Ultrasonic welding principle:

Applying ultrasonic waves to the contact surface of thermoplastic plastics will produce tens of thousands of high-frequency vibrations per second. After the high-frequency vibrations reach a certain amplitude, the ultrasonic energy will be transmitted to the welding area through the upper weldment. Due to the large acoustic resistance of the welding area, that is, the two welding interfaces, local high temperatures will occur. In addition, due to the poor thermal conductivity of plastic, it cannot be dissipated in time and accumulates in the welding area, resulting in rapid melting of the contact surface of the two plastics, coupled with fusion under a certain pressure. After the ultrasonic wave stops, the pressure continues for a few seconds to solidify and form a strong molecular chain to achieve the purpose of welding.


Advantages of ultrasonic welding:

Short welding cycle;
Support non-planar welding.

 Disadvantages of ultrasonic welding:

There are flash edges, which are prone to debris;
High mechanical stress;
Processing materials are limited by shape and size.


In laser projection welding, the laser beam penetrates the upper projection part and irradiates the lower laser-absorbing part. The laser energy is converted into heat from the energy absorbed by the dye or auxiliary particles in the absorbing part. The absorbing component melts, and by thermal conduction, the heat is conducted to the upper projection component. Before welding begins, the two parts come into contact with each other under external pressure. During the welding process, the part is locally heated, and the thermal expansion of the material provides additional internal welding pressure. Under the combined action of internal and external welding pressure, the two parts are firmly welded together. The relative movement of the laser beam and the welding component travels throughout the welding.

Advantages of laser plastic welding:

Welding equipment does not need to come into contact with the bonded plastic parts;
fast;
No rough edges;
Strong welding;
Can produce air-tight or vacuum-tight structures;
Reduce thermal damage and thermal deformation;
Resins of different compositions or colors can stick together;
Equipment maintenance costs are low.

 

Disadvantages of laser plastic welding:

The initial equipment investment cost is high;
There are special requirements for substrate performance;

          
Compared with ultrasonic welding, the advantages of laser welding for welding plastic parts include: high welding precision, firm sealing, airtightness, and watertightness, less resin degradation during the welding process, less debris generated, and the product surface can be around the weld tight connection. Laser welding has the advantage of leaving no residue and is more suitable for pharmaceutical products and electronic sensors controlled by the State Food and Drug Administration.

It is easy to control and can weld workpieces with small size or complex shape and structure. Because the laser is easy to control with computer software, the laser output can flexibly reach every detail of the part. Laser welding can weld areas that are difficult to reach with ultrasonic welding methods, and weld products with complex shapes or even three-dimensional geometries.

Compared with ultrasonic welding methods, laser welding greatly reduces the vibration stress and thermal stress of the product. This means that the internal components of the product or device will age more slowly and can be used on products that are easily damaged. A variety of different materials can be welded. For example, polycarbonate can be joined by near-infrared laser, and glass fiber reinforced black polybutylene terephthalate can be joined, but ultrasonic welding methods cannot achieve this.