Machining operations such as reaming, boring or milling create undesirable extruded sharp edges at the entry and exit side of the machined holes. These sharp burrs / extruded edges act as stress concentration regions for fatigue crack propagation in safety critical aerospace components. In this paper, results of an experimental investigation carried out on surface integrity of titanium based alloy during mechanized edge profiling process are presented. In the Mechanized Edge Profiling (MEP) process the primary sharp edges created as result of hole machining are removed using a hard point countersink tool and the secondary sharp edges produced due to countersinking/chamfering the hole entry and exit side edges are radiused using nylon impregnated silicon carbide brushes. On-machine edge profiling experiments were conducted using compliant Flexhone™ and Novoflex™ globular abrasive brushes on highly stressed bolt/flange holes. Brushing speed and feed rate were identified as key process variables. Nylon impregnated with silicon carbide 320 grit brush showed good performance when brushing at a speed of 5000rpm and 5000mm/min feed rate which produced a very consistent and controlled secondary edge radius of 0.3±0.2mm up to 30 holes. An acceptable surface roughness (Ra) of less than 0.5μm on the chamfer and bore surfaces were achieved.

Bottoms-up cost analysis has been a mainstay of commoditized industry and manufacturing processes for years, however a holistic objective supply chain analysis to inform research and investment in the development of early stage technologies has not. The potential for rapid adoption of wide bandgap (WBG) semiconductors, specifically silicon carbide (SiC), highlights a need to understand the drivers of location-specific manufacturing cost, global supply chains, and plant location decisions. Further, ongoing research and investment, necessitates analytical analysis to help inform the roadmap of SiC technologies. In collaboration with PowerAmerica the project explores the bottoms-up cost analysis of wafers, devices, modules, and variable frequency motor drives at the anticipated manufacturing levels. Leveraging these models, it outlines how the cost reduction potential of proposed research advances can be quantified.

The high quality surface can exhibit the irreplaceable application of single crystal silicon carbide in the fields of optoelectronic devices, integrated circuits and semiconductor. However, high hardness and remarkable chemical inertness lead to great difficulty to the smoothing process of silicon carbide. Therefore, the research presented in this paper attempts to smooth silicon carbide wafer with photocatalysis assisted chemical mechanical polishing (PCMP) by using of the powerful oxidability of UV photo-excited hydroxyl radical on surface of nano-TiO 2 particles. Mechanical lapping was using for rough polishing, and a material removal model was proposed for mechanical lapping to optimize the polishing process. Several photocatalysis assisted chemical mechanical polishing slurries were compared to achieve fine surface. The theoretical analysis and experimental results indicate that the material removal rate of lapping process decreases in index form with the decreasing of abrasive size, which corresponds with the model developed. After processed with mechanical lapping for 1.5 hours and subsequent photocatalysis assisted chemical mechanical polishing for 2 hours, the silicon carbide wafer obtains a high quality surface with the surface roughness at Ra 0.528 nm The material removal rate is 0.96 μm/h in fine polishing process, which is significantly influenced by factors such as ultraviolet irradiation, electron capture agent (H 2 O 2 ) and acidic environment. This combined method can effectively reduce the surface roughness and improve the polishing efficiency on silicon carbide and other hard-inert materials.

Dye-Sensitized Solar Cells (DSSC) are third generation solar cells used as an alternative to c-Si solar cells. DSSC are mostly flexible, easier to handle and are less susceptible to damage compared to c-Si solar cells. Additionally, DSSC is an excellent choice for indoor application as they perform better under diverse light condition. Most DSSCs are made of liquid medium sandwiched between two conductive polymer layers. However, DSSCs have significantly lower efficiencies compared to silicon solar cells. Also, use of liquid medium resulting in leaking of liquid, and occasional freezing during cold weather, and thermal expansion during hot weather conditions. DSSC can be manufactured in small quantities using relatively inexpensive solution-phase techniques such as roll-to-roll processing and screen printing technology. However, scaling-up the DSSC manufacturing from small-scale laboratory tests to sizeable industrial production requires better and efficient manufacturing processes. This research studies the feasibility of using additive manufacturing technique to fabricate electrodes of DSSC. The study aims to overcome the limitations of DSSCs including preventing leakage and providing more customized design. Experimental studies are performed to evaluate the effects of critical process parameters affecting the quality of electrodes for DSSC. Volume resistivity test is performed to evaluate the efficiency of the electrodes. In this study, the electrodes of DSSC are successfully fabricated using Fused Disposition Modeling (FDM) 3D printing technique. The results of this study would enable additive manufacturing technology towards rapid commercialization of DSSC technology.

