Layered Manufacturing Techniques Research Articles

Old materials - new capabilities: lattice materials in structural mechanics

Lattice materials (LM) are a novel concept stemming from the combination of crystallography and structural optimisation algorithms. Their practical applications have become real with the advent of versatile additive layer manufacturing (ALM) techniques and the development of dedicated CAD/CAE tools. This work critically reviews one of the major claims concerning LMs, namely their excellent stiffness-to-weight performance. First, a brief literature review of spatially uniform LMs is presented, focusing on specific strength of standard engineering materials as compared with novel structures. An original modelling and optimisation is carried out on a flat panel subject to combined shear and bending load. The calculated generalised specific stiffness is compared against reference values obtained for a uniform panel and the panel subjected to topological optimisation. The monomaterial, a spatially repetitive solution turns out to be poorly suited for stiff, lightweight designs, because of suboptimal material distribution. Spatially non-uniform and locally size-optimised structures perform better. However, its advantage over manufacturable, topologically-optimised conventional designs can at best be marginal (< 10%). Cubic-cell lattices cannot replace conventional bulk materials in the typical engineering use. The multi-cell-type and multi- -material lattice structures, albeit beyond the scope of this article, are more promising from the point of view of mechanical properties. The possibility of approaching the linear scaling reported in the recent litterature can make them an attractive option in ultra-low weight designs.

Fracture resistance of 3D printed adhesively bonded DCB composite specimens using structured interfaces: Experimental and theoretical study

The use of adhesive joints is widespread in lightweight composite structures, whereby interfaces between adherents play a crucial role in terms of the fracture resistance of the component. The appearance of recent Additive Layer Manufacturing (ALM or 3D printing) techniques opens a new paradigm regarding the design of interfaces, allowing the reproduction of nature-inspired geometric definitions to be accomplished. In this paper, the mechanical performance of double cantilever beam (DCB) specimens with trapezoidal patterned interfaces using ALM in long-fibre composites are investigated from an experimental point of view. Special attention is devoted in this study to the analysis of the influence of the aspect ratio A/λ (A = amplitude, λ = wavelength) of the structured interface on the fracture toughness of such specimens. The experimental data reveal a notable increase of the critical energy release rates in comparison with flat interface profiles. A map of different trapezoidal interface profiles, whose corresponding fracture properties are satisfactorily predicted by means of a novel theoretical model within a wide range of interface definitions is presented. The results obtained demonstrate the potential benefits arising from the production of bonded joints with patterned trapezoidal interfaces, which can lead to tougher and promising performances in service.

Auxetics and Other Systems of Anomalous Characteristics

Auxetics and Other Systems of Anomalous Characteristics

Investigation on the effect of surface modification of 3D printed parts by nanoclay and dimethyl ketone

ABSTRACTFused deposition modeling (FDM) has emerged as one of the most utilized 3D printing technique. However, the surface properties of the FDM built parts lacks integrity due to layer by layer manufacturing technique. Therefore, post treatment is done on FDM printed parts. In the present research work, an effort has been made to improve the surface properties of the 3D printed parts by surface modification via chemical/nanoparticles. Nanoclay and dimethyl ketone were utilized for the surface modification of acrylonitrile butadiene styrene specimens. Parameters namely nanoclay content, immersion time, heat treatment and layer thickness were investigated to study their effect on surface roughness, surface hardness and dimensions. Also, the effect of nanoclay on UV absorbance of 3D printed parts was observed. Structural and morphological analysis was performed to characterize the surface of the 3D printed specimens after surface modification process. The results show that the surface roughness was reduced by 94.9%, surface hardness was increased by 9.7% while maintaining minimum dimensional deviation of −0.03 and +0.07 mm. Also, UV absorbance was increased in 350–380 nm range. The results of the present study highlight the capability of the surface modification process for improving the surface properties of FDM parts.

