Bab 28 solid state welding (1)

solid state welding

Solid State Welding

Processes

Ir Tri Prakosa, M Eng.

Proses Manufaktur II, Januari 2010

INTRODUCTION

 This lecture describes processes in which

joining takes place without fusion (melting) of the workpieces

 Unlike the processes described in previous lecture, no liquid (molten) phase is present in the joint

 The principle of solid-state welding is best

demonstrated with the following example

produce a strong joint.

 Heat and some movement of the mating

surfaces by plastic deformation may be

employed to improve the strength of the joint

 Applying external heat improves the bond by

diffusion

 Small interfacial movements on the faying

surfaces (contacting surfaces of the two pieces

to be joined) disturb the surfaces, breaking up oxide films and generating new and clean

surfaces, thus improving the strength of the

bond

 Heat may also be generated by friction, which is utilized in friction welding

 Electric-resistance heating is utilized extensively

in resistance welding processes with numerous applications

 In explosion welding, very high contact

pressures are developed, causing welding of

the interface

 This lecture concludes coverage of welding

processes

 The topics of the metallurgy of welding, welding

design, weld quality, and welding process

selection are described next week

 Other joining processes such as brazing,

soldering, adhesive bonding and mechanical

fastening methods are covered in the next two weeks

COLD WELDING (CW)

of the mating parts be ductile.

 The interface is usually cleaned by wire

brushing prior to welding

 An example is the bonding of aluminum and

steel, where a brittle intermetallic compound is formed at the interface

 The best bond strength and ductility is obtained with two similar materials

Cold Welding (CW)

 Cold welding can be used to join small

workpieces made of soft, ductile metals

 Applications include electrical connections and

welding wire stock

Roll bonding

 The pressure required for cold welding can be

applied through a pair of rolls Hence the

process is called roll bonding.

Ilustrasi skematik proses roll

bonding, atau cladding.

Roll bonding

 Developed in the 1960s, roll bonding is used for

manufacturing certain U.S coins

 The process can be carried out at elevated

temperatures (hot roll bonding)

 Typical examples are cladding pure aluminum over aluminum-alloy sheet and stainless steel over mild steel for corrosion resistance

ULTRASONIC WELDING

Ultrasonic Welding (USW)

 In ultrasonic welding (USW), the faying surfaces

of the two members are subjected to a static

normal force and oscillating shearing

(tangential) stresses

 The shearing stresses are applied by the tip of a

transducer (the following Figure-a), similar to

that used for ultrasonic machining.

 The frequency of oscillation generally ranges

from 10 kHz to 75 kHz, although both lower and higher frequencies than these can be employed

Ultrasonic Welding (USW)

 The energy required increases with the

thickness and hardness of the materials being joined

 Proper coupling between the transducer and the

tip (called sonotrode, from the word sonu, as

contrasted to electrode) is important for efficient

operation

Ultrasonic Welding (USW)

 The shearing stresses cause plastic

deformation at the workpiece interfaces,

breaking up oxide films and contaminants and thus allowing good contact and producing a

strong solid-state bond

 Temperatures generated in the weld zone are usually in the range of one-third to one-half the melting point (absolute scale) of the metals

joined

 Therefore no melting and fusion take place

Ultrasonic Welding (USW)

 In certain situations, however, temperatures can

be sufficiently high to cause metallurgical

changes in the weld zone

 The mechanism of joining plastics by ultrasonic welding is different from that for metals, and

melting takes place at the interface, because of their much lower melting temperatures

Ultrasonic Welding (USW)

 The ultrasonic welding process is reliable and versatile It can be used with a wide variety of metallic and nonmetallic materials, including

dissimilar metals (bimetallic strips)

 It is used extensively in joining plastics and in the automotive and consumer electronics

industries for lap welding of sheet, foil, and thin wire and in packaging with foils

Ultrasonic Welding (USW)

 The welding tip can be replaced with rotating

disks (Figure b) for seam welding structures,

 Moderate skill is required to operate the

equipment

(b) Pengelasan sambungan ultrasonik menggunakan roller.

