Dynamic ideality for electron beam welding

Abstract

Experimental methods for evaluating performance of electron beams are both time consuming and costly, with favourable parameters chosen based on a subjective standard. Correlation of the weld geometry against conventional machine input parameters such as voltage, focus, and current involves complex interaction phenomena. This renders it difficult to deconvolute the influence of these inputs against applied energy distributions within a setup. In this work, a process window was generated across a range of weld powers and speeds with focal positions adjusted to achieve the same nominal spot size and hence mitigate input parameter interaction phenomena. The variability of spot size using this method can be reduced by 90% against using the conventional method of optically acquiring weld focus. To reduce reliance on empirically derived heuristics in parameter selection, weld performance was quantified through an aggregated output quality termed ‘ideality’ as a function of conventional weld geometry, imperfections, and characteristic microstructural evolution/transformation. The ideality metric was shown as a method of achieving the least harmful compromise of parameter conflicts. A method of using a thermal process model to perform subsequent optimisation of ideality was presented. The ability to characterise inputs as a function of beam properties rather than machine inputs serves as a useful method to optimise weld procedures and serve as a basis for comparison between setups. While electron beam welding is used in this study to propose ideality, process outputs and inputs can be substituted for other process-specific outputs and inputs, enabling adoption for most manufacturing processes.