Basic Research On Roll-to-Roll Embossing Of Shark-skin-inspired Drag-reduction Micro-riblets

With the increasingly serious of energy crisis, drag-reducing has become an urgent need. The micro-riblets on shark skin have the function of drag-reducing and antifouling. Imitative shark skin with 7%drag reduction has been produced on the inspiration of shark skin. However, it is still a problem to replicate large-area shark skin surface both with high accuracy and high efficiency. In order to solve the above problem, the research was conducted as follows:Firstly, PMMA template with micro-riblets was got by hot embossing with pretreated shark skin as a mold. And the influences of mold temperature, the pressure holding time and pressure on the forming quality were studied. The results showed that PMMA template possess almost similar micro-structure with that of the shark skin template. The average central height value is 32.3μm, which decreased by 3.6%when compared with shark skin template. The average central width value is 100μm, which increased by 5.2%.Secondly, make the PMMA sample as replication template after conductive treatment. Then the micro-electroforming process was conducted to transfer the micro-riblets of PMMA to copper plating. The effects of electroforming parameters on shape accuracy were studied. After parameter optimization, the micro-riblets on copper plating with average central height as 31.5μm were got, which decreased by 2.5%when compared with hot embossing template. When compared with shark skin template, the central height decreased by 6%.The testing results showed that scale groove structures keep invariable in the electroforming process with high replication precision.Thirdly, choose copper plating as tool electrode to conduct the electro-discharge tests on NAK80 surface. Study the effects of cathode current density and loop combination on electrode wear and replication precision, also the influence of height difference between scales on machining precision was studied. The results showed that micro-grooves with clear profile were got when the height difference is small; when choose cathode current density as 3 A/dm2, the electrode wore little and the replicate precision is high; the electrode wear and machining quality of PS+NP loop are better than SC+GM loop.Finally, the Roll-to-Roll embossing experiments on PET were conducted with PMMA template and NAK80 template as rolling mold, respectively. And the effects of mold temperature, rolling gap and pressure on forming quality were studied. The results showed that lower mold temperature, higher pressure and lower rolling speed are critical to good forming quality. When adopt PMMA mold, the accuracy of PET surface structure was better with central height as 25μm and central width as 90μm, while its life is short. When adopt NAK80 mold, the morphology of micro-riblets exhibits discontinuous and incomplete, however, the life of NAK80 mold is longer than PMMA mold. There almost no lose after repeated rolling.