ISSN 2303-4521

PERIODICALS OF ENGINEERING AND NATURAL SCIENCES

Vol. 4 No. 1 (2016)
Available online at: http://pen.ius.edu.ba

Solid State Welding and Application in Aeronautical Industry

Enes Akca*, Ali Gursel

International University of Sarajevo Faculty of Engineering and Natural Sciences

Sarajevo, Bosnia and Herzegovina

enesakca@hotmail.com.tr, eakca@ius.edu.ba

Abstract

In this study solid state welding andapplication in aeronautic industryhave been researched. The solid state welding
technicisused in the industrial production fields such as aircraft, nucleer, space industry, aeronautic industry, ect.,
actually solid state welding is a process by which similar and dissmilar metals can be bonded together. Hence a
material can be created as not heavy but strong strength. Beside, advantages and disasvantages of solid state welding
have been discussed. Also the diffusion welding and friction welding which belong to the solid state welding is
obsevered in aeronautic industry.
Keywords: solid state welding, aeronautic industry,diffusion welding, dissimilar materials

1 Introduction

Welding is a metal joining process which produces

Disadvantages of Solid State Welding:
coalescence of metals by heating them to suitable
 Internal stresses, distortions and changes of micro-
temperatures with or without the application of pressure
structure in the weld region,
or by the application of pressure alone, and with or
 Harmful effects: light, ultra violate radiation, fumes,
without the use of filler material. Basically, welding is
high temperature,
used for making permanent joints. It is used in the
manufacture of automobile bodies, aircraft frames, Also there are many kinds of welding processes;
railway wagons, machine frames, structural works, tanks,  Arc welding;
furniture, boilers, general repair work and ship building. o Carbon arc welding,
o Shieled metal arc welding (SMAW),
Advantages of Solid State Welding:
o Submerged arc welding (SAW),
 Strong and tight joining, o Metal inert gas welding (MIG,GTAW),
 Cost effectiveness, o Tungsten inert gas welding (TIG, GTAW),
 Simplicity of welded structures design, o Electroslag welding (ESW),
 Welding processes may be mechanized and o Plasma arc welding (PAW),
automated.  Resistance Welding (RW);
o Spot welding (RSW),
o Flash Welding (FW),
o Resistance butt welding (UW),
o Seam welding (RSEW),
DOI: 10.21533/pen.v4i1.46 1
  Gas Welding (GW); and design of new materials are shaping the way welding
o Oxyacetylene welding (OAW), is implemented and process and product are being
o Oxyhydrogen welding (OHW), designed.
o Pressure gas welding (PGW), This article focuses on the application of solid state
 Solid state welding (SSW); welding in aeronautical industry, and on the trends in the
o Forge welding (FOW), industry that can be expected from progress at a
o Cold roll welding (CRW), fundamental level. It describes the following processes:
o Friction welding (FRW), friction welding and diffusion welding.
o Explosive welding (EXW),
o Diffusion welding (DFW),
o Ultrasonic welding, 2 Solid State Welding (SSW)
 Thermit welding (TW),
 Electron beam welding (EBW), Solid State Welding is a welding process, in which two
 Laser welding (LW), work pieces are joined under a pressure providing an
intimate contact between them and at a temperature
Solid-state welding describes a group of joining essentially below the melting point of the parent material.
techniques which produces coalescence at temperatures Bonding of the materials is a result of diffusion of their
below the melting point of the parent materials without interface atoms [2].
the addition of third material. External pressure and
relative movement may or may not be used to enhance Advantages of Solid State Welding:
the joining process.  Weld (bonding) is free from microstructure defects
This group of joining techniques includes e.g. friction (pores, non-metallic inclusions, segregation of alloying
(stir) welding, cold pressure welding,diffusion welding, elements),
explosion welding,electromagnetic pulse welding, , and  Mechanical properties of the weld are similar to those
ultrasonicwelding. In all of these joining methods, of the parent metals,
propercontrol of the process parameters (time,  No consumable materials (filler material, fluxes,
temperature, and pressure individually or in shielding gases) are required,
combination) results in the coalescence of the parent  Dissimilar metals may be joined (steel - aluminum
materials without melting or only negligible melting at alloy steel - copper alloy).
the interface. Technically, solid-state welding methods
Disadvantages of Solid State Welding:
are not welding processes in the traditional sense since
the materials do not reach their melting point, but can be  Thorough surface preparation is required (degreasing,
rather compared with the traditional forging techniques oxides removal, brushing/sanding),
[1].  Expensive equipment.

