S. Yang, M.M. Mohebi and J.R.G. Evans
The purpose of this paper is to present a new powder‐based solid freeforming method based on conventional furnace sintering after co‐deposition of mould and part powder materials.
Abstract
Purpose
The purpose of this paper is to present a new powder‐based solid freeforming method based on conventional furnace sintering after co‐deposition of mould and part powder materials.
Design/methodology/approach
Based on acoustic powder deposition, both mould and part powder materials are delivered simultaneously into the forming area according to the cross section of the 3D computer file. The part is formed in the form of loose powder surrounded by the mould powder again in a loose state. The whole assembly can then be sintered by a conventional method and the mould powder, which has a higher sintering temperature than that of part powder, remains in the loose state after sintering and can be removed.
Findings
Complex‐shaped components containing re‐entrant cavities and the capability of being made with 3D functional gradients can be rendered directly as a powder preform suitable for subsequent compaction or direct sintering in a conventional furnace. The flowability and compatibility of the powders need to be selected carefully and the track distance between part/mould powders is important for forming a vertical wall.
Research limitations/implications
The main factors affecting building from powder tracks are identified, including the effect of track distance at an interface on integrity, discontinuous feeding on bends and the effects of fill strategies. The flow rates of the part and mould powder as well as their geometrical maps are controlled computationally. Materials and instrumental aspects are discussed.
Originality/value
This paper describes a method to produce complex‐shaped object without residual stress and expensive lasers and the process could be modified to include 3D functional gradients.
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The chapter addresses the use of corporate social responsibility (CSR) as an indicator of social change and progress towards sustainability by analysing how stakeholders shift…
Abstract
The chapter addresses the use of corporate social responsibility (CSR) as an indicator of social change and progress towards sustainability by analysing how stakeholders shift their CSR perceptions in different economic conjunctures between visions that are closer to communication or to governance as structures of network interaction. A matrix is presented that defines four models of CSR perception by integrating theoretical approaches of CSR framed by market or by society, by communication or by governance. Stakeholders’ perceptions are then positioned in the matrix through qualitative analysis of the diverse definitions, constructions and positions with respect to CSR made and adopted by corporate agents, social stakeholders and communicators in their discourses. The study proves that changes in how actors perceive and explain self-governed CSR do not depend so much on economic factors as on the networks of stakeholder interaction through communication and governance. Mapping CSR stakeholders’ perceptions indicates changes and limiting actors, but is not enough to isolate the triggers of those changes. The maps provide a starting point for further exploration of (de)politicization, framing, and understanding of CSR communication and governance, and for the analysis of the limitations of the current model of CSR self-governance. The theoretical approach and methodology provide a framework that integrates communication and governance as relational structures of network interaction in CSR.
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Epidemiology is often described as “the basic science of public health” (Savitz, Poole & Miller, 1999; Syme & Yen, 2000). This description suggests both a close association with…
Abstract
Epidemiology is often described as “the basic science of public health” (Savitz, Poole & Miller, 1999; Syme & Yen, 2000). This description suggests both a close association with public health practice, and the separation of “pure” scientific knowledge from its application in the messy social world. Although the attainability of absolute objectivity is rarely claimed, epidemiologists are routinely encouraged to “persist in their efforts to substitute evidence for faith in scientific reasoning” (Stolley, 1985, p. 38) and reminded that “public health decision makers gain little from impassioned scholars who go beyond advancing and explaining the science to promoting a specific public health agenda” (Savitz et al., 1999, p. 1160). Epidemiology produces authoritative data that are transformed into evidence which informs public health. Those data are authoritative because epidemiology is regarded as a neutral scientific enterprise. Because its claims are grounded in science, epidemiological knowledge is deemed to have “a special technical status and hence is not contestable in the same way as are say, religion or ethics” (Lock, 1988, p. 6). Despite the veneer of universality afforded by its scientific pedigree, epidemiology is not a static or monolithic discipline. Epidemiological truth claims are embodied in several shifting paradigms that span the life of the discipline. Public health knowledges and practices, competing claims internal and external to epidemiology, and structural conditions (such as current political economies, material technologies, and institutions) provide important contexts in which certain kinds of epidemiological knowledge are more likely to emerge.
