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The main objective of this paper is to analyse all stages of the CastForm™ polystyrene (CF) pattern fabrication process, identify the reasons leading to inferior quality, and outline techniques for its improvement and reduction of failures.

This paper describes rapid manufacturing of patterns for shell or flask investment casting using the laser sintering (LS) technique with CF material. The process involves data preparation, LS fabrication of a “green” part, cleaning, and wax infiltration. All process stages are equally important for successful project completion in terms of pattern quality and delivery time. A failure at any stage requires a part or pattern to be produced again, which would incur additional time and cost.

The conducted experiments show how the CF material strength varies at different process stages and temperatures. Cleaning and wax infiltration are considered the main reasons for part distortion and breakage.

The paper proposes a new approach for wax infiltration. Deformation and breaking of unsupported features could be reduced or eliminated by introducing a supporting structure under these features.

Owing to the operating principle of powder bed fusion processes, selective laser sintering (SLS) requires effective management of the mixture ratio of processed material previously exposed to the high temperatures of processing with new virgin material. Therefore, this paper aims to fully understand the effect that the successive reprocessing has in the powder material and to evaluate its influence on the properties of SLS parts produced at different building orientations.

Polyamide 12 material with 0%, 30% and 50% of virgin powder and parts produced from them were studied through five consecutive building cycles and their mass, mechanical, thermal and microstructural properties were evaluated. Then, the experimental data was used to validate a theoretical algorithm of prediction capable to define the minimum amount of virgin powder to be added on the processed material to produce parts without significant loss of properties.

Material degradation during SLS influences the mass and mechanical properties of the parts, exhibiting an exponential decay property loss until 50% of the initial values. The theoretical algorithms of reprocessing proved the appropriateness to use a mixture of 30% of virgin with 70% of processed material for the most common purposes.

This paper validates a methodology to define the minimum amount of virgin material capable to fulfil the operational specifications of SLS parts as a function of the number of building cycles, depending on the requirements of the final application.

The use of theoretical models of prediction allows to describe the degradation effects of SLS materials during the sintering, ensuring the sustainable management of the processed powder and the economic viability of the process.

The purpose of this paper is to evaluate the energy consumed to fabricate nylon parts using selective laser sintering (SLS) and to compare it with the energy consumed for injection molding (IM) the same parts.

Estimates of energy consumption include the energy consumed for nylon material refinement, adjusted for SLS and IM process yields. Estimates also include the energy consumed by the SLS and IM equipment for part fabrication and the energy consumed to machine the injection mold and refine the metal feedstock required to fabricate it. A representative part is used to size the injection mold and to quantify throughput for the SLS machine per build.

Although SLS uses significantly more energy than IM during part fabrication, this energy consumption is partially offset by the energy consumption associated with production of the injection mold. As a result, the energy consumed per part for IM decreases with the number of parts fabricated while the energy consumed per part for SLS remains relatively constant as long as builds are packed efficiently. The crossover production volume, at which IM and SLS consume equivalent amounts of energy per part, ranges from 50 to 300 representative parts, depending on the choice of mold plate material.

The research is limited to material refinement and part fabrication and does not consider other aspects of the life cycle, such as waste disposal, distributed 2 manufacturing, transportation, recycling or use. Also, the crossover volumes are specific to the representative part and are expected to vary with part geometry.

The results of this comparative study of SLS and IM energy consumption indicate that manufacturers can save energy using SLS for parts with small production volumes. The comparatively large amounts of nylon material waste and energy consumption during fabrication make it inefficient, from an energy perspective, to use SLS for higher production volumes. The crossover production volume depends on the geometry of the part and the choice of material for the mold.

A key characteristic of powder bed fusion for polymers is that also the non-processed powder in the powder bed is exposed to elevated temperatures. This alters the properties of the remaining powder, which is compensated by refreshing the used powder with new powder. Nonetheless, it is discarded after a certain number of process iterations, which is economically and ecologically highly disadvantageous. Research works intensively to analyse and reduce the concurring effects responsible for powder ageing. This study aims to give a comprehensive overview of the cumulative changes in the powder and the printed parts when conducting several subsequent build cycles.

New polyamide powder (PA12) was used in a total of nine subsequent build cycles with constant sintering parameters and without powder refreshing. After each iteration, the powder and parts were tested for their morphological, thermal and rheological properties.

The results are related to three main changes in the powder during the build cycles: decreasing bulk density (through agglomeration), increasing melt viscosity (through polyamide post-condensation) and increasing melting peak and onset temperatures (through thermal annealing of the powder).

Even though the ageing of PA12 powder in powder bed fusion is well-known, it is not yet fully understood. Studies are not complete and due to different ageing conditions only partially comparable. The detailed study aims to help understand the related effects of powder ageing for process-relevant properties and to show which factors require control to limit the powder ageing.

The selective laser sintering (SLS) process is one of the leading rapid prototyping techniques. This paper presents two rapid tooling (RT) methods based on the SLS process. The first method employs the SLS process to build tooling inserts in copper polyamide that can be used for fabrication of a limited number of pre‐production parts in the same material and manufacturing process as the final production parts. The second method, the RapidTool^TM process, is a RT solution for manufacture of pre‐production and production tools for injection moulding and die‐casting. The paper also discusses the applications and limitations of these RT methods.

Additive manufacturing is today a viable industrial solution alongside traditional processes. Techniques like selective laser sintering (SLS) address the issues of digital production and mass customization in a variety of materials. Composite parts can be obtained with specific functional and mechanical properties. Building orientation during additive manufacturing often causes anisotropy of parts' properties that is still unspecified in technical information. The purpose of this paper is to investigate the mechanical performances and failure mechanisms of an aluminium‐filled polyamide and of a new alumina‐polyamide composite produced by SLS, in comparison with unfilled PA.

