CERES :: Browsing by Author "Alcock, Jeffrey R."

Browsing by Author "Alcock, Jeffrey R."

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Open Access
Analysis and development of an aqueous tape casting ceramic process
(Cranfield University, 2005-11) Mortara, L.; Alcock, Jeffrey R.
The laboratory scale process developed by Navarro [Navarro, 2001 ] for the production of pyroelectric ceramics was used as a case study for the design of a high-level methodology for the scale-up of ceramic processes. A twofold approach was adopted as the basis of the methodology to perform the process scale-up. A "process focussed" approach was used that considered the sequence of processing operations, their feasibility on a larger scale and the potential problems foreseeable for a scaled-up process. Secondly, a "product focussed" approach analysed the quality of the product in respect to the customer requirements (the specifications).This approach also concerned the analysis of the process potential to perform within an essential tolerance interval. This aim was pursued through the use of a statistical technique, the Statistical Process Control. With the product focussed approach, the mechanical and electrical characteristics of the wafers obtained with the laboratory scale process were compared with the industrial requirements. The ceramic wafers possessed satisfactory characteristics except for their strength. The processing parameters were investigated in order to optimise the sintered ceramic microstructure and to understand their relative influence on the achievement of adequate characteristics for allowing handling and machining. Sintered density and grain size were studied as functions of green density and firing temperature. Increasing the green density from the original 37% to approximately 65% of the theoretical density by means of warm pressing allowed the wafers to achieve a more homogeneous microstructure and a higher sintered density up to approximately 97% of the theoretical. Thanks to the increase in green density, the sintering temperature could be reduced by 100°C and the total sintering time was shortened by 190 minutes. The samples produced with warm pressing were more resistant as 75% of them survived during the poling and machining test, in contrast with the 5% of the original samples. The suitability of the warm pressing technique to increase the green density up to 5 g.cm 3 (61 % of the theoretical density) was investigated by means of the statistical process control tool. A correct design of the press equipment was judged the most relevant factor for determining the control and the capability of the process. A rheological study was directed to understand how the slurry ingredients influenced the ceramic suspension, the green tape density and morphology. Two preparation routes were compared in order to discriminate among the effects induced by the electrosteric dispersant and the polyvinyl alcohol binder on the PZT particles suspension. It was shown how the dispersant influenced both the suspension characteristics and the comminution efficiency of the milling. The binder was shown to adsorb onto the ceramic particles. A model was proposed describing the interaction among ingredients which suggested that the adsorbing polymer induced particles flocculation by bridging mechanism, especially when added to stabilised slurries. As a result, PVA was judged inappropriate for tape casting of this PZT powder as it yielded low green density tapes.
Open Access
Aqueous colloidal processing and green sheet properties of lead zirconate titanate (PZT) ceramics made by tape casting
(Elsevier Science B.V., Amsterdam., 2004-01-01T00:00:00Z) Navarro, A.; Alcock, Jeffrey R.; Whatmore, Roger W.
An aqueous system for tape casting PZT ceramics was developed using poly (vinyl alcohol) binder, poly (propylene glycol) plasticizer, D3021 dispersant and Surfynol SE-F wetting agent. Screening experiments were performed to assess the stability of the suspension in the presence of the dispersant by performing pH, conductivity and Zeta potential measurements. Viscosity measurements were used to find the optimum level of dispersant needed to produce a stable slip at pH 10.2. Subsequently, the rheological and mechanical characteristics were also investigated.
Open Access
Capabilities of proprietary intermediate telehealth devices
(2011-10-28T00:00:00Z) Adeogun, Oluseun; Tiwari, Ashutosh; Alcock, Jeffrey R.
