bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of Friction Stir Welding of High Density Polyethylene
Authors: Sheikh-Ahmad Jamal , Ali Dima , Jarrar Firas , Deveci Suleyman
Published: September 2018

Friction stir welding of high density polyethylene sheets was performed at different rotational and welding speeds and the material temperature close to the welding zone was monitored by infrared thermography and thermocouple measurements. Welding quality was evaluated by macrostructure analysis and tensile testing. Fracture surfaces of the tensile specimens were also analyzed. It was found that weld quality is highly dependent on the temperature of the material in the welding zone. For some specific welding conditions the welding process was unstable due to elevated temperatures reaching the melting point of HDPE. Instability of the welding processes was characterized by cyclic material temperatures and down forces. Decreasing the welding speed and increasing the rotational speed was found to improve weld quality.
Effects of Power Generation on the Opportunistic Maintenance Strategy for Wind Turbines Considering Reliability
Authors: Zhang Chen , Gao Wei , Yang Tao , Guo Sheng , Ding Honggang
Published: September 2018

Corrective maintenance and preventive maintenance are two common maintenance strategies used in the wind farms, whose drawbacks are obvious and significant. Opportunistic maintenance strategy takes advantage of the dependencies existing among the wind turbine components and implement combined maintenance actions to reduce the huge downtime cost. The opportunistic maintenance strategy for wind turbines has made a great progress, as well as the strategy considering imperfect and condition-based maintenance. However, existing maintenance strategy researches are usually concerned with the maintenance itself and the effects of power generation are barely considered. Nowadays, a current research trend in manufacturing system is the integration of maintenance and production planning. In this paper, the effects of power generation on opportunistic maintenance strategy for wind turbines considering reliability are researched. The opportunistic maintenance reliability threshold is not constant and depends on the real-time power generation. Numerical examples are used to illustrate the economical advantages of this proposed strategy over traditional opportunistic maintenance strategy. Moreover, the optimal maintenance combination is also provided.
Evaluation of CFRP Hole Quality in Low Frequency Vibration-Assisted Dry Drilling of CFRP/Ti Stacks
Authors: Yang Haojun , Chen Yan , Xu Jiuhua
Published: September 2018

Low frequency vibration assisted drilling (LFVAD) is regarded as one of the most promising process in CFRP/Ti stacks drilling. This work carries the investigation of the difference between conventional drilling and LFVAD based on kinematic model. The experiments are conducted under varied vibration amplitude to a specific feed rate, also under varying spindle speeds, feed rates when the ratio of amplitude to feed rate is fixed. Then the hole quality of CFRP is evaluated based on the analysis of drilling force, chip morphology, chip extraction. The results show that there is rarely no difference between conventional drilling and LFVAD in drilling mechanism when the drilling diameter is over 1 mm. Because the impact effect caused by drill vibration is already weak. It is found that the severe mechanical damage of the CFRP holes surface could be significantly reduced due to the fragmented chips obtained in vibration drilling. The maximum instantaneous feed rate combined with feed rate and amplitude plays a significant role in CFRP hole quality. Lower maximum instantaneous feed rate results in better hole wall quality and less entry delamination. Spindle speed has no visible influence on entry delamination, while higher spindle speed improves the hole surface quality due to the resin coating phenomenon.
Thermal Design and Testing of a Passive Helmet Heat Exchanger With Additively Manufactured Components
Authors: Cage Kailyn , Vaughn-Cooke Monifa , Fuge Mark , Lucero Briana , Spernjak Dusan , Bernardin John
Published: September 2018

Additive manufacturing (AM) processes allow for complex geometries to be developed in a cost- and time-efficient manner in small-scale productions. The unique functionality of AM offers an ideal collaboration between specific applications of human variability and thermal management. This research investigates the intersection of AM, human variability and thermal management in the development of a military helmet heat exchanger. A primary aim of this research was to establish the effectiveness of AM components in thermal applications based on material composition. Using additively manufactured heat pipe holders, the thermal properties of a passive evaporative cooler are tested for performance capability with various heat pipes over two environmental conditions.

This study conducted a proof-of-concept design for a passive helmet heat exchanger, incorporating AM components as both the heat pipe holders and the cushioning material targeting internal head temperatures of ≤ 35°C. Copper heat pipes from 3 manufactures with three lengths were analytically simulated and experimentally tested for their effectiveness in the helmet design. A total of 12 heat pipes were tested with 2 heat pipes per holder in a lateral configuration inside a thermal environmental chamber. Two 25-hour tests in an environmental chamber were conducted evaluating temperature (25°C, 45°C) and relative humidity (25%, 50%) for the six types of heat pipes and compared against the analytical models of the helmet heat exchangers.

