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1
Welding 1
Materials Engineering
INTRODUCTION
Classifying joining processes
JOINTS
ALAKKAL ZÁRÓ SÚRLÓDÁSSAL ZÁRÓ JOIN BY MATERIAL
Ék-, csap-, szegecskötés
Tengelyagy-kötések
Elemek a helyzetbiztosításhoz
Pattintó-, feszítő- és
szorítókötések
Karimás- és
csavaros kötések
Sajtolt tengelyagy-kötések
Rugalmas közbenső
elemekkel
Rugalmas közbenső elemek
nélkül
WELDED
JOINTS
SOLDERED
JOINT
GLUED JOINTS
CLOSE WITH FORM CLOSE BY FRICTION
Positioning parts
Axis connections
Tensioning and
pressing parts
Key, pin and bolt
Shaft coupling,
clutches, screw
connections
Stamped axis-hub connections
with or without
flexible parts
Historical overview 1
1724: Desaguliers joins lead rods by compression and torsion.
1849: Staite patents joining metals by electric arc.
1866: Thomson patents resistance butt welding.
1887: Benardosz makes spot welding by graphite electrodes.
1895: Goldschmidt designs thermite welding.
1906: Gas welding spreads around the industry.
1908: Kjellberg patents coated electrodes.
1915: Resistance spot welding is used to produce car bodies.
1919: Roberts and von Nuys performs shielding gas tests.
1929: Dultshevskiy patents the submerged arc welding.
1935: Shielded arc welding experiments at Union Carbide.
1946: Cold pressure welding process has been validated.
1949: Electroslag welding was validated in Paton Institution.
1957: Electron-beam welding has been developed.
1963: Fisrt indutrial robots are put in operation.
1969: Experimental welding operations made in the space.
1995: Friction Stir welding process was developed.
Historical overview 2
• Based on the source of energy used to create joint
• Based on the filler material type
• Based on the protection of the weld
• Based on the level of mechanizing or automation
• Based on the technological parameters.
Most frequently the source of energy is the classifying criterion.
Classifying the welding processes
Another possible arrangement
HŐMÉRSÉKLET
ERŐ
SAJTOLÓ HEGESZTÉSEK
ÖMLESZTŐ HEGESZTÉSEK
Meleg-sajtoló hegesztések Hideg-sajtoló hegesztések
Olvadási hőmérséklet
TEMPERATURE
PRESSURE
Melting temperature
Hot pressure welding pr. Cold pressure welding pr.
PRESSURE WELDING PROCESSES
FUSION WELDING
PROCESSES
8
Creating a weld bead
ENERGY MATERIAL
BY PHASE
LIQUID SOLID
BY PRESSURE
WITHOUT
PRESSURE
W. PRESSURE
BY ENERGY
THERMIC
MECHANIC
OTHER
THERMOMECHANIC
CLASSIFICATION CLASSIFICATION
Y
The role of heating at pressure welding
2
31
2
32
2
212
1 egy
T
dt
dk f ,,
Rp0,2
(d/dt)1
Y
T
(d/dt)2
Heating:
Y decreases welding time shortens
FF
Y
eqv
Yeqv
10
Resistance spot welding
Crystallization under
force creates the weld.
Higher joint strength
Creating the weld bead – melting processes
12
Creating the weld bead – melting processes
Dendritic
crystallization
Fusion zone
solidifiedBase metal
1.
grain
grain
liquid
Tipical cross
section
Fusion zone
solidifiedBase metal
liquid1.
grain
grain
1.
grain
grain
1.
grain
grain
Prefered
growing
direction
Prefered
growing
direction
Fusion zone
Base metal solid liquid
Solid-liquid
boundary
Fusion zone
Base metal liquid
solid
Solid-liquid
boundary
Sub-
grains
Hexagonal subgrain cross section
Creating the weld bead – pressure processes
Orientáció különbség
a
l
a
A sajtoló hegesztés feltétele:
l a Orientáció különbség 0°
orientation difference
Condition of the pressure welding processes:
orientation difference
att
ract
ive forc
ere
puls
ive forc
e
orientation difference
Condition of pressure welding:
l a ...... orientation difference 0°
14
BASIC MANUAL PROCESSES
15
Manual metal arc welding
Roles of the flux covering
• Stabilizing the arc (K, Na, Ca decreases theemission energy and the ionization potential).
• Evolving gas (organic matters, for example cellulose (C6H10O5)n and from CaCO3)
• Deoxidizing, denitridizing (Mn, Si, Al, V, Ti, etc.)
