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research-article  
Raja Kountanya and Dr. Changsheng Guo
J. Manuf. Sci. Eng   doi: 10.1115/1.4037969
Specific material removal rate q' is calculated for 5-axis grinding in a virtual machining simulation environment (VMSE). The axis-symmetric tool rotational profile is arc-length parameterized. The twisted grazing curve due to the concurrent translation and rotation in every move is modeled through an exact velocity field and areal material removal rate density q'' formulation on the tool surface. Variation of q' and equivalent chip thickness h within the instantaneous engagement contour is calculated considering its portion in the front of the grazing curve. Illustrative results with a 5 - axis impeller blade finishing simulation are shown. The results were benchmarked against an average q' calculated from the instantaneous material removal rate from the VMSE. As a function of time, maximum chip thickness hmax within the extents of contact along the tool profile in every move showed more isolated peaks than corresponding q'max. Maximum cumulative material removed per unit length Q'max along the tool profile from all the moves was calculated to predict axial location of maximum risk of cutter degradation. Q'max and hmax are useful metrics for tool path diagnosis and tool wear analysis.
research-article  
Dmitrii Ardashev and Aleksandr Dyakonov
J. Manuf. Sci. Eng   doi: 10.1115/1.4037939
The paper offers a simulation model of the grinding force with account for the current condition of the grinding wheel's working surface - the value of the abrasive grain blunting area. The model of blunting area takes into account various wear mechanisms for abrasive grains: the mechanical wear is realized on the provisions of the kinetic theory of the strength of a solid subjected to cyclic loads, and the physicochemical wear is based on the intensity of interaction between the abrasive and the treated material at grinding temperatures. The offered model of the grinding force takes into account the unsteady stochastic nature of the interaction between abrasive grains of the grinding wheel and the working surface and the intensity of workpiece material deformation resistance. The model is multifactoral and complex and can be realised by supercomputer modeling. The numerical implementation of the model was performed with application of supercomputer devices engaging parallel calculations. The performed experiments on measurement of the grinding force during circular grinding have shown a 10 percent convergence with the calculated values. The developed grinding force model can be used as a forecast model to determine operational functionality of grinding wheel when used in varying technological conditions. Keywords: grinding force, abrasive grain blunting area, wear
TOPICS: Grinding, Grinding wheels, Modeling, Wear, Temperature, Kinetic theory, Stress, Simulation models, Deformation
research-article  
Suya Prem Anand P, Arunachalam N and L Vijayaraghavan
J. Manuf. Sci. Eng   doi: 10.1115/1.4037940
Advanced ceramic materials like sintered and pre-sintered zirconia is frequently used in the biomedical applications, where Minimum Quantity Lubrication (MQL) assisted grinding is required to achieve a good surface finish instead of conventional flood coolant. However, the insufficient cooling and wheel clogging are the major problems that exist in the MQL grinding process, which depends upon the type of work piece material and the grinding wheel being used. The present study is to determine the performance of the grinding wheels on pre-sintered zirconia under MQL conditions in terms of grinding forces, specific energy, surface integrity and wheel wear. Experiments are conducted with two different types of grinding wheels as silicon carbide (SiC) and diamond grinding wheels under the same condition. The results indicated that the diamond wheel provided a better surface finish and reduced tangential force under MQL condition, compared to the conventional silicon carbide wheel. This was due to the reduction of wheel loading in the diamond grinding wheel. The specific energy of diamond grinding wheel was reduced with higher material removal rate compared to the conventional silicon carbide wheel. The ground surfaces generated by the diamond grinding wheel showed a fine grinding marks with better surface finish. The percentage of G-ratio calculated for the diamond wheel was higher than the SiC wheel by 77 percent. This was due to the sliding of the grains and less wheel loading in the diamond wheel. The costs difference between the wheels were discussed for evaluation of sustainability.
