Influence of Bulk Temperature on Laser-Induced Periodic Surface Structures on Polycarbonate

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

Marek Mezera, Jörn Bonse, Gert-willem Römer. Influence of Bulk Temperature on Laser-Induced Periodic Surface Structures on Polycarbonate. Polymers 201911(12), 1947; https://doi.org/10.3390/polym11121947

Abstract

In this paper, the influence of the bulk temperature (BT) of Polycarbonate (PC) on the occurrence and growth of Laser-induced Periodic Surface Structures (LIPSS) is studied. Ultrashort UV laser pulses with various laser peak fluence levels F0 and various numbers of overscans (NOS) were applied on the surface of pre-heated Polycarbonate at different bulk temperatures. Increased BT leads to a stronger absorption of laser energy by the Polycarbonate. For NOS<1000 High Spatial Frequency LIPSS (HSFL), Low Spatial Frequency LIPSS perpendicular (LSFL-I) and parallel (LSFL-II) to the laser polarization were only observed on the rim of the ablated tracks on the surface but not in the center of the tracks. For NOS≥1000 , it was found that when pre-heating the polymer to a BT close its glass transition temperature ( Tg ), the laser fluence to achieve similar LIPSS as when processed at room temperature decreases by a factor of two. LSFL types I and II were obtained on PC at a BT close to Tg and their periods and amplitudes were similar to typical values found in the literature. To the best of the author’s knowledge, it is the first time both LSFL types developed simultaneously and consistently on the same sample under equal laser processing parameters. The evolution of LIPSS from HSFL, over LSFL-II to LSFL I, is described, depending on laser peak fluence levels, number of pulses processing the spot and bulk temperature.

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.