FRICTION WELDING

Friction Welding (FRW)

 In the joining processes that have been

described so far, the energy required for

welding such as chemical, electrical, and

ultrasonic, is supplied externally

 In friction welding (FRW), the required heat for welding is, as the name implies, generated

through friction at the interface of the two

members being joined

 Thus the source of energy is mechanical

Friction Welding (FRW)

 It can be demonstrated the significant rise in

temperature from friction by rubbing our hands together fast or sliding down a rope rapidly

 In friction welding, one of the members remains stationary while the other is placed in a chuck or collet and rotated at a high constant speed

 The two members to be joined are then brought into contact under an axial force (next Figure)

Friction Welding (FRW)

Urutan operasi pada proses pengelasan gesekan:

1 Komponen sebelah kiri diputar pada kecepatan tinggi.

2 Komponen sebelah kanan didekatkan dan diberi gaya aksial.

3 Gaya aksial ditingkatkan; flash mulai terbentuk.

4 Komponen sebelah kiri dihentikan putarannya; pengelasan selesai Selanjutnya flash dapat dihilangkan dengan pemesinan atau gerinda.

Friction Welding (FRW)

 After sufficient contact is established, the

rotating member is brought to a quick stop, so that the weld is not destroyed by shearing, while the axial force is increased

 The rotating member must be clamped securely

to the chuck or collet to resist both torque and axial forces without slipping

properties at elevated temperatures.

 The shape of the welded joint depends on the rotational speed and the axial pressure applied (the following Figure)

Friction Welding (FRW)

Bentuk daerah fusi pada pengelasan gesekan, sebagai fungsi dari gaya yang diberikan dan kecepatan putaran.

Friction Welding (FRW)

 These factors must be controlled to obtain a

uniformly strong joint

 Oxides and other contaminants at the interface are removed by the radially outward movement

of the hot metal at the interface

Friction Welding (FRW)

 Process capabilities

{ Developed in the 1940s, friction welding can be used

to join a wide variety of materials, provided that one

of the components has some rotational symmetry.

{ Solid, as well as tubular parts, can be joined by this method, with good joint strength Solid steel bars up

to 100 mm (4 in.) in diameter and pipes up to 250

mm (10 in.) outside diameter have been welded

successfully by this process.

{ The surface speed of the rotating member may be as high as 900 m/min (3000 ft/min).

Friction Welding (FRW)

 Process capabilities, con’t

{ Because of the combined heat and pressure, the

interface in FRW develops a flash by plastic

deformation (upsetting) of the heated zone.

{ This flash, if objectionable, can easily be removed by machining or grinding.

{ Friction welding machines generally cost between

$75,000 and $300,000, depending on their size and capacity.

{ They are fully automated, and operator skill required

is minimal if individual cycle times for the complete process are set properly.

Inertia friction welding

 Inertia friction welding is a modification of FRW although the term has been used

interchangeably with friction welding

 The energy required for frictionai heating in

inertia friction welding is supplied through the

kinetic energy of a flywheel

 The flywheel is accelerated to the proper speed, the two members are brought into contact, and

an axial force is applied

 As friction at the interface slows the flywheel,

Inertia friction welding

 The weld is completed when the flywheel comes

to a stop

 The timing of this sequence is important

 If the timing is not properly controlled, weld

quality will be poor

 The rotating mass of inertia friction welding

machines can be adjusted for applications

requiring different levels of energy, which

depend on workpiece size and properties

Inertia friction welding

 In one application of inertia friction welding, a 10-mm (0.4-in.) diameter shaft is welded to automotive turbocharger impellers at a rate of one every 15 seconds

Linear friction welding

 A recent development in friction welding

involves subjecting the interface of the two parts

to be joined to a linear reciprocating motion, as

opposed to the rotary motion required of at least one of the components described thus far

 In linear friction welding, the pans do not have

to be circular or tubular in cross-section

 The process is capable of welding square or

rectangular components, as well as round parts, made of metals or plastics

Linear friction welding

 In this process, one part is moved across the face of the other part using a balanced

reciprocating mechanism

 In one application, a rectangular titanium alloy part was friction welded at a linear frequency of

25 Hz, amplitude of 2 2 mm (0.08 in.), and a

pressure of 100 MPa (15,000 psi) acting on a

240 mm2 (0.38 in.2) interface

 Various other metal pans have been welded

successfully, with rectangular cross-sections as

Friction Stir Welding

Prinsip proses pengelasan stir Pelat paduan aluminium sampai

ketebalan 75 mm (3 in.) dapat dilas dengan proses ini Sumber:

TWI, Cambridge, U.K

RESISTANCE WELDING

Resistance welding (RW)

 Resistance welding (RW) covers a number of

processes in which the heat required for welding

is produced by means of the electrical

resistance between the two members to be

joined

 These processes have major advantages, such

as not requiring consumable electrodes,

shielding gases, or flux

R = resistance, in ohms; and

t = time of current flow, in seconds.