In this paper, the commercial FEM software package Abaqus is employed to model the novel nanomachining process, Vibration Assisted Nano Impact machining by Loose Abrasives (VANILA), which combines the principles of vibration-assisted abrasive machining and tip-based nanomachining to conduct nano abrasive machining of hard and brittle materials. In this novel nanomachining process, an atomic force microscope (AFM) is used as a platform and the nano abrasives injected in slurry between the workpiece and the vibrating AFM probe impact the workpiece and result in nanoscale material removal. Diamond particles are used as the loose abrasives. The effects of impact speed, angle of impacts, and the frictional coefficient between the workpiece and abrasives are investigated using Abaqus. It is found that the impact speed, impact angle, and frictional coefficient between the silicon workpiece and nanoabrasives have big influence on the nanocavity’s size and depth.

Higher temperature assisted processing of silicon, such as in heat-assisted diamond turning, is often being considered to improve surface integrity. At higher temperatures and under mechanical loading and unloading, caused by the moving tool, silicon deforms plastically often in association with occurrence of phase transformations. This paper investigates such phase transformations in rotational scratching of single crystal (100) p-type silicon with a conical diamond tool under various furnace-controlled temperatures ranging from room temperature to 500 °C and at scratching speeds comparable to that used in the diamond turning process (1 m/s). Phase transformation study, using Raman spectroscopy, at various crystal orientations, show differences in phases formed at various temperatures when compared to that reported in indentation. The tendency to form phases is compared between scratched and diamond turned surfaces at room temperature, and also with that reported at low scratching speeds in the literature. Analysis of depths of the scratched groove indicates that that at temperatures beyond a certain threshold, plastic deformation and significant elastic recovery may be causing shallow grooves. This study is expected to help tune heat-assisted diamond turning conditions to improve surface formation.

Machining of hard and brittle materials such as ceramics and semiconductors has been a challenge for many years. They have many applications in optics, MEMS and electronic industries due to their many desirable properties, such as being light weight, strong, and hard. Achieving good surface finish, avoiding surface and subsurface damage and at the same time achieving a high material removal rate are extremely challenging for these materials. Materials such as single crystal silicon and sapphire have a crystal orientation or anisotropy effect which makes their machining even more difficult. Because of this characteristic, their behavior is directional and they have different fracture toughness for each direction. In past works in our research group, it has been demonstrated that machining of brittle materials in ductile regime is possible due to the high pressure phase transformation (HPPT) occurring in the material caused by the high compressive and shear stresses induced by a single point diamond tool tip. In the current study scratch tests were performed on the monocrystal sapphire in four different perpendicular directions and to further augment the process, traditional cutting is coupled with a laser to heat and soften the material to either enhance the ductility, resulting in a deeper cut, or reducing brittleness leading to decreased fracture damage. Results of scratch tests, with and without laser heating, for different cutting loads have been compared. The effect of laser heating was studied by analyzing the image of cuts and verifying the depth of cuts which were made using varying laser power during the process. Microscopic images and three-dimensional profiles of the cuts taken by using a white light interferometer were investigated.

Materials such as glass and silicon dioxide have seen increased applications due to their advantageous properties including high strength and corrosion resistance. However, machining these materials are challenging due to their hard and brittle nature. Even though techniques such as abrasive jet machining have improved machining quality, they typically suffer from low productivity and poor surface integrity with subsurface cracks. This study focuses primarily on attaining high quality machined surface free from sub-surface cracks on BK7 samples by inducing microcracks on to the material. The hypothesis is that microcracks induced by femtosecond laser would synergistically assist the material removal process by weakening the material layer to be removed. As the first phase of research, the cracks are initiated starting from the material surface. Results show that machining laser-treated samples leads to on average 75% force reduction in comparison with machining untreated samples. Laser treated machined samples are produced without subsurface damages, and reduced tool wear is also noted.

This paper presents the research on the machinability studies in micro-milling of (001) silicon wafer. Excessive generation of undesirable surface and subsurface damages such as surface edge chipping often occurs when machined at depth of cut of several hundreds of microns. Ideal machining strategy to reduce the generation of edge chipping is required. Investigations on the effect of machining conditions on the cutting performances and size effect on the specific cutting energy in silicon micro-milling were conducted. These investigations provide understandings on the behavior of cutting mechanism during machining and helps to identify suitable machining parameters for fracture free machining using diamond end mills. Full slot milling were performed along <100> and <110> directions on a (001) surface wafer under various machining conditions. Results show that machined surfaces along <100> were of better quality than those along <110> and is in agreement with previous studies. Furthermore, good machining quality was achieved when machined at depth of cut of 10 μm or feed per tooth of 0.075 μm/tooth, regardless of the machining conditions. In addition, investigation for the size effect on specific cutting energy also shows that brittle mode machining begins when feed per tooth increases beyond 0.4 μm/tooth.

