A method for computing lines of curvature and umbilical points is proposed. These properties, derived for NURBS surfaces, are useful in shape modeling for both aesthetic and functional ...characteristics evaluation. Moreover, the application to the ship-hull design and to the progressive additional lens design, of umbilics and lines of curvature are investigated.
Recently, the possibility of producing medium-to-large batches has increased the interest in polymer powder bed fusion technologies such as selective laser sintering (SLS) and multi jet fusion (MJF). ...Only scant data about the characterization of parts produced by MJF can be found in the literature, and fatigue behavior studies are absent. This study analyzes the material properties of Polyamide 12 (PA12) powders and printed specimens using both SLS and MJF technologies. The morphology, crystalline phases, density, porosity, dimensional accuracy, and roughness are measured and compared; tensile and fatigue tests are performed to assess the effect of the technologies on the mechanical behavior of the produced structures. In addition, lattice structure specimens obtained by different geometric modeling approaches are tested to understand the influence of modeling methods on the fatigue life. The PA12 powders printed by both SLS and MJF mainly show by X-Ray Diffraction γ-phase and a small shoulder of α-phase. The crystallinity decreases after printing the powders both in SLS and MJF technology. The printed parts fabricated using the two technologies present a total porosity of 7.95% for SLS and 6.75% for MJF. The roughness values are similar, Ra ≈ 11 µm along the building direction. During tensile tests, SLS samples appear to be stiffer, with a lower plastic deformation than MJF samples, that are tougher than SLS ones. Fatigue tests demonstrate higher dispersion for MJF specimens and an enhancement of fatigue life for both SLS and MJF printed lattice structures modeled with a novel geometric modeling approach that allows the creation of smoother surfaces at nodal points. Scanning electron microscopy on fracture surfaces shows a brittle failure for the SLS tensile specimens, a more ductile failure for the MJF tensile specimens, a crazing failure mechanism for the SLS fatigue tested samples, and a crack initiation and slow growth and propagation for the MJF fatigue tested samples.
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•Comparison between PA12 Selective Laser Sintering and Multi Jet Fusion technologies.•Different failure mechanisms for SLS and MJF fatigue tested samples.•SLS bulk specimens behave better for stresses higher than 34 MPa.•MJF bulk specimens fatigue curve has a knee at 34 MPa.•Lattice structures modeled with Catmull–Clark algorithm have longer fatigue life.
New polyvinyl siloxane (PVS) materials with enhanced properties have been developed to improve and facilitate implant impression techniques. However, studies on their accuracy are lacking.
The ...purpose of this in vitro study was to determine the accuracy and precision of implant impressions made with some recently introduced materials on a simulated patient requiring an all-on-4 implant-supported prosthesis. Well-established polyether materials were also evaluated as a comparison. The variables considered were material type, consistency, splinting or not splinting techniques, and implant angulation.
A reference master model was made by inserting 4 implants at angles of 0, 5, and 10 degrees. Eighty impressions were made at 37 °C in wet conditions by using a standardized technique. Eight groups (n=10) were created using monophasic, single-viscosity materials (Hydrorise Implant Medium, HIM-ns; Hydrorise Implant Medium, HIM; Honigum Mono, HM; Impregum, IMP), and 2-viscosity materials (Hydrorise Implant Heavy+Light-ns, HIH+L-ns; Hydrorise Implant Heavy+Light, HIH+L; Honigum Heavy+Light, HH+L; and Permadyne and Garant Heavy+Light, PeH+L). Hydrorise materials were used with splinting and not splinting (ns) techniques. The reference points located on the connecting platforms of the transfer copings (TCP) were compared with the same points on the implant connecting platforms (ICP) located in the reference model. The accuracy and precision of the impressions were determined as linear 3D errors and standard deviation between each TCP-ICP couple by using an optical coordinate measuring machine (OCMM).
