Research Papers

J. Micro Nano-Manuf. 2019;7(2):021001-021001-6. doi:10.1115/1.4044219.

The fabrication of microstructured polymer optics enables a multitude of new options in the design of technical optics. However, challenges arise along the varying process chains of mold insert fabrication, integration into molding tools, replication by means of injection compression molding and metrology. In order to study the effects, diffractive optical elements (DOE) and microlens arrays (MLA) are fabricated using two different process chains. DOEs are fabricated using a laser direct writing (LDW) based mold insert fabrication. The MLA mold insert is produced using ultra-precision milling (UP-milling). Both optical parts are replicated using injection compression molding. The occurring effects are discussed and the results show, that with complete process control high quality microstructured polymer optical parts can be produced and characterized.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Micro Nano-Manuf. 2019;7(2):024501-024501-7. doi:10.1115/1.4043344.

Metal additive manufacturing (AM) has been attracting attention as a new manufacturing method, but a surface finishing process is usually needed to improve the surface quality. As a new surface finishing process, ultrasonic vibration-assisted burnishing (UVAB) is promising. In this study, UVAB was performed on an additive-manufactured AlSi10 Mg workpiece to improve its surface/subsurface integrity. The effects of ultrasonic vibration (UV) and lateral tool pass width on the burnishing performance were investigated. It was observed that the surface roughness, filling ratio, and hardness of the surface layer were simultaneously improved after burnishing. This study shows the effectiveness of applying UVAB to improve the surface quality of additive-manufactured products for various industrial uses.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2019;7(2):024502-024502-7. doi:10.1115/1.4043957.

This paper presents our preliminary study of the microstructured surface on microgrooves patterns, which have manufactured using the three-dimensional elliptical vibration texturing (3D-EVT) method. The 3D-EVT method uses a three-dimensional trajectory of elliptical locus of the cutting tool tip in high vibration frequency to fabricate the microstructure or the vibration mark pattern on the machined surface. The experimental study has been done with a variation of the nominal cutting speeds from 300 to 600 mm/min. The preliminary results showed that in the low nominal cutting speed of 300 and 450 mm/min, the microstructured surfaces were not manufactured well due to the bulging existence on the microstructured surface in which it is correlated with the build-up edge phenomena. On the other hand, a relative excellent microstructured surface can be achieved at the higher nominal cutting speed of 600 mm/min. In addition, a lubricant could be used to obtain an excellent microstructured surface to avoid the built-up edge phenomena.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2019;7(2):024503-024503-4. doi:10.1115/1.4043693.

Despite the recent developments of ductile mode machining, microgrinding of bioceramics can cause an insufficient surface and subsurface integrity due to the inherent hardness and brittleness of such materials. This work aims to determine the influence of a two-step grinding operation on zirconia-based ceramics. In this regard, zirconia (ZrO2) and zirconia toughened alumina (ZTA) specimens are ground with ultrasonic vibration assistance within a variation of the machining parameters using two grinding steps and different diamond grain sizes of the tools in each of the machining procedure. White light interferometry, scanning electron microscope, X-ray diffraction (XRD), and four-point bending tests are performed to evaluate surface roughness, microstructure, residual stresses, and flexural strength, respectively. The strategy applied suggests that the finished parts are suitable for certain biomedical uses like dental implants due to their optimum surface roughness. Moreover, concerning the mechanical properties, an increase of the flexural strength and compressive residual stresses of ground ZrO2 and ZTA workpieces were observed in comparison to the as-received specimens. These results, as well as the methodology proposed to investigate the surface integrity of the ground workpieces, are helpful to understand the bioceramic materials response under microgrinding conditions and to set further machining investigations.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2019;7(2):024504-024504-5. doi:10.1115/1.4043417.

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.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2019;7(2):024505-024505-5. doi:10.1115/1.4043647.

A unique rotational double-taper scratching setup is used to study ductile brittle transitions in single crystal (100) p-type silicon using a conical diamond tool at room temperature and scratching speeds ranging between 0.1 m/s and 0.3 m/s. In such a setup, transition from brittle to ductile occurs twice in a single-tapered scratch, during tool entry and tool exit. A well-defined way to determine critical depth of cut via linear crack density per unit crack length is proposed. The scratches were studied using scanning electron microscopy (morphology) and white light interferometry (depth measurements). A comprehensive study of critical depth of cut, compiled from the literature together with data from this study, with scratching speeds from very low to high shows that critical depth of cut decreases from very low scratch speeds to medium scratch speeds and then increases again at very high scratch speeds. An inference from this study is that diamond turning should be conducted at higher cutting speeds than being undertaken today to make use of larger critical depths of cut.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2019;7(2):024506-024506-6. doi:10.1115/1.4043501.

