Mechanical Behavior and Characterization of SLS Processed PA-11 for PA-11/Silica Nanocomposites

Selective laser sintering (SLS) continues to be a promising additive manufacturing process, in which three dimensional shapes are produced through laser sintering and resurfacing of a powder bed. The structural changes of a polyamide 11/carbon black (PA11/CB) powder during a UV-laser sintered printing process were analyzed to ultimately serve as a benchmark for a PA11/CB/SNP nanocomposite printed material. Samples printed with increasing laser area energy density were compared in terms of crystalinity, melt temperature, tensile behavior, essential work of fracture, density, molecular weight and amorphous chain rigidity. A molecular weight increase is found to occur in a stepwise fashion, with the tensile elongation, ultimate tensile strength, essential work of fracture and density following a similar behavior. X-ray diffraction revealed slight changes in dhkl spacing, which correlated well with slight melting peak shoulders shown in differential scanning calorimetry. Similar changes to the mobile amorphous phase were calculated suggesting partial metastable δ′ crystal phase content due to unusual solidification. PA11/CB/SNP nanocomposite powder was developed with both 50 nm and 25 nm SNP. Both solid state shear pulverization and centrifugal mixing proved successful in powder blending. Powder flow measurements at increasing temperature have shown enhanced flow behavior at processing temperatures with increasing SNP. Increases in stiffness and strength as well as decreases in linear reciprocating wear suggest good reinforcement of particle layer boundaries, however brittle behaviour of the higher SNP loaded PA11/CB/SNP parts suggest diminished sintering. Ultimately, it was concluded that colloidal silica can be utilized to greatly change both powder flow and mechanical properties of a SLS printing powder, with these studies have providing a framework for the feasibility of processing and printing nanoparticle coated polymer powders

3D Printing StarPoreⓇ for Bone Tissue Engineering

Since the advent of Tissue Engineering (TE) in the late 1980’s, significant progress has been made within the biomedical landscape. A recently established branch within TE is biofabrication, a field that aims to automate the fabrication of biologically functional materials through the use of additive manufacturing or three-dimensional (3D) printing, among other techniques. Additive manufacturing offers fine control over part porosity, with the capacity to match the complex internal architecture of human bone. Coupled with clinical 3D scanning techniques, 3D printing has the capacity to generate implants that accurately match defected areas. However, due to the limited number of regulatory approved devices for human implantation and high cost of sophisticated powder bed fusion printers, the printing techniques are restricted. To be compatible with regulatory requirements, this work aims to utilise a widely accessible and regulatory approved device, high-density polyethylene (HDPE) to generate bone substitutes. HDPE in the form of StarPore® supplied by industry collaborator Anatomics Pty Ltd, a three-pronged star or trilobal shape, is an established material approved by both the Federal Drug Administration (FDA) in the United States of America and the Therapeutic Goods Administration (TGA) in Australia as a bone substitute for human implantation

Powder Characterization for a New Selective Laser Sintering Polypropylene Material (Laser PP CP 60) after Single Print Cycle Degradation

ArticleExperiments were conducted to characterise a new polymeric powder (Laser PP CP 60) from Diamond Plastics GmbH used in selective laser sintering (SLS) additive manufacturing (AM). Three different batches of the powder were tested in the study; virgin powder, used powder, and a mixture (50% virgin: 50% used) powder. The three batches of powder were subjected to scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and melt flow index (MFI) testing. Scanning electron microscopy was used to determine the morphology of particles. The distribution of powder particle sizes was established by analysing the acquired SEM images using ImageJ software. Differential scanning calorimetry was used to determine the peak melting point, degree of crystallisation, and the sintering window of the powder. Thermogravimetric analysis was utilised to determine temperatures of degradation of the powder considered in the study. Lastly, MFI testing was used to determine the variation of flowability of the powder. It was found that the three batches of powder considered showed poor, but allowable morphology and particle size distribution. The sintering window of the virgin Laser PP CP 60 polypropylene powder increased after a single cycle of printing by 28%, from 21.04℃ (virgin powder) to 26.95℃ (used powder). The sintering window was lower than that for polyamide polymer, which might have contributed to the high shrinkage rates observed during processing of the material, as a narrow sintering window results in difficulties of regulating the cooling rate of the printed parts. The three batches of powder showed high degradation temperatures, which makes the material suitable for SLS processing. Finally, the three batches of powder showed low values of MFI, which indicates that the molten material has a high viscosity. This explains the difficulties experienced in processing the material