Solid-state welding offers specific advantages since the

2.1 Forge Welding (FOW)
base metal do not (or only marginally) melt and re-
solidify [1].The parent metals essentially retain their Forge Welding is a Solid State Welding process, in which
original properties; heat-affected zone problems - which the components are heated to about 1800°F (1000°C) and
generally develop when there is base metal melting - are then forged (hammered). Prior to Forge Welding, the
significantly diminished. Also the formation of parts are scarfed in order to prevent entrapment of oxides
intermetallic phases at the interface which can be brittle in the joint. Forge Welding is used in general blacksmith
and may yield corrosion concerns is largely eliminated or shops and for manufacturing metal art pieces and welded
minimized. Furthermore, when dissimilar metals are tubes [2, 3].
joined, their thermal expansion and conductivity
characteristics have much less influence on the resulting
Advantages of Forge Welding:
joint performance than with fusion welding processes.
 Good quality weld may be obtained,
Solid state welding in the aeronautics industry is  Parts of intricate shape may be welded,
experiencing exciting developments. The widespread  No filler material is required.
application of computers and the improved knowledge

2
Disadvantages of Forge Welding: Cold Welding is widely used for manufacturing bi-metal
steel - aluminum alloy strips, for cladding of aluminum
 Only low carbon steel may be welded, alloy strips by other aluminum alloys or pure aluminum
 High level of the operators skill is required, (Corrosion protection coatings). Bi-metal strips are
 Slow welding process, produced by Rolling technology. Presses are also used for
 Weld may be contaminated by the coke used in Cold Welding. Cold Welding may be easily automated [3,
heating furnace. 4].

2.3 Diffusion Welding (DFW)

Diffusion Welding is a Solid State Welding process, in

which pressure applied to two work pieces with carefully
cleaned surfaces and at an elevated temperature below the
melting point of the metals. Bonding of the materials is a
result of mutual diffusion of their interface atoms [5, 6].
In order to keep the bonded surfaces clean from oxides
and other air contaminations, the process is often
conducted in vacuum. No appreciable deformation of the
Figure 1: Woodcut showing a large ship’s anchor being forged in 18th
century France. The arm and the shaft of the anchor are being forge- work pieces occurs in Diffusion Welding.Diffusion
welded together in this view. Welding is often referred more commonly as Solid State
2.2 Cold Roll Welding (CRW) Welding (SSW). Diffusion Welding is able to bond
dissimilar metals, which are difficult to weld by other
Cold Welding is a Solid State Welding process, in which welding processes:
two work pieces are joined together at room temperature  Steel to tungsten,
and under a pressure, causing a substantial deformation of  Steel to niobium,
the welded parts and providing an intimate contact  Stainless steel to titanium,
between the welded surfaces [3].  Gold to copper alloys.

Diffusion Welding is used in aerospace androcketry

industries, electronics, nuclearapplications,
manufacturing composite materials.

Advantages of Diffusion Welding:

 Dissimilar materials may be welded (Metals,
Ceramics, Graphite, glass),
 Welds of high quality are obtained (no pores,
inclusions, chemical segregation, distortions),
 No limitation in the work pieces thickness.

Disadvantages of Diffusion Welding:

 Time consuming process with low productivity,
 Very thorough surface preparation is required prior to
Figure 2: Cold welding (also cladding) process welding process,
 The mating surfaces must be precisely fitted to each
As a result of the deformation, the oxide film covering the
other,
welded parts breaks up, and clean metal surfaces reveal.
 Relatively high initial investments in equipment.
Intimate contact between these pure surfaces provides a
strong and defectless bonding.Aluminum alloys, Copper
alloys, low carbon steels, Nickel alloys, and other ductile
metals may be welded by Cold Welding.

