Laser radiation can be used to produce holes with diameters ranging from less than one micrometer to several millimeters and large drilling depths. The Fraunhofer Institute for Laser Technology ILT develops various drilling processes from the basics to advanced systems in industrial plants. Laser drilling can be utilized to manufacture vent holes, air-cooling holes, contact drilling holes, filter holes or holes in injection nozzles.
Holes with diameters ranging from approx. one micrometer to several millimeters can be drilled into the workpiece using single-pulse drilling, percussion drilling, trepanning or helical drilling, depending on the thickness of the component and the required quality (precision) and productivity (drilling duration). The following table shows how individual drilling techniques differ in terms of diameter, drilling depth and duration.
| Diameter | Depth | Duration | |
|---|---|---|---|
| Single pulse drilling | 40-700 μm | < 2 mm | < 1 ms |
| Percussion drilling | 50-700 μm | < 20 mm | 0.1-20 s |
| 1-50 μm | < 1 mm | < 1 ms | |
| Trepanning | 0.3-10 mm | < 10 mm | 1-20 s |
| Helical drilling | 10-200 μm | < 2 mm | > 10 s |
Single pulse drilling can be done on-the-fly, achieving up to 300 holes per second with a diameter of, for example, 60 μm in 1 mm sheet thickness. Percussion drilling uses a series of pulses at the same position to achieve deeper holes. Depeneding on the laser beam source used, different hole diameters and drilling depths can be achieved. For drill diameters larger than about 300 μm, trepanning is used, in which the bore is cut out via a relative movement between the workpiece and the laser beam. Helical drilling can be employed, on the other hand, to drill holes that require high geometrical precision and metallurgical quality.
Laser drilling is an alternative to processes such as electron beam drilling, spark erosion, electrochemical drilling and ultrasonic drilling. The laser is preferred, however, when hole diameters of approx. 1 to 500 μm at large aspect ratios (> 1:20) need to be drilled under difficult conditions, such as at a large inclination angle to the workpiece surface or in extremely hard materials (e.g. nickel-based alloys). A challenge here is to minimize both melt layers as well as surface contamination.
Laser drilling processes can be divided into melt-dominated and vaporization-dominated processes. In melt dominated drilling processes – with pulse durations in the range of micro – seconds to milliseconds – the material largely melts and only a small part is vaporized. The resulting vapor pressure expels the molten material from the hole. This drilling method is very productive, but the melt remaining on the bore walls reduces the precision of the bore and can cause cracks in the material. In a vaporization-dominated process – with pulse durations of less than 10 ps – the material is almost completely vaporized, and the heat input into the workpiece is minimal. With an appropriate system technology, cylindrical and conical bores can thus be produced at high precision and a high aspect ratio without generating material defects.
Since pulsed laser radiation operates at high intensity, it can be used to drill precisely in almost all materials such as metals, ceramics, semiconductors, plastics as well as multilayer systems (CFRP, CMCs) made of these materials. Applications include the production of cooling air holes in turbine components such as blades or combustion chambers, holes for fuel filters or injection nozzles as well as vent holes in injection molds for toolmaking.
In addition to advancing the process engineering, Fraunhofer ILT is developing the equipment required to industrially implement these drilling processes. This includes developing special helical drilling optics with rapid deflection of the laser radiation as well as integrating drilling processes into automated production facilities.
Fraunhofer ILT has a large number of modern laser systems for drilling with laser radiation. These include:
Fraunhofer Institute for Laser Technology ILT
