Surface Deviation Research Articles

Performance and durability of additively and subtractively manufactured resin-based onlay restorations after thermomechanical aging.

To evaluate the effect of material type on dimensional stability, occlusal surface wear, fracture resistance, and failure behavior of resin-based onlay restorations. A mandibular right first molar typodont was prepared and digitized using an intraoral scanner to virtually design an onlay restoration with the minimum occlusal thickness of 1.5mm. Resin-based onlay restorations (n = 15 per group) were fabricated either additively from 2 different resins indicated either for definitive or interim use or subtractively with a composite resin. After cementing onlays to corresponding dies, each of them was digitized before and after thermomechanical aging (B-STL and A-STL), and then subjected to load-to-failure test to evaluate fracture resistance. The B-STL and A-STL of each onlay were also compared to assess the dimensional stability and occlusal surface wear. One-way analysis of variance and Tukey honestly significant difference tests were used to evaluate dimensional stability, occlusal surface wear, and fracture resistance. The chi-square test was used to evaluate the Weibull modulus and characteristic strength among the groups (α = 0.05). Material type affected investigated outcomes (p<0.001). The additively manufactured resin indicated for definitive use led to the highest external surface deviations and the additively manufactured resin indicated for interim use led to the highest mesiodistal width deviations (p≤0.033). The onlays fabricated from the additively manufactured resin indicated for definitive use had the highest occlusal surface wear, while those in composite resin had the lowest (p≤0.006). The composite resin onlays had the highest fracture resistance values and reliability (p≤0.035). Tested subtractively manufactured composite resin had the lowest occlusal surface wear with the highest fracture resistance and reliability. Additively manufactured resins had lower dimensional stability, while tested resin for additively manufactured definitive restorations had the highest occlusal surface wear.

Shape Accuracy Improvement of the Flange Turning Process in Aluminum Aerosol Can Production

This study investigates the flange turning process in the production of aluminum aerosol bottles. Aluminum discs are lubricated, extruded, trimmed, washed, painted, and lacquered before undergoing necking, where flange turning ensures a secure, aesthetically pleasing fit. Errors in flange turning, such as uneven or tapered surfaces, can compromise bottle functionality and appearance. To address this, experiments were performed with different tool geometries, feed rates, and rotational speeds. The investigations aimed to achieve flat, consistent flange surfaces with minimal deviation from the desired geometry. Two main variables were examined: a 1 s waiting time at the end position and variations in feed rate and cutting depth. The waiting time improved flatness, halving surface deviations, while regrinding the tool reduced flatness errors to a tenth of the original values. Higher feed rates and speeds also enhanced surface quality, with flatness errors ranging from 371 μm to 75 μm. Overall, this study demonstrates that optimizing parameters like cutting angle, feed rate, and rotational speed, along with a waiting period, significantly enhances surface accuracy. These findings support more efficient production processes for aluminum aerosol bottles.

Thermoelastic damping in bi-layered micro/nanobeam resonators using the dual-phase-lag generalized heat conduction model

The existing analytical investigations on thermoelastic damping (TED) in laminated micro/nanobeam resonators have generally neglected the thermal axial force and rarely considered the time lagging in the heat transfer. However, laminated beams will very likely exhibit stretching-bending coupling deformation due to the deviation of the physical neutral surface from the beam mid-surface. Furthermore, the TED in layered beams has been predicted by using the energy rather than the complex frequency approach. In this presentation, TED in bi-layered micro/nanobeams is analyzed based on the Euler-Bernoulli beam theory and the dual-phase-lag (DPL) generalized heat conduction theory by considering the thermal axial force. Analytical solutions for the TED in bi-layered micro/nanobeams are developed by using both the complex frequency approach and the energy method. Numerical results are presented to examine the effects of the thermal axial force and DPL relaxation times on the TED in the laminated beam resonators for different physical and geometrical parameters, vibration modes and mechanical boundary conditions, which reveal that the thermal axial force will increase (decrease) the TED in metal/ceramic (ceramic/ceramic, metal/metal) bi-layered beams. The maximum underestimation for the TED due to neglecting the thermal axial force will reach about 7 % in Ag/Si beam and 15 % in Cu/Si3N4 beam. The DPL effect on the TED is closely related to the material properties of the laminas and their volume fractions. For the Ag/Si beam with the thickness less than 1nm, influence of the DPL relaxation on the TED becomes significant which changes continuously from the negative contribution to the positive one with the increase in the volume fraction of the Si from 0 to 1. However, the DPL effect can be ignored in the bi-layered beams with micrometer size.

