Tool Wear Behavior in μ-turning of Nimonic 90 Under Vegetable Oil-Based Cutting Fluid

The characteristics such as high hardness and shear modulus, low thermal conductivity, strain hardening of Nickel-based superalloys lead to high machining forces and temperature, poor surface quality and integrity, rapid tool wear, etc. The present article investigates the tool wear mechanism of the tungsten carbide (WC) tool in µ-turning of Nimonic 90 under dry, wet, and vegetable oil-based cutting fluid (VCF). Canola oil is used as vegetable oil. Three different combinations of cutting speed, feed rate, and depth of cut are considered for analysis. The tool wear is characterized using optical and scanning electron microscopy. Machining with VCF shows an approximate reduction of flank wear width in the range of 12%-52% compared to dry and wet conditions. The main wear mechanisms observed on the tool flank and rake face are abrasion, built-up edge adhesion, and edge chipping. The VCF considerably reduces the adhesion and abrasion and, hence, increases tool life. The chips produced in dry conditions are found fractured and uneven, whereas, it had an uneven lamella structure in wet conditions. The VCF found reducing the plastic deformation in each cutting condition, as a result, producing fine lamella structured chips.

Anodic Dissolution Behaviour of Passive Layer During Hybrid Electrochemical Micromachining of Ti6Al4V in NaNO3 Solution

Titanium and its alloys are considered as difficult to cut material classes, and their processing through the traditional machining methods is a painful task. These materials have an outstanding combination of properties like high specific strength, excellent corrosive resistance, and exceptional bio-compatibility; therefore, they have broad fields of application like aerospace, MEMS, bio-medical, etc. Electrochemical micromachining (ECMM) is a very vital process for the production of micro-domain features in difficult-to-machine materials. The machining issue with ECMM for titanium and their alloys is the passive layer formation, which hinders the dissolution and causes stray removal. To overcome these issues, a hybrid ECMM approach has been proposed by using a diamond abrasive tool combined with ECMM. The present study focuses on the detailed characterization of the passive layer formed using the hybrid approach. Through the use abrasive tool, the abrasive grits scoop the passive layer by the mechanical grinding action, formed in micro-drilling on the Ti6Al4V alloy to expose a new surface for further dissolution. The micro-holes were produced incorporating the abrasive tool and then compared by the holes created using a cylindrical tool (tool without abrasive). The taper and the stray dissolution of the micro-holes were also compared, produced at different applied potentials. The minimum average entry overcut and exit overcut of the hole were obtained as 29 µm and 3 µm, respectively, also a micro-hole with the lowest taper of 2.7°, achieved by the use of the abrasive micro tool.

A Comparison of Characteristics of Periodic Surface Micro/Nano Structures Generated Via Single Laser Beam Direct Writing and Particle Lens Array Parallel Beam Processing

Changing material surface micro/nano structures using laser beam texturing is a valuable approach in wide applications such as control of cell/bacterial adhesion and proliferation, solar cells and optical metamaterials. Here we report a comparison of the characteristics of surface micro/nano structures produced using single beam laser direct writing and particle lens array parallel laser beam patterning. A Nd:YVO4 nanosecond pulsed laser at 532 nm wavelength was used in the laser direct writing method to texture the stainless steel surface submerged in water and in air with different scanning patterns. Changes in surface morphology, wettability, surface chemistry and optical reflectivity were analyzed. In the particle lens array method, an excimer nanosecond laser at 248 nm wavelength was adopted to produce surface patterns on GeSbTe (GST) film coated on a polycarbonate substrate by splitting and focusing a single laser beam into millions of parallel breams. Single beam laser direct writing shows that the surface of high roughness and oxygen percentage content presented high wettability and low reflectivity characteristics. However, the controllability of the type of surface micro/nano patterns is limited. The parallel laser beam processing using particle lens array allows rapid production of user designed periodic surface patterns at nano-scale overcoming the optical diffraction limit with a high degree of controllability. Controlling the uniformity of the particle lens array is a challenge.

Design of Precision Hot Embossing Machine for Micro-Patterning on PMMA

A microfluidic chip requires micro-channels to be created on a substrate. This paper focuses on the design and development of a precision hot embossing machine for replication of microstructures on a PMMA substrate. Kinematic coupling using three spherical balls in radial v-grooves is used to achieve precise positioning of the mold insert with the base. Flexure based parallel guidance mechanism is used for one DOF motion required for the embossing process. The mechanism allows the motion of the mold normal to the substrate surface. Flexure based kinematic coupling with the thermal center is designed to mitigate thermal stress build-up during heating and cooling of the mold insert. An Arduino-based micro-controller is developed to control the temperature profile during the process. A prototype is fabricated and experiments are performed with an aluminium mold insert on a PMMA substrate. The result shows the feasibility of the concept and the set-up can be used to develop a cost-effective precision hot embossing machine for creating micro-patterns for microfluidic applications.

