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The purpose of this paper is to prepare metal/polymer composite materials prepared by additive manufacturing (AM) technology.

The effect of sintering parameters including laser power, scanning speed and slice thickness on strength and accuracy of selective laser sintering (SLS) parts were analyzed experimentally. Then, the laser sintering mechanism of nylon-12 coated copper was discussed through analyzing the interfacial reaction of nylon-12 and copper. The SLS parts were infiltrated with epoxy resin to meet the strength requirements of injection molding.

In this study, mechanical mixed nylon-12/copper and nylon-12 coated copper composite powders were investigated and compared as SLS materials. An effective dissolution–precipitation method was proposed to prepare nylon-12 coated copper powders with better processing and mechanical properties. The bending strength and modulus of fabricated parts after infiltration with epoxy reach 65.3 MPa and 3,200 MPa, respectively.

The composite materials can be used in the manufacture of injection molds with a conformal cooling channel for the production of common plastics in prototype quantities, showing a broad application prospect in rapid tooling.

The purpose of this paper is to reinforce the selective laser sintering (SLS) parts of nylon‐12 using organically modified montmorillonite (OMMT).

A dissolution‐precipitation process is developed to prepare an OMMT/nylon‐12 composite powder (3 wt% OMMT). X‐ray diffraction (XRD) was used to characterize nanostructure features. The dispersion of OMMT in the nylon‐12 matrix was observed by scanning electron microscope (SEM). The effect of OMMT on the thermal properties of nylon‐12 was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The mechanical properties of the SLS parts made from the composite powder and neat nylon‐12 powder were measured and compared.

The X‐ray diffraction and SEM results indicate that the OMMT is intercalated by nylon‐12 molecular chains and uniformly dispersed in the nylon‐12 matrix during the dissolution‐precipitation process, and thus the OMMT/nylon‐12 intercalated nanocomposites are formed. The DSC and TGA results show that the OMMT can increase the melting enthalpy, relative crystalline content, crystallization temperature and thermal stability of nylon‐12. The tensile strength, tensile modulus, flexural strength, flexural modulus and impact strength of the SLS specimens made from the composite powder are 23.2, 31.7, 18.7, 32.4 and 8.4 percent higher than those of neat nylon‐12 SLS specimens, respectively, while the elongation at break decreases by 17.5 percent.

The conclusion of forming intercalated nanocomposites was drawn from the XRD results in the present work. Further work should be done to observe the nanostructures of the materials by transmission electron microscope.

A dissolution‐precipitation process was used to prepare OMMT/nylon‐12 composite powders for SLS process. During the preparation process the OMMT could be intercalated by nylon‐12 molecular chains and uniformly dispersed in the nylon‐12 matrix, thus forming the OMMT/nylon‐12 intercalated nanocomposites. Therefore, the mechanical and thermal properties of nylon‐12 SLS parts were enhanced.

The purpose of this study was to assess the suitability of micro-computed tomography as a non-destructive method to investigate the morphology of nylon 12 parts produced by high-speed sintering (HSS). The investigation of the effect of changes in the lamp power on the properties of the fabricated parts was another purpose of this study.

Nylon 12 parts were manufactured using HSS with various lamp powers. Morphological properties of the parts were measured using micro-computed tomography. Ultimate tensile strength, elongation at break and Young’s modulus of the prepared parts were determined and compared. The effect of lamp power on the properties of the parts was then studied.

This paper proposes micro-computed tomography as a suitable technique to study the 3D structure of the parts produced by HSS. The effects of lamp power on the properties of the produced parts were also discussed.

The findings could result in an improvement in customisation of the parts for various applications through varying the lamp power. The level of lamp power could be tailored to obtain suitable part properties for a target application.

This study strengthens the fact that HSS is a promising additive manufacturing technique to produce nylon 12 parts, and the properties of the parts could be maximised using a suitable level of lamp power. The results showed that micro-computed tomography could be used as an efficient technique to investigate the morphology of the sintered parts.

This study aims to report the preparation, selective laser sintering (SLS) processing and properties of a new nylon elastomer powder. The effects of solvent, dissolution temperature and time and cooling method and speed on the particle size and morphologies of the prepared nylon elastomer powder are investigated.

The prepared nylon elastomer power possesses the particle size of around 50 mm and is spherical in shape, indicating that this study provides the feasible dissolution-precipitation process, a distillation cooling method and a suitable solvent to prepare nylon elastomer powders.