Krista M. C. Cline and Catherine M. Bain
While research on intergenerational service learning has focused on the benefits for the students, very few studies have focused on the older adults who are the recipients of the…
Abstract
While research on intergenerational service learning has focused on the benefits for the students, very few studies have focused on the older adults who are the recipients of the service learning. For the current study, we were interested in the benefits of service learning for both the college students and the older adults who participated in a service-learning course. Qualitative data were collected from both the students in a sociology of aging service-learning class and the older adults who participated as recipients of the service learning. Data from the students were collected via student journals and open-ended questionnaire responses written by the students. Data from the older adults were collected via interviews by the students as well as open-ended questionnaire responses written by the older adults. The following themes emerged as benefits to students: (1) a better understanding and less fear of aging; (2) a desire to learn more about older adults; (3) a desire to engage more with older adults. The themes for the benefits to the older adults included (1) improved social connections and companionship and (2) becoming family. We found that engaging in intergenerational service-learning courses is beneficial to all those who are involved.
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Keywords
- Service learning
- older adults
- aging
- community engagement
- higher education
- liberal arts education
- academic growth
- professional development
- sociology
- personal development
- academic development
- non-traditional learning
- qualitative research
- community
- gerontology
- assisted living
- interviews
- social connections
- leadership
- integrated learning
- public service
- student centered pedagogy
- continuing care retirement community
A. Öchsner and J. Gr´cio
This paper attempts to cover the thermal processes in syntactic metal foams. Regularshaped cubic closed‐cell structures with spherical pores are investigated by means of the…
Abstract
This paper attempts to cover the thermal processes in syntactic metal foams. Regularshaped cubic closed‐cell structures with spherical pores are investigated by means of the finite element method. Based on the numerical modelling of the microstructure, the effective macroscopic thermal properties are evaluated. Different relative densities (0.95 ‐ 0.5) and different base materials (aluminium and iron) are considered. Furthermore, the influence of the geometry, i.e. spherical ‐ cubical for 3D and circular ‐ rectangular for 2D models, is investigated. The focus is on such cellular materials where the transport of heat is dominated by solid conduction and thermal radiation; contributions from gaseous conduction and convection are neglected.
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Xuesong Lu, Yoonjae Lee, Shoufeng Yang, Yang Hao, Julian Evans and Clive Parini
The aim of this paper is to provide an easy method of extrusion freeforming to fabricate microwave electromagnetic bandgap (EBG) crystals. EBG crystals are periodic dielectric…
Abstract
Purpose
The aim of this paper is to provide an easy method of extrusion freeforming to fabricate microwave electromagnetic bandgap (EBG) crystals. EBG crystals are periodic dielectric structures that can block wave propagation and generate a bandgap. These crystals can be used in high capability antennae, electromagnetic wave semiconductors, microresonators, high‐reflectivity mirrors and polarizing beam splitters.
Design/methodology/approach
The effects of extrusion process parameters and paste characteristics were investigated. Finally, one‐period and two‐period woodpile EBG crystals with bandgaps in the frequency region of 90‐110 GHz were fabricated and the bandgap was measured.
Findings
The filament diameter is influenced by whether extrusion is carried out with or without a substrate and by the free fall‐distance from the nozzle. The quality of lattice structures is dependent on paste flow and properties. A ceramic paste with 60 vol. % (the fraction of ceramic powder based on solvent‐free polymer) was well suited to fabrication. The solvent content also influenced the fabrication. The experimental results show that under ∼12 per cent solvent mass fraction in the paste and relatively high extrusion ram velocity (more than 0.014 mm/s) at a pressure of 14 MPa, samples with high quality were fabricated.
Originality/value
This paper demonstrates that the rapid prototyping method of extrusion freeforming can be applied for the fabrication of EBG crystals from ceramic powders and the important factors which influence the product quality are identified.
