Current Research & Developments in Materials for Mega Energy Systems
Forming & Welding of Components- Recent Advances Manufacturingf orProcesses Mega Energy Systems Manu Factus : Latin for ‘made by hand’
Definition: A Well organized method of converting raw material to end product
End Product: Value and utility added to output.
Metal Forming Material Joining
Fundamentals Joining techniques Advances in forming Welding metallurgy Intelligent forming Intelligent welding Unconventional Historical development of forming of materials The purpose of a forming operation is to enforce a change in shape or properties of the metal by application of external forces and / or temperature, without altering its chemical composition.
Period Metals and Casting Forming Process Before 4000 B.C Gold,copper and meteoritic iron Hammering 1000-1 B.C. Cast iron, cast steel Stamping of coins 1000-1500 A.D. Blast furnace, type Wire drawing,gold silver metals,casting of bells,pewter smith work 1600-1800 Brass, zinc, cast iron, steel Rolling and Extrusion 1800-1900 A.D. Centrifugal casting,Bessemer Steam hammer, steel process,electrolytic rolling,seamless tube aluminum,nickel steels,Babbitt, piercing,steel rail rolling, galvanized steel, powder continuous rolling , metallurgy, tungsten steel, open electroplating hearth steel 20 th Century Cold extrusion (steel), explosive forming, precision forging, die design by analytical methods, net shape forming Requirements of a good manufacturing system • Product should meet design requirement, Economical and High Quality • Should be flexible and responsive to new technology • High productivity: Best utilization of available resources. Steps in Modern Manufacturing
Definition of product need, marketing information CAD CAM Design, Analysis & Conceptual design Production & Engineering drawings Quality Assurance
Materials Process Selection Pilot Production
Assignment 1 Discuss various parameters to be considered in Manufacturing of a paper clip Some Basic Concepts
Stress –strain curve: • Obtained from the uniaxial tension test • Provides some information on the inherent formability of the material – Yield stress – Ductility – Strain hardening – Toughness and resilience – Strain hardening characteristics – Strain rate sensitivity – Effect of temperature on flow properties – Modulus of elasticity
n σσσF = K. ε for room temperature
Assignment 2 Obtain K and n for given data Comment on the values Cold Hot Working Warm Working working
Temperature < 0.3 Tm > 0.6 Tm 0.3 – 0.6 Tm
Advantages Higher strength Higher reductions Optimum Good surface finish Lower forming loads combination of Good tolerances Good product ductility ductility and strength Easy handling
Disadvantages Lower reductions Oxidation Industrially still not Intermediate HT Poor surface finish extensively used Higher forming load Poor tolerances Difficult handling Special tools Strain Rate sensitivity index, m discriminates the hot, cold & warm working mechanism. Machine discriminates the mechanism of deformation.
Log Plot of “m” vs “θθθ” m Cold Warm work Work
V Hot h Work
V / h = strain rate, s -1
Forming Temperature, θθθ ConventionalConventional MetalMetal FormingForming ProcessesProcesses
Forging Rolling
Wire/Tube drawing Extrusion Deep drawing Defects in Forming Process related or material related
Cracking during forming Flow localisation – inhomogeneous deformation Adiabatic shear bands – under severe conditions forms cracks Poor tolerances of the products – improper die design Centre bursts – extrusion and wire drawing Orange peel effect – sheet metal forming (large grain size) Alligatoring – rolling
Workability = f (material) . f (process) Optimisation is required with respect to material and process Objective: HolisticHolistic approachapproach Understanding Microstructural Evolution during Processing Microstructure: A function of temperature, strain strain rate etc.
