High-quality Microchannels Research Articles

Ultrafast Laser Fabrication of Microchannels on Aluminium Alloy Substrate

Aluminium alloy 6061 has a versatile application within industrial heat exchangers, heat sinks, chemical equipment, and frames of aircraft and ships. Its physical and mechanical properties such as lightweight, high strength, corrosion resistance, and thermal and electrical conductivity make it a suitable material choice for these applications. Within thermal and micro-electromechanical applications, such as heat exchanges, radiators, and heat sinks used in microelectronics, the dissipation of heat plays an important role. For optimum heat dissipation, a higher surface area is required. This can be achieved by modifying the surface by fabricating microchannels. A number of processing techniques are used for fabricating microchannels on different materials. A laser is a flexible non-contact machining tool that may be used to create any profile or contour on practically any material. In recent times due to the advancement in laser technology, the use of ultrafast laser material processing is one potential route toward further extending the fabrication of high-quality microchannels without defects caused due to heat-affected zones and in a sustainable manner. In this paper, we present an experimental work of fabrication of microchannels on an aluminium alloy 6061 surfaces by using a low power (<4 W) 400 fs laser system. The dimensional accuracy of the fabricated microchannels is assessed using scanning electron microscopy and 3D profilometry. Furthermore, as processing speed and scale is of importance in industrial laser processes, the use of scanning optics is examined as a means of developing a rapid and scalable ultrafast laser process.

Using third-harmonic radiation of Nd:YAG laser to fabricate high-quality microchannels for biomedical applications

In this work, the third harmonic radiation (337 nm) of an Nd:YAG laser was used to fabricate microchannel on UV photoresistive material. The laser radiation was focused on a photoresistive layer formed on a transparent nonmetallic substrate. The dimensions of the fabricated microchannel could be optimized by precise control of some processing parameters, such as laser power, beam radius and irradiation time. The width of channel formed in this work was minimized down to 1μm with highly sharp internal edges and uniform inclination at the neck region. This technique can be effectively used for the mass production of high quality and uniform microstructures for microfluidic devices in biomedical applications.

Experimental and numerical investigation of cutting forces in micro-milling of polycarbonate glass

Polycarbonates have found important applications in various types of industries including optical, automotive, aerospace, biomedical, and defense manufacturing industries. Conventional mechanical machining has the capability to create complex multi-scale parts and components for various materials including polymeric materials. This study investigates the cutting forces generated during the machining of polycarbonate glass using the micro-milling process. The goal of this research is to machine high quality micro-channels in polycarbonates for microfluidic applications. Both experimental investigation and numerical simulations using the Finite Element Method (FEM) have been carried out to assess the cutting forces generated in three directions during machining of polycarbonate. The effectiveness of tool coating on the reduction of cutting forces has been investigated. It was found that with the careful combination of depth of cut and feed rate, the ductile mode machining of polycarbonate can be achieved, which produces lower cutting forces, that could result in improved surface finish and low tool wear. Both lower and higher of depths of cut were found to generate higher cutting forces due to dragging action and higher tool-workpiece contact area respectively. The Finite Element Method (FEM) was found to be effective in simulating the cutting forces with acceptable range of errors, and thus, could be used to predict cutting forces at the parametric combinations beyond the capacity of the machine or without carrying out further expensive experimentation, for which the chances of tool failure are higher.

Experimental investigations of nanosecond-pulsed Nd:YAG laser beam micromachining on 304 stainless steel

The demand for miniaturized components is increasing day by day as their application varies from industry to industry such as biomedical, micro-electro-mechanical system and aerospace. In the present research work, high-quality micro-channels are fabricated on 304 stainless steel by laser beam micromachining process with nanosecond Nd:YAG laser. The laser pulse energy (LPE), scanning speed (SS) and scanning pass number (SP No.) are used as the process parameters, whereas the depth and width of the kerf as well as the surface roughness are used to characterize the micro-channels. It is found that the kerf depth, width and surface roughness decrease with increase in the SS. The kerf depth sharply increases with increase in the SP No. The kerf width is minimum at 30 mJ LPE, 400 µm s‒1 SS and 10 SP No. The minimum surface roughness is observed at 30 mJ LPE, 500 µm s‒1 SS and 10 SP No. The oxygen content is found to gradually decrease with the distance from the centre of the micro-channel. Based on the experimental results, optimized input parameters can be offered to control the micro-channel dimensions and improve their surface finish effectively on stainless steel.

