Flash is a common issue that can occur during ultrasonic welding, where excess material is pushed out from the welded area. Here are some ways to reduce flash in ultrasonic welding:

1. Adjust the amplitude: The amplitude controls the amount of energy being delivered to the parts. If the amplitude is too high, it can cause excess material to be pushed out as flash. By adjusting the amplitude, you can find the right level of energy to reduce flash.
2. Increase the pressure: Increasing the pressure applied during ultrasonic welding can help to reduce flash. This helps to ensure that the material is held tightly together during the welding process.
3. Improve the clamping: Proper clamping of the parts being welded is crucial in minimizing flash. If the parts are not held tightly enough, it can cause excess material to be pushed out as flash. Make sure the parts are securely clamped in place.
4. Reduce the weld time: Reducing the time that the ultrasonic energy is applied can help to reduce flash. By finding the right balance of time and energy, you can reduce flash while still achieving a strong weld.
5. Use a horn or booster with a lower energy concentration: Horns and boosters with a lower energy concentration can help to reduce flash. This is because they deliver energy over a larger area, which helps to distribute the energy more evenly and reduce the chances of excess material being pushed out.

By implementing these techniques, you can minimize flash and achieve high-quality ultrasonic welds.