Effects of mould wear on hydrophobic polymer surfaces replicated using plasma-treated and laser-textured stainless steel inserts

Results of the work in the Laser4Fun project has been published as:

Jean-Michel Romano, Jorge Fantova-Sarasa, Carlos Concheso, Mert Gulcur, Behnam Dashtbozorg, Antonio Garcia-Giron, Pavel Penchev, Hanshan Dong, Ben R. Whiteside, Stefan S. Dimov. (2020) Effects of mould wear on hydrophobic polymer surfaces replicated using plasma-treated and laser-textured stainless steel inserts. Tribology – Materials, Surfaces & Interfaces, 1-13.

Abstract

The mass production of polymeric parts with functional surfaces requires economically viable manufacturing routes. Injection moulding is a very attractive option, however, wear and surface damage can be detrimental to the lifespan of replication masters. In this research, austenitic stainless steel inserts were hardened by low temperature plasma carburising and then different micro and nano scale surface textures, inspired by Lotus leaves and Springtail skins, were laser fabricated. A commonly available talc-loaded polypropylene was used to produce 5000 replicas and thus to investigate the evolution of surface textures both on inserts and replicas together with their functional response. The progressive wear or surface damage on the inserts during the injection moulding process had a clear impact on surface roughness and peak-to-peak topographies of the replicas. In general, polymer replicas produced with the carburised inserts retained wetting properties for longer periods compared with those produced with the untreated replication masters.

Link(s)

https://doi.org/10.1080/17515831.2020.1785234

Lotus-leaf inspired surfaces: hydrophobicity evolution of replicas due to mechanical cleaning and mould wear

Results of the work in the Laser4Fun project has been published as:

Jean-Michel Romano, Antonio Garcia-Giron, Pavel Penchev, Mert Gulcur, Ben R. Whiteside, Stefan S. Dimov. (2020) Lotus-leaf inspired surfaces: hydrophobicity evolution of replicas due to mechanical cleaning and mould wear. Journal of Micro and Nano Manufacturing, 8(1): 010913.

Abstract

Inspired from the low wetting properties of Lotus leaves, the fabrication of dual micro/nanoscale topographies is of interest to many applications. In this research, superhydrophobic surfaces are fabricated by a process chain combining ultrashort pulsed laser texturing of steel inserts and injection molding to produce textured polypropylene (PP) parts. This manufacturing route is very promising and could be economically viable for mass production of polymeric parts with superhydrophobic properties. However, surface damages, such as wear and abrasion phenomena, can be detrimental to the attractive wetting properties of replicated textured surfaces. Therefore, the final product lifespan is investigated using mechanical cleaning of textured PP surfaces with multipurpose cloths following the ASTM D3450 standard. Second, the surface damage of replication masters after 350 injection molding cycles with glass-fiber-reinforced PP, especially to intensify mold wear, was investigated. In both cases, the degradation of the dualscale surface textures had a clear impact on surface topography of the replicas and thus on their wetting properties, too.

Link(s)

https://doi.org/10.1115/1.4046097

Experimental investigation of processing disturbances in laser surface patterning.

Results of the work in the Laser4Fun project has been published as:

Antonio Garcia-Giron, Jean-Michel Romano, Afif Batal, Aleksandra Michalek, Pavel Penchev and Stefan Dimov. Experimental investigation of processing disturbances in laser surface patterning. Optics and Lasers in Engineering (2020) 126, 105900. doi: 10.1016/j.optlaseng.2019.105900.

Abstract

Laser surface patterning has attracted a significant interest from industry and research due to its promising applications in surface functionalisation. However, there are specific issues and limitations associated with the beam delivery, especially when processing 3-D surfaces and/or setting up routines for executing complex multi-axis processing strategies. In particular, there are common processing disturbances that affect the resulting surface topographies and profiles and their respective functional responses, i.e. geometrical distortions of resulting surface patterns, focal offset distance (FOD) and variations of beam incident angle (BIA). A method to investigate the effects of these factors in laser patterning 3-D surfaces is presented in this research, especially how their effects can be analysed independently by conducting empirical studies on planar surfaces. A pilot implementation of the proposed methodology is reported for producing channel-like patterns on stainless steel plates with a super-hydrophobic functional response. The results are discussed in detail to show how the effects of processing disturbances on topographies, profiles and areal parameters together with the respective functional responses of patterned planar surfaces can be analysed and then used to set constraints in pre-processing 3-D surfaces for follow up laser patterning.

Correlating nano-scale surface replication accuracy and cavity temperature in micro-injection moulding using in-line process control and high-speed thermal imaging.

