Aarhus Kommunes Biblioteker (Teknisk Bibliotek), Ingerslevs Plads 7, Aarhus, Denmark. Representative: V. NEDERGAARD PEDERSEN (Librarian).
THE centripetal forces at work in the world seem to draw all human associations into larger groups. Work Study has been no exception to this, as the formation of a European…
Abstract
THE centripetal forces at work in the world seem to draw all human associations into larger groups. Work Study has been no exception to this, as the formation of a European Federation six months ago indicates. Another manifestation of the same tendency is the letter we print from a correspondent suggesting that there is only room for one professional organisation for Work Study in this country.
S.O. Onuh and K.K.B. Hon
The problem of inaccuracies of models manufactured by layer manufacturing technology has greatly limited its intended level of exploitations especially in the down‐stream…
Abstract
The problem of inaccuracies of models manufactured by layer manufacturing technology has greatly limited its intended level of exploitations especially in the down‐stream applications and integration into the FMS and CIM. The principles of cellular manufacturing together with various examples of its application and benefits are well documented. Increased competition combined with customer demand for quality, speed, product performance and lower costs are putting an ever‐greater burden on manufacturing. Not only do products need to be launched faster than ever, but also manufacturing needs to be flexible in rapidly retuning its facilities. The move to cellular manufacturing, TQM or CIM or other techniques alone is thus no longer enough. Instead, the challenge is increasingly one of compressing the time it takes to continually “re‐invent” the manufacturing system in order to meet the prevailing demands of the market place. This paper presents a comparative study on the effects of hatch patterns on stereolithography models using epoxy‐based resin in a CIM environment. A unique experimental investigation has been carried out with two new hatch patterns, Divergent Star‐weave, (DSW), and Diagonal Divergent Star‐weave (DDSW), which have significantly improved the stereolithography product quality, and reduced lead time thus yielding a significant tool in agile manufacturing.
Details
Keywords
P.M. Dickens, R. Stangroom, M. Greul, B. Holmer, K.K.B. Hon, R. Hovtun, R. Neumann, S. Noeken and D. Wimpenny
The Tooling and Casting subgroup of the European Action on Rapid Prototyping (EARP) has undertaken a project to investigate the problems associated with using rapid prototype…
Abstract
The Tooling and Casting subgroup of the European Action on Rapid Prototyping (EARP) has undertaken a project to investigate the problems associated with using rapid prototype models as sacrificial patterns for investment casting. The accuracy and surface finish of the models and the castings were also assessed so that a comparison could be made. Models from each process were manufactured by different members of EARP and then three foundries were each given a set of models to convert to castings. Observes that one of the oldest metal manufacturing techniques, which dates back to 4000‐6000 BC, is being used with one of the most modern ‐ rapid prototyping.
Details
Keywords
M.M. Savalani, L. Hao, P.M. Dickens, Y. Zhang, K.E. Tanner and R.A. Harris
Hydroxyapatite‐polymer composite materials are being researched for the development of low‐load bearing implants because of their bioactive and osteoconductive properties, while…
Abstract
Purpose
Hydroxyapatite‐polymer composite materials are being researched for the development of low‐load bearing implants because of their bioactive and osteoconductive properties, while avoiding modulus mismatch found in homogenous materials. For the direct production of hydroxyapatite‐polymer composite implants, selective laser sintering (SLS) has been used and various parameters and their effects on the physical properties (micro and macro morphologies) have been investigated. The purpose of this paper is to identify the most influential parameters on the micro and macro pore morphologies of sintered hydroxyapatite‐polymer composites.
Design/methodology/approach
A two‐level full factorial experiment was designed to evaluate the effects of the various processing parameters and their effects on the physical properties, including open porosity, average pore width and the percentage of pores which could enable potential bone regeneration and ingrowth of the sintered parts. The density of the sintered parts was measured by weight and volume; optical microscopy combined with the interception method was used to determine the average pore size and proportion of pores suitable to enable bone regeneration.
Findings
It was found that the effect of build layer thickness was the most influential parameter with respect to physical and pore morphology features. Consequently, it is found that the energy density equation with the layer thickness parameter provides a better estimation of part porosity of composite structures than the energy density equation without the layer thickness parameter. However, further work needs to be conducted to overcome the existing error of variance.
Originality/value
This work is the first step in identifying the most significant SLS parameters and their effects on the porosity, micro and macro pore morphologies of the fabricated parts. This is an important step in the further development of implants which may be required.
Details
Keywords
Civil Aircrew Technical Training Course The College of Aeronautical and Automobile Engineering, Chelsea, started in July a new course of evening classes in aircrew technical…
Abstract
Civil Aircrew Technical Training Course The College of Aeronautical and Automobile Engineering, Chelsea, started in July a new course of evening classes in aircrew technical training.
Han Chen and Yaoyao Fiona Zhao
Binder jetting (BJ) process is an additive manufacturing (AM) process in which powder materials are selectively joined by binder materials. Products can be manufactured…
Abstract
Purpose
Binder jetting (BJ) process is an additive manufacturing (AM) process in which powder materials are selectively joined by binder materials. Products can be manufactured layer-by-layer directly from three-dimensional model data. The quality properties of the products fabricated by the BJ AM process are significantly affected by the process parameters. To improve the product quality, the optimal process parameters need to be identified and controlled. This research works with the 420 stainless steel powder material.
Design/methodology/approach
This study focuses on four key printing parameters and two end-product quality properties. Sixteen groups of orthogonal experiment designed by the Taguchi method are conducted, and then the results are converted to signal-to-noise ratios and analyzed by analysis of variance.
