Computational Study of Reinforcement Mechanisms of Cuttlefish Bone Inspired Structure for 3D Printing

Cuttlebone, the internal shell structure of a cuttlefish, presents a unique labyrinthian wall-septa design that promotes high energy absorption, porosity, and damage tolerance. This structure offers us an inspiration for the design of lightweight and strong structures for potential applications in mechanical, aerospace and biomedical engineering. However, the complexity of the cuttlebones structural design makes its fabrication by traditional manufacturing techniques not feasible. The advances in additive manufacturing (3D printing) make highly complex structures like cuttlebone possible to manufacture. In this work, the authors sought to establish comparative data between cuttlebone structures and some common support structures used in additive manufacturing. The structures compared to cuttlebone in this work include the cubic, honeycomb and triangular support structures. This was accomplished by using CAD modeling and simulation software. This study found that the cuttlefish structures had higher average stress values than the others but similar average strain values. This leads to a higher modulus of elasticity for the cuttlebone structures. The data suggests that further research into cuttlebone structures could produce future designs that improve upon the current well-established additive manufacturing support structures. Further study will be performed for the 3D printing of cuttlebone inspired structures by using various types of materials, such as soft and rigid polymers, functional ceramics, composites, and metals.

Investigation of the Regenerative Potential of Human Bone Marrow Stem Cell-Seeded Polycaprolactone Bone Scaffolds, Fabricated Using Pneumatic Microextrusion Process

Pneumatic MicroExtrusion (PME) is a direct-write additive manufacturing process, which has emerged as a robust, high-resolution method for the fabrication of a broad spectrum of biological tissues and organs. However, the PME process is intrinsically complex, governed by bio-physio-chemical phenomena as well as material-process interactions. Hence, investigation of the influence of consequential factors on bone scaffold fabrication as well as investigation of cell-scaffold interactions would be an inevitable need. The objective of the work is to investigate the biocompatibility as well as the histological properties of PME-fabricated porous bone scaffolds, composed of polycaprolactone (PCL). To achieve this objective, a media extraction of the scaffold material was tested for cytostatic or cytotoxic activity with the aim to: (i) assess the fabricated scaffolds’ feasibility of use in regenerative medicine, and (ii) determine their structural integrity in a modelled in-vivo environment. In addition, the scaffolds were inoculated with an established osteosarcoma cell line (SAOS-2) and cultured for seven days to investigate the scaffold architecture and cell integration potential. A histological examination was performed on the seeded scaffolds for further in-depth analysis of cell-scaffold interaction. Overall, the results of this study pave the way for future investigation of stem cell incorporation into PME-fabricated PCL scaffolds toward the treatment of osseous fractures and defects.

Anisotropic Cutting Force Characteristics in Milling of Maraging Steel Processed Through Selective Laser Melting

Additive manufacturing process of maraging steel has been studied for high value parts in aerospace and automotive industries. The hybrid additive / subtractive manufacturing is effective to achieve tight tolerances and surface finishes. The additive process induces anisotropic mechanical properties of maraging steel, which depends on the laser scanning direction. Because anisotropy in the workpiece material has an influence on the cutting process, the surface finish and the dimension accuracy change according to the direction of the cutter feed with respect to the laser scanning direction. Therefore, the cutting parameters should be determined to control the cutting force considering material anisotropy. The paper discusses the cutting force in milling of maraging steel stacked with selective laser melting, as an additive manufacturing process. Anisotropic effect on the cutting forces is proved with the changing rate of the cutting force in milling of the workpieces stacked by repeating laser scanning at 0/90 degrees and 45/−45 degrees. The cutting forces, then, are analyzed in the chip flow models with piling up of orthogonal cuttings. The force model associates anisotropy with the shear stress on the shear plane. The changes in the cutting forces with the feed direction are discussed in the cutting tests and analysis.

