Computer-aided design, computer-aided manufacturing, computer-aided analysis, reverse engineering and rapid prototyping are tools that play an important key role within product design. These are areas of technical knowledge that must be part of engineering and industrial design courses’ curricula. This paper describes our teaching experience of computer-aided tools for product design centred on the development of a proposed project. The pedagogic model, the teaching objectives and methodology are described and discussed. The competencies acquired within the development of the project have stimulated the design and manufacturing of several artefacts within the students’ final-year project. A conceptual vehicle, a washing machine and a tricycle were products designed by students and are presented.

O design de produtos implantáveis no corpo humano, dito design fisiológico, contém especificidades projectuais ao nível da sua metodologia. São produtos estruturalmente mais exigentes, onde a selecção de materiais assume um papel crucial na prossecução de uma maior eficácia funcional e com índices de segurança máximos. Neste artigo aborda-se as características do design fisiológico e os factores que devem ser tidos em conta no design e na inovação de um dispositivo biomédico, no presente caso de uma prótese de substituição da articulação da anca. E salientada a importância da influência que a estrutura viva [tecido ósseo ou outro tipo de tecido biológico vivo] tem sobre as diversas condicionantes do desenvolvimento do implante. As formas como as células ósseas reagem a um implante, considerado como um “intruso", e como se pode condicionar o seu comportamento fisiológico é objecto de descrição pormenorizada. Este artigo permitirá ao leitor ter uma percepção das diferenças de desenvolvimento projectual entre um produto convencional e um dispositivo implantável [próteses de anca e joelho, implantes dentário e temporomandibular, etc.].

This paper describes the study performed to determine the influence and optimize computer numerical control (CNC) set-up parameters to manufacture rapid prototype parts. The competitiveness of CNC was assessed relative to conventional rapid prototyping techniques by comparing dimensional precision, quality of the prototype, execution times and costs. CNC machine set-up parameters were first optimized using specimens of part of a hand dorsum model. Based on these findings, a CNC hand model was manufactured and compared with others manufactured by laminated object manufacturing (LOM), selective layer sintering (SLS) and stereolithography (SLA) rapid prototyping (RP) techniques. Overall, the study evidenced that CNC milling can be more or as competitive as the RP techniques tested. In fact, the CNC prototype was manufactured in significantly less time, was less expensive and presented excellent quality of dimensional control and surface texture. However, the quality of the CNC prototype is subject to expertise of the computer aided design/manufacture (CAD/CAM) operator.

Poly(methyl methaerylate) (PMMA) is commonly used as acrylic bone cement to fix bone implants. In vivo degradation of bone cement may lead to a decrease in mechanical properties and result in aseptic loosening. Creeping can promote failure of the implant. This study used dynamic mechanical thermal analysis (DMTA) equipment, in the 0.01 to 50 Hz frequency range, to investigate the dynamic viscoelastic relaxation characteristics of CMW (TM), PROFIT QUIRURGICO and PALACOS PMMA-based bone cements. Their initial moduli were measured as 2450, 1850 and 1710 MPa, respectively. Relaxation master curves displayed similar features. The DMTA temperature range was between 20 and 75 degrees C. Predictions for long-term relaxation moduli were analyzed and compared against published experimental data. The comparison revealed that master curves obtain using the time-temperature-superposition principle (TTSP) present a much slower relaxation modulus compared to long-term experimental data above 1000 s. However, extrapolations based on a time-power law applied to isothermal experimental data allow better long-term predictions.

The purpose of this study was to compare costs and dimensional control parameters between same geometry parts obtained by same prototyping techniques using different material moulds. Vacuum casting was used to obtain prototypes of a three-blade helix of a motor boat propeller. Aluminium and room temperature vulcanising (RTV) rubber moulds were manufactured and tested within the study. Manufacturing costs and dimensional control parameters were used within the comparison study. For the dimensional deviation performance factor used, no significant differences were observed relatively to the dimensional control parameters measured. However, the average deviations were smaller for the RTV rubber mould prototype.

The development of a new cemented hip prosthesis is certainly a complex task to improve actual performance and success rates. This study presents a methodology applied to design and develop a novel hip stem concept. It was based on the comparison of performance of best cemented stems on the market. A simplified numerical model of the hip replacement was used to generate the final geometry of the femoral stem. Realistic numerical models also allowed us to determine cement mantle stresses of commercial stems that were compared with those obtained for the new concept stem. Fatigue tests performed allowed us to determine the density of cracks in the cement mantles and debonding at the interfaces. Detail design geometry of the new stem concept were analyzed, namely the collar position and orientation, medial radius of the stem geometry and geometry tip to minimize the magnitude of the cement stresses. The new model was prototyped and tested through in vitro fatigue tests. The novel hip prosthesis presents an innovative collar, ‘‘organic’’ geometry sections and a geometry tip that minimizes the magnitude of stresses. The new stem reduces the cement stresses in an average of 25% relatively to the commercial stems used in the study.

CAD systems have greatly affected the way which engineers perform their function. Computers have simplified and eliminated many of repetitious tasks and the gap between computer models and physical products has significantly shortened. These tools have stimulated the impetus for product development but the manufacturing processes still depends on human skills which ultimately reduce errors and produce better products. Complex shapes representing the patient’s anatomy are widely applied, namely in computer-assisted surgery and manufacturing of customized implants. These type of models represent a challenge for the reverse engineering processes and are not comparable with the demands of regular geometric models. In order to create a replica, data is processed in a series of steps that transforms the initial data obtained from the physical model into a three dimensional digital model. Most commonly it is necessary to include filtering, segmentation, mesh smoothing and surface generation. These steps can strongly affect the accuracy of the model. It is therefore necessary to find a compromise between the finest accuracy and maximum deviation acceptable to reduce computer processing time and achieve the best model. This study shows an iterative and alternating process to produce more accurate complex geometry models.

Computer-aided technologies have allowed new 3D modelling capabilities and engineering analyses based on experimental and numerical simulation. It has enormous potential for product development, such as biomedical instrumentation and implants. However, due to the complex shapes of anatomical structures, the accuracy of these technologies plays an important key role for adequate and accurate finite element analysis (FEA). The objective of this study was to determine the influence of the geometry variability between two digital models of a human model of the mandible. Two different shape acquisition techniques, CT scan and 3D laser scan, were assessed. A total of 130 points were controlled and the deviations between the measured points of the physical and 3D virtual models were assessed. The results of the FEA study showed a relative difference of 20% for the maximum displacement and 10% for the maximum strain between the two geometries.