bluuebunny/crossref_metadata_2025_split huggingface dataset:
Freeform fabrication of ionomeric polymer‐metal composite actuators
Authors: Malone Evan , Lipson Hod 
Published: January 2007

PurposeTo seek to produce low‐voltage, soft mechanical actuators entirely via freeform fabrication as part of a larger effort to freeform fabricate complete electromechanical devices with lifelike and/or biocompatible geometry and function.Design/methodology/approachThe authors selected ionomeric polymer‐metal composite (IPMC) actuators from the literature and the authors' own preliminary experiments as most promising for freeform fabrication. The authors performed material formulation and manual device fabrication experiments to arrive at materials which are amenable to robotic deposition and developed an SFF process which allows the production of complete IPMC actuators and their fabrication substrate integrated within other freeform fabricated devices. The authors freeform fabricated simple IPMC's, explored some materials/performance interactions, and preliminarily characterized these devices in comparison to devices produced by non‐SFF methods.FindingsFreeform fabricated IPMC actuators operate continuously in air for more than 4 h and 3,000 bidirectional actuation cycles. The output stress scaled to input power is one to two orders of magnitude inferior to that of non‐SFF devices. Much of this difference may be associated with process‐sensitive microstructure of materials. Future work will investigate this performance gap.Research limitations/implicationsDevice performance is sufficient to continue exploration of SFF of complete electromechanical devices, but will need improvement for broader application. The feasibility of the approach for producing devices with complex, non‐planar geometry has not been demonstrated.Practical implicationsThis work demonstrates the feasibility of freeform fabricating IPMC devices, and lays groundwork for further development of the materials and methods.Originality/valueThis work constitutes the first demonstration of complete, functional, IPMC actuators produced entirely by freeform fabrication.
Residual stresses in selective laser sintering and selective laser melting
Authors: Mercelis Peter , Kruth Jean‐Pierre 
Published: January 2007

PurposeThis paper presents an investigation into residual stresses in selective laser sintering (SLS) and selective laser melting (SLM), aiming at a better understanding of this phenomenon.Design/methodology/approachFirst, the origin of residual stresses is explored and a simple theoretical model is developed to predict residual stress distributions. Next, experimental methods are used to measure the residual stress profiles in a set of test samples produced with different process parameters.FindingsResidual stresses are found to be very large in SLM parts. In general, the residual stress profile consists of two zones of large tensile stresses at the top and bottom of the part, and a large zone of intermediate compressive stress in between. The most important parameters determining the magnitude and shape of the residual stress profiles are the material properties, the sample and substrate height, the laser scanning strategy and the heating conditions.Research limitations/implicationsAll experiments were conducted on parts produced from stainless steel powder (316L) and quantitative results cannot be simply extrapolated to other materials. However, most qualitative results can still be generalized.Originality/valueThis paper can serve as an aid in understanding the importance of residual stresses in SLS/SLM and other additive manufacturing processes involving a localized heat input. Some of the conclusions can be used to avoid problems associated with residual stresses.
Improving accuracy of powder‐based SFF processes by metal deposition from a nanoparticle dispersion
Authors: Crane Nathan B. , Wilkes J. , Sachs E. , Allen Samuel M. 
Published: January 2007

PurposeSolid freeform fabrication processes such as three‐dimensional printing (3DP) and selective laser sintering (SLS) produce porous parts. Metal parts produced by these processes must be densified by sintering or infiltration to achieve maximum material performance. New steel infiltration methods can produce parts of standard alloy compositions with properties comparable to wrought materials. However, the infiltration process introduces dimensional errors due to both shrinkage and creep — particularly at the high temperatures required for steel infiltration. Aims to develop post‐processing method to reduce creep and shrinkage of porous metal skeletons.Design/methodology/approachThe proposed process treats porous metal parts with a nanoparticle suspension that strengthens the bonds between particles to reduce creep and sintering shrinkage during infiltration. The process is tested by comparing the deflection and shrinkage of treated and untreated cantilevers heated to infiltration temperatures. The method is demonstrated with an iron nanoparticles suspension applied to parts made of 410 SS powder.FindingsThis process reduced creep by up to 95 percent and shrinkage by 50 percent. The best results were obtained using multiple applications of the nanoparticles dried under a magnetic field. Carbon deposited with the iron is shown to provide substantial benefit, but the iron is critical to establish strong bonds at low temperatures for minimal creep.Research limitations/implicationsThis work shows that dimensional stability of porous metal skeletons during infiltration processes can be significantly improved by treatment with nanoparticles. The increased dimensional stability afforded by this technique can combine the excellent properties of homogenous infiltration with substantially improved part accuracy and open up new applications for this manufacturing technology.Originality/valueThe work shows how solid freeform fabrication processes can be improved.
Development of SLS fuel cell current collectors
Authors: Chen Ssuwei , Murphy Jeremy , Herlehy Jason , Bourell David L. , Wood Kristin L. 
Published: January 2007