Many of the heat pipes tested were good conduits for moving the heat from the head to the evaporative wicking material. All heat pipes had Coefficients of Performance under 3.5 when tested with the lateral system. Comparisons of the analytical and experimental models show the need for the design to incorporate a re-wetting reservoir. This work on a 2-dimensional system establishes the basis for design improvements and integration of the heat pipes and additively manufactured parts with a 3-dimensional helmet.
Structural Design of Hybrid Processing Unit Chassis for Airborne Electronic Systems
Authors: Santoro Daniele , Lecci Umberto , Quadrini Fabrizio , Santo Loredana
Published: September 2018

Defence&Aerospace applications greatly benefit from the weight reduction of their payloads. On one hand, a reduced weight leads to lower fuel consumption and thus a greater flight range. On the other, higher load factors reduce the overall flight envelope. In the case of mast mounted naval or terrestrial units (e.g shelters), mass budgets are strongly limit. The need of producing very light structures leads to the use of composite materials but drawbacks arise from the definition of a robust design methodology.

The present work aims at defying an integrated experimental-numerical approach to design complex composite structures. The unit chassis of a hybrid processing unit for airborne application is taken as case study. Material properties are extracted from laboratory tests and integrated with nominal data. A finite element model is calibrated and used to predict the behavior of a chassis wall under harmonic load condition.
Effect of Heat Treatment on Corrosion Properties of Selective Laser Melted Stainless Steel Parts
Authors: Sarkar Sagar , Jha Saumya Ranjan , Nath Ashish Kumar
Published: September 2018

One of the most popular additive manufacturing processes among today’s manufacturing industries is Selective Laser Melting (SLM) in which very intricate shapes can be fabricated directly from its three dimensional digital design data by melting metal powders using laser. Layer by layer deposition of material about different build axes make SLM parts anisotropic in nature. Also, non-uniformity in thermal loading at top and bottom surfaces of a SLM part leads to inhomogeneous microstructure and may change electro-chemical properties across the part. Suitable heat treatment as a post processing technique can reduce this anisotropy and produce homogeneous microstructure leading to reproducible mechanical and electrochemical properties. Depending upon the application in actual industrial scenarios, SLM parts may be subjected to corrosive media and thus may affect service life of the part. In the present study, effect of different heat treatment namely solution annealing, ageing, overaging on corrosion properties of SLM 15-5 Precipitation-Hardened (PH) stainless steel have been studied. Various metallurgical characterizations have been carried out wherever required to support experimental observations. As-built specimens have approximately six times higher pitting potential which may be attributed to higher nitrogen content present in as-built specimens but corrode more over time than solution annealed (SA) specimens. Relatively bigger size pits and non-uniformity in their distributions can be attributed to residual stresses and inhomogeneous microstructure associated with as-built SLM specimens respectively. Specimen undergone standard ageing condition (H900) corrodes least over time among all the heat treatment conditions considered in the present study. However, in this case, a large number of shallow pits can be observed from the corroded surface. Overaged (H1150) specimens corrode more than H900 specimens but pitting starts late in case of H1150 specimens since pitting potential is almost ten times higher in the former case. Increased ageing temperature and soaking time (Mod H900 (SA)) increases formation of higher Cr23C6 precipitates than that of H900 condition and hence corrode more over time. Ageing without solution annealing (Mod H900 (AB)) leads to higher corrosion and larger pit size non-uniformly distributed over the corroded surface than that of Mod H900 (SA) condition which may be attributed to presence of residual stresses and non-uniform precipitation throughout the matrix. Present study will be useful for selecting suitable heat treatment yielding desired corrosion resistance for SLM stainless steel parts.
Cooling Process for Directional Solidification in Directed Energy Deposition
Authors: Ishiyama Keiya , Koike Ryo , Kakinuma Yasuhiro , Suzuki Tetsuya , Mori Takanori
Published: September 2018

Additive manufacturing (AM) for metals has attracted attention from industry because of its great potential to enhance production efficiency and reduce production costs. Directed energy deposition (DED) is a metal AM process suitable to produce large-scale freeform metal products. DED entails irradiating the baseplate with a laser beam and launching the metal powder onto the molten spot to produce a metal part on the baseplate. Because the process enables powder from different materials to be used, DED is widely applicable to valuable production work such as for a dissimilar material joint, a graded material, or a part with a special structure.

With regard to parts with a special structure, directional solidification can prospectively be used in the power plant and aerospace industries because it can enhance the stiffness in a specific direction via only a simple process. However, conventional approaches for directional solidification require a special mold in order to realize a long-lasting thermal gradient in the part. On the other hand, from the viewpoint of thermal distribution in a produced part, DED is able to control the gradient by controlling the position of the molten pool, i.e., the position of the laser spot. Moreover, unlike casting, the thermal gradient can be precisely oriented in the expected direction, because the laser supplies heat energy on the regulated spot.