PVS materials were generally better than polyether materials, with Hydrorise materials (HIM and HIH+L) showing significantly better accuracy and precision (30.9 ±14.4 μm and 28.7 ±15.5 μm, respectively) than IMP and PeH+L polyethers (44.2 ±16 μm and 43.8 ±17.6 μm, respectively; P<.001). Honigum materials were statistically similar to Hydrorise materials (P=.765). The values shown by Hydrorise nonsplinted groups (HIH+L-ns and HIM-ns) were not statistically different from those of the splinted polyether impressions (P=.386). The viscosities (monophasic or heavy+light) had no effect on accuracy, but monophasic material positively influenced precision (HIM and HIH+L, P=.001). No correlation was found between implant angulation and accuracy (multilevel analysis and Kendall rank correlation coefficient=-0.065; P=.133).
Recently introduced materials designed for implant impressions showed significantly higher accuracy and precision; even with the unfavorable nonsplinting technique, the new materials performed similarly to, or better than, polyether materials. Although the transfer coping splinting technique generally improved the accuracy and precision of Hydrorise materials, the effect was significant only within HIH+L groups.
To compare the reference geometry approach to the best-fit (or superimposition) approach in the estimation of geometric accuracy relevant to the digital and the analog workflow to fabricate a ...complete denture. Starting from a model of an edentulous maxilla, the two measuring methodologies were tested to estimate the geometric accuracy of the intaglio surface of the complete dentures fabricated by CNC milling and injection molding. Eight areas of interest were defined at the intaglio surface of the denture base; a sensitivity analysis determined the minimum number of measuring points to calculate a reliable
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error value. A repeatability analysis was performed to assess the consistency of this experimental reference geometry approach with respect to the clinic acceptable requirements. For the analog workflow, the comparison of the reference geometry results to the best-fit results showed a − 76 (post-dam) ÷ 169 µm (right flange) range of the
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mean value for the reference geometry approach, to be compared to − 15 (left crest) ÷ 146 µm (right tuberosity) range for the best-fit approach. For the digital workflow, the same comparison showed a − 21 (left crest) ÷ 51 µm (left flange) range for the reference geometry approach, compared to a − 20 (left crest) ÷ 23 µm (left flange) for the best-fit approach. The best-fit approach results in an underestimation of mean
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error values and their distribution over the entire prosthesis. The reference geometry approach correctly estimates error values while focusing on the identification of sources of errors in the manufacturing process.
Innovative design methods and manufacturing technologies, such as lattice structures optimization and additive manufacturing, allow for the production of functional and extremely complex components. ...Recent literature shows limits in geometric modeling and data exchange, highlighting some improvements in the design of variable density lattice structures mainly for powder bed fusion technologies. Similar improvements are not available for material extrusion (MEX) technologies which show technological and numerical limits related to the computer numerical control programming language (G-code) generated by computer aided manufacturing (CAM) software. This work aims at overcoming the limits in fabricating graded density shell-based lattice structures for MEX technology by using the infill patterns available in the CAM software and editing the G-code based on a density map defined by volumetric models. Combining two usually separated phases, i.e., the geometric modeling and the CAM processing, several advantages are obtained, considering at the same time some of the technological constraints.The proposed approach is tested on a cubic sample and on a bracket fabricated by a fused filament fabrication technology. The results show that the method allows for the reduction of design efforts, amount of data exchanged, and processing time, obtaining an effective G-code and consistent components.
The marginal gap and ceramic bond strength of metal-ceramic restorations are important for success. However, studies evaluating the marginal gap and ceramic bond strength of fixed partial dentures ...(FPDs) produced with 3D printing technologies such as selective laser melting (SLM) are scarce.
The purpose of this in vitro study was to investigate the marginal gap of cobalt-chromium (Co-Cr) alloy frameworks produced by SLM technology before and after ceramic firing. Additionally, the metal-ceramic bond strength was evaluated with the Schwickerath crack-initiation test according to the International Standards Organization (ISO) 9693-1:2012.
