11. surfacing and shape welding

2003

11.

Surfacing

and Shape Welding

11. Surfacing and Shape Welding 146

DIN 1910 (“Weld-

ing”) classifies the

welding process

according to its

applications: weld-

ing of joints and

surfacing. Accord-

ing to DIN 1910

surfacing is the

coating of a work-

piece 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. Sur-

facing carried out with wear-resistant materials in preference to the base metal ma-

terial 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 produced which allow the appro-

priate-to-the-type-of-duty joining of dis-

similar materials and/or of materials

with differing properties, Figure 11.1.

A buffering, for instance, is an interme-

diate 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 primary forming as

well as for joining by primary forming.

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base metal/ surfacing metal

similar

for repair weldingl

dissimilar

hardfacing (wear protection)

cladding (corrosion prevention)

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

l

l

l

Figure 11.1

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Components -Kinds of Stress

m 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

m

m

m

m

m

m

m

m

m

Figure 11.2


In case of surfacing - as for all fabrica-

tion processes - certain limiting con-

ditions have to be observed. For ex-

ample, 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 metals is avail-

able. In dependence on the welding

method as well as on the selected ma-

terials, filler metals in the form of wires,

filler wires, strips, cored strips, rods or

powder are applied, Figure 11.4.

The filler/base metal dilution is rather

important, as the desired high-quality

properties of the surfacing layer dete-

riorate with the increasing degree of

dilution.

A weld parameter optimisation has the

objective to optimise the degree of dilu-

tion in order to guarantee a sufficient

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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

q

q

q

q

q

q

q

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Boundary Conditions in Surfacing

component(material)

coating

coatingmaterial(filler)

surfacingmethod

stresscompatibility

manufacturingconditionsavailability

consumable

Figure 11.3

Figure 11.4


adherence of the layer with the minimum metal dissimilation. A planimetric determi-

nation of the surfacing and penetration areas will roughly assess the proportion of

filler to base metal.

When the analysis

of base and filler

metal is known, a

more precise calcu-

lation is possible by

the determination of

the content of a cer-

tain element in the

surfacing 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 welding methods are not only suit-

able for joining but also for surfacing.

In the case of the strip-electrode

submerged-arc surfacing process

normally strips (widths: 20 - 120mm)

are used. These strips allow high clad-

ding rates. Solid wire electrodes as well

as flux-cored strip electrodes are used.

The flux-cored strip electrodes contain

Definition of Dilution

© ISF 2002br-er11-05e.cdr

surface built up by welding FB

penetration area F P

base metal

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

surfacing layer FM

base metal FM

FP

F + FP B

A = 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

%

Cr

perc

enta

ges

by m

ass

µm0 100 200

distance

300 500

10

%

0

20

30

Ni p

erce

ntag

es b

y m

ass

µm0 100 200 300 500

distance

Figure 11.6


certain alloying elements. The strip is continuously fed into the process via feed roll-

ers. Current contact 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 supplied 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 mechanically in order to avoid slag inclusions during overwelding. The

arc wanders along the lower edge of the strip. Thus the strip is melted consistently,

Figure 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


Figure 11.9 shows the cladding of a roll barrel. The coating is deposited helically

while the workpiece is rotating. The weld head is moved axially over the workpiece.

The macro-section and possible weld defects of a strip-electrode submerged-arc sur-

facing process are depicted in Figure 11.10.

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Figure 11.9

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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


Electroslag surfacing using a strip electrode is similar to strip-electrode SA sur-

facing, Figure 11.11. The difference is that the weld filler metal is not melted in the

arc but in liquefied 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.

TIG weld surfac-

ing is a suitable

surfacing method

for small and com-

plicated contours

and/or low quanti-

ties (e.g. repair

work) with normally relatively low

deposition rates. The process princi-

ple has already been shown when the

TIG joint welding process was ex-

plained, Figure 11.12. The arc is

burning between a gas-backed non-

consumable tungsten electrode and

the workpiece. The arc melts the base

metal and the wire or rod-shaped

weld filler metal which is fed either

continuously or intermittently. Thus a

fusion welded joint develops between

base metal and surfacing bead.

In the case of MIG/MAG surfacing

processes the arc burns between a

consumable wire electrode and the

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molten pool

Figure 11.11


Process Principle ofTIG Weld Surfacing

rod/ wire-shapedfiller metal

arc

shielding gas nozzle

base metal(+ / ~) surfacing bead

tungsten electrode(- / ~)

Figure 11.12


workpiece. This

method allows

higher deposition

rates. Filler as well

as solid wires are

used. The wire

electrode has a

positive, while the

workpiece to be

surfaced has a

negative polarity,

Figure 11.13.

A further development of the TIG welding process is plasma welding. While the TIG

arc develops freely, the plasma welding arc is mechanically 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 cen-

trally 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

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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 arcwelding arc

filler metal

shielding gas

conveying gas

plasma gas

tungsten electrode

TA

UNTA

Figure 11.14


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 shield-

ing gas, protects

the surfacing bead

and the adjacent

high-temperature

zone from the sur-

rounding influence.

The applied gases

are mainly inert

gases, as, for ex-

ample, Ar and He

and/or Ar-/He mix-

tures.

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

valves, extruder 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 surfacing and base

metal, is shown enlarged on the right side of Figure 11.15 (blow-up). It shows hard-

facing with cobalt which is high-temperature and hot gas corrosion resistant.

