Laser Based Manufacturing of Wind Turbine Components

Transcription

1 EPSCoR Wind Energy Meeting Laser Based Manufacturing of Wind Turbine Components PhD Student: Li Shi Professor: Hongtao Ding Laser Material Processing Lab Mechanical Engineering, The University of Iowa 11/29/2012

2 Materials Used Annually (Metric Tons -1,000kg) Wind Turbine Components, Raw Materials & Cost 600, , ,000 Controller 300, ,000 Generator 100,000 Yaw drive 0 TOWERS NACELLES ROTORS Yaw motor Anemometer Nacelle Gearbox Power cable Brake Tower TURBINE TOTAL Worldwide Blade U.S. Rotor Rotor Raw Materials Used for Different Parts of Wind Turbine during Component Cost Tower 26.30% Rotor Blades 22.20% Rotor Hub 1.37% Rotor Bearings 1.22% Main Shaft 1.91% Main Frame 2.80% Cables 0.96% Gearbox 12.91% Generator 3.44% Yaw System 1.25% Pitch System 2.66% Power Converter 5.01% Transformer 3.59% Brake System 1.32% Nacelle Housing 1.35% Screws 1.04% Laser Material Processing Lab 2

3 Wind Turbine Reliability Problems Gearbox failure* Bearing failure Wind turbines have grown larger Led to large, multistage gearboxes and large bearings Component reliability has suffered Many require replacement/overhaul at 5-7 years Drives up the cost of ownership Laser Material Processing Lab 3

4 Downtime (Hours) Wind Turbine Reliability Problems Load Crack initiation Subsurface microstructure Crack propagation Facture 180, , ,000 Fatigue marks & fracture Crack #1: Gearbox & bearings White layer Bearing micropitting 120, ,000 80,000 60,000 Bearing macropitting 40,000 20,000 0 Laser Material Processing Lab 4

5 Conventional Manufacturing Process (a) Gear manufacturing process Raw Steel Tempering Lathe Drilling & Boring Gear Hobbing Key Seater Gear Tooth Grinding Aperture Grinding Surface Grinding Heat Treatment (b) Bearing manufacturing process Raw Steel Hot Forging Machining Semi-fine Grinding Heat Treatment Grinding Surface Packing Assemble/ Fine Washing Washing/ Rust Preventive Raceway Grinding Centerless Grinding Laser Material Processing Lab 5

6 Laser Material Processing Laser Assisted Machining (LAM) Laser Hardening (LH) Laser Peening (LP) One step machining process to replace hard turning & grinding for large bearings and shafts of hard steel. Fast phase transformation process to replace conventional heat treatment processes for large bearings & gears of complex geometry. Innovative surface enhancement technique to improve fatigue, corrosion and wear resistance for critical wind turbine components. Laser Material Processing Lab 6

7 Lab Development Laser Material Processing Lab 7

8 Laser Assisted Machining A hybrid method of shaping difficult-tomachine materials which combines laser technology with traditional machining methods. Laser thermally softens the material. Accurate temperature control is the key. Machining modeling and microstructure prediction Optimize surface microstructure in terms of grain size and phase composition for improvement of resistance to wear, fatigue and corrosion. Benefits: Improve machinability for tough alloys, ceramics, CMC & MMC. Improve material removal rate & surface finish. Reduce cost! Laser Material Processing Lab 8

9 Laser Hardening Laser hardening Surface hardening process for complex part Very localized laser heat. Thermal & phase transformation models. Complex parts Advantages of LH: Local hardening restricted to the prescribed location Excellent quality, speed and stability Reduced heat effect on surrounding material Minimal distortion No surface cracking Low surface oxidation (Bailey and Shin, 2009, ASME/MSEC2009) Laser Material Processing Lab 9

10 Laser Peening The process of peening metal using a high energy pulsed laser. Produce micro dimples to improve surface lubrication and refine surface microstructure. Introduce compression with minimal cold working using laser shock waves. Dislocation-based microstructure evolution model Fatigue modeling Laser Peening Nanosecond laser pulse Plasma plume Water curtain (Confining medium) Paint or thin Al foil (Ablative layer) Target Laser peened surface S-N curve * (*, Fabbro et al. 1996) Laser Material Processing Lab 10

