Machining analysis of unidirectional and bi-directional flax-epoxy composite laminates

Natural fibers, and more particularly, flax fibers, have a considerable potential as replacements for synthetic fibers. These fibers are of significant economic and environmental interest because they are natural products, are biodegradable, and unlike synthetic fibers, are entirely recyclable. They are also less expensive than synthetic fibers, less abrasive for machining, and their specific properties (strength-to-weight ratio) are comparable to those of glass fibers. Consequently, they thus provide economic and environmental benefits for companies. Unfortunately, machining knowledge with respect to this kind of material is low, and research in this domain has barely begun. The objective of this study is to describe the machinability of unidirectional and bidirectional flax/epoxy composites and to analyze the influence of cutting parameters and fiber orientation on cutting forces and surface finish. Milling tests were performed on unidirectional composite laminates with two different tools. The results show that the surface finish and cutting forces depend largely on the feed rate, and to a lesser extent, on the cutting speed. The PCD cutting tool, with a zero helix angle, showed the best performances as compared to the CVD cutting tool, which had a different geometry. The former provided a better surface finish, a lower delamination factor, and lower cutting forces. The material was found to be easy to machine and low abrasive, since no tool wear was observed following the cutting tests. Finally, it was found that an intermediate feed rate value and a high cutting speed were the best of all parameters tested for achieving a low cutting force level, low surface roughness, and high throughput.