Accepted Manuscripts

Technical Brief  
Pablo Fook and Oltmann Riemer
J. Micro Nano-Manuf   doi: 10.1115/1.4043693
Despite the recent developments of ductile mode machining, micro-grinding 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 concerning different diamond grain sizes and a variation of the machining parameters. White light interferometry, scanning electron microscope, x-ray diffraction and 4-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 prosed to investigate the surface integrity of the ground workpieces, are helpful to understand the bioceramic materials response under micro-grinding conditions and to set further machining investigations.
TOPICS: Ceramics, Grinding, Machining, Bending strength, Residual stresses, Surface roughness, Mechanical properties, Vibration, Scanning electron microscopes, X-ray diffraction, Brittleness, Diamonds, Grain size, White light interferometry, Biomedicine
Technical Brief  
Chirag Alreja and Sathyan Subbiah
J. Micro Nano-Manuf   doi: 10.1115/1.4043647
A unique rotational double-taper scratching set up 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 to 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 the present study, with scratching speeds from very low to high show 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.
TOPICS: Ductile-brittle transition, Silicon, Fracture (Materials), Scanning electron microscopy, Cutting, White light interferometry, Density, Temperature, Crystals, Brittleness, Diamond tools, Diamond turning
Technical Brief  
Fábio O. Campos, Anna Carla Monteiro Araujo and Shiv G Kapoor
J. Micro Nano-Manuf   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.
TOPICS: Titanium, Micromilling, Surface roughness, Titanium alloys, Cutting, Machinability, Metals, Aluminum, Mechanical properties, Corrosion resistance, Biocompatibility
Technical Brief  
Jean-Michel Romano, Ralf Helbig, Fotis Fraggelakis, Antonio Garcia-Giron, Carsten Werner, Rainer Kling and Stefan Dimov
J. Micro Nano-Manuf   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.
TOPICS: Metals, Lasers, Surface texture, Manufacturing, Titanium alloys, Light scattering, Metal surfaces, Fluence (Radiation measurement), Process monitoring, Stainless steel
Technical Brief  
Akinori Teramachi and Jiwang Yan
J. Micro Nano-Manuf   doi: 10.1115/1.4043344
Metal additive manufacturing 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 AlSi10Mg workpiece to improve its surface/subsurface integrity. The effects of ultrasonic vibration 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 improving the surface quality of additive-manufactured products for various industrial uses.
TOPICS: Metals, Vibration, Additive manufacturing, Surface quality, Surface finishing, Manufacturing, Surface roughness
Technical Brief  
Recep Onler, Sundar V. Atre and Burak Ozdoganlar
J. Micro Nano-Manuf   doi: 10.1115/1.4043345
This paper presents an investigation of green micromachining 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 micro-scale features on ceramics is to use mechanical micromachining when the ceramics are at their green state. This approach, referred to as green micromachining (GMM), considerably reduces the forces and tool wear with respect to micromachining of sintered ceramics. As such, fundamental understanding on green micromachining 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 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 ploughing and rubbing along the cutting region was observed even with a sharp diamond tool.
TOPICS: Aluminum nitride ceramics, Micromachining, Ceramics, Cutting, Thrust, Diamond tools, Binders (Materials), Metal cutting, Particulate matter, Wear, Crystals, Tungsten, Microscale devices

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