Advanced EDM Hole-Drilling Technology for the Most Demanding Turbine Engine Requirements

As aerospace manufacturers strive to improve engine performance and reduce fuel consumption, the need for advanced hole-drilling capabilities in electrical discharge machining (EDM) has grown substantially. New engines are being designed with special diffuser cooling film holes for improved airflow efficiency, along with special thermal coatings to raise the engine operating temperature to meet the requirements necessary for performance, fuel economy and component life.

Other industries increasingly are looking for more efficient small-hole manufacturing capabilities as well. Power-generation equipment manufacturers produce gas turbine engines with similar requirements to the aerospace field, but in larger components. As a result, the efficiency, quality and productivity of EDM hole-drilling operations is critical in achieving proper airflow and engine component cooling. As many new turbine engine programs begin to enter and ramp-up for full production, suppliers throughout the manufacturing base are re-examining and investing in advanced EDM hole-drilling technologies to gain greater throughput and improve efficiencies to meet the changing production demands.

Demands Unique to Blades and Vanes

Many cooling holes are simple, round holes concentrated on the leading or trailing edge of a component; however, more complex cooling-hole geometries, such as diffusers, feature tapered or funnel shapes that lead into a finished “through hole.” These through hole and diffuser holes enhance airflow for cooling, and the diffuser hole shapes can have variations in geometry and depth on the same part. In addition, they are machined to blend into the complex 3-D shape of part detail.

Blade and vane components typically have a hollow interior for weight saving and internal airflow. During the EDM hole-drilling process, the cooling film holes break into these internal cavities. To preserve the correct airflow, it is critical that no back-wall impingement, or back-striking, occurs during drilling. Back-striking happens when the drilling electrode comes in contact with the opposite internal cavity wall, creating a hole or divot on the internal surface, which can cause disruptions in airflow and subsequently create a hot spot within the engine component.

Metallurgical quality is also an important concern. The most crucial characteristics are the recast (the re-adhered molten material) and heat-affected zone (altered microstructure and hardness area of the underlying base material), which could impact the operating life cycle of the component.

Selecting the Ideal EDM Hole-Drilling Solution

With a variety of EDM hole-drilling technologies available on the market, it is critical for manufacturers to understand the unique advantages and disadvantages of each machine, including oil- and water-based platforms. This type of evaluation typically begins with the nature of hole features required, including size, shape and quality.

In the case of cooling film holes for turbine engine blades and vanes, water-based EDM hole drilling machine platforms, such as Makino’s EDBV-Series machines, are typically best suited based on their speed and productivity output. The EDBV-Series machines are configured with unique technologies that are ideally suited for turbine engine cooling film hole production requirements:

• C-axis spindle rotating up to 1,000 rpm with a vibration control finger mechanism helps to
  provide stable and consistent operation with full long-length electrodes.
• Fully integrated 2-axis rotary table supplies access to multiple areas of the workpiece.
• Fully submerged machining operation helps to improve EDM hole drilling speeds by up to
  10 times that of conventional technologies, and eliminates overspray and slip hazards in the production environment.
• Programmable rise-and-fall work tank offers excellent open access to the work zone while supporting and simplifying automation integration.
• Proprietary, highly sensitive breakthrough detection circuit can sense cavity-wall breakthrough
  in just one second. That translates to breakthrough detection to within approximately 0.040 inches
  to 0.060 inches (1.0mm to 1.5mm) of machining depth.
• Automatic tool change (ATC) and automatic guide change (AGC) systems afford hours of unattended operation and programmable, automated capabilities for machining varying hole diameters. The complete tool exchange is also performed within 30 seconds.
• Achieve consistent metallurgical quality with recast and heat-affected zone (HAZ) levels of
  under 12 µm (0.0005 inches), using optimized speed settings.
• Standard water quality and thermal cooling systems include water filtration, water deionization
  to control conductivity, and a water chilling unit to maintain the water at the same temperature as
  the machine casting (improves accuracy and repeatability).
• Simplified canned cycle programming of cooling hole and diffuser hole machining is achieved on the intuitive and user-friendly Hyper-i control.

The EDBV-Series machines can also be applied to a variety of applications outside of aerospace, extending the value of the machines and giving manufacturers the opportunity to enter additional markets, such as energy and power generation. Manufacturers can also integrate these platforms within automated systems to achieve even greater productivity, faster return on investment and lower per-piece costs, further enhancing competitiveness.

Discover what type of EDM hole-drilling machine platform is best suited for your manufacturing operations in Makino’s complimentary white paper, “Selecting the Appropriate EDM Technology for Hole-Drilling Applications.”