Ultrasonic Assisted Creep Feed Grinding of Inconel 718

The paper details the effects of depth of cut and vibration amplitude when ultrasonic assisted (US) creep feed grinding Inconel 718 with an open structured alumina based wheel. The workpiece was actuated at a constant frequency (∼20.5 kHz) via a block sonotrode attached to a 1 kW piezoelectric transducer-generator system. A full factorial experimental array comprising 12 tests was conducted involving variation in depth of cut (0.1, 0.5 and 1.0 mm), amplitude of vibration (high and low) and grinding condition (with and without vibration). Wheel speed and table feed were fixed at 30m/s and 600 mm/min respectively for all tests. Application of ultrasonic vibration resulted in reductions in vertical (Fv) and horizontal (Fh) force components by up to 28% and 37% respectively, however greater wheel wear (30-60% lower G-ratio) occurred under hybrid operation due to increased grit/bond fracture. SEM micrographs of the slots machined with US assistance revealed higher levels of side flow/ploughing in comparison to standard creep feed ground specimens. Additionally, more overlapping grit marks were visible on surfaces subject to ultrasonic assisted grinding. Increasing amplitude of vibration produced lower grinding forces (up to 30% for Fv and 43% for Fh) but higher workpiece surface roughness (up to 24%). Topographic maps of grinding wheel surface replicas indicated that use of US vibration generally led to an increase in the number of active cutting points on the wheel.