For years, the manufacturing industry has struggled to mechanically drill holes that are less than 0.25mm in diameter. Industry professionals have found that laser drilling serves as a great alternative for this type of small hole drilling, particularly when it comes to hard and brittle materials. Drilling has become known as one of the most successful and vital applications of industrial lasers. When working with metals, fiber laser drilling is used to produce very small orifices for cooling channels in air turbine blades and nozzels.
Many factors come into play for direct hole drilling. Some of those parameters include the wavelength, quality of the laser beam, pulse duration, intensity, and pulse repetition rate.
Laser ablation is frequently necessary to remove paint or coating layers of laminate from solid material or base metal with which a manufacturing team is working. The removal of this layer or coating makes the base material easier to access and adapt to further processing or hole drilling. With laser ablation the cutting laser in the process usually works at a small or shallow depth, making its precision and accuracy an essential reason for its industry value.
A laser beam is used to eradicate or remove the object's layered surface. Because of the non-contact nature of the laser ablation process and the now exposed base metal’s conductive surfaces, holes can be EDM drilled in hard-to-machine surfaces and materials as usual without any further post processing to accommodate the coating process; (the need to mask holes for coating is eliminated).
Laser ablation works because the laser beam used for ablation is focused onto a substrate then vaporizes the material away that sits on the surface of the object. By controlling the intensity, wavelength and pulse length, laser ablation machine operators can control the amount of material that is removed from the object.
Within industries that include aero engine and industrial gas turbines, manufacturers have struggled for decades to develop a process chain for the efficient production of cooling holes in various turbine components. Generally, producers of crucial industry parts must drill the cooling holes into these precision components prior to the application of thermal barrier coatings (TBCs), which are highly advanced material systems, which technicians apply to the metallic surfaces of aero-engine or gas turbine parts operating at elevated temperatures. Unfortunately, these coatings are non-conductive and make the hole drilling EDM process impossible. Traditionally the cooling holes were drilled prior to coating thus requiring labor intensive and costly masking operations to be performed to protect the holes from being plugged when the coating was applied. With laser ablation, coatings can be uniformly applied to the base material without any masking required. Laser ablation then “scrubs away” the coating where a hole is to be drilled thus allowing the conductive metal to be exposed as needed. EDMed cooling holes can then be installed. Cooling holes are now free of any potential coating blockage and the Thermal Barrier Coating is more evenly applied to the overall surface of the part.
Once parts are coated with Thermal Barrier Coating or TBC, the ceramic nature of TBC renders the part as insulated and unable to pass an electrical current between the base material and any electrical conductive tool such as required for EDM for cooling holes. Thus, holes must be drilled prior to coating. With Laser Ablation; which can precisely remove material such as a small patch of TBC exactly where the hole needs to be placed; exposing base conductive material; and with the EDM process needed to drill small cooling holes; holes can be installed. The advantage of laser ablation is realized by installing the holes after coating and avoiding the need for tedious, labor intensive, costly, time consuming, and not always successful masking of holes that were installed before the TBC application.
Additionally, the TBC coating will be more evenly applied to the surface of a part without the interruption of masked holes thus producing a more consistent flowpath area of high pressure turbine components. Although Laser Ablation adds processing steps to the hole drilling sequence, the processes added are more consistent and automated as compared to the masking of individual holes in preparation for the coating process.
Finally, depending upon the overall thickness of the base material being drilled for the cooling hole and the shape of the cooling hole itself; the same laser used to perform the patch removal or “scrubbing” of the coating can be used to perform the drilling of the cooling hole. Thus fewer operations, fewer set-ups and lower lead times.
At Hi-Tek Manufacturing, we place great value in laser ablation as it stands today and for what it promises in the future to improve our own processing services. To learn more about our laser ablation capabilities, contact us directly.