Salvatore Gerbino

Stereolithography in oral implantology: a comparison of surgical guides.

This article presents the use of stereolithography in oral implantology. Stereolithography is a new technology that can produce physical models by selectively solidifying an ultraviolet-sensitive liquid resin using a laser beam, reproducing the true maxillary and mandibular anatomic dimensions. With these models, it is possible to fabricate surgical guides that can place the implants in vivo in the same places and same directions as those in the planned computer simulation. A 70-year-old woman, in good health, with severe mandibular bone atrophy was rehabilitated with an over-denture supported by 2 Branemark implants. Two different surgical planning methods were considered: 1) the construction of a surgical guide evaluating clinical aspects, and 2) the surgical guide produced by stereolithographic study. The accuracy of surgical planning can reduce the problems related to bone density and dimensions. Furthermore, the stereolithographic study assured the clinicians of a superior location of fixtures in bone. Surgical planning based on stereolithographic technique is a safe procedure and has many advantages. This technologic advance has biologic and therapeutic benefits because it simplifies anatomic surgical management for improved implant placement.

Improving comfort of shoe sole through experiments based on CAD-FEM modeling

It was reported that next to style, comfort is the second key aspect in purchasing footwear. One of the most important components of footwear is the shoe sole, whose design is based on many factors such as foot shape/size, perceived comfort and materials. The present paper focuses on the parametric analysis of a shoe sole to improve the perceived comfort. The sensitivity of geometric and material design factors on comfort degree was investigated by combining real experimental tests and CAD-FEM simulations. The correlation between perceived comfort and physical responses, such as plantar pressures, was estimated by conducting real tests. Four different conditions were analyzed: subjects wearing three commercially available shoes and in a barefoot condition. For each condition, subjects expressed their perceived comfort score. By adopting plantar sensors, the plantar pressures were also monitored. Once given such a correlation, a parametric FEM model of the footwear was developed. In order to better simulate contact at the plantar surface, a detailed FEM model of the foot was also generated from CT scan images. Lastly, a fractional factorial design array was applied to study the sensitivity of different sets of design factors on comfort degree. The findings of this research showed that the sole thickness and its material highly influence perceived comfort. In particular, softer materials and thicker soles contribute to increasing the degree of comfort.

A computer-aided tool to quickly analyse variabilities in flexible assemblies in different design scenarios

In automotive and aeronautic fields, controlling the final shape of flexible assemblies (with sheet metal parts) is a key issue. Even assuming as known the shape errors in single manufactured parts, the assembly process can cause wide variability due to their flexibility and to the choice of fixtures and clamps as well as to the fastening technique adopted. Here it is strategic to analyse different assembly configurations at the beginning of the design phase and chose the one that assures less variability on the key characteristics to be achieved. This paper presents a FEM-based computer tool able to statistically analyse variations occurring in assembly processes of flexible parts. After assigning fixtures, clamping points, fastening joints and assembly sequence, the tool quickly outputs the statistical variability of the key characteristics. It is so possible to span a variety of design solutions predicting failures and controlling final variations. A case study will show how it works.

Flatness, circularity and cylindricity errors in 3D printed models associated to size and position on the working plane

The purpose of this paper is to assess the main effects on the geometric errors in terms of flatness, circularity and cylindricity based on the size of the printed benchmarks and according to the position of the working plane of the 3D printer. Three benchmark models of different sizes, with a parallelepiped and cylinder shape placed in five different positions on the working plane are considered. The sizes of models are chosen from the Renard series R40. Benchmark models are fabricated in ABS (Acrylonitrile Butadiene Styrene) using Zortrax M200 3D printer. A sample of five parts for each geometric category, as defined from the R40 geometric series of numbers, is printed close to each corner of the plate, and in the plate center position. Absolute Digimatic Height Gauge 0-450mm with an accuracy of ±0.03mm by Mitutoyo is used to perform all measurements: flatness on box faces, and circularity/cylindricity on cylinders. Results show that the best performances, in terms of form accuracy, are reached in the area center printable while they decrease with the sample size. Being quality a critical factor for a successful industrial application of the AM processes, the results discussed in this paper can provide the AM community with additional scientific data useful to understand how to improve the quality of parts which may be obtained through new generations of 3D printer.

FEM and BEM Stress Analysis of Mandibular Bone Surrounding a Dental Implant

In the present work the structural behaviour of a mandible with a dental implant, considering a unilateral occlusion, is numerically analysed by means of the Finite Element Method (FEM) and the Boundary Element Method (BEM). The mandible, whose CAD model was obtained by computer tomography scans, is considered as completely edentulous and only modelled in the zone surrounding the implant. The material behaviour of bone is assumed as isotropic linear elastic or, alternatively, as orthotropic linear elastic. With reference to the degree of osteo-integration between the implant and the mandibular bone, a partial osteo-integration is considered; consequently a nonlinear contact analysis is performed, with allowance for friction at the interface between implant and bone. A model of a commercial dental implant is digitised by means of optical 3D scanning process and fully reconstructed in all its geometrical features. Special attention is drawn to the mathematical reconstruction of the CAD model in order to facilitate the meshing process in the BEM environment and reduce the geometrical imperfections generated during the CAD to CAE translation process. The results of FEM and BEM analyses in terms of stress distribution on the mandible are compared in order to benchmark the two methodologies against accuracy and pre-processing efforts.

A CAD-Based Methodology for Motion and Constraint Analysis According to Screw Theory

The need for a designer to have a tool able to do motion and constraint analysis, to check for the under-constrained and/or over-constrained status of an assembly, is strategic in a design contest where several changes are made during the design process by using CAD. Traditional kinematic tools provide little information on over-constraints at 3D level. Screw theory has been already used in mechanical assemblies, in a top-down design, to do motion and constraint analysis. This theory is here used to analyze mechanical assemblies in the contest of a feature-based CAD system. The structure of the CAD assembly is captured and described as assembly graph, similar to Datum Flow Chain, through which the motion or constraint status of any part (in terms of twist and wrench matrices), can be obtained. The underlying algorithm is based on the Kirchoff’s rules successfully applied by Davies to mechanisms. How to automatically create the assembly graph, detect the useful loops and then write the loop kinematic equations is described. Three case studies are presented related to CAD assemblies of mechanisms built up in SolidWorks® CAD system by Dassault Systemes from which assembly constraints have been acquired.Copyright

BE analysis of shaft-hub couplings with polygonal profiles

Abstract In the mechanical transmission field, shaft–hub couplings with polygonal profiles play an interesting role because of their characteristics of self-alignment, lack of projecting elements (responsible for high stress concentration) and constructive compactness. Other characteristics, like transmission of static/oscillating torque load, even with small overall dimensions, and easy hub interchangeability, make such couplings competitive with the traditional ones based on keys and splined shafts. This work concerns a study on steel made polygonal couplings, with trochoidal three-lobe profile, and is aimed to highlight the contact stress and strain state of shaft–hub interface, with reference to particular profile geometric parameters. From Mechnik’s and Kollmann’s works, in which the analysis was performed by the Finite Element Method, this work develops a CAD/CAE methodology for coupling design, oriented to an efficient integration between CAD systems and BEM solvers. The stress analysis is carried out with a Boundary Element code (BEASY) well suited for this kind of contact problems while coupling geometric model is made by Pro/Engineer, a solid parametric modeller.