Effective methods for fabricating trapezoidal shape microchannel of arbitrary dimensions on polymethyl methacrylate (PMMA) substrate by a CO2 laser

The typical triangular-shaped microchannels fabricated by CO2 laser-based microchanneling of polymethyl methacrylate yield low performance in heat sinks, chemical reactors, and other microfluidic devices. Trapezoidal and rectangular microchannels are more commonly used and desired. To fabricate high-quality trapezoidal microchannels using a CO2 laser on polymethyl methacrylate substrates, a two-pass fabrication method is introduced using the offset ratio of 45% to yield a clean cross section. To determine the optimal process parameters to achieve trapezoidal microchannels of desired dimensions, the effects of process parameters were further investigated and groups of equations were derived based on nonlinear regression models. A microfluidic chip was fabricated to compare the performance of triangular and trapezoidal microchannels of the same cross sectional area. The results demonstrated the superior performance of the trapezoidal microchannel fabricated using two-pass fabrication. This indicates that the two-pass fabrication method is a viable rapid and economic solution for fabrication of high-quality microchannels on polymethyl methacrylate-based devices.

Channel polymer optical waveguides embedded in glass: Design, fabrication and characterization

In this work, the design, fabrication and experimental evaluation of new channel polymer optical waveguides embedded in glass are reported. We show that high quality microchannels in glass, without roughness on the walls, make possible the fabrication of new channel optical waveguides by filling the microchannels with a polymer. Guided light through those new optical waveguides is demonstrated experimentally. The commercial software OlympIOs was used to design multimode and monomode channel polymer optical waveguides. The microchannels in glass substrate were fabricated by using a laser lithography system and wet-etching procedures. The spin-coating technique was applied to deposit the polymer inside the microchannels. The end-coupling method was implemented for the waveguides characterization. Theoretical and experimental results have confirmed light confinement as well as guided modes propagation by these new channel optical waveguides.

Study of Machining Microchannels on Quartz by the Laser-Induced Plasma

In order to fabricate high-quality microchannels in a fused silica, the fundamental frequency laser with the wavelength of 1064nm of a Q-switched Nd:YAG laser and the mixing laser composed of 70 percent second harmonic laser and 30 percent fundamental frequency laser are used to irradiate a fused silica substrate respectively to induce the plasma, by which microchannels in a fused silica substrate were fabricated.The result show that the interior wall of the microchannels processed by mixing laser are smoother and the drilling rate is faster than ones processed by fundamental frequency. Furthermore, the depth of the microchannels processed by the mixing laser is up to 8mm, longer than the depth of 4mm reported at present. The reasons of causing to the differences between two kinds of processing are analyzed.

Fabrication of microchannels in glass using focused femtosecond laser radiation and selective chemical etching

We use the combination of femtosecond laser dielectric modification and selective chemical etching to fabricate high-quality microchannels in glass. The photoinduced modification morphology has been studied in fused silica and in borosilicate glass BK7, using ultra-high spatial resolution techniques of selective chemical etching followed by atomic force or scanning electron microscopy. The analysis shows that the high differential etch rate inside the modified regions, is determined by the presence of polarization-dependent self-ordered periodic nanocracks or nanoporous structures. We also investigate the optimum irradiation conditions needed to produce high-aspect ratio microchannels with small symmetric cross-sections and smooth walls.

Micromachining of complex channel systems in 3D quartz substrates using Q-switched Nd:YAG laser

A novel microchannel fabrication technology for quartz using a Q-switched Nd:YAG laser is presented. Complex 3D channel systems inside quartz substrates can be constructed directly using a laser beam by controlled fracturing, and high-quality microchannels can be fabricated by melting quartz using a laser-induced plasma. The behavior of laser-induced plasmas in drilling microchannels is discussed. The diameter of the microchannels can be controlled from 25 to 200 μm. The average roughness of the interior channel wall is less than 0.2 μm. Currently, microchannels longer than 4 mm in fused-quartz cubes can be achieved using laser-induced plasmas.