TOPICS: Grinding, Diamonds, Wheels, Grinding wheels, Finishes, Silicon, Biomedicine, Floods, Sustainability, Coolants, Wear, Lubrication, Cooling, Ceramics
research-article  
Ellis Taylor and Tom Slatter
J. Manuf. Sci. Eng   doi: 10.1115/1.4037889
This work considered the finishing precision grinding process at a small ferrous metal roll manufacturer. A design of experiments methodology was used to evaluate the process and ascertain whether the degree of confidence gained from the process offers an acceptable level of risk in the conformance of end products to customer requirements. A thorough identification of the process variables and measurement considerations relevant to the process was carried out, before assessing and categorizing these variables using the grinding cycle as a 'black box' system. Coolant temperature, environment temperature, work speed, and traverse speed were all considered against measured size change, surface finish and circular run-out in a full factorial experimental design. The experiments were carried out on a manual cylindrical grinding machine retrofitted with digital encoders on the driven axes, with a chrome plated roll 300mm in diameter as the workpiece. Experiments were conducted over a period of 11 months during which the machine used was part of ongoing production environment. The results show that control of temperature, both of the coolant and of the environment in which the machine was operated, was the most important of the variables studied, but the skill of the machine operator remains dominant in the process overall.
TOPICS: Temperature, Iron alloys, Grinding, Machinery, Coolants, Experimental design, Risk, Finishes, Cycles, Grinding equipment, Finishing
research-article  
Danni Wang, Frank Peters and Matthew C. Frank
J. Manuf. Sci. Eng   doi: 10.1115/1.4037890
A semi-automated grinding system for the post-processing of metalcastings is presented. Grinding is an important procedure in a foundry, where the removal of gates, flash, and weld-repaired areas is performed. While grinding of repetitive locations on higher production castings can be automated, it is not practical for larger castings (e.g. > 200 kg) that are produced in smaller volumes. Furthermore, automation is even more challenging because locations of the required grinding is not a constant; depending on the unique conditions of each component. The proposed approach is intended for a simple x-y-z positioner (gantry) device with a feedback controlled grinding head that enables automated path planning. The process begins with touch probing of the surfaces that contain the anomaly requiring grinding, and then the system automatically handles the path planning and force control to remove the anomaly. A layer-based algorithm for path planning employs a search-and-destroy technique where the surrounding geometry is interpolated across the grind-requiring surface patch. In this manner, each unique condition of the casting surface after initial torch or saw cutting can be handled cost effectively without the need for human shaping and the egregious ergonomic problems associated. Implementation of the proposed grinding control is prototyped at a lab scale to demonstrate the feasibility and versatility of this strategy. A significant contribution of the work is the layer-based algorithm that allows an effective automation of the process planning for grinding, avoiding programming or code generation altogether.
TOPICS: Grinding, Path planning, Algorithms, Cutting, Feedback, Force control, Geometry, Computer programming, Casting, Production planning
research-article  
Bing Yao, Farhad Imani, Aniket S. Sakpal, Edward (Ted) Reutzel and Hui Yang
J. Manuf. Sci. Eng   doi: 10.1115/1.4037891
Metal-based Powder-Bed-Fusion additive manufacturing (PBF-AM) is gaining increasing attention in modern industries, and is a promising direct manufacturing technology. Additive manufacturing (AM) does not require the tooling cost of conventional subtractive manufacturing processes, and is flexible to produce parts with complex geometries. Quality and repeatability of AM parts remain a challenging issue that persistently hampers wide applications of AM technology. Rapid advancements in sensing technology, especially imaging sensing systems, provide an opportunity to overcome such challenges. However, little has been done to fully utilize the image profiles acquired in the AM process and study the fractal patterns for the purpose of process monitoring, quality assessment and control. This paper presents a new multifractal methodology for the characterization and detection of defects in PBF-AM built components. Both simulation and real-world case studies show that the proposed approach effectively detects and characterizes various defect patterns in AM images and has strong potential for quality control of AM processes.