PurposeThis paper aims to present a new fabrication method for fuel cell current collectors. Demonstration of its usefulness and discussion of its impact on current collector design and performance are also given.Design/methodology/approachThe selective laser sintering (SLS) technique is used to create green parts followed by a high temperature curing process and pressureless infiltration treatment to meet basic part design requirements.FindingsA material system and process satisfying both manufacturing constraints and product property requirements can be used for fabrication of current collectors via SLS. Relative particle size and composition of the constituents play an important role in successful manufacture of the plates. Strategies to improve electrical conductivity are also discussed.Originality/valueA new manufacturing method has been developed for the construction of fuel cell current collectors that could generate opportunities for performance enhancement and fuel cell application by eliminating the constraints imposed by traditional fabrication processes.
An experimental investigation of the surface roughness of parts produced by LOM process
Authors: Kechagias John 
Published: January 2007

PurposeTo investigate the influence of different process parameters of the laminated object manufacturing (LOM) process on the roughness of vertical surfaces alongZ‐axis on ZX‐plane of parts produced by LOM.Design/methodology/approachThe process parameters tested were layer thickness, heater temperature, platform retract, heater speed, laser speed, feeder speed and platform speed. A typical test part has been used, and matrix experiments were carried out based on Taguchi design. Optimal process parameter values were identified and finally, a regression model was applied onto the experimental results, and compared with bibliography models, using arbitrary experiments.FindingsThe statistical analysis of the experimental results showed that the surface roughness depends mainly on the heater temperature, layer thickness, and laser speed. Moreover, the regression model gave good predictions when heater temperature values were within the initial experimental area and inaccurate predictions when heater temperature takes the value 200°C.Research limitations/implicationsFuture work should involve extensive matrix experiments using parameters such as dimensions of test part (Xmax,Ymax,Zmax), hatch spacing inXandYdirections, and delay time between sequential layers.Practical implicationsUsing the extracted regression model, vertical surface roughness can be predicted and selected proprietary process parameter values. This means minimization of post processing time, easier disengagement between supporting frame and part, easier decubing, process optimization, and less finishing.Originality/valueThis methodology could be easily applied on different materials and initial conditions for optimisation of LOM processes.
Design and production of fixtures for free‐form components using selective laser sintering
Authors: Grazia Violante Maria , Iuliano Luca , Minetola Paolo 
Published: January 2007

PurposeTo introduce an innovative method for the design of supporting elements to be applied to the free‐form components during the dimensional control.Design/methodology/approachThis paper shows an innovative procedure based on reverse engineering and rapid prototyping techniques for the realization of fixtures fitting the geometry of free‐form elements. The application of the procedure have been made on a sheet metal free‐form element. After the design and manufacturing of the supporting elements, some uniformly distributed measurements have been made on the sheet metal component. A coordinate measuring machine (CMM) has been used in order to get dimensional information and to give the IT class location of the component.FindingsThe use of the CMMs for the dimensional control of the production elements requires the availability of an adequate supporting system above all if the control concerns free‐form components with complex forms. This influences considerably the final quality of the measurements mainly if the control concerns free‐form components with complex forms, not bound to classic geometric entities. The supporting systems commonly used foresee the utilization of standard elements (clamps, magnets, suction cups and plates and others) ideal for the parts with regular geometry but that can cause inconveniences if applied to free‐form elements and long times for the part supporting. The supporting elements of our paper fit to the geometry of free‐form component.Research limitations/implicationsFor the production of the supporting elements, the chosen technique has been the selective laser sintering with the use of the Pa‐Al powders (alumide). This material has a limited mechanical resistance such to guarantee a control up to 500 parts. For this reason, in a future research we would produce these fixtures using sintered metal materials.Practical implicationsThe possibility to guarantee a correct dimensional control in the case of free form components using fixtures that fit to the geometry of free form components.Originality/valueThe paper shows an innovative procedure to get fixturing elements that fit to the geometry of free‐form component and provide stability and immobility to the component during the inspection phase.
Non‐toxic flexible photopolymers for medical stereolithography technology
Authors: Bens Arthur , Seitz Hermann , Bermes Günter , Emons Moritz , Pansky Andreas , Roitzheim Barbara , Tobiasch Edda , Tille Carsten 
Published: January 2007