In this study, the applicability of DED to directional solidification in Inconel® 625 is theoretically and experimentally evaluated through metal structure observation and Vickers hardness measurements. Furthermore, the effect of two different cooling processes on directional solidification is also considered with the aim of improving the mechanical stiffness of a part produced by DED. The observations and experimental results show that both the cooling methods (baseplate cooling and intermittent treatment with coolant) are able to enhance the hardness while retaining the anisotropy.
Optimization Design of Nonuniform Cellular Structures for Additive Manufacturing
Authors: Han Yafeng , Lu Wen F.
Published: September 2018

Cellular structures are broadly applicable to lightweight design and multifunctional applications. Especially, with unprecedented fabrication freedom provided by additive manufacturing (AM), design and optimization of nonuniform cellular structures have recently attracted great research interests. Topology optimization is one of the most powerful tools to obtain the optimized material distribution, and much research have been conducted to optimize cellular structures with the help of this optimization technique. In general, the optimized cellular structure is generated based on a predefined ground structure, and thickness of each strut is then decided based on the optimization result. However, many existing studies did not consider the constraints of AM processes, such as some generated struts may be too thin to be manufactured. Besides, only load support structure was considered in these studies. Other applications, such as heat dissipation or energy absorption, were rarely researched. In this paper, a novel cellular structure design method, which considered both functionality and manufacturability, is proposed. Different from other methods, wall thickness of the structure was set as a constant. To get the optimized material distribution, variable cell sizes were applied. Because of uniform wall thickness, the smaller the unit cell is, the higher its volume fraction will be. By mapping small unit cells to high density area and large cell to low density area, the final optimized cellular structure can be generated. In addition, because smaller unit cells have higher surface-to-volume ratio, this method can also be applied to solve heat transfer problem. Two examples, minimum compliance design of a cantilever beam and maximum heat dissipation efficiency design of a CPU heat sink, were conducted to validate the proposed method.
Layerwise In-Process Quality Monitoring in Laser Powder Bed Fusion
Authors: Imani Farhad , Gaikwad Aniruddha , Montazeri Mohammad , Rao Prahalada , Yang Hui , Reutzel Edward
Published: September 2018

The goal of this work is to understand the effect of process conditions on part porosity in laser powder bed fusion (LPBF) Additive Manufacturing (AM) process, and subsequently, detect the onset of process conditions that lead to porosity from in-process sensor data. In pursuit of this goal, the objectives of this work are two-fold:

(1) Quantify the count (number), size and location of pores as a function of three LPBF process parameters, namely, the hatch spacing (H), laser velocity (V), and laser power (P).

(2) Monitor and identify process conditions that are liable to cause porosity through analysis of in-process layer-by-layer optical images of the build invoking multifractal and spectral graph theoretic features.

This is important because porosity has a significant impact on the functional integrity of LPBF parts, such as fatigue life. Furthermore, linking process conditions to sensor signatures and defects is the first-step towards in-process quality assurance in LPBF. To achieve the first objective, titanium alloy (Ti-6Al-4V) test cylinders of 10 mm diameter × 25 mm height were built under differing H, V, and P settings on a commercial LPBF machine (EOS M280). The effect of these parameters on count, size and location of pores was quantified based on X-ray computed tomography (XCT) images. To achieve the second objective, layerwise optical images of the powder bed were acquired as the parts were being built. Spectral graph theoretic and multifractal features were extracted from the layer-by-layer images for each test part. Subsequently, these features were linked to the process parameters using machine learning approaches. Through these image-based features, process conditions under which the parts were built was identified with the statistical fidelity over 80% (F-score).
Outer Diameter to Thickness Ratio Effect on Tube Flaring Behavior
Authors: Pier Bradley F. , Nikhare Chetan P.
Published: September 2018

Tube forming is one of the main manufacturing techniques for processing of tubular components. This process is subdivided depending on the processing i.e., tube end forming either to expand or reduce the section. One of these tube end forming techniques is a flaring process. Most applications for flaring tube ends, utilizes a conical tool for flaring the tube either till a particular deformation to achieve a desired shape or till failure to characterize the material properties. The relationship between the flaring behavior during the process based on the outer diameter and thickness of the tube was experimentally characterized in this paper for variety of tube sizes. Further flaring limits were analyzed in these considered tube sizes. For this four outer diameter to thickness ratio were experimented and results were analyzed. Further numerical simulations were performed to match the results. A closer look on the required force-displacement curve is presented and unique regions were identified. Based on the data an empirical equation is proposed. This equation provides a concept based on material or process stiffness. It is believed that once an equation is established and variables are linked to the parameter a more better prediction can be carried out for flaring the tubes.
Molecular Dynamics Simulation Study of Liquid-Assisted Laser Beam Machining Process
Authors: James Sagil , Anand Menon Vivek , Parmar Mayur
Published: September 2018