Additive manufacturing trueness and internal fit of crowns in resin modified with a commercially available ceramic composite concentrate

Inorganic fillers can be incorporated into additively manufactured (AM) resins to improve their properties, and a ceramic composite concentrate has been recently marketed for this purpose. However, knowledge on the printability of AM resins modified with this concentrate is lacking. The purpose of this in vitro study was to evaluate the manufacturing trueness and internal fit of AM crowns in a dental resin modified with a commercially available ceramic composite concentrate. A maxillary right first molar typodont tooth was prepared and digitized to design a crown in standard tessellation language (STL) format. This STL file was used to fabricate a total of 30 AM crowns, 10 with a resin with no fillers for interim restorations (AM-I), 10 AM-I resin incorporated with ceramic composite concentrate (AM-IR), and 10 with a ceramic-filled resin intended for definitive restorations (AM-D). The modification of the AM-IR resin was performed by mechanically mixing 30wt% of a commercially available ceramic composite concentrate into AM-I. An intraoral scanner was used to digitize all crowns, which were then seated on the prepared typodont abutment and rescanned. The manufacturing trueness of each crown was measured in 4 regions (overall, external, intaglio, and marginal) and reported with root mean square (RMS) estimates. The internal gaps were calculated by using a triple scan protocol. The intaglio surface deviations were assessed with the Kruskal-Wallis and Dunn tests, while the remaining data were analyzed with the 1-way analysis of variance and Tukey honestly significant difference tests (α=.05). AM-IR had the highest overall and external RMS and had higher intaglio RMS than AM-D (P≤.001). AM-I had the lowest marginal RMS (P≤.002). AM-IR had the highest average gap values (P≤.027). AM-IR crowns mostly had lower trueness and high internal gaps. However, the differences among the tested materials in fabrication trueness and average gap values were small, and internal gaps were within the previously reported thresholds.

Insights into geometric deviations of medical 3d-printing: a phantom study utilizing error propagation analysis

BackgroundThe use of 3D-printing in medicine requires a context-specific quality assurance program to ensure patient safety. The process of medical 3D-printing involves several steps, each of which might be prone to its own set of errors. The segmentation error (SegE), the digital editing error (DEE) and the printing error (PrE) are the most important partial errors. Approaches to evaluate these have not yet been implemented in a joint concept. Consequently, information on the stability of the overall process is often lacking and possible process optimizations are difficult to implement. In this study, SegE, DEE, and PrE are evaluated individually, and error propagation is used to examine the cumulative effect of the partial errors.MethodsThe partial errors were analyzed employing surface deviation analyses. The effects of slice thickness, kernel, threshold, software and printers were investigated. The total error was calculated as the sum of SegE, DEE and PrE.ResultsThe higher the threshold value was chosen, the smaller were the segmentation results. The deviation values varied more when the CT slices were thicker and when the threshold was more distant from a value of around -400 HU. Bone kernel-based segmentations were prone to artifact formation. The relative reduction in STL file size [as a proy for model complexity] was greater for higher levels of smoothing and thinner slice thickness of the DICOM datasets. The slice thickness had a minor effect on the surface deviation caused by smoothing, but it was affected by the level of smoothing. The PrE was mainly influenced by the adhesion of the printed part to the build plate. Based on the experiments, the total error was calculated for an optimal and a worst-case parameter configuration. Deviations of 0.0093 mm ± 0.2265 mm and 0.3494 mm ± 0.8001 mm were calculated for the total error.ConclusionsVarious parameters affecting geometric deviations in medical 3D-printing were analyzed. Especially, soft reconstruction kernels seem to be advantageous for segmentation. The concept of error propagation can contribute to a better understanding of the process specific errors and enable future analytical approaches to calculate the total error based on process parameters.

