Rui J. Neto

The use of finite element simulation for optimization of metal forming and tool design

Abstract When producing a new component there is usually a trial and error stage to tune the process in order to obtain a part without defects, using the right quantity of raw material. At this stage, the previous experience of designers and manufacturers should give an important aid to reduce trials. However, the use of new materials associated with new shape designs creates the possibility of new behaviours. For this reason, while producing a component it is very important that we get some directions in order to avoid possible defects in it. For such an objective, the finite element simulation has been proving that, at the design stage, it can give important answers in analysing the process and predicting the defects that may occur. Therefore, modifications can be made easily, before tool manufacturing and part production, reducing the trial and error stage and its associated costs. This paper presents the modelling of components with complex shape to be manufactured by closed die forging and sheet metal forming and one tries to show how numerical simulation may help in defining the shape and size of initial material or blank and predict the forces needed to define the press to be used in the process, as well as the possible defects.

The Importance of Rapid Tooling in Product Development

Rapid Prototyping emerged in 1987 with stereolithography. After a medium growth rate of 22%, it began to decrease in the final years of the 20 th century, in parallel with a growing interest in Rapid Tooling (RT) systems. In fact, the idea behind RT responds better to the growing interest of the industry in reducing the time to market of new products and respective cost. The rapid production of a tool prototype allows the manufacturer to have a better overall control of the new product development process, not only of the product itself visual aids for engineering, ergonomics, and fit but also of the processing technology by having a prototype tool at an early stage of the process. The RT concept is not clearly defined yet, since there are two investigation and development perspectives. One of them is centralized in completely original technologies of directly manufacturing of prototype tools. The other one deals with indirect technologies based on a model manufactured by a RP (Rapid Prototyping) technology. This communication intends to better clarify the classification of the different RT systems and their respective stage of development at the moment.

Mathematical Models for Particulate Filled and Milled Fibre Reinforced Composites

Due to the low price, low density, good dimensional stability and accuracy, ease and speed of processing, and good workability, liquid epoxy resins are frequently considered ideal materials for manufacturing models and prototype tools of certain complexity. The good mixture capacity with other reinforced materials, in particulate or fibre form, leads to composite materials with intermediate properties that result from the combined action of the constituents. Starting from epoxy based systems suited for high temperatures, different dispersed materials, like aluminium particles, milled carbon and glass fibres were added to the polymeric matrix for Rapid Tooling applications. Aluminium is intended to increase the thermal conductivity of the tool, while the milled fibres improve the wear resistance of the composite tool. In this communication mathematical models for mechanical behaviour of these epoxy matrix composites are discussed. The research is essentially focused on the elastic modulus, because the properties related with the material failure are difficult to analyse due to the complexity of the mechanism that controls the failure of polymer based composite materials. Halpin-Tsai-Nielsen and Halpin-Tsai models were applied to the particulate filled and fibre reinforced epoxy systems, respectively. A critical analysis of the mismatches detected between the experimental and the theoretical values allowed us to propose a semi-empirical model more suited to the results obtained. Parameters related with the particle-matrix and fibre-matrix interface influence the mechanical behaviour of the particulate and milled fibre reinforced composites.

An engineering-based approach for design and fabrication of a customized nasal prosthesis

Background and aim: Facial defects (from neoplasms, trauma, etc.) can be functionally and emotionally devastating. A non-invasive treatment for these defects is the application of external prostheses. Conventionally, these prostheses are fabricated by an anaplastologist through a manual procedure, which is an expensive and time-consuming approach. Current advances in computational and engineering tools report an improvement in design and manufacturing of silicone prostheses. This demand motivated this study that aims to develop a methodology for fabricating customized nasal prostheses. Technique: In this study, an 80-year-old woman with a total defect of the nose is considered as case-study. The proposed methodology entails six tasks: (a) data acquisition, (b) three-dimensional reconstruction, (c) prosthesis design, (d) moulds fabrication, (e) prosthesis manufacturing and (f) final fittings. Discussion: The presented approach showed encouraging outcomes since it saves time, reduces costs and allows the achievement of prosthesis with the minimum contact and discomfort to the patient, disclosing excellent aesthetic and functional results. Clinical relevance Custom-made nasal prostheses with minimum contact and discomfort for the patient can be achieved using an engineering approach based on digital technologies and additive manufacturing that is cost-effective and less time-consuming than the manual procedure.

