Assessment of weld integrity of a moulded plastic component by destructive and non-destructive examination.
Programme of Work
A vapour separator, made of Hostaform® C13031 (POM), see Figure 1, was welded using linear vibration welding (LVW). This is one of the most widely used welding techniques for thermoplastics for under the bonnet applications.
Verification of weld quality was done by visual inspection and microtoming and, although there were tell-tale signs of poor weld (Figures 2a, 2b, 2c), computed tomography (CT) scans provided the most revealing flaws.
The component was reported to have passed the general QA tests and during the burst test surpassed the bursting pressure requirement of 3 bars and the safety design factor of 5 bars, but still some components failed within the warranty period whilst in service.
Design rules for welding dictate critical dimensions, which should be adhered to if a good weld is to be expected. In most investigations there is no access to the welded locations of the component, therefore their quality cannot directly be compared to the design rules.
Non-destructive qualitative assessment of the welded joint was carried out using an X-Tek HMXCT 225 X-ray Micro-focus machine. Computed Tomography (CT) images and videos were obtained and scrutinised. The information obtained was indicative of poor welding procedures, Figures 3-5.