EU Project MERLIN Needs and Demands for the Manufacture of Next Generation Jet Engine Components

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1 EU Project MERLIN Needs and Demands for the Manufacture of Next Generation Jet Engine Components Jeff Allen AKL International Laser Technology Congress 9 th May 2012 The information in this document is the property of Rolls-Royce plc and may not be copied or communicated to a third party, or used for any purpose other than that for which it is supplied without the express written consent of Rolls-Royce plc. This information is given in good faith based upon the latest information available to Rolls-Royce plc, no warranty or representation is given concerning such information, which must not be taken as establishing any contractual or other commitment binding upon Rolls-Royce plc or any of its subsidiary or associated companies.

2 MERLIN Project Summary 2 The concept of the MERLIN project is to: Reduce the environmental impact of air transport using Additive Manufacturing (AM) techniques in the manufacture of civil aero engines Develop AM techniques, at the level 1 stage, to allow environmental benefits including: - near 100% material utilisation - no toxic chemical usage - no tooling costs - impact the manufacture of future aero engine components (current buy to fly ratios result in massive amounts of waste) These factors will drastically reduce emissions across the life-cycle of the parts Also be added in-service benefits because of the design freedom in AM Light-weighting and the performance improvement of parts will result in reduced fuel consumption and reduced emissions MERLIN will seek to develop the state-of-the-art by producing higher performance additive manufactured parts in a more productive, consistent, measurable, environmentally friendly and cost effective way

3 MERLIN Areas for Progression 3 The MERLIN consortia have identified the following areas where a progression of the state-of-the art is needed to take advantage of AM: Productivity increase Design or Topology optimisation Powder recycling validation In-process NDT development In-process geometrical validation High specification materials process development

4 MERLIN - Beneficiaries 4 Rolls-Royce WSK "PZL - Rzeszow" S.A. Industria de Turbo Propulsores MTU LPW Technologies Ltd Turbomeca Volvo Aero Corporation TWI Limited Fraunhofer - Gesellschaft zur Forderung der angewandten Forschung e.v. ILT Association pour la Recherche et le Developpement des Methodes et Processus Industries (ARMINES) ASOCIACION CENTRO DE INVESTIGACION EN TECNOLOGÍAS DE UNION LORTEK BCT University West Frederick Research Centre Total Budget - 7.1m Project Launch Jan 2011 Project End Dec 2014

5 MERLIN Work Packages 5 WP1 - Project Definition and Specification WP2 - Shape - Topology optimisation, modelling and validation WP3 - Process Development - Process development, process monitoring and control, and thermal management WP4 - In-Process NDT development and integration, geometrical measurement and control WP5 - Post Processing - Mechanical testing, analysis, recycling validation and heat treatment WP6 - Technology Demonstration - Environmental and through lifecycle evaluation WP7 - Management WP8 - Dissemination and Exploitation

6 Overview of Technologies & Selection A wide range of processes exist, with varying attributes in terms of precision, cost, integrity, etc. 6 As with subtractive manufacture, there is no single best process ; selection needs to consider application, including material, size, shape type and complexity, access, inspection and validation. Heat Source/Material Form Combinations Very good surface finish & precision Slow build rate Material Form Small parts only Low build rate Heat Source Powder Stream (Various types) Powder Bed Wire Laser (Various types) Focussing Lens Lens series Mirrors (focussing /deflection coils for EB Electron Beam x Electric Arc x x SMD Powder bed Filters Laser heat source Low cost (100% wire utilisation & medium process speed) Good for titanium parts with low/medium complexity Full fusion Good surface finish Large working envelope Cell installed at AMRC (Sheffield) Argon chamber / vacuum for EB Potential for high build rates Material utilisation varies Options for Repair, Hybrid & OEM Potential for component tailoring Electron Beam systems emerging Requirement for vacuum system with EB

