CAD Surface Research Articles

Minimal surface-guided higher-order mesh generation for CAD models

This paper presents a novel method for generating higher-order meshes for CAD surfaces by leveraging minimal surface theory to improve element shapes. We explore the concept of higher-order mesh distortion through deformation gradients and introduce an energy function designed to minimize the surface area of these meshes, providing a theoretical justification for its effectiveness in untangling. The process of mesh generation starts with segmenting CAD surfaces into linear elements, followed by the insertion of higher-order nodes within these elements. These nodes are then projected onto the CAD surface to form the initial higher-order elements. By optimizing energy functions related to minimal surfaces and the projection distances, we achieve high-quality, geometrically accurate higher-order surface meshes. Our method has been validated on complex geometries, showcasing its potential in creating effective higher-order meshes for industrial CAD models.

Modified experimental adhesive with sepiolite nanoparticles on caries dentin treated with femtosecond laser and photodynamic activated erythrosine. An in vitro study

AimTo assess the effect of CAD surface conditioners and their effect on Ra and SBS of tooth-colored filling material adhered to CAD surface with adhesive modified with 1 % Sep-NPs. Also, the DC of modified EA and its effect on the rheological properties. MethodsNinety human molars with carious extension up to the middle third of occlusal dentin were included. The teeth were then arbitrarily allocated into three groups based on the type of surface conditioning received (n = 30) Group 1 (PA), Group 2 (FS laser), and Group 3 (Ery PS). Ten samples from each group underwent Ra analysis using a stylus profiler. Twenty samples from each cohort were distributed into two subcategories based on the application of unmodified EA (A) and Sep-infiltrated EA (B). Composite restoration was built followed by SBS and failure mode analysis. Scanning electron microscopy and Energy dispersive X-ray EDX were assessed of sepiolite NPs. Degree of conversion (DC) and rheological analysis of the modified adhesive and unmodified adhesive were also performed. One-way analysis of variance (ANOVA) and the Tukey post hoc test were employed to conduct comparisons between the different groups. ResultsThe highest score of Ra and bond strength were displayed by Group 1B (PA + Sep-NPs filled EA) (17.32 ± 1.43 MPa) samples. Nevertheless, the lowest values were established by Group 3A (Ery-PS + EA) (13.45 ± 0.80 MPa) treated teeth. An increase in Ra resulted in a rise in SBS.DC decreased with the incorporation of 1 % Sep-NPs in EA compared to unmodified EA. ConclusionConditioning of CAD with PA and FS laser shows high surface roughness and favorable adhesion to experimental adhesive modified with 1 % Sep-NPs. Modified adhesive with 1 % Sep-NPs decreases DC and rheological properties.

Carbon nanotube-modified adhesive to caries affected dentin conditioned with Nd: YAP laser, phosphoric acid, and photoactivated-erythrosine

AimDentin conditioned with phosphoric acid (PA) Nd: YAP laser, and photoactivated-Ery(Erythrosine) on microleakage, shear bond strength (SBS) degree of conversion (DC), and rheological assessment of adhesive-infused with carbon nanotubes (CNTs). Material and methodCarious ninety-six human mandibular molars were included. Specimens were disinfected and allocated into three groups based on surface pretreatment (n = 32) Group 1 (PA), Group 2 (Nd: YAP) laser, and Group 3 (Photoactivated-Ery). Conditioned groups were further divided into two 2 subgroups based on the application of unmodified ERA and CNTs-modified ERA. Composite restorations were placed on the CAD surface and thermal aging of the samples was performed. The microleakage assessment was conducted using a dye penetration test. Universal testing machine (UTM) assessed SBS bond failure was evaluated using a stereomicroscope. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analyses of CNT, and Fourier Transform Infrared FTIR of adhesives were performed. One-way ANOVA and Tukey post hoc analyzed the outcomes. ResultsGroup 1B samples (PA+ CNTs modified adhesive) presented the minimum marginal leakage and highest bond integrity. Group 2A (Nd:YAP laser+Unmodified adhesive) displayed the maximum scores of microleakage and lowest bond strength. ConclusionPhotoactivated Ery-PS can serve as an alternative to phosphoric acid for conditioning CAD. Incorporating CNT in adhesive significantly enhanced bond integrity and marginal seal with no significant difference in DC.

