Giovanni Lucchetta

A combined DFMA and TRIZ approach to the simplification of product structure

Abstract In order to tackle the problem of part count reduction more effectively, an approach that combines the design for manufacture and assembly (DFMA) method with the theory of inventive problem solving (TRIZ) is presented in this paper. This new approach was developed by merging the common characteristics and connecting the complementary aspects of the two methods, which were then applied to the redesign of a satellite antenna.

Flatness optimization of micro-injection moulded parts: the case of a PMMA microfluidic component

Micro-injection moulding (µ-IM) has attracted a lot of interest because of its potential for the production of low-cost, miniaturized parts in high-volume. Applications of this technology are, amongst others, microfluidic components for lab-on-a-chip devices and micro-optical components. In both cases, the control of the part flatness is a key aspect to maintaining the components functionality. The objective of this work is to determine the factors affecting the flatness of a polymer part manufactured by µ-IM and to control the manufacturing process with the aim of minimizing the in-process part deformation. As a case study, a PMMA microfluidic substrate with overall dimensions of 10 mm diameter and 1 mm thickness was investigated by designing a µ-IM experiment having flatness as the experimental response. The part flatness was measured using a micro-coordinate measuring machine. Finite elements analysis was also carried out to study the optimal ejection pin configuration. The results of this work show that the control of the µ-IM process conditions can improve the flatness of the polymer part up to about 15 µm. Part flatness as low as 4 µm can be achieved by modifying the design of the ejection system according to suggested guidelines.

Antibiotic-free composite bone cements with antibacterial and bioactive properties. A preliminary study

Two bone cements (Palacos R® and Palacos LV®) based on polymethylmethacrylate (PMMA), clinically used in several cemented prosthetic devices, have been enriched with silver containing bioactive glass powders and compared with the plain commercial ones. The obtained composite cements have been subjected to a preliminary characterization by means of morphological and compositional analyses, compression mechanical tests, bioactivity test (by soaking into simulated body fluids), leaching tests and in vitro antibacterial test (count of colonies forming units, McFarland index evaluation, inhibition zone evaluation). The glass powders appeared uniformly dispersed inside the PMMA matrix and good mechanical properties (in compression) have been reached. The composite cements showed a bioactive behavior (since they developed hydroxyapatite on their surface after soaking in simulated body fluid) and a good antibacterial performance. The release of silver ions, which is the principal reason of antibacterial properties, is mainly reached after the first hours of contact with the leaching solution, as it is expected for a reasonable prevention of bacterial colonization during in vivo applications.

A New Approach to the Optimization of Blends Composition in Injection Moulding of Recycled Polymers

The use of recycled polymers is widespread for the injection moulding of many commodity plastic parts. Recycled polymers are usually blended with virgin polymers to obtain the best trade-off between cost and low melt viscosity. This last constraint is necessary to avoid short shots and to minimize the clamp force of the required injection moulding machine and, therefore, the process cost. The current industrial approach to this problem is to select the polymer blend by trial and error. In this paper a new approach to the minimisation of the overall manufacturing cost is proposed. It is based on a rheological model of the blend which has been developed from experimental tests according to the mixture design technique. The approach has been validated through an industrial case study.

Integrated Design Analysis for Product Simplification

A systematic methodology is presented for product structure simplification through an integration of Design for Manufacture and Assembly (DFMA) with the Theory of Invention Problem Solving (TRIZ). A new functional model is combined with a selection of TRIZ problem solving tools that are identified as effective in product structure simplification. DFMA analysis is used to evaluate alternative concepts. Application of the combined approach is illustrated through a case study of a heavy duty stapler.

Injection molded polymeric micropatterns for bone regeneration study.