Liquid Assisted Laser Beam Micromachining (LA-LBMM) process is advanced machining process which can overcome the limitations of traditional laser beam machining processes. LA-LBMM process uses a layer of a liquid medium such as water above the substrate surface during the application of laser beam. During LA-LBMM process, the liquid medium is used both in static mode in which the water is still or in a dynamic mode in which the water flows over the substrate with a specific velocity. Experimental studies on LA-LBMM process have shown that the cavity machined has a better surface finish due to a reduction in the amount of re-deposition and recast material. While LA-LBMM process promises significant improvement in laser-based micromachining applications, the process mechanisms involved in LA-LBMM process is not well understood. In the past, finite element simulation studies on LA-LBMM process is studied which could only find the temperature distribution on the substrate during machining. A clear understanding of the role of water medium during the LA-LBMM process is lacking. This research involves the use of Molecular Dynamics (MD) simulation technique to investigate the complex and dynamic mechanisms involved in the LA-LBMM process both in static and dynamic mode. The results of the MD simulation are compared with those of Laser Beam Micromachining (LBMM). The study revealed that machining during LA-LBMM process showed higher removal compared with LBMM process. The LA-LBMM process in dynamic mode showed lesser material removal compared with static mode as the flowing water carrying the heat away from the machining zone. Formation of nanoscale bubbles along with shockwave propagation is observed during the simulation of LA-LBMM process. The findings of this study provide further insights to strengthen the knowledge base of LA-LBMM process.
Investigation on the Tool Wear Model and Equivalent Tool Life in End Milling Titanium Alloy Ti6Al4V
Authors: Guo Kai , Yang Bin , Sun Jie , Sivalingam Vinothkumar
Published: September 2018

Titanium alloys are widely utilized in aerospace thanks to their excellent combination of high-specific strength, fracture, corrosion resistance characteristics, etc. However, titanium alloys are difficult-to-machine materials. Tool wear is thus of great importance to understand and quantitatively predict tool life. In this study, the wear of coated carbide tool in milling Ti-6Al-4V alloy was assessed by characterization of the worn tool cutting edge. Furthermore, a tool wear model for end milling cutter is established with considering the joint effect of cutting speed and feed rate for characterizing tool wear process and predicting tool wear. Based on the proposed tool wear model equivalent tool life is put forward to evaluate cutting tool life under different cutting conditions. The modelling process of tool wear is given and discussed according to the specific conditions. Experimental work and validation are performed for coated carbide tool milling Ti-6Al-4V alloy.
VESPER: Visual Exploration of Similarity and Performance Metrics for Computer-Aided Design Repositories
Authors: Ramanujan Devarajan , Bernstein William Z.
Published: September 2018

VESPER (Visual Exploration of Similarity and PERformance) is a visual analytics system for exploring similarity metrics and performance metrics derived from computer-aided design (CAD) repositories. It consists of (1) a data processing module that allows analysts to input custom similarity metrics and performance metrics, (2) a visualization module that facilitates navigation of the design spaces through coordinated, interactive visualizations, and (3) a report generation module that allows analysts to export lifecycle data of selected repository items as well as the input metrics for further external validation. In this paper, we discuss the need, design rationale, and implementation details for VESPER. We then apply VESPER to (1) sustainability-focused exploration of parts, and (2) exploration of tool wear and surface roughness in machined parts.
An Efficient Method for Online Identification of Steady State for Multivariate System
Authors: Xu Honglun , Wu Jianguo , Tseng Tzu-Liang (Bill)
Published: September 2018

Most of the existing steady state detection approaches are designed for univariate signals. For multivariate signals, the univariate approach is often applied to each process variable and the system is claimed to be steady once all signals are steady, which is computationally inefficient and also not accurate. The article proposes an efficient online method for multivariate steady state detection. It estimates the covariance matrices using two different approaches, namely, the mean-squared-deviation and mean-squared-successive-difference. To avoid the usage of a moving window, the process means and the two covariance matrices are calculated recursively through exponentially weighted moving average. A likelihood ratio test is developed to compare the difference of the two covariance matrices and to detect the steady state. The intensive numerical studies and real case study show that the proposed method can accurately detect the steady state of a multivariate system.
A Study on Micro-Milling of Aluminium 6061 and Copper With Respect to Cutting Forces, Surface Roughness and Burr Formation
Authors: Kumar A. Sravan , Deb Sankha , Paul S.
Published: September 2018

