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Cristina RENZI

Ricercatore t.d. art. 24 c. 3 lett. A presso: Dipartimento di Ingegneria "Enzo Ferrari"


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Pubblicazioni

2020 - A design methodology for an innovative racing mini motorcycle frame [Articolo su rivista]
Angelo, L. D.; Di Stefano, P.; Renzi, C.; Leali, F.
abstract

Sports equipment design is a young and evolving engineering discipline focused on the best simultaneous optimization of user and product as a system. In motorsports, in particular, the final performance during a race depends on many parameters related to the vehicle, circuit, weather, and tyres and the personal feelings of every single driver. Top teams in high-tech categories can invest huge amounts of money in developing simulators, but such economic commitment is not sustainable for all those teams that operate in minor but very popular categories, such as karts or mini-motorcycles. In these fields, the most common design approach is trial and error on physical prototypes. Such an approach leads to high costs, long optimization times, poor innovation, and inefficient management of the design knowledge. The present paper proposes a driver centred methodology for the design of an innovative mini racing motorcycle frame. It consists of two main phases: the drivers’ feelings translation into engineering requirements and constraints, and the exploration of the design solution space. Expected effects of the application of the proposed methodology are an overall increase in the degree of innovation, time compression, and cost reduction during the development process, with a significant impact on the competitiveness of small racing teams in minor categories.


2020 - Automotive Design Engineering: Material and Processes Selection Problems [Capitolo/Saggio]
Renzi, C.; Di Angelo, L.; Leali, F.
abstract

Multicrieria Decision-making methods (MCDM) are efficiently used as a support to engineering design, even if tested procedures and experience-based approaches are often preferred in SMEs and several industrial contexts. An extended critical review investigates how decision-making methods can help solving engineering design problems in automotive design. In particular, in this work, a classification of decision-making methods related to engineering design, is proposed, in which decisional techniques are matched with the design phases, and to corresponding automotive industry design problems. In literature a large amount of paper is dedicated to the selection of materials and manufacturing processes in the detail design phase. Also, hybrid methods, namely a combination of decision-making methods with other mathematical methods will be investigated to overcome some methodological drawbacks in MCDM methods. Due to the high impact of the problem in both industrial and research field, this work could help increasing production rate by reducing redesign errors related to material/processes selection problems, and concurrently transferring the knowledge of decision-making methods within the industrial context.


2018 - Integrated geometrical and dimensional tolerances stack-up analysis for the design of mechanical assemblies: an application on marine engineering [Articolo su rivista]
Renzi, Cristina; Ceruti, Alessandro; Leali, Francesco
abstract

This paper presents a knowledge based engineering environment methodology to support the designer in the correct setting of geometrical and dimensional tolerances in assemblies of mechanical components. The procedure is based on the definition of the functional requirements needed to allow the proper working of the assembly; in the further, a software tool is used to do a statistical analysis of the assembly relations, providing an estimation of the components waste due to poor compliance to the tolerances. A case study given by the design of a marine power transmission is presented: the methodology leads to the change of some tolerances to improve the design by reducing the number of waste components. The strength of the methodology is represented by the fact it can help unskilled designers in the correct setting of tolerances in drawings.


2018 - Predicting tolerance on the welding distortion in a thin aluminum welded T-joint [Articolo su rivista]
Renzi, Cristina; Panari, Davide; Leali, Francesco
abstract

Welding is a widely accepted process used in the assembly of aluminum chassis structures in the automotive industry. Finite element analysis (FEA) is usually adopted to predict distortions caused in the welding process. However, only nominal distortions result from FEA simulations. Welding distortions could be more accurately predicted by introducing the prediction of tolerances due to a modification of the input parameters. The aim of this work is therefore to introduce the tolerance evaluation in the FEA model, by varying the welding input parameters (geometrical and dimensional tolerances on the parts, heat input…). To find the most suitable FEA model to investigate welding process tolerance, three FEA models are compared: one is the thermo-elastic-plastic (TEP) model, and two are based on the inherent strain method. The case study uses a thin (2 mm) aluminum T-joint, which is commonly used in automotive chassis assembly. Results deriving from FEA simulations were compared with experimental data. Among the various input parameters affecting the welding process, the authors combined the dimensional tolerance on the plate thickness with the variability of the heat input. The results provided a tolerance range value for the angular distortion of the T-joint.


