The specific aim of this study was to gain insight into the influence of scaffold pore size, pore shape and permeability on the in vitro proliferation and differentiation of three-dimensional (3-D) ...human periosteum-derived cell (hPDC) cultures. Selective laser melting (SLM) was used to produce six distinct designed geometries of Ti6Al4V scaffolds in three different pore shapes (triangular, hexagonal and rectangular) and two different pore sizes (500μm and 1000μm). All scaffolds were characterized by means of two-dimensional optical microscopy, 3-D microfocus X-ray computed tomography (micro-CT) image analysis, mechanical compression testing and computational fluid dynamical analysis. The results showed that SLM was capable of producing Ti6Al4V scaffolds with a broad range of morphological and mechanical properties. The in vitro study showed that scaffolds with a lower permeability gave rise to a significantly higher number of cells attached to the scaffolds after seeding. Qualitative analysis by means of live/dead staining and scanning electron micrography showed a circular cell growth pattern which was independent of the pore size and shape. This resulted in pore occlusion which was found to be the highest on scaffolds with 500μm hexagonal pores. Interestingly, pore size but not pore shape was found to significantly influence the growth of hPDC on the scaffolds, whereas the differentiation of hPDC was dependent on both pore shape and pore size. The results showed that, for SLM-produced Ti6Al4V scaffolds with specific morphological and mechanical properties, a functional graded scaffold will contribute to enhanced cell seeding and at the same time can maintain nutrient transport throughout the whole scaffold during in vitro culturing by avoiding pore occlusion.
Selective laser melting (SLM) is an additive manufacturing process in which functional, complex parts are produced by selectively melting consecutive layers of powder with a laser beam. This ...flexibility enables the exploration of a wide spectrum of possibilities in creating novel alloys or even metal–metal composites with unique microstructures. In this research, Ti6Al4V-ELI powder was mixed with 10wt.% Mo powder. In contrast to the fully α′ microstructure of Ti6Al4V after SLM, the novel microstructure consists of a β titanium matrix with randomly dispersed pure Mo particles, as observed by light optical microscopy, scanning electron microscopy and X-ray diffraction. Most importantly, the solidification mechanism changes from planar to cellular mode. Microstructures after heat treatment indicate that the β phase is metastable and locate the β transus at ∼900°C, and tensile properties are equal to or better than conventional β titanium alloys.
This paper discusses the principle and the relevance of an in situ monitoring system for selective laser melting (SLM). This system enables the operator to monitor the quality of the SLM job on-line ...and estimate the quality of the part accordingly. The monitoring system consists of two major developments in hardware and software. The first development, essential for a suitable monitoring system, is the design of a complete optical sensor set-up. This set-up is equipped with two commercially available optical sensors connected to a field-programmable gate array (FPGA) which communicates directly with the machine control unit. While the sensors ensure a high-quality measurement of the melt pool, the FPGA’s main task is to transfer the images from the sensors into relevant values at high sample rates (above 10 kHz). The second development is the data analysis system to translate and visualize measured sensor values in the format of interpretable process quality images. The visualization is mainly done by a “mapping algorithm,” which transfers the measurements from a time-domain into a position-domain representation. Further off-line experiments illustrate an excellent compatibility between the in situ monitoring and the actual quality of the products. The resulting images coming out of this model illustrate melt pool variations which can be linked to pores that are present in the parts.
The use of rapid prototyping (RP) technology for rapid tooling and rapid manufacturing has given rise to the development of application-oriented composites. The present paper furnishes succinct notes ...of the composites formed using main rapid prototyping processes such as Selective Laser Sintering/Melting, Laser Engineered Net Shaping, Laminated Object Manufacturing, Stereolithography, Fused Deposition Modeling, Three Dimensional Printing and Ultrasonic Consolidation. The emphasis of the present work is on the methodology of composite formation and the reporting of various materials used.
Purpose - This paper provides an overview of the different binding mechanisms in selective laser sintering (SLS) and selective laser melting (SLM), thus improving the understanding of these ...processes.Design methodology approach - A classification of SLS SLM processes was developed, based on the binding mechanism occurring in the process, in contrast with traditional classifications based on the processed material or the application. A broad range of commercial and experimental SLS SLM processes - found from recent articles as well as from own experiments - was used to explain the different binding mechanism categories.Findings - SLS SLM processes can be classified into four main binding mechanism categories, namely "solid state sintering", "chemically induced binding", "liquid phase sintering - partial melting" and "full melting". Most commercial processes can be classified into the latter two categories, which are therefore subdivided. The binding mechanism largely influences the process speed and the resulting part properties.Research limitations implications - The classification presented is not claimed to be definitive. Moreover some SLM SLM processes could be classified into more than one category, based on personal interpretation.Originality value - This paper can be a useful aid in understanding existing SLS SLM processes. It can also serve as an aid in developing new SLS SLM processes.