In the present study, micro-milling of aluminium 6061 alloy and copper was undertaken. TiAlN coated two-flute flat end milling cutters of 0.5 mm diameter were used for conducting micro-channel milling experiments with minimum quantity lubrication (MQL) as the cutting environment. The effect of process parameters namely cutting velocity (vc) and feed per flute (fz) on the cutting forces, surface roughness and burr width are reported. RMS values of longitudinal feed force (FX), transverse cutting force (FY) and vertical thrust force (FZ) were measured and the maximum values for Al 6061 are 0.33 N, 0.16 N and 0.21 N respectively, and the same for copper are measured to be 0.11 N, 0.17 N and 0.22 N respectively. Average surface roughness along the milling direction (Ra) at the bottom surface of the micro-channel was measured. Smoother surfaces were generated at lower feed per flute in both the materials. Ra is found to be varying from 28.2 nm to 86.9 nm for Al 6061, and for copper, the range is from 4.9 nm to 32.7 nm. SEM images of the micro-channels were analysed and top burr width was measured in both up-milling and down-milling directions. Higher feed per flute produced smaller burrs in both up-milling and down-milling directions. Maximum burr width for Al 6061 is measured to be 12.86 μm and 15.28 μm in up-milling and down-milling direction respectively, and for copper, the same are measured to be 12.84 μm and 20.46 μm respectively.
Feasibility Study of On-Machine Inspection of Micro Milling Cutter Runout
Authors: Zhang Xi , Si Chunying , Shi Yuanyuan
Published: September 2018

During the process of micro machining, the existence of tool runout not only aggravates the wear and breakage of the cutter, but also seriously affects the surface quality of the parts. In order to observe the runout of micro-milling cutter, a detection method based on machine vision was proposed in this paper, which can calculate the tool runout by measuring the maximum value of external fluctuation of the cutter assembly near the tool tip. The proposed method can realize the direct measurement of radial runout of a micro-milling cutter. A dedicated prototype measuring system was established, which includes an on-machine measurement unit, a controller and the software. To obtain the images of maximum profile of the cutter at different angles, the cutter should be perpendicular with the optical axis of camera lens in the on-machine measurement unit. The experiments verified that the proposed method is feasible and the developed measurement system can fulfill the needs of industrial applications.
A Temperature Model for Synchronized Ultrasonic Torrefaction and Pelleting of Biomass for Bioenergy Production
Authors: Sun Mingman , Yang Yang , Zhang Meng
Published: September 2018

Low energy and volumetric density of cellulosic biomass has been a challenge hindering its large-scale utilization as a bioenergy resource. Torrefaction is a thermochemical pretreatment process that can significantly enhance the properties of biomass as a fuel by increasing the heating value and thermal stability of biomass materials. Densification of cellulosic biomass by pelleting can greatly increase the volumetric density of biomass to improve its handling efficiency. Currently, torrefaction and pelleting are processed separately, which consumes a great amount of time and energy. In addition, it is more difficult to pellet torrefied biomass than untreated biomass. Synchronized ultrasonic torrefaction and pelleting has been developed to address these challenges. Synchronized ultrasonic torrefaction and pelleting can produce pellets of high energy and volumetric density in a single step, which tremendously reduces the time and energy consumption compared to that by the prevailing multi-step method. This novel fuel upgrading process can increase biomass temperature to 473–573 K within tens of seconds to realize torrefaction. Studying the temperature distribution is a crucial key to understand the fuel upgrading mechanism since pellet energy density, thermal stability, volumetric density, and durability are all highly related to temperature. In this research, a physics-based temperature model is developed to explain torrefaction temperatures measured experimentally and to provide guidelines to optimize process variables to produce high quality pellets that can be used as a sustainable fuel.
Design of an Octo-Strain Specimen for Biaxial Tension Testing
Authors: Milner Justin L. , Gnäupel-Herold Thomas
Published: September 2018

A custom biaxial testing fixture was designed to evaluate a new specimen geometry for complex loading paths. Biaxial testing is commonly used to evaluate work-hardening behavior of sheet metal in biaxial tension to study the accumulation of plastic strains to determine the anisotropic yield loci. The current state-of-the-art specimen geometry that is used for biaxial testing is the cruciform specimen. Cruciform specimens are machined into a geometry that resembles a cross with four arms arranged at 90 degrees. However, this geometry is prone to premature failure and non-homogenous strain distribution within the gauge region. These problems persist even with the addition of complex features (e.g., slits and multi-step pockets). Therefore, the primary goal of the new specimen geometry is to achieve a large and uniform strain field within the gauge region. One of the main problems of the cruciform specimen is the formation of stress concentration within the gauge region. Therefore, the proposed specimen geometry is comprised of four additional arms between the existing cruciform arms. This geometry is termed an ‘Octo-Strain’ specimen after the eight arms that are arranged in a 45-degree planar pattern. It is hypothesized that the additional arms will stabilize the stress concentrations and, thus, achieve increased failure strain and uniformity as compared to the cruciform geometry. This work focuses on the comparison of the cruciform specimen to the Octo-Strain specimen during balanced biaxial deformation of mild steel. It is found that the Octo-Strain specimen achieved twice the failure strain and increased strain uniformity within the gauge region as compared to the cruciform specimen.
Fabrication of Gellan Gum Tubular Structure Using Coaxial Needles: A Study on Wall Thickness and Encapsulation
Authors: Yu Ilhan , Chen Roland , Grindrod Samantha
Published: September 2018