Abstract Objective: Proprietary intermediate telehealth devices are those which are specifically designed as connectors between the entities of telehealth systems. This article seeks to understand what are the capabilities of such devices and then to investigate how these are clustered on the current generation of devices. Materials and Methods: Fourteen current-generation devices available from 12 device providers were selected and analyzed. Four categories of questions were composed to evaluate the devices: setup/ configuration, available features, inputs, and outputs. Results: Data were collected and synthesized on the following capabilities: availability from suppliers, setup, environments of use, multiple-condition monitoring, multiuser capabilities, prompts, reminders and alerts, interaction with the health professional, access to historical data, device inputs, and their transfer technology. Conclusions: There are three main roles for proprietary intermediate devices in telehealth systems: displaying information to the patient; receiving data manually/automatically; forwarding results and questionnaire responses to another entity. Provider Perspective: Intermediate devices are usually part of closed proprietary systems. Providers produce disease-customisable devices. Connectivity is considerably ahead of the current generation of point-of-care devices. However, little data are available on connection to rest of the proprietary system. Patient Perspective: It shows clear benefit that one intermediate device can be potentially used with several chronic conditions. Simple setup, authentication procedures, and automatic data transfer are key design aspects. Health Professional Perspective: Little direct interaction with the health professional was observed. Payer Perspective: Details of costs of devices are generally unavailable; system providers indicate that cost variability is based on "user requirements."
Open Access
Categorisation of visualisation methods to support the design of Human-Computer Interaction systems
(Elsevier, 2016-02-02) Li, Katie; Tiwari, Ashutosh; Alcock, Jeffrey R.; Bermell-Garcia, Pablo
During the design of Human-Computer Interaction (HCI) systems, the creation of visual artefacts forms an important part of design. On one hand producing a visual artefact has a number of advantages: it helps designers to externalise their thought and acts as a common language between different stakeholders. On the other hand, if an inappropriate visualisation method is employed it could hinder the design process. To support the design of HCI systems, this paper reviews the categorisation of visualisation methods used in HCI. A keyword search is conducted to identify a) current HCI design methods, b) approaches of selecting these methods. The resulting design methods are filtered to create a list of just visualisation methods. These are then categorised using the approaches identified in (b). As a result 23 HCI visualisation methods are identified and categorised in 5 selection approaches (The Recipient, Primary Purpose, Visual Archetype, Interaction Type, and The Design Process).
Open Access
Characterization of shrinkage effects in micro-injection moulding (µ-IM)
(Cranfield University, 2013-10) Annicchiarico, Daniele; Alcock, Jeffrey R.
This thesis characterizes the effects on shrinkage in microinjection moulding. The literature review considers four branches of investigation (material properties, processing parameters, mould design and specimen design). Two research gaps rise from the analysis of the literature review: the absence of a standardized methodology for measuring shrinkage of moulded parts at the micro-scale, and the absence of optimization stage that implements multiple quality criteria. Adequate research routes are set in order to address these gaps. The conventional standard for determining shrinkage at the macro scale is adapted to the micro-scale and this bridges the first gap. The micro-mould replicates the same design of the standard, and a preliminary stage solves some mouldability problems: the implemented mould extended the mouldability range of processing parameters for improving the reliability of results. After the micro-mould validation, the study of shrinkage at the micro-scale considers the influence of five processing parameters: the mould and melt temperature, the holding time and pressure, then the injection pressure. The design of experiment approach identifies the critical parameters that affect moulding, post-moulding and total shrinkage in parallel to and normal to the flow direction within an interval of confidence of 95% for POM and 90% for 316L feedstock. Statistical tools analyse the results, and the trends of critical factors found confirmation in the literature. This methodology at the micro-scale can fill the first gap because it is on purpose designed for the micro-scale. Moreover, the binder of feedstock is a mixture of POM based polymers, and the use of a common platform permits to compare directly the two materials and highlight the influence of powder loading. The optimization stage adopts desirability functions for achieving optimized values that simultaneously fulfil two requests: minimize shrinkage and maximize moulded part mass. The analysis of the literature review shows that few papers adopt multiple quality criteria approach as methodology for optimizing the results, and none consider jointly part mass and shrinkage. The optimized processing parameters allow moulding “optimized specimens”, and results demonstrate that their total shrinkage and part mass achieve the requests. Even if the use of desirability functions produce results thatrepresents a compromise between the requests, the results show that overall shrinkage decreases and part mass increases. This approach demonstrates its reliability and bridges the second gap. The last part of the thesis investigates the 316L feedstock behaviour for filling micro-features parallel to and normal to the flow oriented. The moulded features are investigated for studying the replication quality and the effect of the orientation of channels with dimension close to the feedstock lower mouldability value. These informations are available in the literature only for polymers, and the contribution of this part of thesis is to fill this gap by analysing a feedstock. The statistical approach permits to identify the critical factors that affect the feature replication quality. Optical investigations allow to identify the 316L feedstock lower mouldability value and to observe the influence of the orientation of features with dimensions near the lower limit.
