Search

Manufacturing industries have taken a leap with the coming of polymer composites and have been much broadly explored in this era. Composites with ceramic reinforcements to polymer matrices have proven potentially efficient in improving mechanical properties. This work explores the idea in implementing PLA-silicon nitride composites in manufacturing through conventional injection molding and modern 3D printing techniques. The study points to the better strength enhancement of tensile, flexural and impact test results in composites in the lower additive weight ratio of 95:05, substantiated by a detailed mechanical and morphological analysis of specimens in three different weight ratios. The specimens printed by 3D printing show a negligible variation in the strength parameters when compared to the injection-molded counterparts, which in effect extends the scope of further research in the area.

The Robinson Research Institute at Victoria University Wellington is building a series of superconducting motors over the next six years to demonstrate technology pathways for the transport industry, including aviation. Our target topology for these machines uses rotor-mounted superconducting field coils and a superconducting stator in an air-core configuration. To avoid eddy current heating in the stator cryostat, electrically conductive materials must be eliminated. At the same time, heat generated due to AC losses in the stator must be transferred efficiently and evenly from the superconductor to the cryo-coolant, in order to avoid localised film boiling. And finally, the coil structural support needs to closely match the thermal expansion characteristics of the superconductor wires and likely other G10 structural pieces to avoid debilitating stresses and lost support.In this study, we investigated the opportunity to use additively manufactured (AM) polymers with a range of filler materials as the structural support for a motor coil. A range of commercially available candidate materials have been identified and test coupons manufactured using either Selective Laser Sintering (SLS) or Fused Deposition Modelling (FDM). The material properties of the test coupons have been measured from room temperature down to cryogenic temperatures. This data was used to design, analyse and manufacture the support structure for a stator saddle-coil, and the coil wound with aluminium wire to simulate Conductor on Round Core (CORC) cable. Initial thermal cycle testing has been carried out to assess the performance of the composite.

Duplex stainless steels come under the difficult-to-machine category, considering the loss of the sensitive balance between the constituent phases due to thermal and mechanical working effects. Selective laser melting is emerging as an additive process for achieving near-net shape manufacturing solutions with these steels. Nevertheless, post-printing machining is essential to varying degrees and the machinability responses of the laser melted duplex stainless steels need sufficient attention. This paper addresses this gap, considering the experimental evaluation of the mechanics of machining with laser melted duplex stainless steels. Specimens printed with the most promising laser melting process conditions are evaluated for machinability, comparing with the wrought counterparts and also ascertaining the differential responses between the as-built and solution annealed states. Cutting forces and thermal measurements confirm better machinability with the laser melted samples which is an interesting finding considering the possibility of laser melting, machining, and post-process heat treatment as the best possible sequence of processing duplex stainless steels to circumvent the difficulties in machining.

Fused deposition modelling is the most popular method of 3D printing with a variety of polymers, but the raw materials are commonly in the filament form. Research has demonstrated the ability to use pellets for this process, which are easier to produce than filaments. Apart from the savings on the pre-processing, the approach also combines the good attributes of both injection moulding and 3D printing and referred to as extrusion 3D printing. Direct printing of pellets is especially suited for thermosensitive polymers, with which, repeated or excessive heating may lead to degeneration. Also, polymers that are too soft do not qualify for filament-based extrusion. PLA is a popular choice for fused deposition modelling in the filament form but is often too brittle. A softer version of PLA composite based on PBAT and cellulose fibres is proposed here for 3D printing. Considering the lack of stiffness of the filaments, direct extrusion from pellet form is evaluated. Regardless of form, the polymer material system satisfied the stringent conditions of consolidation as dictated by the dynamic combination of extrusion and rasterised material deposition. Experimental evaluation based on meso-structural and mechanical property analyses indicate the new pellet-based material system to be suitable and to perform well. The novelty of the material and process combination is that the printed samples were actually comparable mechanically to the injection moulded counterparts, which is an extraordinary achievement, considering the shortcomings typical of material consolidation in additive manufacturing.

Abstract

Additive manufacturing (AM) has made long strides in the recent past and rapidly evolved into a promising alternative in specific applications. The aircraft industry is not an exception to this. The true just-intime production possibility is critical for the aircraft maintenance industries, though the lack of material freedom is a major hurdle. Several fire-retardant materials were investigated for AM in the aerospace context, but mainly for fused deposition modeling (FDM). The material consolidation constraints in FDM led to the expansion to the use of selective laser sintering (SLS) to some extent. Nevertheless, the material options are still limited, proprietary, and lack scientific insights into the material consolidation mechanics. Attempts are made in this paper to fill this gap, evaluating a new fire-retardant material for processing by SLS. Experiments conducted to ascertain the material, process, structure, and consolidation relationships indicated energy density levels 0.062–0.070 J/mm2with laser power 13 W and scan speed varied slightly around 390 mm/s to give the best laser sintering and mechanical property results in polyetherimide powders.

