High throughput laser drilling with high power lasers using a two-dimensional polygon mirror scannerThursday (25.06.2020) 09:40 - 10:00 Room 2
The throughput of laser processes is typically limited by the available laser power or the speed of distributing the laser energy onto the workpiece. Since the development of laser sources brought out high average power lasers in the last years, the deflection speed became the limiting factor. At this time, polygon mirror scanners with ultra high deflection speed up to 1000 m/s are available at the market. Thus, subsequently laser pulses can be distributed on the surface without overlap even with pulse repetition rates in the MHz-range. If the pulse repetition rate and the target position are synchronized, the technology can be used for high throughput multi pass laser drilling. This process requires, that all laser pulses used for a certain bore hole have to hit the same material position. In processing with a polygon mirror scanner, a bore hole is treated only with a single pulse per scan. That in turn requires a very high position accuracy between the scans. To obtain this exact pulse synchronization, the scanner has to calculate the required pulse repetition rate from the area to be machined considering the current position and the scan speed. To avoid positioning errors, this calculation has to be done in real-time.
The following study investigates the laser drilling process employing a two-dimensional polygon mirror scanner distributing the laser power on the surface without an external workpiece handling system. The aim of this study is a process with increased throughput and high position accuracy employing the maximum available laser power. A nanosecond-pulsed fiber laser with a maximum average laser power of 1 kW and a pulse energy of up to 1 mJ is used to perform the experiments. Its wavelength is 1030 nm and the pulse duration is set between 30 and 240 ns. The pulse repetition rate varies in the range between 1 and 4 MHz depending on the spacing between the drilling holes of 100 or 200 µm and the scan speed, which was set in the range between 100 and 400 m/s. The experiment was performed on silicon wafers and stainless steel with thicknesses of 180 µm and 200 µm, respectively. The drilling holes are arranged rectangularly or hexagonally . As a result, possible drilling speeds of more than 10,000 holes/s were obtained. The accuracy of the process is evaluated using the drilling hole diameter at the laser entrance and exit side of the material. Furthermore, it is shown, how the diameter can be influenced with variable processing parameters.
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