GFH has created a system that allows cutting or machining processes to continue with no restrictions even in acceleration and deceleration phases, with no decrease in precision.
Ultra-short pulse lasers are being used for more and more applications, especially in micro machining. But in case of complex contours with tight angles and curves, the fixed time intervals between the laser pulses can become a problem: when machining has to be slowed due to the geometry, more pulses fall into a narrow range and overlap. This can affect the material. As a result, entire production processes often have to be executed at the slowest required speed in order to consistently maintain the same laser pulse spacing.
Thanks to variable control, the full kinematic performance of the processing center can be utilized. Even deceleration and acceleration phases become productive primary processing time as a result. This reduces the production time by up to 50 percent compared to conventional techniques.
GFH GmbH, a specialist for laser micro-processing equipment, has now developed a system for the flexible adjustment of pulses according to the respective current effective velocity. Parts that were cut using this process are being presented for the first time at EMO 2013.
With the pulse-on-demand method developed by GFH, the pulse frequency is regulated according to the current effective velocity at all times. This allows equidistant pulses to be achieved in any contour. (Left: processing without pulse-on-demand, right: processing with pulse-on-demand)
Reduced heating during machining is generally considered one of the biggest advantages of short pulse lasers compared to longer pulse systems. Since the light only acts on the surface for a few picoseconds or femtoseconds with each pulse, melting and distortion are significantly reduced. However, these high-performance sources of laser radiation work at a fixed fundamental frequency. Changing this would influence the available pulse energy in many cases. Therefore the pulse frequency for conventional processing machines is established for every process and remains constant. If for example a sharp curve needs to be processed slowly in order to ensure that the desired contour accuracy is obtained, several pulses concentrate in a small space which may impair the quality of the results. The overall speed is often set to the lowest individual measurement along the geometry in order to avoid this, but this massively reduces the possible throughput. Non-productive time where no processing can take place at all remains, even with this strategy, due to accelerating and decelerating at the beginning and end of production.
Based on the effective velocity information of the CNC, the system calculates the suitable interval lengths in real time for the respective processing step and regulates the laser accordingly.
Equidistant Pulses Depending on Acceleration and Speed
The pulse-on-demand process developed by GFH on the other hand uses the effective velocity information of the real-time CNC in order to achieve equidistant pulse spacing even during acceleration. After the control unit of the CNC machine determines the movement path in advance, the allowable speeds at each point are derived. On this basis the core of the system calculates, in real time, the interval lengths that will result in continuous equidistant pulse spacing and regulates the laser accordingly. Since not all radiation sources are suitable for this process, special short pulse lasers from Time-Bandwidth are installed here. Even positive and negative acceleration phases can be compensated in this manner, allowing them to be used as full-fledged primary processing time. Depending on the complexity of the geometry, the associated time savings can be tremendous.
Up to 50 Percent Shorter Processing Time
In looking at a concrete example of an area with a size of 500x500 µm2, which is being machined with hatching of 20 µm at a speed of 1000 mm/s, the processing time using the pulse-on-demand method is 31 s. To obtain machining results of identical quality with conventional means, the laser would have to be deactivated during acceleration. The processing time of 1 min 6 s would be more than twice as long with this strategy. At the same time, the repeat accuracy is so great with the new method that the full output of the system kinematics at up to 2000 mm/s with acceleration of up to 20 m/s² can be used without impairing the precision of the contour, resulting in further time savings.
The new system permits homogenous removal, even with highly temperature-sensitive materials.
The variable pulse control system can be integrated into all GFH processing centers when needed. It is not only suitable for temperature-sensitive materials where the robustness of the production process depends on preventing heat development, but leads to a productivity increase of up to 50 percent for virtually all contour machining processes. The process is being presented for the first time at this year's EMO in Hanover.
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