2017 - A review on decision-making methods in engineering design for the automotive industry [Articolo su rivista]
Renzi, Cristina; Leali, Francesco; Di Angelo, Luca
abstract

Decision-making methods have proven to be an effective support to engineering design. However, it is proved that very often designers prefer tested procedures and experience-based approaches. Many reasons have been discussed in the literature, dealing with consolidated design habits of people and companies, high cost in terms of time consumption, and lack of tools and knowledge. The paper systematically investigates, through an extended critical review, how decision-making methods can be used by automotive designers to solve the most common engineering problems involved along the design process. In particular, the paper proposes an original classification of the most widely used decision-making methods in engineering design, a match between such techniques with the typical design phases, and a mapping of their application into the automotive field. This research can be considered as a further step to transfer the state-of-the-art knowledge on decision- making methods to the industrial context, establishing a common background for practitioners and researchers.


2017 - A systematic user-centred framework for engineering product design in small- and medium-sized enterprises (SMEs) [Articolo su rivista]
Gherardini, Francesco; Renzi, Cristina; Leali, Francesco
abstract

The systematic integration of user needs in the product design is a key issue in industry, especially for small- and medium-sized enterprises (SMEs), which suffer a lack of engineering methods and resources. Moreover, most of the approaches described in the literature are not flexible enough to be tailored on the SMEs’ needs, involve users only in the early design phases and are not fully accessible due to the high cost in their implementation. The present paper proposes a user-centred design methodological framework specifically focused on SMEs, which supports the designer from both design and manufacturing aspects along the engineering product design process. The framework integrates engineering methods with Web-based software tools, which enable the communication and the concurrent work of the design team, and supports direct participation of users. Beside state-of-the-art methods, the framework allows the integration of specifically tailored techniques. The framework is successfully validated through an industrial case study developed in collaboration with an Italian SME. As a result, the design of an injection-moulded housing and the related interfaces of a biomedical electronic device are achieved with a reduction of uncertainty and development time, by involving users throughout the design phases and suggesting methods and tools on the basis of the designers’ know-how and SME’s specific resources.


2017 - Integrated design method for optimal tolerance stack evaluation for top class automotive chassis. In Advances on Mechanics, Design Engineering and Manufacturing (pp. 1013-1022). Springer International Publishing. [Relazione in Atti di Convegno]
Panari, Davide; Renzi, Cristina; Vergnano, Alberto; Bonazzi, Enrico; Leali, Francesco
abstract

The tolerances of welded chassis are usually defined and adjusted in very expensive trials and errors on the shop floor. Computer Aided Tolerancing (CAT) tools are capable to optimize the tolerances of given product and process. However, the optimization is limited since the manufacturing process is already mostly defined by the early choices of product design. Therefore, we propose an integrated design method that considers the assembly operations before the detail design of the chassis and the concept design of the fixture system. The method consists in four phases, namely functional analysis in the CAD environment, assembly sequence modelling in the CAT tool, Design Of Simulation Experiment on the stack of the tolerance ranges and finally optimization of the tolerances. A case study on a car chassis demonstrates the effectiveness of the method. The method enables to selectively assign tight tolerances only on the main contributors in the stack, while generally requiring cheaper assembly operations. Moreover, a virtual fixture system is the input for the assembly equipment design as on optimized set of specifications, thus potentially reducing the number of trials and errors on the shop floor.


2016 - A genetic algorithm-based integrated design environment for the preliminary design and optimization of aeronautical piston engine components [Articolo su rivista]
Renzi, Cristina
abstract

The enhancement of the early design stages, in the production of aeronautical engines, has been shown decisive, for developing efficient and reliable final products. Nevertheless, in most of industrial engineering design problems, the amount of design variables is large. Moreover, several nonlinearities characterize the behaviour of the physical phenomena involved and the derivatives are seldom known for all the functions. Besides, objective functions exhibit several local extremes, whereas the designer as well as the practitioner is usually interested in the global one. In this context, stochastic and evolutionary optimization have been shown capable to provide reliable solutions while keeping the computational cost at a reasonable level. Existing tools for the design and optimization of engine components deal with the optimal and detailed design of specific engine components, thus requiring several computational time and efforts to gain optimized design parameters. Hence, existing tools fit for later design phases. Conversely, this paper proposes an integrated design and optimization environment, for automatically designing optimal aeronautical piston engine configuration, still in the conceptual design stage. The optimization is performed using the MATLAB genetic algorithm (GA) toolbox®, while the automatic design of the optimized components is carried out in cascade to the optimization phase. In particular, a single-objective GA is used to evaluate the optimal dimensions of engine components related to motion, namely: crankshaft, connecting rods and screws, flywheel, propeller shaft and torsional vibration damper. For testing the efficiency of the integrated environment, the conceptual design of components of a 4-in-line Diesel aeronautical piston engine is proposed, starting from an existing similar engine. Results show a reduction of the 20 % of weight of the crankshaft in comparison to the original configuration. The proposed environment seems to be a promising tool for a fast and reliable conceptual design of piston engines for aeronautical purposes.