• Alloying (alloys depending on base material, in the form of ferro-alloys as Fe-Si, Fe-Ti, Fe-Cr etc.)
• Making up the slag (from rutile, from organic materials, from SiO2 and MnO etc.)
• Decrease the cooling speed, metallurgic processes
• Increase the melting rate (melting efficiency can reach 220 %).
Applications based on the type of flux covering
• Acid flux electrode should be applied when the welding position is simple but the penetration to be reached is high.
• Cellulose flux electrode is used for tubes root pass welding (transmission line tubes).
• Rutile flux electrode is used for „around the house” type of works and when the expected mechanical properties are at medium level.
• Basical electrodes are used for constructions where mechanical properties are important and high.
18
Welding parameters
• Wire diameter: de=1,5 ÷ 6 mm
• Current: I = 30 ÷ 500 A (I = (30÷60) x de, A)
• Arc voltage: U = 20 ÷ 50 V (U = 0,04 I + 20, V)
• Welding speed: vweld= 80 ÷ 200 mm/min
• Pull out length: Lpull= 100 ÷ 400 mm.
Pull out length means the length of the weld seam
that can be made with the efficient length of the
electrode.
By the pull out length, the cross section of the weld
and the heat input (welding speed) can be well
controlled.
19
DC and AC current can be applied produced by:
• Welding transformers
• Welding rectifiers
• Welding generators
Characteristics:
(internal regulation)
Welding power sources
U
I
L1 L
L
Δ I
power sourceelectric arc
working point
20
Application of manual arc welding
• Widely used in every segment of the industry, because of its simplicity, and low price. Practically there is suitable electrode for every type of material, easy to learn the procedure and does not require high capital investment.
• Strongly alloyed steels are welded with flux covered electrodes in 75 % of the cases.
• For surface welding most welding materials are available in the form of flux covered electrodes.
• Disadvantage is the low melt-off efficiency, the ratherstrong contribution of the human factor, and it is hard to apply for non-ferrite based metals.
21
Oxyfuel-gas welding
Disso gas: Acetylene is dissolved in acetone to enable
acetylene pressure up to 30 bar. The pressure bottle is filled
with porous material (cement, asbestos, carbon), so the
gas can not get concentrated in a small volume. The
porous material soaks up the gas-fluid mixture.
(In a few cm3 volume – approx. a walnut 16x15x24mm –
acetylene is explosively dissociating.)
Disso gas pressure bottle Oxygen pressure bottle
22
• Primary reaction:
• Secondary reaction (now
oxygen is coming from
the air):
QHCOOHC 2222 2
QOHCOOHCO 2222 22
32
Burning of acetylene
23
Burning gas and oxygen
mixed based on the theory
of injector-effect.
Gas blowing through
the little diameter
hole arrives into a
bigger volume, this
way its pressure
decreases.
Welding torch and reductor
Backward welding is applied for thin metal sheets
(s ≤ 3 mm), forward welding is used for thicker metal sheets
and tubes. In case of forward welding the weld bed is
heated, so bigger penetration can be reached.
Hegesztés iránya Hegesztés iránya
Balra hegesztés Jobbra hegesztés
Welding direction Welding direction
Welding technique
welding direction welding direction
backward welding foreward welding
25
• Natural flame (for steels and copper)
• Oxidizing flame(for welding of brass)
• Carburizing flame(for aluminum and its alloys)
Natural Oxidizing Carburizing
Applied flame types
26
Application of oxyfuel-gas welding
Welding parameters:
• dh = 1....10 mm (filler material diameter)
• pC2H2 = 0,1....0,6 bar
• pO2 = 2....5 bar
• vweld = 10....100 mm/min
• VC2H2 = 1.....50 l/min
• VO2 = 1.....55 l/min.
• On-site welding, FMCG assembly applications.
• Repairs (for example car chassis).
• For FMCG assemblies –central heating, water, gas piping – other procedures are hard to apply.
27
The process:
• Preheating for flashing-
point temperature
• Burning with oxygen
• Blowing out the products
of combustion to form
the gap
Oxyfuel-gas cutting
28
• The material must be capable to burn in oxygen
• Flash point temperature must be lower than melting point.
• Melting point of the oxide must be lower than that ofthe metal itself.
• The combustion productmust be a fluid, so it can be flown out to form the gap.
Well cuttable materials:
Weldable unalloyed and low alloyed steels.
(Alloying materials usually decrease weldability.)
C, %
A könnyű lángvághatóság határa
T, ºC
2,1
4,3 0,8
Limit of well cuttability
Oxyfuel-gas cutting conditions
Limit of good cutting
Flash
point