What are the processes that affect ultrasonic welding

Plastic ultrasonic welding includes process parameters such as amplitude, welding time, welding pressure, etc. These process parameters and their interactions all have an impact on welding quality.

Influence of amplitude

　Amplitude is the primary selection process parameter for ultrasonic welding of plastics. The material has a suitable amplitude range at a specific ultrasonic frequency.

Amplitude range required for ultrasonic welding of thermoplastics below 20kHz

Within a suitable amplitude range, the increase in amplitude is conducive to the diffusion of ultrasonic energy, thereby improving the strength of the welded joint.

In the amplitude range of 40～53/μm, it is found that the welding strength of PP increases with the increase of the amplitude; the study of PP and glass fiber reinforced polypropylene composites in the amplitude range of 25～40μm shows that the welding strength increases with the increase of the amplitude.

The thickness of the molten layer decreases slightly with the increase of the amplitude, which leads to an increase in the shear strength of the welded joint and a decrease in the bending strength. The amplitude required for plastic welding is also affected by the type of welding and the frequency of the welding equipment. The amplitude required for inserting and riveting is relatively large, while the amplitude required for plane welding is relatively small.

The effect of welding time

For a good welded joint, the proper welding time must be selected. Too long and too short welding time will cause the strength of the welded joint to decrease.

When welding PP and high-density polyethylene, the strength of the welded joint increases with the increase of welding time. When the welding time exceeds a certain value (about 1.5s), the strength of the welded joint begins to decrease. ABS and PS have similar situations in remote welding, and the turning point is around 2.4s. In the orthogonal test of ultrasonic welding of PVC sheets and PP packaging bags, it is found that the welding time also has a turning point, which is 0.29s and 5s, respectively.

The welding time is not affected by the thickness of the material, and the ultrasonic welding of the film also has a better welding time.

Influence of welding pressure

When other factors are determined, the pressure within a certain range can achieve better welding strength.

The glass fiber reinforced polypropylene composite material has been lapped and tested. The joint strength increases with the pressure when the pressure is less than 0.15MPa. When the pressure exceeds 0.15MPa, the joint strength reaches a relatively stable state, about 35MPa; when the welding pressure is Above 0.4MPa, polypropylene will be severely squeezed out of the matrix and the strength of the welded joint will decrease.

Welding pressure has a great influence on the thickness and orientation of the welding melting zone. As the welding pressure increases, the thickness of the molten layer decreases, and the orientation degree of the welded joint increases. The macroscopic manifestation is that the welding pressure increases and the shear strength of the joint along the orientation direction increases. The bending strength perpendicular to the orientation direction decreases.

Influence of welding head descending speed

Under certain conditions, the faster the welding head descends, the higher the strength of the welded joint. In the ultrasonic welding process, the high descending speed can obtain high contact pressure, which is conducive to the close contact of the welding interface and the full diffusion of molecules.

Use 25, 50, 100mm/s three welding head descending speeds to weld HS1000, and the average welding joint strength is higher when the descending speed increases to 100mm/s, reaching 28.38MPa.

The influence of holding time and holding pressure

After the ultrasonic is stopped, in order to make the welding specimens close to each other and solidify, so that the two workpieces can be welded together well, a certain pressure needs to be maintained for a certain period of time. The required time and pressure are the holding time and holding pressure. .

The holding time and holding pressure have a positive effect on the strength of welded joints, but compared to other process parameters, holding time and holding pressure have little effect on the strength of welded joints.

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