Rheological weldability
[1] The process of welding thermal plastics requires three general steps, first is surface preparation.
This relationship is attained through experimental measurement of the resultant deformation as a function of an applied force.
[3] Melt rheology has shown to be an accurate method in determining the polymer's molecular structure.
Consequently, for the evaluation of weldability, viscosity of molten thermoplastics (polymer melts) have to be taken into account since welding is a rapid process.
) for most polymer melts, weldability is better where temperature and shear rate (movement) are higher within the entire cross-section of the welding region.
A material's ability to deform elastically while resisting flow is called plasticity.
[3] A polymer's response to fast and large deformation forces is a non linear behavior and is more representative of the reactions experienced during the welding processes.
[5] During operation of a welding process, the softened or molten portion of thermoplastics (polymer articles) is able to flow through the interface.
), implying better weldability where shear rate (movement) is higher within the entire cross-section of the welding region.
) data at various temperatures for a polymer, activation energy (Ea) can be calculated via Arrhenius equation:[7][8][9] Where: The absolute value of the activation energy (|Ea|) can be calculated by taking the natural logarithm of the Arrhenius equation.
This action requires the polymer to be in a molten state where the melt viscosity and flow behavior have a drastic influence on the amount of diffusion and entanglement.
[5] While a rheological analysis can provide reasonable insight to a material's weldability,[2] in most cases production welding is typically prefaced with a series of tests to verify compatibility between both base materials as well as the process employed.
With polymers, these residual stresses are in part due to the squeeze flow rate leading to a specific molecular alignment direction, ultimately influencing the weld strength and overall quality.
