Characterisation of nylon 6,6 vibration welds

TWI Industrial Member Report Summary 483/1993

By: S M Stevens

Background

Nylon 6,6 (PA 6,6) is a semicrystalline engineering thermoplastic which is widely used for light engineering applications. In order to understand the structure/property relationships in PA 6,6 welds, it is necessary to evaluate factors such as crystallinity and molecular orientation, and weld morphology. This report describes work that is part of an ongoing project at TWI to generate data on the structural and morphological changes which occur in thermoplastic welds.

In this work, PA 6,6 vibration welds were made using various welding times (representing an extreme range from 2 to 7 seconds) intended to produce a range of tensile properties. An FTIR-microspectrometric method was developed at TWI to measure crystallinity and orientation in these welds. Transmitted light microscopy, and scanning electron microscopy on etched samples, were used to examine the morphology of the welds. The fracture surfaces of broken tensile specimens were studied using transmitted and reflected light microscopy, and scanning electron microscopy.