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Brief Introduction to Principles of Different Welding Methods
Ultrasonic Welding:
The ultrasonic plastic welding technology uses a signal generator to generate a high-frequency sine wave signal, which is converted to high-frequency mechanical vibrating energy through a transducer. The vibration is enlarged and coupled on the plastic workpiece to be welded by an amplitude transformer bar and a welding head. The high-frequency friction under high pressure can generate an instant high temperature on the contact plastic surface and melt it. After a short period of pressure retaining and cooling when the ultrasonic stops, the two plastic workpieces are welded together. Normally, the entire welding process lasts less than 1s and the weld joint has the same strength as the base material.
The ultrasonic welding has the advantages of fast speed, low operation cost and good appearance and is the preferred process for the batch production of secondary connection of small thermoplastic parts such as electronic packaging, plastic stationery and disposable medical consumables, etc..
After adjustment of the ultrasonic handpiece and the tool equipment, the ultrasonic welder can also be used for rivetting welding, spot welding, seam welding, forming, splitting and implanting.
Hot Plate Welding:
A hot metal plate is used to directly heat the surface of plastic part to be welded. The hot plate will be removed when the desired penetration depth is reached and the two plastic parts are pressed together and cool down while keeping the pressure, thus fulfilling the purpose of welding.
The hot plate welding, not limited by the part material and size and having good welding tightness, can be used for the welding of ultrasonic refractory plastic parts, such as PP and nylon, and big-size profiled workpieces, such as combination auto lamp, extension tanks and household appliance parts.
Spin friction welding:
During welding, one plastic part is fixed and the other is driven by a motor for high speed rotation to make relative friction on the contact surfaces of the two plastic workpieces and generate high temperature for melting. When stopping, the pressure applied on the workpieces enables the two workpieces to solidify together.
Enjoying high welding strength and good tightness, the spin friction welding is not limited by workpiece material and size and can be used for welding of revolved workpieces with heavy wall thickness and high demand of connecting strength, such as high pressure water valves, industrial filter elements, offshore floats, oil track plugs of automobile engines, etc..
If a servo motor is used for driving, accurate angular positioning of the workpiece can be achieved.
High-frequency Welding:
High-frequency electric field generated by a vacuum tube selfoscillator enables internal molecules to perform high-frequency movement and generate heat from impact. Then the material is pressed fit to fulfill the purpose of welding.
High-frequency welding is only applicable to thermal sealing of plastic film having polar molecules, such as trademarks, raincoats, plastic bags and water beds, etc..

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