Optimization of Ceramic Shells for Contact with Reactive Alloys

Companies are continuously under pressure to innovate their products and processes. In Portugal, there are already several examples of enterprises that have chosen research groups, associated to universities, to straighten collaboration seeking the development of new materials and advanced technological processes, to produce components with complex shapes, high surface quality, and others, at low cost, for continuously more demanding applications. Unfortunately, these cases are still a very small number, and many efforts have to be done to enlarge the collaboration university-companies. Ti and other reactive alloys are important groups of metals that are under intense and continuous research and development. For example, the high mechanical properties, low density, osteointegration behavior, corrosion resistance to fluids and tissues of the human body, the ability to be sterilized, and the possibility to obtain complex shapes, makes Ti a very attractive material for medical applications. The investment casting process, using lost wax or lost rapid prototyping models, allows designers a great amount of freedom and capacity to quickly produce castings of high dimensional accuracy and excellent surface quality suitable for different applications. Many of the castings obtained by this process are immediately ready for use, avoiding costly machining operations and joining processes, making the process very attractive to produce precision parts in Ti and other reactive alloys. However, the high reactivity of the Ti raises several compatibility problems with the traditional materials employed on the ceramic shells for casting steels and non ferrous alloys. The fragile surface layer obtained on the interface Ti-ceramic shell, result of the Ti reaction with oxygen and nitrogen of the shell, significantly reduces the mechanical properties of the cast parts, making them useless. The aim of the present work is the study of the interface properties of the Ti-ceramic shell, in order to be able to manufacture ceramic shells of low chemical reactivity for the investment casting process of reactive alloys, namely; titanium alloys, inconel, aluminotitanates, and others. Ceramic shells manufactured with calcium and yttria stabilized zirconia and other non reactive ceramics were employed and the metallic interface characterized in terms of microscopic and microhardness properties.

Contribution of the Phase-Matrix Interface to the Behaviour of Aluminium Filled Epoxies

Polymeric materials present mechanical and thermal limitations that disable their use in the mould manufacturing. Nevertheless, an adequate selection of the polymeric matrix and the dispersed materials allows the possibility to achieve performances closer to the metals and their alloys. These new materials are attractive solutions for applications that have less demanding mechanical properties, as is the case of the rapid tooling applications where a small number of parts are required. The composites were obtained from a mixture of an epoxy resin with fine and coarse aluminium particles. One can state that besides the dispersed phase resistance overcome the matrix one, its contribution to the global resistance of the composite is restricted, because the fracture surface lies basically in the matrix and interfaces. As the matrix section under load is reduced, with the increment of the dispersed phase, the composite properties turn out to be dependent on the interfaces quality and resistance. This is particularly true when fine aluminium particles are used. The interface contribution to the global composite properties depends basically on two parameters, the binding quality between the matrix and the dispersed phase, and the interface extension per unit volume. This paper studies the main contribution of the phase-matrix interface in the mechanical behaviour of aluminium filled epoxy. Introduction Aluminium filled resins are frequently employed in the area of Rapid Prototyping (RP) and Rapid Tooling (RT) to manufacture moulds for production of small series of plastic parts [1-3]. The strength of these composites is very sensitive to the different phase properties and to the respective concentrations. Furthermore, as shown in this study, the interface also seems to be an important parameter in the composite mechanical behaviour. The adhesive resistance through the interface depends essentially on the extension and quality of the adhesive bonding. The chemical complexity of the epoxy systems and the respective interfacial interactions with the aluminium surfaces represents an extra difficulty in the interpretation of the adhesive bonding mechanism. Different theories are under development to explain the adhesion mechanism, and how it affects the interface resistance [4, 5]. Experimental Two epoxy systems for high (A) and medium (B) temperature (see Table 1) were mixed with aluminium particles of two different classes, fine (F) and coarse (C), with an average equivalent diameter of 45.5 μm (PD 200 grade) and 1400 μm (size distribution from 500 to 2000 μm), respectively (Fig. 1). Eight composites were manufactured, A1 to A4 and B1 to B4. The matrix epoxy system is represented by a letter and the aluminium class by a number (Table 2). The flexural strength and Charpy impact tests were performed according to ASTM D790-02 and D5942-98 standards, respectively. The ASTM D1002-94 standard was used to determine the shear strength of the aluminium-resin interface adhesive bonding. Materials Science Forum Online: 2004-05-15 ISSN: 1662-9752, Vols. 455-456, pp 635-638 doi:10.4028/www.scientific.net/MSF.455-456.635