TOPICS: Additive manufacturing, Metals, Machining, Quality control, Simulation, Manufacturing technology, Fractals, Process monitoring, Tooling, Imaging
Review Article  
Stefania Altavilla, Francesca Montagna and Marco Cantamessa
J. Manuf. Sci. Eng   doi: 10.1115/1.4037763
Product Cost Estimation still draws the attention of researchers and practitioners, even though it has been extensively discussed in the literature for more than twenty years. This is due to its central impact in affecting company performance. Nowadays, the adoption of cost estimation methods seems to be limited despite the multitude of examples and applications available. A possible reason is related to the multitude of approaches and techniques that instead of representing a guide for spreading possible implementations, actually create confusion and ambiguity on its appropriateness for a particular application. Hence, this paper aims to provide a systematic review of the recent literature in the field of Product Cost Estimation and investigates, in detail, which are the aspects that can enable a more conscious decision on the type of technique that can be adopted. This resulted in the identification of five different perspectives, which can be taken simultaneously into account and by combining the different viewpoints, a new multilayer framework is derived, with a specific focus on the whole product life cycle. The proposed framework can be used as a decision-making tool for both researchers and practitioners. In fact, the former can benefit from the new structure, as a way to identify new areas of possible research opportunities. The latter is provided an operative guide for the application in industrial contexts.
TOPICS: Cycles, Decision making, Ambiguity
research-article  
Xiaohua Liu, Tianfeng Zhou, Lin Zhang, Wenchen Zhou, Jianfeng Yu, James Ly Lee and Allen Y. Yi
J. Manuf. Sci. Eng   doi: 10.1115/1.4037707
Localized rapid heating process utilizing nano-scale carbide-bonded graphene coated silicon molds is a high-efficiency and energy-saving technique for large-volume micro-optical polymer fabrication. The graphene coating is used as a rapid heating film because of its high electrical conductivity and low surface resistivity. A significant feature of this new approach is that only a very small fraction of the polymer substrate in which the temperature is raised to above transition temperature (Tg), contribute most of the deformation and optical property change, while the bulk of the polymer substrate is unchanged during the process. In this study, Finite element method (FEM) simulation was utilized to interpret the temperature increasing of graphene and heat transfer between graphene and polymethylmethacrylate (PMMA) during localized rapid heating. Experiments were then carried out under different voltages to validate the feasibility and accuracy of the numerical model. Afterwards, the refractive index variation of the PMMA block resulting from the non-uniform thermal history in molding was demonstrated by simulation modeling. Based on the simulation results, a new refractive index variation prediction model was further built to evaluate the refractive index variation distribution along the radial direction of a molded PMMA. Finally, wavefront variation of a PMMA lens molded by localized rapid heating were obtained according to FEM model and verified by optical measurements with a Shack-Hartmann wavefront sensor (SHWFS). The wavefront variation in the PMMA lens molded by conventional method was also measured.
TOPICS: Optics, Simulation, Molding, Refractive index, Polymers, Heating, Graphene, Finite element methods, Lenses (Optics), Computer simulation, Temperature, Heat transfer, Electrical conductivity, Deformation, Coating processes, Coatings, Sensors, Optical measurement, Manufacturing, Nanoscale phenomena, Phase transition temperature, Silicon, Simulation results, Electrical resistivity
research-article  
Qiong Liu, Youquan Tian, Chao Wang, Freddy O. Chekem and John Sutherland
J. Manuf. Sci. Eng   doi: 10.1115/1.4037710
In order to help manufacturing companies quantify and reduce product carbon footprints in a mixed-model manufacturing system, a product carbon footprint oriented multi-objective flexible job-shop scheduling optimization model is proposed. The production portion of the product carbon footprint, based on the mapping relations between products and the carbon emissions within the manufacturing system is proposed to calculate the product carbon footprint in the mixed-model manufacturing system. Non-Dominated Sorting Genetic Algorithm-II(NSGA-II) is adopted to solve the proposed model. In order to help decision makers to choose the most suitable solution from the Pareto set as its execution solution, a method based on grades of product carbon footprints is proposed. Finally, the efficacy of the proposed model and algorithm are examined via a case study.
