Dimension-based failure analysis of formed internal threads in AlSi10Mg cast profiles using coupled DT/NDT testing methods

Abstract

The production of detachable joints in lightweight components using friction drilling and internal thread forming processes could be considered as a lightweight design strategy, which can reduce material and time consumption and enhance the thread strength by imposing a further work-hardening into the subsurface of the formed threads. Pre-study indicated that oversizing the friction drilled bores as a pilot bore can hinder the complete deformation of the thread profiles during the thread forming process. This work investigates the effect of process parameters in the friction drilling process (friction drill speeds and diameter) on the quality of the drilled bores and following formed threads. Computed tomography was chosen to measure the dimension deviation of manufactured bores and threads. Comparing the deviation with the measured static and dynamic strengths declared that increasing the tool diameter by 0.1 mm increased the inner volume of the friction drilled bore, which led to an incomplete deformation of the thread profiles and decreased static and cyclic strength accordingly. Although the friction drilling with an adaptive speed reduced the oversizing of the created bore in comparison to the friction drilled bores with a constant speed, measuring the volume of the formed threads into mentioned bores indicated an opposite trend. While the formed M6-threads into the friction drilled bores with constant speed showed a better strength by subjecting to a quasi-static load, manufactured threads with an adaptive speed indicated a higher dynamic strength. The fatigue tests were monitored through NDT methods by measuring the change in deformation-induced temperature and ACPD potential. The measured results were correlated to plastic strain up to failure corresponding to occurring softening, hardening, or possible crack initiation and propagation in thread profiles.