Introduction. Online course on Analysis and Modelling of Welding. G. Phanikumar Dept. of MME, IIT Madras

Transcription

1 Introduction Online course on Analysis and Modelling of Welding G. Phanikumar Dept. of MME, IIT Madras

2 Classification of Manufacturing Processes Manufacturing Processes Ingot Casting Shape Casting Power Metallurgy Casting Processes Machining Processes Turning, Boring Drilling, Milling Grinding Forging Extrusion Sheet Metal Forming Forming Processes Joining Processes

3 Classification of Joining Processes Joining Processes Mechanical Fastening Soldering Adhesive Joining Brazing Welding

4 Different Welding Processes Arc Welding: SMAW, GMAW, GTAW, SAW, FCAW, PAW Welding Processes Solid state Welding: USW, FRW, EXW Resistance Welding: Spot, Seam, Projection Beam Processes: LBW, EBW

5 Five basic joint designs BUTT LAP TEE CORNER EDGE

6 Four basic types of fusion welds Bead / Surface Weld Groove Weld Fillet Weld Plug Weld

7 Bead / Surface Welds Bead / Surface Weld For butt welds No edge preparation Thin sheets of metal Building up surfaces Weld overlay

8 Groove Welds For butt welds Thicker materials Full thickness welding Detailed edge preparation Multi-pass welding Groove Weld

9 Groove preparations Ref: Wikipedia, public domain. Contributed by Benrunge

10 Fillet Welds Fillet Weld For Tee, Lap and Corner joints No edge preparation

11 Plug Welds Hole drilled on the top sheet To replace bolts and rivets When excess deposit is not desirable by design Plug Weld

12 Five Welding Positions Flat g Vertical Up Vertical Down Overhead Arrow shows the direction of motion of the electrode / torch. The torch is held approximately normal to this direction.

13 Classification of Welding Consumable Electrode Non-consumable Electrode Fusion Welding Autogenous Filler Homogeneous Heterogeneous Flux protected Single Pass Inert gas protected Multi Pass

14 Some terminology Traverse rate : velocity of the welding source : m/s Heat Input : ratio of power to velocity : J/m Rate of heat input or heat intensity : W/m 2 Heat intensity distribution : Q(x,y)

15 Overview of few welding processes SMAW : Shielded (Manual) Metal Arc Welding GMAW: Gas Metal Arc (MIG) Welding GTAW: Gas Tungsten Arc (TIG) Welding PAW: Plasma Arc Welding SAW: Submerged Arc Welding EBW: Electron Beam Welding LBW: Laser Beam Welding

16 Electric Arc Generated between two conductors of electricity, upon application of voltage and separated by a small distance Presence of ionisable gas Sustained electric discharge through ionized gas column between the two electrodes Electrode Workpiece

17 Role of gases in arc welding Inert / active Shielding effect Stability of arc Gas CO 2 O 2 N 2 H 2 Ar He Ionization Potential 14.4 ev 13.2 ev 14.5 ev 13.5 ev 15.7 ev 24.5 ev Ref: Welding Metallurgy, 2 nd Edition by Sindo Kou, Wiley-Interscience ISBN:

18 Voltage Arc characteristics OCV Longer Arc Shorter Arc Normal operating range Current Ref: Principles of Welding Technology, 3 rd Edition by L. M. Gourd, ISBN:

19 Electrode Polarities Direct Current Straight Polarity (DCSP) : Electrode is negative. Deeper penetration. Direct Current Reverse Polarity (DCEP) : Electrode is positive. Enhanced deposition rate for consumable electrode. Alternating Current (AC) : Polarity is switched at a frequency.

20 DCEN DCEP AC Workpiece Workpiece Workpiece 70% Heat to workpiece 30% Heat to Electrode 30% Heat to workpiece 70% Heat to Electrode Surface Cleaning 50% Heat to workpiece 50% Heat to Electrode Surface cleaning half-the-time

21 Temporal profiles SP RP Balanced Sine Wave Unbalanced Sine Wave Square Wave

22 Spatial-temporal characteristics of arc Voltage, Current, Efficiency Wave form : flat, square, sine, unbalanced sine etc. Pulsing effects (Peak value, base value) Frequency (Hz) Traverse rate (m/s) Electrode path : arc oscillation, frequency and amplitude etc.

