Microscale shaping and rounding of ridge arrays and star pattern features on nickel mould via electrochemical polishing

Abstract

High quality micro mould tools are critical for ensuring defect-free production of micro injection moulded products. The demoulding stage of the micro injection moulding can adversely affect the surface integrity due to friction, adhesion and thermal stresses between the metallic mould and polymeric replicated part. In the present work, we propose the use of precision electropolishing (EP) as a shaping and polishing process to control the draft angle and fillet radius of micro features in order to ease demoulding. Typical defects that occur in replicated polymer parts include cracks, burrs and distorted features. A nickel mould having multiple linear ridges and star shape patterns was designed for the present investigation to have characteristic dimensions ranging from 10 μm to 150 μm and with various aspect ratios to study the effect of electropolishing on modifying the shape of micro features and surface morphology. A transient 2D computational analysis has been conducted to anticipate the effect of shaping on the Ni mould after electrochemical polishing with non-uniform material removal rates, based on the distribution of current density. The experimental results indicate that after shaping using EP, the draft angle of star-patterns and linear patterns can be effectively increased by approximately $3.6^\circ$, while the fillet radius increases by up to 5.0 μm. By controlling the electropolishing process, the surface roughness can be maintained under 50 nm. This work uses a green and environmental friendly nickel sulfamate electrolyte which can be effective for shaping of nickel micro features without causing any surface deposition.

Keywords

Micro feature shaping and electropolishing / Micro mould tools / Green electrolyte / Demoulding micro patterns

References

[1] Zhang H, Zhang H, Guan T, et al. Prototyping and production of polymeric microfluidic chip. Adv Microfluid Nanofluid, 2021.

[2] Abdulhameed A, Halim MM, Halin IA. Simulation and experimental validation of the interplay between dielectrophoretic and electroosmotic behavior of conductive and insulator particles for nanofabrication and lab-on-chip applications. Colloid Surface A, 2023, 663: 131065.

[3] Davis R, Singh A, Jackson MJ, et al. A comprehensive review on metallic implant biomaterials and their subtractive manufacturing. Int J Adv Manuf Tech, 2022, 120(3/4): 1473-1530.

[4] Wang X, Li C, Zhang Y, et al. Influence of texture shape and arrangement on nanofluid minimum quantity lubrication turning. Int J Adv Manuf Tech, 2022, 119(1/2): 631-646.

[5] Wang Y, Weng C, Deng Z, et al. Fabrication and performance of nickel-based composite mold inserts for micro-injection molding. Appl Surf Sci, 2023, 615: 156417.

[6] Li J, Ma H, Liu W, et al. Effects of cavity thickness and mold surface roughness on the polymer flow during micro injection molding. Polymers, 2023, 15(2): 326.

[7] Moazzez B, O'Brien SM, Merschrod SEF. Improved adhesion of gold thin films evaporated on polymer resin: applications for sensing surfaces and MEMS. Sensors, 2013, 13(6): 7021-7032.

[8] Chen J, Yang J, Zhou M, et al. Self-assembled monolayers of alkanethiols on nickel insert: Characterization of friction and analysis on demolding quality in microinjection molding. Micromachines, 2021, 12(6): 636.

[9] Peixoto C, Valentim PT, Sousa PC, et al. Injection molding of high-precision optical lenses: a review. Precis Eng, 2022, 76: 29-51.

[10] Zhang N, Zhang H, Stallard C, et al. Replication integrity of micro features using variotherm and vacuum assisted microinjection moulding. CIRP J Manuf Sci Tec, 2018, 23: 20-38.

[11] Liarte E, Zambrano V, Gracia LA, et al. Demoulding process assessment of elastomers in micro-textured moulds. Open Res Europe, 2022, 1: 120.

[12] Zariatin DL, Kiswanto G, Ko T. Investigation of the micro-milling process of thin-wall features of aluminum alloy 1100. Int J Adv Manuf Tech, 2017, 93: 2625-2637.

[13] Raza S, Nadda R, Nirala C. Real-time data acquisition and discharge pulse analysis in controlled RC circuit based Micro-EDM. Microsyst Technol, 2023, 29(3): 359-376.

[14] Arruebo M, Fernández-Pacheco R, Ibarra MR, et al. Magnetic nanoparticles for drug delivery. NanoToday, 2007, 2(3): 22-32.

[15] Schoenherr M, Ruehl H, Guenther T, et al. Adhesion-induced demolding forces of hard coated microstructures measured with a novel injection molding tool. Polymers, 2023, 15(5): 1285.

[16] Jong WR, Li TC, Chen YW, et al. Automatic recognition and construction of draft angle for injection mold design. Journal of Software Engineering and Applications (JSEA), 2017, 10(1): 78-93.

[17] Łosiewicz B. Electrodeposition mechanism of composite coatings. Solid State Phenom, 2015, 228: 65-78.

[18] Obilor AF, Pacella M, Wilson A, et al. Micro-texturing of polymer surfaces using lasers: a review. Int J Adv Manuf Tech, 2022, 120(1/2): 103-135.

[19] Lee H, Yi A, Choi J, et al. Texturing of polydimethylsiloxane surface for anti-reflective films with super-hydrophobicity in solar cell application. Appl Surf Sci, 2022, 584: 152625.

