A Review of the Tribology of 3D-Printed Polymers and Polymer Composites

3D-printed polymers and polymer composites are increasingly used in sliding and abrasive contacts, but their friction and wear cannot be transferred directly from data for moulded polymers, because printing creates layered interfaces, process-specific surface textures and position-dependent crystallinity. This systematised critical review analyses 289 experimental studies and grades the evidence for each step linking the printing process to internal structure, surface, contact conditions, wear mechanisms and component life. Four findings stand out. First, the orientation of layers and rasters relative to sliding is associated with a switch between wear controlled by shear of interlayer bonds and wear controlled by crossing of surface ridges; coding orientation as {contact face, layer normal, raster/fibre direction} explains several apparently contradictory results. Second, test conditions dominate absolute wear rates, which for printed neat PEEK span 2.6 decades, with the largest contrast between contact configurations, so effects must be compared within studies. Third, only 3 of 245 full-text studies report all core contact and statistical information; a minimum reporting set is proposed. Fourth, only three printed-versus-conventional comparisons isolate the manufacturing route. Established findings include the failure of hardness as a general wear predictor and friction reduction by oil and grease; lubricant storage in designed porosity remains probable.