Owing to their attractive combination of mechanical properties, high heat conductivity and low weight, the Al-Si alloys found a large number of applications in the Additive Manufacturing field for ...automotive, aerospace and domestic industries. However, due to their high reflectivity and heat conductivity, they are harder to process by Selective Laser Melting. This work elaborates on both the optimisation of process parameters, in order to get nearly fully dense parts, and the material properties resulting from this specific material process combination. A process parameter window is defined, in which the formed melt pool is stable and meets the set requirements. In this process window, the parameter set for optimal density is defined. It is shown that AlSi10Mg parts produced by SLM have mechanical properties higher or at least comparable to the cast material because of the very fine microstructure.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Selective laser melting (SLM) is used to manufacture dense NiTi parts. The microstructure and texture are assessed (before and after annealing followed by furnace cooling) and linked to the ...compression behaviour and shape memory response. It is shown that SLM strongly orients the fine austenite subgrains towards the building direction. This texture induces the highest spring back along the building (vertical) direction and the lowest along the horizontal direction after compression. The compressive stiffness, on the other hand, is the highest along horizontal direction and the lowest in vertical direction. The internal stresses due to SLM processing are another factor that may induce large martensite plates, decreasing the spring back. Although post-annealing (followed by furnace cooling) annihilates these large SLM stress-induced martensite plates, it is unsuccessful to achieve completely isotropic properties. The furnace cooling after annealing may even segregate austenite and martensite within SLM solidified tracks, causing a mixed shape memory response.
The number of industrial applications of Computed Tomography (CT) is large and rapidly increasing. After a brief market overview, the paper gives a survey of state of the art and upcoming CT ...technologies, covering types of CT systems, scanning capabilities, and technological advances. The paper contains a survey of application examples from the manufacturing industry as well as from other industries, e.g., electrical and electronic devices, inhomogeneous materials, and from the food industry. Challenges as well as major national and international coordinated activities in the field of industrial CT are also presented.
► Selective laser melting as a production tool for porous Ti6Al4V structures. ► Significant mismatch between designed and as-produced properties. ► Decreasing mismatch using a micro-CT-based ...protocol. ► Mismatch of pore size decreased from 45% to 5%. ► Increased morphological controllability increases mechanical controllability.
Despite the fact that additive manufacturing (AM) techniques allow to manufacture complex porous parts with a controlled architecture, differences can occur between designed and as-produced morphological properties. Therefore this study aimed at optimizing the robustness and controllability of the production of porous Ti6Al4V structures using selective laser melting (SLM) by reducing the mismatch between designed and as-produced morphological and mechanical properties in two runs. In the first run, porous Ti6Al4V structures with different pore sizes were designed, manufactured by SLM, analyzed by microfocus X-ray computed tomography (micro-CT) image analysis and compared to the original design. The comparison was based on the following morphological parameters: pore size, strut thickness, porosity, surface area and structure volume. Integration of the mismatch between designed and measured properties into a second run enabled a decrease of the mismatch. For example, for the average pore size the mismatch decreased from 45% to 5%. The demonstrated protocol is furthermore applicable to other 3D structures, properties and production techniques, powder metallurgy, titanium alloys, porous materials, mechanical characterization, tomography.
Enhanced bone tissue regeneration and improved osseointegration are among the most important goals in design of multifunctional orthopedic biomaterials. In this study, we used additive manufacturing ...(selective laser melting) to develop multifunctional porous nitinol that combines superelasticity with a rationally designed microarchitecture and biofunctionalized surface. The rational design based on triply periodic minimal surfaces aimed to properly adjust the pore size, increase the surface area (thereby amplifying the effects of surface biofunctionalization), and resemble the curvature characteristics of trabecular bone. The surface of additively manufactured (AM) porous nitinol was biofunctionalized using polydopamine-immobilized rhBMP2 for better control of the release kinetics. The actual morphological properties of porous nitinol measured by microcomputed tomography (e.g., open/close porosity, and surface area) closely matched the design values. The superelasticity originated from the austenite phase formed in the nitinol porous structure at room temperature. Polydopamine and rhBMP2 signature peaks were confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy tests. The release of rhBMP2 continued until 28 days. The early time and long-term release profiles were found to be adjustable independent of each other. In vitro cell culture showed improved cell attachment, cell proliferation, cell morphology (spreading, spindle-like shape), and cell coverage as well as elevated levels of ALP activity and increased calcium content for biofunctionalized surfaces as compared to as-manufactured specimens. The demonstrated functionalities of porous nitinol could be used as a basis for deployable orthopedic implants with rationally designed microarchitectures that maximize bone tissue regeneration performance by release of biomolecules with adjustable and well-controlled release profiles.
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