2016 - A Multicriteria Decision-Making Application to the Conceptual Design of Mechanical Components [Articolo su rivista]
Renzi, Cristina; Leali, Francesco
abstract

Early design is crucial for the success of the final product. In the conceptual design phase, several constraints, criteria, objectives and disciplines have to be considered. To this aim, multidisciplinary optimization has proven effective for the solution of engineering design problems, even in the industrial every-day practice, to improve and simplify the work of designers in a successful quest of the best compromise solution. In this paper, a multicriteria decision-making (MCDM)-based design platform for early optimal design of industrial components is proposed. In a group decision-making context, the selection of the most suitable component among several possible layouts is performed by means of a group Fuzzy Technique for Order of Preference by Similarity to Ideal Solution approach. Hence, a multi-objective optimization is performed on the selected component by applying a multi-objective particle swarm optimization for finding optimal component dimensions. An industrial case study is presented for showing the efficiency of the multicriteria decision-making-based design platform, regarding an innovative and low-cost solution to increase the duration of heel tips in women’s shoes.


2016 - APPLICAZIONE DELLA NORMA ISO 16792:2006 PER LA SPECIFICAZIONE GEOMETRICA DI PRODOTTO 3D IN AMBITO AUTOMOTIVE [Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; Gherardini, Francesco; Renzi, Cristina; Bonazzi, Enrico; Leali, Francesco
abstract

Accanto alla documentazione tecnica di prodotto mediante disegni ed annotazioni 2D, nella pratica industriale è fortemente sentita l’esigenza di gestire le informazioni tecniche di prodotto direttamente nell’ambiente di modellazione CAD 3D. Con l’obiettivo di migliorare la gestione del ciclo di vita di prodotto tramite modelli 3D, i produttori di software CAD 3D commerciali e l’industria stessa, soprattutto in ambito automotive ed aerospace, hanno generato molteplici soluzioni che tuttavia risultano individualizzate e non univoche. La normativa tecnica ISO definisce linee guida per la specificazione geometrica di prodotto 3D, che tuttavia risultano solamente in parte accolte da un punto di vista industriale e commerciale. In questo scenario, il presente studio vuole verificare l’implementazione dei contenuti della norma ISO 16792:2006 in alcuni CAD 3D commerciali selezionati. Mediante un benchmark industriale opportunamente identificato, i CAD 3D sono comparati sulla base di criteri redatti secondo la norma ISO 16792:2006 stessa. I risultati ottenuti permettono di individuare, per ogni CAD 3D analizzato, eventuali gap operativi ed i relativi interventi volti a garantire il raggiungimento di un livello comune di applicabilità della norma e di leggibilità della documentazione tecnica 3D generata.


2016 - REDESIGN FOR ENVIRONMENT OF WOODEN PACKAGING FOR BULK RECYCLING AND RECOVERY. ARPN Journal of Engineering and Applied Sciences VOL. 11, NO. 1, JANUARY 2016. [Articolo su rivista]
Vergnano, Alberto; Renzi, Cristina; Leali, Francesco
abstract

Society increasingly demands for effective waste management policies to make industries more environmentally sustainable. Organizations are even issuing directives to drive choices about these policies. In particular, modern industries produce a lot of packaging, which soon become waste, even before product usage. Research can face the problem with improvements in recycling and recovery processes. However, even if recycling and recovery would enable waste to have still a value, most costs and benefits are determined at the design stage. Therefore, Design for Environment criteria must be adopted in the design tasks, from the early conceptual design when the main design solutions are defined. The design criteria to assess possible design choices must consider all the environmental impacts of packaging over its lifecycle. The present work focuses on Redesign for Environment of packaging solutions. Following a systematic design process, we use different criteria to evaluate the effects of design solutions on packaging, since waste can be seen just as one of the main phases of packaging life. To this purpose, we adopt the stages of the waste hierarchy set by the EU Waste Framework Directive 2008/98/EC as design evaluation criteria. The waste hierarchy sets a priority order for five life cycle stages that a packaging can go through. The stages of the hierarchy can be differently weighted according to the costs and benefits they involve. The proposed Design for Environment method based on the waste hierarchy criteria is finally applied in the redesign of an industrial case study. The packaging solution as foldable wooden crates were chosen for their capability to already comply with the first stages of the hierarchy, that is reducing waste with high customization to customer requirements and crate reuse. Hence, the case study improved the next stages with easing the wood recycle and recovery processes


