Search results

Owing to the operating principle of powder bed fusion processes, selective laser sintering (SLS) requires effective management of the mixture ratio of processed material previously exposed to the high temperatures of processing with new virgin material. Therefore, this paper aims to fully understand the effect that the successive reprocessing has in the powder material and to evaluate its influence on the properties of SLS parts produced at different building orientations.

Polyamide 12 material with 0%, 30% and 50% of virgin powder and parts produced from them were studied through five consecutive building cycles and their mass, mechanical, thermal and microstructural properties were evaluated. Then, the experimental data was used to validate a theoretical algorithm of prediction capable to define the minimum amount of virgin powder to be added on the processed material to produce parts without significant loss of properties.

Material degradation during SLS influences the mass and mechanical properties of the parts, exhibiting an exponential decay property loss until 50% of the initial values. The theoretical algorithms of reprocessing proved the appropriateness to use a mixture of 30% of virgin with 70% of processed material for the most common purposes.

This paper validates a methodology to define the minimum amount of virgin material capable to fulfil the operational specifications of SLS parts as a function of the number of building cycles, depending on the requirements of the final application.

The use of theoretical models of prediction allows to describe the degradation effects of SLS materials during the sintering, ensuring the sustainable management of the processed powder and the economic viability of the process.

With the technological progress, high-performance materials are emerging in the market of additive manufacturing to comply with the advanced requirements demanded for technical applications. In selective laser sintering (SLS), innovative powder materials integrating conductive reinforcements are attracting much interest within academic and industrial communities as promising alternatives to common engineering thermoplastics. However, the practical implementation of functional materials is limited by the extensive list of conditions required for a successful laser-sintering process, related to the morphology, powder size and shape, heat resistance, melt viscosity and others. The purpose of this study is to explore composite materials of polyamide 12 (PA12) incorporating multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GNP), aiming to understand their suitability for advanced SLS applications.

PA12-MWCNT and PA12-GNP materials were blended through a pre-optimized process of mechanical mixing with various percentages of reinforcement between 0.50 wt.% and 3.00 wt.% and processed by SLS with appropriate volume energy density. Several test specimens were produced and characterized with regard to processability, thermal, mechanical, electrical and morphological properties. Finally, a comparative analysis of the performance of both carbon-based materials was performed.

The results of this research demonstrated easier processability and higher tensile strength and impact resistance for composites incorporating MWCNT but higher tensile elastic modulus, compressive strength and microstructural homogeneity for GNP-based materials. Despite the decrease in mechanical properties, valuable results of electrical conductivity were obtained with both carbon solutions until 10^–6 S/cm.

The carbon-based composites developed in this research allow for the expansion of the applicability of laser-sintered parts to advanced fields, including electronics-related industries that require functional materials capable of protecting sensitive devices against electrostatic discharge.

The purpose of this paper is to develop and test an extension of a previously conceived framework for improving and embedding project management (PM) practice in organisations. The framework identifies the most useful project management improvement initiatives (PMIIs) and the key factors for embedding PM practice. However, professionals need guidance on how to operationalise such framework in their organisations, therefore a method for applying the framework is developed.

The method being proposed for applying the framework is demonstrated and tested with a large University–Industry consortium case study. During the case study analysis three research methods were applied: participant observation, document analysis and focus groups.

In what concerns both the PMIIs and key embedding factors in the framework, the proposed method comprises their acknowledgement, scoring, relevance analysis, selection and planning. The detailed report on how the framework was applied in the particular case study also sheds light on how University–Industry consortiums can make use of PM to become more successful.

The research was performed using only one case study which limits the generalisability of its findings.

Detailed guidance is provided for applying the framework’s both constructs, “improving” and “embedding”, through a set of clear steps.

The paper shows the explanatory power of the framework for improving and embedding PM practice in a case study, demonstrating that the method for its application is practical and suitable.

We present a critical literature review debating Brazilian research on social and environmental accounting (SEA). The aim of this study is to understand the role of politics in the construction of hegemonies in SEA research in Brazil. In particular, we examine the role of hegemony in relation to the co-option of SEA literature and sustainability in the Brazilian context by the logic of development for economic growth in emerging economies. The methodological approach adopts a post-structural perspective that reflects Laclau and Mouffe’s discourse theory. The study employs a hermeneutical, rhetorical approach to understand and classify 352 Brazilian research articles on SEA. We employ Brown and Fraser’s (2006) categorizations of SEA literature to help in our analysis: the business case, the stakeholder–accountability approach, and the critical case. We argue that the business case is prominent in Brazilian studies. Second-stage analysis suggests that the major themes under discussion include measurement, consulting, and descriptive approach. We argue that these themes illustrate the degree of influence of the hegemonic politics relevant to emerging economics, as these themes predominantly concern economic growth and a capitalist context. This paper discusses trends and practices in the Brazilian literature on SEA and argues that the focus means that SEA avoids critical debates of the role of capitalist logics in an emerging economy concerning sustainability. We urge the Brazilian academy to understand the implications of its reifying agenda and engage, counter-hegemonically, in a social and political agenda beyond the hegemonic support of a particular set of capitalist interests.