Resistance welding (RW)

 The equation above is often modified to

represent the actual heat energy available in the weld by including a factor K which represents

the energy losses through radiation and

conduction

 Thus the equation becomes H = I2RtK, where

the value of K < 1

Resistance welding (RW)

 The total resistance in these processes, such as

in the resistance spot welding shown in the next Figure, is the sum of the following:

a) Resistance of the electrodes

b) Electrode-workpiece contact resistances.

c) Resistances of the individual parts to be welded.

d) Workpiece-workpiece contact resistances (faying

surfaces).

Resistance welding (RW)

 The actual temperature rise at the joint depends

on the specific heat and thermal conductivity of the metals to be joined

 Thus because they have high thermal

conductivity, metals such as aluminum and

copper require high heat concentrations

 Similar as well as dissimilar metals can be joined

by resistance welding

 The magnitude of the current in resistance

welding operations may be as high as 100,000

A, although the voltage is typically only 0.5-10 V

Resistance welding (RW)

 Developed in the early 1900s, resistance

welding processes require specialized

Resistance welding (RW)

 Operator skill required is minimal, particularly

with modern machinery

 Safety precautions are similar to those for other welding operations

 There are five basic methods of resistance

welding: spot, seam, projection, flash, and upset welding

 Lap joints are used in

the first three processes,

and butt joints

in the last two

Resistance Spot Welding

 In resistance spot welding (RSW), the tips of

two opposing solid cylindrical electrodes contact the lap joint of two sheet metals, and resistanceheating produces a spot weld

Resistance Spot Welding

 In order to obtain a good bond in the weld

nugget, pressure is also applied until the current

is turned off

 Accurate control and timing of the electric

current and pressure are essential in resistance welding

 The strength of the bond depends on surface

roughness and the cleanliness of the mating

surfaces

 Thus oil, paint, or thick oxide layers should be

removed before welding

Resistance Spot Welding

 The presence of uniform , thin oxide layers and

other contaminants is not critical

 The weld nugget is generally 6-10 mm

(0.25-0.375 in.) in diameter.

Penampang lasan titik, memperlihatkan manik lasan dan penekanan elektroda pada permukaan pelat Proses ini

merupakan proses yang paling sering digunakan pada pabrikasi lembaran

Resistance Spot Welding

 The surface of the weld spot has a slightly

discolored indentation

 Currents range from 3000 A to 40,000 A,

depending on the materials being welded and their thickness

Resistance Spot Welding

 Process capabilities

{ Spot welding is the simplest and most commonly

used resistance welding process.

{ Welding may be performed by means of single (most common) or multiple electrodes, and the required

pressure is supplied through mechanical or

pneumatic means.

Resistance Spot Welding

 Process capabilities

{ The rocker-arm type spot welding machines are normally used for smaller parts, with press-type machines being used for larger workpieces.

Ilustrasi skematik mesin pengelasan titik dengan lengan

yang dioperasikan dengan rocker-arm pneumatik

Resistance Spot Welding

 Process capabilities, con’t

{ The shape and surface condition of the electrode tip and accessibility are important factors in spot

Resistance Spot Welding

 Process capabilities, con’t

{ Spot welding is widely used for fabricating sheet

metal.

{ Examples range from attaching handles to steel cookware, to rapid spot welding of automobile bodies with multiple electrodes.

stainless-{ An automobile may have as many as 10,000 spot welds.

Examples of Spot Welding

(a) dan (b) peralatan masak dan bagian knalpot yang dilas titik (c) Robot yang dilengkapi dengan mesin pengelasan titik dan dikendalikan dengan

(a)

(b)

(c)

Spot Welding Example

Robot yang dilengkapi dengan peralatan las titik dan dioperasikan dengan pengendalian komputer dalam jalur produksi masa untuk

Resistance Spot Welding

 Process capabilities, con’t

{ Modern equipment used for spot welding is computer controlled for optimum timing of current and pressure and the spot-welding guns are manipulated by

programmable robots.

Mesin pengelasan titik otomatis; ujung pengelasan dapat bergerak dalam tiga arah Lembar seluas 2.2 m X 0.55 m

Resistance seam welding (RSEW)

 Resistance seam welding (RSEW) is a

modification of resistance spot welding, wherein the electrodes are replaced by rotating wheels or

rollers

Proses pengelasan sambungan, dengan rol berputar berfungsi sebagai elektroda.

Resistance seam welding (RSEW)

 With continuous ac power supply, the electrically conducting rollers produce continuous spot welds whenever the current reaches a sufficiently high level in the ac cycle

 These are actually overlapping spot welds and

produce a joint that is liquid tight and gas tight

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