Mattia Mele, Giampaolo Campana, Gregorio Pisaneschi and Gian Luca Monti
Multi jet fusion is an industrial additive manufacturing technology characterised by high building speed and considerable properties of the parts. The cooling phase represents a…
Abstract
Purpose
Multi jet fusion is an industrial additive manufacturing technology characterised by high building speed and considerable properties of the parts. The cooling phase represents a crucial step to determine productivity, since it can take up to 4.5 times the building time. The purpose of this paper is to investigate into effects of cooling rate on parts manufactured by multi jet fusion. Crystallinity, density, distortions and mechanical properties of specimens produced through an HP multi jet fusion 4200 are examined.
Design/methodology/approach
An experimental activity is carried out on specimens cooled down at three different rates. Properties of the parts are analysed by means of differential scanning calorimetry, optical microscopy, three-dimensional scanning and tensile testing.
Originality/value
The present work makes a contribution to the body of knowledge providing correlations between the cooling phase of multi jet fusion and part properties. These results can be used to choose the right balance between production time and product quality.
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Mattia Mele, Giampaolo Campana and Gian Luca Monti
The amount of radiated energy is known to be a crucial parameter in powder-bed additive manufacturing (AM) processes. The role of irradiance in the multijet fusion (MJF) process…
Abstract
Purpose
The amount of radiated energy is known to be a crucial parameter in powder-bed additive manufacturing (AM) processes. The role of irradiance in the multijet fusion (MJF) process has not been addressed by any previous research, despite the key role of this process in the AM industry. The aim of this paper is to explore the relationship between irradiance and dimensional accuracy in MJF.
Design/methodology/approach
An experimental activity was carried out to map the relationship between irradiance and dimensional accuracy in the MJF transformation of polyamide 12. Two specimens were used to measure the dimensional accuracy on medium and small sizes. The experiment was run using six different levels of irradiance. For each, the crystallinity degree and part density were measured.
Findings
Irradiance was found to be directly proportional to part density and inversely proportional to crystallinity degree. Higher irradiance leads to an increase in the measured dimensions of parts. This highlights a predominant role of the crystallisation degree and uncontrolled peripherical sintering, in line with the previous literature on other powder-bed AM processes. The results demonstrate that different trends can be observed according to the range of sizes.
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Mattia Mele, Giampaolo Campana and Gian Luca Monti
The purpose of this paper is to develop a physical model able to predict the shape of the capillarity effect in multi-jet fusion when two facing edges mutually affect each other…
Abstract
Purpose
The purpose of this paper is to develop a physical model able to predict the shape of the capillarity effect in multi-jet fusion when two facing edges mutually affect each other. The work also aims at testing the consistency of such a model with experimental observations.
Design/methodology/approach
An analytical model of the phenomenon is developed considering the surface tension of the polymer melt adhering to the unfused powder. The general equilibrium equations are solved by imposing the boundary conditions corresponding to the case of two close facing edges, in which the shapes of the menisci are mutually influenced. The analytical model is validated through an experimental activity. Specifically, a set of parallelepipeds with variable width was manufactured using an HP Multi Jet Fusion 4200. The morphologies of capillarities were captured via three-dimensional scanning and compared with those predicted by the model.
Findings
The results of this study demonstrate that the average error to the experimental capillarity profile is lower than that obtained by existing methods. Particularly, considerable improvements are achieved as far as the maximum capillarity height is concerned. The manufactured specimens exhibit a change in slope near the edges, which is arguably attributable to coating powder and other effects not included in the analytical model.
Originality/value
The model presented in this study differs in hypotheses from previous methods in literature by assuming a null derivative of the capillarity shape in the central point of the meniscus. This allows for a more accurate prediction of the defect morphology in the case of close facing edges.
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Mattia Mele, Giampaolo Campana and Gian Luca Monti
Multi-jet fusion (MJF) process is based on a polymeric powder bed that is heated and irradiated by infra-red lamps. The layer under construction is jetted with inks to provide the…
Abstract
Purpose
Multi-jet fusion (MJF) process is based on a polymeric powder bed that is heated and irradiated by infra-red lamps. The layer under construction is jetted with inks to provide the desired heat management conditions for selective melting. Depending on several process variables, manufactured parts can exhibit lifting of the borders of the top surface of the shape under construction. This phenomenon is related to the capillarity effect. As a result, the top surface of MJF-manufactured parts can present a peculiar convex shape. This study aims to propose a solution that instead induces the capillarity effect outside of the part under construction.