PurposeTo describe the development of a novel polyether(meth)acrylate‐based resin material class for stereolithography with alterable material characteristics.Design/methodology/approachA complete overview of details to composition parameters, the optimization and bandwidth of mechanical and processing parameters is given. Initial biological characterization experiments and future application fields are depicted. Process parameters are studied in a commercial 3D systems Viper stereolithography system, and a new method to determine these parameters is described herein.FindingsInitial biological characterizations show the non‐toxic behavior in a biological environment, caused mainly by the (meth)acrylate‐based core components. These photolithographic resins combine an adjustable low Young's modulus with the advantages of a non‐toxic (meth)acrylate‐based process material. In contrast to the mostly rigid process materials used today in the rapid prototyping industry, these polymeric formulations are able to fulfill the extended need for a soft engineering material. A short overview of sample applications is given.Practical implicationsThese polymeric formulations are able to meet the growing demand for a resin class for rapid manufacturing that covers a bandwidth from softer to stiffer materials.Originality/valueThis paper gives an overview about the novel developed material class for stereolithography and should be therefore of high interest to people with interest in novel rapid manufacturing materials and technology.
Cooperation in regional new venture support networks: experiences from Germany
Authors: Kautonen Teemu , Koch Lambert T. 
Published: January 2007

PurposeTo introduce new venture support networks (NVSN) as a topical instrument in German entrepreneurship policy, and to discuss critically the problems in achieving cooperation between the member organizations in these networks.Design/methodology/approachConceptual analysis with illustrative empirical examples derived from 17 semi‐structured interviews with actors involved in the German federal NVSN initiative “EXIST – Entrepreneurs from Universities”.FindingsIdentifies two major sources of obstacles to achieving cooperation in politically initiated NVSN: heterogeneous actor structure; and lack of culture as a network due to the “artificial” political origin of the network.Research limitations/implicationsThe paper only identifies problem areas and illustrates these with empirical examples. Further research is required so as to analyse how the problem areas could be improved.Practical implicationsIdentified problem areas should be considered when planning (entrepreneurship) policy initiatives that include inter‐organizational cooperation.Originality/valueIntroduces and critically analyses a topical and so far little studied phenomenon of entrepreneurship policy.
Are performance differences between family and non‐family SMEs uniform across all firm sizes?
Authors: Kotey Bernice 
Published: January 2007

PurposeThe purpose of this study is to examine the impact of firm size on performance (measured as profits, growth, efficiency and liquidity) differences between family and non‐family small‐ to medium‐sized enterprises (SMEs).Design/methodology/approachThe samples of 441 family and 473 non‐family firms were divided into four size groups and performance differences analysed for each size group using MANOVA.FindingsThe findings indicate that family SMEs perform at least as well as non‐family SMEs. Although the two types of firms shared several similar performance characteristics at the small level, certain differences were evident. Performance differences between family and non‐family SMEs became prominent at the critical growth phase (20‐49 employees), reached an optimum at 50‐99 employees and narrowed again thereafter. For family firms, the benefits of higher gross margins and efficient use of assets began to wane after 100 plus employees but the disadvantages of lower employee performance continued.Research limitations/implicationsThe study could be improved by a longitudinal examination of the same firms across various growth stages. Further, the findings may be industry‐specific and not generally applicable.Practical implicationsThe findings show that greater resources do not necessary lead to better performance and that non‐family firms could benefit from more efficient use of resources. The findings also confirm that the benefits of the informal system are not sustainable at larger firm sizes and that larger family firms would benefit from improved management of employee performance.Originality/valueThe pattern of performance differences observed between family and non‐family SMEs is unique to the paper. The paper shows that differences in performance between the two types of firms noted in the literature do no hold at all firm sizes.
Enterprising talk: a case of self construction
Authors: Mills Colleen E. , Pawson Kylie 
Published: January 2007