Does relative bracket base area affect the accuracy of reconstructed buccal surface in the virtual bracket removal technique?

BackgroundVirtual bracket removal (VBR) facilitates efficient retainer fabrication for fixed orthodontics in a digital workflow. This study is aimed at assessing the influence of the relative bracket base area (RBA), representing the proportion of the labial/buccal surface area intended for removal, on the surface reconstruction accuracy in the VBR technique.Methods196 teeth from seven resin dental models were included. The maximal bracket base surface area (MBA) was determined by the rectangular area extending to the lateral edges of the tooth labial/buccal surface. On each tooth, diverse RBA percentages (20–100% in 10% increments) of the MBA was removed, respectively. Following removal, the buccal surfaces of the teeth were digitally reconstructed. Subsequently, the root mean square (RMS) values, which represent the surface deviations between the reconstructed and original dentitions was calculated for each tooth. The obtained RMS values were compared within and among groups of different RBAs and compared with the clinically acceptable limit (CAL) of 0.05 mm.ResultsAs the RBA increased, there was a discernible trend of elevated RMS values, both for the overall dentition and each specific tooth type. Among the lower teeth, the molars consistently displayed the highest RMS values in almost all groups, with significantly higher mean/median RMS values compared to the lower incisors (P < 0.05), excluding the 0.2MBA group. Specifically, across all tooth types, the mean/median RMS values in groups with 20–80% MBA were significantly lower than CAL of 0.5 mm (P < 0.05). This trend persisted for all tooth types in the 0.9MBA group except the lower canines and molars.ConclusionThe mean/median RMS values elevated as the RBA increased. VBR technique remains sufficiently accurate for retainer fabrication, provided that the RBA remains below 80% of the MBA for lower canines and molars and 90% for all the other tooth types. Notably, residual bonding materials should be considered in clinical use because they are also removed in VBR and thereby constitute a portion of RBA.

A quantitative, image-based analysis of the spreading performance of PolyArylEtherKetone polymer powders during Powder Bed Fusion Additive Manufacture

Powder spreadability in the powder bed fusion process is normally visually assessed by the machine operator through repeat trials at room temperature or elevated temperatures. Some studies used powder rheology results as an indicator of the powder spreadability. This study presents a novel method of image-based analysis for the assessment of polymer spreading quality for powder bed fusion and demonstrates that the subjective assessment of the machine operator can be replaced by quantitative and measurable data. Twenty-four developmental grade PolyArylEtherKetone powders were tested. Images of the powder bed surface were analysed in MATLAB and the relationships with the powder rheology established through statistical analysis. The two methods for calculating surface deviations from variations in the greyscale images showed to be sensitive to the recoater travel and presented a strong correlation with the Normalised Aeration Sensitivity (NAS), a powder rheology parameter identified in a previous study as the most significant parameter able to categorise powder flow and spreadability based on a yes/no response.

A Digital Engineering Analysis of an Additively-Manufactured Turbine Vane

Abstract Additive manufacturing (AM) has transformed the ability to accelerate gas turbine component research and development at a fraction of the cost and time associated with conventional manufacturing. However, whereas prior works have assessed manufacturing variability in cast turbine airfoils, limited data are available to understand the impact of as-built deviations in AM turbine parts. As metal additive airfoils are becoming more prevalent in research turbine architectures, it is increasingly important to understand the effects of potential hardware deviations specific to additively-manufactured parts. With this goal in mind, the current study utilizes a digital engineering approach to evaluate the aerodynamic impact of surface deviations on a high-pressure turbine vane design created for research purposes. Reynolds-averaged Navier–Stokes-based computational fluid dynamics studies derived from structured light scans of as-built turbine vanes are used to quantify performance relative to design-intent geometries. Further computational analyses compare results from individual serialized parts with an average vane doublet geometry serving as a surrogate for the entire wheel. Particular emphasis in the study focuses on external surface defects caused by internal cooling features that are inherent through additive manufacturing and how these features can impact the vane performance. Ultimately, this study identifies specific regions of the vane that are subject to increased sensitivity, which benefits future designers intending to use AM as a tool for turbine research and development.