Results of the work in the Laser4Fun project has been published as:

Federico Baruffi, Mert Gulcur, Matteo Calaon, Jean-Michel Romano, Pavel Penchev, Stefan Dimov, Ben R. Whiteside and Guido Tosello. Correlating nano-scale surface replication accuracy and cavity temperature in micro-injection moulding using in-line process control and high-speed thermal imaging. Journal of Manufacturing Processes (2019) 47, 367-381.
doi: 10.1016/j.jmapro.2019.08.017.

Abstract

Micro-injection moulding (μIM) stands out as preferable technology to enable the mass production of polymeric components with micro- and nano-structured surfaces. One of the major challenges of these processes is related to the quality assurance of the manufactured surfaces: the time needed to perform accurate 3D surface acquisitions is typically much longer than a single moulding cycle, thus making impossible to integrate in-line measurements in the process chain. In this work, the authors proposed a novel solution to this problem by defining a process monitoring strategy aiming at linking sensitive in-line monitored process variables with the replication quality. A nano-structured surface for antibacterial applications was manufactured on a metal insert by laser structuring and replicated using two different polymers, polyoxymethylene (POM) and polycarbonate (PC). The replication accuracy was determined using a laser scanning confocal microscope and its dependence on the variation of the main μIM parameters was studied using a Design of Experiments (DoE) experimental approach. During each process cycle, the temperature distribution of the polymer inside the cavity was measured using a high-speed infrared camera by means of a sapphire window mounted in the movable plate of the mould. The temperature measurements showed a high level of correlation with the replication performance of the μIM process, thus providing a fast and effective way to control the quality of the moulded surfaces in-line.

Lotus-leaf inspired surfaces: hydrophobicity evolution of replicas due to mechanical cleaning and tool wear

Results of the work in the Laser4Fun project has been published as:

Jean-Michel Romano, Antonio Garcia-Giron, Pavel Penchev, Mert Gulcur, Ben R. Whiteside, Stefan Dimov. Lotus-leaf inspired surfaces: hydrophobicity evolution of replicas due to mechanical cleaning and tool wear. 3rd World Congress on Micro and Nano Manufacturing (September 2019), 289-292.

Abstract

Inspired from the dewetting properties of Lotus leaves, the fabrication of dual micro/nano-scale topographies is of interest for many applications. In this research, superhydrophobic surfaces are fabricated by a process chain combining ultrashort pulsed laser texturing of steel inserts and injection moulding to produce polypropylene parts. This manufacturing route is very promising and could be economically viable for mass production of polymeric parts with superhydrophobic properties. However, surface damages, such as wear and abrasion phenomena, can be detrimental to the attractive wetting properties of replicated textured surfaces. Therefore, the final product lifetime is investigated by mechanical cleaning of the textured polypropylene surface with multipurpose cloths following the ASTM D3450 standard. Secondly, the surface damage of replication masters after 350 injection moulding cycles with glass-fiber reinforced polypropylene, to intensify tool wear, was investigated. The degradation of surface textures on replicas had a clear impact on surface topography and thus on their wetting properties.

PhD degree awarded to Jean-Michel Romano

On August 20th, 2019, Jean-Michel Romano successfully defended his PhD thesis, titled “Laser-based manufacturing routes for functionalizing surfaces” and was awarded the degree of Doctor of Philosophy.

The work was carried out at the University of Birmingham (UK) under the supervision of Prof. Stefan Dimov. The now Dr. Jean-Michel Romano, was an Early Stage Researcher (ESR) of the Laser4Fun project. The examination board was composed by Prof. Lin Li, Director of Laser Processing Research Centre at the University of Manchester and Dr. Nan Gao, Lecturer of Bio-medical Engineering at the Department of Mechanical Engineering at the University of Birmingham.

We congratulate Jean-Michel with this achievement!

Summary PhD thesis

Robust functional surfaces are of a growing industrial interest for a range of optical, easy-to-clean, anti-icing and non-fouling applications. At the same time, nature is a great source of inspiration for micro/nano-scale surface structures with tailored functional properties. There are a number of competing technologies for producing such structures but ultrashort laser processing is emerging as one of the most promising for fabricating bio-inspired surfaces. However, the technology has limitations and its capabilities have to be augmented to achieve the required high-throughput in manufacturing products that incorporate functional surface topographies. Therefore, this research investigates a promising process chain that combines synergistically the capabilities of laser texturing with complementary surface engineering and replication technologies. Several large-area laser texturing techniques are investigated, namely Direct Laser Writing (DLW), Laser-Induced Periodic Surface Structures (LIPSS) and microlenses-induced Photonic Jet (PJ) texturing. The research advances the knowledge in laser-based surface functionalization and also in factors affecting the functional response and durability of laser structured surfaces.