In plasma arc hot

wire surfacing the

base metal is

melted by an oscil-

lating plasma torch,

Figure 11.16. The

weld filler metal in

the form of two

parallel wires is

added to the base

metal quite inde-

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section A

GW

ZW

Figure 11.15

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workpiece

wires from spool

plasma powersourceshielding

gas

arc

plasma gas

tungstenelectrode =

~

surfacingbead

hot wire power source

weld pool

Figure 11.16


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

application of a separate power source. The plasma arc with a length of approx. 20

mm is oscillating (oscillation width between 20 to 50 mm). The two wires are fed in a

V-formation at an angle of approx. 30° and melt in the high-temperature region in the

trailing zone of the plasma torch.

For surfacing purposes, besides the arc-welding methods, the beam welding meth-

ods laser beam and electron beam welding may also be applied. Figure 11.17 shows

the process principle of laser surfacing. The powder filler metal is added to the laser

beam via a powder

nozzle and the pow-

der gas flow is, in

addition, constricted

by shielding gas

flow.

Friction surfacing

is, in principle, simi-

lar to friction welding

for the production of

joints which due to

the different materi-

als are difficult to

produce with fusion

welding, Figure

11.18.

The filler metal is

“advanced” over the

workpiece with high

pressure and rota-

tion. By the pressure

and the relative

movement frictional

heat develops and

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Werkstück

laser beam

surfacing bead

shieldinggas nozzle

powder nozzle

powder flow

shielding gas

direction ofthe oscillation

Figure 11.17

© 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 11.18


puts the weld filler end into a pasty condition. The advance motion causes an adher-

ent, “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 different surfacing methods shows that the application fields are

limited - dependent 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 welded. Another criterion for the selection of a surfacing method is the deposition

rate. In the case of cladding large surfaces a method with a high deposition rate is

chosen, this with regard to profitability.

In thermal spraying the filler metal is melted inside the torch and then, with a high

kinetic energy, discharged onto the unfused but preheated workpiece surface.

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

cal interlocking 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. Plas-

tics may be sprayed as well. The utilisation of filler metals in thermal spraying is rela-

tively low.

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

spraying and arc

spraying.

In powder flame

spraying an oxya-

cetylene flame pro-

vides the heating

source where the

centrally fed filler

metal is melted,

Figure 11.19. The

kinetic energy for

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rotation

bulge

force

surfacing layer

base metal

filler metal

advance

Figure 11.19


the acceleration and atomisation of the filler metal is produced by compressed gas

(air).

In contrast to pow-

der flame spraying,

is for flame spray-

ing a wire filler

metal fed mechani-

cally into the centre

cone, melted, at-

omised and accel-

erated in direction

of the substrate,

Figure 11.20.

In plasma arc spraying an internal, high-energy arc is ignited between the tungsten

cathode and the anode, 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 en-

ergy 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 produced from

molten weld metal

only. In comparison

to cast parts this

method brings

about essentially

more favourable

mechano-

technological mate-

rial properties, es-

pecially a better

toughness charac-

teristic. The reason

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spraying materialcompressedair

workpiece

flame conefuel gas-oxygenmixture

spray deposit

Figure 11.20

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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 11.21


for this lies mainly in the high purity and the homogeneity of the steel which is helped

by the repeated melting process and the resulting slag reactions. These properties

are also put down to the favourable fine-grained structure formation which is

achieved by the repeated subsequent thermal treatment with the multi-pass tech-

nique. Also in contrast with the shapes produced by forging, the workpieces pro-

duced by shape welding show quality advantages, especially in the isotropy and the

regularity of their toughness and strength properties as far as larger workpiece thick-

nesses are con-

cerned. In Europe,

due to the lack of

expensive forging

equipment, very

high individual

weights may not be

produced as forged

parts.

Therefore, shape

welding is, for cer-

tain applications, a

sensible techno-

logical 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.

Plasma Powder Spraying Unit


powder injector

jet of particles

copper anode

plasmagas

coolingwater cooling water tungsten cathode arc

anodecarrier

middleframe

gasdistributor

isolationring

backframe

Figure 11.22

Shape Welding - Integration


shape welding

forming(forging)

joining(welding)

primary forming(casting)

Figure 11.23


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tractionmechanism

joist turntable

phase 1

phase 3

phase 5

phase 2

phase 4

phase 6

phase 7

Figure 11.26

The higher tooling costs in forging make the shape welding method less expensive;

this applies to parts with certain increasing complexity. This comparison is, however,

related to relatively low numbers of pieces, where the tooling costs per part are ac-

cordingly higher,

Figure 11.24.

Figure 11.25 shows

the principal proce-

dure for the produc-

tion of typical

shape-welded

parts. Cylindrical

containers are pro-

duced with the

“Baumkuchenme-

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Shape Welded Goblet (1936)

Figure 11.24


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

Töpfermethode

Klammeraffe

Figure 11.25


thode” method: the filler metal is wel-

ded by submerged-arc with helical

movement in multiple passes into a

tube which has the function of a trac-

tion 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 Töpfer method. On the traction

mechanism a rotationally symmetrical

part with a semicircle cross-section is

produced which is later separated and

welded to an elbow, Figures 11.26

and 11.27. The Klammeraffe method

serves the purpose to weld external

connection pieces onto pipes. A portable unit which is connected with the pipe welds

the connection pipe in a similar manner to the Töpfer method.

In the case of elec-

tron beam surfac-

ing the filler metal

is added to the

process in the form

of a film, Figure

11.28.

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Production of a Pipe Bendby Shape Welding

testing

1. welding of the half-torus2. stress relief annealing3. mechanical treatment4. seperating/ halving5. folding6. welding togehter7. stress relief annealing8. testing

Figure 11.27

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shaf

ts

boile

r sh

ell r

ings

brac

es

sphe

rical

cap

s

pipe

ben

ds

forged products

shape-weldedproducts

complexity of the parts

€/kg

Figure 11.28

11. surfacing and shape welding

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