metal transfer during welding

1. MODE OF METAL TRANSFER
IN WELDING

2.  History
 Introduction
 Forces that affect the metal transfer
 Classification of mode of metal transfer
 Parameter that affect the metal transfer
 Defects
 General points

3.  After Bronze Age and the Iron Age Sir
Humphry Davy in 1800 discovered Short
pulsed electric arc welding.
 Around 1900, all automatic arc welding
worked on alternating current (A.C)
discovered.

4.  The transfer of molten metal from the tip of
electrode to base metal.
 Arc welding and Consumable electrode

5.  Gravity Force
 Surface Tension force
 Electromagnetic Pinch Effect
 Drag Force

6.  Detaching Force - electrode pointed
downward
 Retaining Force – electrode pointed upward

7. Fg = mg
= ρV g
where,
ρ = density of
electron material
V= volume of molten droplet
g=acc. Due to gravity (~9.81)

8.  Retain droplet on the tip of electrode.

9. Fs = 2πγ r f(r/c)
γ = surface tension
r = radius of electrode
C =(2γ)/ (mgб)
f(r/c)=complex function varies
from 0.6-1.0
c =constant of capillarity of
electrode material

10.  Only detachment of the molten droplet
 Repelling force

12. 2R4)Fp= 100 I2 × µ × (2R2 –r2) ÷ (8ᴨ
where,
I=current in conductor
µ=magnetic permeability
R=conductor radius
r=small diameter where pinching
happens

13.  Due to the flow of gas around the drop
 Detaching the droplet from tip of electrode

14. All forces acting in metal transfer process

16. A) With Electrode
1. Short Circuit
a. Dip Transfer
2. Globular
a. Repelled Transfer
3. Spray
a. Explosive Transfer
4. Slag Enveloped
B) With Rod
1. Short Circuit
a. Dip Transfer
2. Globular
a. Repelled Transfer

17.  Periodic bridging of gap between the
electrode and work piece.
 Heavy current flow occurs
 Decrease - surface tension, viscosity.
 Increase - electro motive, hydro dynamic
force.

19.  Short circuit mode of metal transfer.
 Electrode is fed into weld pool
 Fast pace

21.  Molten metal droplets is detached in globular
form.
 Action of gravity
 Arc length is medium to long

22.  Mode of globular transfer
 After detachment droplet not travelled into
weld pool
 Force -reverse plasma jet,
 Cause poor weld transfer and Excessive
spatters.

24.  High current density that tends to high temp.
 Increase pinch effect
 Depending upon the current density spray
mode have three stages:-
1. Projected transfer (high)
2. Streaming transfer (medium)
3. Rotary transfer (low)

25.  Droplet spattered (on the tip after
detachment)
 Formation of gas bubbles

27.  It is used in some application or according to
job.
 wet welding, under water welding etc
 Not used generally.

28. PULSED METAL ARC TRANSFER

32.  Weld power source
 Electrode polarity
 Shielding gas
 Emissive flow rate
 Welding Position

33.  In spray metal transfer mode
1. Large Heat Affected Zone(HAZ).
2. Creaks appearance.

34.  In short circuit metal transfer mode
1. More spatters.
2. Low speed.
3. Solid particle inclusion.
4. Sometime porosity.

35.  In globular metal transfer mode
1. Rough weld bead.
2. Blow holes
3. Pin holes.

36.  In slag enveloped mode of metal
transfer
1. Slag inclusion causes creaks
2. Porosity
3. Under cuts photomicrograph

38.  Spray metal transfer – costly , high current
and voltage, skill required.
 Generally used globular and pulsed short
circuit metal transfer in industry.
 According to efficiency:-
Spray
transfer
Short
circuit
Globular
slag
enveloped