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.

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)

Mechanical durability of hydrophobic surfaces fabricated by injection moulding of laser-induced textures

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

J.-M. Romano, M. Gulcur, A. Garcia-Giron, E. Martinez-Solanas, B.R. Whiteside and S.S. Dimov. Mechanical durability of hydrophobic surfaces fabricated by injection moulding of laser-induced textures. Applied Surface Science 476 (2019) 850-860

Abstract

The paper reports an investigation on the mechanical durability of textured thermoplastic surfaces together with their respective wetting properties. A range of laser-induced topographies with different aspect ratios from micro to nanoscale were fabricated on tool steel inserts using an ultrashort pulsed near infrared laser. Then, through micro-injection moulding the topographies were replicated onto polypropylene surfaces and their durability was studied systematically. In particular, the evolution of topographies on textured thermoplastic surfaces together with their wetting properties were investigated after undergoing a controlled mechanical abrasion, i.e. reciprocating dry and wet cleaning cycles. The obtained empirical data was used both to study the effects of cleaning cycles and also to identify cleaning procedures with a minimal impact on textured thermoplastic surfaces and their respective wetting properties. In addition, the use of 3D areal parameters that are standardised and could be obtained readily with any state-of-the-art surface characterisation system are discussed for monitoring the surfaces’ functional response.

Link(s)

Jean-Michel Romano awarded for his paper at WCMNM2018

JMR_WCMNM2018_awardOn the 20th September 2018, the World Congress on Micro and Nano Manufacturing took place in Portoroz, Slovenia. Jean-Michel Romano, an Early Stage Researcher (ESR) in the Laser4Fun project, was awarded of the Honorable Mention Paper Award for his contribution entitled “Towards large area submicron surface texturing by femtosecond laser irradiation of microparticle arrays”.

The award was presented by the scientific committee chair: Dr. Irene Fassi, National Research Council (CNR), Italy; Dr. Samuel Bigot, Cardiff University, UK; and Prof. Dr. Joško Valentinčič, University of Ljubljana, Slovenia.

WCMNM2018 LogoWCMNM 2018 was jointly organised by the Multi Material Micro Manufacturing association (4M), the International Institution for Micro Manufacturing (I2M2) and the International Forum on Micro Manufacturing (IFMM).

Antonio García Girón and Jean-Michel Romano attended WCMNM 2018

JMR_at_WCMNM2018A delegation of the University of Birmingham participated in the 2nd World Congress on Micro and Nano Manufacturing (WCMNM 2018) that took place on September 18-20, 2018 in Portoroz, Slovenia. WCMNM 2018 is a joint conference of the 13th International Conference on MicroManufacturing (ICOMM), the Multi Material Micro Manufacture (4M), and the International Forum on Micro Manufacturing (IFMM). It was the opportunity for ESRs Antonio García Girón and Jean-Michel Romano to disseminate results of the Laser4Fun project to a large community of micromanufacturing experts, coming from Northamerica, Europe and Japan.

FoWCMNM2018 Logor more information:
http://www.4m-association.org/conference/2018

Combined Surface Hardening and Laser Patterning for Producing Wear Resistant Hydrophobic Surfaces

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

Antonio Garcia-Giron, Jean-Michel Romano, Y. Liang, Behnam Dashtbozorg, Hanshan Dong, Pavel Penchev, Stefan Dimov. Combined Surface Hardening and Laser Patterning for Producing Wear Resistant Hydrophobic Surfaces. 2nd World Congress on Micro and Nano Manufacturing (September 2018); doi: 10.3850/978-981-11-2728-1_16

Abstract

This work reports a laser patterning method for producing surfaces with dual scale topographies on ferritic stainless steel plates that are hardened by low temperature plasma surface alloying. Nitrogen and carbon based gasses were used in the alloying process to obtain surface layers with an increased hardness from 172 HV to 1001 HV and 305 HV, respectively. Then, a nanosecond infrared laser was used to pattern the plasma treated surfaces and thus to obtain super-hydrophobicity, by creating cell- or channel-like surface structures. The combined surface hardening and laser patterning approach allowed super-hydrophobic surfaces to be produced on both nitrided and carburised stainless steel plates with effective contact angles higher than 150°. The hardened layers on nitrided samples had cracks and was delaminated after the laser patterning while on plasma carburised samples remained intact.  The results showed that by applying the proposed combined approach it is possible to retain the higher hardness of the carburised stainless steel plates and at the same time to functionalise them to obtain super-hydrophobic properties.