Open Access
Comparison and evaluation of the Telehealth systems using a discrete event simulation
(Cranfield University, 2012-10) Griscenko, Natalia; Tiwari, Ashutosh; Alcock, Jeffrey R.
The telehealth is the delivery of health-related services at a distance using communication technologies. The telehealth provides important benefits: allows to provide the access to the healthcare service reducing need for a physical stay and decreasing the healthcare cost. This industry’s popularity and the importance constantly increases because of the number of rapid increase of the population share a ected by the chronic diseases. However, the telehealth service development requires substantial investment of finances, time and substantial expertise. A method of comparison and evaluation of the current telehealth systems helps to create the telehealth service while minimising an amount of the resources wasted. The method to simulate, evaluate, and compare the telehealth systems have been created through the review of the state-of-the-art techniques of evaluation and comparison of the existing telehealth systems. Then, it was applied to several the real life telehealth systems. The outcome of this work is (i) the method to construct Discrete Event Simulation (DES) models of the telehealth systems, (ii) twelve the DES models of the current telehealth systems, (iii) the list of suggestions for the future research to increase the quality of the DES models, (iv) the method to choose parameters and to develop metrics to evaluate the telehealth systems, (v) the method to define an approach to compare the telehealth systems, (vi) the evaluation and comparison results of twelve the current telehealth systems. The bottom line of the current research is that the simulation is an e ective way to evaluate and compare the telehealth systems. The DES approach is a viable way of gaining an insight into the telehealth systems properties, although it requires a substantial amount of the future research to mature the method to evaluate and compare the telehealth systems.
Open Access
Correlation of sintered microstructure with green density in thick film PZT
(Trans Tech Publications, 2003-06-28T00:00:00Z) Mortara, L.; Navarro, A.; Whatmore, Roger W.; Alcock, Jeffrey R.
High density and low grain size are essential for the production of thick-film ceramics, in order that they possess adequate strength for any subsequent processing steps. In this paper sintered density and grain size were studied as function of green density and firing temperature. Wafers possessing a higher green density showed a more homogeneous microstructure and a higher sintered density.
Open Access
Creating movable interfaces by micro-powder injection moulding
(Elsevier, 2013-09-09) Attia, Usama M.; Hauata, M.; Walton, I.; Annicchiarico, Daniele; Alcock, Jeffrey R.
This paper presents a novel in situ technique to produce articulated components with high-precision, micro-scale movable interfaces by micro-powder injection moulding (μPIM). The presented process route is based on the use of micro-scale sacrificial layer between the movable subcomponents which is eliminated during the debinding step, creating a dimensionally-controlled, micro-scale mobile interface. The fabrication technique combines the advantages of micro-powder overmoulding, catalytic debinding and sintering. The demonstrated example was a finger bone prosthesis joint consisting of two sub-components with an interface between components of 200 μm in size. The geometries of the sub-components were designed such that they are inseparable throughout the process whilst allowing them to move relative to each other after the debinding stage. The components produced showed the feasibility of the process route to produce readily-assembled meso-, and potentially micro-, scale articulated systems
Open Access
Data uncertainty assessment and information flow analysis for product-service systems in a library case study
(Inderscience, 2010-12-31T00:00:00Z) Durugbo, Christopher; Erkoyuncu, John Ahmet; Tiwari, Ashutosh; Alcock, Jeffrey R.; Roy, Rajkumar; Shehab, Essam
The provision of service is increasingly becoming a key driver for delivering customer value. This emphasis on service provision is promoted by approaches such as Product-Service Systems (PSSs) that deliver value in use based on integrated products and services. However, to achieve effective delivery of services, it is important to manage information flow and data uncertainty associated with information requirement. The paper proposes a methodology that consists of: (a) the assessment of data uncertainty through the numeral, unit, spread, assessment and pedigree approach and a pedigree matrix consisting of data uncertainties to be scored based on their influence on the system; and (b) the analysis of information flow by means of data flow diagrams that depict information exchanges and an info-dynamic engine that measures the efficiency and recommends improvements for information flows in PSSs. A library case study was undertaken to show how such a methodology can be applied.
