Eligiusz W. Postek, Roland W. Lewis and David T. Gethin
This paper sets out to present developments of a numerical model of squeeze casting process.
Abstract
Purpose
This paper sets out to present developments of a numerical model of squeeze casting process.
Design/methodology/approach
The entire process is modelled using the finite element method. The mould filling, associated thermal and thermomechanical equations are discretized using the Galerkin method. The front in the filling analysis is followed using volume of fluid method and the advection equation is discretized using the Taylor Galerkin method. The coupling between mould filling and the thermal problem is achieved by solving the thermal equation explicitly at the end of each time step of the Navier Stokes and advection equations, which allows one to consider the actual position of the front of the filling material. The thermomechanical problem is defined as elasto‐visco‐plastic described in a Lagrangian frame and is solved in the staggered mode. A parallel version of the thermomechanical program is presented. A microstructural solidification model is applied.
Findings
During mould filling a quasi‐static Arbitrary Lagrangian Eulerian (ALE) is applied and the resulting temperatures distribution is used as the initial condition for the cooling phase. During mould filling the applied pressure can be used as a control for steering the distribution of the solidified fractions.
Practical implications
The presented model can be used in engineering practice. The industrial examples are shown.
Originality/value
The quasi‐static ALE approach was found to be applicable to model the industrial SQC processes. It was found that the staggered scheme of the solution of the thermomechanical problem could parallelize using a multifrontal parallel solver.
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Roland W. Lewis, Eligiusz W. Postek, Zhiqiang Han and David T. Gethin
To present a numerical model of squeeze casting process.
Abstract
Purpose
To present a numerical model of squeeze casting process.
Design/methodology/approach
The modelling consists of two parts, namely, the mould filling and the subsequent thermal stress analysis during and after solidification. Mould filling is described by the Navier‐Stokes equations discretized using the Galerkin finite element method. The free surface is followed using a front tracking procedure. A thermal stress analysis is carried out, assuming that a coupling exists between the thermal problem and the mechanical one. The mechanical problem is described as an elasto‐visco‐plastic formulation in an updated Lagrangian frame. A microstructural solidification model is also incorporated for the mould filling and thermal stress analysis. The thermal problem is solved using enthalpy method.
Findings
During the mould‐filling process a quasi‐static arbitrary Lagrangian‐Eulerian (ALE) approach and a microstructural solidification model were found to be applicable. For the case of the thermal stress analysis the influence of gap closure, effect of initial stresses (geometric nonlinearity), large voids and good performance of a microstructural model have been demonstrated.
Research limitations/implications
The model can also be applied to the simulation of indirect castings. The final goal of the model is the ability to simulate the forming of the material after mould filling and during the solidification of the material. This is possible to achieve by applying arbitrary contact surfaces due to the sliding movement of the cast versus the punch and die.
Practical implications
The presented model can be used in engineering practice, as it incorporates selected second‐order effects which may influence the performance of the cast.
Originality/value
During the mould‐filling procedure a quasi‐static ALE approach has been applied to SQC processes and found to be generally applicable. A microstructural solidification model was applied which has been used for the thermal stress analysis only. During the thermal stress analysis the influence of gap closure and initial stresses (geometric nonlinearity) has been demonstrated.
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David T. Gethin and Shahrir Abdullah
Presents a quasi three‐dimensional formulation for filling a thin section cavity which is derived under the assumption that no transverse flow occurs in the gap. A no‐slip…
Abstract
Presents a quasi three‐dimensional formulation for filling a thin section cavity which is derived under the assumption that no transverse flow occurs in the gap. A no‐slip condition was applied on all surfaces occupied by the fluid and a slip condition on all air‐filled (empty) surfaces. The formulation was developed to analyse the sections which lie in the xy‐plane or may be oriented arbitrarily in three‐dimensional space. Solves the discretized thickness‐integrated finite element flow equations by using the implicit mixed velocity‐pressure formulation, and uses the volume of fluid (VOF) method to track the free surfaces. Presents numerical examples which confirm the accuracy of the formulation and demonstrate how it can be used to model the filling of planar and three‐dimensional thin section cavities of irregular shape.