Effect of layered manufacturing techniques, alloy powders, and layer thickness on metal-ceramic bond strength

Statement of problemDirect metal laser sintering (DMLS) and direct metal laser melting (DMLM) have become popular for fabricating the metal frameworks of metal-ceramic restorations. How the type of layered manufacturing device, layer thickness, and alloy powder may affect the bond strength of ceramic to metal substructure is unclear. PurposeThe purpose of this in vitro study was to evaluate the bond strength of dental porcelain to metal frameworks fabricated using different layered manufacturing techniques (DMLS and DMLM), Co-Cr alloy powders, and layer thicknesses and to evaluate whether a correlation exists between the bond strength and the number of ceramic remnants on the metal surface. Material and methodsA total of 75 bar-shaped metal specimens (n=15) were fabricated using either DMLS or DMLM. The powder alloys used were Keramit NP-S and EOS-Cobalt-Chrome SP-2 with layer thicknesses of 20 μm and 30 μm. After ceramic application, the metal-ceramic bond strength was evaluated with a 3-point-bend test. Three-way ANOVA followed by the Tukey honest significance difference test were used for statistical analysis (α=.05). De-bonding surface microstructure was observed with scanning electron microscopy. Energy dispersive spectroscopy analysis was conducted to evaluate the correlation between ceramic remnants on the metal surface and bond strength values. ResultsThe mean bond strength value of DMLS was significantly higher than that of DMLM. While no statistically significant difference was found between layer thicknesses, alloy powders closely affected bond strength. Statistical comparisons revealed that the highest bond strength could be achieved with DMLS-Cobalt-Chrome SP2-20μm, and the lowest bond strength was observed in DMLS-Keramit NP-S-20μm (P≤.05). No correlation was found between porcelain remnants on the metal surface and bond strength values. ConclusionsThe layered manufacturing device and the alloy powders evaluated in the current study closely affected the bond strength of dental porcelain to a metal framework. However, layer thickness did not affect the bond strength.

Impresión 3D para la construcción: un enfoque basado en el procedimiento y los materiales

Las aplicaciones de impresión 3D para construcción se encuentran en una fase inicial de desarrollo, tanto en lo referente a materiales y piezas como a procedimientos. Dichas limitaciones se deben a la especificidad del sector, el coste de la maquinaria necesaria y una ausencia de un patrón procedimental característico. El artículo presenta una metodología innovadora para superar estas limitaciones mediante un flujo de trabajo sencillo que permita el uso generalista de brazos robóticos mediante software integrativo y un uso de materiales optimizado. Asimismo se expone la integración de diseño y fabricación combinando Sistemas de Integración Robótica y técnicas de Fabricación por Deposición. Finalmente se muestra un modelo de optimización de material y patrones de relleno inteligentes. Se expone una pieza real de 0,4 x 0,4 x 1,5 metros como demostrador tecnológico de gran escala.

Surface modification of additive manufactured components by ultrasonic cavitation abrasive finishing

Powder Bed Fusion (PBF) is a group of powder-bed based layered Additive Manufacturing (AM) techniques for direct fabrication of metal and metal alloys. Despite its advancements, the surface quality of as-built PBF components remains unsatisfactory. In this paper, a new post-process finishing technique, based on ultrasonic cavitation effects in a solid-liquid mixture, is introduced for PBF-built components. Trials were conducted on side surfaces of Inconel 625 manufactured by Direct Metal Laser Sintering (DMLS). Results have demonstrated that this technique improves Ra values of as-built Inconel 625 side surfaces by up to 45% after 30min of processing time. Scanning electron microscopic images revealed that most small-sized partially melted powders were removed through heterogeneous cavitation nucleation on the specimens’ rough initial surface. A secondary fine-scale erosion mechanism by micro-abrasives, accelerated by cavitation bubble collapses, further depressed difficult-to-remove irregularities.