7 Overview Powder Bed Small Parts Blown Powder Repair Hybrids Advantages V.good precision of deposition Good surface finish Good material properties Good utilisation of powder Uses established basic technology Automatic operation Better at overhung surfaces Can make shapes which were previously impossible Advantages System development Easy Inert atmosphere operation High Deposition rate capability Usable for additive manufacture Usable for repair Relatively wide process window Low heat input to substrate Limitations Relatively low build rates Not straightforward to achieve sub 10ppm oxygen levels Need to build on a flat base Relatively low build volume Limited range of materials at present Limitations Low Powder usage efficiency No so good at overhung surfaces Tend to have rough surface finish Need complex manipulation systems for 3D parts Can get scatter on material properties 7

8 Business Opportunities 8 Reduced time to market Simple/minimal tooling, Reduced material cost Reduced waste material (high buy-to-fly ratio) Reduced removal operations No roughing, Minimal finishing, Less WIP Repair capabilities to support aftermarket opportunities Lower total life cycle cost Enhanced product opportunities Design for NNS Additive Bosses Additive Flanges Built up Leading / Trailing Edge

9 Design Opportunities 9 Graded & Tailored Materials Can change the alloy composition throughout the shape of the component, avoiding abrupt changes in material properties Add desired properties to a part only in the areas they are needed without abrupt changes in alloy composition eg: Hard facing for integral bearing tracks on shafts Organic Shapes Can be used to produce components previously not capable of being manufactured, minimum weight and maximum strength structures akin to natural shapes such as: butterfly wings (eg: isogrids) graded spheroidal void structures such as wood and bone Geodesic structures Skeletal or polygon faceted structures with high specific stiffness, such as the Beijing National Stadium. Material efficient designs Image courtesy of Optomec Inc.

10 Powder Bed - Modes Powder Powder Bed Bed - Modes - Modes 10 Rapid Prototyping Mode Rapid Development Prototyping parts Mode Short Small Lead numbers time Ability Short Development Lead to change time parts design Ability Short to until Lead change time the last minute design Ability until to change the design last Expect minute until the to last pay minute a premium Expect to on pay price a premium on price OEM* Parts Manufacture Mode Have to compete with established processes High cost of Qualification Need Powder Supply Chain Need Parts Supply Chain * Original Equipment Manufacture

11 Issues Specific Cost of Deposited Material 11 Assumes a self checking, self controlling, serialised, production system Specific cost of deposited material is primarily a function of build rate and powder cost - Raw Material Cost - Material Usage Efficiency - Technical support time (programming and development) - Process Labour Cost - Capital Cost - depreciation - Machine Utilisation - Power Cost and usage - Power Conversion Efficiency (wall:delivery) - Build Rate (incorporating feature and surface control) - Consumable form - Set-up time - Planned maintenance & consumables - Associated costs of ancillary processing, - e.g. machining, heat treatment, inspection

12 Issues Multiple Spots 12 In very simple terms to a first approximation! Material Props = fn Crystal Structure Crystal Structure = fn Cooling rate Cooling Rate = fn Molten Pool Size Molten Pool size = fn Spot size Specific Cost of deposited material = fn deposition rate Deposition rate = fn Spot size Surface Finish = fn Spot Size (larger spots give coarser surface finish) Ie: Practical systems reach a limit on max spot size This limits the deposition rate & surface finish and defines the material properties Points towards the use of Multiple Spots

13 Issues Material Properties 13 UTS Between Cast and Forged Fatigue Dependent on level of micro cracking Creep Fine grain structure tends to lower creep performance Anisotropy Deposition Parameters can be optimised to minimise anisotropy Fracture Toughness (Hot Creep Rupture) Can be problematic if the resulting grain structure exhibits epitaxial grain growth Surface Finish External Surfaces Internal Surfaces Effect on fatigue life

14 Issues Maximum Component Size 14 Limited by the tank size of the powder bed system This is presently typically 250 x 250 x 250 Development systems are planned for 400 x 400 x 400 Then 600 x 600 x 600

15 Issues Powder Source 15 Limited number of sources approved for powder supply into Aerospace Expensive and long term to Approve new suppliers Development usage is small cf Production Difficult to predict future requirements Ti 6-4 supply particularly difficult Gas Atomised Plasma Rotating Electrode Powder (PREP) Specialist Nickel Superalloys difficult to supply to specification Particle size distribution Chemistry Morphology Trace elements eg Lanthanum & Yttrium are difficult to control at low ppm levels