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Mark Butler, Michael Savic, David William Best, Victoria Manning, Katherine L. Mills and Dan I. Lubman
The purpose of this paper is to examine the strategies utilised to facilitate the wellbeing of workers of an alcohol and other drug (AOD) therapeutic community (TC)
Abstract
Purpose
The purpose of this paper is to examine the strategies utilised to facilitate the wellbeing of workers of an alcohol and other drug (AOD) therapeutic community (TC)
Design/methodology/approach
This paper reports on the findings of a qualitative study that involved in-depth interviews with 11 workers from an Australian AOD TC organisation that provides both a residential TC program and an outreach program. Interviews were analysed using thematic analysis
Findings
Three main interconnected themes emerged through analysis of the data: the challenges of working in an AOD TC organisation, including vicarious trauma, the isolation and safety of outreach workers and a lack of connection between teams; individual strategies for coping and facilitating wellbeing, such as family, friend and partner support and self-care practices; organisational facilitators of worker wellbeing, including staff supervision, employment conditions and the ability to communicate openly about stress. The analysis also revealed cross-cutting themes including the unique challenges and wellbeing support needs of outreach and lived experience workers.
Research limitations/implications
Rather than just preventing burnout, AOD TC organisations can also play a role in facilitating worker wellbeing.
Practical implications
This paper discusses a number of practical suggestions and indicates that additional strategies targeted at “at risk” teams or groups of workers may be needed alongside organisation-wide strategies.
Originality/value
This paper provides a novel and in-depth analysis of strategies to facilitate TC worker wellbeing and has implications for TC staff, managers and researchers.
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Melissa Thomas-Hunt, Meredith Gethin-Jones and Susan Fleming
Marissa Mayer has been asked to think about factors that were impacting Google's ability to innovate and adjust its strategy so that the organization could remain one of the…
Abstract
Marissa Mayer has been asked to think about factors that were impacting Google's ability to innovate and adjust its strategy so that the organization could remain one of the world's foremost leaders in technology. In an industry (and at a company) that was changing and growing exponentially, it would be difficult to pinpoint specific variables and trends. But Mayer knew that one element crucial to Google's ongoing success would be its ability to recruit the best talent available and foster an environment that would encourage that talent to generate the best ideas. As Mayer contemplated how to ensure this, she considered that women currently represented only a small fraction of Google's engineers, suggesting a missed opportunity.
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David Tudor Gethin, Eifion Huw Jewell and Tim Charles Claypole
Printed flexible circuits that combined conventional silicon technology will enable the realisation of many value added products such as smart packaging for the fast moving…
Abstract
Purpose
Printed flexible circuits that combined conventional silicon technology will enable the realisation of many value added products such as smart packaging for the fast moving consumer goods (FMCG) industry. This paper aims to describe an investigation into integrating silicon and printable circuits for the FMCG packaging industry and this would allow products with features such as brand protection, time temperature indicators, customer feedback and visual product enhancement. Responding to interest from the FMCG packaging industry, an investigation was carried out which investigated the printing conductive silver ink on common packaging substrates.
Design/methodology/approach
Standard IC mounting patterns were screen printed using two conductive silver materials (one high silver content traditional paste and one lower silver content gel polymer) to four plastic and three paper substrates which represent common FMCG substrates (HDPE, BOPP, PET and three paper substrates). Materials were characterised in terms of material rheology whereas prints were characterised through electrical performance and printed film topology.
Findings
There was a significant interaction between the substrate, silver ink formulation and the resultant line quality, line topology and conductivity. On paper substrates, the absorption of binder into the substrate resulted in denser silver packing and higher conductivity for the paste material. Higher conductivities were obtained on the substrates capable of withstanding higher curing temperatures. On the polymer substrates higher conductivity could be obtained by lower content silver materials due to the denser particle packing in the cured ink film as a result of its higher solvent/lower solids components.
Research limitations/implications
Further work should examine the interactions for other printing processes commonly used in the FMCG industry such as rotogravure of flexography and should also examine nano particle materials. Further work should also address the mechanical adhesion of silicon logic on the substrates and bottlenecks in processing.
Practical implications
The lower silver content gel material potentially provides material cost reduction by a factor of between 4 and 7 for the same conductivity. The gel material also has potential for more uniform performance across all substrate types. Typically 3.1 Ω/cm resistance values are achieved on all substrates for 300 micron lines.
Originality/value
For those in the field of smart packaging the work has highlighted the interaction between silver materials and non PET/PEN substrates in flexible printed circuits. It has demonstrated the implications of rheology, substrate absorbency and materials processing temperature on circuit design. For those seeking printing process understanding it has provided further validation to support material transfer mechanisms in the screen printing process.
