surfacing and shape welding

7/21/2019 Surfacing and Shape Welding

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Surfacing

and Shape Welding


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11. Surfacing and Shape Welding 151

2005

DIN 1910 (Welding) clas-

sifies the welding process

according to its applica-

tions: welding of joints

and surfacing. According

to DIN 1910 surfacing is

the coating of a workpiece

by means of welding.

Dependent on the applied

filler material a further

classification may be

made: deposition repair

welding and surfacing for

the production of a composite material with certain functions. Surfacing carried out with wear-

resistantmaterials in preference to the base metal material is called hardfacing; but when

mainly chemically stable filler materials are

used, the method is called cladding. In the

case of buffering, surfacing layers are pro-

duced which allow the appropriate-to-the-

type-of-duty joining of dissimilar materials

and/or of materials with differing properties,

Figure 11.1.

A buffering, for instance, is an intermediate

layer made from a relatively tough material

between two layers with strongly differing

thermal expansion coefficients.

Figure 11.2 shows different kinds of stresses

which demand the surfacing of components.

Furthermore surfacing may be used for pri-

mary forming as well as for joining by primary

forming.

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base metal/ surfacing metal

similar

for repair welding

dissimilar

hardfacing (wear protection)

cladding (corrosion prevention)

buffering (production of an appropriate-to-the-type-of-duty joint of dissimilar materials)

Figure 11.1

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Components -Kinds of Stress

wear caused by very high impact and compressive stress

wear by friction (metal against metal) during high impact and compression stress

strong sanding or grinding wear

very strong wear caused by grinding during low impact stress

cold forming tools

hot forming tools

cavitation

wear parts (plastics industry)

corrosion

temperature stresses

Figure 11.2


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In case of surfacing - as for all fabrication processes - certain limiting conditionshave to be

observed. For example, hard and wear-resistant weld filler metals cannot be drawn into solid

wires. Here, another form has to be selected (filler wire, continuously cast rods, powder).

Process materials, as for example SA welding flux demand a certain welding position which

in terms limits the method of welding.

The coating material must be selected with view to the type of duty and, moreover, must be

compatible with the base metal, Figure 11.3.

For all surfacing tasks a large product line of welding filler metalsis available. In depend-

ence on the welding method as well as on the selected materials, filler metals in the form of

wires, filler wires, strips, cored strips, rods or powder are applied, Figure 11.4.

The filler/base metal dilutionis rather important, as the desired high-quality properties of the

surfacing layer deteriorate with the increasing degree of dilution.

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Boundary Conditions in Surfacing

component(material)

coating

coatingmaterial(filler)

surfacingmethod

stresscompatibility

manufacturingconditionsavailability

consumable

Figure 11.3

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Materials for Surfacing

wearing protection (armouring)

corrosion prevention

hard facing on

cobalt base

nickel base

iron base

ferritic to martensitic chromium steel alloys

soft martensitic chromium-nickel steel alloys

austenitic-ferritic chromium-nickel steel alloys

austenitic chromium-nickel steel alloys

Figure 11.4


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A weld parameter optimisation has the objective to optimise the degree of dilution in order to

guarantee a sufficient adherence of the layer with the minimum metal dissimilation. A

planimetric determination

of the surfacing and pene-

tration areas will roughly

assess the proportion of

filler to base metal. When

the analysis of base and

filler metal is known, a

more precise calculation is

possible by the determina-

tion of the content of a cer-

tain element in the surfac-

ing layer as well as in the

base metal, Figure 11.5.

Figure 11.6 shows record charts of an electron

beam microprobe analysis for the elements

nickel and chromium. It is evident that - after

passing a narrow transition zone between

base metal and layer the analysis inside

the layer is quasi constant.

As depicted in Figure 11.7 almost all arc weld-

ing methods are not only suitable for joining

but also for surfacing.

Definition of Dilution

ISF 2002br-er11-05e.cdr

surface built up by welding FB

penetration area FP

base metal

(X-content - X-content ) [% in weight]

(X-content - X-content ) [% in weight]surfacing layer FM

base metal FM

FP

F + FP BA = x 100%

A = x 100%

D

D

FM: weld filler metal A : dilutionD

Figure 11.5

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Microprobe Analyses

10

0

20

30

%

Crpercentagesbym

ass

m0 100 200

distance

300 500

10

%

0

20

30

Nipercentagesbym

ass

m0 100 200 300 500

distance

Figure 11.6


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In the case of the strip-electrode submerged-arc surfacing process normally strips

(widths: 20 - 120mm) are used. These strips allow high cladding rates. Solid wire electrodes

as well as flux-cored strip electrodes are used. The flux-cored strip electrodes contain certain

alloying elements. The strip is continuously fed into the process via feed rollers. Current con-

tact is normally carried out

via copper contact jaws

which in some cases are

protected against wear by

hard metal inserts. The

slag-forming flux is sup-

plied onto the workpiece in

front of the strip electrode

by means of a flux support.