Basic Properties: Processes Physical chemical and mechanical Performance Materials of Components Constant true strain rate compression tests
1. Load-Stroke data 2. Adiabatic temperature Rise (ATR) Methodology for development Evaluate Elastic slope for load deflection data of Processing maps
True Stress-Strain Curves
Correction in Flow stress for ATR SAFE PROCESSING WINDOW
Flow Stress vs. Temperature
Evaluate strain rate sensitivity (m)
Evaluate efficiency of power dissipation ( η= 2m/(m+1)
Evaluate instability parameter (ξ=log(m/(m+1))/log(strain rate))
Plot η and ξ superimposed in temperature and log(strain rate) space
Processing Maps INDUSTRIAL VALIDATION OF PROCESSING MAPS
0.5 µµµm
Map representing the domain of various processes for 304L SS 1.5 µµµm RefiningRefining ofof ProcessingProcessing WindowWindow basedbased onon ActivationActivation EnergyEnergy MapsMaps
25
20 Refined window 600 15 m µ µ µ µ 10
600 5
GrainSize Variance, 0 800 900 1000 1100 1200 Temperature,o C Grain Size Variance in stainless steel 316L
Refined window
Activation energy contours for type 316L
Minimum variance is noticed in ‘Refined Window’ UTS Variance in stainless steel 316L C Scan ultrasonic examination to characterise product microstructures Forged to 50%; 1000 0C Little skew in the deformation
Coarse grains in dead metal zone
Fine grains in deformation zone
Fine grains in This methodology can be adopted for one shear band on-line monitoring IntelligentIntelligent ProcessingProcessing ofof MaterialsMaterials
Processing Process environment sensors
Material Microstructure microstructure sensors
Goal state property Controller envelope Machine dynamics Structure/property relations Material dynamics Process Goal state Optimisation microstructure
The IPM loop for a typical materials processing step Manufacturing Technology for Fabrication of Main Vessel of PFBR OD 12900 mm Petal Requirement: OR 6450 + 7 mm The out of roundness shall be within + 12 mm on 13 m dia.
mm for resisting Seismic Loads 5 5 25 +
7 Problem: + 7
12600 + 0 5 5 Control of Spring Back in the 51 3 4 9 1 35 R O petals during forming R
O 40 30 Solution: OD 7830 mm Model Based Process Design
Crown
Final Assembling of Petals FEM Based Process Design for Plate Forming
FEM Simulation of Double CurvaturePlate Material & Frictional Forming on 300 mm X 300 mm X 15 mm Property Data : Flow curves, FEM Model for thick plates {316L(N)} E, Poisson’s ratio, Friction Petal Forming factor Validation and Tuning-up of the FEM Model Bending trials on 300 X 300 mm X 15 mm thick plates in Fomas Ltd.
FEM Simulation of Petal Forming Comparision of Results of Simulation and Experiments
Formed Petal Finalisation of FEM Solution Scheme for Profile within Desired Petal Forming Tolerance limits?
Correction No Yes of Die and Punch Profile for springback Extract Sectional Profiles of the Die and the Punch (Final Profile Designs)
The error in the model prediction is within 250 µµµm Formed Petal Tooling Petal Thickness : Cylindrical portion : 15 mm Dished end : 20 mm
Specified Form Tolerance : 12 mm Achieved Tolerance : 9.5 mm
o Distortion control by … • Suitable choice of welding heat Safety vessel input, joint type, root gap & welding sequence
– Welding Consumables • Filler wires & electrodes developed indigenously
Thickness : Cylindrical portion : 25 mm Dished end : 30 mm
Specified Form Tolerance : 12 mm Main vessel Achieved Tolerance : 8 mm UNCONVENTIONAL FORMING EXPLOSIVE FORMING
WORKING PRINCIPLE • EXPLOSIVE IS DETONATED AT A CERTAIN DISTANCE FROM THE WORKPIECE. • THE ENERGY IS TRANSMITTED THROUGH A FLUID MEDIUM TO THE WORKPIECE HELD ON THE FEMALE DIE. ADVANTAGES • NO PUNCH IS NEEDED • COMPLECATED SHAPES CAN BE PRODUCED. • BOTH LIGHT AND HEAVY GAUGE MATERIALS CAN BE FABRICATED. HYDROHYDRO FORMINGFORMING WORKING PRINCIPLE A FLUID FILLED FORMING CHAMBER SER5VES AS THE UPPER BLANK HOLDER AND FEMALE DIE. LOWER DIE IS PUNCH ATTACHED TO HYDRAULIC PISTON AND BLANK HOLDER RING. THE PUNCH MOVES UPWARD INCREASEING PRESSURE AND PUSHES THE BLANK INTO THE FLEXIBLE DIE CHAMBER THE DIPHRAGM WRAPS THE BLANK AROUND THE PUNCH. ADVANTAGES DEEP DRAWING IS POSSIBE WITHOUT ANNEALING. NO WRINKLING and LESS COST. ELECRTROELECRTRO HYDRAULICHYDRAULIC FORMINGFORMING
