FDM process

Material and Accuracy The available materials for FDM process are Acrylonitrile Butadiene Styrene (ABS), Poly-carbonate (PC)-ABS Blend, PC, and Polyphenylsulfone (PPSF) and polylactic acid (PLA). 

Special polyamide formulations improve fdm processing and performance... 

A number of reports show how each parameter in the FDM process contributes to the quality (less distortion) and functionality of printed parts. The complexity of the 3D printing process arises from the number of variables which are used to define the operation of the 3D printer machine and the material. Bearing in mind the possibility of producing solid or shell objects, the correct selection of the manufacturing parameters contributes to the improvement of the properties, such as density, porosity, layer thickness, and material properties (ViUalpando et al. 2014). The intrinsic layer parameters such as printing and feed roller speeds and, extrusion temperature should not be ignored in any optimisation process (Fig. 7.3). 

Too et al. (2002) conducted a study relating the layer microstructure obtained from gaps between the filaments ranging from 0 to 0.5 mm. This study allowed the development of an understanding of the versatility of the FDM process to obtain matrix-like structures with a consistent pore distribution. Compressive tests were performed to determine how the gap between the filaments affects the mechanical behaviour of ABS P400 printed parts. It was found that by setting the gap to 0.2 mm which yielded a measured porosity of 59 % caused a decrease of the compressive strength by half compared with no gap samples. 

Fused deposition modeling (FDM) is an extrusion process developed by Stratasys. Parts are built up in layers from extruded plastic strands. In principle, the FDM process is suitable for all materials that can be melted and extruded. Plastics such as ABS, ABSi, PC-ABS, PC, PC-ISO, and PPSF are typical of the materials used. The material for extrusion must be in filament form, with a circular cross-section and a diameter between 1 and 2 mm. The initial data in 3D CAD form are generally converted to SLA format, and this data is used to create 2D cross-sections as slices through the part to be produced. Although the material solidifies very quickly, structures made of support material are needed for cantilever structures. These supporting structures are subsequently easy to remove. Filaments of different materials are needed for the part and the supporting structure. Drive rollers carry the two filaments to an electrically heated plastifier, where the filaments are heated to just below melting temperature (Fig. 7.3). 

Plastic bodies made by FDM using a suitable LDS material can be laser direct structured. Successful tests have been carried out with PC and PC-ABS [120]. The support materials necessary for the FDM process do not have any negative effect on LDS. The geometric surface structure of the FDM parts, however, can restrict the possible areas of application. Tests of the FDM process using a PBT modified with an LDS additive have shown that, because of the wavy surface structure, an extra smoothing step has to be inserted prior to the LDS operation [134,186). 

The industrial importance of the FDM process commercialized by Stratsys Inc. greatly benefits from the wide range of processed materials and their convenient application form. Figure 11 serves to illustrate the process schematically. 

Figure 11 Schematic illustration of the FDM process. (1) Vertically movable building platform (2) horizontally movable, heated deposition unit with nozzles for (3) model material and (4) support material ...

Figure 13 Application of FDM-processed composite scaffolds for bone regeneration tissue engineering applications. Alternative approaches for...

In order to prepare thin fdms of (SN) on plastic or metal surfaces, several processing techniques have been investigated, e.g., the electroreduction of [SsNs]" salts. Powdered (SN) is prepared by the reaction of (NSC1)3 with trimethylsilyl azide in acetonitrile/ The sublimation of (SN) at 135°C and at pressure of 3 x 10 Torr. produces a gas-phase species, probably the cyclic [SsNs] radical, that reforms the polymer as epitaxial fibres upon condensation/... 

Such reactions processes are responsible for the transition from PS formation to electropolishing with increasing potential as typically revealed in an i-V curve.18 PS formation can occur when the surface is not or only partially covered by oxide. Once the whole surface is covered with an oxide film further reaction can only proceed through the formation of oxide followed by its dissolution. Further increasing the potential will only result in an increase of oxide fdm thickness. On the other hand, increasing HF concentration will increase the dissolution rate of oxide. The presence of oxide on the silicon surface in the PS formation region and its increase with potential have been experimentally observed.98... 

A three-dimensional simulation method was used to simulate this extrusion process and others presented in this book. For this method, an FDM technique was used to solve the momentum equations Eqs. 7.43 to 7.45. The channel geometry used for this method was essentially identical to that of the unwound channel. That is, the width of the channel at the screw root was smaller than that at the barrel wall as forced by geometric constraints provided by Fig. 7.1. The Lagrangian reference frame transformation was used for all calculations, and thermal effects were included. The thermal effects were based on screw rotation. This three-dimensional simulation method was previously proven to predict accurately the simulation of pressures, temperatures, and rates for extruders of different diameters, screw designs, and resin types. 

Another cause of interest in this technique is due to the fact that the crystals in most as-deposited CD fdms are very small. Considering the current interest in nanoparticles, CD is an excellent technique to deposit nanocrystalline fdms. More specifically, if the nanocrystals are small enough, they exhibit size quantization, the most obvious manifestation of which is an increase in the optical bandgap with decrease in crystal size, as was shown for CD CdSe [17] and later for CD PbSe [18,19]. In fact, the changes in optical spectra that occurred in these films as a function of nanocrystal size were exploited to provide information on the different mechanisms of the deposition process [20]. 

Considering that homogeneous precipitation of metal chalcogenides (mainly sulphides) by reaction between metal ions and dissolved chalcogen is well established, the main difference between this deposition and similar reactions seems to be that the products adhere to a substrate to give a visible fdm (in this case) rather than only precipitate. Whether this is connected with the redissolu-tion/redeposition process that occurs with the Sn-S system or has some other explanation is important. If the former, it may be limited to only those systems that behave similarly. Otherwise it is not unreasonable to expect that other metal sulphides and selenides (possibly also tellurides, although tellurium tends to be much less soluble, if at all, in such solvents) may be deposited as films in this manner. 

Field-desorption mass spectrometry (FDMS), where no evaporation prior to ionization is required, has been successfully used in the analysis of in volatile phosphonium salts113, although a direct thermal process gave similar spectra114. In the case where the FD spectra are complex, a chemical ionization technique may give wider applicability115. The cation is the base peak for monophosphonium salts when the [2M + anion]+ cationic species is the one for bisphosphonium compounds. 

Conventional electron impact or chemical ionization mass spectrometry requires that volatilization precede ionization and this is clearly a limiting factor in the analysis of many biochemically significant compounds. A newer ionization technique, field desorption (FD) (1, 2 ) removes this requirement and makes it possible to obtain mass spectrometric information on thermally unstable or non-volatile organic compounds such as glycoconjugates and salts. This development is particularly significant for those concerned with the analysis of glycolipids and we have therefore explored the suitability of field desorption mass spectrometry (FDMS) for this class of compounds. We have evaluated experimental procedures in order to enhance the efficiency of the ionization process and to maximize the information content of spectra obtained by this technique. 

FDM was applied to electrochemical problems very early [4], but it was in the 1960s when Feldberg developed the basis of digital simulation of electrochemical processes by means of the box method, which at present is considered as a FEM-like method (see [5]). 

There are many numerical issues that we must discuss before proceeding to applications of FDM when solving polymer processing problems. The most important are,... 

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