Assessment of clinical reproducibility for intraoral scanning on different anatomical regions for the complete maxillary edentulous arch with two intraoral scanners

ObjectivesThere are no in vivo studies comparing multiple intraoral scanners for the completely edentulous maxilla to PVS impressions. Investigations comparing intraoral scanners to polyvinyl siloxane impressions focus on comparing the overall scan and not individual anatomical regions. This study aims to evaluate two intraoral scanners and compare the results for different anatomical regions on the completely edentulous maxillary arch. Materials and methodsNineteen patients were recruited with a completely edentulous maxilla. A custom tray was constructed, and a sectional border moulded polyvinyl siloxane impression was made then scanned. An intraoral scan of the edentulous maxilla with a Trios 4 (3Shape, B/V) and Medit i700 (Medit corporation) was then captured. The scans were analysed for negative and positive surface deviations along with root mean square for distinct anatomical regions compared to the polyvinyl siloxane impression. A two-way ANOVA followed by Tukey HSD post hoc tests for each scanner was conducted for all anatomical regions to determine differences between the regions. ResultsThere was no significant difference between the two intraoral scanners included in this study for all anatomical regions or for the overall scan (0.435, 0.38), palatal vault (0.18, 0.181), ridge (0.218, 0.209), and post dam (0.233, 0.229) anatomical regions. Significantly higher deviation (p<0.05) was observed for the peripheral regions (0.607, 0.557) for each intraoral scanners Trio 4 and Medit i700. ConclusionDifferent intraoral scanners can capture all areas of a completely edentulous maxilla consistently, when compared to a polyvinyl siloxane impression, apart from the peripheries. Clinical significanceCare should be taken when scanning the peripheries. These regions are problematic to capture with an intraoral scanner. Border moulding should still be considered the optimal impression technique for the completely edentulous maxilla. The intraoral scanners investigated did not make a difference for the anatomical regions investigated.

An in-vitro study on accuracy of modular templates used to fully guide implants in combination with bone reduction for complete arch restorations: Experts versus students

ObjectivesThis in-vitro study evaluates the accuracy of modular surgical templates used to fully guide implants in combination with bone reduction, performed by expert and students, for complete arch restorations. MethodsAll the procedures were performed by dental students of the final year and an expert clinician, on twelve edentulous mandible models. A virtual implant planning, simulating a complete arch restoration on six implants were performed. Three different surgical guides were designed and printed to allow conventional fully guided implant placement (group 1); fully guided implant placement with modular guides (group 2); and fully guided implant placement after bone reduction, with similar, modular guides (group 3). After implant placement, optical scans of the study models were taken. Surface deviation and accuracy were evaluated and compared between groups and subgroups. ResultsA total of 12 surgical templates were used. Of these, Two templates in each group were used by two different students, while, the other six templates were used by an expert clinician as follows: one template with screwed anchor pins and one with pushed anchor pins in each group. A total of 72 implants were placed. Statistically significant difference was found between different template designs, when the implants were placed by an expert clinician. No statistically significant difference was found between expert and students, except the deviation in an angle value (students 2.13±1.46° versus expert 0.90±0.91°; P Value=0.0447) in the group 3. A statistically significant difference was found in favor of screwed anchor pins, in the group 1, in horizontal deviation (screwed pins 0.18±0.13 mm versus pushed pins 0.56±0.28 mm; P Value=0.0124; Table 5). No statistically significant difference was found between different template designs when the fully guided implants were placed by students, in both angle and horizontally (P=0.2787 and P=0.6601, respectively). A statistically significant difference was found between groups when the implants were placed by an expert clinician, with better value using screwed anchor pins, in the horizontal plane (P= 0.0293) but not in angle (P= 0.3380). ConclusionsModular templates provide a similar level of accuracy to conventional, one-piece guides. Screwed pins should be used to fix the base portion of the modular guides. Further clinical studies are needed to confirm these preliminary results. Clinical SignificanceModular surgical guides provide comparable accuracy to conventional, single-piece guides, however they offer more possibilities, helping in bone reduction and immediate loading procedures. Screwed anchor pins used to fix the base portion of the modular guides provide better final results than pushed pins.

