In the process of plastic welding, the joining of two soft plastic material is done in four stages preparation, pressure, heat and then cooling. The creation of strong molecular bonding between the two plastic parts is the objective of the process. Many methods of welding are available for welding in plastic components. On the basis of component type and material weld-ability, the method of welding is adopted. The heat is supplied at the point where the weld joint is to be generated and the pieces are brought together to join them. 

The filler rod is used in the process. When the filler material start melting, the fusion between the specimen and filler material will start. To obtain a good quality weld joint, the good material for filler rod is necessary. A good filler material will contain the porosity as less as possible. The porosity diminishes the quality of joint. The use of filler material is optional, it can be avoided by using an appropriate method of welding in which filler material is not necessarily used. Thermosetting plastics cannot be joined by this method. Neither, it can be used as a filler material.

Plastic Welding Process:-

As mention above the process will be done in four stages –
  1. Preparation: - in the preparation of plastic welding the surfaces of the specimen are cleaned up. The surface should be free of dust, slag, oil etc. the appropriate method should be determined and equipment of that method should be arranged.
  2. Pressure: - this process of welding is performed by keeping the workpieces under pressure. There are certain advantages of using pressure during welding. It compresses the workpieces with the heat and create better bonding in the material on the molecular level. Problem of blow holes can be reduced because of compression. Pressure helps to retain the location and alignment of workpieces and better contact can be maintained between the surfaces of the workpieces.
  3. Heat: - this is the important part of the process when the joint is produced by applying the heat on the specimen. At the mating surface of specimen, the heat is provided to melt the material then the fusion process will start. And bonding at molecular level will be created. For better joints, the elevated temperature should be high. The higher presence of heat will cause the high quality of molecular bonding. Plastic welding is not a time taking process because very small portion of workpieces would be melted. Higher temperature will help in getting a tough joint without heating large area of the workpieces.
  4. Cooling: - After the material successfully passed from heating stage. The cooling of the parts will be done. This provides hardness and toughness to the joint. A proper cooling is important in the plastic welding, otherwise the joint would be weak and brittle. It is basically the recrystallization of material where the refinement of grain structure of material will happen. A good micro structure can be obtained by providing a proper cooling time to the system.
Welding methods used for plastic welding: -
  • Arc welding
  • Gas welding
  • Friction welding
  • Spin welding (spinning)
  • Injection welding
  • Ultrasonic welding, etc.

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