Flexural Modulus of Lasersintered PA 2200

Processing and characterization of a carbon black-filled electrically conductive Nylon-12 nanocomposite produced by selective laser sintering

Objectives: To compare two of the most popular rapid prototyping processes of Stereolithography (SLA) and Selective Laser Sintering (SLS) from a product-based perspective, to help customers analyze them and make a choice between the two. Methods: This paper includes the qualitative testing of identical specimens created by SLA and SLS. The specimens are evaluated on the parameters of dimensional accuracy, tensile strength, water absorption, surface roughness, density, Vickers hardness and microscopic defect structure. The outcome of this study aims at helping people to understand SLS and SLA better in terms of the products they create so that it becomes easier for users to make a choice between the two. It also aims at highlighting the above mentioned statistical information about SLA and SLS so that they may be improvised and enhanced in the future. Findings: Based on the tests conducted, it was confirmed that the SLA specimens were better than the SLS specimens in the tensile strength, water absorption, surface roughness and density tests. The SLS specimens outperformed the SLA specimens in the dimensional accuracy and Vickers hardness tests. Thus it was concluded that the SLA specimens exhibited better mechanical and physical characteristics than the SLS specimens.

Introduction: Nowadays the additive manufacturing technologies become more and more popular as they suggest good reproducibly and fast production process. One of the most generally used approach is a fabrication of a pattern, that is later replaced by casting. Modern concept usually utilizes materialized CAD models, that are milled by CAM or 3D printed and later those patterns are invested and casted. It is important for practice to be clarified whether this production method is competitive to the rapid manufacturing and subtractive fabrication methods. Materials and Methods: A STL-file with bar framework retained by four implants is used for fabrication of four group of objects. Each group of frameworks is fabricated by different technology as follows: Direct Metal Laser Sintering, Milling and hybrid technology with different investment materials (WiroFine? and Bellavest? SH). All the implant analogs are fixe into a stone plate, scanned and imported in Dental Designer, 3Shape? software. Once the frameworks are ready, they are used as a matrix for attachment and repositioning of the implant abutments according to their configuration. Then the analogs are fixed into the same stone base, which is scanned, as its image is merged to the one before the realignment procedure. The discrepancies are observed. Results: The most accurate reproduction is achieved by DMLS technology, followed milled framework. The hybrid technology shows less accuracy than contemporary methods. Therefore by using an investment material with higher expansion coefficient its accuracy is improved and makes it an alternative method to rest which are observed. Conclusion: Nowadays these contemporary technologies still remain expensive. At the same time the suggested modification of conventional casting process allows better accuracy to be achieved at lower price.

In recent days, the additive manufacturing process plays a vital role in the production of tool electrodes, which are used in the electrical discharge machining (EDM) process. In this work, the copper (Cu) electrodes prepared using the direct metal laser sintering (DMLS) process are used for the EDM process. The performance of the DMLS Cu electrode is studied by machining the AA4032-TiC composite material using the EDM process. Then the performance of the DMLS Cu electrode is compared with the conventional Cu electrode. Three input parameters, such as peak current (A), pulse on time (s), and gap voltage (v), are selected for the EDM process. The performance measures, which are determined during the EDM process, are material removal rate (MRR), tool wear rate, surface roughness (SR), microstructural analysis of machined surface, and residual stress. At a higher pulse on time, more material was removed from the workpiece surface and thus MRR is enhanced. Likewise, at a higher peak current, the SR is amplified and thus wider craters are formed on the machined surface. The residual stress on the machined surface has influenced the formation of craters, microvoids, and globules. Lower SR and residual stress are attained by using DMLS Cu electrode, whereas MRR is higher when using conventional Cu electrode.

Today’s challenges in Architecture and Engineering arise from ever more complex networks of boundary conditions, which often address contradicting environmental, social and economic aspects. Within this context, finding a single best solution for a construction type or planning method to solve these challenges, is often not possible. In pursuit of efficient solutions for both digital modelling and actual construction, we are discovering new hybrids as forerunners of our creative profession. In this context, we are also discovering new fields of application for textile architecture for both products and planning techniques beyond their classic application for membrane structures. The current paper on ‘new hybrids’ will address this potential and show new fields of application, where knowledge from textile architecture is the starting point for developing new design and construction methods, using traditional building materials. The current paper reviews some recent developments of design and construction principals in textile architecture and gives an outlook, towards how these can be transferred, onto the development of a new filament-based timber material.

