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/).

Automated summary

In the secondary/machining process of composites, it is important to compare the microstructure features of tool wear and machined surface mechanisms when machining different types of fibers. This experimental study investigated the dry-end milling of two polypropylene (PP)-based composites made of kenaf and glass fibers. Surprisingly, cutting glass fiber/PP resulted in lower tool wear but adverse machined surface finishes, indicating the need to consider the appropriate criterion for tool life determination.