Nanotechnology has been presenting successful applications in several field, such as electronics, medicine, energy and new materials. However, the high cost of investment in facilities, equipment and materials as well as the lack of some experimental analysis at the nanoscale can restrain research in nanotechnology. The implementation of accurate computer models can alleviate this problem. This work investigates the Leidenfrost effect at the nanoscale using molecular dynamics simulation. Models of water droplets with diameters of 4nm and 10nm are simulated over gold and silicon substrates. To induce the Leidenfrost effect, droplets at 293K were deposited on the substrates at 373K. As a baseline, simulations were run with substrates at room temperature. Results show that for substrates at 293K, the 4nm droplet has higher position variability than the 10nm droplets. For substrates at 373K, the 4nm droplets have higher velocities than the 10nm droplets. The wettability of the substrate also influences the Leidenfrost. Droplets over the gold substrate which has hydrophobic characteristics have higher velocities as compared to droplets over silicon that has a hydrophilic behavior. Moreover, the Leidenfrost effect was observed at the boiling temperature of water (373K) which is a significantly lower temperature than reported in previous experiments at the microscale.

Mimicking the unique hierarchical, multiscale structures of natural biological materials is a promising approach to create novel materials with outstanding properties. One of the challenges, however, is the lack of scalable fabrication methods capable of making such complex structures. In this study, a multilayer nanocomposite has been synthesized by incorporating an ultrasonic spray deposition technique. The spray deposition system was used to deposit nanoparticles on substrate foils, which were consolidated to synthesize the multilayer composite. A patterned mask was used to create micro-patterns with nanoscale structures. A magnesium alloy, AZ31, foils were used as the matrix material. A mixture of nano-silicon carbide (nano-SiC) and aluminum alloy, Al6061, particles was used as the reinforcement phase in the deposited patterns. A three point bend test and a small punch test were carried out to evaluate the mechanical properties. A multilayer composite consisting of circular micro-patterns with SiC nano-structure was successfully created. The patterned composite showed an enhancement in the flexural yield strength and the flexural ultimate strength of 43% and 30% respectively, compared with the uniform multilayer composite without the patterns.

Motivated by previous work on three-dimensional (3D) fabrication inside dielectrics, we report experimental results of 3D modification inside intrinsic silicon wafers using laser pulses with 1.55 μm wavelength and 3.5 ns pulse duration. Permanent modification in the form of lines is generated inside silicon by tightly focusing and continuously scanning the laser beam inside samples, without introducing surface damage. Cross sections of these lines are observed after cleaving the samples, and are further analyzed after mechanical polishing followed by chemical etching. With the objective lens corrected for spherical aberration, tight focusing inside silicon is achieved and the optimal focal depth is identified. The laser-induced modification has a triangular shape and appears in front of the geometrical focus, suggesting significant absorption in those regions and resulting in reduced energy density. The morphology of modified regions is found to be dependent on the laser polarization.

