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What Are The Factors That Affect Ultrasonic Welding?

Ultrasonic welding uses high-frequency vibration to transmit to the surfaces of two objects to be welded. Under pressure, the surfaces of the two objects are rubbed against each other to form fusion between the molecular layers. During the soldering process, there are occasional glitches. What are the main factors that affect the success of welding?

1. Welding system frequency

Typical welding system frequencies are 15Khz, 20Khz, 30Khz, 35Khz and 40Khz. It is necessary to select a suitable welding frequency according to the requirements of product size, internal component type, strength and appearance.

2. Materials

For the welding of plastics, only thermoplastics are suitable for welding. Because they can melt within a specific temperature range. Thermosetting plastics degrade when heated and cannot be welded using ultrasonic waves.

The weldability of thermoplastics depends on material stiffness or elastic modulus, density, coefficient of friction, thermal conductivity, specific heat capacity, glass transition temperature Tg or melting temperature Tm.

Generally speaking, rigid plastics exhibit excellent far-field welding performance because they transfer vibrational energy more easily. Soft plastics with low elastic modulus are more difficult to weld because they attenuate ultrasonic vibrations. The opposite is true for ultrasonic riveting or spot welding. The softer the plastic, the easier it is to rive or spot weld.

3. Welded joint design

The most critical and important factor affecting welding is the joint design. Engineers should carefully consider and evaluate when a part is in the design stage. Welded joints are available in a variety of designs, each with their own characteristics and advantages. Which design to choose depends on the type of plastic, part geometry, welding requirements, injection molding capabilities, appearance requirements, etc.

4. Tooling and welding head

Generally speaking, customers will choose the same brand of tooling and welding head as the welding machine. In fact, you can freely choose tooling and welding heads from other brands, as long as the welding head frequency is the same as the equipment.

The welding head material can choose aluminum alloy, titanium alloy and hard alloy steel. Tooling materials can choose aluminum alloy, stainless steel and resin mold. How to choose a material generally takes into account the type of plastic, glass fiber content of the material, joint structure and size, welding strength and service life. For example, for extended life, carbide-steel horns are an excellent choice.

5. Welding parameters

During the welding process, the welding parameters will affect the welding result. These parameters include amplitude, weld pressure, trigger pressure, weld distance, and weld energy.

Different types of plastics require different amplitudes. The amplitude can be fine-tuned by the percentage setting in the software, or can be adjusted in a large range by changing the amplitude modulators with different ratios. Welding pressure can be adjusted by knob or software setting. Trigger pressure means that when the welding head presses the product and the pressure reaches a certain set value, the device starts to emit ultrasound, and the value can be adjusted through the knob or software settings.