NeurCADRecon: Neural Representation for Reconstructing CAD Surfaces by Enforcing Zero Gaussian Curvature

Despite recent advances in reconstructing an organic model with the neural signed distance function (SDF), the high-fidelity reconstruction of a CAD model directly from low-quality unoriented point clouds remains a significant challenge. In this paper, we address this challenge based on the prior observation that the surface of a CAD model is generally composed of piecewise surface patches, each approximately developable even around the feature line. Our approach, named NeurCADRecon , is self-supervised, and its loss includes a developability term to encourage the Gaussian curvature toward 0 while ensuring fidelity to the input points (see the teaser figure). Noticing that the Gaussian curvature is non-zero at tip points, we introduce a double-trough curve to tolerate the existence of these tip points. Furthermore, we develop a dynamic sampling strategy to deal with situations where the given points are incomplete or too sparse. Since our resulting neural SDFs can clearly manifest sharp feature points/lines, one can easily extract the feature-aligned triangle mesh from the SDF and then decompose it into smooth surface patches, greatly reducing the difficulty of recovering the parametric CAD design. A comprehensive comparison with existing state-of-the-art methods shows the significant advantage of our approach in reconstructing faithful CAD shapes.

Topology optimization of curved thick shells using level set method and non-conforming multi-patch isogeometric analysis

We present a novel framework for topological shape optimization of curved non-conforming multi-patch and trimmed thick-shells subjected to external loads. Our method integrates the level set method (LSM) with a diffuse interface, a Hadamard shape derivative, and multi-patch isogeometric analysis (IGA) into a gradient descent algorithm to systematically capture the evolution of the shape. This integration enables us to directly manipulate CAD-compatible geometries and analysis techniques and to obtain the results as a CAD surface. The novelty lies in the utilization of multi-patch IGA models based on NURBS functions, which allows us to simultaneously maximize the stiffness and minimize the volume of the shell by searching for an optimal material distribution within its middle surface. The material is modeled under a small strain assumption in linear elasticity using a Reissner–Mindlin kinematic shell model in plane stress. The effectiveness of our approach is demonstrated on several curved conforming and non-conforming multi-patch geometries in 3D.

Effect of Different Modification Techniques on Mechanical and Physical Properties of E-Max CAD Substrate

The world's best-selling glass-ceramic is IPS E.Max CAD. It is known for its versatile applications and is appropriate for the effective manufacturing of comprehensive dental restorations. This experimental study aimed to evaluate the morphological changes, surface roughness, and micro-hardness after modification techniques with KHF2 and NH4HF2 acid etching on e-max cad substrate. Materials and Methods: Forty disc shape of E.Max CAD specimens (thickness 3mm and diameter 10mm) were fabricated and divided into four groups according modification techniques (control group, sandblasting by 70µm of Al2O3, etching with 70 mg of KHF2 and etching with 70mg of NH4HF2),10 samples for each group. Surface roughness, micro-hardness, and microstructure changes of e-max CAD substrate have been measured. Results: The higher mean value for the surface roughness (Ra) was in the group (ECNH4HF2), followed by (ECKHF2) whereas the lowest mean value of surface roughness was in the group (ECC) followed by (ECSB). While for the micro-hardness test, the (ECKHF2) group demonstrated the highest mean value in comparison with other treated groups. Finally, SEM results for both untreated and sandblasted groups revealed there is a smooth and no deep morphological change for their surfaces. While the SEM analysis revealed that the e-max cad surfaces after KHF2 and NH4HF2 showed rough morphology with fine grains result and random porosities. Conclusions: Etching with KHF2 and NH4HF2 yielded higher microstructure changes and roughness than other techniques. While KHF2 etchant was more effective on E.Max CAD surface micro-hardness in comparison with other treated groups.