Pure titanium is the ideal metallic material to be used for producing dental implants due to its good corrosion resistance and biocompatibility. However, pure titanium does not present high mechanical resistance, which can be a limiting factor. Recently, the pure titanium is being replaced by titanium alloy with aluminum and vanadium (Ti–6Al–4V). This study deals with micromilling machinability of pure titanium and Ti–6Al–4V considering mechanical properties, the forces measured during the process, surface roughness, top burr height, and chips morphology. The cutting tests are performed for the constant depth of cut and cutting speed, and a range of feed per tooth from 0.5 to 4.0 μm/tooth. Results show no significant differences in roughness and burr formation, whereas higher forces are found for the titanium alloy compared to pure metal. Both materials produce long chips for smaller feeds.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2019;7(2):024507-024507-4. doi:10.1115/1.4043941.

Magnesium alloys have a good potential as structural biomaterials for temporary implant applications because of their self-degradation properties and biocompatibility. The surface condition is important for such applications, and lasers are often used to modify the surface characteristics of such components. In this context, the media through which the laser beam passes before reaching the surface to be irradiated is also of interest. In particular, laser irradiation in liquids affects the thermal energy delivery to the surface of the material, which in turns influences the formation of surface structures. In this work, rare earth containing WE54 Mg alloy has been irradiated under air and through a simulated body fluid (SBF) layer using a 500 watt pulsed Nd: YAG laser. As compared to direct laser surface treatment through air, laser irradiation through SBF generates new surface structures and deposition of ions issued from the SBF solution. Scanning electron microscope combined with energy dispersive spectroscopy (EDS) was used for the examination of surface structures formation and determination of elemental composition. Mesenchymal stem cells (MSC) culture was performed on laser modified WE54 alloy surface, and the MSC cytocompatibility on SBF-treated substrates was evaluated by the PrestoBlue™ assay test method. Cell reproducibility was observed on the SBF laser-treated surface which indicated that cell viability was improved by the surface treatment. The deposition of calcium and phosphorus ions on the WE54 surface was beneficial for cell viability. These results motivate the potential use of SBF-based films for biomedical purposes.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2019;7(2):024508-024508-5. doi:10.1115/1.4043959.

In drilling, chip-clogging results in increased drilling temperature, excessive tool wear, and poor hole quality. Especially, in microdrilling, low rigidity of the tool and inability of cutting fluid to penetrate narrower tool–workpiece interface significantly reduce the drilling performance. A novel bubble-mixed cutting fluid delivery method proposed in this research aims toward achieving a high-performance micro deep-hole drilling process with a significant reduction in the consumption of cutting fluid. Experimental results show that the bubble-mixed cutting fluid delivery method achieves lower thrust force during drilling, higher drilled depth before tool breakage, and lower dimensional and circularity errors when machining deep holes in comparison with dry cutting or conventional flood delivery method. It is also found that the smaller-sized bubbles effectively penetrate the tool–workpiece interface during the drilling producing deeper holes by better chip evacuation and cooling.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2019;7(2):024509-024509-5. doi:10.1115/1.4043345.

This paper presents an investigation of green micromachining (GMM) forces during orthogonal micromachining green-state AlN ceramics. Green-state ceramics contain ceramic powders within a binder; processed samples are subsequently debound and sintered to obtain solid ceramic parts. An effective approach to create microscale features on ceramics is to use mechanical micromachining when the ceramics are at their green state. This approach, referred to as GMM, considerably reduces the forces and tool wear with respect to micromachining of sintered ceramics. As such, fundamental understanding on GMM of ceramics is critically needed. To this end, in this work, the force characteristics of powder injection molded AlN ceramics with two different binder states were experimentally investigated via orthogonal cutting. The effects of micromachining parameters on force components and specific energies were experimentally identified for a tungsten carbide (WC) and a single crystal diamond tools. As expected, the thrust forces were seen to be significantly larger than the cutting forces at low uncut chip thicknesses when using the carbide tool with its large edge radius. The cutting forces are found to be more sensitive to uncut chip thickness than the thrust forces are. When a sharp diamond tool is used, cutting forces are significantly larger than the thrust forces even for small uncut chip thicknesses. The specific energies follow an exponential decrease with increasing uncut chip thickness similar to the common trends in metal cutting. However, due to interaction characteristics between cutting edge and ceramic particles in the green body, evidence of plowing and rubbing along the cutting region was observed even with a sharp diamond tool.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2019;7(2):024510-024510-5. doi:10.1115/1.4044266.

This study compares fluid velocity magnitude and direction for three different glassy carbon (GC) electrode systems effecting alternating current (AC) electroosmotic pumping. The flow behavior is analyzed for electroosmotic pumping performed with asymmetric coplanar electrodes. Subsequently, effects of adding microposts array of two different heights (40 μm and 80 μm) are studied. Experimental results demonstrate that as peak-to-peak voltage is increased above 10 V peak-to-peak, the flow reversal is achieved for planar electrodes. Utilization of microposts-enhanced asymmetric electrodes blocks the flow reversal and alters the magnitude of the fluid velocity at the application of larger voltages (above 10 V peak-to-peak). Understanding of the consequences of three-dimensional geometry of asymmetric electrodes would allow designing the electrode system for AC electroosmotic pumping and mixing, as well as bidirectional fluid driving with equal forward and backward flow velocities.

Commentary by Dr. Valentin Fuster

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