Comparison between Cold Incremental and Stretch Forming of Flax Fiber-Reinforced Polypropylene Composites

Incremental sheet forming, born as a versatile and cost-effective alternative to traditional procedures to deform incrementally and without dedicated dies flat metal sheets into complex three-dimensional shapes, has recently been gaining attention as a forming technique for polymers and composites. Among these, natural fiber-reinforced thermoplastics have been climbing in popularity because natural fibers are widely available, act as effective polymer reinforcement, and make the composite semi-biodegradable. Through compression molding and using natural woven fabrics, it is also possible to achieve good fiber/matrix coupling without compromising the environmental benefits with chemical coupling agents and/or treatments. This experimental study compares cold incremental and stretch forming processes of flax woven fabric-reinforced polypropylene composites for the manufacture of spherical caps. By considering formability, geometrical accuracy, forming forces, power, and energy consumption, the study highlights the effectiveness of incremental forming applied to these biobased composites, without resorting to full counter dies and heating stages.