CAD/CSG dual-layer hybrid geometric Monte Carlo particle transport method

The CAD and CSG hybrid modeling for the Monte Carlo particle transport simulation improves the geometric accuracy and calculation efficiency. We propose a CAD/CSG dual-layer hybrid geometric Monte Carlo particle transport method, which divides the geometry into two layers, the CAD layer and the CSG layer, and overlaps them to build up the hybrid geometric model for particle transport simulation. The new method’s accuracy is verified to prove that the new method has the same accuracy as that of CSG modeling alone or CAD modeling alone. The efficiency advantages of the new method are tested to know that increasing the number of CSG surfaces and reducing the number of CAD surfaces improve the efficiency. The efficiency advantages begin to appear compared to CAD modeling alone when the ratio of the number of CSG surfaces to the number of CAD surfaces reaches 4:6, about an improvement of 10%. Increasing the proportion of CSG surfaces improves the efficiency advantages, and smaller geometric tolerances accentuate the efficiency advantage.

Alternating size field optimizing and parameterization domain CAD model remeshing

Tessellating CAD models into triangular meshes is a long-lasting problem. Size field is widely used to accommodate varieties of requirements in remeshing, and it is usually discretized and optimized on a prescribed background mesh and kept constant in the subsequent remeshing procedure. Instead, we propose optimizing the size field on the current mesh, then using it as guidance to generate the next mesh. This simple strategy eliminates the need of building a proper background mesh and greatly simplifies the size field query. For better quality and convergence, we also propose a geodesic distance based initialization and adaptive re-weighting strategy in size field optimization. Similar to existing methods, we also view the remeshing of a CAD model as the remeshing of its parameterization domain, which guarantees that all the vertices lie exactly on the CAD surfaces and eliminates the need for costly and error-prone projection operations. However, for vertex smoothing which is important for mesh quality, we carefully optimize the vertex's location in the parameterization domain for the optimal Delaunay triangulation condition, along with a high-order cubature scheme for better accuracy. Experiments show that our method is fast, accurate and controllable. Compared with state-of-the-art methods, our approach is fast and usually generates meshes with smaller Hausdorff error, larger minimal angle with a comparable number of triangles.

Phycocyanin-loaded silver nanoparticles activated with photodynamic therapy and Nd: YAG laser for caries-affected dentin disinfection: Impact on Streptococcus mutans survival rate and shear bond strength to the tooth-colored restorative material

AimsTo assess the impact of various cavity disinfectants PC-PDT (Phycocyanin activated by Photodynamic therapy), PC@AgNPs-PDT (Phycocyanin and silver nanoparticles activated by PDT), and Nd: YAG laser on the survival rate of S.mutans and the bond integrity of composite restoration MethodsSixty human mandibular molars that scored 4 and 5 based on ICDAS criteria were included. The infected dentin was removed while the CAD was preserved based on visual, tactile, and staining assessment. S.mutans were cultured on the CAD of twenty samples. All the specimens were indiscriminately distributed into four groups based on cavity disinfection (n=20 each includes n = 5 each group incubated with S.mutans) Group 1: CHX, Group 2: Nd:YAG laser, Group 3: PC-PDT and Group 4: PC@AgNPs-PDT. S.mutans survival rate was assessed for each group(n = 5). Forty samples underwent composite bonding for SBS and failure mode assessment using universal testing machine (UTM) and stereomicroscope. The calculations for the mean and standard deviation (SD) and their comparison among different groups were performed using a one-way analysis of variance (ANOVA) and the Tukey post hoc test (p ≤ 0.05) ResultsCAD surface treated disinfected with PC@AgNPs-PDT yielded the lowest survival rates (0.13 ± 0.05 CFU/ml) and highest SBS (17.23 ± 1.45 MPa). Group 1 (CHX) unveiled the highest survival rate of S.mutans (0.33 ± 0.12 CFU/ml). However, Group 2 (Nd:YAG Laser) (11.87 ± 0.67 MPa) presented the lowest SBS ConclusionThe combination of Phycocyanin loaded with silver nanoparticles and activated with Photodynamic therapy demonstrates the highest antimicrobial potential and bond strength of composite restorations.