23 Shielded metal arc welding Power source and controls Arc Electrode holder Shielding gas Work cable Electrode Coating Arc Electrode Work Electrode cable Solidified slag Weld metal Base metal

24 What is in the Flux? Role of a Flux : Protection, Deoxidation, Stabilization and Metal Addition Constituent Iron oxide Titanium oxide Calcium fluoride Potassium silicate Magnesium oxide Cellulose Calcium carbonate Ferro-manganese, Ferro-chrome Ferro-silicon Role Slag former, arc stabilizer Slag former, arc stabilizer Slag former, fluxing agent Arc stabilizer, Binder Fluxing agent Gas former Gas former, Arc stabilizer Alloying changes Deoxidizer

25 Feed control Gas metal arc welding Control system Gas out Gun control Wire Gas in Shielding gas source Shielding gas Solid wire electrode Current conductor Travel Shielding gas Nozzle Gun Work piece Wire feed drive motor Welding machine Voltage control Solidified weld metal Base metal Molten weld metal Arc

26 GMAW Photographs from the facilities in Materials Joining Laboratory, Department of MME, IIT Madras

27 Metal transfer modes Globule transfer Droplets close to or larger than diameter of the electrode Reach base material by gravity Leads to spatter Spray transfer Fine droplets Reach base material by EM force Short-circuit transfer Small and fast solidifying weld pools

28 Gas tungsten arc welding Inert gas supply Cooling water supply AC or DC Welder Travel Torch Drain Filler wire Tungsten electrode Work piece Foot pedal (optional Solidified weld Arc Molten weld metal

29 TIG Photographs from the facilities in Materials Joining Laboratory, Department of MME, IIT Madras

30 Plasma arc welding Tungsten electrode Plasma gas Shielding gas Power supply Power supply Transferred arc Work piece Non transferred arc

31 PAW Photographs from the facilities in Materials Joining Laboratory, Department of MME, IIT Madras

32 Submerged Arc welding Wire reel Flux hopper Wire feed motor Unused flux recovery tube Contact tube Voltage and current control Work piece Ground Granular flux covers the weld and the arc

33 Photographs from the facilities in Materials Joining Laboratory, Department of MME, IIT Madras SMAW

34 Electron beam welding High voltage insulator Upper column Electron gun Electromagnetic lens Vacuum chamber Column valve To high vacuum Deflection coil to vacuum Workpiece Schematic of a typical EBW gun

35 Laser beam welding Cavity tube Half mirror Focusing lens Workpiece Reflection mirror Laser beam Laser element Xe lamp Basic features of an Nd : YAG laser

36 Intensity of heat sources Process Heat source intensity (W/m 2 ) SMAW, FCAW 5x10 6 5x10 8 GTAW, GMAW 5x10 6 5x10 8 PAW 5x LBW, EBW Ref: Principles of Welding by Robert W. Messler, Wiley-VCH (2004) ISBN:

37 Heat input to work piece Heat input vs power density More damage to work piece Gas Welding processes Arc welding processes (GMAW, GTAW, etc.) Less damage to work piece Higher penetration, Welding speed, Weld quality Capital cost High energy beam welding processes (EBW, LBW) Power density of heat source Ref: Welding Metallurgy, 2 nd Edition by Sindo Kou, Wiley-Interscience ISBN:

38 Summary of features Feature/Process GTAW GMAW PAW LBW EBW Heat Source Arc Arc Plasma Arc Laser beam Electron beam Protection Shielding gas Shielding gas Shielding gas None / Shielding gas Rate of Heat Input Aspect Ratio of Weld Vacuum Medium Medium High High Very High Max Penetration 3 mm 5 10 mm Up to 20 mm 25 mm 150 mm Advantages High quality weld Continuous and Automated Materials Joined Most common metals Most common metals Longer arc length Most common metals Any location where light can reach, high speed, accuracy Reflectivity Issues Precision, accuracy, deep and narrow welds Vacuum Issues Ref: Materials and Processes in Manufacturing, 9 th Edition by E. Paul DeGarmo et al., Wiley. ISBN:

39 End of Introduction