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History
Introduction
Forces that affect the metal transfer
Classification of mode of metal transfer
Parameter that affect the metal transfer
Defects
General points
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.
The transfer of molten metal from the tip of electrode to base metal.
Arc welding and Consumable electrode
F(g) = mg
= б V g
where,
б= density of electron
material
V= volume of molten droplet
g=acc. Due to gravity (~9.81)
F(s) = 2 γ 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
F(p)= 100 (I2) × µ × (2R2 –r2) ÷ (8 2R4)
where,
I=current in conductor
µ=magnetic permeability
R=conductor radius
r=small diameter where pinching
happens
A) With Electrode
1. Short Circuit
1.1 Dip Transfer
2. Globular
2.1 Repelled Transfer
3. Spray
3.1 Explosive Transfer
4. Slag Enveloped
B) With Rod1. Short Circuit1.1 Dip Transfer
2. Globular2.1 Repelled Transfer
Periodic bridging of gap between the electrode and work piece.
Heavy current flow occurs
Decrease - surface tension, viscosity.
Increase - electro motive, hydro dynamic force.
Mode of globular transfer
After detachment droplet not travelled into weld pool
Force -reverse plasma jet,
Cause poor weld transfer and Excessive spatters.
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)
It is used in some application or according to job.
wet welding, under water welding etc
Not used generally.
In short circuit metal transfer mode
1. More spatters.
2. Low speed.
3. Solid particle inclusion.
4. Sometime porosity.
In slag enveloped mode of metal transfer
1. Slag inclusion causes creaks
2. Porosity
3. Under cuts photomicrograph
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