Welding of plastic

May 1, 2023 welding of plastic 1

• Presented By:• SHYED FARHAN ALI• Chemical Engg. (IIIrd Year)• 1413351903

WELDING OF PLASTIC


CONTENT

1. Introduction2. Classification of plastic welding3. Welding Rod4. Hot Sealing5. Hot plate welding6. Hot gas welding7. Ultrasonic welding8. Friction welding9. Laser welding


INTRODUCTION

Mechanical fasteners, adhesives, and welding processes can all be employed to form joints between engineering plastics. Mechanical fasteners can join two components quickly, but they do not provide leak tight joint, and the localized stresses may cause them to pull free of the polymeric material. Adhesives can provide good properties and fully sound joints, but they are difficult to handle and slow to cure. Also joint preparation & surface cleanliness need to be given importance in adhesive bonding. Welding can be used to produce bonded joints with mechanical properties that approach those of parent material. The plastic welding is confined to thermoplastic polymers because these materials can be softened by heat. Thermosetting polymers once hardened cannot be softened again on heating. The heat required for welding thermoplastic polymers is less than that required for metals. Plastic welding processes can be divide into two groups: - a) Processes involving mechanical movement – ultrasonic welding, friction welding,

vibration welding. b) Processes involving external heating – hot plate welding, hot gas welding and

resistive and implant welding



CLASSIFICATION OF PLASTIC WELDINGWelding process are categorized by the heating method that is used.Two general categories are:• External heating• Internal heatingExternal heating:• It rely on convection & conduction to heat the weld surface.• Hot tool, hot gas, extrusion, implant induction, implant resistance

weldingInternal heating:• It rely on conversion of mechanical energy into heat through

surface friction. • Further divided into internal mechanical, Internal

electromagnetic heating Ultrasonic , Friction , Laser , RF welding.


Welding RodA plastic welding rod, also known as a thermoplastic welding rod, is a rod with circular or triangular cross-section used to bind two pieces of plastic together. They are available in a wide range of colors to match the base material's color. Spooled plastic welding rod is known as "spline".


Heat SealingHeat sealing is the process of sealing one thermoplastic to another similar thermoplastic using heat and pressure. The direct contact method of heat sealing utilizes a constantly heated die or sealing bar to apply heat to a specific contact area or path to seal or weld the thermoplastics together. Heat sealing is used for many applications, including heat seal connectors, thermally activated adhesives and film or foil sealing.


High temperature hot plate welding:

• The tool is not coated with release agent.

• The tool is heated to 300c to 400c.• Once the parts are disengaged fro the

tool any residual material is either oxidized away or mechanically removed.

Non contact hot plate welding:• 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.


Applications of hot plate welding:• Polyethylene (PE) pipe

welding for gas line installations.

• Fuel tank assemblies for the automotive industries.

Limitations:• 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 WeldingThis 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.Compressed air, nitrogen, hydrogen, oxygen or carbon dioxide is heated by an electric coil as it passes through a welding gun.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.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.


Applications of hot gas welding:• It is used for fabricate pipelines,

pond liners, and a wide variety of vessels.

• Used to join broken plastics easily.

Advantages :• Easy to use.• Thermoplastics can be welded

easily.Limitations:• Slow manual process cannot be

used in mass production.


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 -field0 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.


Advantages:• Used in mass production because the

welding time are relatively short.• Applicable for both amorphous and semi

crystalline thermoplastics.• Used to bond dissimilar materials.

Limitations:• Horn size is limited to design constraints.• The process and tools must be adapted to

the materials to be welded.

Applications :• Food packaging, computer components,• Challenging and critical application is the

standard disposable butane lighter.


• The friction welding of thermoplastic (also called spin welding) is based on the same principle as that employed for welding metals.

• In this process one of the substrates is fixed, while the other is rotated with a controlled angular velocity.

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

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

There are four main variations :• Linear welding• Orbital welding• Spin welding• Angular welding

Friction Welding


Advantages:The advantages of friction welding are high weld quality and the simplicity and reproducibility of the process.

Limitations:It is suitable only for applications in which at least one of the components is circular and requires no angular alignment.

Applications:Used to make thermoplastic manifolds for the automotive industries


LASER WELDING There are two modes of laser beam welding:

• Surface heating• Through transmission infrared (TTIr) welding

Surface heating:• 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.

• 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.

TTIr welding:• 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.

• This absorption results in heating and melting of the interface and allows the parts to be welded.


Advantages of TTIr welding:• It is a pre-assembled method.• Speed and flexibility.• It can also weld unsupported internal

walls with complex curvature if the optical properties.

• Weld quality is very good.

Limitations of TTIr welding:• One of the component must be

relatively transparent to IR radiations.

Applications:• Brake fluid reservoirs, automotive

marking lights.


REFERENCES

1)E.Paul Degarmo, J.T Black, Ronald A Kohser, Materials and processes in manufacturing, Prentice Hall, India.2)Robert A Grimm, Welding processes for plastics, Advance materials and processes, vol 147, 1995.3)Joining plastics in production, The welding institute4)Grewell D.A.; Benatar A.; Park J.B. (2003). Plastics and Composites Welding Handbook. Hanser Publishers, Munich.5) www.google.com6)www.wikipedia.com

http://www.wikipedia.com/


THANK YOU

Engineering

Welding of plastic