Metal‐based powder systems for selective laser sintering applications provide flexibility in the part geometry and promise a high quality profile regarding their material technologies characteristic. In this field of application, materials have to fulfil high demands on their properties already in the conceptual phase of development. For the integration of selective laser sintered parts into the development process, determining their properties using material engineering methods is absolutely essential. This paper concerns with the methods of material analysis, the particular material properties of sintered metals and finally with the description of the properties of the powder systems EOS DirectSteel 20 and 3D Laser Form ST100 in comparison to conventional materials used in automotive engines and power trains.

Rapid prototyping is an effective way to build prototypes. This process, now called AM (Additive Manufacturing), is suited to realize functional single part or for small batch production. Evolution of AM is now in the way of serial production. In the field of medical applications and more precisely dentistry, AM is a way of increasing numbers of elements produced compared to classic production by lost wax casting. To increase production quality, it is necessary to have a high monitoring and control of process and properties of production. In the case of AM using (DMLS: Direct Metal Laser Sintering), a lot of parameters can have an influence on the elements production quality such as powders quality, laser behavior or sintering time… The goal of this work is to study the serial production quality using a DMLS system (Phenix System PM100). This system is used in production of cobalt-chromium elements for dental applications. The study was done on a period of 6 months with recording results of almost 120 productions and was focused on a quantity of around 7000 dental elements produced. In a first part, number of elements per production, room temperature and hygrometry, powder reloading, maintenance, production stops and new operators are recorded. Material properties of some elements produced such as dimensional properties, density, porosity and crystallographic phases are monitored. Materials analysis has led to ensure the elements quality produced by the Phenix system and results are discussed in this work. In a second part, we focused on the production analysis with the recorded data. Analysis leads to define 2 ratios: production ratio RP defined as [Elements Number]/ [Productions Number] and the efficiency production PE defined as the ratio RP/[Stopped production number]. By calculating RP and PE values with collected data on the Phenix system, a PM 100 efficiency production modeling has been established. The PM 100 production modeling can help to understand that increasing the production ratio RP value leads to have efficiency production PE high variation. On another hand, collecting production parameters leads to increase production efficiency.

Direct metal laser sintering is an additive manufacturing process which is capable of fabricating three-dimensional components using a laser energy source and metal powder particles. Despite the numerous benefits offered by this technology, the process maturity is low with respect to traditional subtractive manufacturing methods. Relationships between key processing parameters and final part properties are generally lacking and require further development. In this study, residual stresses were evaluated as a function of key process variables. The variables evaluated included laser scan strategy and build plate preheat temperature. Residual stresses were measured experimentally via neutron diffraction and computationally via finite element analysis. Good agreement was shown between the experimental and computational results. Results showed variations in the residual stress profile as a function of laser scan strategy. Compressive stresses were dominant along the build height (z) direction, and tensile stresses were dominant in the x and y directions. Build plate preheating was shown to be an effective method for alleviating residual stress due to the reduction in thermal gradient.

Rapid prototyping and design advancements in aviation gas turbine engine components are being made possible through the laser-fusion powder-bed additive manufacturing processes. However, with improvements in design, a comprehensive understanding of the fatigue performance of these components under realistic stress states characteristic of their in-service conditions is critical in ensuring their durability. Inconel 718 (IN718) is commonly employed as the substrate material for gas turbine engine components, and has been reported to yield improved axial mechanical properties when developed through the direct metal laser sintering (DMLS) process. However, the torsional fatigue properties of heat-treated Inconel 718 is yet unexplored. Given the nature of gas turbine engine components to endure multiaxial stresses (axial and torsional), this study is novel in that it reports the torsional fatigue properties of heat-treated DMLS Inconel 718. Completely reversed torsional fatigue tests under angle of twist control are performed on specimens manufactured along the horizontal, diagonal and vertical build orientations, providing the first set of torsional fatigue properties of additively manufactured heat-treated Inconel 718, contributing to a critical understanding of the performance of these components under cyclic shear.