Findings
Five sets of optimal parameters are concluded and verified by four group confirmation tests. Finally, by taking the optimal parameters, the end-product quality properties are significantly improved.
Originality/value
These optimal parameters can be used as a guideline for selecting proper printing parameters in BJ to achieve the desired properties and help to improve the entire BJ process ability.
Details
Keywords
Olav Torp, Ingemund Jordanger, Ole Jonny Klakegg and Yvonne C.B. Bjerke
The purpose of the paper is 1) to address the importance of contingency at the right level when defining project control baseline, including cost reserves / “room to manoeuvre”…
Abstract
Purpose
The purpose of the paper is 1) to address the importance of contingency at the right level when defining project control baseline, including cost reserves / “room to manoeuvre” and 2) present proactive uncertainty management as a regime to ensure cost effective management of project reserves and contribute to project success.
Design/Methodology/Approach
The paper is a combination of literature study and quantitative research on how contingency develops during the lifetime of a case project. The investigation into the case project includes document study into quantitative material from the case project. The combination of empirical material and theory makes the discussion robust.
Findings
Unrealistic low cost uncertainty will lead to unrealistic low contingency. The case study from a Norwegian mega project shows a contingency of 15 per cent in addition to expected costs. The case study shows that by continuous opportunity management and risk reduction, the needs for management reserves are systematically reduced and the contingency is controlled.
Research Limitations/Implications
This research is limited to one case study. A higher number of cases are necessary to generalise the findings. However, the authors would claim that the systematic mapping of need for management reserve towards the project contingency, and a continuous uncertainty management system will help to obtain cost effective management. The findings from the case study could be applied on similar cases.
Practical Implications
The case study shows a way of setting contingencies and managing contingencies through systematic uncertainty management.
Originality/Value
Improved management of project provisions will increase the value of future projects.
Details
Keywords
J. Deckers, K. Shahzad, J. Vleugels and J.P. Kruth
The purpose of this paper is to assess a new powder metallurgy process to make alumina parts through indirect selective laser sintering (SLS). Density measurements, some…
Abstract
Purpose
The purpose of this paper is to assess a new powder metallurgy process to make alumina parts through indirect selective laser sintering (SLS). Density measurements, some geometrical assessments and scanning electron microscopy (SEM) microstructural analyses are performed after each stage of the process, allowing an objective overview to be provided of the challenges and possibilities for the processing of high density technical ceramic parts through SLS of ball milled alumina/polyamide powder agglomerates.
Design/methodology/approach
The powder production by ball milling, SLS, cold isostatic pressing (CIP) or quasi isostatic pressing (QIP), debinding and sintering (FS) stages of the powder metallurgy process were sequentially investigated.
Findings
Alumina parts with a density up to 94.1 per cent could be produced by a powder metallurgy process containing an SLS step. Microstructural investigation of the sintered samples reveals an alumina matrix with a grain size of ∼5 μm and two different kinds of pore morphologies, i.e. long elongated pores, which stem from the intergranular spacings during SLS, and intermediate pores, which likely originate from larger polyamide agglomerates in the ball milled powder. Also, QIPing at elevated temperatures is found to be a promising alternative for CIPing at room temperature to increase the final part density.
Research limitations/implications
Cracks, long elongated pores and intermediate pores remained in the sintered parts. Homogenizing the microstructure of the parts through optimizing the composite starting powder, the deposition during SLS, the SLS parameters and QIPing parameters is essential to overcome these limitations.
Practical implications
Homogenizing the starting powder mixture and the microstructure of the SLS material is the key issue for producing ceramic parts through indirect SLS.
Originality/value
Indirect SLS of ceramics has hardly been reported and the combined use of SLS and QIPing is innovative in the field of indirect SLS of ceramics.
Details
Keywords
Yashwant Kumar Modi and Kiran Kumar Sahu
This study aims to optimize the process parameters of ZPrinter® 450 for measured porosity (MP) and compressive strength (CS) of calcium sulfate-based porous bone scaffold using…
Abstract
Purpose
This study aims to optimize the process parameters of ZPrinter® 450 for measured porosity (MP) and compressive strength (CS) of calcium sulfate-based porous bone scaffold using Taguchi approach.
Design/methodology/approach
Initially, a porous scaffold with smallest pore size that can be de-powdered completely is identified through a pilot study. Five printing parameters, namely, layer thickness (LT), build orientation (BO), build position (BP), delay time (DT) and binder saturation (BS), each at three levels have been optimized for MP and CS of the fabricated scaffolds using L27 orthogonal array (OA), signal-to-noise ratio and analysis of variance (ANOVA).
Findings
The scaffolds with 600 µm pores could be de-powdered completely. Optimum levels of parameters are LT2, BO1, BP2, DT1 and BS1 for MP and LT1, BO1, BP2, DT1 and BS2 for CS. The ANOVA reveals that the BS (49.12%) is the most and BP (8.34%) is the least significant parameter for MP. LT (50.84%) is the most, BO (33.79%) is second most and DT (2.59%) is the least significant parameter for CS. Taguchi confirmation test and linear regression models indicate a good agreement between predicted and experimental values of MP and CS. The experimental values of MP and CS at the optimum levels of parameters are found 38.12% and 1.29 MPa, respectively.
Originality/value
The paper presents effect of process parameters of ZPrinter® 450 on MP and CS of calcium sulfate-based porous scaffolds. Results may be used as guideline for powder bed binder jetting three-dimensional printing of ceramic scaffolds.