Particle damping is one of the promising damping techniques in effectively suppressing chatter in boring process. In earlier studies, granular particles are packed with the single particle type used to suppress chatter. This paper attempts at a novel hybrid approach in particle damping to increase the effectiveness of chatter suppression and enhance the machining stability. In this hybrid approach, Copper and Zinc particles are used together in equal proportion for packing inside the boring bar. The study finds this combined packing significantly improves the damping characteristic compared to the unmodified boring bar and also bar packed with single (Cu or Zn) particle type. The assessment benchmarks were the dynamic characteristics, modal analysis, damping ratio, logarithmic decrement and resonance gap of the machining system, as well as the displacement amplitude of the boring bar and the surface roughness of the work piece. The displacement amplitude of the boring bar and the surface roughness of the work piece in the combined packing case are reduced by 55% and 80% respectively when it is compared to the unmodified case.

Chatter or self-excited vibration during machining process is always a serious problem which reduces intended dimensional accuracy. This investigation is mainly about reducing induced vibration through the electroless coating of nickel-phosphorus (Ni-P) on high carbon steel (EN 31) boring bar. The high carbon steel (EN31) substrate has been electroless coated with nickel-phosphorus at varying pH values (4, 5 and 6), and the damping effect of pH values on material deposition has been investigated. The coated substrate was subjected to heat treatment process and the influence of pH values and heat treatment process on structural stabilities of the coated specimens were analyzed using impact hammer test, and scanning electron microscope, energy-dispersive X-ray micro analysis and X-ray diffraction technique were used to study the structural changes in the Ni-P-coated boring bars. The pH values and heat treatment processes were found to play a significant role in improving the damping properties of the boring bars. The boring bar coated at 4 pH values resulted in better deposition of nickel and phosphorous over the substrate and offered better damping properties to the substrate. The heat treatment process on the coated specimen was found to render a crystalline structure to the substrate, thus offering improved damping proprieties to the materials. B S. Chockalingam