3
2.4 Explosion Welding (EXW)

Explosive Welding is a Solid State Welding process, in Advantages of Explosive Welding

which welded parts (plates) are metallurgically bonded as
a result of oblique impact pressure exerted on them by a  Large surfaces may be welded,
controlled detonation of an explosive charge.  High quality bonding: high strength, no distortions,
One of the welded parts (base plate) is rested on an anvil, no porosity, no change of the metal microstructure,
the second part (flyer plate) is located above the base  Low cost and simple process,
plate with an angled or constant interface  Surface preparation is not required.
clearance.Explosive charge is placed on the flyer plate.
Detonation starts at an edge of the plate and propagates at Disadvantages of Explosive Welding:
high velocity along the plate.The maximum detonation
 Brittle materials (low ductility and low impact
velocity is about 120% of the material sonic velocity.The
toughness) cannot be processed,
slags (oxides, nitrides and other contaminants) are
 Only simple shape parts may be bonded: plates,
expelled by the jet created just ahead of the bonding
cylinders,
front.Most of the commercial metals and alloys may be
 Thickness of flyer plate is limited - less than 2.5” (63
bonded (welded) by Explosive Welding.Dissimilar metals
mm),
may be joined by Explosive Welding:
 Safety and security aspects of storage and using
 Copper to steel, explosives.
 Nickel to steel,
 Aluminum to steel, Explosive Welding is used for manufacturing clad tubes
 Tungsten to steel, and pipes, pressure vessels, aerospace structures, heat
 Titanium to steel, exchangers, bi-metal sliding bearings, ship structures,
 Copper to aluminum. weld transitions, corrosion resistant chemical process
tanks [5].

Figure 3: Explosive welding showing the initial setup and the process of explosive welding with the propagating shock wave.

Figure 4: Friction welding: (a) no contact, (b) parts brought into contact to generate friction heat, (c) rotation stops and axial pressure applied,
(d) final product showing the flash.

4
2.5 Friction Welding (FRW)

Friction welding is a solid-state welding process in which

coalescence is achieved by frictional heat combined with
Advantages of Ultrasonic Welding:
pressure. The heat is generated by the friction between
the two components surfaces, usually by rotation of one  Dissimilar metals may be joined,
part relative to the other. Then the parts are driven toward  Very low deformation of the work pieces surfaces,
each other with sufficient force to form a metallurgical  High quality weld is obtained,
bond. The sequence is portrayed in the figure for the  The process may be integrated into automated
typical application of this operation, welding of two production lines,
cylindrical parts.  Moderate operator skill level is enough.

The axial compression force upsets the parts, and the Disadvantages of Ultrasonic Welding:
material displaced produces a flash. The flash must be
subsequently trimmed to provide a smooth surface in the  Only small and thin parts may be welded,
weld region. No filler metal, flux, or shielding gases are  Work pieces and equipment components may fatigue
required. at the reciprocating loads provided by ultrasonic
Machines used for friction welding have the appearance vibration,
of an engine lathe. They require a powered spindle to turn  Work pieces may bond to the anvil.
one part at high speed and a means of applying an axial
force between the rotating part and the non-rotating part.
3 Solid State Welding Processes for
With its short cycle times, the process is suitable for mass Aeronautics
production. It is applied in the welding of various shafts
and tubular parts of similar or dissimilar metals. One The nature of welding in the aeronautical industry is
typical application of friction welding is to coalesce characterized by low unit production, high unit cost,
medium-carbon steel shanks to carbide tips in producing extreme reliability, and severe operating conditions [7].
twist drills. These characteristics point towards the more expensive
and more concentrated heat sources such as plasma arc,
2.6 Ultrasonic Welding (USW)
laser beam and electron beam welding as the processes of
Ultrasonic Welding is a Solid State Welding process, in choice for welding of critical components. But mostly
which two work pieces are bonded as a result of a diffusion welding and friction welding techniques are
pressure exerted to the welded parts combined with used in the industry, and it has been growing
application of high frequency acoustic vibration permanently[8].
(ultrasonic).
Ultrasonic vibration causes friction between the parts,
which results in a closer contact between the two
surfaces with simultaneous local heating of the contact
area. Interatomic bonds, formed under these conditions,
provide strong joint.Ultrasonic cycle takes about 1 sec.
The frequency of acoustic vibrations is in the range 20 to
70 KHz. Thickness of the welded parts is limited by the
power of the ultrasonic generator.Ultrasonic Welding is
used mainly for bonding small work pieces in
electronics, for manufacturing communication devices,
medical tools, watches, in automotive industry. Figure 5: Conventional structure and integrated plan for door panel
using SPF/DFW

