Refurbishing Turbine Engine Components with Multi-Axis Laser Machining Systems

Turbine engine repair and refurbishing is a rapidly growing business requiring specialized equipment and experience. Leading engine manufacturers are more frequently outsourcing this activity, demanding the highest quality work from their suppliers. This requires a dedication to continually improving the laser processes and quality while providing fast turnaround time. 

TL Precision Welding Inc. of Houston, Texas is a 12 person laser contract shop started in 1997 that serves this important and growing area of the turbine engine industry. TL Precision Welding was founded by Quang Tran originally to provide fabrication services to the industrial market in the Houston, Texas area. Tran emigrated from Vietnam to the United States in 1978. He has lived and attended schools in the Houston area, graduating from Texas A & M with a Bachelor of Science degree in biochemistry and chemical engineering. 

Success at TL Precision’s early engine refurbishing work has led to new opportunities in laser processing, company growth and a broadening of TL Precision’s laser capabilities. In an era of general economic decline, this is an industry niche with promising growth simply because of the sheer number of turbine engines, both land based and aero engines in operation and the constant need for engine maintenance. One leading turbine engine manufacturer for aircraft alone reports 25,000 engines in active service, all of which are continuously monitored for periodic maintenance. 

The high value engine components, such as turbo combustors, nozzle guide vanes, blades and other transition parts, for both land and aerospace engines, are regularly refurbished and put back into service. To keep maintenance costs as low as possible and to extend time between overhaul, engine manufacturers are requiring suppliers like TL Precision to improve their processes. 

TL Precision has met this challenge by becoming an expert at refurbishing these components but also positioning itself with new equipment and skills to handle new laser machining work as well. In 2008, TL Precision purchased their second system from LASERDYNE SYSTEMS, maintaining a tradition commonplace for LASERDYNE SYSTEM users. TL Precision uses these systems for drilling difficult to machine materials such as Inconel 617, Titanium and Hastelloy X. These are the base materials used to make land based gas turbine engines. The result – the company is attracting substantial new laser processing work. 

Recreating Turbine Engine Holes
A significant amount of engine overhaul calls for the repair and refurbishing of engine components’ air flow holes. Large combustor components have thousands of these small airflow holes of various sizes and shapes. The holes are designed to maximize engine thrust by selectively cooling critical components, and are precision drilled using laser processes in carefully plotted, complex patterns over the part’s contoured surfaces. The holes also are contoured and angled to the part surface to maximize air flow, reduce engine noise and minimize fuel requirements. Hole angles vary from 90° to just 20° to the surface and require a high degree of complex and agile positioning and dimensional precision. 

The challenge with refurbishing air flow holes in these complex parts is that they must be “re-created” in the same position and with the identical precision size characteristics as the original part when new, according to Quang Tran, president of TL Precision. 

“Recreating precision holes in a used part is often more difficult than generating precision holes in a new part,” Tran reports. “In recreating the hole, there’s no margin for error because most of these holes are positioned closely together and have diameters as small as 0.020" and require tolerance accuracies as tight as ±0.002". To position and laser process each of these holes accurately – without damaging the part – requires the very best multi-axis laser machining technology and a high level of operator skill. We have both with the LASERDYNE 790 system, the LASERDYNE BeamDirector and the continuing support of LASERDYNE SYSTEMS.” 

SYSTEMS RE-CREATE COMBUSTOR HOLES
“Our LASERDYNE 790 BeamDirector systems are the keys to doing this work successfully,” Tran says. “These systems are often the same models used by OEM’s to make the parts originally so there are both hardware and software compatibility which helps facilitate the refurbishing process. Using the same programming coordinates as when the part was processed new, our operators employ LASERDYNE features to re-establish the hole location and align the laser beam to it. Our operators verify hole location and beam alignment so there is no chance of error using LASERDYNE’s “through-the-lens” viewing feature, which magnifies clearly all hole features (magnification is 45 times). Every hole is thereby processed and verified individually.” 

TL Precision utilizes percussion drilling and trepanning processes to recreate cooling holes. Percussion drilling, most frequently used, is a method that generates a hole with only the laser’s focused beam diameter. The beam is focused at the point where the hole is. A single pulse or a series of pulses remove the material in the beam path, with an assist of co-axial flowing gas until the hole is recreated. For existing holes, slag, exhaust refuse and other foreign material that have built up in the holes during engine operation, is removed cleanly and accurately. 

Trepan drilling is a similar but less frequently used method in this engine refurbishing process. Trepanning does not rely on the laser beam size to give the final dimensions of the finished hole. With the part held stationary, the laser beam is moved with simultaneous multiple action motion to create the hole by cutting the periphery of the shape. 

Tran explains that while this hole refurbishing process often requires a manual “point and shoot” technique, it is consistently accurate and faster than any other known method. “That, plus with our new LASERDYNE 790 system we have current technology in our laser systems and trained operators that can easily process new parts when we get this kind of order. We are using all of LASERDYNE’s automatic and quality features that are designed into their systems,” Tran says. 

UTILIZING THE FULL POTENTIAL
Tran and his laser system operators are fast becoming champions of the LASERDYNE multi-axis laser technology. Take for example, LASERDYNE’S Automatic Focus Control (AFC) feature. “What we often must do manually to recreate a hole, we can do automatically to make new holes in new parts with AFC,” Tran states. 

AFC guides the motion system, maintaining critical focus position and following the contour of the part regardless of slight surface irregularities. With AFC, all machine axes react to sensing of the part surface, creating unlimited R-axis correction with high speed and unmatched sensitivity. AFC also allows top machine speeds so productivity is maximized without downtime or scrapped parts. 

Another important capability with Mr. Tran’s laser systems is a variation of percussion drilling called “drill-on-the-fly.” This is a feature whereby laser beam pulses are delivered to the part by the stationary laser while the part is rotated. The hole placement is a function of rotational speed and laser pulse frequency. If multiple pulses are required, “drill-on-the-fly” software developed by LASERDYNE engineers is utilized to synchronize the movement of the part to the laser pulses, ensuring that multiple pulses are delivered to the exact location required. By changing the laser pulse energy, pulse count or lens focal length, the characteristics of the drilled hole size and taper can be controlled to meet the requirements of the part. Drill-on-the-fly software also allows changes of the pulse shape during the process to improve hole geometry. 

“We continue to build on our laser processing knowledge with these LASERDYNE systems. LASERDYNE engineers are always available for consultation and additional training if we need it. Our systems have tremendous capabilities and we continue to have nothing but positive results as we acquire more varied and difficult part projects,” Tran concludes.

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