Degradation behaviour and reuse of selective laser sintering PA12 powders

Dissertação de mestrado integrado em Engenharia de MateriaisA Sinterização Seletiva a Laser (SLS), é uma tecnologia da família da manufatura aditiva, um ramo da engenharia que se dedica à produção de peças prontas ao uso através da construção/impressão das mesmas camada-a-camada, usando a matéria-prima em forma de pó. Esta técnica, destina-se sobretudo à impressão de materiais poliméricos, entre eles a poliamida 12 (PA12), permitindo uma grande liberdade de geometrias e boa qualidade das peças impressas, seja ela visual ou em termos de propriedades mecânicas. Após o fabrico por esta tecnologia, uma quantidade significativa de pó não é sinterizada, sendo então recolhido para reaproveitamento. No entanto existem fenómenos de degradação, especialmente térmica, limitando a sua reutilização, sendo que os fornecedores geralmente aconselham a que o número de reutilizações não ultrapasse as 12 e sempre com uma mistura de 50% de material virgem. Estes fenómenos de degradação foram estudados, através de ensaios de caracterização mecânica (testes de tração uniaxial), caracterização térmica por DSC, caracterização visual através de observação do estado das peças impressas e visualização do pó ao SEM e caracterização da porosidade por tomografia computorizada (CT). Com estes, foi concluído que, uma degradação do pó é evidente, especialmente do ponto de vista visual, afetando as características da peça impressa e comprometendo o seu correto funcionamento. O fator mais relevante notado, foi o aumento da porosidade interna das peças impressas, que para os ciclos mais avançados testados foi de tal maneira elevado que levou ao colapso das paredes da peça para o seu interior. No entanto, devido ao facto de esta tecnologia possuir um método de reciclagem bastante seletivo, os efeitos da degradação são atenuados, nomeadamente no que toca ao desempenho mecânico, que não piorou significativamente para os ciclos testados. Concluiu-se então, que a degradação do pó reutilizado em impressões por SLS tem de ser tido em conta e compreendido, mas esta tecnologia em si, mesmo quando utiliza matéria-prima virgem ou pouco reutilizada, já apresenta dificuldades em reproduzir resultados repetitivos.Selective Laser Sintering (SLS) is an additive manufacturing technology dedicated to the production of parts through a layer-by-layer printing process, using a building material in the form of powders. This technique is intended mainly for the printing of polymeric materials, such as polyamide 12 (PA12), enabling enormous geometrical freedom and good quality of printed parts, either in terms of visual aspect, or mechanical properties. In SLS, after the manufacturing process, a large quantity of the powders is not sintered, which is recovered for reuse. However, degradation phenomena are present in this unsintered powder, namely thermal degradation, which limits its reuse. Thus, the suppliers advise a maximum of 12 cycles of reuse and always with a ratio of 50% virgin material. These phenomena were studied through a series of characterization techniques, mechanical analysis (uniaxial tensile tests), thermal characterization by DSC, visual characterization of printed parts, visualization of the powders by SEM, and porosity characterization by computed tomography (CT). With these, it was concluded that it is evident both visually and performance-wise. The most relevant factor noted, was the increase in internal the porosity of the printed parts, which for the most advanced cycles tested was so extreme that forced the printed part´s walls to collapse on each other. However, due to this technology having a very selective recycling process, the effects of degradation are minimized, namely when mechanical behaviour is concerned, which did not worsen significantly for the cycles tested. It was concluded that degradation of the reused powder used in SLS printing, has to be considered and comprehended, but this technology, even when new or semi-new powder is used, already presents reproducibility and repetitiveness problems

Powder bed fusion for electromechanical plastic components in high voltage electric vehicle applications.

Over the years, Injection Molding has been the ruling process to manufacture polymeric components for the automotive industry. By this process, excellent properties and fully dense parts can be achieved. Injection Molding can be pricey if a production batch size is not big enough to justify the high costs of the molds. With the increasing demand for Electric Vehicles, the need for plastic parts with a combination of good mechanical and dielectric properties could grow significantly. When low production volumes are required, Additive Manufacturing of polymeric components can be considered as an alternative to Injection Molding. For this to happen, the behavior of parts produced by Additive Manufacturing need to be tested in order to demonstrate their mechanical capabilities and as electrical insulators within a high voltage level, at which components and devices utilized in Electric Vehicle applications are tested. In this work, tensile and electrical insulation specimens manufactured from polyamide (PA12) by Selective Laser Sintering (SLS) and HP- Multi Jet Fusion (MJF) in three build orientations were tested and compared to equivalent specimens produced by Injection Molding. For analyzing their mechanical properties, tensile tests were carried out according to the ISO-527 standard. To evaluate their efficiency as electrical insulators, voltage withstand (HIPOT) tests were performed to the specimens at a voltage level of 4kV AC and within a temperature range between 20 and 100°C. The test results obtained by the tensile experiments denoted that the parts produced by Powder Bed Fusion for these experiments presented brittle behavior at fracture, with a maximum elongation at break between 10-26%. The maximum achieved tensile strength values represented almost 74% of the ones obtained by the injection molded equivalent specimens. As electrical insulators, the HIPOT test results showed that SLS specimens with a thickness of 2mm withstood a 4kV AC voltage load comparably as the injection molded parts. The Radiation- Absorbing Material present in the HP-MJF fusing agent could be a contributor for dielectric breakdown on the tested specimens. Therefore, the applicability of the HP-MJF process is questionable for high voltage environments and within the test conditions employed

