Process of spin welding

Four different phases can be distinguished in the vibration welding process; the solid friction phase, the transient phase, the steady-state phase and the cooling phase.

In the solid friction phase, heat is generated as a result of the friction between the two surfaces. This causes the polymer material to heat up until the melting point is reached. The heat generated is dependent on the applied tangential velocity and the pressure.

In the second phase, a thin molten polymer layer is formed which grows as a result of the ongoing heat generation. In this stage heat is generated by viscous dissipation. At first only a thin molten layer exists and consequently the shear-rate and viscous heating contributions are large. As the thickness of the molten layer increases the degree of viscous heating decreases.

Thereafter, (start of third phase) the melting rate equals the outward flow rate (steady state). As soon as this phase has been reached, the thickness of the molten layer is constant. The steady-state is maintained until a certain "melt down depth" has been reached at which point the rotation is stopped.

At this point (phase 4) the polymer melt cools and solidification starts, while film drainage still occurs since the welding pressure remains. After all the material has solidified, drainage stops and the joint is formed.

Process parameters

Spin welding is restricted to cylindrical parts with a maximum diameter of about 250 mm (10 in). 3D-contours cannot be welded and the relative position of the parts cannot be adjusted. Large batch sizes are possible. Typical process parameters for spin welding are:

- tangential velocity: 3-15 m/s (10-50 ft/s)
- rotational speed: 1,000-18,000 rpm (depending on the part diameter)
- welding time: 0.25-1s
- holding time: 0.5-1s
- cycle time: 1-2 seconds
- weld pressure: 2-5 MPa (300-700 psi).

Materials

Most DSM thermoplastics, like Stanyl, Akulon, Arnite and Xantar, can be spin welded. Spin welding of soft plastics, such as Arnitel, is problematic.