Study on meshing and dynamic characteristics of herringbone gear pair considering tooth surface wear and modification

Due to errors and tooth surface wear of herringbone gear is inevitable. And tooth surface modification is the key technology to improve gear performance. Therefore, this paper studies the influence of tooth surface uneven wear and modification on herringbone gear pair's meshing and dynamic characteristics with errors. Firstly, herringbone gear pair meshing characteristic analysis model based on discrete tooth surface is established. Secondly, herringbone gear pair bending-torsion coupling dynamic characteristic analysis model considering friction is established, and the dynamic frictional force analysis process is given. Thirdly, combined with Archard's wear theory, the tooth surface uneven wear amount is obtained. The tooth surface uneven wear amount is substituted into meshing matrix as a tooth surface deviation. Finally, the meshing and dynamic characteristics of herringbone gear pair considering tooth surface wear and modification are studied by using the established analysis model of meshing characteristics and dynamic characteristics. The calculation results show that without tooth surface modification, tooth surface wear will deteriorate the meshing and dynamic characteristics rapidly. However, reasonable tooth surface modification can effectively improve meshing and dynamic characteristics of gear pair, so that the gear pair can still maintain stable transmission under wear condition.

Effect of build orientation on the fabrication trueness of additively manufactured implant-supported complete arch interim fixed prostheses.

To evaluate how build orientation affects the fabrication trueness of additively manufactured implant-supported complete arch prostheses by comparing them to subtractively manufactured high-impact polymer-based prostheses. An edentulous maxillary model with four implants at canine and first molar regions bilaterally was digitized (ATOS Core 80 5MP) to design a reference implant-supported complete arch prosthesis standard tessellation language file (RF-STL). The STL file was used to manufacture prostheses additively in five different orientations according to the build platform (AM-0, 0-degree; AM-15, 15-degree; AM-30, 30-degree; AM-45, 45-degree; AM-90, 90-degree) or subtractively (SM-HIP, control) (n = 10). The prostheses were digitized with an intraoral scanner (Trios 3) to generate their STLs (TF-STL). After superimposing TF-STLs over the RF-STL with a metrology-grade analysis software program (Geomagic Control X), surface deviations at four regions (overall, occlusal, overall without occlusal, and abutments), linear deviations at each abutment site, and interimplant distance deviations (canine-to-molar, canine-to-canine, and molar-to-molar) were calculated. One-way analysis of variance and Tukey HSD tests were used for the statistical analyses (α = 0.05). AM-90 mostly had the highest surface deviations, while AM-0 had the lowest overall, and lowest overall without occlusal region deviations (p ≤ 0.022). SM-HIP had the lowest occlusal region deviations (p < 0.001). AM-90 had the highest linear deviations (p < 0.001). AM-15 had higher canine-to-molar deviations than SM-HIP (p = 0.042). SM-HIP had the highest canine-to-canine deviations, while AM-90 had higher deviations than AM-0 and AM-30 (p ≤ 0.026). AM-45 and AM-90 had the highest and AM-0 had the lowest molar-to-molar deviations (p ≤ 0.013). AM-0 mostly had higher trueness and AM-90 mostly had lower trueness within tested outcomes. Additively manufactured prostheses mostly had lower canine-to-molar distances and higher molar-to-molar distances, whereas SM-HIP prostheses consistently had higher distances than the design file.