Compared to pure nylon 12, the nylon elastomer has a lower part bed temperature and a wider sintering window for the SLS process. The wider sintering window indicates the better SLS processibility. The lower part bed temperature is beneficial to the recycling of material and the decrease in the requirement of SLS equipment.

The nylon elastomer in this study has a lower part bed temperature and a wider sintering window for the SLS process. The wider sintering window indicates better SLS processibility. The lower part bed temperature is beneficial to the recycling of material and the decrease in the requirement of SLS equipment.

The purpose of this paper is to report a new method, the dissolution‐precipitation process, to prepare nylon‐coated metal powders for the indirect selective laser sintering (SLS) process.

The nylon‐12 coated carbon steel powders were prepared by the dissolution‐precipitation process. The powder characteristics are examined by scanning electron microscope (SEM) and laser diffraction particle size analysis. The effect of the applied laser energy density on the three‐point bend strength and dimensional accuracy of the SLS specimens are studied. The influence of nylon‐12 content on the bend strength are also investigated.

The SEM and laser diffraction particle size analysis results indicate that the steel particles are well coated by nylon‐12 resin. The bend strength of the SLS specimens increases with increasing the applied energy density until it reaches a maximum value, and then further increasing energy density will cause the decrease in the bend strength. The bend strength of the SLS specimens increases with increasing the nylon‐12 content over the investigated range. The dimensional errors in the X‐Y‐and Z‐directions are all increased with the increase in energy density.

This paper only concerns the preparation and SLS of the coated powders. Further investigations are planned into post‐processing, such as binder decomposition and high‐temperature sintering, of the green parts made from the coated powders.

This paper provides a useful method for preparing nylon‐coated metal powders for making metal parts by the indirect SLS process.

The purpose of this paper is to present results of an investigation, where the elastic tensor based on the engineering constants of sinterized Nylon 12 is characterized and is modeled considering a transversely isotropic behavior as a function of apparent density (relative mass density).

The ultrasound propagation velocity measurement through the material in specific directions by means of the pulse transmission method was used, relating the elastic tensor elements to the phase velocity magnitude through Christoffel's equation. In addition conventional uniaxial tensile tests were carried out to validate the used technique. Laser sintering of Nylon 12 powder (Duraform PA) has been performed at different laser energy densities, fabricating cube‐shaped coupons as well as dogbone flat coupons, using an SLS 125 former DTM machine.

Correlations for each one of the Young moduli, Shear constants and Poisson's ratios, presenting an exponential behavior as a function of the sintering degree, were generated. In addition, as the apparent density reaches a maximum value of 977 kg/m³ at an energy density of 0.032 J/mm², the material behaves in an almost isotropic form, presenting average values for the Young modulus, Shear modulus and Poisson's ratio corresponding to 2,310 MPa, 803 MPa and 0.408, respectively.

The research is limited only to one type of material within the elastic range. Validation of the Young modulus measured along one direction only is performed using a tensile test machine, due to the difficulties in evaluating Poisson's ratios and Shear moduli using conventional tests.

The results presented can be applied to virtual design and evaluating processes such as finite element analysis.

The paper incorporates detailed information regarding the complete elastic characteristics of Nylon 12, including additional measurements of the Shear moduli and Poisson's ratios not studied previously.

Additive manufacturing (AM) of thermoplastic polymers for powder bed fusion processes typically requires each layer to be fused before the next can be deposited. The purpose of this paper is to present a volumetric AM method in the form of deeply penetrating radio frequency (RF) radiation to improve the speed of the process and the mechanical properties of the polymer parts.

The focus of this study was to demonstrate the volumetric fusion of composite mixtures containing polyamide (nylon) 12 and graphite powders using RF radiation as the sole energy source to establish the feasibility of a volumetric AM process for thermoplastic polymers. Impedance spectroscopy was used to measure the dielectric properties of the mixtures as a function of increasing graphite content and identify the percolation limit. The mixtures were then tested in a parallel plate electrode chamber connected to an RF generator to measure the heating effectiveness of different graphite concentrations. During the experiments, the surface temperature of the doped mixtures was monitored.

Nylon 12 mixtures containing between 10% and 60% graphite by weight were created, and the loss tangent reached a maximum of 35%. Selective RF heating was shown through the formation of fused composite parts within the powder beds.

The feasibility of a novel volumetric AM process for thermoplastic polymers was demonstrated in this study, in which RF radiation was used to achieve fusion in graphite-doped nylon powders.