A specific focus is set on the evaluation of primary and secondary anisotropy in the case of metal or ceramic filler, as well as on the specific contribution of powder distribution modes and joining phenomena. Macroscopic mechanical tests and the observation of joining and failure micro‐mechanisms are integrated.

The results prove the absence of relevant anisotropy amongst specimens that are produced with the axis parallel to the plane of powder deposition. Samples whose axis is parallel to the growth direction Z, instead, reveal a significantly different response with respect to other orientations.

An original explanatory model is assumed and validated, based on an anisotropic distribution of the reinforcing particles during parts' production, which determines the efficacy of the strengthening mechanisms during crack propagation.

The purpose of this paper is to discuss the opportunities and challenges of mass customisation (MC), together with the possibilities for enablement using the technologies of rapid manufacturing (RM).

A thorough evaluation of numerous approaches to RM of customised products is presented, with particular focus on relative advantages and limitations of each technology. To demonstrate the applicability of specific techniques, case studies from both consumer and medical applications are reported based on original research.

The paper highlights not only the opportunities for RM technologies, but also the limitations of specific processes. This approach provides guidance for practitioners in the selection of appropriate technologies for MC enablement.

The focus of this practitioner review is limited to proprietary RM materials and systems which are already commercially available, with relatively little attention given the technologies presently in development.

Whilst RM and MC have already received much attention in the literature, comparatively little consideration has been given to the unification of both concepts. This paper has particular emphasis on this unification with respect to the selection of appropriate technologies, and presents an appraisal of existing applications making use of RM. Through this approach, practitioners gain information in the selection of appropriate technologies for MC.

Polymer laser powder bed fusion (PBF-LB/P) is an additive manufacturing technology that is sustainable due to the possibility of recycling the powder multiple times and allowing the fabrication of gears without the aid of support structures and subsequent assembly. However, there are constraints in the process that negatively affect its adoption compared to other additive technologies such as material extrusion to produce gears. This study aims to demonstrate that it is possible to overcome the problems due to the physics of the process to produce accurate mechanism.

Technological aspects such as orientation, wheel-shaft thicknesses and degree of powder recycling were examined. Furthermore, the evolving tooth profile was considered as a design parameter to provide a manufacturability map of gear-based mechanisms.

Results show that there are some differences in the functioning of the gear depending on the type of powder used, 100% virgin or 50% virgin and 50% recycled for five cycles. The application of a groove on a gear produced with 100% virgin powder allows the mechanism to be easily unlocked regardless of the orientation and wheel-shaft thicknesses. The application of a specific evolutionary profile independent of the diameter of the reference circle on vertically oriented gears guarantees rotation continuity while preserving the functionality of the assembled mechanism.

In the literature, there are various studies on material aging and reuse in the PBF-LB/P process, mainly focused on the powder deterioration mechanism, powder fluidity, microstructure and mechanical properties of the parts and process parameters. This study, instead, was focused on the functioning of gears, which represent one of the applications in which this technology can have great success, by analyzing the two main effects that can compromise it: recycled powder and vertical orientation during construction.

This study aims to propose the reuse of PA12 (powder) in another AM process, binder jettiinng, which is less sensitive to the chemical and mechanical degradation of the powder after multiple cycles in the laser system.

The experimental process for evaluating the reuse of SLS powders in a subsequent binder jetting process consists of four phases: powder characterization, bonding analysis, mixture testing and mixture characteristics. Analyses were carried out using techniques such as Fourier Transform Infrared Spectroscopy, scanning electron microscopy, thermogravimetric analysis and stress–strain tests for tension and compression. The surface roughness, color, hardness and density of the new mixture were also determined to find physical characteristics. A Taguchi design L8 was used to search for a mixture with the best mechanical strength.

The results indicated that the integration of waste powder PA12 with calcium sulfate hemihydrate (CSH) generates appropriate particle distribution with rounded particles of PA12 that improve powder flowability. The micropores observed with less than 60 µm, facilitated binder and infiltrant penetration on 3D parts. The 60/40 (CSH-PA12) mixture with epoxy resin postprocessing was found to be the best-bonded mixture in mechanical testing, rugosity and hardness results. The new CSH-PA12 mixture resulted lighter and stronger than the CSH powder commonly used in binder jetting technology.

This study adds value to the polymer powder bed fusion process by using its waste in a circular process. The novel reuse of PA12 waste in an established process was achieved in an accessible and economical manner.

Orange peel formation remains to be understood clearly because it is difficult to directly observe a laser-sintered process in a partcake. Therefore, this study aims to provide insight into the orange peel formation mechanism through the nondestructive observation of laser-sintered specimens and their surrounding powders.

This study observed polyamide 12 powder in the vicinity of a laser-sintered specimen via X-ray computed tomography (CT) scanning. The specimen for nondestructive observation was 3D modeled in a hollow box using 3D CAD software. The boxes built using a laser-sintering system contained unsintered surrounding powder and sintered specimens. The box contents were preserved even after the boxes were removed from the partcake. After X-ray CT scanning, the authors broke the boxes and evaluated the unevenness formed on the specimen surface (i.e. the orange peel evaluation).

Voids (not those in sintered parts) generated in the powder in the vicinity of the specimen triggered the orange peel formation. Voids were less likely to form in the build with a 178.5° powder bed than in the build with a 173.5° powder bed. Similarly, the increment in laser energy density effectively suppressed void formation, although there was a tradeoff with overmelting. Thin-walled parts avoided void growth and made the orange peel less noticeable.

To the best of the authors’ knowledge, this study is the first to observe and understand the relationship between voids generated in the powder in the vicinity of sintered parts and orange peel formation.