16 Issues Residual Stress/Distortion 16 Material structure is defined when the deposit is hot Thermal contraction must take place during cooling to ambient Results in a combination of: residual stress distortion in the part Cracking Aim to accommodate thermal contraction effects in the form of residual stresses which are below the material UTS Can stress relieve in some cases May result in enforced overbuild to allow the finished shape to be machined from the distorted geometry EB processes preheat the powder bed results in reduced residual stress Dev work to use auxiliary lasers to preheat laser powder bed processes at ILT Can use Preheated base plates to minimise distortion & cracking on cooling Need C for high performance Ni superalloys

17 Issues - Process Window 17 Note that for superalloys there are definite practical limits to rate: The effect of distortion and cracking though these are not insurmountable Fine melt pool size allows development of optimised parameters for reduced segregation Rate is limited by consumable feed process control and thermal management General (laser powder) deposition processing window For high temperature alloys, solidification effects and the thermo-mechanical effects of deposition and heat treatment / post processing must be considered. This is due to crack sensitivity / strain aging and end microstructure requirements. Power density (increasing as a function of increasing spot radius. Linked to consumable feed rate and local dynamic heat sink. Solidification cracking Excess segregation Lack of inter-run fusion Travel speed, linked to location Adapted (After Reed) Liquation Power density (increasing as a function of increasing spot radius. (hypothesised) Superalloy Process Window Dilution Bead profile aspect ratio No fusion Consumable feed rate (After Steen) Porosity Energy per unit length related to velocity

18 Process Capability 18 Need a process suitable for routine use on the shop floor Stable Repeatable Predictable Eg: Powder Bed Intra bed variance Inter-build variance Inter machine variance Inter Operator variance Depends on the maturity of the system Measurement and control of Key Process Variables

19 Issues - Integrity of Deposited Material 19 There are many claims with regard to density and forged properties, What do they mean? Usually that the porosity is usually fine Interface encompassing fusion zone and HAZ Boss But aero-applications can experience arduous loading regimes, including: Stress rupture Fatigue Dynamic loading does that always mean that the material is homogeneous? Pad The maximum flaw-size is significant for component life Flaws of various sizes will randomly intersect test bars. Scatter in performance and tight acceptance thresholds show the importance of control Schematic (not to scale) of flaws dispersed through a mechanical test block.

20 Properties of Thin Walls 20 Outer surfaces of parts are subjected to abrasive blast Removes adhered powder particles Normalises surface finish Abrasive blast results in a 100µ thick surface layer contains cracks (fatigue initiation sites) Material properties would not be expected to be the same as the bulk material Particular problem when performing stress analyses of components with thin (c.0.5mm) walls Unknown material properties for FE Model FE modellers tend to err on the cautious resulting in designs which are perceived to be overweight Erodes the business case for WXB Noise attenuators Need to establish the properties of thin walls for input in to FE Stress models 500µ 100µ 300µ 100µ 100µ thick layer from abrasive blast - Contains cracks - Unknown material Properties Usable thickness of base material reduced to 300µ Unknown effect on base material from defects in the surface layer

21 Surface finish 21 External Surface Finish Surface finish is generally a function of: Orientation of surface in build tank Deposition Rate Powder Size distribution Laser Processes Smoother Surface Finish Lower Deposition rate Electron Beam processes Rough surface Finish Higher deposition rates General approach is to have different sets of parameters for skin and fill sections of the build Need to optimise this approach to maximise surface finish quality whilst maximising the overall deposition rate Need to look further at improving surface finish on overhung & low angle surfaces Internal Surface Finish Need a method of post processing internal surfaces to achieve an acceptable surface finish Chemical? Electro Polish? Abrasive media? Need to use designs which are optimised to give best internal surface quality

22 Summary 22 Need to Develop: Systems with economically competitive deposition rates and capacities Deposition Parameters and Techniques for High Temperature Nickel Superalloys Powder sources with suitable Quality and Cost Capable NDE techniques Methods of Topological Optimisation Post processing methods to give acceptable Surface Finish & Materials Properties