Impact of machining-induced surface defects on the edge formability of commercially pure titanium sheet at room temperat
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Impact of machining‑induced surface defects on the edge formability of commercially pure titanium sheet at room temperature J. S. Kwame1 · E. Yakushina2 · P. Blackwell1,2 Received: 30 November 2019 / Accepted: 4 November 2020 © The Author(s) 2020 OPEN
Abstract Despite the good properties of titanium, which have drawn the interest of various industries over the years, one of the major drawbacks of this material is its poor machinability. This has largely been attributed to its low thermal conductivity and elastic modulus. The ability to attain the optimum sheet edge performance during forming is dependent on the quality of the edges produced. Also, the demanding nature of aerospace part design has provoked the interest of both industry and academia to continually explore avenues tailored at enhancing part performance. The sort of edge surface integrity produced for aerospace part fabrication thus becomes a vital consideration in the quest to ensuring prime performance of components. This work seeks to study the influence of different machining-induced surface defects on the sheet edge performance of CP-Ti (grade 2) at room temperature. Hole expansion test was used to assess the edge surface formability of CP-Ti with different machining-induced edge defects. The research found that machining-induced surface defects act as stress concentration sites during the hole expansion test and have a major impact on the material flow. Electro-discharge machined edges were observed to exhibit high edge formability compared to laser and abrasive water jet cut edges due to the impact of machining-induced microstructural changes. Keywords Edge defects · Hole expansion test · Edge formability · Edge forming limit List of symbols HET Hole expansion test HER Hole expansion ratio df Final hole diameter d0 Initial hole diameter LFR Limiting forming ratio dmax Maximum inside the diameter of finished flange COPn Crack opening distance D1, D2 Final hole diameter at random points 1 and 2 Dcorrected Final hole diameter without crack opening ε1 Major strain ε2 Minor strain Ra Arithmetic average height surface roughness AWJ Abrasive water jet EDM Electric discharge machining
RD Sheet rolling direction HCP Hexagonally close packed EBSD Electron backscatter diffraction
1 Introduction Owing to their good mechanical properties and relatively low density, titanium and its alloys have been widely utilised in the aerospace industry for a variety of applications both in the airframe and in the engines [1]. There are a number of variants of the commercially pure titanium (CP-Ti) alloy generally reflecting differing oxygen contents. They all feature a predominantly alpha-grained hexagonally close packed (HCP) microstructure, which contributes to a reduced formability at room temperature due to the availability of limited
* J. S. Kwame, [email protected] | 1Department of Design, Manufacturing and Engineering Management, University of Strathclyde, Glasgow, UK. 2Advanced Forming Research Centre (AFRC), University of Stra
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