Abstract
Thermoplastic materials hold great promise for next-generation engineered and sustainable plastics and composites. However, due to their thermoplastic nature and viscoplastic material response, it is difficult to predict the properties of surfaces generated by machining. This is especially problematic in micro-channel machining, where burr formation and excessive surface roughness lead to poor component-surface integrity. This study attempts to model the influence of size effects, which occur due to the finite sharpness of any cutting tool, on surface finish and burr formation during micro-milling of an important thermoplastic material, polycarbonate. Experimental results show that the depth of cut does not affect either surface finish or burr formation. A proposed new sideflow model shows the dominant effect of cutting-edge radius and feed rate on surface finish, while tool edge roughness, coating and feed rate have the most pronounced influence on burr formation. Overall, a good agreement between the experimental data and the proposed size effect model for the machining of thermoplastic material was found. Based on these results, tool geometry and process parameters may be optimized for improved surface integrity of machined thermoplastic components.
Highlights
The cross-linking of individual polymer chains suppresses this thermoplastic response, which is the reason for the improved strength and melting points observed in thermosetting materials
This work aims to investigate the impact of size effect on surface quality and burr formation during micro-milling of polycarbonate, which will open the path for understanding the machining behavior of thermoplastic polymers and composites at a micro-scale
The minimum chip thickness effect could be considered as one of the most important size effects. This effect arises due to the finite sharpness of the cutting edge, which will transition from cutting to ploughing at a critical minimum value of the uncut chip thickness, hmin
Summary
Rather than thermosetting plastics, which offer increased strength but are inherently non-recyclable, thermoplastics can be recovered by simple heating to melt and liberate the material from other constituents. Alauddin et al [1] studied the machining behavior of plastics, including thermoplastics and elastomers. Plastics, known as polymers, are comprised of long chains of monomers, which feature carbon/carbon covalent bonds. When long polymeric chains are intertwined without permanent bonds attaching these chains, the material response is thermoplastic, i.e., the material will readily flow plastically when sufficient heat is supplied (typically at relatively low temperatures). The cross-linking of individual polymer chains suppresses this thermoplastic response, which is the reason for the improved strength and melting points observed in thermosetting materials
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