The Impact of Adhesive-Containing Nanoparticles of ZrO2and TiO2 on Antimicrobial Effectiveness, the Strength of Bonding, and the Extent of Microleakage in Dentin Affected by Caries

Aims: Zirconium oxide (ZrO2) and Titanium dioxide (TiO2) nanoparticles (NPs) in-cooperated in a three-step etch and rinse adhesive against Lactobacillus survival rate, shear bond strength (SBS) and marginal leakage on CAD. Methods: Ninety premolars having occlusal carries to the middle third of the dentin were included. Inoculation of Lactobacillus on CAD surface was performed on 30 samples. The remaining 60 samples were then divided into three groups based on primer applied in three steps etch and rinse (n = 20) Group 1 (Optibond FL), Group 2: (Optibond FL + TiO2), and Group 3: (Optibond FL + ZrO2). The survival rate was assessed on the 30 samples. The remaining 60 samples were applied with Optibond FL bonding agent and composite restorative material. Microleakage, SBS, and failure mode were analyzed. The means and standard deviations (SD) were compared utilizing ANOVA followed by a post hoc Tukey multiple comparison test. Results: Specimens in Group 1 demonstrated the maximum numbers of Lactobacillus species and marginal leakage values. Group 2 specimens displayed the minimum count of bacteria, lowest microleakage scores, and highest bond values. However, Group 1 specimens showed the lowest bond integrity. Conclusions: ZrO2 and TiO2 NPs filled dental adhesive demonstrated better antimicrobial efficacy and bond strength. They also cause a reduction in marginal leakage at the resin dentin interface.

Caries affected disinfection using Phycocyanin activated by PDT, Holy Basil, and Ti-sapphire laser on adhesive bond strength, microleakage, and bond failure

AIMTo investigate the effect of different cavity disinfectants, Phycocyanin (PC), Ocimum Sanctum (OS), and Ti Sapphire Laser, on the bond integrity and microleakage of resin restorations. Material and method60 human mandibular molars were extracted and prepared based on ICDAS scores of 4 and 5. To obtain the CAD surface, a visual examination was supported by tactile sensation and a dye for caries detection. Samples were randomly allocated into 4 groups based on cavity disinfectants applied (n = 15). Group 1: Specimens disinfected with CHX, Group 2: Specimens disinfected with Ti sapphire laser, Group 3: Specimens disinfected with Phycocyanin activated by Photodynamic therapy, and Group 4: Specimens disinfected with OS. Following the disinfection of the CAD surfaces, composite bulk-fill restorative material was bonded to each specimen and all samples were subjected to thermocycling. Ten samples from each group underwent SBS testing performed on a universal testing machine. Five samples were subjected to a microleakage analysis. ResultThe maximum microleakage scores were displayed by Group 3: PC (0.521 nm) treated specimens. Whereas, and minimum microleakage was exhibited by Group 4: OS (0.471 nm). Group 4: OS (23.06±0.21 MPa) treated group displayed the maximum bond scores of resin adhesive to the CAD surface. However, Group 3: PC (21.67±0.24 MPa) treated specimens exhibited the lowest bond scores. Failure mode analysis revealed that among all the investigated groups the predominant type of failure was cohesive failure i.e., Group 1 (80%), Group 2 (80%), Group 3 (70%), and Group 4 (90%). ConclusionOcimum Sanctum, Phycocyanin activated by Photodynamic therapy, and Ti-sapphire laser for disinfection of caries-affected dentin have shown promise in terms of improved bond strength and reduced microleakage

Hybridized isogeometric method for elliptic problems on CAD surfaces with gaps

We develop a method for solving elliptic partial differential equations on surfaces described by CAD patches that may have gaps/overlaps. The method is based on hybridization using a three-dimensional mesh that covers the gap/overlap between patches. Thus, the hybrid variable is defined on a three-dimensional mesh, and we need to add appropriate normal stabilization to obtain an accurate solution, which we show can be done by adding a suitable term to the weak form. In practical applications, the hybrid mesh may be conveniently constructed using an octree to efficiently compute the necessary geometric information. We prove error estimates and present several numerical examples illustrating the application of the method to different problems, including a realistic CAD model.

Disinfection of caries-affected dentin using activated vitamin B2 and diode laser with total-etch technique. An assessment of adhesive bond