Tubular structures of hydrogel are used in a variety of applications such as 3D cell culturing for delivery of nutrient supplies. The wall thickness of the tube determines the speed of diffusion or delivery rate. In this study, we aimed to fabricate tubular structures with varying of wall thicknesses using a thermal-crosslinking hydrogel, gellan gum, with the coaxial needle approach. The wall thickness is controlled by changing the flow rate ratio between the inner (phosphate-buffered saline) and outer needles (gellan gum). A simulation model was developed to estimate the proper extrusion speed to allow the gellan gum to be extruded around its glass transition temperature. While keeping the extrusion rate of gellan gum fixed, different PBS extrusion rates were tested to investigate the printability to form continuous tubular structures, range of printable wall thickness, and possibility to form tubes with closed ends to encapsulate fluid or drug inside the tube. The ranges of printable wall thickness with two pairs of coaxial needle were identified. It was found that at about 200% of the baseline PBS extrusion speed, a maximum of 20% difference in wall thickness can be achieved, while a close end can still be formed.
Investigation on Smoothing Silicon Carbide Wafer With a Combined Method of Mechanical Lapping and Photocatalysis Assisted Chemical Mechanical Polishing
Authors: Yuan Zewei , Cheng Kai , He Yan , Zhang Meng
Published: September 2018

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-TiO2 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 (H2O2) 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.
Robot Assisted Additive Manufacturing of Thin Multifunctional Structures
Authors: Bhatt Prahar M. , Peralta Max , Bruck Hugh A. , Gupta Satyandra K.
Published: September 2018

Thin multifunctional structures need to be composed from many different materials. Currently, very few additive manufacturing processes are capable of working with multiple materials. Additive manufacturing processes that work with multiple different materials pose significant constraints on material options. This significantly limits the kind of multifunctional structures that can be produced using additive manufacturing. A robot assisted sheet lamination based additive manufacturing system is developed in this paper. The system utilizes a 6-DOF robotic manipulator to perform the manufacturing operations such as cutting, assembly, tape-layup, and bonding to build the part layer by layer. A flexible ornithopter wing have been built using the proposed system. We have characterized the system in terms of part performance as well as automation efficiency.
Unified Control of Production, Capacity, and Pre-Emptive Maintenance of Fused Filament Fabrication Process
Authors: Badarinath Rakshith , Tien Kai-Wen , Prabhu Vittaldas
Published: September 2018

The quest for smarter manufacturing is motivating the need for operational decisions to be made in real-time to adapt to uncertainties. Prevailing decision-making techniques typically consider each manufacturing function in isolation to reduce the complexity, which in turn leads to sequential decision-making where prior decisions become constraints for subsequent decisions. This paper proposes a unified approach for simultaneously controlling the timing of production events, the timing of maintenance events, and physical processing capacity. Moreover, the control algorithms can be fully distributed and exploit physics-based models for processes and remaining-useful-life of machinery components in real-time decision-making. Fused Filament Fabrication (FFF) additive manufacturing process is used as an example in the paper to demonstrate the unified approach. Dynamics of the resulting unified control system is modeled using non-linear discontinuous differential equations. Computer simulations are used to illustrate dynamic interactions between production and maintenance functions. Benchmarking of the unified control approach for randomly generated datasets show superior performance compared to other commonly used scheduling heuristics by about 48%.
Mesoscopic Simulation Model to Predict Temperature Distribution and Melt Pool Size During Selective Laser Scanning
Authors: Shrestha Subin , Chou Kevin
Published: September 2018

Selective Laser Melting (SLM) has been a major subject of study in the field of powder bed additive manufacturing (AM) process. It is desired to know the melt pool size and the associated thermal gradient during the powder melting process. However, there are challenges associated with accurately measuring the melt pool size as a whole by experiment alone. Therefore, the combination of experimental and numerical study may help analyze the melt pool shape in a better way. In this study, a 3D powder scale model using volume of fluid (VOF) approach has been developed using ANSYS FLUENT. A temperature dependent material property is defined and then volumetric heat source is applied to melt the powder particles. The single track results obtained from the simulation are compared with the experiment and the results show that single track width predicted by the simulation is in good agreement with the experimental counterpart. The predicted track width is within 10% error.
Towards Continuous Production of Shaped Honeycombs
Authors: Calisch Sam E. , Gershenfeld Neil A.
Published: September 2018