2014 - A review on artificial intelligence applications to the optimal design of dedicated and reconfigurable manufacturing systems [Articolo su rivista]
Renzi, Cristina; Leali, Francesco; Cavazzuti, Marco; Andrisano, Angelo Oreste
abstract

Reconfigurable manufacturing systems (RMS) are considered the future of manufacturing, being able to overcome both dedicated (DMS) and flexible manufacturing systems (FMS). In fact, they provide significant cost and time reductions in the launch of new products, and in the integration of new manufacturing processes into existing systems. The goals of RMS design are the extension of the production variety, the adaption to rapid changes in the market demand, and the minimization of the investment costs. Despite the interest of many authors, the debate on RMS is still open due to the lack of practical applications. This work is a review of the state-of-the-art on the design of cellular RMS, compared to DMS, by means of optimization. The problem addressed belongs to the NP-Hard family of combinatorial problem. The focus is on non-exact meta-heuristic and artificial intelligence methods, since these have been proven to be effective and robust in solving complex manufacturing design problems. A wide investigation on the most recurrent techniques in DMS and RMS literature is performed at first. A critical analysis over these techniques is given in the end.


2013 - Selecting alternatives in the conceptual design phase: an application of Fuzzy-AHP and Pugh’s Controlled Convergence [Articolo su rivista]
Renzi, Cristina; Leali, Francesco; Pellicciari, Marcello; Andrisano, Angelo Oreste; Berselli, Giovanni
abstract

The selection of conceptual design alternatives is crucial in product development. This is due both to the fact that an iterative process is required to solve the problem and that communication among design team members should be optimized. In addition, several design constraints need to be respected. Although the literature offers several alternative selection methods, to date, only very few are currently being used in industry. A comparison of the various approaches would improve the knowledge transfer between design research and practice, helping practitioners to approach these decision support tools more effectively. This paper proposes a structured comparison of two decision support methods, namely the Fuzzy-Analytic Hierarchy Process and Pugh’s Controlled Convergence. From the literature debate regarding selection methods, four relevant criteria are identified: computational effort, suitability for the early design stages, suitability for group decision making, and ease of application. Finally a sensitivity analysis is proposed to test the robustness of each method. An industrial case study is described regarding an innovative and low-cost solution to increase the duration of heel tips in women’s shoes. The selection of conceptual design alternatives of the heel tip presents complex challenges because of the extremely difficult geometric constraints and demanding design criteria.


2012 - Metodo di progettazione di sistemi di fixture per l’assemblaggio di telai automobilistici mediante analisi di sensibilità [Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; Ansaloni, Matteo; Berselli, Giovanni; Bonazzi, Enrico; Gherardini, Francesco; Leali, Francesco; Pellicciari, Marcello; Pini, Fabio; Renzi, Cristina; Vergnano, Alberto
abstract

I sistemi di fixture influenzano enormemente i processi di assemblaggio in molti campi della meccanica, in quanto influiscono direttamente sul calcolo della catena di tolleranza. La memoria illustra un metodo di progettazione che permette di comparare e valutare differenti sistemi di fissaggio, considerando sia la posizione che il tipo di locatori. Poiché i sistemi di fixture possono essere considerati dei sistemi multi-prestazionali, il confronto viene eseguito attraverso l’impiego di opportuni indici di sensibilità. Il metodo è stato applicato ad un caso di studio in ambito automotive relativo alla saldatura in continuo di estrusi in allumino, con l’obiettivo di garantire misure di gap con la minore variabilità possibile.


2012 - Selecting alternatives in the conceptual design phase: application of Fuzzy-AHP and Pugh’s controlled convergence [Relazione in Atti di Convegno]
Pellicciari, Marcello; Renzi, Cristina; Leali, Francesco; Andrisano, Angelo Oreste; Berselli, Giovanni
abstract

