Investigation on microstructure characteristics of tool wear and machined surface mechanisms while milling: kenaf vs glass fiber-reinforced composites

In composites' secondary/machining process, there is still a requirement for a compar-ative assessment of microstructure features of tool wear and machined surface mech-anisms while machining natural fiber against glass fiber-based composites. This experimental study uniquely investigates the dry-end milling of two polypropylene (PP)-based composites made of 30 wt.% discontinuous reinforcements -kenaf and glass fibers (GF). Surprisingly, though, GF are much harder (GF:5.84 GPa > kenaf:0.15 GPa) and abrasive (silicon content, GF:24.16% > kenaf:0.57%) than kenaf inclusions, cutting GF/PP resulted in relatively lower tool wear (z0.0 8 mm) but contrarily showed adverse machined surface finishes (>8 mm) depicting tearing-dragging mechanisms with fuzzy textures. This cautions on the appropriate consideration for the tool's life-determining criterion -i.e., whether it should be based on the tool wear or surface finish. While machining GF/PP material, the tool wear growth on the cutting edges was significantly restricted by the formations of continuous-robust microstructural transfer protective film (TPF) characterized by strong Si + O, Al + O, and Fe + O tribo-chemical reactions through the interesting wear mechanisms associated with tribological phenomena. However, thin-patch type microstructural TPFs consisting of weak Si + C bonds occurred on tool edge regions while machining kenaf/PP. Better mechanical properties and fiber -matrix adhesion of GF/PP influenced by fiber dimensions and their higher aspect ratios (GF:27.60 > kenaf:7.20) decisively seem to have a dominant effect on limiting the tool wear. Chip micrographs clarified the cutting of GF/PP and kenaf/PP occurred by pre-dominant melt-extrusion and shearing respectively.(c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).