An industrially feasible process for the fast mass-production of molded polymeric micro-patterned substrates is here presented. Microstructured polystyrene (PS) surfaces were obtained through micro injection molding (μIM) technique on directly patterned stamps realized with a new zirconia-based hybrid spin-on system able to withstand 300 cycles at 90 °C. The use of directly patterned stamps entails a great advantage on the overall manufacturing process as it allows a fast, flexible, and simple one-step process with respect to the use of milling, laser machining, electroforming techniques, or conventional lithographic processes for stamp fabrication. Among the different obtainable geometries, we focused our attention on PS replicas reporting 2, 3, and 4 μm diameter pillars with 8, 9, 10 μm center-to-center distance, respectively. This enabled us to study the effect of the substrate topography on human mesenchymal stem cells behavior without any osteogenic growth factors. Our data show that microtopography affected cell behavior. In particular, calcium deposition and osteocalcin expression enhanced as diameter and interpillar distance size increases, and the 4-10 surface was the most effective to induce osteogenic differentiation.

Polymer Injection Forming (PIF) Of Thin‐Walled Sheet Metal Parts — Preliminary Experimental Results

Polymer Injection Forming (PIF) is a new technology to manufacture sheet metal/polymer macro‐composite components in a one‐operation production process. During the process, a metal blank is shaped inside an injection mould by using the injection pressure of the molten polymer. In the same step the polymer is permanently bonded to the metal sheet creating a fully finished product in only one production step. Thus, the PIF technology is a combination of the injection moulding and sheet metal forming processes. In this paper, the influence of the main injection moulding process parameters on the sheet metal formability has been experimentally investigated. The results show that melt temperature and clamp force have a great effect on the sheet deformation since they affect respectively the ductility of the sheet metal and the degree of pure drawing. In order to maximize sheet metal formability avoiding the flash formation, the main process parameters have been optimized.

A New Approach For The Validation Of Filling Simulations In Micro Injection Moulding

In manufacturing polymer micro products, numerical simulations are used with the same purposes as in conventional injection moulding, mainly the optimization of micro components design, the optimization of process parameters and the decrease of production costs. Dedicated simulations softwares fail to correctly describe the melt flow in microstructures, mainly because phenomena such as tendency of polymers to slip in micro‐channels, micro scale surface effects, and micro scale rheological behaviour are not considered. Therefore, accuracy of computer aided engineering simulations still needs to be improved. The main objective of this work is to evaluate whether the present numerical codes are suitable to characterize melt flow patterns in a micro cavity. In order to test the accuracy of the software, real and simulated experiments were performed and used to investigate the filling of a micro moulded component.

The evaluation of vacuum venting and variotherm process for improving the replication by injection molding of high aspect ratio micro features for biomedical application

The aspect ratio achievable in replicating micro features is one of the most important process characteristics and it is a major manufacturing constraint in applying injection molding in a range of micro engineering applications. Vacuum venting has been reported to be an effective technique in replicating micro features by microinjection molding. High surface-to-volume ratio and reduced dimensions of micro parts promote the instantaneous drop of melt temperature and consequently lead to incomplete filling. This study aims to investigate the effects of variotherm process, cavity evacuation and their interaction on the production of a micro fluidic filter for biomedical applications. A low-viscosity polystyrene and a cyclic olefin copolymer were molded applying a combination of mold evacuation and a rapid mold temperature variation that keeps the cavity temperature above the glass transition temperature during the injection phase. The research revealed the importance of these molding technologies in enhanci...

Wear-resistant cobalt-based coatings for injection moulds by cold spray

In this study, cold spray and high-velocity oxy fuel processes were respectively used in applying cobalt-based and nickel-based alloys on steel injection moulds. Effects of changes in the main cold spray deposition parameters and in powder composition of the cobalt-based alloy were optimised in terms of machinability and hardness improvements. A four-cavity mould was configured to allow the comparison of wear resistance between coated and heat-treated inserts in severe operating conditions. Real parts were produced by injection moulding, using a glass–fibre-reinforced polymer. Surface topography of the inserts was characterised in defined key-zones after polishing and at each scheduled stop of the moulding process. Experimental results showed that steel mould inserts coated by thermal spray and then polished can be a valid alternative to heat-treated steel for most applications.