Proceedings of the 3rd Pacific International Conference on Application of Lasers and Optics 2008

MANUFACTURE AND REPAIR OF AERO ENGINE COMPONENTS USING LASER TECHNOLOGY (INVITED PAPER)

Paper (405)

Ingomar Kelbassa1, Patrick Albus1, Jens Dietrich1, Jan Wilkes2

1 Lehrstuhl fuer Lasertechnik, RWTH Aachen University, Steinbachstrasse 15, Aachen, 52074, Germany

2Fraunhofer ILT, Steinbachstrasse 15, Aachen, 52074, Germany

Abstract

This paper gives an overview about developed and industrially implemented manufacture and repair processes such as Laser Metal Deposition (LMD) and Selective Laser Melting (SLM) for additive manufacture and repair of parts and Laser Drilling (LD) for manufacture of instrumentation holes. Characteristic features of the processes are described and discussed. Components under investigation are e.g. High Pressure Compressor (HPC) BLISKs, High Pressure Turbine (HPT) Vanes and Blades, HPT Liners and Combustor Swirlers made of Titanium and Nickel base alloys such as Ti-6Al-4V, Ti-6246, In 718, Rene 80, Mar-M 002, Mar-M 247, and CMSX-4. The paper is completed by the presentation of installed machines at the customer’s site.

Introduction

Manufacture and repair of newly developed and high-value aero engine components made of Titanium and Nickel base alloys have become more and more subjects of current R & D work starting with feasibility studies, over process developments yielding in certified processes and industrially implemented machines and systems engineering. Using Laser technology enables the OEMs to manufacture parts which cannot be manufactured with conventional technologies such as milling and casting and the MROs to repair parts which are known to be not repairable to date.

Characteristic features

Laser Metal Deposition (LMD)

By proper adaptation of the process layout and process parameters, the LMD process results in repaired layers and volumes free of any defects such as micro cracks and bonding defects, and porosity is minimized. Newly developed modular compact powder nozzles (off-axis/coaxial, fig. 1 [2]) guarantee contamination-free

LMD for different part geometries by generation of a proper local shielding gas atmosphere. The mechanical properties of the LMD materials after appropriate heat treatment fulfill the specifications of the forged or cast raw material. [1, 2, 3, 4, 5, 6, 7, 8]

Figure 1: New coaxial powder nozzle with integrated

shielding gas supply [2]

LMD minimizes component distortion in comparison with conventional deposition welding techniques. LMD produces nearly net-shape results. The typical oversize is in the range of 100 – 300 µm. A closed-centre process chain including CAD/CAM/NC coupling is available for process implementation on genuine components. Process monitoring and control by pyrometry and camera-based systems for quality assurance aspects are currently under investigation. [1, 2, 3, 4, 5, 6, 7, 8]

Selective Laser Melting (SLM)

The investigations are carried out using an experimental SLM system developed at Fraunhofer ILT. The setup comprises a diode pumped Nd:YAG Laser operated in cw operation mode with a maximum output power of 170 W, a sealed and gas purged processing chamber with an inert gas atmosphere

40 mm

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containing less than 10 ppm of oxygen and a preheated build platform that can be heated up to 900 °C. Parts made of In 718 are fully dense. Figure 2, left, shows a polished cross section of a part manufactured by SLM. There are virtually no pores in the material and bonding defects can be completely avoided when using a sufficiently high Laser power. In the etched cross section (fig. 2, right) the layers and melting tracks become visible.

Figure 2: Polished (left) and etched (right) cross

sections of parts made of In 718 manufactured by SLM

Laser Drilling (LD)

For the determination of suitable process parameters and a suitable process layout for manufacture of instrumentation holes in HPT Nozzle Guide Vanes (NGVs) made of Mar-M 002 pulsed Nd:YAG Laser radiation and a 5-axes working station is used. The process layout used is 5-axes trepanning, containing two subsequent steps (fig. 3):

1) Drilling of a through hole by percussion drilling

2) Smoothing of the hole by 5-axes circular movement (trepanning)

Figure 3: Manufacture of a through hole by trepanning

(top view)

The geometrical specification of the hole exit diameter of 1.15 ± 0.05 mm is achieved (fig. 4). The holes are conical with a taper of less than 1.2. The thickness of the recast layer is less than 70 µm.