Stereolitography, the Front Edge of Rapid Prototyping

Based on the annual sales volume, stereolitography (SLA) can be considered a Rapid Prototyping (RP) technology with a promising future. Besides being the pioneering equipment, when RP took the first steps in 1988, this technology has been developed with interesting and fast innovations, and a great activity in patents registration. One can assist to a strong research seeking the enlargement of the system capacity to produce large and micro-size parts, and simultaneously impose the technology as a mass production process that is evolving towards a true Rapid Manufacturing (RM) technology. SLA is an excellent tool to materialize concepts and ideas due to the high-resolution capacity, transparency and fine details of the models and prototypes that can be produced. In this study, the state of art of SLA is analyzed and the recent innovations are presented, and considering that the authors have a considerable experience in supervising design students, from different universities, some of the more emblematic projects that were developed at INEGI – Institute of Mechanical Engineering and Industrial Management, are presented. SLA and direct conversion processes were combined to produce new products in materials such as glass, ceramics and metals, for different industrial sectors.

Conversion of rapid prototyping models into metallic tools by ceramic moulding - an indirect rapid tooling process

INEGI developed a process to convert models made by rapid prototyping or conventional techniques into metallic moulds. The main purpose is to rapidly obtain prototype tools by casting a metal into a ceramic mould produced by mixing in variable proportions, ceramic particles, a liquid binder and a catalyst added to start a sol-gel reaction. This liquid slurry is poured into the box containing the mould to be reproduced. After a short period of time the ceramic mixture acquires a rubber consistency. The pattern is removed from the ceramic mould, which is fired and sintered in order to generate an inert mould with the desired strength in which most alloys can be cast. The effect of ceramic materials (shape, granulometric distribution, chemical composition), sintering conditions (time and temperature) and casting conditions (mould preheating temperature and pouring temperature) were studied in order to obtain ceramic moulds and, subsequently, metallic moulds with tailored properties (accuracy reproduction of details, low roughness and high mechanical strength).

Post-process Influence of Infiltration on Binder Jetting Technology

Despite the fast and ongoing advances of Additive Manufacturing processes (AM) in last years, including three-dimensional printing (3DP), models produced by the latter are not as strong as the ones made by other AM technologies. This challenge raises the concern to improve post-processing to create competitive mechanical strengths, which in turn requires specific knowledge that has not focused on applied studies of current plaster-based materials. The aim of this study is to characterize the base material, and to measure the influence of infiltration post processing on flexural and tensile strengths of 3D printed parts. VisiJet® PXL Core was characterized in terms of grain size and chemical composition. Green printed specimens were infiltrated with epoxy resin, cyanoacrylate, magnesium sulphate and water, as recommended by the supplier of equipment and materials for 3DP, and their influence on flexural and tensile strengths was analysed. The increase in flexural strength, up to 450%, in the specimens infiltrated with epoxy resin, relatively to the ones without infiltration (green body), suggests the importance of this post-process. The data obtained by mechanical test were lower regarding the data stipulated by the materials producers. Large standard deviations on mechanical strength, compared with the standard deviation of the green body, are characteristic of the manual processes (brush and drip), suggesting the necessity to establish methodologies to allow homogeneous infiltration and controlled dosages, as well as the use of alternative infiltrates.

Rapid Prototyping and Rapid Tooling Applied in Product Development of Ceramic Components

In Portugal, product development in decorative ceramic industry is usually done using traditional methodologies. In most of the cases use manual modelling, that is very slow, highly inaccurate and demands skilled persons, which are difficult to find and too much time consuming to train. These methodologies, highly misadjusted to the new marketing demands, tend to decrease companies competitiveness. This paper explains some of the work that has been done at INEGI, seeking the introduction of new methodologies for product development of decorative ceramic components, using CAD 3D design or engineering tools. Traditionally in the Portuguese ceramic industry, only few products are developed using CAD 3D tools. Considering that CAD 3D files are used since the beginning of the project, it is possible to accelerate the optimization of the geometry, producing, by different rapid prototyping technologies, solid models, like the ones obtained with SLA, SLS and LOM processes. However, more important than this first stage, is the prototype production tools based on LOM rapid prototyping models, which offer important time and money savings. On future mass production, the prototype files used for RP tools generation, can also be used in a more accurate and high quality CNC tools production.