Welding of plastics

Welding of plastics

Presented By:

K. Ashish (11681A0328)

CHRISTU JYOTI INSTITUTE OF TECHNOLOGY & SCIENCECOLOMBONAGAR, YESHWANTHAPUR, JANGOAN, DIST: WARANGAL

Contents

0 Introduction

0 Classification of plastic welding

0Hot plate welding

0Hot gas welding

0Ultrasonic welding

0 Friction welding

0 Laser welding

0 Conclusion

0References

Introduction

0There are many products too complex to model as a single part. Thus assembly of sub-components is critical for manufacturing of many products.

0The methods for joining plastic components can be divided into three major categories:

0 Mechanical joining

0 Adhesive bonding

0 Welding

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.

Classification of plastic welding0 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.

Hot plate welding

0 It is the simplest of the mass production techniques to join plastics.

0A heated plate is clamped between the surfaces to be joined until they soften.

0The plate is then withdrawn and the surfaces are brought together again under controlled pressure for a specific period.

0The fused surfaces are allowed to cool, forming a joint.

0The tool is often coated with non-stick material ( teflon) to act as a release agent.

0Hot plate welding includes two kinds:0 High temperature hot plate welding.

0 Non contact hot plate welding.

0High 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.

0Non 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.

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

Hot gas welding

0This 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.

0The 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.

0To 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.

0Applications 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.

0Advantages :

0 Easy to use.

0 Thermoplastics can be welded easily.

0 Limitations:

0 Slow manual process cannot be used in mass production.

Ultrasonic welding0 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.

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

Friction welding0The 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.

0When the parts are pressed together, frictional heat causes the polymer to melt and a weld is created on cooling.

0Major welding parameters include rotational speed, friction pressure, forge pressure, weld time and burn off length

0There are four main variations :0 Linear welding

0 Orbital welding

0 Spin welding

0 Angular welding

0Advantages:

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.

0Applications:

0 Used to make thermoplastic manifolds for the automotive industries

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 partstobe welded.

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.

Conclusion

0Two type of plastic welding's:

0External heating

0 Internal heating

0External heating :0 hot tool, hot gas, implant induction, implant resistance welding.

0 Internal heating

0Ultrasonic , friction , laser , RF welding.

0Hot gas welding is easy to use and used to weld the broken plastic with low cost

0TTIr welding is latest most efficient of all types but one of the work piece should b transparent to IR radiations .

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