AimThe present study aims to evaluate the bond integrity of composite restoration bonded to CAD after disinfection using pineapple peel extract (PPE) Diode laser (DL) and riboflavin (RF) activated by photodynamic therapy (PDT). Material and MethodsForty human permanent mandibular molars were collected, disinfected, and mounted in poly-vinyl pipes. Carious infected dentin was removed and CAD was disinfected. Samples were divided into 4 groups based on disinfection. Group 1: CAD disinfected with CHX; group 2: CAD disinfected with diode laser; CAD disinfected with PPE and CAD sterilized with riboflavin. Following disinfection, CAD surfaces were applied with the etch-and-rinse adhesive system and bonding agent and restored with a composite restoration. Samples were placed in a thermocycler to simulate oral aging and then mounted on the universal testing machine (UTM) for shear bond strength (SBS) testing. Failure mode was assessed using a steriomicroscoscope at 40X magnification. One-way analysis of variance (ANOVA) compared the mean SBS and failure type obtained to identify intergroup differences. Similarly, for multiple group comparison, the Tukey HSD test was used keeping the level of significance at 0.05. ResultsCAD disinfected with chlorhexidine (CHX) established the highest bond integrity of the restoration. However, group 2 CAD disinfected with DL displayed the lowest bond values. It was also observed that dentin disinfected using CHX demonstrated comparable SBS values to CAD disinfected with PPE and CAD disinfected with RF. ConclusionRF and PPE displayed comparable outcomes of SBS of composite restoration bonded to CAD to that of CHX. DL displayed lower bond integrity than the other investigated groups. Further studies are recommended to deduce the findings of the existing study.

Algorithm of CAD Surface Generation for Complex Pipe Model in Industry 4.0 Background.

The current pipeline surface generation algorithm cannot get the angle information of the corner of complex pipeline surface, which leads to the poor accuracy of the algorithm, the slow speed of 3D point cloud intelligent mosaic, and the large number of effective points. Therefore, a CAD surface generation algorithm for complex pipeline model under the background of Industry 4.0 is designed, extracting and rendering the wireframe model and extracting background of the complex pipeline video. We obtain the angle information of the corner points of the complex pipeline surface, extract and match the feature of the dense point cloud, and construct the 3D point cloud data mosaic model. The pipe surface is generated by using double-nodal B-spline. The experimental results show that the precision and stability of the proposed method are high. In the early stage, the proposed method uses ISS feature extraction algorithm to extract feature of point cloud data, which improves the positioning accuracy effectively and enhances the 3D point cloud intelligent stitching speed.

Initial solution estimation of one-step inverse isogeometric analysis for sheet metal forming with complex topologies

The one-step inverse isogeometric analysis method has been successfully applied in sheet metal forming with simple geometries. Generally, actual stamping parts frequently contain numerous trimmed NURBS-based CAD surfaces. The key step in sheet metal forming is to unfold the undevelopable CAD model onto a planar domain and obtain a good initial solution. In this study, we estimate the initial solution of stamping parts with complex topologies using an energy-based algorithm. The trimmed surface analysis technique and Nitsche’s method are adopted for trimmed and multi-patch isogeometric analysis. A new coordinate transformation system is used to avoid special treatment for negative angle and vertical wall problems, which are common in metal sheet forming. We demonstrate our algorithm with three examples and compare the results with one-step inverse isogeometric analysis of simple geometry or the traditional finite element method. These examples illustrate the performance of the new method and its applicability for the integration of design and analysis in sheet metal forming with complex topologies.

Design and development of ‘Mehndi’ applicator

‘Mehndi’ is a popular art form to decorate body parts like real tattoos quickly and temporarily without pain or long-term treatment. This work is towards the automation of ‘Mehndi’ craftsmanship. The strategy for automation of craftsmanship is to implement CAD/CAM as a tool in an integrated manner for the traditional piece of ‘Mehndi’ workmanship to produce this work in a quick span of time with the utmost precision. A 3D printing machine with extruder assembly on Z-axis drive, named as ‘Mehndi applicator’ has been designed and developed which has the ability to apply single layer of paste on hand as similar as to traditional form of craftwork performed by skilled person. This applicator is improvised with modern CAD/CAM tools. It makes use of a digital scanning device with Python programmable control to produce the scanned data of hand, which could be transformed into accurate CAD surface model and consequently into automated extruder tool path along the ‘Mehndi’ pattern projected on the hand surface.

