Laser shock punching: principle and influencing factors

Laser shock punching is a novel shearing process, which utilizes the pressure of pulsed TEA-CO 2 laser-induced shock waves to cut foils in the micrometre range. Thin foils are difficult to cut with conventional shearing processes, because the cutting clearance scales with the foil thickness. By using a shock wave instead of a punch to transmit the cutting force, the cutting clearance ceases to exist. In order to realise single pulse cutting, certain requirements have to be met. On the one hand it is compulsory to produce high enough operating pressures. On the other hand the cutting edge still has to be “sharp” relatively to the only micrometre thick foils. If those requirements are fulfilled, the maximum cuttable foil thickness correlates with the geometrical ratio of pressurized area to cutting path length, which can roughly be described via a balance of forces between the applied force via pressure and the required force for cutting. For foils in the micrometre range size effects have to be considered. Apart from the already mentioned challenges with the geometrical scaling of the cutting edge, single grain effects are relevant for laser shock punching. If the grain size is in the range of the foil thickness, only incomplete cutting can be realised as the foil tends to rupture within the pressurized area and the cut edge exhibits an increased and inhomogeneous burr formation. Based on the identified influencing factors, the possibilities and process limits of laser shock punching can be evaluated.