Edge Profiling of Titanium Alloys and Attainable Surface Quality

Machining operations such as reaming, boring or milling create undesirable extruded sharp edges at the entry and exit side of the machined holes. These sharp burrs / extruded edges act as stress concentration regions for fatigue crack propagation in safety critical aerospace components. In this paper, results of an experimental investigation carried out on surface integrity of titanium based alloy during mechanized edge profiling process are presented. In the Mechanized Edge Profiling (MEP) process the primary sharp edges created as result of hole machining are removed using a hard point countersink tool and the secondary sharp edges produced due to countersinking/chamfering the hole entry and exit side edges are radiused using nylon impregnated silicon carbide brushes. On-machine edge profiling experiments were conducted using compliant Flexhone™ and Novoflex™ globular abrasive brushes on highly stressed bolt/flange holes. Brushing speed and feed rate were identified as key process variables. Nylon impregnated with silicon carbide 320 grit brush showed good performance when brushing at a speed of 5000rpm and 5000mm/min feed rate which produced a very consistent and controlled secondary edge radius of 0.3±0.2mm up to 30 holes. An acceptable surface roughness (Ra) of less than 0.5μm on the chamfer and bore surfaces were achieved.