machined surface and good burr-free cutting edges.
With regard to heat accumulation, the influence of the ablation threshold must be considered. Due to material property values, not all laser pulse energy causes melting. In the surrounding area of the beam focus and in deeper layers of material, the thermal effects do not reach a threshold, resulting in residual heat input. Because the threshold effect is linearly related to the square root of the pulse width, the femtosecond pulse heat input is much lower than that of long pulses or continuous lasers. By adjusting the beam deviation strategy, even high pulses at a frequency of 100,000 Hz can ensure that the heat accumulation in the area is at a low level and promote the processing of heat-sensitive materials.
In addition, non-thermal energy melting in the femtosecond range only requires a low-pressure auxiliary gas, so the gas flow does not change the fine structure.
Cutting experiment results
Copper and titanium sheets with a thickness of 20 to 40 μm are used to demonstrate the cutting of slits with a width of 20 to 100 μm and a length of 1 to 2 cm. The test was processed with a 10W femtosecond laser (JenLas femto 10 from Jenoptik) in the laboratory, plus an galvanometer scanner. When selected components are industrial materials, the results can be directly transferred to the results of industrial applications. Cut straight in single mode and multimode to find the best melting conditions. The cutting quality depends on the sharpness or thermal deformation of the edges.
Beam quality is determined by good focus and cutting accuracy. The beam quality of a thin-plate laser like JenLas femto 10 is approaching theoretical limits. Good cooling and thermal control of thin disks results in high quality beams. Sheet lasers do not need to worry about reflections from the workpiece.