[20] Jianwei JW, Ajmal KM, Zejin Z, et al. Electrochemical polishing of tungsten: an investigation of critical spatial frequency and ultimate roughness. J Electrochem Soc, 2022, 169(4): 043509.

[21] Li M, Chen Y, Luo W, et al. Demolding force dependence on mold surface modifications in UV nanoimprint lithography. Microelectron Eng, 2021, 236: 111470.

[22] Kim SH, Asay DB, Dugger MT. Nanotribology and MEMS. Nano Today, 2007, 2(5): 22-29.

[23] Chang WT, Hwang IS, Chang MT, et al. Method of electrochemical etching of tungsten tips with controllable profiles. Rev Sci Instrum, 2012, 83: 083704.

[24] Chen X, Yuan Q. Capillary adhesion around the shapes optimized by dissolution. Adv Mater Interfaces, 2023, 10(13): 2202380.

[25] Zaki S, Zhang N, Gilchrist MD. Electropolishing and shaping of micro-scale metallic features. Micromachines, 2022, 13(3): 468.

[26] Li D, Zhang Y, Liu Y, et al. Injection moulding of mechanical micro-manufactured structures for optically encoding plastic surfaces. Opt Mater, 2022, 123.

[27] Zhang H, Zhang N, Fang F. Investigation of mass transfer inside micro structures and its effect on replication accuracy in precision micro electroforming. Int J Mach Tool Manuf, 2021, 165: 103717.

[28] Saitta L, Arcadio F, Celano G, et al. Design and manufacturing of a surface plasmon resonance sensor based on inkjet 3D printing for simultaneous measurements of refractive index and temperature. Int J Adv Manuf Tech, 2023, 124(7/8): 2261-2278.

[29] Zhang N, Liu J, Zhang H, et al. 3D printing of metallic microstructured mould using selective laser melting for injection moulding of plastic microfluidic devices. Micromachines, 2019, 10(9): 595.

[30] Martinho PG, Pouzada AS. Alternative materials in moulding elements of hybrid moulds: structural integrity and tribological aspects. Int J Adv Manuf Tech, 2021, 113(1): 351-363.

[31] Shao L, Pan B, Hou R, et al. User-friendly microfluidic manufacturing of hydrogel microspheres with sharp needle. Biofabrication, 2022, 14(2): 025017.

[32] Bolat G, De la Paz E, Azeredo NF, et al. Wearable soft electrochemical microfluidic device integrated with iontophoresis for sweat biosensing. Anal Bioanal Chem, 2022, 414(18): 5411-5421.

[33] Li L, Li H, Kou G, et al. Dynamic camouflage characteristics of a thermal infrared film inspired by honeycomb structure. J Bionic Eng, 2022, 19(2): 458-470.

[34] Guan B, Pai JH, Cherrill M, et al. Injection moulding of micropillar arrays: a comparison of poly (methyl methacrylate) and cyclic olefin copolymer. Microsyst Technol, 2022, 28: 2083-2091.

[35] Chu Q, Wu A, Tan T, et al. Electropolishing behavior of niobium in choline chloride-based deep eutectic solvents. Appl Surf Sci, 2021, 550: 149322.

[36] Kityk A, Protsenko V, Danilov F, et al. Enhancement of the surface characteristics of Ti-based biomedical alloy by electropolishing in environmentally friendly deep eutectic solvent (Ethaline). Colloid Surface A, 2021, 613: 126125.

[37] Jeong J, Yoon W, Chung B, et al. Fabrication of eco-friendly graphene nanoplatelet electrode for electropolishing and its properties. Appl Sci-basel, 2021, 11(7): 3224.

[38] Kumar R. MEMS based cantilever biosensors for cancer detection using potential bio-markers present in VOCs: a survey. Microsyst Technol, 2019, 25(9): 3253-3267.

[39] Pong-Ryol J, Tae-Sok J, Nam-Chol K, et al. Laser micro-polishing for metallic surface using UV nano-second pulse laser and CW laser. Int J Adv Manuf Tech, 2016, 85(9): 2367-2375.

[40] Yang B, Ai Y. Facile fabrication of CuO nanosheets and in situ transmission electron microscopy/X-ray diffraction heating characterization of microstructure evolution. Phys Status Solidi A, 2022, 219(6): 2100617.

[41] Shen H, Liao C, Zhou J, et al. Two-step laser based surface treatments of laser metal deposition manufactured Ti6Al4V components. J Manuf Process, 2021, 64: 239-252.

[42] Du L, Guo B, Dong Y, et al. A wearable omnidirectional inertial switch of security detection for the elderly. Microsyst Technol, 2022, 28: 2011-2021.

[43] Zhao Y, Qian S, Zhang Y, et al. Experimental study on uniformity of copper layer with microstructure arrays by electroforming. Int J Adv Manuf Tech, 2021, 114(7): 2019-2030.

[44] Zaki S, Zhang N, Gilchrist MD (2022) Potentiodynamic polarization behaviour of Ni for shaping and electropolishing of micro-mould tools. In: Proceedings of the 38th international manufacturing conference (IMC38), University College Dublin, Dublin

[45] Paul R, Hackert-Oschätzchen M, Danilov I, et al. 3D multiphysics simulation of jet electrochemical machining of intersecting line removals. Procedia CIRP, 2019, 82: 196-201.

Funding

Science Foundation Ireland http://dx.doi.org/10.13039/501100001602(16/RC/3872)