Key parameters controlling surface quality and dimensional accuracy: a critical review of FFF process

Fused filament fabrication (FFF) is an additive manufacturing process, which constructs physical items by fused melt material, selectively deposited layer-by-layer through a heated extrusion mechanism. Parameters’ selection and control in FFF are of utmost importance since they significantly affect the surface quality (SQ) and dimensional accuracy (DA) of the FFF printed parts. In the present paper, initially, the FFF process is briefly presented. Next, a cause-and-effect diagram exhibits the process parameters’ categorization with the SQ and DA of the manufactured parts. Then, according to the robust design theory, the process parameters are divided into three classes, i.e., the signal, the control, and the noise. This classification supports the selection of appropriate FFF printers, according to the control parameters, whereas it facilitates the optimization of the SQ and DA of printed parts, concerning the signal parameters. Finally, the impact of each parameter on SQ and DA is presented, supported by an extensive literature review. Overall, the process parameters’ optimization is critical for the SQ and DA. Therefore, they should be adjusted to achieve higher quality and less post-processing work. © 2022 Taylor & Francis

Quality performance evaluation of thinwalled PLA 3D printed parts using the taguchi method and grey relational analysis

This paper investigates the quality performance of FDM 3D printed models with thin walls. The design of experiments method (DOE) was used and nine models of the same size were fabricated in a low-cost 3D printer using polylactic acid (PLA) material. Two limited studied parameters were considered (extraction temperature and wall thickness), each one having three levels. External X and Y dimensions were measured using a micrometer, as well as four surface roughness parameters (Ra, Rz, Rt, Rsm) with a surface tester. Two optimization techniques (the Taguchi approach and Grey relational analysis) were utilized along with statistical analysis to examine how the temperature and wall thickness affect the dimensional accuracy and the surface quality of the parts. The results showed that high extraction temperature and median wall thickness values optimize both dimensional accuracy and surface roughness, while temperature is the most important factor. © 2020 by the authors

Neural networks for predicting kerf characteristics of CO

The current work is a follow-up of previous research published by the authors and investigates the effect of CO2 laser cutting with variable cutting parameters of thin 3D printed wood flour mixed with poly-lactic-acid (PLA/WF) plates on kerf angle (KA) and mean surface roughness (Ra). The full factorial experiments previously conducted, followed a custom response surface methodology (RSM) to formulate a continuous search domain for statistical analysis. Cutting direction, standoff distance, travel speed and beam power were the independent process parameters with mixed levels, resulting to a set of 24 experiments. The 24 experiments were repeated three times giving a total of 72 experimental tryouts. The results analyzed using analysis of variance (ANOVA) and regression, to study the synergy and effect of the parameters on the responses. Thereby, several neural network topologies were tested to achieve the best results and find a suitable neural network to correlate inputs and outputs, thus; contributing to related academic research and actual industrial applications

Effects of adenotonsillectomy on R-R interval and brain natriuretic peptide levels in children with sleep apnea: A preliminary report

Objectives: Obstructive sleep apnea is associated with decreased R-R interval length and overall R-R interval variability in the electrocardiogram along with increased morning brain natriuretic peptide (BNP) blood levels. These findings indicate enhanced sympathetic tone and cardiac strain. In this study, it was hypothesized that adenotonsillectomy (AT) in children with sleep apnea is accompanied by improvement in polysomnography indices, increase in length and variability of R-R interval, and reduction in BNP levels. Methods: Polysomnography and measurements of morning BNP levels were performed before and 46 months after AT. Mean and standard deviation of R-R interval were calculated from polysomnography electrocardiogram recordings. Results: Twenty-one children were studied. Apnea-hypopnea index and log-transformed BNP levels decreased postoperatively from 8.4 +/- 7.6 episodes/h and 2.2 +/- 0.7, to 1.8 +/- 1.4 episodes/h and 1.9 +/- 0.3, respectively (p < 0.05). Mean R-R interval increased from 703.2 +/- 137.4 ms (Stage 2), 699.3 +/- 135.8 ms (Stage 3), 707.4 +/- 128.9 ms (Stage 4) and 660.5 +/- 140.1 ms (Stage REM), to 773.5 +/- 122.7 ms (Stage 2), 765.7 +/- 73.7 ms (Stage 3), 771.2 +/- 71.6 ms (Stage 4), and 738.6 +/- 81.7 ms (Stage REM), respectively (p < 0.05 for comparisons pre- vs. post-operatively). Standard deviation of R-R in Stage 2 increased from 88.5 +/- 29.6 to 122.7 +/- 67 ms (p = 0.045). Conclusions: Increase in nocturnal length of R-R interval and decrease in BNP levels after AT for sleep apnea may reflect postoperative reduction in sympathetic tone and cardiac strain. (C) 2011 Elsevier B.V. All rights reserved

Outcome of TORS to tongue base and epiglottis in patients with OSA intolerant of conventional treatment

Purpose Transoral robotic surgery (TORS) of the tongue base with or without epiglottoplasty represents a novel treatment for obstructive sleep apnea (OSA). The objective was to evaluate the clinical efficacy of TORS of the tongue base with or without epiglottoplasty in patients who had not tolerated or complied with conventional treatment (continuous positive airway pressure or oral appliance). Methods Four-year prospective case series. The primary outcome measure was the apnea-hypopnea index (AHI) in combination with the Epworth Sleepiness Score (ESS). Mean oxygen saturation levels (SaO2) before and after TORS on respective sleep studies were also recorded. Secondary outcome measures included operative time and complications. Patient reported outcome measures (PROMs) assessed included voice, swallow and quality of life. Results Fourteen patients underwent TORS for tongue base reduction with ten having additional wedge epiglottoplasty. A 64 % success rate was achieved with a normal post-operative sleep study in 36 % of cases at 6 months. There was a 51 % reduction in the mean AHI (36.3 ± 21.4 to 21.2 ± 24.6, p = 0.02) and a sustained reduction in the mean Epworth Sleepiness Score (p = 0.002). Mean SaO2 significantly increased after surgery compared to pre-operative values (92.9 ± 1.8 to 94.3 ± 2.5, p = 0.005). Quality of life showed a sustained improvement 3 months following surgery (p = 0.01). No major complications occurred. Conclusions TORS of the tongue base with or without epiglottoplasty represents a promising treatment option with minimal morbidity for selected patients with OSA. Long-term prospective comparative evaluation is necessary to validate the findings of this study

Tonsilloplasty Versus Tonsillectomy in Children With Sleep-Disordered Breathing: Short- and Long-Term Outcomes

Objectives/Hypothesis: Adenoidectomy and tonsillectomy (TE) is the standard treatment for obstructive sleep-disordered breathing (SDB) in children with adenotonsillar hypertrophy. Tonsilloplasty (TP) is a new surgical technique that includes partial TE. The purpose of this study was to assess the short-and long-term outcomes of TP compared to TE. Study Design: A comparison study. Methods: Children with SDB and tonsillar hypertrophy underwent TP or TE. The two groups were compared regarding immediate postoperative course and long-term effects. Results: Fifty-one children (age, 6.3 +/- 2.5 years) underwent TE, and 50 children (age, 5.9 +/- 2.1 years) had TP. The TP group had significantly less intraoperative bleeding compared to the TE group (25.6 +/- 8.2 vs. 38.3 +/- 12.3 mL, P .05). Conclusions: TP is an alternative surgical method for treatment of SDB related to tonsillar hypertrophy with favorable postoperative course and comparable long-term results