5
 Figure 6: Manufacturing of reinforced structures in titanium by a combination of SPF and DFW32

3.1 Diffusion welding in Aeronautics Industry titanium stimulated much research with the goal of
accomplishing a similar process with aluminum[11, 12,
It is a solid-state welding process that produces a weld by 13].
the application of pressure at elevated temperature with The fundamental difference between DFW of titanium
no macroscopic deformation or relative motion of the and aluminum is that titanium can dissolve its oxides, and
pieces [9]. The aeronautic industry is the major user of aluminum cannot [13]. Therefore, the residual oxide at
DFW25. This process has proven particularly useful the interface of aluminum joint dramatically reduces the
when combined with the superplastic forming (SPF) of strength of the diffusion weld. This problem has
titanium alloys. In this case, complicated geometries can prevented the SPF/DFW of aluminum from being
be obtained in just one manufacturing step as shown in generally adopted [14, 15].
Figure 6. The quality and low cost of the joint enables in
some cases the substitution of riveted aluminum
components with SPF/DFW titanium replacements.
Figure 5 shows a possible improvement for the door panel
of an aircraft fuselage [10, 11]. The conventional
fabrication consisted of 16 parts held together by 500
fasteners. It was proposed to replace that design by a 2-
sheet assembly, integrally stiffened produced by
SPF/DFW. Figure 8 shows an exit hatch for the British
Aerospace Bae 125/800. The application of SPF/DFW
reduces the original riveted aluminum design from 76
detail parts and 1000 fasteners to a titanium version with
only 14 details and 90 fasteners with a total cost savings Figure 7: Wing access panel for the airbus A310/A320 made of
of 30%. Figure 7 shows a wing access panel for the titanium SPF/DFW33
Airbus A310 and A320 in which switching from riveted
aluminum to SPF/DFW titanium achieved a weight
saving in excess of 40%. The success of SPF/DFW with

6
 and friction welding which belong to solid state welding
have been investigated, in the aeronautic industry.
Weight reduction and improved damage tolerance
characteristics were the prime drivers to develop new
family of materials for the aeronautical industry, like
Fiber/Metal Laminated (FML) or Metal Matrix
Composites (MMC). Those advanced materials cannot be
welded by conventional techniques because the high
temperatures involved would destroy their properties. For
such materials, diffusion welding is an attractive solution
because it is a solid state joining technique, which is
normally carried out at a temperature much lower than the
melting point of the material.
The range of applications for this type of welding on
aeronautic industry is vast and includes: structural aircraft
sections, blades of aircraft engines, electronic
components, helicopters rotor parts, space shuttle
fuselage, exhaust components for gas turbines [22].

Figure 8: Exit hatch for the BAe 125/800 made of titanium

SPF/DFW33

3.2 Friction welding in Aeronautics Industry

In this process, the joining of the metals is achieved Figure 9: The components of an airplane
through mechanical deformation. Since there is no In the near future, Airbus planes (A318 and A3XX) will
melting, defects associated with melting-solidification feature fuselage stringers laser welded to the airplane
phenomena are not present and unions as strong as the skin. Looking further into the future, it is likely that
base material can be made [15, 16]. This process can join friction welding will be applied on airplane structural
components with a relatively simple cross section. It is components, since it can reliably join alloys of the series
used for the joining of aluminum landing gear 2xxx and 7xxx [23, 24].
components [17]. Linear friction (fretting) welding was
considered by General Electric and Pratt & Whitney as an Also, it is reasonable to expect that the amount and
alternative for the manufacture and repair of high criticality of EBW of titanium in future military aircraft
temperature alloy blisks for jet engines [18, 19]. Although will increase. The use of castings in aircraft is increasing;
little was disclosed about these processes, they do not this will surely bring up new challenges that had not been
seem to have evolved into commercial applications [20, present with wrought alloys. Besides that, diffusion
21]. welding is getting more and more useful in aeronautic
industry.