The non-molten flux can be

extracted and returned to

the flux circuit.

Should the slag developed

on top of the welding bead

not detach itself, it will

have to be removed me-

chanically in order to avoid

slag inclusions during

overwelding. The arc wan-

ders along the lower edge

of the strip. Thus the strip

is melted consistently, Fig-

ure 11.8.

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inert gas-shielded arc weldingmetal-arc welding submerged arc welding

arc spraying

plasma spraying

electroslag welding

- stick electrode- filler wire

- MIG / MAG- MIG cold wire- filler wire

TIG welding

- TIG cold wire

plasma welding

- plasma powder- plasma hot wire

- wire electrode- strip electrode

arc welding with self-shieldedcored wire electrode

- filler wire

- powder- wire

- wire electrode

Figure 11.7

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flux support

filler metal

slag

surfacing bead

drive rolls + -

flux application

base metal

power source

Figure 11.8


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Figure 11.9 shows the

cladding of a roll barrel.

The coating is deposited

helically while the work-

piece is rotating. The weld

head is moved axially over

the workpiece.

The macro-section and

possible weld defects of a

strip-electrode submerged-

arc surfacing process are

depicted in Figure 11.10.

Electroslag surfacing us-

ing a strip electrode is

similar to strip-electrode SA

surfacing, Figure 11.11.

The difference is that the

weld filler metal is not

melted in the arc but in liq-

uefied welding flux the

liquid slag as a result of

Joule resistance heating.

The slag is held by a slight

inclination of the plate and

the flux mound to prevent it

from running off.

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coarse grain zone lack of fusion mirco slag inclusions sagged weld

crack formationin these areas of

the coarse grain zoneundercutsgusset

base metal

Figure 11.10

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Figure 11.9


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TIG weld surfacingis a suitable surfacing method for small and complicated contours and/or

low quantities (e.g. repair work) with normally relatively low deposition rates. The process

principle has already been shown when the TIG joint welding process was explained, Figure

11.12. The arc is burning

between a gas-backed non-

consumable tungsten elec-

trode and the workpiece.

The arc melts the base

metal and the wire or rod-

shaped weld filler metal

which is fed either continu-

ously or intermittently. Thus

a fusion welded joint devel-

ops between base metal

and surfacing bead.

In the case of MIG/MAG surfacing proc-

esses the arc burns between a consumable

wire electrode and the workpiece. This

method allows higher deposition rates. Filler

as well as solid wires are used. The wire elec-

trode has a positive, while the workpiece to be

surfaced has a negative polarity, Figure

11.13.


Process Principle ofTIG Weld Surfacing

rod/ wire-shapedfiller metal

arc

shielding gas nozzle

base metal(+ / ~) surfacing bead

tungsten electrode(- / ~)

Figure 11.12

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molten pool

Figure 11.11


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A further development of

the TIG welding process is

plasma welding. While the

TIG arc develops freely, the

plasma welding arc is me-

chanically and thermally

constricted by a water-

cooled copper nozzle. Thus

the arc obtains a higher

energy density.

In the case of plasma arc

powder surfacing this

constricting nozzle has a

positive, the tungsten electrode has a negative polarity, Figure 11.14. Through a pilot arc

power supply a non-transferred arc(pilot arc) develops inside the torch. A second, separate

power source feeds the transferred arc between electrode and workpiece. The non-

transferred arc ionises the centrally fed plasma gas (inert gases, as, e.g., Ar or He) thus

causing a plasma jet of high energy to emerge from the nozzle. This plasma jet serves to

produce and to stabilise the arc striking ability of the transferred arc gap. The surfacing filler

metal powder added by a feeding gas flow is melted in the plasma jet. The partly liquefied

weld filler metal meets the

by transferred arc molten

base metal and forms the

surfacing bead. A third gas

flow, the shielding gas, pro-

tects the surfacing bead

and the adjacent high-

temperature zone from the

surrounding influence. The

applied gases are mainly

inert gases, as, for exam-

ple, Ar and He and/or Ar-/He mixtures.

