Variants of MIG/MAG Flux Cored Arc Welding (FCAW)

Transcription

1 Variants of MIG/MAG Flux Cored Arc Welding (FCAW) Professor Pedro Vilaça * * Contacts Address: P.O. Box 14200, FI Aalto, Finland Visiting address: Puumiehenkuja 3, Espoo pedro.vilaca@aalto.fi ; Skype: fsweldone * ISO 4063:2009 -Welding and allied processes - Nomenclature of processes and reference numbers. (Establishes a nomenclature for welding and allied processes, with each process identified by a reference number) January 2015 Agenda Synergic GMAW Plug GMAW Narrow Gap GMAW Multi-wire GMAW AC GMAW Cold Metal Transfer GMAW Hybrid Laser GMAW FCAW Self-Shielded FCAW with Active Shielding Gas FCAW with Active Shielding Gas of Metallic Core

2 Fundaments: Synergic GMAW Electronic control system stability of the Electric Arc based on databases that contain the synergic constants that allow to implement welding parameters previously developed in order to optimize results Use appropriate sources of power, allowing: Direct command of current (I is independent of the value of wire feeding speed ) Modulation of the current using pulsed current trapezoidal wave Sources with static characteristic, depending on the type of control of arc stability (Horizontal to control the voltage and Vertical to control the current) 3 Synergic GMAW Advantages: All the advantages mentioned above for the GMAW pulsed... + Good control of arc stability... + Databases that allow the implementation of the optimal welding parameters under either constant current or pulsed current... + "One Knob Machine" - What makes it easier to use by the operator or to be easily automated or robotic implemented 4 2

3 Synergic GMAW Control CC (Constant Current) / VC (Variable Current ): Last generation control, brings together the capabilities of synergic control (constant current good for high resistive material) and arc voltage (good for low resistive materials), which were the 1 st generation power sources Works on all types of materials Allows transfer mode in axial drop spray and controlled short-circuit (minimizing the problem of lack of fusion and spatter) Source of static variable characteristic, that is, during the peak period supply curve have type I cte (vertical), at the base period curve is type V cte Feeder with variable speed or fixed 5 Synergic GMAW Parameters selection: In practical terms the users need not carry the programming of many parameters Just enter the welding conditions (e.g., shielding gas composition, type and diameter of the wire electrode) and select the transfer mode: DIP / or Pulse Spray 6 3

4 Synergic GMAW Applies to DC constant (no pulse) for short-circuit (DIP) and Spray: WFS I I 2 where: e, are synergic parameters 7 Synergic GMAW Applies to DCEP pulse current establishing a procedure for determination of 4 variables: Ip; tp (peak period parameters); Ib; tb (base period parameters) of drop-spray transfer : I m I p t t p p I t b b t b 8 4

5 Synergic GMAW Transfer Mode desired Axial Pulverization with drops of the similar size of wire diameter A single drop deployment, for each pulse, and preferably in the last third of the pulse duration (so that the drop reaches the bath melting at a high temperature to promote good dilution) 9 Synergic GMAW 10 5

6 Ip, peak current (A) Synergic GMAW One drop per pulse transition current tp, peak period (ms) 11 Synergic GMAW Several wave shapes: 12 6

7 Working equations: Synergic GMAW Synergic equations: WFS I F t I m p I 1 t p t b t p p m I t I b b t b 2 p 4 equations ; 4 unknowns t p F R F I K I m WFS E I m 2 p t Parâmetros Sinérgicos: R ; E ; K ; ; (; I b ) p I b e t b must ensure stability of the arc and not allow the weld pool solidify or arc extinguish 13 Synergic GMAW All synergic constants depend on: wire composition; wire diameter; gas composition I p >> I transition to assure drop-spray Drop diameter Wire diameter Controlled by drop volume = (WFS/F) x A and: F/I m = R (where: A area of electrode wire transversal section) 1 drop per pulse I p2 x t p = K (K Synergic constant characteristic of material and diameters) 14 7

8 Sample of typical values: E (WFS= E x Imédio) Synergic GMAW Steel, fio Ø 1,2 3,0 m/min/100a Stainless Steel, fio Ø 1,2 3,2 m/min/100a Al, fio Ø 1,2 4,4 m/min/100a R (F/Imédio = R) Steel, fio Ø 1,2 50 Hz/100A Stainless Steel, fio Ø 1,2 70 Hz/100A Al, fio Ø 1,2 90 Hz/100A K (Ip 2 x Tp = K) Steel, fio Ø 1,2 490 A 2.s Stainless Steel, fio Ø 1,2 315 A 2.s Al, fio Ø 1,2 130 A 2.s 15 Application: Plug GMAW Overlap joints thin plates (thickness 5 mm) Overlap joints mean thicknesses ( 5mm < thickness 12 mm) Resistance spot welding GMAW 16 8