Direct metal laser sintering (DMLS) is an additive manufacturing process that uses 3D CAD data as a digital information source and a high-power laser beam which create three-dimensional metal parts by fusing fine metallic powder. DMLS was developed by the EOS firm of Munich, Germany. In this study, alloy 718 was built up by ytterbium fiber laser by fusing pre-alloyed powder in argon gas. Tensile specimens were cut from the buildup cubic. The specimens were cut along two orientations. One (0°-specimen) was cut along the building direction, another (90°-specimen) was cut perpendicular to the direction. As-deposited specimen and STA (Solution heat treatment and aged) specimen were prepared. We observed the dendrite and the coarse columnar grains which grew up along the building direction. STA improved the proof and tensile strengths at ambient temperature. Tensile properties of buildup material were comparable with conventional materials. At the ambient temperature, the buildup material showed isotropic tensile properties; however, at 650℃, 90°-specimen exhibited half ductility compared to the 0°-specimen.

Additive Manufacturing (AM) has recently attracted huge attentions as a technology for the next generation of industry. Particularly for the manufacturing purposes, various aspects of AM are being studied and applied, such as prototypes for assembly tests, jig production, and actual parts manufacturing. Selective Laser Sintering (SLS) using polyamide is easy to apply to various industries, such as its superior mechanical properties and higher design freedom, but design that takes into account variation in dimensions after manufacture often leads to costly and time-consuming problems. As a way to reduce deformation in the production process, previous studies approached experimentally about the effects of thermal deformation or residual stress on deformation. This is difficult to apply to a specimen of various shapes and sizes and also has limitations as a common solution to dimensional inaccuracies. To propose a solution for mitigating shape deformation of AM part, this paper focused on the effect of phase change of material among various processing parameters that cause shape deformation and tries to present an analytic model. Modeling on the melting and sintering phenomena of powder was presented using Euler-Bernui beam equation. The proposed model was verified by measuring the density variation of manufactured AM components and analyzing the correlation between the degree of contraction and the energy density. Factors such as layer thickness, part thickness, and part placement height were identified to have significant effects on the actual deformation. It is also confirmed that dimensional accuracy of parts that show large deformation by bending has increased by 64.2% when a calibration model is applied through manufacturing of actual parts. Time and cost can be saved for industrial application of AM by applying this proposed calibration model. In addition, by using this model more efficiently in the CAD design process, dimensional accuracy can be enhanced.

Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) are parent Additive Manufacturing processes using a laser to solidify metallic, ceramic, polymer or composite powders. During the process, the object is built layer by layer. A laser source is responsible for the consolidation, by local heating. The light is deviated by a scanning head according to the instructions of an STL file. Then partial fusion of the particles takes place, followed by a solidification of the liquid created. Kinetics of these steps are very high and play an important role in the final microstructure (rearrangement of the particles, pore creation, residual stresses). In the case of polymers and composites the technique is now well understood and widely used, but for metals and ceramics it suffers from a lack of precision, surface roughness and poor mechanical properties. The goal of this Ph.D. work is to understand the effect of the thermal gradients on the consolidation process, using different laser parameters (power, pulse frequency, scan speed,…). In SLS, microscopic thermal gradients arise, due to the fact that the laser is pulsed and that only the exterior of the powder particles is molten. A thermal model to describe the interaction between a laser beam and a (spherical) grain is proposed. This model allows for the incorporation of the latent heat of fusion and for a realistic surrounding. The absorbed laser intensity is modeled by means of the Mie theory. Experiments where two particles of powder are isolated and illuminated by the laser are carried out in order to measure the interparticular necks and the volume of liquid formed for different repetition rates. The thermal model leads to good predictions of the particles final sintering state. Fluid flow models are investigated in order to determine the dynamic of the molten liquid. The main issue is to explain the capillary flow mechanisms leading from the molten material to the neck formation. Two models are derived to simulate the fluid flow between the particles. The first one simulates a capillary flow between two parallel plates. The second one deals with energetic considerations arising from Frenkel's principle. In both cases, the final output is the liquid life-time necessary to get the interparticular neck lengths experimentally observed. We point out that the two models predict the same liquid lifetime, although they are derived with different hypotheses. In SLM, continuous lasers are used and one has to deal with macroscopic thermal gradients, since the particles are completely molten. A very high laser power is used and the negative thermal effects (like thermal stresses or balling effects) are important. A solution to control them is to adjust the scanning strategy. Four scanning strategies are investigated for material with different thermal conductivities. The three-dimensional model used to describe the laser-matter interactions and the temperature evolution of the scanned powder bed allows for a finite latent heat (Stefan-problem) and for conductivity modifications due to the consolidation. We show that this finite element thermal model can be efficiently used to anticipate most of the problems (like cracks or balling) arising in practice. The benefit of avoiding thermal gradients is shown, in particular by EBSD analysis. Finally, applications of the SLS/SLM technique on different pieces built during this work are shown. A new way to build support structure is also proposed.

