Ultrasonic welding is a precise and efficient method for joining thermoplastic materials. To achieve strong and leak-proof welds, it is crucial to understand and control various factors that directly influence the welding process. These controllable parameters, including down speed, amplitude, welding time, holding time, and welding pressure, play a significant role in determining the quality and integrity of the final weld. This blog explores these factors in detail, providing insights into how they can be optimized for superior welding performance.

1. Down Speed: Ensuring Controlled Approach

What is Down Speed? Down speed refers to the vertical velocity at which the ultrasonic welding machine’s carriage moves toward the part to be welded. This movement begins from the carriage's rest position and continues until the welding horn makes contact with the part.

Why is it Important? Controlling the down speed is essential, particularly in applications involving thin films or delicate materials. A slower down speed allows for a gentler approach, reducing the risk of damaging the part or misaligning the welding components. If the down speed is too fast, it can cause the horn to impact the fixture abruptly, leading to poor weld quality or even part damage.

Optimal Settings: For thin films, it is recommended to set the down speed on the lower end of the scale. For example, a setting of 1.5 on a scale from 0 to 10 is often ideal, where 0 prevents any carriage movement. This careful control ensures a smooth and controlled descent, allowing for precise alignment and better welding outcomes.

2. Amplitude: The Critical Welding Parameter

What is Amplitude? Amplitude in ultrasonic welding refers to the peak-to-peak displacement of the ultrasonic horn during the welding process. It determines the intensity of the ultrasonic vibrations transmitted to the parts being welded.

Why is it Important? Amplitude is arguably the most critical factor in ultrasonic welding. It directly influences the energy transfer to the welding interface, affecting the melting and bonding of the materials. Properly adjusted amplitude ensures that sufficient energy is applied to create a strong weld without causing material degradation or excessive flash.

How to Calculate Amplitude: Amplitude can be calculated using the following equation:

Equation 1: A_output = A_conv × G_booster × G_horn

Where:

• A_output is the output amplitude at the horn,
• A_conv is the converter's average output amplitude (provided by the manufacturer),
• G_booster is the gain of the booster,
• G_horn is the gain of the horn.

Example Calculation: Given that A_conv = 17 μm, G_booster = 1.5, and G_horn = 2.2, the output amplitude at the horn would be:

A_output = 17 μm × 1.5 × 2.2 = 56.1 μm

This calculation provides a clear understanding of how to achieve the desired amplitude for optimal welding performance.

3. Welding Time: Controlling Energy Application

What is Welding Time? Welding time is the duration during which the ultrasonic vibrations are applied to the part. It is the period over which the ultrasonic stack (converter, booster, and horn) is actively transmitting energy to the materials being welded.

Why is it Important? The welding time determines how long the materials are exposed to ultrasonic energy, influencing the amount of heat generated and the extent of material melting. Too short a welding time may result in insufficient bonding, while too long a time could lead to excessive melting, material degradation, or flash.

Optimal Range: In practice, the welding time should be carefully adjusted based on the material properties and the desired weld strength. A typical range might be between 0.5 to 2.0 seconds, depending on the specific application. Fine-tuning within this range can help achieve a balance between strong bonding and minimal flash.

4. Holding Time: Ensuring Solidification and Bonding

What is Holding Time? Holding time refers to the period during which pressure is maintained on the welded part after the ultrasonic vibrations have ceased. This allows the molten material to cool and solidify under controlled conditions, ensuring a strong bond.

Why is it Important? Proper holding time is crucial for preventing defects such as welding flash and ensuring that the bond formed during welding is uniform and robust. If the holding time is too short, the bond may be weak or uneven; if too long, it can lead to unnecessary cycle time extension without additional benefits.

Optimal Range: The holding time typically ranges from 0.5 to 3 seconds, depending on the material and the specific application. This range provides enough time for the molten material to solidify and form a strong, leak-proof bond without causing excess welding flash.

5. Welding Pressure: Securing the Part for Optimal Bonding

What is Welding Pressure? Welding pressure is the force applied by the ultrasonic welder’s pneumatic carriage to hold the parts together during the welding process. It ensures that the parts remain in contact and aligned while the ultrasonic energy is applied.

Why is it Important? Welding pressure plays a dual role: it ensures that the parts stay in place during welding, and it aids in the fusion of the materials as they soften and melt. Proper pressure settings are essential for achieving consistent welds and preventing issues such as voids or weak bonds.

Optimal Range: The pressure setting should be tailored to the material and thickness of the parts being welded. A typical range might be between 1.72 to 4.82 bar. Modern ultrasonic welding machines often allow for dynamic pressure adjustments, increasing or decreasing the pressure based on the material's vertical collapse distance during welding. This adaptability can enhance weld quality and consistency.

Conclusion

Achieving strong and leak-proof welds in ultrasonic welding requires careful attention to several controllable factors: down speed, amplitude, welding time, holding time, and welding pressure. By optimizing these parameters, manufacturers can enhance weld strength, improve consistency, and reduce defects, leading to higher quality and more reliable welds. Understanding and fine-tuning these factors is key to mastering the ultrasonic welding process and ensuring the success of your welding applications.

For more details, please feel free to write to info@kuberpolyfilms.com.