WORKING PRINCIPLE CAPACITOR BANK DELIVERS A PULSE OF HIGH CURRENT ACROSS TWO ELECTRODES THIS PRODUCES SHOCK WAVE IN THE SORROUNDING FLUID. THE WORKPIECE KEPT IN CONTACT WITH THE FLUID DEFORMS INTO AN EVACUATED DIE.. ADVANTAGES RAPID PRODUCTION. SAFE TO OPERATE. DIE AND EQUIPMENT COST IS LOW. SUMMARYSUMMARY
Holistic Forming Management:
Approach Features Management Issues Result
Study of individual variables Synergism of variables is Costly Poor reliability neglected Long time
Modelling Simplistic but Less expensive Poor reliability complementary to High expertise experimental approach
Integration of Machine- A combination of Less expensive Robust Process Material-Environment- experiments and High Expertise Idealised Forming widows modelling
Idealised + Intelligent Ensuring 6 σσσ quality on High Expertise Robust process Forming the basis of holistic A favoured and quality approach techno-econamic management approach ASSIGNMENTS AssignmentAssignment Manufacturing of a Paper Clip
• What is the function • How long does it last • How critical is the part • Material Metallic - what type Non metallic – plastic • Dimension Diameter of clip Shape of clip • Method of manufacturing Manual Automated • Function based design Stress, Strain Life of clip Stiffness • Style Appearance,Color,Finish Plating,painting Assignment 2 A steel plate is hot rolled from 40 mm to 10 mm in 6 passes. The reduction in each pass is 5 mm. Neglecting the spring back, calculate engineering strain and true strain Between the consecutive passes Cumulative strain just by adding the strains calculated in each pass Cumulative strain calculated based on the formula Comment on 2 and 3 with respect to engineering strain and true strain
Note: Use Excel sheet for the calculation of strains
t − t 0 f * 100 Where t is initial thickness Engineering Strain = t 0 0 and tf is final thickness t True Strain = Ln ( 0 ) * 100 t f Initial thickness: 40 mm
Engineering Strain True Strain
Final % Wrt initial % Wrt initial Rolling thickness redn. Cumulative thickness redn. Cumulative thickness
Pass1 35 12.5 12.5 12.5 13.3 13.3 13.3 Pass 2 30 14.2 26.7 25.0 15.4 28.7 28.7 Pass 3 25 16.6 43.4 37.5 18.2 47.0 47.0 Pass 4 20 20.0 63.4 50.0 22.3 69.3 69.3 Pass 5 15 25.0 88.4 62.5 28.7 98.0 98.0 Pass 6 10 33.3 121.7 75.0 40.5 138.6 138.6
Main conclusion True strains are additive with respect to each pass Engineering strains are not additive Assignment 3
• Manufacturing the steam generator dished end – Suggest suitable forming processes and their advantages and disadvantages
25000
Schematic of Cable Winch & Dished End Steam Generator Manufacturing of Dished end
Process – Hot forging and machining Starting material: Round stock of appropriate size Hot forge the lower end to create the cup portion Side upset the top half to square cross section Partition this square half with suitable dies Machine the component QUIZ
Match the following
1 Alligatoring a) Increase in strength and decrease in ductility 2. Finite element method b) Conservation of mass 3. Processing maps c) Extrusion defect 4. Spring back d) Moderate increase in strength and ductility 5. Warm working e) Strength remains same and good product ductility 6. Metal Forming f) Rolling defect 7. Hot working g) Extrusion / tube drawing 8. Centre burst h) Technique to identify “safe window” for processing 9. Seamless pipes i) Release of lockedin elastic strains 10. Cold working j) A numerical tool used for simulation of metal forming processes Welding and Fabrication Challenges in Mega Energy
• Welding ProcessesSystems – Arc welding – Beam Welding Processes – Solid state welding processes – Advanced Joining Processes • Science of Joining of Materials – Preventing cracking – Ensuring Performance – Consumable development and selection • Welding Automation – Process Automation – Welding Robotics – Intelligent welding • Cladding and Surfacing • Applications advanced welding techniques for Weldability
• Weldability defined as: – The capacity of a metal to be welded under the fabrication conditions imposed into a specific, suitably designed structure, and to perform satisfactorily in the intended service. » AWS Welding Handbook, Vol. 4, 7th Edition Welding, to begin with ………..