Complex thermal histories in samples made by selective laser melting (SLM) lead to residual stress development, affecting the quality of the final product. SLM process parameters influence the melt temperature and the geometrical features of the molten pool. To investigate the effects of laser power and scan speed on transient temperature and residual stress evolutions and distributions during SLM process, a 3D finite element model has been established. Simulation results have shown that either increasing the laser power or reducing the scan speed causes a higher level of residual stress at the end of a scan track. To validate the simulation results, Ti–6Al–4V samples were made by SLM with varying process parameters and the sizes of melt pools on the top layer as well as the interlayer cracks and lack of fusions defects observed in the samples correlated well with the results from the finite element simulations.

Metal matrix composites are formed by adding certain filler particles to selected base metals to combine the good properties of both in the resulting composite and were proved to be quite promising in numerous applications. The main bottleneck lies in the processing methods, as the traditional solutions often lead to a loss of control on the dispersion of the filler material. The point-by-point consolidation mechanisms typical of additive manufacturing are proposed here as a possible means of enhancing this control over the composition of the metal matrix composites. Selective laser-melted composites with stainless steel 316L as the base metal and Si3N4as the filler phase are evaluated in the current study. The results clearly indicated that the dispersion of the filler particles is more controlled, as they are pushed and segregated around the solid front boundaries. The tensile strength of the composites is better than the pure 316L when laser-melted under appropriate process conditions. The surface quality is also substantially enhanced with the metal matrix composites.

Abstract

PMMA/β-TCP composites were evaluated to be suitable for laser sintering earlier, but the possible after effects are not known yet. Effects of sintering on the biological nature and the influences of critical compositions and process parameters have not been investigated so far. The current research attempts this, first identifying experimentally the most suitable laser process conditions for the specific grades of PMMA and β-TCP and then subjecting single layer sintered samples to FTIR analysis and in vitro studies involving MTT and ALP assays, alizarin red S tests, and real-time PCR analyses. While the laser interactions are not detrimental, the biological responses are generally positive proving the selective laser sintering of PMMA/β-TCP composites to be a potential approach for specific medical applications.

Fused deposition modelling is one of the additive manufacturing techniques in which part quality is often influenced by stair-step effects and internal meso-structures. Adaptive slicing employing slices of varying thicknesses was attempted as a means of overcoming some of these problems, but with limited success, while speed and time of printing often lead to further complications. On the other hand, curved layer deposition is proved to improve surface quality and part strength in specific cases. This research brings both flat and curved layer approaches together through specific algorithms developed and employed combining the two to process given parts. The mixed slicing method is applied successfully to three test cases, practically implemented on a test bed, and proved to be feasible and effective.

Polymethylmethacrylate (PMMA) is a synthetic resin, widely used for bio-medical applications and is usually mixed with some other ingredients to form a soft substrate, which gradually hardens. Medical implants and other products of different shapes are generated either by moulding while it is still soft or by machining further to hardening. While these methods limit the freedom to achieve the much needed geometrical complexities, porosity also gets adversely affected. Rapid prototyping or additive manufacturing techniques allow for complex shapes to be easily produced together with a degree of control over the porosity. Though fused deposition modelling was attempted earlier with PMMA, more promising approaches such as selective laser sintering attained very little attention in this regard. In particular, the mechanism of material consolidation and the effects of significant process parameters on critical responses need sufficient attention, and this paper attempts this by experimental means.

Abstract

Fused deposition modeling involves line-by-line and layer-by-layer deposition of a semisolid polymer, and the material consolidation mechanisms eventually result in a composite of the polymer substrate with interspersed inter-road voids. Considering the potential capability of the process for direct digital production of end-use parts with materials of engineering significance, methods such as adaptive slicing were attempted targeting better part qualities together with improved production times. While adaptive slicing was attributed with several useful qualities, a careful consideration reveals that most of these attempts were mere mathematical approaches, with very little or no theoretical and experimental evaluation of the actual effects. Theoretical models predicting the mechanism of inter-road bonding through solid-state sintering existed for a while, and with the advent of advances made in understanding the inter-road coalescence and mechanism of material consolidation, it is necessary to revisit adaptive slicing and establish the true attributes. This article attempts this through mathematical and experimental evaluation, considering in particular, the time- and speed-dependent variation of the inter-road coalescence.

