Laser processing shaped holes

One of the "hottest" topics in the manufacture of turbine engine components in Asia today is the production of shaped holes by laser processing. Both aero-engine and land-based turbine OEMs and their respective supply chains are showing a keen interest in the available processes and resulting shapes. They often describe a preferred solution with expected results. Their interest is tempered by technical limitations either experienced directly or rumoured through industry sources.
 The reasons for the high level of interest in producing shaped holes by laser processing are simple: shaped holes can provide superior cooling for a turbine engine component. Proper design of cooling components with shaped holes will result in fewer holes to accomplish a superior result. Fewer holes mean shorter production cycle times, lower production costs, and a lower cooling air requirement. Properly put into practice, results in a more efficient and cost effective engine. The specific interest in laser processing comes from its speed relative to competitive methods and the ability to produce shaped holes in parts with thermal barrier coatings (TBC).
The use of shaped holes is well documented. Shaped holes have been effectively used in hot section components of turbine engine for many years. Some engine component manufacturers employ conventional plunge electrical discharge machining (EDM) to produce these holes. Others use laser processing to produce shaped holes on specific parts. The driver for choosing one process over the other in the past, and even more so today, is a combination of cost and flexibility. It is difficult to argue that laser processing is not only quicker but is a more flexible manufacturing process. When all factors are examined, laser processing is also simply more cost effective.

Laser processing is faster, more cost effective than EDM
In evaluating shaped hole processing using laser and EDM technologies, it is important to define and understand two basic terms used to describe all shaped holes (whether EDM or laser produced). These terms are diffuser and metering section.
Diffuser describes the section of the hole that contains the "shape". It is on the exit side of the air path and is used to spread, or diffuse, a film of air over the part surface. The design criterion for diffusers is beyond the scope of this article. Suffice to say that over the years different models have given design engineers an opportunity and tools to be creative in the describing and placing of holes. When examining a part with shaped holes what appear to be different shapes are the result of the angle at which the holes are drilled in relation to the surface and their placement on the components. A wide variety of shapes is often only the result of these two factors. Metering section refers to the cylindrical, portion of the hole produced by either a percussion or trepan laser drilling process. Diameters ranging from 0.010-inch (0.25 mm) to 0.035-inch (0.89 mm) are common in turbine engine components. An Interesting observation from the work performed at LASERDYNE SYSTEMS is that a length to diameter requirement for metering holes is not universally observed, as seen in the following case studies.

EDM for making shaped holes and its limitations
Designers of turbine engine components do not want to be limited to the hole processing techniques discussed in the examples above. The alternative they most often choose is to use conventional EDM with a shaped eleNike Air Max