With the demand for complex, individualized and functionalized products with respect to constantly decreasing life cycles, additive manufacturing processes such as the process of selective laser sintering (SLS) has increasingly been of industrial interest. These processes are being used more and more to produce models, prototypes and partially finished products made of plastic, metal or ceramic and require neither a tool nor a form. Affected by decreasing installation spaces and increasing functional densities, flexible methods for circuit board application and their combination with additive manufacturing are in the focus of electronic industry research activities. In the context of this article both a thermoplastic polymer polybutylene terephthalate (PBT) which has been prepared to defined powder fractions with cryogenic milling, and the established and commercially available SLS material (PA12, PA2200) were the subject of a dry coating process with LDSadditives. Subsequently, these LDS-powders were processed with SLS to form test specimens. Finally their surface was structured and metallized through the LPKF-LDS-process (Laser-Direct- Structuring). Based on these metallized specimens, the metallization was studied as a function of an LDS-additive filling ratio. To uncover positive synergy effects from additively manufacturing the polymer body, the metallization was analyzed in terms of shape and adhesive strength.

Multi-walled carbon nanotubes/silicone conductive nanocomposites are of great significance because of their unique electrical and mechanical properties and are expected to open up a new field of applications as smart functional materials. Especially their noticeable piezoresistive behaviors can be utilized to produce flexible tactile sensors with large sizes but low costs. To enhance the sensitivity of the piezoresistive property, a foaming procedure was introduced to the conductive polymeric composites. A series of novel multi-walled carbon nanotubes/silicone conductive foamed nanocomposites were fabricated with different types of foaming agents to obtain a diverse porous structure. The porous structures of the foams, the distribution and orientation state of the multi-walled carbon nanotubes in the silicone matrix were both observed using a laser microscope and SEM with or without a compressive load. The influences of the porous structure and porosity on the foam were studied. It was found that a different porosity and different voids structure affected the density, elastic modulus, resistivity as well as piezoresistive property significantly. A piezoresistive model for the conductive fillers reinforced elastomeric composites was developed, the calculated results of resistive variations were used to compare to the measured values. Although the overall trends of the resistance changes matched, notable separations were found between the theoretical values and the measured values, which are thought to be caused by the viscoelasticity of the silicone matrix.

A new W-band transceiver circuit design is introduced for wireless high speed data transmission applications that relies entirely on commercially available 77 GHz automotive radar MMIC (monolithic millimeterwave integrated circuits) and thinfilm ceramics. The advantage of this approach is twofold. Firstly, already well established technology can be utilized for a new field of applications. Secondly, the resulting higher production volume due to deeper market penetration lowers the MMIC cost and therefore benefits likewise the automotive as well as the telecommunications market. A study of geographically correlated link-ranges shows that 779 m-2.4 km can be achieved depending on the required link availability. A super heterodyne transceiver design using a quasi PSK modulation is proposed. Measured results of two passive system components are presented exemplarily.