Lasers make it possible to machine very small, blind, unusually shaped and precisely tapered holes. They can drill holes at steep angles and process difficult-to-machine materials. A single set-up can produce hundreds of different sizes over a 3D surface.
The JK Lasers' range of pulsed Nd:YAG lasers drill metals, coated metals, some ceramics and graphite composites. These lasers create discrete pulses of controllable energy, peak power, and temporal profile (or shape) which are well suited for drilling. The key to laser drilling with a pulsed Nd:YAG is the peak power.
Even a lower average power pulsed YAG laser can drill well since the interaction with the material is defined by the peak power and pulse energy parameters.
Laser Drilling Benefits
- Non-contact process (no tooling wear or breakage, minimal material distortion);
- Highly accurate and consistent results;
- Precise control of heat input;
- Ability to produce small diameter holes with high aspect ratios;
- Ease of programming and adaptability to automation;
- Increased production rates with faster setup times and less tooling;
- Flexibility in changeovers for prototypes and small-batch manufacturing;
- Versatility (the same tool can be used for laser welding and laser cutting);
- Capacity for a high degree of beam manipulation (including the ability to drill shallow angles and shaped holes);
- Capability of some laser systems to drill multiple features simultaneously;
- Ability to process a wide range of materials.
Percussion laser drilling
Percussion laser drilling means adjusting the laser’s focus spot size to determine the hole size. There is no relative motion between the laser beam and the part during the drilling process. The parameters and number of pulses are chosen to produce a good quality hole.
Laser driling holes in the 25µm to 1000µm diameter range is possible using this method but the limits vary according to the material. Most percussion drilled holes are in the 300µm-600µm diameter range.
Percussion drilling allows a special drilling regime termed drilling 'on-the-fly' to greatly increase hole drilling speed. Drilling on the fly is usually performed on round turbine engine parts and uses signals from the motion systems encoders to trigger the laser at specific, consistently-spaced hole locations around the part.
If ten pulses are required to percussion drill a hole then a drill on-the-fly system will rotate the part ten times ,sending a laser pulse to each hole location per revolution. Laser drilling speed is increased because indexing time is eliminated from the cycle time.
Percussion drilling can take advantage of pulse-shaping to improve the interaction of the laser beam with the material. This can also help control taper and improve the drilling speed.
Pulse shaping is programming the laser’s pulse temporal profile. By breaking up a long drilling pulse into two three or four shorter segments, separated by off-time, the hole quality can be improved and speed increased. Debris coming out of the hole can interfere with end of a long duration pulse so breaking it up improves efficiency and reduces drilling time. Using a pulse shape with a lower peak power segment at the beginning can create a hole that has less initial bell-mouth taper.
Trepan laser drilling
Trepan laser drilling requires a motion system to allow piercing with the laser and then motion of the beam relative to the part to 'cut' out the hole. Trepanning allows for a diameter tolerance about half that of percussion drilling. It enables the creation of shaped holes with a tailored taper or changing cross section with depth using a multi-axis system. This requires a system with good accurate motion capability and high-level programming capability. Trepanning also enables the cutting of specific shapes and large holes as well as complex 3D trimming of large parts.
Holes drilled in metals are judged by the hole diameter tolerance, taper, recast thickness, and micro cracking. Hole diameter in percussion drilled holes is generally less than +/- 50µm and in trepanned holes the tolerance tightens to about +/- 25µm. Recast is the molten metal that resolidifies around the hole’s inner diameter. Recast thicknesses vary with the alloy and hole depth but is generally less than 100µm. Hole depth can be as high a 50mm but most drilling tasks have hole depths of less than 15mm.
White Paper: Advancements in Laser Drilling for Aerospace.