Industry is facing the management of geometrical deviations along the entire lifecycle of the product. It is helped by digital twin tools that may minimise the geometrical deviations from nominal of products. The new digital twin tools allow to manage geometrical variations through a set of steps fully related by modern information and communication technologies that establish a continuous and unambiguous flow of information among the different steps of this digital process along the whole product lifecycle. They are based on data coming from manufacturing, assembly and inspection. The available large data sets from manufacturing and inspection allow to develop new and more accurate simulation models that realistically consider form deviations and process signature, i.e. the pattern left by the manufacturing process on the produced part surfaces. The present work introduces a digital twin tool to support the lightweight design of assemblies in composite material. It establishes a continuous and unambiguous flow of variation information from the part design to assembly, passing through manufacturing by considering the manufacturing signature. It was applied to a case study and the obtained results agree with the experimental ones.

The dimensional and geometrical variations of each part of an assembly have to be limited by tolerances able to ensure both a standardised production and a certain level of quality, which is defined by satisfying functional requirements. The appropriate allocation of tolerances among the different parts of an assembly is the fundamental tool to ensure assemblies that work correctly at lower costs. Therefore, there is a strong need to develop a tolerance analysis to satisfy the requirements of the assembly by the tolerances imposed on the single parts. This tool has to be based on a mathematical model able to evaluate the cumulative effect of the single tolerances. Actually there are some different models used or proposed by the literature to make the tolerance analysis of an assembly constituted by rigid parts, but none of them is completely and univocally accepted. Some authors focus their attention on the solution of single problems found in these models or in their practical application in computer-aided tolerancing systems. But none of them has done an objective and complete comparison among them, analysing the advantages and the weakness and furnishing a criterion for their choice and application. This paper briefly introduces two of the main models for tolerance analysis, the Jacobian and the torsor. These models are briefly described and then compared showing their analogies and differences. The evolution of these two models, known as unified Jacobian-torsor model, is presented too.

The dimensional and geometrical variations of each part have to be limited by tolerances in order to guarantee quality and, at the same time, a decrease of manufacturing costs. Therefore, how to allocate the tolerances among the different parts of an assembly is the fundamental tool to ensure assemblies that work rightly at lower costs. Tolerance analysis allows evaluation of the cumulative effect that the single tolerances assigned on the components has to satisfy the functional requirements of the whole assembly. The results of the tolerance analysis are meaningfully conditioned by the adopted mathematical model. The purpose of this work is to analyse the most significant models for tolerance analysis. The first part of the paper describes a description of the most common criteria used to categorise existing models for tolerance analysis. Taxonomy is then suggested that may be a useful tool to help evaluate, compare and select such models. Five of the most representative models are explained and discussed in detail in order to identify their strong points and their limitations.

Titanium alloys are widely used in aeronautics that demands a good combination of high strength, good corrosion resistance and low mass. The mechanical properties lead to challenges in machining operations, such as high process temperature as well as rapidly increasing tool wear. In this work, three carbide end mills have been used in machining of titanium alloy Ti-6Al-4V. The first tool is coated with TiAl; the second and the third are coated with multi-layers or with a single layer of TiAlN. The cutting force and the tool life have been experimentally investigated and put into relationship with the process parameters under dry cutting condition. The quality of the machined surfaces has been evaluated by measuring the roughness of the machined surfaces. Finally, the correlation among cutting force variation, tool wear propagation and surface roughness has been analyzed and discussed. These three tools demonstrate to be able to maintain their hardness and other mechanical properties at the high cutting temperatures that they encountered.