9 Plug GMAW Application: Overlap joints thin plates (thickness 5 mm) Overlap joints mean thicknesses ( 5mm < thickness 12 mm) Resistance spot welding GMAW 17 Plug GMAW Special features: Special nozzles Weld cycle timers Superficial cleaning Open hole in top plate, for higher thickness Typical imperfections: Pores Lack of fusion between both plates 18 9

10 Plug GMAW Accessories: 19 Narrow Gap GMAW Applications: Multi filling runs Grove: < 18º Automatic or mechanized 20 10

11 Narrow Gap GMAW Fundaments: Positioning the tip of the electrode high power with 100% duty-cycles Ensure the lateral fusion of groves Special techniques for the rotation of the tip of the electrode (two wire coils or tubes of contact with the hole in spiral) Special shielding protection Special nozzles and electrical insulation Backings 21 Narrow Gap GMAW 22 11

12 Multi-Wire GMAW Mode Pulse / Pulse Mode Pulse / Conventional Mode Conventional/ Conventional 23 Multi-Wire GMAW Factor Traditional MAG technique TANDEM welding (robotic) (mechanized) L&O rate [ /min] 0,093 0,080 V S [m/min] 0,35 0,70 OF 0,7 0,8 V d [m/min] 4,1 wire no.1: 6,2 wire no.2: 6,0 M d [kg/m] 0, C d [ /kg] 1,43 1,43 N g [l/min] C g [ /l] 0, Costs of welding [ /m]: 0,64 0,43 Factor Traditional MAG technique TANDEM welding (robotic) (mechanized) L&O rate [ /min] 0,093 0,080 V S [m/min] 0,25 0,50 OF 0,7 0,8 V d [m/min] 6,5 wire no.1: 7,6 wire no.2: 6,8 M d [kg/m] 0, C d [ /kg] 1,43 1,43 N g [l/min] C g [ /l] 0,0026 0,0026 Costs of welding [ /m]: 1,02 0,66 Data for costs calculation and costs of welding of 1 m long fillet weld (3 mm throat thickness, 165 A average current intensity, Ar+18%CO2) Data for costs calculation and costs of welding of 1 m long fillet weld (5 mm throat thickness, 230 A average current intensity, Ar+18%CO2) 24 12

13 AC GMAW 25 AC GMAW 26 13

14 AC GMAW 27 AC GMAW Fundaments: Synergic Pulse power sources with control of current AC Period DC EN : heating Period DC EP : drop detachment Applications: Mainly aluminiums alloys Low thicknesses ( 5mm) Automatization and Robotization 28 14

15 CMT (Cold Metal Transfer) GMAW Oscillating wire process wire advances and retracts at 66 Hz 29 CMT (Cold Metal Transfer) GMAW 30 15

16 CMT (Cold Metal Transfer) GMAW Penetration level for bead on plate Note: STT (Surface Tension Transfer ) and FastRoot, are others variants of GMAW of low Heat Input 31 (Fumes Formation Rate FFR) CMT (Cold Metal Transfer) GMAW Fume box (mm): 1. Air flow probe 2. Filters 3. Welding gun Wire Diameter mm] 1.2 mm Current [A]

17 Hybrid Laser GMAW Combination of laser light and an electrical arc into an amalgamated welding process has been known since the 1970s, but has only recently been used in industrial applications. There are three main types of hybrid welding process, depending on the arc used; GTAW, PAW arc or GMAW augmented laser welding. While GTAW augmented laser welding was the first to be researched, GMAW is the first to go into industry and is commonly known as hybrid laser welding 33 FCAW Fundaments 34 17

18 FCAW Fundaments Fusion welding process using the same basic fundaments and equipment of conventional or synergic GMAW Depending on the type of consumable there are 3 main groups of solutions: FCAW Self-Shielded FCAW with Active Shielding Gas FCAW with Active Shielding Gas of Metallic Core FCAW Fundaments Weld pool protection, and filler metal drops are shielded from: Decomposition of the flux (as shielding gas) Support of the Active Shielding Gas (CO 2 e mixtures Ar + CO 2 ) Shielding of the weld during cooling is achieved through the slag created due to the decomposition of the flux 36 18

19 FCAW FCAW Self-Shielded FCAW FCAW Self-Shielded: Applications Mainly outdoor applications Better for plain steels (no alloy) Structures, Tubes e Panels 38 19

20 FCAW FCAW with Active Shielding Gas 136/ FCAW FCAW with Active Shielding Gas: Applications Weld indoor environment Weld all type of materials including stainless steels Applies in all typical GMAW construction Metallic core enables greater profitability, robotic applications (slag almost non-existent), should only be used in the Low position Basic and Rutile for high structural demand applications Weld in all positions 40 20