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workpiece

+-

oscillation

feed direction

shielding gas

arc

surfacing bead

shielding gas nozzle

contact tube

weld filler metal power source

wire feed deviceshielding gas

Figure 11.13

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power sources

HIG

U

workpiece oscillation

surfacing bead

pilot arc

welding arc

filler metal

shielding gas

conveying gas

plasma gas

tungsten electrode

TA

UNTA

Figure 11.14


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The method is applied for surfacing small and medium-sized parts (car exhaust valves, ex-

truder spirals). Figure 11.15 shows a cross-section of armour plating of a car exhaust valve

seat. The fusion line, i.e.,

the region between surfac-

ing and base metal, is

shown enlarged on the

right side of Figure 11.15

(blow-up). It shows

hardfacing with cobalt

which is high-temperature

and hot gas corrosion

resistant.

In plasma arc hot wire

surfacing the base metal

is melted by an oscillating

plasma torch, Figure 11.16.

The weld filler metal in the form of two parallel wires is added to the base metal quite inde-

pendently. The arc between the tips of the two parallel wires is generated through the appli-

cation of a separate power

source. The plasma arc

with a length of approx. 20

mm is oscillating (oscilla-

tion width between 20 to 50

mm). The two wires are fed

in a V-formation at an an-

gle of approx. 30 and melt

in the high-temperature

region in the trailing zone

of the plasma torch.br-er11-16e.cdr

workpiece

wires from spool

plasma powersource

shieldinggas

arc

plasma gas

tungstenelectrode

=

~

surfacingbead

hot wire power source

weld pool

Figure 11.16

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section A

GW

ZW

Figure 11.15


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For surfacing purposes,

besides the arc-welding

methods, the beam weld-

ing methods laser beam

and electron beam welding

may also be applied. Fig-

ure 11.17 shows the proc-

ess principle of laser sur-

facing. The powder filler

metal is added to the laser

beam via a powder nozzle

and the powder gas flow

is, in addition, constricted

by shielding gas flow.

Friction surfacingis, in principle, similar to friction welding for the production of joints which

due to the different materials are difficult to produce with fusion welding, Figure 11.18.

The filler metal is advanced over the workpiece with high pressure and rotation. By the

pressure and the relative movement frictional heat develops and puts the weld filler end into

a pasty condition. The advance motion causes an adherent, spreaded layer on the base

metal. This method is not applied frequently and is mainly used for materials which show

strong differences in their melting and oxidation behaviours.

A comparison of the differ-

ent surfacing methods

shows that the application

fields are limited - de-

pendent on the welding

method. A specific

method, for example, is

the low filler/base metal

dilution. These methods

are applied where high-quality filler metals are

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rotation

bulge

force

surfacing layer

base metal

filler metal

advance

Figure 11.18

Figure 11.17


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welded. Another criterion for the selection of a surfacing method is the deposition rate. In the

case of cladding large sur-

faces a method with a high

deposition rate is chosen,

this with regard to profit-

ability.

In thermal spraying the

filler metal is melted inside

the torch and then, with a

high kinetic energy, dis-

charged onto the unfused

but preheated workpiece

surface.

There is no fusion of base and filler metal but rather adhesive binding and mechanical inter-

locking of the spray deposit with the base material. These mechanisms are effective only

when the workpiece surface is coarse (pre-treatment by sandblasting) and free of oxides.

The filler and base materials are metallic and non-metallic. Plastics may be sprayed as well.

The utilisation of filler metals in thermal spraying is relatively low.

The most important methods of thermal spraying are: plasma arc spraying, flame spraying

and arc spraying.

In powder flame spraying

an oxyacetylene flame pro-

vides the heating source

where the centrally fed filler

metal is melted, Figure

11.19. The kinetic energy for

the acceleration and atomi-

sation of the filler metal is

produced by compressed

gas (air).

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spraying materialcompressedair

workpiece

flame conefuel gas-oxygenmixture

spray deposit

Figure 11.19

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compressed air

gas mixture

adjustable wirefeed device

spraying wire spray deposit

spraying jet non-bindingsprayed particles(loss in spraying)

fusingwire tip

Figure 11.20


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In contrast to powder flame

spraying, is for flame

sprayinga wire filler metal

fed mechanically into the

centre cone, melted, atom-

ised and accelerated in

direction of the substrate,

Figure 11.20.