TOPICS: Manufacturing, Machine shops, Carbon, Manufacturing systems, Algorithms, Optimization, Emissions
research-article  
Roby Lynn, Mahmoud Dinar, Nuodi Huang, James Collins, Jing Yu, Clayton Greer, Thomas M. Tucker and Thomas Kurfess
J. Manuf. Sci. Eng   doi: 10.1115/1.4037631
Direct digital manufacturing (DDM) is the creation of a physical part directly from a computer-aided design (CAD) model with minimal process planning and is typically applied to additive manufacturing (AM) processes to fabricate complex geometry. AM is preferred for DDM because of its minimal user input requirements; as a result, users can focus on exploiting other advantages of AM, such as the creation of intricate mechanisms that require no assembly after fabrication. Such assembly-free mechanisms can be created using DDM during a single build process. In contrast, subtractive manufacturing (SM) enables the creation of higher strength parts that do not suffer from the material anisotropy inherent in AM. However, process planning for SM is more difficult than it is for AM due to geometric constraints imposed by the machining process; thus, the application of SM to the fabrication of assembly-free mechanisms is challenging. This research describes a voxel-based computer-aided manufacturing (CAM) system that enables direct digital subtractive manufacturing (DDSM) of an assembly-free mechanism. Process planning for SM involves voxel-by-voxel removal of material in the same way that an AM process consists of layer-by-layer addition of material. The voxelized CAM system minimizes user input by automatically generating toolpaths based on an analysis of accessible material to remove for a certain clearance in the mechanism's assembled state. The DDSM process is validated and compared to AM using case studies of the manufacture of two assembly-free ball-in-socket mechanisms.
TOPICS: Machining, Manufacturing, Production planning, Computer-aided design, Computer-aided manufacturing, Geometry, Additive manufacturing, Anisotropy, Clearances (Engineering)
research-article  
Clayson C. Spackman, James F. Nowak, Kristen Mills and Johnson Samuel
J. Manuf. Sci. Eng   doi: 10.1115/1.4037603
The 3D printing of fiber-reinforced soft composites (FrSCs) is a layer-by-layer material deposition process that alternates between inkjet deposition of an ultraviolet (UV) curable polymer layer and the stamping of electrospun fibers onto the layer, to build the final part.While this process has been proven for complex 3D geometries, it suffers from poor fiber transfer efficiencies that affect the eventual fiber content in the printed part. In order to address this issue, it is critical to first understand the mechanics of the fiber transfer process. To this end, the objective of this paper is to develop a cohesive zone-based finite element model that captures the competition between the 'fiber-carrier substrate' adhesion and the 'fiber-polymer matrix' adhesion, encountered during the stamping process used for 3D printing FrSCs. The cohesive zone model parameters are first calibrated using independent micro-scale fiber peeling experiments involving both the thin-film aluminum carrier-substrate and the UV curable polymer matrix. The predictions of the calibrated model are then validated using fiber transfer experiments. The model parametric studies suggest the use of a roller-based stamping unit design to improve the fiber transfer efficiency of the FrSC 3D printing process. Preliminary experiments confirm that for a 0.5 inch diameter roller, this new design can increase the fiber transfer efficiency to ~97%, which is a substantial increase from the 55% efficiency value seen for the original flat-plate stamping platen design.