Open Access
A descriptive model of the current microelectromechanical systems (MEMS) development process
(2009-08-24T00:00:00Z) Sagoo, Jeevan; Tiwari, Ashutosh; Alcock, Jeffrey R.
This paper uses the IDEFØ process modelling technique to present an ‘As-Is' model for the current process of developing generic MEMS devices, this new model is based on information from current practitioners. The model shows a seven- stage process, from customer requirement specification to testing and verification, with multiple iterative loops between several stages of the model. Process-constraints on current MEMS development are also reported in the paper. A comparison was attempted between this As-Is model and the candidate models for future MEMS development available in literature. Differences include the number and placement of process iteration stages and the quantity and type of the development activities. Further comparison is difficult, partly because of the different approaches, taken to represent MEMS development stages and development flows, used by different autho
Open Access
Design and fabrication of a three-dimensional microfluidic device for blood separation using micro-injection moulding
(Sage, 2013-12-03) Attia, Usama M.; Marson, Silvia; Alcock, Jeffrey R.
Micro-manufacturing is a fast developing area due to the increasing demand for components and systems of high precision and small dimensions. A number of challenges are yet to be overcome before the full potential of such techniques is realised. Examples of such challenges include limitations in component geometry, material selection and suitability for mass production. Some micro-manufacturing techniques are still at early development stages, while other techniques are at higher stage of manufacturing readiness level but require adaptation in part design or manufacturing procedure to overcome such limitations. This article presents a case study, where the design of a micro-scale, biomedical device is adapted for functionality and manufacturability by a high-volume micro-fabrication technique. Investigations are described towards a disposable three-dimensional, polymer-based device for the separation of blood cells and plasma. The importance of attempting a three-dimensional device design and fabrication route was to take advantage of the highthroughput per unit volume that such systems can, in principle, allow. The importance of a micro-moulding fabrication route was to allow such blood-containing devices to be cheaply manufactured for disposability. Initial device tests showed separation efficiency up to approximately 80% with diluted blood samples. The produced prototype indicated that the process flow was suitable for high-volume fabrication of three-dimensional microfluidics.
Open Access
The design and manufacture of biomedical surfaces
(Technische Rundschau, Hallwag Publishers; 1999, 2007-08-01T00:00:00Z) Ramsden, Jeremy J.; Allen, David M.; Stephenson, David J.; Alcock, Jeffrey R.; Peggs, G. N.; Fuller, G. D.; Goch, G.
Surfaces are the primary place of contact between a biomaterial and its host organism. Typically, prostheses have to fulfil demanding structural and mechanical requirements, yet the material best for those functions may be bio- incompatible. Surface treatment or coating provides a means to overcome that problem, which means both integration within the host physiology and stabilization with respect to corrosion and wear. The adsorption of biomacromolecules is pivotal for biocompatibility. The impossibility of keeping proteins away from most implants means that very careful consideration has to be given to this aspect, and both prevention (for bloodstream implants) and promotion (for bone replacement and repair) occur with equal importance. This paper also considers the metrology of relevant physical and chemical aspects of surfaces.
Open Access
Design of experiment for the optimisation of deep reactive ion etching of silicon inserts for micro-fabrication
(SPIE, 2012-12-31) Wallis, K.; Shaw, Christopher P.; Alcock, Jeffrey R.
The following paper describes a design of experiments investigation of the deep reactive of pillar structures on a silicon wafer. The etched wafers would subsequently be used as masters for the fabrication of nickel mould inserts for microinjection moulding. Undercuts occur when the pillar base has a smaller cross-section than the apex of the pillar. They therefore affect tolerances of the subsequent nickel mould, its strength and its de-mouldability from the silicon form. The response measured in these experiments was the degree of undercut of micro-scale (10 μm x 10 μm x 40 μm, 5 μm x 5 μm x 40 μm and 2 μm x 2 μm x 40 μm) The literature suggests that gas pressure, platen power, gas flow rate, phase switching times and mask size can all affect the degree of undercut. After examination of this literature, and of manufacturers guidelines, three parameters were selected for experimental testing: platen power, C 4F 8 gas flow rate during the passivation phase and switching times. Switching times was found to be the only statistically significant parameter for both 10x10 μm and 5x5 μm pillars. The 2x2 μm pillars were not successfully replicated and could therefore not undergo statistical evaluation.