PurposeThis paper presents a case study that explores the experiences and sensemaking of a new start entrepreneur in New Zealand. The primary aim of the case was to theorise new entrepreneurs' sensemaking about risk in order to provide a framework for further study.Design/methodology/approachData for the case were gathered using a semi‐structured interview technique. These data were then coded and analysed using an approach inspired by grounded theory. As the purpose was to examine both what the subject said about her entrepreneurial experience and the conceptual frameworks she drew upon to do this, the analysis integrated techniques employed in discourse analysis and educational psychology.FindingsThe analysis produced a theoretical model that suggests the entrepreneur's perceptions of self shaped the perception of risk and then structured the way in which risks were addressed or avoided.Practical implicationsThis case and the questions that the theoretical model raises have significant implications for entrepreneurs, policy makers and educators. We expect the lines of enquiry suggested by this case will provide a framework for further research on new start entrepreneurs' sensemaking and in so doing help address the dearth of knowledge about New Zealand's new start entrepreneurs' behaviour, particularly in relation to risk assessment.Originality/valueThe case draws attention to the interplay between identity and new start entrepreneurial behaviour and in so doing challenges us to look at new start behaviour in a new way. It raises questions about the centrality of the notion of risk in new start entrepreneurs' rationales for the enterprise development decisions they make.
Entrepreneurial behaviour in the Greek public sector
Authors: Zampetakis Leonidas A. , Moustakis Vassilis 
Published: January 2007

PurposeWhile the term “entrepreneurship” was almost exclusively associated with private sector, it is now found with increasing frequency in the literature on the public sector and public administration. However, research on public entrepreneurs remains restricted to top and middle managers and elected politicians and focuses on policy promotion and initiatives concerning public sector transformation. The perpose of the present article is to extend earlier research to the empirical assessment of entrepreneurial behaviour among front line staff in the Greek public sector.Design/methodology/approachA scale of entrepreneurial behaviour was assessed. A short, self‐report questionnaire was administered to a random sample of 237 public servants working at prefecture level, which is the second level of government in Greece. Exploratory and confirmatory factor analysis of the entrepreneurial behaviour scale contributed to the formation of a hierarchical factor structure with a super‐ordinate entrepreneurial behaviour factor and three lower‐level factors.Research limitations/implicationsThe reported research relied on self‐reports and on a sample from the Greek public sector. Moreover, data are cross‐sectional and alternatives relationships may exist. Future research should be multinational and longitudinal to test the assumptions of the present study and should encompass variables of actual entrepreneurial behaviour.Practical implicationsThe research findings demonstrate that the concept of “public entrepreneurship” is relevant for the average civil servant and reveals facets of entrepreneurial behaviour of front line staff. Moreover, the study finds evidence that there is a positive correlation between the supportive context, as expressed by encouragement of initiatives and access to managerial information, and entrepreneurial behaviour among public servants. As a result, policy makers should take the appropriate measures to build a supportive context for public entrepreneurship.Originality/valueThe research findings are original and unique and are based on established models and theories from the literature on private sector entrepreneurship. The results are based on a sample of public servants working in different prefectures in Greece. In addition, respondents come from different organisational units across each prefecture. The research findings are useful to academics and to policy makers interested in fostering public entrepreneurship.
Igniting the entrepreneurial spirit: is the role parents play gendered?
Authors: Kirkwood Jodyanne 
Published: January 2007

PurposeThe family has the potential to be a breeding ground for entrepreneurs and may be key place where the entrepreneurial spirit is ignited. However, to date there has been little empirical research on how parents may influence their children's subsequent decision to start a new venture.Design/methodology/approachThis study adopts a qualitative approach to investigate, via in‐depth semi‐structured interviews, the experiences of 50 entrepreneurs (25 men and 25 women).FindingsParents influenced participants' decision to create a new venture in a number of ways and two key gender differences were noted in this parental influence. The first related to how the participants were influenced differently by their mothers and fathers, with fathers playing the primary role in the new venture creation decision. The second was differences between how the women and men participants described the ways they were influenced by their parents. Many women entrepreneurs looked to their parents for advice, support and encouragement, while some men desired independence from their parents (primarily fathers) or were trying to compete with them.Research limitations/implicationsLimitations exist due to the sample size and the complexity of motivations for starting a new venture. This study should be followed by more extensive research, addressing the further research questions and directions that are posed.Originality/valueThis empirical study contributes to the literature by enhancing our limited understanding of how parents influence the decision to start a new venture.