4 Conclusion
References
Welding processes and solid state welding processes have
been researched, and the application of diffusion welding 1. European Aluminium Association, Version 2015.

7
2. H.Kreye, “Melting Phenomena in Solid State Friction Stir Welding“, Jiujiang University, China,
Welding Processes“, welding research supplement, 2011.
1977. 19. M.Aonuma and K.Nakata,“ Dissmilar Metal Joining
3. Valery Marinoc,“ Manufacturing Technology“. of 2024 and 7075 Aluminium Alloys to Titanium
4. D. Kopeliovich,“ Solid State Welding (SSW)“. Alloys by Friction Stir Welding“, Tokyo
5. D. Kopeliovich,“ Classification of Welding Metropolitan Industrial Technology Research
Processes“. Institude, Japan, 2011.
6. G.S.Hoppin and T.F.Berry,“ Activated Diffusion 20. Rathod, M. and Karale, T., "Friction Stir Welding of
Bonding“, welding research supplement, 1970. Aluminium-Alloys," SAE Technical Paper 2014-28-
7. Shaw, C.B. “Welding Research for Aerospace in 0015, 2014.
USA, in International Congress on Welding 21. T. Pan,"Friction Stir Spot Welding (FSSW) - A
Research“, Boston, MA, 1984. Literature Review," SAE Technical Paper 2007-01-
8. A.P.Costa, E.C.Botelho, M.L.Costa, N.E.Narite, and 1702, 2007.
J.R. Tarpani,“ A Review of Welding Techonologies 22. Cary H.B., “Modern Welding Technology“, Prentice
for Thermoplastic Composites in Aerospace Hall, 1998.
Applications“, Brazil, 2012. 23. Eagar T.W., “Energy Sources Used for Fusion
9. Dunkerton, S.B. and C.J. Dawes,“The Application of Welding“ in ASM Handbook, 1993.
Diffusion Bonding and Laser Welding in the 24. W.D. Brewer, R.K. Bird, and T.A. Wallace,
Fabrication of Aerospace Structures, in Advanced “Titanium Alloys and Processing for High Speed
Joining of Aerospace Metallic Materials“, Aircraft“, Nasa Langley Research Center, Hampton
Oberammergau, Germany: Advisory Group for Virginia 23681-0001.
Aerospace Research & Development (NATO), 1985. 25. E. Akca and A. Gursel,“The importance of
10. Williamson, J.R.“Diffusion Bonding in Superplastic interlayers in diffusion welding – A review“
Forming/Diffusion Bonding, in Welding Technology Periodicals of Engineering and Natural Sciences,
for the Aerospace Industry“ Las Vegas, NV: vol 3, no 2, pp. 12-16, 2015.
American Welding Society, 1980.
11. Stephen, D. and S.J. Swadling,“Diffusion Bonding in
the Manufacture of Aircraft Structure, in Advanced
Joining of Aerospace Metallic Materials“,
Oberammergau, Germany: Advisory Group for
Aerospace Research & Development (NATO), 1985.
12. Patricio F. Mendez,“ New Trends in Welding in the
aeronautic industry“, Massachusetts Institute of
Technology, USA.
13. Institude Superior Tecnico,“Diffusion Welding in
Aeronautic Industry“, 2007.
14. Rose F., "A Rapid Method for Diffusion Bonding
Aerospace Structures," SAE Technical Paper
650780, 1965.
15. Muser C., "Diffusion Bonded Structures for
Application to Air Transport Aircraft," SAE
Technical Paper 680331, 1968.
16. Viliam Sinka,“The Present and Future Prospects of
Friction Stir Welding in Aeronautics“, Brazil, 2014.
17. Irving, B., “Sparks Begin to fly in Nonconventional
Friction Welding and Surfacing“, Welding Journal,
1993.
18. Y.Chen, C. Liu, and G. Liu,“ Study on the joining of
Titanium and Aluminum Dissimilar Alloys by