Fused Deposition Modeling (FDM) is one of the most popular Rapid Prototyping (RP) techniques. Initially used as means of producing 3D prototypes aiding in rapid product development, FDM found a significant application in medical models and with machine and material improvements is currently destined to be a true manufacturing process, challenging some of the traditional approaches. The material characteristics and part qualities however, are inferior, considering the heterogeneous structures characterized by the air gaps resulting from raster orientations. Current research is focused on improving the mesostructure through appropriate deposition schemes, adaptive slicing being one of the approaches. This paper reviews some of the adaptive slicing schemes and discusses software and hardware developments undertaken for the practical implementation of one of the schemes for producing test parts.

This paper describes a curved-layer additive manufacturing technology that has the potential to print plastic components with integral conductive polymer electronic circuits. Researchers at AUT University in New Zealand and the National University of Singapore have developed a novel Fused Deposition Modeling (FDM) process in which the layers of material that make up the part are deposited as curved layers instead of the conventional flat layers. This technology opens up possibilities of building curved plastic parts that have conductive electronic tracks and components printed as an integral part of the plastic component, thereby eliminating printed circuit boards and wiring. It is not possible to do this with existing flat-layer additive manufacturing technologies as the continuity of a circuit could be interrupted between the layers. With curved-layer fused deposition modeling (CLFDM) this problem is removed as continuous filaments in 3 dimensions can be produced, allowing for continuous conductive circuits.

This paper describes an additive manufacturing technology that has the potential to print plastic components with integral conductive polymer electronic circuits. This could have a major impact in the fields of robotics and mechatronics as it has the potential to allow large wiring looms, often an issue with complex robotic systems, to be printed as an integral part of the products plastic shell. This paper describes the development of a novel Fused Deposition Modeling (FDM) process in which the layers of material that make up the part are deposited as curved layers instead of the conventional flat layers. This opens up possibilities of building curved plastic parts that have conductive electronic tracks and components printed as an integral part of the plastic component, thereby eliminating printed circuit boards and wiring. It is not possible to do this with existing flatlayer additive manufacturing technologies as the continuity of a circuit could be interrupted between the layers. With curved-layer fused deposition modeling (CLFDM) this problem is removed as continuous filaments in 3 dimensions can be produced, allowing for continuous conductive circuits.

As several of the free form fabrication processes progress with continuous process and material improvements, the feasibility of Rapid Manufacturing becomes more and more of a reality. Defined as the use of a Computer Aided Design (CAD) based automated additive manufacturing process to construct parts that are used directly as finished products and components, some of the rapid manufacturing processes are already competing with traditional processes such as injection moulding and progress is being made in applying the new technologies to the processing of metals, envisioning additive manufacture of high strength parts of unlimited complexity. While there have been quite a few successful attempts in the rapid production of complex medical implants using titanium alloys, 3D printing of sand moulds opens up yet another rapid manufacturing front, allowing for the rapid casting of aluminium and magnesium alloys. The effectiveness of such processes is yet to be researched in terms of process and product characteristics and the overall economy. This paper attempts to review some of the promising rapid manufacturing technologies for light metals processing and presents results of experimental investigations conducted to evaluate the effectiveness of the rapid casting process currently researched at the Rapid Product Development Centre of AUT University.

This research aims to identify how meltpool temperature is determined by process parameters in Laser-Based Powder Bed Fusion (LB-PBF) and the effect of meltpool temperature and heat treatment temperature on microstructure and tensile properties. The study illustrates how crystallographic features in 316L stainless steel were developed in response to the meltpool temperature and induced energy density of LB-PBF manufacture, and by post manufacture heat treatment. For this research, 25 samples based on a Taguchi Design of Experiments (DoE) with five parameters over five levels were printed. To improve precision, the DoE was repeated three times and a total of 75 samples were produced. A thermophysical-based analytical model was developed to measure the meltpool temperature and subsequently surface tension of the liquid in melting zones. Then, a statistical method was used to identify the effective process parameters in tensile properties including ultimate strength, fracture strain and toughness. The microstructural evaluation and crystallographic features were presented to identify the governing mechanisms for the discussed phenomena. This result verify that the meltpool temperature is a driving factor for the microstructural evolution and observed crystalographic features. Results showed that samples with lower meltpool temperatures have smaller grain sizes, superior strength and toughness properties. The crystallographic analysis showed the weak texture and anisotropic properties are dominant by the preferred orientation growth. The geometrically necessary boundary values were also found to be a driving factor for fracture strain. The originality of this paper is identifying the effect of process parameters on meltpool temperature using an analytical model that is developed based on the thermophysical properties of the feedstock. Characterizing the effect of meltpool temperature in crystallographic features are also another contribution of this paper.