Open Access
Design of experiment studies for the fabrication processes involved in the micro-texturing of surfaces for fluid control
(Cranfield University, 2013-11) Wallis, Kirsty; Alcock, Jeffrey R.
This thesis focuses on the use of a design of experiment approach to examine the significance of process factors and interactions on the fabrication of micro- textured surfaces. The micro-textured surfaces examined contain pillar and hole features ranging from 80 – 2 micrometers in diameter. The processes examined are the deep reactive ion etching of silicon wafers for the production of silicon mould inserts and the micro-injection moulding of polypropylene, high density polyethylene and 316LS stainless steel replicate samples of the silicon mould insert. During the deep reactive ion etching of the silicon wafers the design of experiment approach was used to determine the significant of platen power, C4F8 gas flow and switching times to the presence of pillar undercut of 10 x 10, 5 x 5 and 2 x 2 micrometer pillars. Undercuts occur when the pillar base has a smaller cross-section than the apex of the pillar. Switching times was found to be the only statistically significant parameter for both 10 x 10 and 5 x 5 micrometer pillars. The design of experiment approach is used in the micro-injection moulding of polypropylene, high density polyethylene and 316LS stainless steel replicates to examine the significance of mould temperature, cooling time, holding pressure and injection speed on the part and buffer mass of the produce samples, the height and width of pillar on the replicate surfaces and the variation of the replicated pillars height and width from the original silicon mould insert. Examination of the high density polyethylene replicates found that mould temperature was the most significant factor regarding pillar dimensions (and variation from the silicon mould insert) across the range of pillar sizes. Upon examination of the polypropylene replicates it was found that the factor of most significance on pillar dimensions varied across the different pillar sizes. Holding pressure was identified as the most significant factor with regards to the 53 x 29 and 19 x 80 micrometer pillars. Injection speed was found to be most significant for the 25 x 25 and 19 x 29 micrometer pillars. Cooling time was found to be most significant with regards to the 30 x 10, 25 x 10, 20 x 10 and 15 x 10 micrometer pillars. While ii mould temperature was found to be most significant for the 20 x 20, 15 x 15 and 10 x 30 micrometer pillars. The interaction between mould temperature and injection speed was also found to be the most significant factor with regards to the 43 x 29 and 25 x 30 micrometer pillars. Examination of the 316LS replicates found that mould temperature was the most significant factor regarding pillar dimensions for 80 x 80 and 19 x 80 micrometer pillars. While holding pressure was found to be most significant to the 29 x 29 micrometer pillars and injection speed was identified as most significant to the 53 x 80 micrometer pillars. The samples produced during the design of experiment investigations were then used to examine the effect of surface texturing on droplet behaviour. Droplet contact angles were examined on polypropylene, high density polyethylene and silicon samples structured with 10 – 2 micrometer pillar. Initial droplet contact angles were found to be higher on the polypropylene samples than the high density polyethylene or silicon samples. With the lowest initial contact angles being found for the silicon inserts. Droplet ‘channelling’ and evaporation were examined on silicon, polypropylene, high density polyethylene and 316LS samples structured with micro-channel surface pillars and holes ranging from 80 – 2 micrometer in diameter. Contact pinning of the droplet to the surface via the three- phase contact-line was noted during observations of droplet ‘channelling’. This pinning effect was observed at all sample tilt angles (30 - 90 o ). With regards to droplet evaporation, the droplets were noted to evaporate evenly (with no or limited contact pinning) on all unstructured surfaces and the surfaces structured with hole features. On the surfaces structured with pillar features, the droplets appeared too evaporated along the surface gradient from the smallest pillars to the largest.
Open Access
Design practices used in the development of microfluidic devices: a services-based view
(Inderscience, 2016-12-01) Tiwari, Ashutosh; Alcock, Jeffrey R.; Turner, Christopher J.
This paper presents the current state of microfluidic design from a practitioner’s perspective. The capture of microfluidic design practice was facilitated through a combination of industry survey and expert interviews, allowing the authors to draw out models for microfluidic design. Exploration of the current practice of microfluidic design showed that formal design methodologies were not in use. This research has also found that sub-section interactions have been addressed in an inadequate fashion by current design practices. The work presented in this paper outlines the scope for further research in the development of a formal design methodology for microfluidics.
