Download Fundamentals of Metallurgy

WELDING
Welding is a process of permanent joint production by formation of
interatomic bonds origination between the parts being joined.
Welding methods
Welding by fusion
Welding by pressure
– Electric arc welding
– Cold welding
– Gas welding
– Friction welding
– Plasma welding
– Ultrasonic welding
Plasma welding
Friction welding
WELDING
Electric arc welding
U, V
а
Scheme of direct current
welding arc: 1 – electrode; 2 – base metal;
b
Static volt-ampere arc characteristic (а);
external characteristics of current sources for welding (b)
3 – bath of liquid metal; 4 – arc column
The welding arc is a powerful stable electric discharge burning between
electrodes in the atmosphere of ionised gases and vaporised metals.
WELDING:
Electric arc welding
Manual metal-arc welding
circuit diagram:
1 – A.C. mains supply;
2 – neutral;
3 – live;
4 – fused switch;
5 – primary cables;
6 – current control;
7 – welding set;
8 – welding cable;
9 – electrode holder;
10 – electrode;
11 – work-piece;
12 – work support;
13 – return current cable;
14 and 15 – earth
Diameter of electrode d is chosen depending
on welded metal thickness:
where s is the thickness of welded metal, mm.
WELDING
Electric arc welding
2–
Automatic submerged arc welding (SAW):
1 – sliding conductor ; 2 – feeder; 3 – welding wire; 4 – liquid slag; 5 –layer of flux; 6 – slag crust;
7 – welded seam; 8 – basic metal; 9 – pool of liquid metal; 10 – arc zone
Advantages of the process:
– the most productive way of welding;
– high quality of a seam;
– low production cost of 1 m of seam;
– welding metal up to 20 mm thickness for one pass without cutting of edges.
Application: in serial and mass production, such as manufacturing of boilers, tanks, ship hulls, bridge beams,
welded pipes with a direct and a spiral seam, wheels.
WELDING
Resistance welding
Resistance butt welding (RW):
1 – current supply clips; 2 – billets; 3 –
motionless plate; 4 – mobile plate; 5 –guide; 6 –
welding transformer; 7 – flexible buses
Flash welding (FW)
Advantages of the process:
– cleaning of surfaces is not necessary;
– welding parts of a complex section and with the different shape of the section;
– dissimilar metals can be welded.
Application: welding of rings, wheels, the end tool (drills, mills, taps), rods, rails, reinforcement, pipes.