GFH Choosing the right pulse in laser micromachining
Germany – Laser micromachining is used for the fabrication of tooling inserts for micro-injection moulding applications. Tests have shown that by selecting the right pulse duration, cycle times can be reduced by as much as 70%.
In comparison with conventional fabrication methods such as milling, turning and grinding, laser machining allows for a much higher removal precision. But precision isn't the only concern in fabrication processes – economic feasibility also plays a role: The removal requirements should be achieved in the shortest possible time, with good quality results and cost-effectively as well. Tests by the laser machining experts at GFH GmbH have shown that in order to achieve these goals, it is essential to adjust the pulse duration according to the material and application.
The pulse duration is a key parameter in fabrication processes. Nanosecond pulses, for example, offer a higher removal rate with limited quality, since removal in this case primarily takes place by way of the liquid phase when the material melts due to the long application time of the laser. The quality achieved with removal processes can be increased significantly by using short-pulse laser systems operating in the picosecond range – but at the expense of a considerably longer machining time, which has made it harder for this technology to gain a foothold in the market. Thanks to the continuous advances made in beam source technology, femtosecond lasers which are suitable for industrial use are now creating the opportunity to combine a high removal rate with good quality. So GFH performed studies in order to analyse the efficiency and quality of femtosecond-range pulses on a variety of materials.
Tests on different materials for the pulse duration
The tests looked at different parameter settings for the pulse duration, pulse energy and repetition rate (the length of the pause between two pulses in Hertz). The beam source was a laser with a maximum average power of 15 W, capable of generating pulse durations in the range of 240 fs to 10 ps. It was used to machine samples out of 1.4301 stainless steel, VGH2 carbide and the ceramic aluminium nitride. Then the removal rate in units of cubic millimetres per minute was calculated and the quality was analysed under a microscope. The results of the tests showed that the removal rate for stainless steel can be increased by a factor of 3 by reducing the pulse duration from 10 ps to 900 fs. The opposite was found for ceramics, aluminium nitride in this case. Here the removal rate was increased by raising the pulse duration from 900 fs to 10 ps. This means that metals and dielectric materials have different optimal pulse duration values. Thus cycle times can be reduced by up to 70% by selecting the respective appropriate duration – 900 fs for metals, 10 ps for dielectric material.
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