Design/methodology/approach
A specific design is developed to avoid the capillarity effect in MJF. It is based on an analytical model that was previously developed by the authors to estimate the shape and extent of the capillary on top surfaces of benchmark components. The proposed methodology is established by the predicted calculation of maximum values of capillarity rise and length, and safety factors. A fin-shaped geometry is designed to avoid the capillarity effect. An experimental campaign is implemented to verify the effectiveness of the proposed solution. Prototypes are manufactured by an HP MultiJet 4200 in the original design and the so-called finned-riser design, by adding a well-dimensioned appendage on the top surface to shift the capillarity effect outside the border of the part under construction. Measurements are done by a CAM2 ScanArm contactless measuring system to achieve the real shape of top surfaces. Geomagic Control X software by 3D systems is used to evaluate the quality of measured surfaces in comparison with the expected geometry of the top plane of the benchmark.
Findings
The investigated approach involves adding an auxiliary finned-shape appendage, which acts similarly to the risers in foundry technology, to the top surface of the part that is being produced by MJF technology. The procedure and rules for determining the dimensions of the fin are established based on physical considerations and process modelling. The method is then applied to a prototype part, which is designed to highlight the effectiveness of the finned-riser design for improving the dimensional accuracy of the top surfaces of products manufactured by the MJF process. Experimental measurements of top surfaces of the original benchmark are compared to the same ones in the case of the finned-riser benchmark. Reported results are satisfactory, and the capillary effect occurred in the fins outside the border edges of the part. Further developments are planned to extend the proposed design.
Originality/value
MJF technology is attracting large interest from manufacturers to produce mass customised products. The quality of manufactured parts could be affected by peculiar defects related to process parameters. The present work aims to show a method to avoid the capillarity effect. It is based on an original analytical model developed by the authors and implemented successfully in the case of a benchmark geometry.
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Ezequiel Poodts and Giangiacomo Minak
The purpose of this paper is to demonstrate the applicability of an indirect rapid tooling technique to the autoclave forming of carbon fibre reinforced plastic laminates.
Abstract
Purpose
The purpose of this paper is to demonstrate the applicability of an indirect rapid tooling technique to the autoclave forming of carbon fibre reinforced plastic laminates.
Design/methodology/approach
A rapid prototyping machine was used to process a photo elastic resin to fabricate the pre‐moulds. Liquid particle‐filled epoxy resin was poured in the pre‐mould and cured in an oven. Real autoclave process conditions were then applied to the mould several times to assess the geometrical stability and the accuracy of the produced parts, measured using a laser 3D scanner.
Findings
This paper reports the procedures developed for the rapid manufacture of carbon fibre reinforced plastic components.
Research limitations/implications
The method is applicable to components of small to medium dimensions (max 500 mm).
Originality/value
This is a pioneer attempt towards the rapid manufacturing of high performances composite components. It has been presented for patenting purposes (Gian Luca Monti, Ezequiel Poodts, Giangiacomo Minak, and Cristiano Fragassa. Pat. Pending Nr. PS2010A000026, 2010).
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Federica Pascucci, Oscar Domenichelli, Enzo Peruffo and Gian Luca Gregori
This article investigates the relationship between family ownership and export performance in the context of SMEs while also considering the moderating role of the financial…
Abstract
Purpose
This article investigates the relationship between family ownership and export performance in the context of SMEs while also considering the moderating role of the financial dimension and, in particular, financial constraints and financial flexibility.
Design/methodology/approach
We select a sample of 1,132 Italian SMEs to examine through an econometric analysis the role and impact of family ownership and the financial moderating variables being used on their export performance.
Findings
The results indicate that there is a U-shaped relationship between family ownership and export performance: the highest levels of export performance correspond to the lowest and highest family ownership levels, whereas when a mixture of family and nonfamily ownership exists, the performance suffers because of “conflicting voices” dominating strategic visions and approaches, harming the firm's export commitment. Moreover, the findings show that lower financial constraints and/or stronger financial flexibility improve the relationship between family ownership and export performance.
Research limitations/implications
Our findings show that the ownership structure is important for export performance; in particular, firms should avoid a mixture between family and nonfamily ownership because it is detrimental to export performance. Moreover, Italian SMEs need to develop sources of financing other than the banking channel, and policy makers should favour this process to overcome financial constraint problems and improve financial flexibility. Limitations concern the use of other econometric approaches and measurement variables to further investigate the connection between family ownership and export performance.
Originality/value
The present study enhances the comprehension of the complex relationship between family ownership and export performance by documenting the relevance of the level of family ownership and considering the moderating role of financial constraints and flexibility.