Maria Cristina Valigi

Wear Distribution Detection of Knee Joint Prostheses by Means of 3D Optical Scanners

The objective of this study was to examine total knee polyethylene inserts from in vitro simulation to evaluate and display—using a 3D optical scanner—wear patterns and wear rates of inserts exposed to wear by means of simulators. Various sets of tibial inserts have been reconstructed by using optical scanners. With this in mind, the wear behavior of fixed and mobile bearing polyethylene knee configurations was investigated using a knee wear joint simulator. After the completion of the wear test, the polyethylene menisci were analyzed by an innovative 3D optical scanners in order to evaluate the 3D wear distribution on the prosthesis surface. This study implemented a new procedure for evaluating polyethylene bearings of joint prostheses obtained after in vitro wear tests and the proposed new approach allowed quantification of the contact zone on the geometry of total knee prostheses. The results of the present study showed that mobile TKPs (total knee prosthesis) have lower wear resistance with respect to fixed TKPs.

A Parametric Study on Friction Instabilities in Mechanical Face Seals

ABSTRACT The present article aims to analyze and evaluate how dynamic parameter design influences the behavior of mechanical face seals and improves their performance by detecting undesirable phenomena like stick–slip and ringing. Those phenomena occur in situations of boundary lubrication. A new lumped parameter model is proposed to study mechanical face seals used in automotive cooling water pumps in order to examine how dynamic parameters such as mass, moment of inertia, and stiffness are involved in stick–slip phenomena. The aim of this work is to provide a practical design tool to predict stick–slip conditions and to choose the optimal mechanical specifications. Numerical simulations demonstrate how the critical service conditions vary with design parameters and permit tabulation of the results.

Study of Wear of Planetary Concrete Mixer Blades Using a 3D Optical Scanner

Performance optimization of a concrete mixer is fundamental in many industrial technologies. Wear is one of the main phenomena to be forecast and tested during the design and service of mechanical components. In all the concrete mixers types, blades suffer the wear more than other components.Two different blade shapes have been tested in order to evaluate the wear rates and which of them has the best performance in terms of wear resistance. One of the two shapes has been designed in order to minimize wear rates and to allow longer durability, on the basis of a theoretical approach.To guarantee the consistence of the comparison, the two different blades have been tested in a dedicated planetary concrete mixer, with the same operating conditions (time-period, same mixture and mixer).The purpose of this paper is to show optical non-contact measurements of worn blades operating in a planetary concrete mixer in order to evaluate wear rates and to validate the efficiency of the new blade design.Copyright

A New Automated 2 DOFs 3D Desktop Optical Scanner

The goal of this research work was to create a completely automated desktop 3D optical measuring system for parts having freeform and complex surfaces, with high and certifiable resolution, precision and accuracy to be suitable for metrology. The proposed device is based on the principle of structured light active triangulation. The hardware system consists of an optical system, with a 2 degrees of freedom (DOFs) motorized tilt-rotational table and a framework providing fixtures for a proper location of the target specimen. The software module is able to synchronize the optical and mechanical systems after optical and mechanical calibrations. The mesh representing the measured object is registered automatically by stitching together all the single 3D data sets acquired at each movement of the positioning system. The quality of the result is evaluated by checking the difference between a certified reference model and the measured data.

Chatter Marks and Vibration Analysis in a S6-High Cold Rolling Mill

S6-high rolling mill is an advanced mode to work the steel: it allows the use of very small work rolls laterally guided by individually adjustable side support rolls, which are supported by two rows of roller bearings mounted in cassettes. In this paper the vibrations generated in a S6-high cold rolling mill are analyzed with the aim to investigate the problem of skid marks generation. Such marks are regular, parallel marking across the width of strip metal that not only significantly affects the mill performance, but also reduces surface quality of the strip steel. The defects of the strip are the consequence of insurgence of vibrations, generically denominated ‘chatter’. The analyzed rolling mill has six rolls able to roll steel strip coming directly from hot rolling mill train. The purpose of the present work is to identify the reason of the excitation in order to limit the problem. A solution based on empirical observations, vibration analysis and considerations of a model is proposed.

Planetary vertical concrete mixers: Simulation and predicting useful life in steady states and in perturbed conditions

Abstract A simulation environment for the dynamics of planetary concrete mixers has been developed, it is a model-based method using the lumped parameters analysis and integrating the theory of classical mechanics and life analysis. The aim of this work is to give a fast and easy to use tool capable of predicting the behaviour and the useful life of concrete mixers through geometrical and physical parameters. Simulations were conducted in steady states and in perturbed conditions. The gear reduction unit is the part of the mixer under most stress. Results were compared with data obtained from costumers on building sites.

New Challenges in Tribology: Wear Assessment Using 3D Optical Scanners

Wear is a significant mechanical and clinical problem. To acquire further knowledge on the tribological phenomena that involve freeform mechanical components or medical prostheses, wear tests are performed on biomedical and industrial materials in order to solve or reduce failures or malfunctions due to material loss. Scientific and technological advances in the field of optical scanning allow the application of innovative devices for wear measurements, leading to improvements that were unimaginable until a few years ago. It is therefore important to develop techniques, based on new instrumentations, for more accurate and reproducible measurements of wear. The aim of this work is to discuss the use of innovative 3D optical scanners and an experimental procedure to detect and evaluate wear, comparing this technique with other wear evaluation methods for industrial components and biomedical devices.

Numerical Modelling and Simulation of the Hot Rolling Mill Process

In the design of the rolling mill plants, it is fundamental to study the behaviour of the deformation process to assess the main process variables (such as torque and rolling force) in all operating conditions.In this paper, a finite element model is developed and the numerical simulations of the plastic deformation process, in the hot rolling mill of AISI 304 stainless steel, are shown. In the proposed model a Multilinear Isotropic Hardening behaviour of material has been assumed and true stress-true strain curves have been found, taking into account temperature and strain rate. Numerical results are compared with experimental measures regarding an existing hot rolling mill plant.

Stick-Slip Simulation and Detection in Mechanical Face Seals

The present paper proposes a new model and method to detect the occurrence of dynamic instabilities and stick-slip in mechanical face seals used in automotive cooling water pumps, in order to improve their performance. A new tribo-dynamic model is presented and used to examine how many and what design parameters influence stick-slip. Mass, moment of inertia, stiffness, damping ratio, friction relationship, viscosity, roughness and wear, compressive strength of different coupling materials, geometrical specifications and temperature are some of the analyzed parameters. Therefore, this work provides a full overview of the influence of design parameters on the stick-slip phenomenon.Copyright

A Robotic 3D Vision System for Automatic Cranial Prostheses Inspection

The goal of this research work was to create a prototype of a robotic 3D vision system for cranial prostheses automatic inspection. The proposed device is able to automatically scan the entire prosthesis under study by means of an automatic tilt-rotational mechanism and the embedded software allows to generate an automatic inspection report by comparing the specimen with a reference digital sample. The output of the procedure gives information about the geometrical conformity of the new fabricated prosthesis and automatically accept or discard the product. The presented prototype is the first one in literature to have such an automated quality control and rejection procedure in 3D vision and it is also the first robotic vision system applied to cranial prosthesis manufacturing.