Conventional impressions were made, and the definitive cast of a patient requiring a 4-unit FPD was scanned. After designing the FPD, the files were sent to a service center for the fabrication of a metal master model, 80 Co-Cr frameworks, and 80 flat specimens (25×3×0.5 mm) with SLM technology. The marginal gap between frameworks and the abutment tooth of the metal master model was nondestructively measured by using an optical coordinate-measuring machine. A total of 80 sets, consisting of 1 framework and 1 flat specimen, were sent to 80 dental laboratory technicians for ceramic firing. Detailed instructions for correct manipulation of the framework and flat specimen were provided. The marginal gap was remeasured, and the 3-point bend test was used to evaluate metal-ceramic bond strength.
Only 28 of the 80 dental technicians returned the specimens within a prespecified time and/or in adequate condition. The mean ±standard deviation marginal gap of the framework before ceramic firing was 25 ±9 μm and 34 ±12 μm after firing. The difference was statistically significant (P=.001). The mean ±standard deviation 3-point bend strength was 33 ±9 MPa.
Ceramic firing affected the marginal gap; however, all Co-Cr frameworks had a marginal gap lower than 120 μm, which is reported to be a clinically acceptable limit. Most of the specimens (80%) had a metal-ceramic bond strength value higher than the 25-MPa ISO 9693 requirement. Five of 28 dental laboratory technicians were not able to comply with ceramic firing instructions.
The introduction of deterministic NC grinding and polishing operations, in the manufacturing of free-form glass components for precision optics, requires the characterization of surface topography ...evolution as a function of process parameters. In this work, a model based on Reye's wear hypothesis is proposed for the assessment of surface roughness prediction as a function of operating parameters, in the deterministic polishing process of glass moulds. According to Reye's hypothesis, the removed material per unit area is proportional to the work due to the friction force: the removed material per unit area can be computed by adequately integrating the areal material ratio function (Abbott–Firestone curve) of the surface and can be associated with the amplitude roughness parameter; the work due to the friction force per unit area is proportional to the integral of the product of pressure and velocity in the time interval and can be derived from the process parameters by means of the Hertz theory. The model assessment was performed on ground glass flat samples polished with different operating parameters, mapping the surface roughness using an atomic force microscope (AFM). The developed model shows a satisfactory estimate of surface roughness evolution during the polishing process and confirms the experimental results found in the literature for the Preston coefficient.
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•An original modeling approach based on subdivision surfaces was studied.•Selective Laser Sintered lattice samples were manufactured in PA12 and tested.•Subdivision surface modeling ...approach improves fatigue life.•Subdivided lattice has the lowest stress concentration factor.•Subdivided lattice are stiffer than standard lattice.
According to recent studies, a new paradigm in the geometric modeling of lattice structures based on subdivision surfaces for additive manufacturing overcomes the critical issues on CAD modeling highlighted in the literature, such as scalability, robustness, and automation. In this work, the mechanical behavior of the subdivided lattice structures was investigated and compared with the standard lattices. Five types of cellular structures based on cubic cell were modeled: struts based on squared or circular section, with or without fillets and cell based on the subdivision approach. Sixty-five specimens were manufactured by selective laser sintering technology in polyamide 12 and tensile and fatigue tests were performed. Furthermore, numerical analyses were carried out in order to establish the stress concentration factors.
Results show that subdivided lattice structures, at the same resistant area, improve stiffness and fatigue life and reduce stress concentration while opening new perspectives in the development of lattice structures for additive manufacturing technologies and applications.
A 3D numerical model aimed at predicting the deformations of a S355 steel T-joint in both as-welded and post-welding heat treated conditions was developed. Experimental tests were carried out with ...the objective to collect data necessary to the heat source calibration and model validation in terms of microstructure and joint distortions. All metallurgical phenomena were taken into account such as specific volume change and transformation plasticity induced by solid-state phase transformations. A viscoplasticity model for stress relief processing implemented in Sysweld finite elements code was used. Numerical results showed a satisfactory agreement with experimental ones. Further investigations will be necessary to consider also the validation of residual stress relief effects.
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