Development of Cutting Tools With Micro-Textured Surface for High Speed Machining of Ti-6Al-4V

In cutting of Ti-6Al-4V alloy, the cutting speed is limited since a high cutting temperature leads to severe tool wear and short tool life, resulting in poor production efficiency. On the other hand, some recent literature has reported that various beneficial effects can be provided by forming micro-textures on the tool surface in the metal cutting process. In this study, in order to achieve high-performance machining of Ti-6Al-4V, we first investigated the mechanism of the tool failure process for a cemented carbide cutting tool in high-speed turning of Ti-6Al-4V. Based on the results, cutting tools with micro textured surfaces were developed under the consideration of a cutting fluid action. A series of experiments showed that the textured rake face successfully decreases the cutting temperature, resulting in a significant suppression of both crater wear and flank wear. In addition, the temperature zone where the texture tool is effective in terms of the tool life in the Ti-6Al-4V cutting was discussed.

Prediction of Cutting Force in Bone Cutting Using Finite Element Analysis

In orthopedic surgery, bone cutting is an indispensable procedure followed by the surgeons to treat the fractured and fragmented bones. Because of the unsuitable parameter values used in the cutting processes, micro crack, fragmentation, and thermal osteonecrosis of bone are observed. Therefore, prediction of suitable cutting force is essential to subtract the bone without any adverse effect. In this study, the Cowper-Symonds model for bovine bone was developed for the first time. Then the developed model was coupled with the finite element analysis to predict the cutting force. To determine the model constants, tensile tests with different strain rates (10−5/s, 10−4/s, 10−3/s, and 1/s) were conducted on the cortical bone specimens. The developed material model was implemented in the bone cutting simulation and validated with the experiments.

Prediction of Melt-Pool Characteristics in SLM Process for Ti6Al4V Using a Semi-Analytical Model

Selective Laser Melting (SLM) is a powder-based layer-by-layer manufacturing technique to produce metallic customized shape components. The exceptionally high thermal gradient induces residual stress and distorts the part geometry affecting the yield quality. Computational models are instrumental in optimizing the process controls to fabricate high-quality components, and hence several such methods have been explored to simulate the thermal behavior of the process and the heat transfer in the melt-pool. Most of the practiced techniques are computationally expensive, making it infeasible to perform a parametric study. Based on closed-form exact heat conduction solution and Finite Volume Method (FVM), a pseudo-analytical thermal modeling approach has been employed to estimate the melt-pool characteristics and temperature distribution of the SLM process. A moving volumetric Gaussian heat source laser model and Green’s function have been adopted to model the heat input by conduction. The heat loss by conduction and convection has been calculated by implementing Finite Volume discretized equations on a 2-dimensional thin-walled domain with appropriate part boundary conditions. Additionally, the Alternating Direction Implicit iterative technique has been implemented for the fast convergence of the simulation. The model is used to demonstrate the influence of the process parameters and non-linear material phase change for a single-line single layer and multilayer part fabrication. The computed melt-pool dimensions and temperature distribution for varying laser-power, scanning velocity, and layer thickness for Ti6Al4V are validated with the experimental data from the literature with fair agreements.

Toward Intelligent Online Scan Sequence Optimization for Uniform Temperature Distribution in LPBF Additive Manufacturing

Laser powder bed fusion (LPBF) is an increasingly popular approach for additive manufacturing (AM) of metals. However, parts produced by LPBF are prone to residual stresses, deformations, and other defects linked to nonuniform temperature distribution during the process. Several works have highlighted the important role (laser) scanning strategies, including laser power, scan speed, scan pattern and scan sequence, play in achieving uniform temperature distribution in LPBF. However, scan sequence continues to be determined offline based on trial-and-error or heuristics, which are neither optimal nor generalizable. To address these weaknesses, we present a framework for intelligent online scan sequence optimization to achieve uniform temperature distribution in LPBF. The framework involves the use of physics-based models for online optimization of scan sequence, while data acquired from in-situ thermal sensors provide correction or calibration of the models. The proposed framework depends on having: (1) LPBF machines capable of adjusting scan sequence in real-time; and (2) accurate and computationally efficient models and optimization approaches that can be efficiently executed online. The first challenge is addressed via a commercially available open-architecture LPBF machine. As a preliminary step towards tackling the second challenge, an analytical model is explored for determining the optimal sequence for scanning patterns in LPBF. The model is found to be deficient but provides useful insights into future work in this direction.

