The move to turbine engine designs featuring low NOx emissions and greater fuel efficiency has resulted in a major change in design and manufacture of certain engine parts such as combustion chambers. For example, effusion cooling combustor designs use thousands of 0.5 mm diameter, shallow angle (less than 30 degrees from the surface) holes to provide a film of cooling air over the surface of the combustor. A variety of thermal barrier coatings are also used to protect the surface during operation.
Laser drilling is playing a key role in the production of effusion cooling holes. Laser drilling, which uses the focused output of a high power industrial pulsed Nd:YAG laser to trepan the holes, has become the process of choice for producing these because of:
- low heat input
- rapid drilling rates
- ability to drill ceramic coated metals
- a minimum number of process variables contributes to reliable, repeatable processes
This paper reviews the laser drilling process for producing effusion cooling holes, characteristics of the holes, and developments aimed at increasing the throughput and, therefore, reducing the cost for laser drilling. The paper also summarizes the key aspects of the laser system required to produce combustors that meet airflow and other quality (metallurgical) specifications.