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

2312

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 productsof combustion to form

the gap

Oxyfuel-gas cutting

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• 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