Link

https://etheses.bham.ac.uk//id/eprint/9740/1/Romano2019PhD.pdf

Springtail-Inspired Triangular Laser-Induced Surface Textures on Metals Using MHz Ultrashort Pulses

Results of the work in the Laser4Fun project has been published as:

Romano, J.M., Helbig, R., Fraggelakis, F., Garcia-Giron, A., Werner, C., Kling, R., Dimov, S., Springtail-Inspired Triangular Laser-Induced Surface Textures on Metals Using MHz Ultrashort Pulses. J. Micro Nano-Manuf  2019, 7(2), 024504. 

Abstract

Considering the attractive surface functionalities of springtails (Collembola), an attempt at mimicking their cuticular topography on metals is proposed. An efficient single-step manufacturing process has been considered, involving laser-induced periodic surface structures (LIPSS) generated by near-infrared femtosecond laser pulses. By investigating the influence of number of pulses and pulse fluence, extraordinarily uniform triangular structures were fabricated on stainless steel and titanium alloy surfaces, resembling the primary comb-like surface structure of springtails. The laser-textured metallic surfaces exhibited hydrophobic properties and light scattering effects that were considered in this research as a potential in-line process monitoring solution. The possibilities to increase the processing throughput by employing high repetition rates in the MHz-range are also investigated.

Link(s)



Durability and Wear Resistance of Laser-Textured Hardened Stainless Steel Surfaces with Hydrophobic Properties

Results of the work in the Laser4Fun project has been published as:

A. Garcia-Giron, J.M. Romano, A. Batal, B. Dashtbozorg, H. Dong, E. Martinez Solanas, D. Urrutia Angos, M. Walker, P. Penchev, S.S. Dimov (2019) Durability and Wear Resistance of Laser-Textured Hardened Stainless Steel Surfaces with Hydrophobic Properties, Langmuir 35(15) 5353-5363. doi:10.1021/acs.langmuir.9b00398.

Abstract

Hydrophobic surfaces are of high interest to industry. While surface functionalization has attracted significant interest, from both industry and research, the durability of engineered surfaces remains a challenge, as wear and scratches deteriorate their functional response. In this work, a cost-effective combination of surface engineering processes on stainless steel was investigated. Low-temperature plasma surface alloying was applied to increase surface hardness from 172 to 305 HV. Then, near-infrared nanosecond laser patterning was deployed to fabricate channel-like patterns that enabled superhydrophobicity. Abrasion tests were carried out to examine the durability of such engineered surfaces during daily use. In particular, the evolution of surface topographies, chemical composition, and water contact angle with increasing abrasion cycles were studied. Hydrophobicity deteriorated progressively on both hardened and raw stainless steel samples, suggesting that the major contributing factor to hydrophobicity was the surface chemical composition. At the same time, samples with increased surface hardness exhibited a slower deterioration of their topographies when compared with nontreated surfaces. A conclusion is made about the durability of laser-textured hardened stainless steel surfaces produced by applying the proposed combined surface engineering approach.

Link(s)

Subwavelength Direct Laser Nanopatterning Via Microparticle Arrays For Functionalizing Metallic Surfaces

Results of the work in the Laser4Fun project has been published as:

Jean-Michel Romano, Rajib Ahmed, Antonio Garcia-Giron, Pavel Penchev, Haider Butt, Olivier Delléa, Melissa Sikosana, Ralf Helbig, Carsten Werner, Stefan Dimov (2019) Subwavelength Direct Laser Nanopatterning Via Microparticle Arrays For Functionalizing Metallic Surfaces, Journal of Micro- and Nano-Manufacturing 7(1) 010901. doi:10.1115/1.4042964.

Abstract

Functionalized metallic nanofeatures can be selectively fabricated via ultrashort laser processing; however, the cost-effective large-area texturing, intrinsically constrained by the diffraction limit of light, remains a challenging issue. A high-intensity near-field phenomenon that takes place when irradiating microsized spheres, referred to as photonic nanojet (PN), was investigated in the transitional state between geometrical optics and dipole regime to fabricate functionalized metallic subwavelength features. Finite element simulations were performed to predict the PN focal length and beam spot size, and nanofeature formation. A systematic approach was employed to functionalize metallic surface by varying the pulse energy, focal offset, and number of pulses to fabricate controlled array of nanoholes and to study the generation of triangular and rhombic laser-induced periodic surface structures (LIPSS). Finally, large-area texturing was investigated to minimize the dry laser cleaning (DLC) effect and improve homogeneity of PN-assisted texturing. Tailored dimensions and densities of achievable surface patterns could provide hexagonal light scattering and selective optical reflectance for a specific light wavelength. Surfaces exhibited controlled wetting properties with either hydrophilicity or hydrophobicity. No correlation was found between wetting and microbacterial colonization properties of textured metallic surfaces after 4h incubation of Escherichia coli. However, an unexpected bacterial repellency was observed.

Link(s)