Use of the theory of critical distances in predicting medium cycle fatigue failure in five-axis ball end milled components

While casting may have historically been used to make components with free-form surfaces, five-axis milling with ball end cutters is becoming increasingly common. Although this form of production enables the use of more robust billet material rather than cast material, it generates identifiable machining cusps on the component’s surface. A detailed FEA was conducted on CAD modelled specimens with detail of cusps defined allowing the extraction of peak stress values and stress fields generated by distinct geometry of cusps. Two strategies, the TCD-PM and TCD-LM methods, were implemented to predict life of five-axis machined specimens. Results showed that the TCD-LM method tends to be more accurate than the TCD-PM method. The TCD-LM method showed acceptable results for longer life specimens, however 40 % of data was still seen to fall outside acceptable ±2 scatter bands. TCD conservative results are judged to be the drawback of not considering the 3D stress raiser and plasticity effects.