Analytical characterization of polyamide 11 and related polymers used for additive manufacturing

In order to meet the quality requirements for polymers used in additive manufacturing, especially in the laser sintering and the multi jet fusion process, as well as to guarantee high quality of printed parts, a comprehensive characterization of the intrinsic properties of the applied materials is necessary. Therefore, methods were developed and optimized to analytically investigate polyamide 11 and 12 samples both at the macromolecular and the low molecular weight range

Analysis and development of new materials for polymer laser sintering

Laser Sintering is an Additive Manufacturing technology that uses digital files to construct 3-dimensional parts by depositing and consolidating layers of powdered material. Application of the technology for metal and ceramic powders is common but the focus of this work was on polymer laser sintering. A significant drawback for polymer laser sintering is the limited selection of materials currently available for use compared with more conventional processes such as injection moulding. This constrains the usefulness of the technology for designers and engineers. A primary reason for this is a lack of detailed understanding of the development process for new materials for laser sintering. This PhD investigation examines some of the key attributes and requirements needed for successfully implementing new polymer-based laser sintering materials. A strategic method for characterizing and identifying new polymer materials was created utilizing thermal measurements, practical and analytical methods to quantify sintering rate, and degradation studies. Validation of this work occurred through the successful integration of a new laser sintering material at industrial project partner Burton Snowboards. Thermal degradation as a result of the laser sintering process was studied in detail and resulted in the creation of a proposed new parameter: Stable Sintering Region (SSR). The term acknowledges and defines the region above the melting point that is the minimum requirement for sintering to occur and an upper limit beyond which polymer deterioration impedes on mechanical properties. A quantitative approach to define the SSR was developed and explored with three different laser sintering materials, two of which were flexible elastomers. The ability to specifically interpret laser sintering process parameters from thermal degradation characterization was created and used to explore the effects of high energy input on tensile properties and molecular weight. The results of these tests showed the potential to identify an Optimum Sintering Range based on maximizing mechanical properties through the control of energy input and molecular weight. This thesis makes a significant contribution to the knowledge and understanding of polymer laser sintering, especially in the context of materials development. Novel concepts such as the Stable Sintering Region were developed using a theoretical approach and practical measurements and were also thoroughly explored for verification. Additionally, a new method to use a powder characterization technique to predict the actual machine parameters of a material in the laser sintering process was quantified. This has several implications for testing new materials for laser sintering and efficiently identifying appropriate processing conditions

Study of the selective laser sintering process : materials properties and effect of process parameters

Additive manufacturing is attractive because it allows to reduce significantly the development and industrialization phases of part design. Among the promising technologies for thermoplastic parts, the SLS (Selective Laser Sintering) process stands out because of its ability to produce geometries with low dimensional tolerances. This process is based on the displacement of a laser beam that interacts with the powder bed. The attractiveness of additive manufacturing counterbalances, however, with the choice of currently available materials: these are mainly polyamides. Polyaryletherketones (PAEK) suitable to SLS process are still rare on the market and expensive. In this work, various powders have been characterized to deeper understand the properties necessary for their use in SLS and to define their processability temperature window. The absence of suitable PEEK powder led us to develop a new material by blending PEEK with an amorphous thermoplastic, polyethersulfone (PESU). The initially immiscible blends have been compatibilized in order to improve their mechanical properties and to delay their crystallization on cooling. During manufacturing, many process parameters control the melting of the powder, and thus the properties of the parts and their dimensional accuracy. Thus, a statistical analysis of the response of the parameters was led by a design of experiments to extract the most influential parameters. The parametric study, done with the polyamide powder, was carried out by varying five parameters and by looking at their influence on five groups of responses relating to the physical, mechanical and thermal properties as well as to the printing duration of the parts. The design of experiments made it possible to establish the mathematical models of the response surfaces linking the responses to factors and their interactions. These statistical models were used to define an optimal set of parameters. Finally, a combined experimental and numerical simulation approach was conducted to estimate the influence of each laser pass on the degree of crystallinity and the mechanical properties of each layer. The results show that the heating due to the successive laser passes cover a thickness equivalent to 14 deposited layers. However, only the 4 upper layers are significantly thermally affected by the laser pass on a powder layer and thus show an evolution of their degree of crystallinit

Additive manufacturing of carbon fiber reinforced thermoplastic polymer composites

L'abstract è presente nell'allegato / the abstract is in the attachmen