TOPICS: Composite materials, Fibers, Metal stamping, Additive manufacturing, Design, Polymers, Ultraviolet radiation, Adhesion, Rollers, Thin films, Aluminum, Finite element model, Flat plates, Microscale devices
research-article  
Feng Zhang and Arif S Malik
J. Manuf. Sci. Eng   doi: 10.1115/1.4037600
Introduced is an efficient new model to compute the roll-stack deflections and contact mechanics behaviors for metal rolling mills with asymmetric roll crowns. The new model expands the simplified mixed finite element method to consider complex antisymmetric contact conditions of continuously variable crown (CVC) roll diameter profiles designed for use with work-roll shifting on 4-high mills, and intermediate-roll shifting on 6-high mills. Conventional roll-stack deflection models are either more computationally expensive or exploit more simplifying assumptions. Moreover, almost all existing approaches fail to adequately simulate the antisymmetric continuously variable crown contact problem required for model-based control of thickness profile and flatness in hot and cold CVC rolling mills. The presented model efficiently captures bending, shear, and flattening deformations while computing contact interference forces, binary contact locations, and net effects of roll and strip crowns. Strip thickness profiles and contact force distributions predicted by the new model are checked against known theoretical solutions, and compared to predictions from large scale finite element simulations for a 4-high mill with work-roll CVC shifting, and a thin-strip 6-high mill with intermediate-roll CVC shifting.
TOPICS: Rolling mills, Contact mechanics, Strips, Deflection, Engineering simulation, Finite element analysis, Deformation, Metals, Simulation, Shear (Mechanics), Finite element methods
research-article  
Navid Nazemi and R. Jill Urbanic
J. Manuf. Sci. Eng   doi: 10.1115/1.4037604
Laser cladding is a rapid physical metallurgy process with a fast heating-cooling cycle, which is used to coat a surface of a metal to enhance the metallurgical properties of the substrate's surface. A fully coupled thermal-metallurgical-mechanical finite element model was developed to simulate the process of coaxial powder-feed laser cladding for selected overlap conditions and employed to predict the mechanical properties of the clad and substrate materials, as well as distortions and residual stresses. The numerical model is validated by comparing the Vickers microhardness measurements, melt pool dimensions, and heat affected zone geometry from experimental specimens' cross-sectioning. The study was conducted to investigate the temperature field evolution, thermal cycling characteristics, and the effect of deposition directions and overlapping conditions on the microhardness properties of multi-track laser cladding. This study employed P420 stainless steel clad powder on a medium carbon structural steel plate substrate. The study was carried out on three case studies of multi-track bead specimens with 40%, 50%, and 60% overlap. The results provide relevant information for process planning decisions and present a baseline to for downstream the process planning optimization.
TOPICS: Lasers, Steel, Simulation, Mechanical properties, Cladding systems (Building), Stainless steel, Microhardness, Production planning, Residual stresses, Structural steel, Carbon, Optimization, Cycles, Finite element model, Geometry, Computer simulation, Dimensions, Metallurgy, Heat, Temperature, Cooling, Metals, Heating
research-article  
Sebastian Barth, Michael Rom, Christian Wrobel and Fritz Klocke
J. Manuf. Sci. Eng   doi: 10.1115/1.4037598
This paper presents an innovative approach for modeling the grinding wheel structure and the resultant grinding wheel topography. The overall objective of the underlying research work was to create a mathematical-generic grinding tool model in which the spatial arrangement of the components grains, bond and pores is simulated in a realistic manner starting from the recipe-dependent volumetric composition of a grinding wheel. This model enables the user to determine the resulting grinding wheel structure and the grinding wheel topography of vitrified and synthetic resin-bonded CBN grinding wheels depending on their specification and thus to predict their application behavior. The originality of the present research results is a generic approach for the modeling of grinding tools, which takes into account the entire grinding wheel structure to build up the topography. Therefore, original mathematical methods are used. The components of grinding wheels are analyzed and distribution functions of the component's positions in the tools are determined. Thus, the statistical character of the grinding wheel structure is taken into account in the developed model. In future, the presented model opens new perspectives in order to optimize and to increase the productivity of grinding processes.
