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With the implementation of the concept of green environmental protection in industrial production all over the world and the consideration of cost control, plastics, as a kind of renewable non-metallic materials with excellent performance, are increasingly widely used in the design and manufacturing of parts and components in various industries. Traditional metal components are increasingly replaced by plastic components with the same working performance, At the same time, higher requirements are also mentioned for the welding connection technology and welding quality between plastic parts. These changes provide an opportunity for the use of laser welding technology at the level of plastic materials.
● ultrasonic welding
Ultrasonic welding produces joints through high-frequency mechanical vibration. The component to be assembled is pressurized and clamped between the oscillating welding head and the fixed welding head, then at right angles to the contact surface, and receives ultrasonic vibration with a frequency of 20 ~ 40KHz. Alternating high-frequency stress generates heat at the joint interface, resulting in high-quality welding.
The tools used for this process are very expensive, so they are suitable for large production. The application fields include common valves and screening procedures for welding medical equipment on multi head machines, boxes, automotive parts, vacuum cleaner housings, etc.
● friction welding
Friction welding of thermoplastics (also known as "rotary welding") is based on the same principle as metal welding. In this type of welding process, one substrate is fixed and the other substrate rotates at a controlled angular speed. When the components are pressed together, the friction heat causes the polymer to melt, and welding occurs after cooling. Friction welding can produce excellent welding quality, simple welding process and strong repeatability. It is only suitable for the application field where at least one component is circular without angular alignment.
● vibration welding
Vibration welding is also called linear friction welding. The two thermoplastic members rub against each other under appropriate pressure, frequency and amplitude until sufficient heat is generated to melt the polymer. After the vibration stops, the components are aligned with each other, and the molten polymer solidifies to produce welding.
The main advantage of this welding process is that it can weld large complex linear components at high speed. Other strengths include: being able to weld multiple components at the same time, simple welding tools, and basically welding all thermoplastic materials, mainly used in automobile and household appliance industries.
● hot plate welding
For plastic bonding, hot plate welding is a relatively simple mass production technology. The high-temperature hot plate is clamped between the surfaces to be jointed until it softens. At this time, the hot plate is pulled out, the two surfaces are bonded under controlled pressure, and closed together after maintaining for a specific period of time. The molten surface is then allowed to cool to produce welding. The welding tool or heating component is equipped with a built-in electric heater to prevent plastic from adhering to the welding tool.
This welding process is used for a variety of daily necessities, such as vacuum cleaner housing, washing machine and dishwasher components, brake fluid tank, rear light, indicator light and other automotive parts. The disadvantage of hot plate welding method is that the welding speed is slow.
● hot gas welding
Hot gas welding uses a heated air stream (usually air) to heat and melt thermoplastic substrates and thermoplastic electrodes. The base material and welding rod are melted to produce a weld. In order to ensure reasonable and effective welding, appropriate temperature and pressure must be applied to the welding rod, and appropriate welding speed and welding gun position shall be ensured. The main applications include the maintenance of injection molded parts such as chemical storage containers, ventilation ducts and automobile bumpers. Nitrogen is used for oxygen sensitive materials, such as polyethylene; Oxygen produces higher welding strength.
The main advantage of this welding method is that it can weld large and complex components, but the welding speed is slow, and the welding quality completely depends on the welder's skills.
● implant welding
In implant welding, metal inserts are first clamped between components to be welded, and then heated by induction or resistance. When resistance welding is used, it is specified to place wires along the joint to conduct current into the implant; This method is not used when induction welding is used. Implant welding has been used to weld complex joints of large components, including automobile bumpers, electric vehicles and yacht hull.
● principle of plastic laser welding
The most common laser welding method is called laser transmission welding. Firstly, two plastic parts to be welded are clamped together under pressure, and then a short wave infrared laser is directed to the part to be bonded.