Silicon is an excellent transparent material for building IR micro-optical elements such as holographic and blazed gratings, and curvilinear micro-lenses. Shaping this material in 3D with mirror quality finish and single-digit microscale resolution is challenging due to its brittleness and high-melting point. To achieve these patterning characteristics, electron-beam grayscale lithography is typically selected to pattern a 2.5D feature onto a resist thin-film. Subsequently, the film features are transferred into the underlying silicon substrate by deep-reactive ion etching (DRIE) [1]. Small variations in the resist thickness lead to large shape distortions and reduced patterning repeatability. Further, the direct-write nature of e-beam lithography provides for slow throughput. Developing an alternative, parallel and scalable method to nanopatterning silicon with 2.5D geometrical control may impact emerging areas such as the design of sub-wavelength photonic and micro-optic elements for silicon photonics applications. Micro and nanoscale patterning of inorganic semiconductors (e.g. Silicon) requires traditional micromachining processes such as plasma-assisted etching (e.g. DRIE) and wet-etching (e.g. KOH etching). Neither of the aforementioned processes offer the capability to control the geometry in 3D with resolution in the nanoscale range. Thus, it is desirable to develop a low-temperature, low-stress and ambient approach to nanostructuring silicon in 3D. Wet etching approaches are good candidates for achieving such goal because they bypass the need for high-temperature processing and stressing materials beyond the elastic limit. Yet, they still rely on lithographical steps and offer limited sidewall control, restricting the scope of features it can produce. In recent literature, catalyst-based wet etching processes such as metal-assisted chemical etching (MACE) have been shown to pattern high-aspect ratio structures in semiconductors [2–3]. Some researchers have achieved control over the etch profile and etching direction, generating a limited set of interesting 3D objects [4–6]. The degrees of freedom in MACE patterning are still highly constrained due to limited control of the catalyst motion. Additionally, thin-film based MACE relies on intermediate 2D masking steps to pattern the catalyst which are often lithographical. Thus, this indirect approach to patterning silicon increases lead time and processing costs. In this paper, Mac-imprint, a direct imprint configuration of MACE, is introduced to overcome these fundamental barriers. It relies on the use of a catalytic stamp immersed in the etchant and brought against a silicon chip to selectively dissolve it at contact points. Stamps can be reused multiple times to pattern substrates with lifetimes that are dependent solely on its chemical and mechanical degradation. This process is inherently non-lithographic and occurs at room temperature. As a demonstration of its high-resolution capabilities, silicon wafers were patterned with a sinusoidal wave whose pitch and amplitude were 1 μm and 250 nm, respectively. The patterned surface RMS error from the ideal surface was measured to be 13 nm. The key drawback of this approach is the generation of porous defects near the vicinity of the contact interface between stamp and substrate. Its spatial distribution is qualitatively discussed in the context of the diffusion model of MACE [7].

Cold roll bonding (CRB), a fabrication process that proceeds at room temperature, has been widely used in fabricating large-scale sheet metal composites. In this study, the effect of reinforcement particle sizes, ranging from nanoscale to microscale, on the bond strength of cold roll bonded aluminum silicon carbide (Al-SiC) composites has been investigated. The bond strength was measured by the T-peel test. Scanning electron microscope was employed to study the bonding behavior at the interface of the laminate composites. Nanoparticles failed to increase the bond strength compared with the unreinforced Al sample. On the other hand, relatively large particles (tens of micrometers) increased the bond strength noticeably due to the mechanical interlocking introduced by the particles. For the largest particle (60 μm) used in this study, the bond strength was large enough to tear the Al1100 strip during the T-peel test.

The continuous trend towards miniaturization of metallic micro parts of high quality at low costs results in the need of appropriate production methods. Mechanical manufacturing processes like forming and blanking meet these demands. One major challenge for the application of them are so called size effects. Especially the downsizing of the required manufacturing tools and adequate positioning causes higher effort with increasing miniaturization. One promising approach for downsizing of tools is the transfer of knowledge from microsystems technology. This study shows the process behavior of etched silicon punches in microblanking operations. For the application as tool material especially the brittle material behavior and sensitivity against tensile stresses have to be considered. These mechanical loads favor wear in form of cracks and breaks at the cutting edge of the punch and decrease tool life. In a special test rig these wear phenomena were observed in microblanking of copper foils. Although high positioning accuracy between tools and workpiece can be assured within this test rig, scatter of tool life is observable. Therefore, a finite element analysis of the tool load in the microblanking process with special respect to tensile stresses was performed. Within the 3D finite element model multidimensional positioning errors like tilting between punch and die were integrated. Their influence on the tool load in form of increasing tensile stresses is evaluated with respect to the type and magnitude of positioning error. Furthermore, the effects of small outbreaks at the cutting edge on the process behavior and tool load are analyzed.

In this study, single point diamond turning (SPDT) is coupled with the micro-laser assisted machining (μ-LAM) technique. The μ-LAM system is used to preferentially heat and thermally soften the work piece material in contact with a diamond cutting tool. In μ-LAM the laser and cutting tool are integrated into a single package, i.e. the laser energy is delivered by a single mode fiber laser to and through a diamond cutting tool. This hybrid method can potentially increase the critical depth of cut (DoC), i.e., a larger ductile-to-brittle transition (DBT) depth, in ductile regime machining, resulting in a higher material removal rate (MRR). An IR continuous wave (CW) fiber laser, wavelength of 1064nm and max power of 100W with a beam diameter of 10μm, is used in this investigation. In the current study SPDT tests were employed on single crystal silicon (Si) wafer which is very brittle and hard to machine by conventional methods. Different outputs such as surface roughness and depth of cut for different set of experiments were analyzed. Results show that an unpolished surface of a Si wafer can be machined in one pass to get a very good surface finish. The Ra was brought down from 1.2μm to 275nm only in one pass which is a very promising result for machining the Si wafer.