21 FCAW Fundaments Stick-out: 41 FCAW Welding Guns 42 21

22 FCAW Consumables: Electrode Wire 43 FCAW Consumables: Electrode Wire 44 22

23 FCAW Consumables: Electrode Wire 45 Symbol Characteristics Welding type Shielding gas R P B M Rutile, with slow cooling slag Rutile, with fast cooling slag Basic Metallic powder 1 pass and multipass 1 pass and multipass 1 pass and multipass 1 pass and multipass V Rutile or basic/fluorite 1 pass No W Y z FCAW Consumables: Classification Electrodes Basic/fluorite with slow cooling slag Basic/fluorite with fast cooling slag Other types 1 pass and multipass 1 pass and multipass Yes Yes Yes Yes No No 46 23

24 FCAW Consumables: Classification Electrodes (NP EN 758) Type R They are characterized by a transfer of metal in spray, reduced losses by splashing and a Rutile based slag completely covering the weld Designed for single pass and multi-pass welds in the positions flat butt, flat fillet and horizontal They are designed for use with CO2, but can also be used with mixtures of Ar+CO2, improving the transfer in the arc and to reduce spatter 47 FCAW Consumables: Classification Electrodes (NP EN 758) Type P Type P are similar to the Type R but Rutile slag is designed to rapid cooling, allowing welding in all positions In general, these wire electrodes are produced in lower diameters and, when used with CO2, have a transfer in spray When recommended by the manufacturer, the use of mixtures of Ar + CO2 can improve the operational characteristics of the electrode wire, reducing spatter 48 24

25 FCAW Consumables: Classification Electrodes (NP EN 758) Type B They are characterized by a metal transfer drop-spray, with weld beam top surface a slightly convex and a slag that may not cover completely the surface of the weld These wire electrodes can be used in all positions and in multi-pass welding With protection CO2 gas, or mixtures Ar + CO2 The composition of the slag consists of fluorides and alkali metal oxides. The deposits of these cored wire electrodes show excellent resistance to impact (toughness / resilience) and good resistance to cracking in general 49 FCAW Consumables: Classification Electrodes (NP EN 758) Type M They are characterized by a spray transfer of very fine drops and a minimum thickness of slag The composition of the flux inside these wires consists of alloys and iron powder, allow high speeds fusion without the danger of the appearance of lack of fusion These wires are used, with shielding protection of gaseous CO2 or Ar + CO2 Used primarily in positions flat butt, flat fillet and horizontally, in terms of single pass Are the wires with the worst penetration level 50 25

26 FCAW Consumables: Classification Electrodes (NP EN 758) Type V They are used without protective gas and allow a transfer of metal that goes from the globular to slightly spraying The slag produced by these wires electrodes characterized by a range of solidification rate from slow to fast The wires with a slag to cool slowly, are used in all positions in the single pass welding of galvanized steel and steel with aluminum or other coatings 51 FCAW Consumables: Classification Electrodes (NP EN 758) Type W They are used without shielding gas and allow a transfer of metal between the globular and close to spraying Its basic slag fluoride was designed to allow high deposition rates Some wires have added iron powder to inner fluxes providing good operational characteristics The wires of this type are used in welding of single pass and multi pass positions flat butt, flat fillet and horizontally, with some of these wires is possible to weld vertically downward 52 26

27 FCAW Consumables: Classification Electrodes (NP EN 758) Type Y They are used without shielding gas and allow a transfer of metal almost spray Its basic slag fluoride were designed to allow single pass welding, multi pass, in all positions They provide good resistance to cracking and good impact strength at low temperatures 53 FCAW Consumables: Classification (Standard AWS A5.20) Standard AWS A5.20 Plain steel and low alloy Wire Electrode Tensile in Kpsi Chemical Composition of Gas Welding position Cored Wire 54 27

28 FCAW Electrode Wire: Rules to Select Electrode should be metallurgically, physically and chemically compatible with base materials Comply with the dilution of the weld bead Comply with the mechanical properties prescribed for the weld joint Comply with weld current/thickness of base material and weld position 55 FCAW Consumables: Electrode Wire After selecting the electrode wire: Use the shielding gas established by the manufacture FCAW differently from GMAW enables DCEP and DCEN Use the polarity established by the manufacture 56 28

29 FCAW Weld Operation Procedure 57 FCAW Advantages Good penetration control Weld in all positions High productivity Enables easy automatization Enables outdoor application of GMAW benefits High deposition rates of 1,5 a 2,5kg/h (versus SMAW) 58 29

30 FCAW Disadvantages Accessibility and mobility Slag Hydrogen levels Susceptibility to inclusions Demands good skills for the welder Cost of Shielding Gases Cost of Consumables 59 30