What Causes Scars In Ultrasonically Welded Plastics?

In the process of ultrasonic welding, it is common to see scratches, broken joints, or cracks on the welded product surface. As in the ultrasonic welding process, high heat energy will directly contact the surface of the plastic product, and the vibration will also be transmitted to the plastic product.

Causes Of Scarring In Ultrasonic Welded Plastics

When ultrasonic vibration acts on plastic products, the surface of the product is prone to burns, which is common in ultrasonic welding. On the other hand, due to the lack of ultrasonic output energy, when the vibration friction energy is converted into heat energy, it takes a long time to weld to make up for the lack of output power by accumulating heat energy. This welding method is not the vibration friction heat energy achieved in an instant but needs to accumulate heat energy by the welding time, so as to reach the melting point of the plastic product and reach the welding effect, which will cause the heat energy to stay on the surface of the product for too long, the accumulated temperature and pressure will also cause the product to burn, break or rupture. Therefore, factors such as output power, welding time, and pressure must be considered to work together to overcome such situations.

How To Avoid Scarring？

1. Reduce pressure.

2. Reduce the delay time (early vibration).

3. Reduce the welding time.

4. The protection film covers the surface of the plastic product (such as PE bag).

5. Surface treatment of molds and fixtures (hardened or chrome-plated).

6. Reduce the enlargement ratio of the upper mold.

7. For products that are easy to crack or break, the fixture should be made of buffer, such as soft resin or covered cork, etc. (this refers to the case where the welding strength is not affected).

8. For products that are easy to break, add R angle at the right angle.