1380 µm 1196 µm

1388 µm1198 µm

Figure 4: Etched longitudinal sections of through holes

in Mar-M 002 manufactured by LD; Substrate thickness: 6 mm (top) and 10.5 mm (bottom)

Parts and components

Laser Metal Deposition (LMD)

Damping wire grooves of a BR715 HPC Front drum made of Titanium base alloys Ti-6Al-4V and Ti-6246 (fig. 5, left) are repaired by a local reconditioning of the groove wall. The main challenges in this application, affects on the opposite wall (heat input, remelting, etc.), are avoided completely and the processing accessibility is restricted due to the groove geometry (fig. 5, right). [2]

Figure 5: BR715 HPC Front drum (left); Cross section

of reconditioned groove wall (right) [2]

Geometric features on the surface of a BR715 HPT case of Nickel base Nimonic PE16, with a Nickel base In 625 powder additive for bosses, brackets, and flanges, are repaired locally with just one layer deposited (fig. 6). Because of the minimal heat input from the LMD process, distortion of the component is nearly completely avoided. The contamination (oxidation) free LMD result is guaranteed by local gas shielding using the newly developed powder nozzles. [2]

Opposite wall not to be affected

Gro

ove

Repaired groove wall

1. Step: Percussion drilling

2. Step: Trepanning

Finished trepanned through hole

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Figure 6: BR715 HPT Case (left); Repaired flange

detail (right) [2]

On aero engine HPT parts such as NGVs (fig. 7) made of Nickel base Mar-M 002 and Liner 1 parts made of single crystal Nickel base CMSX-4 (fig. 9) mesh structures made of In 625 are applied by LMD. These mesh structures are increasing the bond and shear strength of the Mg Spinell Thermal Barrier Coating (TBC) which is applied by Atmospheric Plasma Spraying (APS) afterwards (fig. 8). Hence, a bond coat between substrate and TBC is no longer required. [9]

Figure 7: HPT stage 2 NGV with mesh structure

manufactured by LMD [9]

Figure 8: HPT stage 2 NGV with mesh structure

manufactured by LMD and coated TBC by APS [9]

Figure 9: HPT stage 1 Liner with mesh structure

manufactured by LMD [9]

Using new cw Ytterbium fiber Laser radiation with a wavelength of λ = 1080 nm, a Laser beam diameter of dL = 280 µm and a max. Laser power of 200 W enables to achieve the specified track width of approx. 340 µm. In case of necessity track widths down to approx. 80 µm are applicable. [9]

Selective Laser Melting (SLM)

Within the European Commission (EC) funded project FANTASIA the processibility of Nickel base alloys by SLM is investigated for the application in aero engine development, manufacturing and repair. Currently the work focuses on two different types of application [5]:

a) The first type of application is the manufacturing of functional prototypes to reduce the product development time. During the development phase of an aero engine, for certain components, various design alternatives have to be tested in order to optimize the aero engine performance, reduce emissions etc.. One example is the geometry of swirlers. Swirlers improve the mixing of air and fuel in the combustion chamber. Using SLM, different design alternatives can be manufactured within a very short time without any tools or casting moulds.

b) The second type of application is the manufacturing of patches for the repair of aero engine components. Today, larger defects such as burn out sections of HPT NGVs cannot be repaired. A new repair approach consists of the following three steps:

1) The damaged section of the vane is removed completely.

2) A patch that fits into the prepared void is manufactured by SLM.

3) The patch is welded into the vane by LMD.

This repair technique could also be used e.g. for engine casings. Individual patches can be manufactured by SLM for each individual damage or deterioration.

If individual units or small quantities of a certain geometry are required, SLM is significantly faster and more cost-effective than e.g. precision casting.

Figure 10 shows an example of a functional prototype made by SLM. This combustor swirler is made of In 718.

