Principle of ultrasonic spot welding machine and introduction of plastic ultrasonic spot welding technology
Ultrasonic spot welding is a method of assembling two thermoplastic plastic parts without forming holes or energy-conducting ribs at a local position. Ultrasonic spot welding produces strong structural welds, which are suitable for large parts, thermoplastic extruded or cast plates, thermoplastic corrugated plates, and workpieces with complex geometric shapes and difficult to access joint surfaces.
Ultrasonic spot welding is often used to connect large metal plates through small local welds. Ultrasonic spot welding of plastics is roughly the same. Compared with other ultrasonic assembly methods, ultrasonic spot welding of plastic parts does not require forming holes or energy-conducting ribs.
1. Principle and mechanism of ultrasonic spot welding machine
The basic principle of ultrasonic spot welding is that the ultrasonic welding head is equipped with a guiding end to guide energy into local points on the upper plate. The ends penetrate the upper plate and enter the lower plate to about half the thickness of the upper plate. Some of the displaced molten plastic is formed into an annular ring by the notch on the guide tip. At the same time, energy is consumed at the interface between the two plates, causing further melting. Some of the molten material on the upper plate is brought into the lower plate, resulting in bonding at the lower plate to form a spot weld. The lower part of the spot weld remains smooth. The mechanism of ultrasonic spot welding is that the guide part of the spot welding tip penetrates the upper part during the ultrasonic vibration process. The displaced molten plastic is molded in the radial resonant cavity of the tip and forms a neat raised ring on the surface of the workpiece. At the same time, energy is released at the interface where frictional heat is generated. When the tip is inserted into the lower section, the displaced molten plastic between the two surfaces flows into the surrounding interface area and forms permanent molecular bonds.
2. Ultrasonic spot welding variants
(1) Inverse spot welding, when inverted spot welding, the fixture is installed with a point welded end, and the flat-bottomed rod-shaped weld head contacts the outside of the part. It can be used where the shape of the part makes ordinary spot welding impractical or requires a blind spot (blind spot). This method can form spot welds on the inner surface.
(2) Custom step tip design (custom step tip design) Custom step tip design is suitable for applications that require a smooth upper surface. Common spot welding tips form too much molten material on the surface, and the cascade design squeezes too much material below the surface. The stepped tip is customized and can be obtained on demand.
3. Features of ultrasonic spot welding
Ultrasonic spot welding can produce strong structural welds, with high bonding strength and short cycle time-generally less than 1s, without the need for molded joint design, and no consumables such as screws, staples, rivets or adhesives, generally There is no need for special fixtures. One side has a beautiful surface and the other side has a neat raised ring. It can be spot welded with a hand-held welding machine, and it can seal multiple layers of materials, which is suitable for automation.
4. Application of ultrasonic spot welding
Ultrasonic spot welding is suitable for large parts, thermoplastic extruded or cast plates, thermoplastic corrugated plates, and workpieces with complex geometries and difficult to access joint surfaces. It is mainly used for flat molded parts without energy guiding ribs, such as semi-finished products, thermoforming, blow molding, extrusion molding, and large flat molded parts. Ultrasonic spot welding is usually used for vacuum forming parts such as blister packs to provide tamper evident sealing. Typical applications of ultrasonic spot welding include fixing of wall panels and ventilation pipes, and spot welding of thermal insulation and plastic parts. It can also be used for large plastic parts such as snowplow parts, trailers, furniture, and parts that require precision or are difficult to weld with ordinary welders.
Typical applications of corrugated plastic:
Compared with other traditional materials, corrugated plastic has the following advantages: It is stronger and more durable than corrugated fiberboard, unlike metal or wood that can rot, rust, mold or corrode, is not affected by moisture, and is resistant to chemicals, grease and dirt. It can be reused. High-density polyethylene (HDPE) corrugated board is most commonly used in corrugated-wall containers. Polypropylene is also frequently used. Typical applications include postal containers, seed trays, meat, fish and agricultural products containers, construction containers, grocery store parts boxes, and turnover boxes. Although special designs including trademarks are available, the cross-shaped structure of the spot welding tip is a typical pattern. Either single-end welding head or multi-end welding head can be used.
In addition to spot welding of double-layer materials, ultrasonic spot welding has been used to seal 6 layers of polypropylene. In order to lower the ultrasonic welding head into the material, it is necessary to use a special welding head with multiple steps to be embedded in each layer. Before the ultrasound is activated, a higher pre-pressure is used to compact each layer. This structure can form very strong spot welds and has a good appearance.
Ultrasonic spot welding is an assembly technology that connects two thermoplastic plastic parts without forming holes or energy-conducting ribs at a local position. The appearance of the bottom layer of the ultrasonic spot welding joint is smooth and clean. There is a raised ring on the surface around the joint.
Ultrasonic spot welding is cost-effective, quick to assemble, does not require additional fasteners, and usually does not require special fixtures. Ultrasonic spot welding can use hand-held welding guns, single-head or double-head desktop spot welding machines, and a group welding device consisting of multiple spot welding heads that can perform multiple welding operations at the same time.
The basic guidelines for ultrasonic spot welding include rigid support under the spot welding area to prevent marks, medium to high amplitude to ensure enough material penetration and low pressure to ensure sufficient melt at the joint surface.
Ultrasonic spot welding produces strong structural welds, which are suitable for large parts, thermoplastic extruded or cast plates, thermoplastic corrugated plates, and workpieces with complex geometries and difficult-to-access joint surfaces. Ultrasonic spot welding is usually used for vacuum forming parts such as blister packs and plastic corrugated boards.