1. Welding of plastics
Presented By:
K. Ashish (11681A0328)
CHRISTU JYOTI INSTITUTE OF TECHNOLOGY & SCIENCE
COLOMBONAGAR, YESHWANTHAPUR, JANGOAN, DIST: WARANGAL
2. Contents
0 Introduction
0 Classification of plastic welding
0 Hot plate welding
0 Hot gas welding
0 Ultrasonic welding
0 Friction welding
0 Laser welding
0 Conclusion
0 References
3. Introduction
0 There are many products too complex to model as a single part. Thus
assembly of sub-components is critical for manufacturing of many
products.
0 The methods for joining plastic components can be divided into three
major categories:
0 Mechanical joining
0 Adhesive bonding
0 Welding
4. 0 Mechanical joining:
0 Mechanical fasteners can join two
components quickly.
0 Use of metallic or polymeric screws, snap-fit,
press –fit.
0 they do not provide leak tight joint.
0 Adhesive bonding :
0 An adhesive is placed between the parts it
serves as the material that joins the part &
transmits load .
0 provide good properties and fully sound join
ts, but they are difficult to handle and slow to
cure.
0 Welding:
0 in welding heat is to melt or soften the
polymer at the interface to be welded
0 Welding can be used to produce bonded
joints with mechanical properties that
approach those of parent material.
5. Classification of plastic welding
0 Welding process are categorized by the heating
method that is used.
0 Two general categories are:
0 External heating
0 Internal heating
0 External heating:
0 It rely on convection & conduction to heat
the weld surface.
0 Hot tool, hot gas, extrusion, implant
induction, implant resistance welding
0 Internal heating:
0 It rely on conversion of mechanical energy
into heat through surface friction.
0 Further divided into internal mechanical,
Internal electromagnetic heating
0 Ultrasonic , friction , laser , RF welding.
6. Hot plate welding
0 It is the simplest of the mass production techniques to join plastics.
0 A heated plate is clamped between the surfaces to be joined until they
soften.
0 The plate is then withdrawn and the surfaces are brought together again
under controlled pressure for a specific period.
0 The fused surfaces are allowed to cool, forming a joint.
0 The tool is often coated with non-stick material ( teflon) to act as a
release agent.
0 Hot plate welding includes two kinds:
0 High temperature hot plate welding.
0 Non contact hot plate welding.
7. 0 High temperature hot plate
welding:
0 The tool is not coated with release
agent.
0 The tool is heated to 300c to 400c.
0 Once the parts are disengaged fro
the tool any residual material is
either oxidized away or
mechanically removed.
0 Non contact hot plate welding:
0 the parts to be welded are bought
near to the tool (1 to 3mm) and
convection and radiation heating
from the tools heats the welding
surfaces.
8. 0 Applications of hot plate welding:
0 Polyethylene (PE) pipe welding for
gas line installations.
0 Fuel tank assemblies for the
automotive industries.
0 Limitations:
0 One major limitation to hot plate
welding is cycle time. A typical
cycle time is 30 to 0 seconds and
larger with larger parts it can be
as long as 30 minutes
9. Hot gas welding
0 This is similar to oxy-acetylene welding of metals. The only difference is
that the open flame of oxy-acetylene welding is replaced by a stream of
hot gas.
0 Compressed air, nitrogen, hydrogen, oxygen or carbon dioxide is heated
by an electric coil as it passes through a welding gun.
0 The process, invented in the mid 20th century, uses a stream of heated
gas, usually air, to heat and melt both the thermoplastic substrate
material and the thermoplastic welding rod.
0 To ensure welding takes place, adequate temperature and pressure must
be applied to the rod, along with the use of the correct welding speed and
gun position.
10. 0 Applications of hot gas welding:
0 It is used for fabricate pipelines,
pond liners, and a wide variety of
vessels.
0 Used to join broken plastics easily.
0 Advantages :
0 Easy to use.
0 Thermoplastics can be welded
easily.