Flange

Repaired flange detail

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Figure 10: Functional prototype of a combuster swirler

made of In 718 manufactured by SLM

Figure 11 shows an example of a patch for the repair of a HPT NGV. In this case the geometric data of the NGV was acquired by computer tomography. Alternatively, 3D CAD data could be used if available. The materials under investigation for this application are Rene 80 and MAR-M 247. Both materials are susceptible to micro crack formation during SLM processing. So far it has not been possible to manufacture crack free components from these two materials. Further experimental investigations are in progress to solve this problem.

Figure 11: Patch for the repair of a damaged HPT NGV; 3D dataset (left); Patch made of Rene 80

manufactured by SLM (right)

Laser Drilling (LD)

Based on the determined suitable process parameters in preliminary investigations following steps are carried out to guarantee a proper manufacture of instrumentation holes in HPT stage 2 NGVs made of Mar-M 002:

1) Design and manufacture of a newly developed fixing device,

2) Development of positioning procedure and

3) Transfer of the determined 5-axes process layout onto the real component via CAD/CAM/NC-coupling

by use of CAD data of the genuine part (fig. 12).

Figure 12: 3D CAD dataset of the genuine part (top);

Detail of the holes to be manufactured (bottom)

Instrumentation holes manufactured by LD in a TBC coated HPT stage 2 NGV are shown in figure 13. Back wall strike can be avoided completely by using Teflon and Copper inserts during processing (fig. 14).

Figure 13: Instrumentation holes manufactured by LD

in a TBC coated HPT stage 2 NGV

20 mm

20 mm

Instrumentation holes manufactured by LD

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Figure 14: Experimental setup including back wall

strike protection by Copper and Teflon inserts

Installed machines

One example of a machine in aeronautics is the LMD machine at KLM, Netherlands (fig. 15, left). The company uses this machine for repairs of aero engine components such as disk labyrinth seals made from 17-4PH (fig. 15, right). [2]

Figure 15: LMD machine for repairing genuine aero

engine components at KLM, Netherlands (left); Repairing disk labyrinth seals (right) [2]

Beginning of 2008, Rolls-Royce Deutschland has installed its first LMD machine at the Oberursel, Germany site. This will help further implement and establish this technology in the aeronautics field of application (fig. 16).

Figure 16: LMD machine for repairing genuine aero

engine components at Rolls-Royce Deutschland, Oberursel, Germany site

Conclusion and Outlook

Laser technology offers new prospects with regard to “not repairable” highly integrated parts and “not repairable by conventional processes” parts. Further development and improvement of Laser technologies combined with ongoing system-engineering advances such as processing heads and powder nozzles with integrated shielding gas supply for LMD, preheating temperatures of more than 900 °C for SLM and a closed-centre process chain with a fully integrated CAD/CAM/NC-coupling for 5-axes process layouts for LD have enabled the Lehrstuhl fuer Lasertechnik and the Fraunhofer ILT in cooperation with OEMs such as Rolls-Royce Deutschland and other aero engine MROs to carry out repairs on what were formerly non-repairable parts.

The standards set by the Lehrstuhl fuer Lasertechnik / Fraunhofer ILT and its industrial partners in the repair of aero engine components over the last few years also benefit the FANTASIA project, a joint European project in which 11 companies from the fields of aerospace and Laser technology and eight R & D centers are taking part. Launched in June 2006, the € 6.5 million project is coordinated by the Fraunhofer ILT and receives funding from the European Commission. It has ambitious objectives: a decrease of at least 40 percent in repair costs and a 40 percent reduction in the repair turnaround time for parts. Some components that previously had to be discarded due to the lack of suitable repair techniques are now repaired with the help of LMD. Six-figure savings are anticipated. It is realistic to expect a reduction of up to 50 percent in raw material and up to 25 percent in post processing.

Acknowledgment

The authors gratefully acknowledge the financial support by the European Commission within the 6th Framework Program Strategic Targeted Research Project FANTASIA: Flexible and near-net-shape generative manufacturing chains and repair techniques for complex shaped aero engine parts – Contract No.: AST5-CT-2006-030855.

Processing head

5-axes working station

Fixing device

HPT stage 2 NGV

Copper

Teflon

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