Laser metal deposition repair applications for Inconel 718 alloy

Laser metal deposition (LMD) is a layer manufacturing technique, which is used in freeform fabrication and repair applications of critical aerospace engine components. This paper focuses on deposition of Inconel 718 material for refurbishment of existing Inconel 718 components. The benefits of LMD process are good metallurgical bonding with less heat-affected zone when compared to traditional metal joining processes. To achieve best bonding between layers of deposited Inconel 718 it is important to optimize laser metal deposition parameters. In order to study the process parameter techniques and their effects on the deposited part from the point of mechanical and metallurgical strengths specific to aerospace applications, Taguchi’s L9 orthogonal array technique has been used. The optimal process parameters have been found from the experimental trails to achieve the fine microstructure, maximum hardness and reduced porosity, which finally lead to good bonding strength of the deposit. Using analysis of variance (ANOVA), effect of process parameters on the deposit were identified and verification tests were conducted to determine performance of the optimal process parameters. X-ray diffraction analysis revealed increased hardness and presence of high intensities of Ni3Al intermetallic elements in the optimized test specimens. The optimized results revealed improved properties in repairing of aero engine components using Inconel 718 powder.

Influence of building orientation on the flexural strength of laminated object manufacturing specimens

This study aims to define the best building orientation for components produced via the Laminated object manufacturing (LOM) technique to enhance their flexural performance. Results of previous research show that components produced via LOM are capable of with-standing higher deflections than components produced through other layer manufacturing techniques. However, the relation between the building orientation and flexural strength of components has not yet been assessed. Four types of specimens have been manufactured using different building orientations for each type. The specimens have been tested in a machine with four loading points to evaluate their failure mode and identify the best building orientation toward flexural loading. The best building orientation in terms of maximum load before failure is 45°. Furthermore, a repetitive failure pattern is found for each tested condition. Building orientation is confirmed to be a relevant parameter in LOM manufacturing by influencing the mechanical properties of components.

Experimental investigation to produce thin-walled sand casting using combination of casting simulation and additive manufacturing techniques

Sand casting process is used by man from olden days to manufacture metallic components. Due to various problems of sand, mold and filling, the process is considered not suitable to produce small intricate castings having thin geometries. Only huge castings are preferred and sophisticated components are completely ruled out of the process. However, the cost-effectiveness of the process is very attractive. The present work is taken up to investigate the possibility of sand mold casting process to produce intricate components having thin sections like automobile cylinder head castings. The project uses additive layer manufacturing technique for pattern development and computer-aided casting simulation technique to analyze mold filling and solidification aspects. Simulations are performed by varying pouring temperature and gating system design which also reduces shop floor trials and lead time. Based on simulation results, experiments are design and conducted using three types of sand, namely air-set sand, dry sand, and sodium-silicate sand. The produced castings are tested for various parameters and found successful. Results obtained from simulation are validated experimentally proving the methodology adopted is very helpful in producing intricate castings economically.

フェムト秒レーザー励起を用いた表面ナノ加工に関する研究

Layer manufacturing technique such as stereolithography is powerful tool to fabricate the 3D shape based on 3D-CAD data. The resolution of the 3D fabrication is limited by the spot size in x and y axis when we use laser to deposit the material by using the laser. As for the resolution in z axis, it is decided by the layer thickness to deposit the material. In the stereolithography by using the laser beam, the material is usually transparent. Thus it is difficult to control the solidification size in z direction, which is the direction of the beam propagation. We suggest a laser surface processing technique is investigated to improve the height resolution of layer manufacturing. In this study, make a challenge to achieve the processing on the surface with processing depth, which is lower than the layer thickness.

Structural and Frictional Performance of Fused Deposition Modelled Acrylonitrile Butadiene Styrene (P430) with a View to Use as Rapid Tooling Material in Sheet Metal Forming

Using additive layer manufacturing techniques, such as Fused Deposition Modelling (FDM), it is possible to produce complex geometry relatively quickly and cheaply. For this reason these processes offer intriguing possibilities for tooling in metal forming processes. A common material utilised in the FDM process is Acrylonitrile Butadiene Styrene (ABS). A series of compression and tensile tests were carried out on FDM ABS test specimens built in a range of orientations. The tensile tests were carried out until fracture and the specimen cross-sections analysed to investigate the cause of failure. In uniaxial tension the vertical build direction was found to be the weakest, failing in a brittle fashion. The FDM material elastic modulus and Poisson’s ratio were found to be isotropic in nature within experimental scatter. The ‘yield’ strength in compression was found to be higher than that observed for equivalent tensile orientations. Following a series of strip pull friction tests using commercially pure titanium as the blank material, it was found that without the utilisation of an interfacial lubricant a favourable frictional performance was achievable on ABS tool surfaces. Due to tool wear however, the frictional performance of these tool pieces deteriorated with increasing sliding distance.