Direct Metal Laser Sintering (DMLS) is an additive manufacturing technology that can construct medium to small size parts very efficiently in comparison to traditional machining processes. The ability of this technology to grow complex parts made of high strength titanium- and nickel-based alloys led to increasing interest from aerospace, defense, and medical industries. Although the technology allows growing parts close to their final shape, the active surfaces still need a finishing operation such as grinding to meet the tight tolerances and surface finish requirements. Due to the novelty of the DMLS technology, and the relatively recent developments of titanium alloy powders, there is a need for testing and validating the capabilities of the components manufactured through a combination of DMLS and grinding processes. This paper presents the findings of an experimental study focused on the effect of various grinding conditions on the surface integrity of titanium alloy (Ti-6Al-4V) specimens produced using DMLS technology. The goal is to identify dressing and grinding conditions that would result in ground surfaces free of defects such as micro-cracks, discoloration of surfaces and/or burn marks due to high heat generated during grinding. The residual stresses were used to quantify the effect of the grinding conditions on the ground surfaces. These investigations were conducted on an instrumented CNC surface grinding machine, using a silicon-carbide grinding wheel and a water-based fluid. The X-ray diffraction method was used to measure the residual stresses. Two batches of specimens were manufactured for these tests. The growing strategy of the specimens and the presence of apparent defects in material structure are considered some of the main causes for the differences observed in the outcomes of the grinding trials. The results of these investigations support the need for continuing research in the additive manufacturing field to develop methods and technologies that will ensure a high level of consistency of the grown parts.

The fabrication of nanoparticle reinforced sheet metal composites may result in composites with promising mechanical, thermal and electrical properties. Cold roll bonding (CRB) is a good candidate for fabricating such composites as it can be easily scaled up for industrial production. Moreover, it eliminates some of the problems accompanied with conventional metal matrix composite (MMC) fabrication methods. This study begins by looking at the effects of surface preparation on the CRB process. Additionally, it looks at fabrication of aluminum-silicon carbide (Al-SiC) composites using CRB and an ultrasonic spray deposition technique. Further, the accumulative roll bonding (ARB) process is investigated as a possibility for increasing the loading capacity of reinforcement particles. The bond strength was tested using a peel test and the bonding and process quality was inspected and analyzed with optical microscopy. The addition of the SiC nanoparticles at the interface increased the bond strength by approximately 1.5 and 2.0 times that of the unsprayed sample. The samples fabricated using ARB were successfully bonded and samples composed of up to 128 layers were successfully fabricated.

Reinforcement with nano-sized particles offers a promising potential to significantly enhance the mechanical, electrical, and thermal properties of a metal matrix composite (MMC). One of the challenges of synthesizing nanocomposites, however, has been the dispersion and control of the nano-reinforcement materials. In this study, a laminate nanocomposite has been synthesized by incorporating ultrasonic spray deposition technique. An ultrasonic spray deposition system was used to deposit nano-particles on substrate foils, which were consolidated to synthesize a laminate composite. Aluminum 6061 (Al6061) alloy foils were used as the matrix material. Nano-silicon carbide (SiC) particles were used as the reinforcement phase (deposited layer). The sprayed foils were stacked together to form the composite. The composite was then consolidated by hot compaction in the semi-solid regime of the Al6061. A three point bend test was carried out to evaluate the mechanical properties. In addition, the suspension and spraying parameters that control the deposited microstructure was studied to help control the final properties of the deposited structure. The yield and ultimate flexural strength of the SiC sprayed Al6061 laminate composite showed an increase (32% and 15%, respectively) compared with that of the unsprayed sample (reference sample) processed at the same condition.

A new variant of the hot embossing process has been conducted with amorphous PEEK films as a model material. Constant Temperature Embossing (CTE) utilizes the crystallizing nature of amorphous polymers such as poly (ether ether ketone) (PEEK), poly (ethylene terephthalate) (PET) and poly (ethylene naphthalate) (PEN) when heated above their glass transition temperature to eliminate the thermal cycling. The key process parameters such as embossing temperature and embossing time depend on the thermal behavior of the amorphous PEEK film. Embossing studies were conducted using silicon tools with microchannel arrays of different aspect ratios, and the films were characterized using scanning electron microscopy and optical profilometry. The process enables a simple isothermal embossing process for polymers that have a glass transition temperature well above the room temperature and also with a wide temperature gap between the glass transition temperature and melting point.