Purpose: Conceptual design and, in particular, selection of conceptual design alternatives are proved to be crucial issues in product development. Selecting alternatives is a complex multicriteria decision making problem and represents a challenging task for engineering designers. Many different methods and techniques have been presented by literature in the last years but just a little use of them is often made by industry, due to several causes. One of them is that more efforts should be spent in presenting clear comparisons between the various approaches from an engineering design point of view. Such problem is tackled by the present paper which proposes the pairwise comparison of two of the most representative and widely used decision support methods. Method: The paper describes, implements and compares within a common framework the Fuzzy-Analytic Hierarchy Process (F-AHP) and the Pugh’s Controlled Convergence (PuCC) methods. A structured analysis of the results obtained by applying them to a common industrial case study is proposed. Four engineering criteria are adopted for their evaluation: complexity of computation, rating of alternatives, compatibility with group decisions making and approach suitability from an early design perspective. Result: The methods are evaluated with respect to a case study focused on the proposal of an innovative and low-cost solution for increasing the duration of heel tips in feminine shoes. The selection of the heel tip conceptual design alternatives presents complex design challenges because of the extremely hard geometric constraints and demanding design criteria. A decision making team is grouped by involving experts from the heels manufacturing industry, designers and manufacturers. Finally a sensitivity analysis is performed to investigate the dependence between the results and the preference weights. Discussion & Conclusion: Conceptual design is part of a heuristic process which requires an iterative approach for searching and manipulating solutions to find new hybrid technical alternatives, and for enhancing the communication within the design team. With respect to such scenario, PuCC seems, without doubts, to be more suitable than F-AHP for selection purposes. Nevertheless, especially for industrial purposes, the latter method has a more analytic form, that makes it proper for a software implementation and, consequently, more useful for engineering applications.


2008 - A very simple and effective method for off-design simulation of modern aircraft piston engines [Relazione in Atti di Convegno]
Francia, D.; Piancastelli, L.; Renzi, C.
abstract

A new generation of aircraft piston engines is currently being introduced on the market. These new engines come directly from the huge experience achieved in the motorcycle and automotive racing and production. However direct use of automotive power unit is not advisable, since car engines work mainly in the first quarter of the power output, while sport motorcycles are used in a very "light" way, with the engines that span several times through the entire range of power outputs and rpm. The other problem is fuel. Aircraft spark ignition engine for ultralight and light aircrafts may continue to use automotive gasoline, while diesel engines for light up to cargo aircraft should use jet(A1) and jp4. However, the large experience obtained from racing/high-performance motorcycles, racing/high-performance cars and common rail engines cannot be ignored. Thousand of hours and billion of Euros have been spent for this development and the results are interesting. This paper tries to calculate the future aircraft engine performance from the many experimental data already available on a certain type of combustion chamber or better from a well defined and experimented cylinder unit. On the other side the "lean-thinking" approach to aircraft engine design may be not applicable. The lean thinking approach tends to prefer the time-to-market to the optimization of the engine unit. With engines that will probably stay on the market for 30 years this approach is not convenient. An important optimization during the design phase is possible with modern CAD tools. Mass and cost reduction may easily reach the 30%. On the other side the "brain storming approach" is not applicable to the heavily-constrained aircraft-engine design, where it is common that inapplicable solutions and ideas seem to be the best during the initial phase even to experts. Our research team developed three different families of engines: the first family uses the cylinder unit of a well proven motorcycle engine, which comes directly from racing and was sold in tenth of thousands in the world market. These spark ignition engines have 4 up to 16 cylinders (Figg. 1, 2), with power from 150 HP to 800 HP. This type of engines have very brilliant power to weight ratios with not superlative fuel consumptions. They are conceived for ultralight aircrafts and helicopters, tilt rotor, tilt shaft and tilt motor power lift V/STOL aircrafts. The second cylinder unit comes directly from the 2 valves FIAT 1900 jtd, that is one of the best two valves turbocharged common rail diesel available on the market. These units span from 4 up to 16 cylinders with power outputs from 175 HP (Fig. 3) up to 1000 HP. They run with jp4, jp8 or jet (A1) and can be bolted directly to the original engine mount of existing light aircraft like Cessna 172/182/337 or can be used in new light aircrafts. The third one is an originally conceived twin combustion chamber diesel family with output power from 600 HP to 4000 HP (hybrid engine) originally conceived for the Hercules C130J, ATR42 or ATR72 aircrafts (Figg. 4, 5). Our hybrid engine is composed by two separate engines: the VD007 diesel and a turboshaft. Each engine moves a separate contra rotating propeller. In ordinary flight the turboshaft works as a turbocharger. In this case the rear propeller is nearly idle. During take off or emergency the turboshaft combustion chamber is activated and additional power is available. In this case pitch is given to the rear propeller that outputs additional useful thrust. All these engines use only the thermo-fluid-dynamics and a few parts of the original cylinder unit, since aircraft application need extended modifications and, in many cases, complete redesign. However on all these engines a large amount of experimental, road and reliability data are available. Their direct application in the aircraft field is a plain mistake, since automotive and motorcycle are very different, but it is not the case to discard all this data