Characteristics of Abs and Pla Material in 3D Printing for Car Backseat Headrest Hanger/Hook Model

Additive manufacturing (AM) is known as the technology which enable using a layer wise in fabrication of a complex part directly from CAD files without using any specific tooling. This manufacturing techniques offers many strategic advantages which include design freedom for the build of complex part geometries which cannot be made in other way, the ability to build functional part in a small size for the end user customization and its ability to do improvement for the expensive part in aerospace and other industries. The aim of this research is to study the effect of process parameter such as layer thickness, infill density and object orientation to the accuracy of printed part measurement with CAD model, surface roughness and mechanical strength of PLA and ABS material. Therefore, it is important to find the optimum value of dimensional accuracy, surface roughness and mechanical strength for both materials. To achieve the optimum value of dimensional accuracy, surface roughness and mechanical strength for both materials, Taguchi method L4 orthogonal array is used to conduct this experiment and Minitab 18 software will analyze the result and shows the best optimum value. The result from ANOVA analysis shows that object orientation gives highest contribution to the dimensional accuracy and surface roughness for both materials. Meanwhile, for mechanical strength layer thickness highly contributed to the ABS material and object orientation for the PLA material. A Car Backseat Headrest Hanger/Hook model is fabricated by the best optimal combination and level of process parameter of mechanical strength.

Multi-resolution 3D CNN for learning multi-scale spatial features in CAD models

Learning multi-scale spatial features from 3D spatial geometric representations of objects such as point clouds, 3D CAD models, surfaces, and RGB-D data can potentially improve object recognition accuracy. Current deep learning approaches learn such features using structured data representations such as volume occupancy grids (voxels) and octrees or unstructured representations such as graphs and point clouds. Structured representations are generally restricted by their inherent limitations on the resolution, such as the voxel grid dimensions or the maximum octree depth. At the same time, it is challenging to learn directly from unstructured representations of 3D data due to non-uniformity among the samples. A hierarchical approach that maintains the structure at a larger scale while still accounting for the details at a smaller scale in specific spatial locations can provide an optimal solution for learning from 3D data. In this paper, we propose a multi-level learning approach to capture large-scale features at a coarse level (for example, using a coarse voxelization) while simultaneously capturing flexible sparse information of the small-scale features at a fine level (for example, a local fine-level voxel grid) at different spatial locations. To demonstrate the utility of the proposed multi-resolution learning, we use a multi-level voxel representation of CAD models to perform object recognition. The multi-level voxel representation consists of a coarse voxel grid containing volumetric information of the 3D objects and multiple fine-level voxel grids corresponding to each voxel in the coarse grid containing a portion of the object boundary. In addition, we develop an interpretability-based feedback approach to transfer saliency information from one level of features to another in our hierarchical end-to-end learning framework. Finally, we demonstrate the performance of our multi-resolution learning algorithm for object recognition. We outperform several previously published benchmarks for object recognition while using significantly less memory during training.

Triangular and Quadrilateral Bezier Discretizations of Trimmed CAD Surfaces and Its Application to the Isogeometric Analysis

Triangular and Quadrilateral Bezier Discretizations of Trimmed CAD Surfaces and Its Application to the Isogeometric Analysis

An investigation on methods for axis detection of high-density generic axially symmetric mechanical surfaces for automatic geometric inspection

The detection of the symmetry axis from discrete axially symmetric surfaces is an interesting topic, which is transversal to various fields: from geometric inspection to reverse engineering, archeology, etc. In the literature, several approaches have been proposed for estimating the axis from high-density triangular models of surfaces acquired by three-dimensional (3D) scanning. The axis evaluation from discrete models is, in fact, a very complex task to accomplish, due to several factors that inevitably influence the quality of the estimation and the accuracy of the measurements and evaluations depending on it. The underlying principle of each one of these approaches takes advantage of a specific property of axially symmetric surfaces. No investigations, however, have been carried out so far in order to support in the selection of the most suitable algorithms for applications aimed at automatic geometric inspection. In this regard, ISO standards currently do not provide indications on how to perform the axis detection in the case of generic axially symmetric surfaces, limiting themselves to addressing the issue only in the case of cylindrical or conical surfaces. This paper first provides an overview of the approaches that can be used for geometric inspection purposes; then, it applies them to various case studies involving one or more generic axially symmetric surfaces, functionally important and for which the axis must be detected since necessary for geometric inspection. The aim is to compare, therefore, the performances of the various methodologies by trying to highlight the circumstances in which these ones may fail. Since this investigation requires a reference (i.e. the knowledge of the true axis), the methodologies have been applied to discrete models suitably extracted from CAD surfaces.