0 Limitations:
0 Slow manual process cannot be
used in mass production.
11. Ultrasonic welding
0 This method uses mechanical vibrations to form the joint. The vibrations are of high
frequency.
0 The parts to be assembled are held together under pressure between the oscillating
horn and an immobile anvil and are subjected to ultrasonic vibrations of frequency
20 to 40 KHz at right angles to the contact area.
0 Alternating high frequency stresses generate heat at joint interface to produce a
good quality weld.
0 ultrasonic welding is divided into two major groups:
0 Near -field
0 Far –field
0 Near-field :
0 The distance between the horn and the weld interface less than 6mm.
0 Far-field:
0 The distance between the horn and the weld interface is greater than 6mm.
12. 0 Advantages:
0 Used in mass production because the
welding time are relatively short.
0 Applicable for both amorphous and
semi crystalline thermoplastics.
0 Used to bond dissimilar materials.
0 Limitations:
0 Horn size is limited to design
constraints.
0 The process and tools must be
adapted to the materials to be welded.
0 Applications :
0 Food packaging, computer
components,
0 Challenging and critical application is
the standard disposable butane
lighter
13. Friction welding
0 The friction welding of thermoplastic (also called spin welding) is based
on the same principle as that employed for welding metals.
0 In this process one of the substrates is fixed, while the other is rotated
with a controlled angular velocity.
0 When the parts are pressed together, frictional heat causes the polymer
to melt and a weld is created on cooling.
0 Major welding parameters include rotational speed, friction pressure,
forge pressure, weld time and burn off length
0 There are four main variations :
0 Linear welding
0 Orbital welding
0 Spin welding
0 Angular welding
14. 0 Advantages:
0 The advantages of friction welding
are high weld quality and the
simplicity and reproducibility of
the process.
0 Limitations:
0 It is suitable only for applications
in which at least one of the
components is circular and
requires no angular alignment.
0 Applications:
0 Used to make thermoplastic
manifolds for the automotive
industries
15. Laser welding
0 There are two modes of laser beam welding:
0 Surface heating
0 Through transmission infrared (TTIr) welding
0 Surface heating:
0 The surfaces of the components to be joined are heated by direct IR/laser exposure
for a sufficient length of time to produce a molten layer, usually for 2 to 10 s.
0 Once the surface is fully melted, the IR/laser tool is with drawn from between the
parts, the parts are forged together, and the melt is allowed to solidify.
0 TTIr welding:
0 It is based on the concept of passing laser radiations through one of the component
to be welded while having the second component absorb the light at the interface.
0 This absorption results in heating and melting of the interface and allows the partsto
be welded.
16. 0 Advantages of TTIr welding:
0 It is a pre-assembled method.
0 Speed and flexibility.
0 It can also weld unsupported internal
walls with complex curvature if the
optical properties.
0 Weld quality is very good.
0 Limitations of TTIr welding:
0 one of the component must be
relatively transparent to IR radiations.
0 Applications:
0 Brake fluid reservoirs, automotive
marking lights.
17. Conclusion
0 Two type of plastic welding's:
0 External heating
0 Internal heating
0 External heating :
0 hot tool, hot gas, implant induction, implant resistance welding.
0 Internal heating
0 Ultrasonic , friction , laser , RF welding.
0 Hot gas welding is easy to use and used to weld the broken plastic with
low cost
0 TTIr welding is latest most efficient of all types but one of the work piece
should b transparent to IR radiations .
18. references
0 1)E.Paul Degarmo, J.T Black, Ronald A Kohser, Materials and processes in
manufacturing, Prentice Hall, India.
0 2)Robert A Grimm, Welding processes for plastics, Advance materials and
processes, vol 147, 1995.
0 3)Joining plastics in production, The welding institute
0 4)Grewell D.A.; Benatar A.; Park J.B. (2003). Plastics and Composites
Welding Handbook. Hanser Publishers, Munich.
0 5) www.google.com
0 6)www.wikipedia.com