Pneumatic Microextrusion-Based Additive Biofabrication of Polycaprolactone Bone Scaffolds: Part II – Investigation of the Influence of Polymer Flow Parameters

Pneumatic micro-extrusion (PME), a direct-write additive manufacturing process, has emerged as a high-resolution method for the fabrication of a broad range of biological tissues and organs. However, the PME process is intrinsically complex, governed by complex physical phenomena. Hence, investigation of the effects of consequential parameters would be an inevitable need. The goal of this research work is to fabricate biocompatible, porous bone tissue scaffolds for the treatment of osseous fractures, defects, and eventually diseases. In pursuit of this goal, the objective of this study is to investigate the influence of material deposition factors — i.e., (i) deposition head temperature, (ii) flow pressure, and (iii) infill pattern — on the mechanical performance of PME-fabricated bone scaffolds. It was observed that the deposition head temperature as well as the flow pressure significantly affected scaffold diameter (unlike scaffold height). In addition, material deposition rate increased significantly as a result of an increase in the deposition temperature; this phenomenon stems from a reduction in Polycaprolactone (PCL) viscosity. Furthermore, there was a direct correlation between the amount of deposited mass and scaffold stiffness. Overall, the results of this study pave the way for future investigation of PME-deposited PCL scaffolds with optimal functional properties for incorporation of stem cells toward the treatment of osseous fractures and defects.

Performance of Low-Cost 3D Printer in Medical Application

Fused Deposition Modelling (FDM) is an additive manufacturing (AM) process that produces a physical object directly from a CAD design using layer-by-layer deposition of the filament material that is extruded via a nozzle. In industry, FDM has become one of the most used AM processes for the production of low batch quantity and functional prototypes, due to its safety, efficiency, reliability, low cost, and ability to process manufacturing-grade engineering thermoplastic. Recently, the market is flooded with the availability of low-cost printers produced by numerous companies. This research aims to investigate the effect of different porosity levels on a scaffold structure produced using a low-cost 3D printer. Comparisons of these porous structures were made in terms of Von-Mises strain, total deformation, as well as compressive stress. Various porosity levels were created by varying printing parameters, including layer height, infill density, and shell thickness by slicing the initial solid CAD file using Repetier Host 3D printing software. Finite Element Analysis (FEA) simulation was then performed on the created scaffold structures by using Ansys Workbench 19.2. The simulation result indicates that the greater porosity level will result in higher total deformation of the structure. Meanwhile, the compression test shows that the minimum strength value obtained was favourable at 22 MPa and had exceeded that of the trabecular femur (15 MPa). However, its porosity level (maximum at 52%) was still below that of the minimum threshold of porosity level of 70 percent. However, the printing parameters currently used can be adjusted in the future. Therefore, it was deduced that the low-cost 3D printer offers promising potential to fabricate different porosity structures with multiple outcomes.

Study on Non-Axisymmetric 3D Curved Surface Turning by Driven-Type Rotary Tool Synchronized With Spindle

Since shifting to electric vehicles as a countermeasure against global warming is not always easy to complete, the hybrid car has been considered as another possible solution. However, based on the calculation of total CO2 emissions, all hybrid cars which will constitute 90% of all cars are expected to be equipped with an internal combustion engine even after 2030. Therefore, further efficiency improvement of the internal combustion engine is necessary. One of the key factors is the variable valve timing and variable lift with the 3D cam mechanism. Since conventional technology uses a complicated link mechanism and servo motor control, this leads a problem to set into small cars or motorcycles because they cannot afford to install the variable valve timing and variable lift with cam mechanism. To solve this problem, a cam shape with a three-dimensional curved surface has been proposed. In order to create this shape, the machining method for non-axisymmetric curved surface turning (NACS-Turning) is required. To build the new system, our research group has proposed a new machining method using a driven type rotary tool and a linear motor driven moving table to enable to achieve NACS-Turning. In this new system, a new tool rotation axis (B axis) is adopted to synchronize its rotational position with the rotational position of the spindle (C axis) holding the workpiece, the X1-, X2-, and Z-Axis positions in total. In this paper, the new hardware configuration is proposed to overcome the present machining accuracy.