The purpose of this paper is to describe work carried out as part of a £350,000 project aimed at improving understanding of polymer sintering processes. This particular package of research was performed in order to identify the effects of different section thicknesses (and therefore different thermal conditions) in parts produced by laser sintering (LS), on the resultant mechanical properties of these parts.

Laser sintered nylon‐12 parts were produced in a range of thicknesses between 2 and 6 mm, and in three different orientations, to identify the effects of each on the tensile properties of these parts.

Results indicated that, at any of the orientations tested, the section thickness had no significant effect on any of the main tensile properties, or on the repeatability of these properties. Crucially, this is in direct contradiction with the trends identified previously in this project, whereby changes in section thickness have been shown to correlate with changes in fracture toughness.

Further work could investigate a wider range of section thicknesses or geometries, in order to continue building a more complete picture of the effects of geometry on laser sintered part properties.

These results are directly applicable to designers using, or wishing to use, LS to manufacture their products.

Whilst there is a large range of published literature on the effects of processing parameters on mechanical properties of laser sintered parts, and on the resolution and accuracy achievable with these, there is minimal information available on the effects of geometry on mechanical properties. This paper therefore represents a novel addition to the global LS knowledge base.

A prosthetic socket worn by an amputee must serve a wide variety of functions, from stationary support to the transfer of forces necessary to move. Because a subject's residual limb changes volume throughout the day, it is desirable that the socket adapt to accommodate volume changes to maintain fit and comfort. The purpose of this paper is to provide steps towards designing a transtibial nylon prothestic socket, fabricated by selective laser sintering (SLS), that automatically adapts to volumetric changes of a residual limb.

An adaptive socket design that has both rigid and compliant regions is proposed to be manufactured by SLS and actuated by inflation. To assess the feasibility of this approach, thin membrane test specimens of various thicknesses and materials were created to understand the relationship between inflation pressure and deflection for SLS manufactured plastics. Finite element analysis (FEA) was assessed as a predictive design tool and verified with the experimental inflation/deflection results.

The initial flat test specimens could only achieve deflection of 2.13 mm at 145 kPa (nylon 12) and 3.38 mm at 340 kPa (nylon 11). A curved specimen is created that met performance goals with 7.67 mm maximum deflection at 714 kPa. FEA for the flat specimens is an accurate predictor of performance, but the results of analyzing the curved specimens are an order of magnitude different from the experimental data.

The success of the physical curved specimens is encouraging for future research, but the FEA will need to be further developed before socket performance can be predicted with confidence.

A socket that does not fit the subject well will cause movement problems, rehabilitation difficulties, and potentially long‐term health issues. This research shows great potential for developing a socket that provides greater comfort and fit.

The purpose of this paper is to measure the effect of process conditions on mechanical properties of laser‐sintered nylon 12 (Duraform^®) and to determine the range of conditions that provide consistent mechanical performance for additive manufacturing.

Tensile test specimens were fabricated over a range of well‐characterized process conditions including laser power, laser speed, scan spacing, layer thickness, build orientation, and build position. Tensile modulus, yield strength, ultimate tensile strength and elongation‐at‐fracture were measured and related to process parameters.

Tensile properties are strongly related to the amount of energy deposited during scanning. Strength and modulus approach their maximum values as the energy deposited exceeds the amount needed to fully melt the applied powder. Elongation‐at‐fracture does not reach its maximum until higher energy‐melt ratio. Performance of blends with reused powder matches that of virgin powder when blend composition is adjusted to a standard melt‐flow index. The volumetric energy density and the energy‐melt ratio are useful for correlating mechanical properties with multiple process parameters and material thermal properties.

This work presents the most extensive data to date on mechanical properties of nylon 12 (Duraform^®) as they relate to the full range of process parameters. These data show that mechanical performance correlates strongly with the volume energy density. In contrast to the area energy density (a.k.a. Andrews Number), this volumetric parameter includes the effect of varying layer thickness and can be related directly to the melting characteristics of the polymer material. Within the parameter range studied, this relationship allows adjustment of one scan parameter for improved speed or dimensional accuracy while ensuring good strength by an offsetting adjustment of another parameter. Such trade‐offs will be important in future manufacturing applications of the laser sintering process. Understanding the energy‐melt ratio provides insight into the relationship between scan conditions and the physics of powder melting and sintering, and offers a methodology to relate results at other bed temperatures and with other polymer powders.