A Paradigm to Produce Customized Ankle Support Using Incremental Sheet Forming

This paper presents a paradigm to produce customized ankle support through the use of reverse engineering (RE) process, which uses the patient's scan data to an optimal form using a computer-aided design (CAD) system and then transferring the three-dimensional CAD model to Incremental Sheet Forming (ISF) technique for the production of tangible prosthesis product. This work is in the direction of forming of such a customized ankle support that minimizes the gap between the implanting prosthesis and the ankle. Such type of products may be prefabricated or customized. Prefabricated products are manufactured according to the standard sizes of different persons and customized are fitted after observing the patient's computed tomography scan. Prefabricated products do not guaranteed that the product will fit or not to the geometry of patient. On the other side, customized products provide more comfort and satisfaction than prefabricated products. RE design process has been implemented in order to acquire CAD model from the patient's scan data and to use this information for computer controlled layered manufacturing technique like ISF.

Selection of steels suitable for additive layer manufacturing

There is an increased demand for specialist metallic powders driven by the growing use of various additive layer manufacturing (ALM) techniques. Currently, there are only a few steel grades available for these processes, but this technical note outlines a methodology for the selection of steel alloys suitable for the application of ALM, the aim of providing guidance on which steels would be worthy of further investigation as potential candidates for powder production.

An active viscoelastic metamaterial for isolation applications

Metamaterials are of interest due to their ability to produce novel acoustic behaviour beyond that seen in naturally occurring media. Of particular interest is the appearance of band gaps which lead to very high levels of attenuation within narrow frequency ranges. Resonant elements within metamaterials allow band gaps to form within the long wavelength limit at low frequencies where traditional passive isolation solutions suffer poor performance. Hence metamaterials may provide a path to high performance, low frequency isolation. Two metamaterials are presented here. An acoustic material consisting of an array of split hollow spheres is developed, and its performance is validated experimentally. The application of an acoustic/mechanical analogy allows the development of an elastodynamic metamaterial that could be employed as a high performance vibration isolator at low frequencies. A prototype isolator is manufactured, and its performance is measured. The passively occurring band gap is enhanced using an active control architecture. The use of the active control system in conjunction with the natural passive behaviour of the metamaterial enables high levels of isolation across a broad frequency range. An eventual goal of the work is to produce such materials on a small scale, and as such the metamaterials developed are designed for, and produced using, additive layer manufacturing techniques.

Investigation into the failure of Inconel exhaust collector produced by laser consolidation

Among layer manufacturing techniques, Laser Consolidation (LC) finds its ideal application in the production of thin-walled metal parts for industrial niches characterised by high innovation and product complexity. To fully exploit the technological potential, developments must be made to assess LC’s repeatability and reliability. Previous studies proved that high strength parts of fine microstructure are obtained if appropriate build strategies are used. The aim of this research is to analyse a racecar exhaust collector, built in Inconel by LC, relating the failure modes and microstructure to the construction plan.The exhaust collector component was built using a custom strategy and was run on a dynamometer before failing after approximately 1200km. An investigation of the failure mechanism was carried out by a primary macroscopic analysis, aided by an X-ray control and dye penetrant test. Metallographic sections were then sampled from the critical areas to study the microstructure and relate it to the manufacturing process.Results proved that the distribution of primary microcracks associated with internal residual stresses caused by the build strategy and aggravated by differential shrinkage during the test thermocycles was responsible for ultimate failure. This issue was a result of build strategy and the non-coaxial laser head, therefore, alternative pathways could be developed capable of removing most, if not all, of the contributory factors. The analysed case suggests that LC build strategy selection is as critical to ensure low cycle fatigue resistance as component design and confirms that LC is effective in the production of advanced technological parts with high geometrical complexity given the correct build strategy.