In plasma arc sprayingan

internal, high-energy arc is

ignited between the tung-

sten cathode and the an-

ode, Figure 11.21. This arc

ionises the plasma gas (argon, 50 - 100 l/min). The plasma emerges from the torch with a

high kinetic and thermal energy and carries the side-fed powder along with it which then

meets the workpiece surface in a semi-fluid state with the necessary kinetic energy. In the

case of shape welding, steel shapes with larger dimensions and higher weights are pro-

duced from molten weld metal only. In comparison to cast parts this method brings about es-

sentially more favourable mechano-technological material properties, especially a better

toughness characteristic. The reason for this lies mainly in the high purity and the homogene-

ity of the steel which is helped by the repeated melting process and the resulting slag reac-

tions. These properties are

also put down to the fa-

vourable fine-grained struc-

ture formation which is

achieved by the repeated

subsequent thermal treat-

ment with the multi-pass

technique. Also in contrast

with the shapes produced

by forging, the workpieces

produced by shape weldingshow quality advantages,

Plasma Powder Spraying Unit


powder injector

jet of particles

copper anode

plasmagas

coolingwater cooling water tungsten cathode arc

anodecarrier

middleframe

gasdistributor

isolationring

backframe

Figure 11.21

Shape Welding - Integration


shape welding

forming(forging)

joining(welding)

primary forming(casting)

Figure 11.22


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Shape Welded Goblet (1936)

Figure 11.23

especially in the isotropy and the regularity of their toughness and strength properties as far

as larger workpiece thicknesses are concerned. In Europe, due to the lack of expensive forg-

ing equipment, very high individual weights

may not be produced as forged parts.

Therefore, shape welding is, for certain appli-

cations, a sensible technological and eco-

nomical alternative to the methods of primary

forming, forming or joining, Figure 11.22.

Figure 11.23 shows an early application which

is related to the field of arts.

The higher tooling costs in forging make the

shape welding method less expensive; this

applies to parts with certain increasing com-

plexity. This comparison is, however, related

to relatively low numbers of pieces, where the

tooling costs per part are accordingly higher,

Figure 11.24.

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shafts

boilershellrings

braces

sphericalcaps

pipebends

forged products

shape-welded

products

complexity of the parts

/kg

Figure 11.24


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tractionmechanism

joist turntable

phase 1

phase 3

phase 5

phase 2

phase 4

phase 6

phase 7

Figure 11.26


Shape Welding Procedures

+ several weld heads possible+ no interruption during weld head failure

- core made of foreign material necessary

applications:shafts, large boiler shell rings, flanges

+ free rotationally-symmetrical shapes+ several weld heads possible+ weld head manipulation not necessary+ each head capable to weld a specific layer+ small diameters possible

- component movement must correspond with the contour- number of weld heads limited when smaller diameters are welded

applications:spherical caps, pipe bends, braces

+ transportable unit

- limited welding efficiency

applications:welding-on of connection pieces

Baumkuchenmethode

Tpfermethode

Klammeraffe

Figure 11.25

Figure 11.25 shows the principal procedure for

the production of typical shape-welded parts.

Cylindrical containers are produced with the

Baumkuchenmethode method: the filler metal

is welded by submerged-arc with helical mo-

vement in multiple passes into a tube which

has the function of a traction mechanism (for

the most part mechanically removed later).

This brings about the possibility to produce

seamless containers with bottom and flange in

one working cycle.

Elbows are mainly manufactured with the

Tpfer method. On the traction mechanism a

rotationally symmetrical part with a semicircle

cross-section is produced which is later sepa-

rated and welded to an elbow, Figures 11.26

and 11.27. The Klammeraffe method serves

the purpose to weld exter-

nal connection pieces onto

pipes. A portable unit

which is connected with the

pipe welds the connection

pipe in a similar manner to

the Tpfer method.


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In the case of electron beam surfacing the

filler metal is added to the process in the form

of a film, Figure 11.28.

ISF 1998

feed direction

metal foil

metal foil feeding

electron beam

surface layer

base material

workpiece

Process PrincipleElectron Beam Surface Welding

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Figure 11.28

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Production of a Pipe Bendby Shape Welding

testing

1. welding of the half-torus2. stress relief annealing

3. mechanical treatment4. seperating/ halving5. folding6. welding togehter7. stress relief annealing8. testing

Figure 11.27

surfacing and shape welding

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