• Since 1930, welding has been the principle means of fabricating critical power plant components for service at elevated temperature.
• This ability to economically create World’s First All Welded sound metallurgical Boiler Drum Fabricated In 1930 bonds between large thickness pressure wall plates and pipes had permitted engineers to Welding introduces significant changes in the structure and properties of the weld metal and heat affected zone which affect the performance of the weld joints in service. This aspect has not been addressed adequately in various fabrication codes and standards Microstructure of different zones in a weld of Cr-Mo Steel
Base metal Outer edge of Weld Metal heat affected zone (HAZ)
Intercritical HAZ Coarse grained HAZ Fine grained HAZ Heat Source Characteristaion of (Eelctric Arc Weld joint Laser beam (Metallurgical Engg; Reistance etc) Physics
Weling Power & Welding Weld Joint Control A Multidisciplinary Design Electrical Engg. & A Multidisciplinary Electronics Subject Mech. Engg
Inspection & Intellegent Welding Welding Automation NDT, IT & Machine Design & Software, Electronics Welding processes
• Vary widely with • Choice of process respect to depends on – Source of heat energy – Quantum of welding employed – Quality of the weld joint – Heat input – Materials to be joined – Shielding provided for – Thickness molten weld metal – Welding speed – Welding position – Joint design – Welding speed – Welding position – Ease of automation – Inspection – Quality of the weld joint – Ease of automation – Extent of melting – Accessebility • Fusion welding • Solid state welding Fusion Welding Processes Solid State Welding Processes Arc Welding Processes Other fusion welding Friction welding process •Shielded metal Arc Friction stir welding (SMA) Gas welding Forge welding •Submerged Arc (SA) Electroslag welding Explosive welding •Flux Cored Arc (FCA) Electron beam Magentic pulse Welding welding Pressure resistance Welding •Gas Tungsten Arc (GTA) Laser beam welding Diffusion welding Ultrasonic welding •Gas Metal Arc (GMA) Capacitor discharge welding •Plasma Arc (PA)
Traditionally, arc welding processes are widely used in power plants Comparison of two arc welding processes
Gas Tungsten Arc Welding Submerged Arc Welding Low heat input and deposition rate Shielding by argon or helium gas High Heat Input & Deposition rate Difficult to automate Use of Flux for shielding Very clean welding process and Automated process excellent properties for weld metal Good Properties Positional welding is possible Only 1G position for welding Economical for thin section: welding Good for thick section without filler addition possible Fully automated GTAW process has been developed now which are used extensively for welded fabrication in power plants Heat Input and Arc efficiency • Heat input (HI) HI (J/mm) = Voltage (V) x Current (I)/ Welding Speed (mm/s) – Heat input affect the structure of the weld metal and its properties • Arc efficiency – An index of how much of the arc energy is transferred to the fused weld metal – High for Submerged arc welding and low for GTAW • Energy is lost in heating the plate, electrode, fusing flux etc. Assignment No.1
• Calculate heat input in the GTAW process with the following parameters – Voltage 12 V, Current 90A, – Length of the weld = 125 mm, duration = 25s
• Explain why arc efficiency is high for submerged arc welding and low for GTA welding? Automation of GTAW for thick section fabrication • High deposition rate • Oscillation of the torch tip to ensure side wall fusion • Pulsing of the arc • Narrow gap • Reduction in the volume of weld metal • Achieving good quality, reducing cracking and improving properties
Other variant of GTA Welding used in power plant Orbital welding machines Tube to tube sheet welding Internal bore welding machines Beam Welding processes Electron beam or laser beam can be used as heat source Very high heat density; narrow fusion zone and HAZ Melting is assisted by ‘key hole’ effect Thick sections can be welded without filler additon High quality deposit Except in the case of fiber delivered lasers, beam is stationary; welding manipulators and work tables are required Not amenable for site welding Welding procedure development for low activation ferritic-martensitic steels for fusion reactor applications
Automatic GTAW weld
Dissimilar Joining Activated TIG Welding ODS alloys: New generation alloys for mega energy systems
Applications Fast breeder and Fusion Reactors Fossil Power Plants Concern Oxide particles dissolve during melting Solution Solid state welding processes
Pressure resistance welding for tubes
Friction stir welding for plates Magnetic pulse welding for tubes