Plastic welding is a welding process in which a molecular bond is created between two compatible thermoplastics. This welding usually offers extreme reduced cycle times and superior strength to chemical bonding and mechanical joining. When welding thermoplastics, generally there are three main steps, namely pressing, heating, and cooling. Pressure is applied, often throughout the stages of heating and cooling, as a result of which melt flow is improved across the interface and proper orientation of the parts is maintained. Plastic welding tools are easily available from plastic welding equipment suppliers. 1. Common Plastic For Welding Plastics are known as plastics for their plasticity, or malleability. In comparison to metals like iron and steel that are used for welding, welding plastics is not as complicated. Barely any equipment is required for the processes that can be readily used to weld the most common plastics. Although the list may not be very comprehensive, the most common plastics that can be used for welding include acrylic and nylon; polycarbonate, polypropylene, polystyrene, polyurethane and polyvinyl chloride or PVC. 2. Pressure There are multiple reasons pressure is used when welding plastics. Primarily, melt layer is compressed so that intermolecular diffusion is encouraged between the two parts, orientation of part is the maintained, surface asperities are flattened so that part contact increases at the joint, and voids from part shrinkage are prevented from forming during cooling. In the past, pneumatic presses were used to apply pressure when for plastic welding, but recently, servo motors have been used for greater control and precision. Now, even Custom Hot Plate, Spin and Ultrasonic servo-driven welders are available from plastic welding equipment suppliers. 3. Heating Forming a melt surface at the surface being fayed is crucial so that intermolecular diffusion occurs and a molecular bond is formed. Polymer chains do not flow in the solid state. Thus, it becomes necessary to melt the joint surface on each part to ensure the diffusion of the plastic molecules across the interface so that the molecules of one part bond with those of the other part. Depending on how much the joint surface is melted, the more possible it becomes to achieve greater molecular movement, and the cycle
time of the welding process is reduced. It is crucial to heat amorphous polymers above their glass transition temperature while it is crucial to heat semi-crystalline polymers above their melting temperature. 4. Cooling The welding is completed once a single solid part is formed after the hardening of the bonded polymer during the cooling stage. The cooling stage for semi-crystalline materials is referred to as the “hold” phase, during which the polymer gets the opportunity to re-crystallize. The final microstructure depends on the rate of cooling. For amorphous polymers, the microstructure solidifies during the cooling stage into the orientation that the melt flow tends to create. The final weld strength depends on the time consumed during the heating stage, the amount of pressure applied during the cooling stage, and the rate of cooling. 5. Techniques There are quite a few potential methods of welding plastics, such as Hot Plate, Implant, Infrared / Laser, Radio Frequency, Spin, Ultrasonics, and Vibration, which are the most common. Primarily, it is the heating methods used during these processes that distinguish them from each other. Different plastic welding machines also have varying in their allowances for cooling and application of pressure. Conclusion Plastic welding is often the most convenient and least costly option when a broken piece of plastic needs to be repaired or two pieces of plastic have to be fused together. This is particularly true since plastic welding machines and tools are readily available from plastic welding equipment suppliers.