Fabrication of Photo-Polymerized PCL Tissue Engineering Scaffolds by Dynamic Masking Rapid Prototyping System

PCL is one of the popular biomaterials used in tissue engineering scaffolds, but it is seldom shaped by photo-polymerization. Layered manufacturing techniques, also known as Rapid Prototyping (RP) processes, provide a great opportunity to fabricate 3D scaffolds without problems such as limited control of pore-size and restricted geometric shapes in traditional methods. In our previous researches, the Biomedical Dynamic Masking Rapid Prototyping System was developed to photo-cure biodegradable materials through visible light. In this research, the Dynamic Masking RP System was modified to photo-polymerize cross-linkable PCL to form tissue engineering scaffolds. The cross-linkable PCL was synthesized by reacting PCL and acryloyl chloride, and dissolved in acetone mixing with photo-initiator. The tensile test and degradation test were performed on the cured PCL samples. Fabrication of single-layer pattern was first tested to understand the system’s capability and showed the errors were within 7%. Two types of scaffold design concepts were adopted—one took square, hexagon, or triangle as a basic element to create 2D grid patterns, and the interconnected pore were produced by offsetting the 2D pattern in alternating layers; the other took a double-sided trapezoid as a unit and arrayed it into tube shape with interconnected pore network. Various PCL porous tube scaffolds have been successfully fabricated in this study. In the future, they can be utilized to cell growth or mass cell duplication applications.

Precision Patterned Thin Films without Photolithography: Additive Manufacturing of Printed Electronics

Additive manufacturing is the application of layer manufacturing techniques to fabricate microelectronic products. These techniques differentiate themselves from incumbent technologies in that they only add material to build the device and are an alternative to subtractive technologies such as lithography that globally coat layers and then etch-away unrequired materials. In this paper we discuss an additive technology that performs material evaporation through shadow masks. This process has shown significant potential for the fabrication of chip packaging, microelectronic devices and circuitry; specifically, high density interposers, fine conductor lines and embedded components such as capacitors, resistors, and transistors. The process is compatible with a number of both rigid and flexible substrates and deposition materials. Examples of devices and lines that have been manufactured by this technique are shown and discussed. Preliminary test data shows line / space resolution that has reached 5 / 20 microns and better.

Additive Manufacturing of Fine Lines and Embedded Electronics for use in Chip Carriers and Microelectronic Systems

Additive manufacturing is the application of layer manufacturing techniques to fabricate microelectronic products. These techniques differentiate themselves from incumbent technologies in that they only add material to build the device and are an alternative to subtractive technologies such as lithography that globally coat layers and then etch-away unrequired materials. In this paper we discuss an additive technology that performs material evaporation through shadow masks. This process has shown significant potential for the fabrication of chip packaging, microelectronic devices and circuitry; specifically, high density interposers, fine conductor lines and embedded components such as capacitors, resistors, and transistors. The process is compatible with a number of both rigid and flexible substrates and deposition materials. Examples of devices and lines that have been manufactured by this technique are shown and discussed. Preliminary test data shows line / space resolution that has reached 15 / 30 microns and better.

기능성 경사 복합재를 이용한 사출금형의 냉각회로 모델링

The cycle time in injection moulding greatly depends on the cooling time of the plastic part that is controlled by cooling channels. Cooling channels are required to facilitate the heat transfer rate from the die to the coolant without reducing the strength of the die. Employing layered manufacturing techniques (LMT), a die embedding conformal cooling channels can be fabricated directly while conventional cooling channels are usually made of straight drilled hole. Meanwhile, H13 tool steel is widely used as the die material because of its high thermal resistance and dimensional stability. However, H13 with a low thermal conductivity is not efficient for certain part geometries. In this context, the use of functionally graded materials (FGMs) between H13 and copper may circumvent a tradeoff between the strength and the heat transfer rate. This paper presents a method for modeling of conformal cooling channels made of FGMs.