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Nicholas A. Conzelmann, Lovro Gorjan, Fateme Sarraf, Lily D. Poulikakos, Manfred N. Partl, Christoph R. Müller and Frank J. Clemens
This study aims to fabricate complex ceramic tetrahedron structures, which are challenging to produce by more conventional methods such as injection molding. To achieve this aim…
Abstract
Purpose
This study aims to fabricate complex ceramic tetrahedron structures, which are challenging to produce by more conventional methods such as injection molding. To achieve this aim, thermoplastic-ceramic composite filaments were developed and printed with unmodified, consumer-grade, fused deposition modelling (FDM) printers instead.
Design/methodology/approach
Al2O3 ceramic powder was mixed with ethylene vinyl acetate polymer as a binder (50 Vol.- per cent) to form a filament with a constant diameter of 1.75 mm. After the printing and thermal treatment stages, the shrinkage and mechanical properties of cuboid and tetrahedron structures were investigated.
Findings
The shrinkage of the parts was found to be anisotropic, depending on the orientation of the printing pattern, with an increase of 2.4 per cent in the (vertical) printing direction compared to the (horizontal) printing layer direction. The alignment of the ceramic particle orientations introduced by FDM printing was identified as a potential cause of the anisotropy. This study further demonstrates that using a powder bed during the thermal debinding process yields sintered structures that can withstand twice the compressive force.
Originality/value
Ceramic FDM had previously been used primarily for simple scaffold structures. In this study, the applicability of ceramic FDM was extended from simple scaffolds to more complex geometries such as hollow tetrahedra. The structures produced in this study contain dense parts printed from multiple contiguous layers, as compared to the open structures usually found in scaffolds. The mechanical properties of the complex ceramic parts made by using this FDM technique were also subjected to investigation.
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M. Bayes, K. Chiba and Y. Kurokawa
The key to the production of high quality multilayer PWBs lies in a clear understanding of the many interactions between the chemical and mechanical processing involved. This…
Abstract
The key to the production of high quality multilayer PWBs lies in a clear understanding of the many interactions between the chemical and mechanical processing involved. This describes some of these interactions, namely those between oxide treatment, lamination and drilling and the subsequent chemical processing steps, up to, and including, copper electroplating. Choice of oxide treatment has consequences that are not limited to the lamination and drilling operations. Process problems, such as ‘pink ring (haloing)’ are discussed in the context of their sensitivity to particular stages in the manufacturing process.
M. Tarik Arafat, Ian Gibson and Xu Li
This paper aims to review the advances in additive manufactured (AM) scaffolds for bone tissue engineering (TE). A discussion on the state of the art and future trends of bone TE…
Abstract
Purpose
This paper aims to review the advances in additive manufactured (AM) scaffolds for bone tissue engineering (TE). A discussion on the state of the art and future trends of bone TE scaffolds have been done in terms of design, material and different AM technologies.
Design/methodology/approach
Different structural features and materials used for bone TE scaffolds are evaluated along with the discussion on the potential and limitations of different AM scaffolds. The latest research to improve the biocompatibility of the AM scaffolds is also discussed.
Findings
The discussion gives a clear understanding on the recent research trend in bone TE AM scaffolds.
Originality/value
The information available here would be useful for the researchers working on AM scaffolds to get a quick overview on the recent research trends and/or future direction to work on AM bone TE scaffolds.
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Jack Hinton, Dejan Basu, Maria Mirgkizoudi, David Flynn, Russell Harris and Robert Kay
The purpose of this paper is to develop a hybrid additive/subtractive manufacturing platform for the production of high density ceramic components.
Abstract
Purpose
The purpose of this paper is to develop a hybrid additive/subtractive manufacturing platform for the production of high density ceramic components.
Design/methodology/approach
Fabrication of near-net shape components is achieved using 96 per cent Al3O2 ceramic paste extrusion and a planarizing machining operations. Sacrificial polymer support can be used to aid the creation of overhanging or internal features. Post-processing using a variety of machining operations improves tolerances and fidelity between the component and CAD model while reducing defects.
Findings
This resultant three-dimensional monolithic ceramic components demonstrated post sintering tolerances of ±100 µm, surface roughness’s of ∼1 µm Ra, densities in excess of 99.7 per cent and three-point bending strength of 221 MPa.
Originality/value
This method represents a novel approach for the digital fabrication of ceramic components, which provides improved manufacturing tolerances, part quality and capability over existing additive manufacturing approaches.