Arc welding GMAW. CTU in Prague Faculty of Mechanical Engineering

Transcription

1 1st semester 2015/2016 Arc welding GMAW CTU in Prague Faculty of Mechanical Engineering Ing. Petr Vondrouš, PhD., IWE

2 GMAW Gas Metal Arc Welding

3 GMAW Definition GMAW stands for Gas Metal Arc Welding GMAW is commonly referred to as MIG or Metal Inert Gas welding During the GMAW process, a solid metal wire is fed through a welding gun and becomes the filler material Instead of a flux, a shielding gas is used to protect the molten puddle from the atmosphere which results in a weld without slag GMAW is the most widely used arc welding process in the United States 3

4 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding GMAW welding GMAW is defined as arc welding using a continuously fed consumable electrode and a shielding gas. Method no. acc. ČSN EN ISO Gas shielded metal arc welding used names GMAW Gas Shielded Metal Arc Welding USA MIG Metal inert gas MAG - Metal active gas

5 1 - Electrode A GMAW electrode is: A metal wire Fed through the gun by the wire feeder Measured by its diameter GMAW electrodes are commonly packaged on spools, reels and coils ranging from 1lb to 1000lbs 5

6 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Filler materials solid and cored wires

7 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Basic parameters Positions Base material Welded thickness Current, voltage Diameter Welding source : all : MAG structural steels MIG- alloyed steels, Al, Cu, Ni alloys : mm short circuit : I = A U = V Spray : I = A U = V : 0,8 1,6 mm : flat, solid wire mostly DCEP, DC+

8 POWER SOURCE WIRE CONTROL & WIRE FEED MOTOR

9 GAS DIFFUSER NOZZLE TRIGGER CONTACT TIP INSTALLED COMPONENTS

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11 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Types of wire feed rolls Steel Solid wire Non ferrous alloys Cored wire

12 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Wire feeders Feeding far away Removable wire feeder PUSH-PULL gun SPOOL-GUN

13 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Welding technigue Left, forward Right, backward welding

14 GMAW Components Let s look a little closer at the GMAW process Travel direction Generally, drag on thin sheet metal and push on thicker materials 4 Shielding Gas Solidified Weld Metal 5 2 Arc Electrode 1 3 Weld Puddle 14

15 2 - Arc An electric arc occurs in the gas filled space between the electrode wire and the work piece Electric arcs can generate temperatures up to 6,000 C 15

16 4 - Shielding Gas GMAW welding requires a shielding gas to protect the weld puddle Shielding gas is usually CO 2, argon Ar, helium He or a mixture The gauges on the regulator show gas flow rate and bottle pressure 16

17 Shielding in GMAW Shielding gas can affect WM mechanical properties Chemical reactions Weld bead shape Arc heat, stability, and starting Surface tension Drop size Puddle flow Spatter Ar Ar-He He CO 2 Important gas characteristics: ionization potential arc start, stability, arc heat heat input heat transfer ratio heat trasfered to WM, heat input influence on surface tenstion drop size, puddle flow, spatter

18 FSW Friction stir welding Metallurgy reactions Inert gas Ar, He no reaction at all Active gas active = reactive Gas dissociation in arc: CO 2 CO + O Melt puddle reaction Fe+O FeO + Q (heat) C+FeO Fe+CO (porositzy) Desoxidation elements - Mn, Si FeO + Mn = MnO + Fe 2FeO + Si = SiO 2 + 2Fe ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování

19 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Desoxidation by filler alloying Structural steel 100%CO 2 wire G3Si1 82% Ar+18% CO 2 wire G3Si1

20 GMAW Process Variables Welding variables Wire Feed Speed (WFS) Voltage Operator controlled variables Travel speed Gun angles Contact tip to work distance (CTWD) Gas flow rate What is the relationship between WFS and amperage? 20

21 Modes of Metal Transfer GMAW is a process that features several distinctive, individual methods and types of metal transfer The mode of metal transfer is determined by a number of welding variables Voltage Amperage Shielding Gas By changing one or more variables, you can go from one metal transfer mode to another 21

22 Modes of Metal Transfer Two common conventional modes of metal transfer are: Short arc Axial spray arc The application, joint design, base material thickness, and properties determine the appropriate mode to use Typical short arc application Typical axial spray arc application 22

23 GMAW MIG/MAG Metal transfer modes According to setting of the welding parameters, there are SEVERAL modes of molten wire transfer to the molten pool: 1. short circuiting small welding parameters, till 150 A, Hz, typical for MMA 2 globular 180 A, Ar 2% O 2 shielding Typical for CO 2 Large spatter not very suitable 3 spray transfer - Above a critical current- high el.-mag. force (Lawrence force), small discrete metal drops, e.g. 320A 4 Rotationg arc at highest current levels Special Pulsed spray transfer - for special invertor sources Pulsing of current can be done

24 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Short circuit dip transfer

25 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Used gas mixtures - Ar + CO2 ( up to 25% ) - Ar + O2 (up to 12% ) IS = A UEO = V

26 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Spray transfer

27 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding No short circuits, used gasses - Ar + CO2 ( do 20% ), - long arc - Ar + O2 ( do 10% ) IS = 500 A UEO = V - can not be done in pure CO2

28 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding Pulse transfer Impuls transfer

29 ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování FSW Friction stir welding change between short and spray tranfer - Ar + CO2 ( do 15% ) - Ar + O2 ( do 8% ) U = V I = A