05 welding processes 6 friction welding

welding processes6 friction welding

Friction Welding

FIGURE 31.3 Sequence of operations in the friction-welding process:

(1) The part on the left is rotated at high speed; (2) The part on the right is

brought into contact with the part on the left under an axial force; (3) The axial

force is increased, and the part on the left stops rotating; flash begins to form:

(4) Afler a specified upset length or distance is achieved, the weld is

completed The upset /ength is the distance the two pieces move inward during

welding after their initial contact; thus, the total length after welding is less than

the sum of the lengths of the two pieces The flash subsequently can be

removed by machining or grinding

1

~ :

Force increased

Flash

{ | Lg Force Beginning of flash

Vv

Speed / Y

à `

Force

Upset jengin

Time

if &

Tota! upset length

>

Friction Welding

The heat required for the weld is generated through friction at the interface One component remains stationery

The other component is gripped in a chuck and rotated at high constant speed

The two members brought together with axial force

After sufficient contact, the rotating member is stopped while axial force is

increased

Oxides & other contaminants at the interface are removed by radial outward

movement of hot metal at the interface

Friction Welding

FIGURE 31.4 Shape of the fusion zones in friction welding as a

function of the axial force applied and the rotational speed

{a) High pressure

or low speed

oc

(b) Low pressure

or high speed

(c) Optimum

Friction Welding

The shape of the welded joint depends on the rotational speed and axial

pressure

Friction welding machines are fully automated

Low operator skill level required

FW can be used to join a wide variety of materials

- Provided that one of the components has some rotational symmetry

Solid or tubular parts can be joined with good joint strength

Because of the combined heat and pressure, the interface develops a flash by

plastic deformation of the heated zone

If desired, the flash can be removed by machining or grinding

Friction Welding

Inertia Friction Welding

A modification of Friction Welding

The necessary energy is supplied by the kinetic

energy of a rotating flywheel

Linear Friction Welding

Use linear reciprocating motion (not rotational)

Process suitable for welding square or

rectangular parts

Metals or plastics

Friction Welding — Ultrasonic Welding

FIGURE 31.2 (a) Components of an ullrasonic-welding machine for

making lap welds The lateral vibrations of the tool tip cause plastic

deformation and bonding at the interface of the workpieces

(b) Ultrasonic seam welding using a roller as the sonotrode

Force

Transducer Mass

Toolholder

Roller Transducer DC

Direction of

Anvil

†

Roller

Workpieces

Support

Friction Welding — Ultrasonic Welding

Ultrasonic Welding

Process is versatile and reliable

Used with wide variety of metallic & non-

metallic materials

— Including dissimilar metals (bimetallic strips)

Useful for:

— Joining plastics

— Packaging with foils

— Lap welding of sheet, foil, thin wire

— Seam welding if one material is:

* sheel, foil, polymer-woven material

Friction Welding — Ultrasonic Welding

Ultrasonic Welding

(a) Lap welds

The faying surfaces of the two components are subjected to:

Static Normal force (applied through sonotrode)}

Oscillating shearing (tangential) stresses (applied by tip of transducer)

Efficient operation depends on proper coupling between transducer and sonotrode Shearing stresses cause plastic deformation at interface; creating clean surfaces for

bonding

Temperatures 1/3 — 1/2 melting point (therefore no melting or fusion)

Different joining mechanism for plastics because plastics have lower melting point

and there is some fusion

(b) Seam welding using roller as sonotrode

The welding tip is replaced by rotating disks for the seam welding of structures in which one component is sheet, foil or polymer-woven material

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