Characterization of the Functional Properties of Pcl Bone Scaffolds Fabricated Using Pneumatic Microextrusion

Pneumatic micro-extrusion (PME) is a direct-write additive manufacturing process, which has emerged as a robust, high-resolution method for the fabrication of a broad spectrum of biological tissues and organs. PME allows for non-contact multi-material deposition of functional inks for tissue engineering applications. In spite of the advantages and engendered potential applications, the PME process is inherently complex, governed by not only complex physical phenomena, but also material-process interactions. Consequently, investigation of the influence of PME process parameters as well as the underlying physical phenomena behind material transport and deposition in PME would be inevitably a need. The overarching goal of this research work is to fabricate biocompatible, porous bone tissue scaffolds for the treatment of osseous fractures, defects, and diseases. In pursuit of this goal, the objectives of the work are: (i) to investigate the influence of seven consequential scaffold design factors and PME process parameters on the mechanical properties of fabricated bone tissue scaffolds; (ii) to explore the underlying dynamics behind material transport in the PME process, using a 3D computational fluid dynamics (CFD) model. To investigate the effects of the design and process parameters, a series of experiments were designed and conducted. Layer height was identified as the most significant factor in this study. An increase in the layer height led to less overlap between subsequent layers, which allowed for more shrinkage and ultimately a reduction in scaffold diameter. In addition, print speed appeared as an influential factor in this study. An increase in the print speed resulted in a decline in linear mass density and thus in the extent of fusion between subsequent deposited layers. Besides, it was observed that there was a strong correlation between deposition mass and compression modulus. Overall, the results of this study pave the way for future investigation of PME-deposited PCL scaffolds with optimal functional and medical properties for incorporation of stem cells toward the treatment of osseous fractures and defects.

Effects of Solution Viscosity on PLLA Porous Microtubes Fabricated by Core-Sheath Electrospinning

Core-sheath electrospinning is a rapid microfabrication process for creating multi-layer polymer microfibers. This paper presents a process based on core-sheath electrospinning to fabricate poly(L-lactic acid) (PLLA) microtubes with nanopores on the tube wall. The morphology of the microtubes mimics human fenestrated capillary vessels. This study investigates the effects of the viscosities of the core and the sheath solutions on the microtube outer diameter and the nanopore size. The core solution shows a dominating influence on the microtube diameter. At the same core solution viscosity level, the microtube diameter is negatively correlated to the core-to-sheath viscosity ratio. The pore size is positively correlated to the microtube diameter. Understanding the effects of solution viscosity on microtube morphology is the prerequisite for process control and microtube product development for future biomedical applications.

Kinematic Design of Functional Nanoscale Mechanisms From Molecular Primitives

Natural nanomechanisms such as capillaries, neurotransmitters, and ion channels play a vital role in the living systems. But the design principles developed by nature through evolution are not well understood and, hence, not applicable to engineered nanomachines. Thus, the design of nanoscale mechanisms with prescribed functions remains a challenge. Here, we present a systematic approach based on established kinematics techniques to designing, analyzing, and controlling manufacturable nanomachines with prescribed mobility and function built from a finite but extendable number of available "molecular primitives." Our framework allows the systematic exploration of the design space of irreducibly simple nanomachines, built with prescribed motion specification by combining available nanocomponents into systems having constrained, and consequently controllable motions. We show that the proposed framework has allowed us to discover and verify a molecule in the form of a seven link, seven revolute (7R) close loop spatial linkage with mobility (degree of freedom) of one. Furthermore, our experiments exhibit the type and range of motion predicted by our simulations. Enhancing such a structure into functional nanomechanisms by exploiting and controlling their motions individually or as part of an ensemble could galvanize development of the multitude of engineering, scientific, medical, and consumer applications that can benefit from engineered nanomachines.

Design and Experimental Validation of a Process Chain for Thin Components Manufacturing by Micro Injection Molding Process

Micro applications, especially in biomedical and optical sectors, require the fabrication of thin polymeric parts which can be commonly realized by micro injection molding process. However, this process is characterized by a relevant constraint regarding the tooling. Indeed, the design and manufacturing of molds could be a very time-consuming step and so, a significant limitation for the rapid development of new products. Moreover, if the design displays challenging micro-features, their realization could involve the use of more than one mold for the fabrication of a single thin part. Therefore, a proper integration of different manufacturing micro technologies may represent an advantageous method to realise such polymeric thin micro features. In this work, a micro-manufacturing process chain including stereolithography, micro milling and micro injection molding is reported. The mold for the micro injection molding process was fabricated by means of stereolithography and micro milling, which allowed to produce low-cost reconfigurable modular mold, composed by an insert support and a removable insert. The assessment of the proposed process chain was carried out by evaluating the dimensions and the surface finishing and texturing of the milled mold cavities and molded components. Finally, a brief economic analysis compares three process chains for fabricating the micro mold showing that proposed one reduces manufacturing cost of almost 61% with the same production time.

Personal Observations of the Effects of COVID-19 Pandemic On Micromanufacturing Research and Education in the United States

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Project-Based Teaching of a Manufacturing Class During the COVID-19 Pandemic

The Plastics Engineering program at the University of Massachusetts Lowell has taught mold design and engineering to undergraduate students for over 60 years. In 2020, the unexpected arrival of the COVID-19 pandemic in March forced the instructors to revisit the class program and objectives. Similar to other academic courses, the class became virtual. This meant redesigning an intensive hands-on manufacturing class into one that could be taught and taken from our home offices while maintaining academic rigor and continuing to meet critical student learning objectives. The timing of the pandemic meant that students, who were completing tooling split designs and starting CNC programming, could not move forward with machining, assembly, and molding. Instead, their projects became virtual learning experiences. This paper provides the analysis and discussion of how new ideas in teaching were implemented to virtually introduce engineering students to the world of plastic manufacturing. The students' work was carried out on plastic part designs of their choice, some of which included thin walls (<2 mm) and micro-scale features (~ 800 ?m) typical of a micro injection molding process.