Visual reconstruction of milling workpiece surface topography based on phase shifting and complementary gray code

When the surface texture of a workpiece is extremely fine, cameras struggle to accurately capture depth information, making conventional machine vision methods insufficient for achieving micrometer-scale three-dimensional surface reconstructions. To overcome this limitation, the study focuses on high-precision 3D reconstruction of the surface morphology of milled workpieces. Given the smoothness of milled surfaces, their susceptibility to overexposure, and the difficulty in extracting depth information from two-dimensional image pixels, the paper proposes a novel method that combines phase-shifting with complementary Gray code to achieve micrometer-level surface reconstruction. The superiority of this method over traditional phase-shifting techniques is demonstrated through comparisons of overall morphology, two-dimensional power spectral density (2D PSD), and the average deviations of sampled surfaces. Results show that the proposed method reduces the average relative error in surface deviations by 25.89% compared to traditional techniques. Furthermore, cross-sectional analyses reveal that the reconstructed point cloud surface more closely mirrors the actual peak-to-valley characteristics of the real surface. Experimental results confirm that this method effectively captures the surface features of milled workpieces, indicating broad potential for applications in precision manufacturing.

Scan accuracy of wireless intraoral scanners while digitizing a combined scan body-healing abutment system

ObjectivesTo investigate the accuracy (trueness and precision) of wireless and wired intraoral scanners (IOSs) when scanning an implant with the combined healing abutment-scan body (CHA-SB) system. MethodsA partially edentulous mandibular model with a CHA-SB at the right first molar site was digitized with 2 wireless (NeoScan 2000 (NW) and TRIOS 4 wireless (T4 W)) and 2 wired (NeoScan 1000 (N) and TRIOS 4 wired (T4)) IOSs 44 times in total (n = 11). The reference scan file was generated by digitizing the same master model and CHA-SB with an industrial-grade optical scanner. All files were imported into a metrology-grade analysis software program to evaluate the surface (root mean square, RMS), linear, and angular deviations of the top part of the SB. The average deviation values defined the precision of the scans. The data were statistically analyzed (α = 0.05). ResultsIOS type affected the surface and angular deviations and the precision (linear deviations on the x-axis) of the scans (p ≤ 0.043). T4 W had lower RMS than N and T4 (p ≤ 0.031). T4 had higher angular deviations than N on the XZ plane and had the lowest angular deviations on the YZ plane (p ≤ 0.011). T4 W scans had higher precision than N scans (p = 0.024). ConclusionDespite some differences in the trueness or precision of scans, tested IOSs mostly enabled similar scan accuracy. Regardless of the IOS, the implant scans had a tendency to tilt mesiobuccally, which can be considered clinically small. Clinical SignificanceTested wireless intraoral scanners may be suitable alternatives to their wired counterparts while digitizing an implant with a combined healing abutment-scan body system in the posterior region. However, the crowns fabricated from tested scans might require buccal, mesial, and occlusal surface veneering and distal surface adjustments.

Impacts of Material and Machine on the Variation of Additively Manufactured Cooling Channels

Abstract While additive manufacturing (AM) can reduce component development time and create unique internal cooling designs, the AM process also introduces several sources of variability, such as the selection of machine, material, and print parameters. Because of these sources, wide variations in a part's geometrical accuracy and surface roughness levels can occur, especially for small internal cooling features that are difficult to post-process. This study investigates how the selection of machine and material in the AM process influences variations in surface quality and deviations from the design intent. Two microscale cooling geometries were tested: wavy channels and diamond-shaped pin fins. Test coupons were fabricated with five different additive machines and four materials using process parameters recommended by the manufacturers. The as-built geometry was measured non-destructively with computed tomography scans. To evaluate surface roughness, the coupons were cut open and examined using a laser microscope. Three distinct roughness profiles on the coupon surfaces were captured including upskin, downskin, and channel walls built at 90 deg to the build plate. Results indicated that both material and machine contribute to producing different roughness levels and very different surface morphologies. The roughness levels on the downskin surfaces are significantly greater than on the upskin or sidewall surfaces. Geometric analysis revealed that while the hydraulic diameter of all coupons was well captured, the pin cross section varied considerably. Along with characterizing the coupon surfaces, cooling performance was investigated by experimentally measuring friction factor and heat transfer. The variations in surface morphology as a function of material and machine resulted in heat transfer fluctuating by up to 50% between coupons featuring wavy channels and 26% for coupons with pin fin arrays. Increased arithmetic mean surface roughness led to increased heat transfer and pressure drop; however, a secondary driver in the performance of the wavy channels was found to be the roughness morphology, which could be described using the surface skewness and kurtosis.