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This chapter focuses on a pathway for the creation of a just and equitable food system in South Africa that contributes to achieving the right to food and livelihoods for all. It…
Abstract
This chapter focuses on a pathway for the creation of a just and equitable food system in South Africa that contributes to achieving the right to food and livelihoods for all. It is based on years of ongoing research on food systems in South Africa and Tanzania as well as a current research project on the impact of COVID-19 regulations on food systems in South Africa, Ghana and Tanzania. The chapter starts with looking at the challenges of the food system in South Africa, the problematic approaches to addressing these challenges and how the situation has been exacerbated by the COVID-19 crisis. Then it explores a different way of looking at and transforming the food system that moves away from the focus on corporate driven solutions and applies a different lens to analysing who the stakeholders are. The argument is for the advancement of economic actors identified by where they sit on the intersecting continuums from more marketised to more socially embedded, from more elite to the subaltern, and from larger to smaller scale. This lens makes it clear which type of enterprises and economic actors need to be supported and the alliances that need to be built to create a pathway to a better food future in the urbanising South African society and perhaps elsewhere as well.
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In its passage through the Grand Committee the Food Bill is being amended in a number of important particulars, and it is in the highest degree satisfactory that so much interest…
Abstract
In its passage through the Grand Committee the Food Bill is being amended in a number of important particulars, and it is in the highest degree satisfactory that so much interest has been taken in the measure by members on both sides of the House as to lead to full and free discussion. Sir Charles Cameron, Mr. Kearley, Mr. Strachey, and other members have rendered excellent service by the introduction of various amendments; and Sir Charles Cameron is especially to be congratulated upon the success which has attended his efforts to induce the Committee to accept a number of alterations the wisdom of which cannot be doubted. The provision whereby local authorities will be compelled to appoint Public Analysts, and compelled to put the Acts in force in a proper manner, and the requirement that analysts shall furnish proofs of competence of a satisfactory character to the Local Government Board, will, it cannot be doubted, be productive of good results. The fact that the Local Government Board is to be given joint authority with the Board of Agriculture in insuring that the Acts are enforced is also an amendment of considerable importance, while other amendments upon what may perhaps be regarded as secondary points unquestionably trend in the right direction. It is, however, a matter for regret that the Government have not seen their way to introduce a decisive provision with regard to the use of preservatives, or to accept an effective amendment on this point. Under existing circumstances it should be plain that the right course to follow in regard to preservatives is to insist on full and adequate disclosure of their presence and of the amounts in which they are present. It is also a matter for regret that the Government have declined to give effect to the recommendation of the Food Products Committee as to the formation of an independent and representative Court of Reference. It is true that the Board of Agriculture are to make regulations in reference to standards, after consultation with experts or such inquiry as they think fit, and that such inquiries as the Board may make will be in the nature of consultations of some kind with a committee to be appointed by the Board. There is little doubt, however, that such a committee would probably be controlled by the Somerset House Department; and as we have already pointed out, however conscientious the personnel of this Department may be—and its conscientiousness cannot be doubted—it is not desirable in the public interest that any single purely analytical institution should exercise a controlling influence in the administration of the Acts. What is required is a Court of Reference which shall be so constituted as to command the confidence of the traders who are affected by the law as well as of all those who are concerned in its application. Further comment upon the proposed legislation must be reserved until the amended Bill is laid before the House.
E.H. Jewell, S.M. Hamblyn, T.C. Claypole and D.T. Gethin
The purpose of this paper is to carry out a comprehensive experimental investigation into the role of screen and conductive carbon material formulation on line conductivity and…
Abstract
Purpose
The purpose of this paper is to carry out a comprehensive experimental investigation into the role of screen and conductive carbon material formulation on line conductivity and printing capability in the screen printing process, to provide design knowledge and further understanding of the screen printing for printed carbon.
Design/methodology/approach
A full factorial experiment was carried out where six carbon materials were printed through ten screens to a polyester substrate under a set of standard conditions.
Findings
Material characterization showed that viscosity and the corresponding viscous and elastic material modulli increased with solids content and that the elastic properties at low shear are significant. The solids carbon content materials were unable to produce the minimum printable line features possible with the low carbon materials. Increasing the solids contents reduced the final cured line resistance, reduced the printed line width, increased the film thickness, increased the cross sectional area and reduced the material resistivity. Material resistivities were around 700 to 950 μΩcm were obtained in the printed lines.
Research limitations/implications
Lower material resistivities were obtained with higher solids materials and it is postulated that the increased visco‐elastic nature of the solids content materials, play a role in determining the microscopic structure of the cured film through alignment of the carbon graphite platelets.
Practical implications
A dataset which allows material, screen and print characteristics has been created allowing process optimization and formulation development to be accelerated.
Originality/value
The work provides insight into the role of material properties and process settings on the electrical and physical characteristics of printed carbon.