TOPICS: Grinding wheels, Modeling, Grinding, Resins
research-article  
Tomasz Bartkowiak and Christopher A. Brown
J. Manuf. Sci. Eng   doi: 10.1115/1.4037601
The objectives of this work are to demonstrate the use of multi-scale curvature tensor analysis for characterizing surfaces of stainless steel created by micro-electric discharge machining (µEDM), and to study the strengths of the correlations between discharge energies and resulting surface curvatures (i.e., principal, Gaussian or mean curvatures) and how they change with scale. Surfaces were created by µ-EDM techniques using energies from 18nJ to 16 500nJ and measured by confocal microscope. The curvature tensor T is calculated using three proximate unit vectors normal to the surface. The multi-scale effect is achieved by changing the size of the sampling interval for the estimation of the normals. Normals are estimated from regular meshes by applying a covariance matrix method. Strong correlations (R2>0.9) are observed between calculated principal maximal and minimal as well as mean and Gaussian curvatures and discharge energies. This method allows detailed analysis of the nature of surface topographies, and suggests that different formation processes governed the creation of surfaces created by higher energies.
TOPICS: Texture (Materials), Tensors, Electrical discharge machining, Stainless steel, Microscopes
research-article  
Fei Tao, Luning Bi, Ying Zuo and A Y C Nee
J. Manuf. Sci. Eng   doi: 10.1115/1.4037608
Disassembly is a very important step in recycling and maintenance, particularly for energy saving. However, disassembly sequence planning is a challenging combinatorial optimization problem due to complex constraints of many products. This paper considers partial and parallel disassembly sequence planning for solving the degrees of freedom in modular product design, considering disassembly time, cost and energy consumption. An automatic self-decomposed disassembly precedence matrix is designed to generate partial/parallel disassembly sequence for reducing complexity and improving efficiency. A Tabu search based hyper heuristic algorithm with exponentially decreasing diversity management strategy is proposed. Compared with the low-level heuristics, the proposed algorithm is more efficient in terms of exploration ability and improving energy benefits. The comparison results of three different disassembly strategies prove that the partial/parallel disassembly has a great advantage in reducing disassembly time, and improving energy benefits and disassembly profit.
TOPICS: Recycling, Maintenance, Degrees of freedom, Algorithms, Optimization, Energy consumption, Product design
research-article  
Brian K. Paul, Kijoon Lee and Hailei Wang
J. Manuf. Sci. Eng   doi: 10.1115/1.4037606
The objective of this study was to develop a strategy for miniaturizing heat exchangers used for the thermal management of sorbent beds within adsorption refrigeration systems. The thermal mass of the microchannel heat exchanger designed and fabricated in this study is compared with that of commercially available tube-and-fin heat exchangers. Efforts are made to quantify the overall effects of miniaturization on system coefficient of performance and specific cooling power. A thermal model for predicting the cycle time for desorption is developed and experiments are used to quantify the effect of the intensified heat exchanger on overall system performance.
TOPICS: Sorbents, Energy efficiency, Thermal management, Heat exchangers, Refrigeration, Cycles, Desorption, Microchannels, Cooling
research-article  
Jiaqiang Zhang, Quan Liu, Wenjun Xu, Zude Zhou and Duc Truong Pham
J. Manuf. Sci. Eng   doi: 10.1115/1.4037605
Service-oriented robotic manufacturing system is an integrated system, in which the industrial robots (IRs) operate within a service-oriented manufacturing model, and can be virtualized and servicelized as services, so as to provide on-demand, agile, configurable and sustainable manufacturing capability services to users in workshop environment. Manufacturing capability of such systems can be divided into three layers, including manufacturing cell layer, production process layer and workshop layer. However, most of existing works carried out the optimization on each layer individually. Manufacturing cells are the component parts of a production process, and there are close relationships between them and can effect the operation and performance for each other, therefore it is essential to jointly consider the manufacturing capability service optimization on both layers. In this context, a cross-layer optimization model is proposed to conquer the existing limitation and provide a comprehensive performance assurance to service-oriented robotic manufacturing systems. The proposed model has different decision-making mechanisms on each layer and the communications and interaction between the two layers can further coordinate the optimizations. A case study based on robotic assembly is implemented to demonstrate the availability and effectiveness of the proposed model.