Impact of scanning strategies on the accuracy of virtual interocclusal records in partially edentulous arch using intraoral scanner: an in vitro study

PurposeTo evaluate the scanning strategies affecting the accuracy of virtual interocclusal records (VIR) in partially edentulous arches using an intraoral scanner in vitro.MethodsA reference model of a partially edentulous arch with implant analogs in positions 45,46 and 47 was constructed. Six pairs of 1-mm diameter metal beads were placed on the gingival tissue as markers for measurement. Four scanning strategies were tested: Quadrant-arch Scan (group 1), Quadrant-arch Scan with Auxiliary occlusal devices (AOD) (group 2), Full-arch Scan (group 3), Full-arch Scan with AOD (group 4). The model was digitalized with a lab scanner as a reference and 15 scans were obtained for each group. The accuracy of VIR was assessed by comparing the experiment data to the reference digital model.ResultsThe mean surface deviations of VIR for Groups 1–4 were 89.4 ± 105.2 μm,95.6 ± 132.8 μm,152.3 ± 159.7 μm and 107.6 ± 138.2 μm respectively. Quadrant-arch scans resulted in lower errors of VIR than full-arch scan (P < 0.001). There was a significant interaction between the AOD and scanning span (P = 0.017). The Quadrant-arch scan with AOD (group 2) produced the least error in the distally extended edentulous area.ConclusionsQuadrant-arch scans showed better accuracy of VIR than full-arch scans across all tooth positions. The combination of AOD and quadrant-arch scan further enhances VIR accuracy in distally extended edentulous areas.

On gear time-varying meshing stiffness calculation considering indexing feeds and processing characteristics of gear shaping processing

Gear shaping causes processing characteristics on gear tooth surfaces (PCGTS), e.g., gear tooth surface deviation (GTSD) and processing textures (PT), which can affect gear meshing performances. Gear shaping simulation is operated to obtain PCGTS with different indexing feeds. An improved contact stiffness method of gear tooth surfaces is developed based on a wedge-shaped contact form to obtain tooth contact stiffness with PT caused by gear shaping. An improved time-varying meshing stiffness (TVMS) method for gears manufactured by gear shaping is developed to calculate TVMS of gears with GTSD and PT under different indexing feed conditions. Effectiveness of the improved TVMS method is validated using the finite element method. Analysis results of the proposed contact stiffness method of gear tooth surfaces indicate that PT caused by gear shaping can aggravate fluctuations of gear tooth contact stress. Analysis results of the proposed TVMS method for gears also indicate that GTSD of gear tooth surfaces caused by gear shaping can reduce their TVMS. The proposed TVMS method of gears can effectively analyze TVMS of gear tooth surfaces via gear shaping and evaluate processing settings of gear shaping to improve gear meshing performances.

Sensitivity analysis and compensation for tooth surface deviation of spiral bevel gear machine tool

To analyze the quantitative mapping relationship between the geometric errors of the five-axis CNC machine tool and the tooth surface deviation of spiral bevel gears, and identify the key geometric errors that affect the machining deviation of the spiral bevel gear tooth surface, a sensitivity analysis method for tooth surface machining deviation of spiral bevel gear based on screw theory and EFAST method is proposed. Firstly, the machining model of the spiral bevel gear tooth surface based on the five-axis CNC machine tool is established. Then, the geometric error transfer model of the machine tool is established based on the screw theory. Combined with the EFAST global sensitivity analysis method, the key geometric errors that affect tooth surface deviation are identified. Finally, the reliability and effectiveness tests are performed by comparing the results to the local sensitivity analysis method and simulating compensation for the key geometric errors. The result of compensation shows that the tooth surface deviation is reduced significantly according to global sensitivity analysis. The feasibility of applying sensitivity analysis to control the tooth surface deviation of spiral bevel gears has been demonstrated.