Honeycomb sandwich panels are widely used for high performance parts subject to bending loads, but their manufacturing costs remain high. In particular, for parts with non-flat, non-uniform geometry, honeycombs must be machined or thermoformed with great care and expense. The ability to produce shaped honeycombs would allow sandwich panels to replace monolithic parts in a number of high performance, space-constrained applications, while also providing new areas of research for structural optimization, distributed sensing and actuation, and on-site production of infrastructure. Previous work has shown methods of directly producing shaped honeycombs by cutting and folding flat sheets of material. This research extends these methods by demonstrating work towards a continuous process for the cutting and folding steps of this process. An algorithm for producing a manufacturable cut-and-fold pattern from a three-dimensional volume is designed, and a machine for automatically performing the required cutting and parallel folding is proposed and prototyped. The accuracy of the creases placed by this machine is characterized and the impact of creasing order is demonstrated. Finally, a prototype part is produced and future work is sketched towards full process automation.
Experimental and Simulation Study of Ultrasonic Additive Manufacturing of CFRP/Ti Stacks
Authors: James Sagil , Sonate Abhishek , Dang Christopher , De La Luz Lenny
Published: September 2018

Carbon fiber reinforced plastic (CFRP) are advanced engineering materials which are recognized as the most sought-after composite for several industrial applications including aerospace and automotive sectors. CFRP have superior physical and mechanical properties such as lightweight, high resilience, high-durability and high strength-to-weight ratio. CFRP composites stacked up with titanium to form multi-layered material stacks to enhance its load bearing capability. Traditional methods of stacking up CFRP and titanium involves using either high strength adhesives or rivets and bolts. The laminate structures joined by these methods often tend to fail during high load-bearing applications. Conventional metal welding technologies use high heat causing high thermal stresses and microstructural damages. Ultrasonic welding is a solid-state joining process, which has the capability of welding dissimilar materials at relatively low temperatures using ultrasonic vibration. Ultrasonic additive manufacturing (UAM) process is an ideal method to weld CFRP and Titanium. During the ultrasonic welding process, two dissimilar materials under a continuous static load are subjected to transverse ultrasonic vibrations, which results in high stress and friction between the two surfaces. This research focuses on the study of ultrasonically welding CFRP and Titanium stacks using UAM process. The study involves experimentation performed on an in-house built UAM setup. Finite element analysis is performed to understand the distribution stresses and strains during the UAM process. In this study, CFRP and Titanium layers are successfully welded using UAM process without causing any melting or significant heating. The finite element analysis study revealed that during UAM process, CFRP/Titanium stacks are subject to repeated cyclic shear stress reversals resulting in a strong weld joint. The stress-strain diagram during the process showed a considerable increase in plastic strain during the UAM process. The outcomes of this study can be used to further the industrial applications of the ultrasonic additive process as well as other ultrasonic welding based processes involving dissimilar materials.
Additive Manufacturing of Nickel-Based Superalloys
Authors: Graybill Benjamin , Li Ming , Malawey David , Ma Chao , Alvarado-Orozco Juan-Manuel , Martinez-Franco Enrique
Published: September 2018

Additive manufacturing enables the design of components with intricate geometries that can be manufactured with lead times much shorter when compared with conventional manufacturing. The ability to manufacture components out of high-performance metals through additive manufacturing technologies attracts industries that wish to develop more complex parts, but require components to maintain their structural integrity in demanding operating environments. Nickel-based superalloys are of particular interest due to their excellent mechanical, creep, wear, and oxidation properties at both ambient and elevated temperatures. However, relationship between process parameters and the resulting microstructure is still not well understood. The control of the microstructure, in particular the precipitation of secondary phases, is of critical importance to the performance of nickel-based superalloys. This paper reviews the additive manufacturing methods used to process nickel-based superalloys, the influence of the process parameters on microstructure and mechanical properties, the effectiveness of various heat treatment regimens, and the addition of particles in order to further improve mechanical properties.
Bioprinting of Liquid Hydrogel Precursors in a Support Bath by Analyzing Two Key Features: Cell Distribution and Shape Fidelity
Authors: Ding Houzhu , Chang Robert C.
Published: September 2018