This work aims to examine the communication on Twitter of the most responsible companies in Spain to identify the topics covered on corporate social responsibility (CSR) from the perspective of happiness and social marketing. In addition, the profiles of the messages that show an association with the impact of the messages have been identified.

An empirical analysis of the Twitter posts of Spain's ten most responsible companies has been carried out. The methodology of this work combines data mining techniques, sentiment analysis and content analysis, both from a quantitative and qualitative approach.

The results show that most brand tweets do not deal with CSR-related topics. The topics they address the most are those related to sports and the weather. From the perspective of social marketing, conversational-type tweets are the most published and have achieved the most significant reaction from the public. In addition, four messages' profiles have been identified based on the company and the emotional connotation associated with the impact, giving rise to more outstanding promotion of social causes.

Our main contribution to this work has been to value positive communication and social marketing to promote better CSR on Twitter. In this sense, it has been verified that there is a relationship between the public's reaction, the affective connotation and the company that issues the messages.

The purpose of this paper is to present the application of Design of Experiments techniques for the analysis of operating parameters of an industrial oven for the heat treatment process of polyethylene terephthalate (PET) bottle filaments.

The focus is on evaluating new ways of operating the transformation process. The main issue is to raise what are the variables interfering with the performance of the oven. The complete 2k factorial for three factors of control was used to analyze the behavior of these variables and their relationships in the specific response parameter for the process.

The results presented in this work allow the company to have greater knowledge about the operation of the equipment. The study showed possibilities of 14.8% energy reduction.

The heat treatment activity was characterized as a critical point in the production process, and techniques with empirical approaches, based on statistical techniques, was an opportunity that the company has to improve the execution of activities without major investments for the quality of the final product. The application of statistical quality techniques showed to be very promising.

The fact that the study was conducted using subjective quality performance makes this work different from others presented in the literature, showing the possibility to apply Design of Experiments using main control factors based on the opinion of experienced personnel involved in the process analyzed.

This chapter is designed with the aim to determine the influence of sociodemographic variables on the capacity to generate social enterprises, such as sex, the student’s country, if only they study or if they study and work, as well as if they participate or direct a social enterprise in university students of Latin American business schools. This research adopted an inductive quantitative approach using a questionnaire. The participants were university students of business schools from Colombia, Mexico and Peru. Second-generation structural equation method (SEM-PLS) was used to analyse the results, using the SmartPLS 3.2.7 software applied to data on 3,739 university students. The results suggest that the entrepreneur role, labour situation, country and sex have a moderating effect in the relation between entrepreneurial orientation and entrepreneurial intention. Also, by using resampling technique Bootstrapping (5,000 times,p < 0.01), significance of the trajectory coefficients (beta) and effect size of the coefficients (beta) were measured to demonstrate significance. Finally, with this research the authors ascertain that entrepreneurial orientation positively influences entrepreneurial intention. thus explaining 42.4% of its variance. This chapter is the first attempt on investigating in university students of Latin American business schools about factors of entrepreneurship orientation and entrepreneurship intention, and has strong potential to contribute to development of policies and strategies to promote the growth of entrepreneurship activities in the universities.

This paper aims to explore the influence of the materials used in moulding blocks of hybrid moulds on the injection moulding setup and the properties of the mouldings.

An instrumented (pressure and temperature) hybrid mould with exchangeable moulding blocks, produced by rapid prototyping and tooling techniques (RPT), was used to produce polypropylene tubular mouldings. The configuration of the mould was varied with combinations of moulding block materials, namely, an epoxy resin composite processed by vacuum casting and steel. The processing conditions were adjusted to obtained steady processing conditions. The mouldings were assessed in terms of the microstructure and the shrinkage.

Due to the properties of the moulding block obtained by RPT being different from tool steel, the injection moulding processing conditions and the plastics parts properties are different when hybrid moulds are used. The cycle time depends on the moulding block properties and must be adjusted to the desired running temperature. The morphology of the mouldings is strongly affected by the thermal properties of the moulding block materials. When different materials are used in the core and the cavity asymmetric structures develop in the part. The shrinkage of the mouldings, when resin cores are used is also affected by the deformation of the core caused by the injection pressure.

This paper makes a contribution to understanding the morphology of semi‐crystalline mouldings obtained using hybrid moulds and enhances the importance of the core deformation on the shrinkage of the mouldings.

This paper analyses the strategies designed by Franco´s dictatorship to address the “problem” of children with physical disabilities, focusing on the relevance given to vocational training.

The paper draws mainly on official documents, reports from international organisations, and Spanish experts' papers.

Francoism turned labour into one of the key pillars of its national project and included vocational training in the different stages of school life. From the mid-1950s, vocational training also became a key factor for the dictatorship's strategy towards disability. Following the recommendations issued by international agencies, Francoism began to adopt different measures towards the rehabilitation of children with disabilities. One of them was the creation, in 1959, of a special unit for adolescents within the National Institute for the Rehabilitation of Invalids. In addition to medical treatment, this unit provided children with education and vocational training.

The value of this paper lies in the fact that the topic it analyses has been little studied. Until now no attention has been given to the special unit for adolescents, despite it being a very interesting example of the medical model of disability and its contradictions. During their stay at the unit children were promised greater autonomy and independence, but their lives also became medicalised and they were forced to collaborate with experts.