Моделирование и оптимизация процесса накатывания роликом AL6061-T6 для достижения минимального отклонения от круглости, минимальной шероховатости поверхности и повышения ее микротвердости

Introduction. Roller burnishing is one of the most common methods of improving the surface quality of parts, wear resistance, microhardness, and corrosion resistance. The process involves compressing and smoothing the workpiece using the pressure of a hardened roller. It is often used to improve part performance and lifespan in sectors including automotive, aerospace, and medical equipment manufacturing. The literature reviewed shows that the roller burnishing process effectively improves the overall surface quality and hardness of the workpiece. In addition, roller burnishing is considered as an affordable method to enhance the functionality and robustness of machined parts by reducing the likelihood of surface defects such as like scratches and cracks. However, very few studies have been reported on the modeling and optimization of roller burnishing of Al6061-T6 for minimum surface roughness, better microhardness, and roundness. The methods of investigation. In the current work, roller burnishing of Al6061-T6 is modeled and optimized for superior microhardness, roundness, and minimal surface roughness. Under dry-cutting conditions, the performance of roller burnishing of Al6061 specimens is assessed in terms of process factors such as cutting speed, feed, and number of passes. Mathematical models to predict the surface roughness, microhardness, and deviation in roundness are developed based on the experimental results. Results and Discussion. The coefficient of correlation for the developed models is found to be close to 0.9, which indicates that it can be reliably used to predict and optimize the roller burnishing of the Al6061-T6. According to this study, the use of the following cutting parameters leads to the lowest variation in roundness (4.282 µm), the better microhardness (119.2 Hv), and the lowest surface roughness (0.802 µm): cutting speed 344 rpm, feed 0.25 mm/rpm and four passes. Further, the study reveals that increasing the number of passes (beyond four) does not significantly improve the surface roughness or microhardness. However, it does lead to a slight increase in the roundness deviation. Therefore, in order to achieve optimal results, it is recommended to use a maximum of four passes during roller burnishing of Al6061 specimens under dry cutting conditions. These results imply that roller burnishing can effectively improve the overall quality and hardness of the workpiece surface. In addition, roller burnishing is considered as an affordable method to increase the functionality and robustness of machined parts by reducing the likelihood of surface defects like scratches and cracks.

Digital analysis of fabrication accuracy and fit in additively and subtractively manufactured implant-supported fixed complete dentures

ObjectivesTo digitally evaluate the trueness and fit of additively and subtractively manufactured fixed complete dentures in materials intended for definitive use. MethodsAn edentulous maxillary model with implants at the left first molar, left canine, right canine, and right first molar site was digitized and a fixed complete denture was designed. This design was used to fabricate fixed dentures in an additively manufactured resin for definitive use (AM), a high-impact polymer composite (SM-CR), and a strength gradient zirconia (SM-ZR) (n = 10). Each fixed denture was digitized and the surface (overall, occlusal, except occlusal, and abutments), linear, and interimplant distance deviations were analyzed. The fit was assessed with the triple-scan protocol. Data were analyzed with Welch analysis of variance and Games-Howell tests (α = 0.05). ResultsSM-ZR led to lower overall deviations than AM, which had the highest occlusal and the lowest abutments deviations (P ≤ 0.007). SM-ZR had the lowest occlusal and SM-CR had the highest except occlusal deviations (P ≤ 0.002). AM mostly had higher linear and SM-CR mostly had higher interimplant distance deviations (P ≤ 0.043). AM led to the highest marginal gap at the left canine site, while SM-CR had the highest and SM-ZR had the lowest gaps at the right canine site (P ≤ 0.022). ConclusionsSM-ZR dentures mostly had trueness and marginal fit similar to or better than the other groups. Tested fixed complete dentures were mostly smaller than the design file in terms of interimplant distances.