Study of surface topography in Abrasive Water Jet machining of carbon foam and morphological characterization using Discrete Wavelet Transform

Abstract

Carbon foam (CFOAM) is a light weight alternative to composite tooling and other applications in aerospace industry. Secondary machining of CFOAM is challenging due to machining induced damage to its thin walled structure and also the production of carcinogenic dust during the conventional machining processes. In this study, machinability of CFOAM was investigated using Abrasive Water Jet (AWJ). Three pressure levels – 200, 275, 350 MPa and jet traverse speed between 2 and 100 mm/s was used to machine 50 mm thick carbon foam. The kerf surface topology and morphology was inspected using non-contact profilometry, optical and scanning electron microscopy. A lumped process parameter – power-to-speed ratio (E˙/u) was effectively used to describe the kerf characteristics in terms of kerf geometry and kerf wall roughness. A novel method using Discrete Wavelet Analysis was proposed to study the surface topology and establish correlation with E˙/u. The most common material removal mechanisms were found to be erosion, cell shape distortion, cell and pore engulfment, ligament fractures, debris entrapment with cell wall cracking. Overall, surface topology and morphology was characterized with a strong correlation with the process parameters which assisted in determining optimal window for AWJ process parameters.