Microextrusion-based bioprinting within a support bath material is an emerging additive manufacturing technique for fabricating complex three-dimensional (3D) tissue constructs. However, there exists fundamental knowledge gaps in understanding the spatiotemporal mapping of cells within the bioprinted constructs and their shape fidelity when embedded in a support bath material. To address these questions, this paper advances quantitative analyses to systematically determine the spatial distribution for cell-laden filament-based tissue constructs as a function of the bio-ink properties. Also, optimal bio-ink formulations are investigated to fabricate complex 3D structures with superior shape integrity. Specifically, for a 1D filament printed in a support bath, cells suspended in low viscosity liquid hydrogel precursors are found to exhibit a characteristic non-uniform distribution as measured by a degree of separation (Ds) metric. In a 2D square wave pattern print, cells are observed to flow and aggregate downstream at certain positions along the in-plane print direction. In a 3D analysis, owing to the high cell density and gravity effects, a non-uniform cell distribution within a printed cylindrical structure is observed in the build direction. From the structural standpoint, the addition of CaCl2 to the support bath activates the hydrogel cross-linking process during printing, resulting in 3D prints with enhanced structural outcomes. This multidimensional print analysis provides evidence that, under the emerging bioprinting support bath paradigm, the printable parameter space can be extended to low viscosity liquid hydrogel precursor materials that can be systematically characterized and optimized for key process performance outcomes in cell distribution and shape fidelity.
Audio-Based Condition Monitoring in Milling of the Workpiece Material With the Hardness Variation Using Support Vector Machines and Convolutional Neural Networks
Authors: Kothuru Achyuth , Nooka Sai Prasad , Liu Rui
Published: September 2018

Machining industry has been evolving towards implementation of automation into the process for higher productivity and efficiency. Although many studies have been conducted in the past to develop intelligent monitoring systems in various application scenarios of machining processes, most of them just focused on cutting tools without considering the influence due to the non-uniform hardness of workpiece material. This study develops a compact, reliable, and cost-effective intelligent Tool Condition Monitoring (TCM) model to detect the cutting tool wear in machining of the workpiece material with hardness variation. The generated audible sound signals during the machining process will be analyzed by state of the art artificial intelligent techniques, Support Vector Machines (SVMs) and Convolutional Neural Networks (CNNs), to predict the tool condition and the hardness variation of the workpiece. A four-level classification model is developed for the system to detect the tool wear condition based on the width of the flank wear land and hardness variation of the workpiece. The study also involves comparative analysis between two employed artificial intelligent techniques to evaluate the performance of models in predicting the tool wear level condition and workpiece hardness variation. The proposed intelligent models have shown a significant prediction accuracy in detecting the tool wear and from the audible sound into the proposed multi-classification wear class in the end-milling process of non-uniform hardened workpiece.
Co-Continuous Piezocomposites With Triply Periodic Phase Interfaces for Enhanced Mechanical Flexibility and Piezoelectricity
Authors: Song Xuan , He Li , Yang Wenhua , Wang Zhuo , Chen Lei
Published: September 2018

A co-continuous piezocomposite architecture is presented to achieve mechanical flexibility and piezoelectricity simultaneously in piezoelectric materials. This architecture is comprised of an active ferroelectric ceramic phase and a passive flexible polymer phase, which are separated by a tailorable phase interface. Triply periodic minimal surfaces are used to define the phase interface, due to their excellent elastic properties and load transfer efficiency. A Suspension-Enclosing Projection-Stereolithography process is used to additively manufacture this material. Post processes including polymer infiltration, electroding and poling are introduced. Piezoelectric properties of the piezocomposites are numerically and experimentally studied. The results highlight the role of tailorable triply periodic phase interfaces in promoting mechanical flexibility and piezoelectricity of co-continuous piezocomposites.
Finite Element Study of Laser Peening on Selective Laser Melted A357 Aluminum Alloy During Tension Test
Authors: Hatamleh Mohammad I. , Sadeh Sepehr , Farooq Tayyub , Malik Arif S. , Qian Dong
Published: September 2018

Laser shock peening (LSP) is an advanced surface treatment technique that can extend fatigue life in metallic components by inducing near-surface compressive residual stresses. In this study, LSP was implemented to induce compressive residual stresses and modify material properties of selective laser melted (SLM) aluminum A357 specimens. An initial hypothesis on the effect of LSP during tension testing was formulated and tested using finite element simulation. The hypothesis was that, due to the LSP-induced tensile residual stress field in the middle of the specimen cross sections, yielding was expected to initiate in this region. True stress-strain curves of two as-built (AB) and two laser shock peened samples were obtained through transverse tensile tests. The single explicit analysis using time dependent damping (SEATD) technique was used to simulate LSP process utilizing Johnson-Cook (J-C) constitutive parameters. J-C parameters for the cast A357 alloy were used for preliminary study. This was followed by the simulation of the transverse tensile test. J-C parameters for SLM A357 alloy were then empirically estimated, and simulations were repeated accordingly. It was found that the specific LSP pattern induced tensile residual stresses along the edges as well as the middle of the test specimen’s cross-section. Axial residual stress and yield strength profiles along three different paths on specimen’s cross-section were compared and yield regions were investigated. This supported the initial hypothesis, but also provided for a more detailed understanding of actual tensile test failure in the specific SLM A357 specimens for the given LSP treatment. In addition, the same LSP treatment on SLM A357 alloy resulted in lower magnitude of compressive residual stress than for cast A357 aluminum alloy.