TOPICS: Optimization, Robotics, Manufacturing systems, Manufacturing, Manufacturing cells, Workshops (Work spaces), Robots, Sustainability, Decision making, Robotic assembly, Integrated systems
research-article  
Jarred Heigel and Brandon Lane
J. Manuf. Sci. Eng   doi: 10.1115/1.4037571
This work presents high speed thermographic measurements of the melt pool length during single track laser scans on nickel alloy 625 substrates. Scans are made using a commercial laser powder bed fusion machine while measurements of the radiation from the surface are made using a high speed (1800 frames per second) infrared camera. The melt pool length measurement is based on the detection of the liquidus-solidus transition that is evident in the temperature profile. Seven different combinations of programmed laser power (49 W to 195 W) and scan speed (200 mm/s to 800 mm/s) are investigated and numerous replications using a variety of scan lengths (4 mm to 12 mm) are performed. Results show that the melt pool length reaches steady state within 2 mm of the start of each scan. Melt pool length increases with laser power, but its relationship with scan speed is less obvious because there is no significant difference between cases performed at the highest laser power of 195 W. Although keyholing appears to affect the anticipated trends in melt pool length, further research is required
TOPICS: Lasers, Machinery, Radiation (Physics), Nickel alloys, Steady state, Temperature profiles
research-article  
Houzhu Ding, Filippos Tourlomousis and Robert Chang
J. Manuf. Sci. Eng   doi: 10.1115/1.4037572
Bioprinted tissue constructs are enabled by microextrusion-based co-printing of cells and hydrogel materials. In this paper, a gelatin-alginate hydrogel material formulation is implemented as the bio-ink towards a 3D cell-laden tissue construct. However, of fundamental importance during the printing process is the interplay between the various parameters that yield the final cell distribution and cell density at different dimensional scales. To investigate these effects, this study advances a multidimensional analytical framework to determine the spatial variations and temporal evolution of cell distribution and cell density within a bioprinted cell-laden construct. In the one dimensional (1D) analysis, the cell distribution and cross-sectional shape for a single printed fiber are observed to be dependent on the process temperature and material concentration parameters. This is illustrated by the reliable fabrication and image line profile analysis of the fiber prints. Round fiber prints with a measured width of 809.552.3 ??m maintain dispersive cells with a degree of dispersion (at 96.8 % that can be achieved at high relative material viscosities under low temperature conditions (21 °C) or high material concentrations (10 % w/v gelatin). On the other hand, flat fiber prints with a measured width of 63.6 ??m coalesce cells towards the fiber midline with that can be fabricated at low relative material viscosities under high temperature (24 °C) or low material concentrations (7.5 % w/v gelatin). In the 2D analysis, a printed grid structure yields differential cell distribution whereby differences in localized cell densities are observed between the strut and cross regions within the printed structure. At low relative viscosities, cells aggregate at the cross regions where two overlapping filaments fuse together, yielding a cell density ratio of 2.060.44 between the cross region and strut region. However, at high relative viscosities, the cell density ratio decreases to 0.960.03. In the 3D analysis, the cell density attributed to the different layers is studied as a function of printing time elapsed from the initial bio-ink formulation. Due to identifiable gravity and extrusion process-induced effects, the cell distribution within the original bio-ink cartridge or material reservoir is altered over time to yield initial quantitative increases in the cell density over the first several printed layers, followed by quantitative decreases in the subsequent printed layers. Finally, in the time-dependent analysis, the evolution of cell density and the emergence of material degradation effects is studied over a time course study. Variable initial cell densities (0.6 x 106 cells/ml, 1.0 x 106 cells/ml, and acellular control group) printed and cross-linked into cell-laden constructs for the 48 hr time course study exhibit a time-dependent increase in cell density owing to proliferation within the constructs that are presumed to accelerate the degradation rate.
TOPICS: Gelatin, Density, Fibers, Viscosity, Inks, Printing, Hydrogels, Struts (Engineering), Biological tissues, Low temperature, Materials degradation, Manufacturing, Reservoirs, Extruding, Shapes, High temperature, Gravity (Force), Temperature

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