11 Microstructure Alterations Metallo-thermo-mechanical coupling White layer formation in hard turning Umbrello et al., 2010, Machining Science and Technology Problems No feed back of phase change on material constitutive model. Formation of white layer due to grain refinement has rarely been considered. Laser Material Processing Lab 11

12 Physics-based Process Modeling LAM LH LP 3D thermal model Finite element machining model Dislocation-based grain refinement model Phase transformation kinetics model 3D thermal model Phase transformation kinetics model Laser-induced shock pressure model Dislocation-based grain refinement model Fatigue model Residual stress Hardness Phase composition Grain size Heated affect zone White layer Surface finish Dislocation density Reliability of components. Fatigue Wear Corrosion Laser Material Processing Lab 12

13 Thermal Modeling Developed 3d thermal model for laser material processing of complex (cylindrical) geometry One step laser material process Applicable for LAM, LH and laser cladding of parts with complex profiles Programmed in Fortran, Computational efficient! Tool path 3d mesh Laser Material Processing Lab 13

14 Phase Transformation Kinetics Austenitization t 2 Q L 2D0 exp dt RT() t t 1 Martensitic Transformation * Ms T 1 f f e m Total strain increment Thermal strain E P T V TrP T ifi T Phase changes in hypo-eutectoid steel during heating Volumetric dilatation V 1 V f 3 V Laser Material Processing Lab 14 14

15 Surface Nano-crystallization by LP Surface nano-crystallization of copper by LP Laser Material Processing Lab 15

16 Dislocation Density-Based Grain Refinement Model A dislocation cell structure is assumed to form during deformation, which consists of two parts, dislocation cell walls and cell interiors, and to obey a rule of mixtures. Evolutions of the dislocation densities in cell interiors and cell walls are governed by : c w * * 1 3b 3 w r w 1 f 61 f fb * w r c bd 6 1 * f 1/ 3 bdf r c 2 3 k r c r 1/ n c r o c c o 1/ n r w ko o w r w The first terms correspond to the generation of dislocations due to the activation of Frank Read sources. Estrin et al., 1998, Acta Materialia The second terms denote the transfer of cell interior dislocations to cell walls where they are woven in. The last terms represent the annihilation of dislocations leading to dynamic recovery in the course of straining. Laser Material Processing Lab 16

17 Microstructure Prediction in Machining of Bearing Steels White layer formation Temp, C Phase TM γ+tm γ TM γ M γ γ+tm M TM TM Grain size, µm V=91.4 m/min V=274.3 m/min Laser Material Processing Lab Refined microstructure produced at low-to-moderate cutting speeds were mainly caused by severe plastic deformation (SPD). White layer formation at high cutting speeds was caused by both thermally driven phase transformation and grain refinement due to SPD 17

18 Laser Assisted Machining/Hardening Integration of CNC Machine with Fiber Laser for Laser- Assisted Machining and Laser Hardening Design and integrate a vertical Haas toolroom CNC mill with a 500W fiber laser for laser-assisted machining and lase hardening processes. The students will design and manufacture a fiber laser beam delivery system for both machining and hardening operations, control and synchronize the laser power with the mill PLC, and design a DAQ system for force and temperature measurement. Laser Material Processing Lab 18

19 Laser Assisted Machining/Hardening Setup Laser Material Processing Lab 19

20 Laser Peening Design a Nanosecond Laser Processing Platform for Bulk Micro/Nano Material Processing This project will design a laser peening/forming platform of a high energy nanosecond pulsed laser. The students will design a nanosecond pulse laser peening/forming setup, design and install/align the optics, control a motorized XY table for laser material processing. Laser Material Processing Lab 20

21 Laser Peening Setup Mirrors Objective 1: Nano-crystalline grain structure Nanosecond Laser Polarizer Lens Initial coarse grain Refined grains Half-wave Plate Water tank Work-piece Beam dump Linear motion stages TEM Finite element simulation Microstructure evolution model Computer controlled process Laser traveling direction Objective 2: Micro-scale patterning Micro squares Micro overlapped dimples Single laser impact SEM Laser Material Processing Lab 21 Surface profile