Open Access
Design rationale for the regulatory approval of medical devices
(Cranfield University, 2012-09) Sagoo, Jeevan; Tiwari, Ashutosh; Alcock, Jeffrey R.
Design rationale is a methodology aimed at capturing and representing design decisions according to a designated structure. Additionally, these design decisions and their underlying arguments can be made available for examination at a later date. The literature review identified that there is currently a lack of information describing the use of design rationale methods and computational support tools with the medical device domain. Furthermore, the review of literature has also recognised that there are no existing guidelines available for medical device manufacturers and regulatory authorities to follow in order to capture and represent the design decisions in the case of medical devices. Medical devices are instruments which are used for diagnosis, screening, monitoring, or the treating of patients suffering from disease, injury, or disability. Medical devices are products that require rigorous regulation before they can be placed onto the market. If problems are encountered with a device once it has been placed onto the market, the device is recalled by the relevant regulatory authority. Device recalls can often result in the device manufacturers having to evaluate the design decisions that were made during the product development stages in order to address the reported problems and implement a solution. As a result, medical device manufacturers can incur unexpected rework and/or redesign costs, and in even more severe circumstances, incur high litigation costs. This research; reviews the state-of-the-art in design rationale and identifies its key capabilities, analyses design rationale’s feasibility for use with the medical device domain, identifies the regulatory approval processes for medical devices and compares them, analyses the possibilities of utilising design rationale with the regulatory approval of medical devices, and develops a set of guidelines. The guidelines detail the necessary steps that are required to capture and represent the design decisions for medical devices. The utility of this contribution has been verified through the process of validation with experts and researchers.
Open Access
Developing Microelectromechanical Systems (MEMS)
(Cranfield University, 2008-09) Sagoo, Jeevan; Tiwari, Ashutosh; Alcock, Jeffrey R.; Engineering and Physical Sciences (EPSRC)
Intellectually and technologically, the art of design is one of the oldest forms of mankind’s expression of creativity. Since the early days of primitive man to now, humans have discovered needs that require functional artefacts to perform necessary operations. There are vast differences in the appearance and applications of such artefacts which have varied with time. Developing artefacts to fulfil the new and changing requirements presents a creative response to problem solving at the macro and micro scales. Developments in technology have progressed rapidly driven by the requirement to create smaller artefacts that possess a larger variety of functions. The current developments of micro and nano scale devices have the potential of triggering a technological revolution in many fields. The healthcare industry is utilising micro and nanotechnology applications and aiming these to provide quicker and more affordable medical diagnostic equipment such as the lab on a chip. This is currently being developed to provide a point of care testing to analyse blood samples for different viruses, in a miniature blood testing laboratory which is in the space of a microchip, and providing the appropriate response in a real time environment. Some of these devices are still in the conceptual phases with the possibility for future large volume manufacturing however; the development of microelectromechanical systems or MEMS as they are more commonly known, is performed by the experts with an intuitive based approach. In such context, this thesis proposes a theoretical model for the development of MEMS devices by examination of literature in; generic product development processes used in the engineering and manufacturing areas and capturing how MEMS are currently developed. Parallel to this, development practices currently deployed for MEMS as performed by the experts and practitioners have been illustrated in the form of an As-Is model validated by MEMS experts. The use of IDEF0 to model the existing MEMS development process has provided the necessary tool to analyse the existing process, recognise the limitations, identify the areas of improvement and implement these into a To-Be model proposed for future MEMS development validated by domain experts.
Open Access
Epoxy-based fibre reinforced nanocomposites
(John Wiley & Sons, Ltd, 2007-10-31T00:00:00Z) Njuguna, James A. K.; Pielichowski, Krzysztof; Alcock, Jeffrey R.
The modification of epoxy resins with nanoparticles could endow the materials with some superior properties such as broadening of the glass transition temperatures, modest increases in the glassy modulus, low dielectric constant, and significant increases in key mechanical properties. In the last 15 years, some studies have shown the potential improvement in properties and performances of fibre reinforced polymer matrix materials in which nano and micro-scale particles were incorporated. From the existing literature, considerable effort has been given to the synthesis and processing of these unique polymers, but relatively little work has focused on the fibre reinforced epoxy composites. The purpose of this work, therefore, is to review the available literature in epoxy- fibre reinforced composites manufactured using carbon nanotubes, carbon nanofibre and nanoclays for reinforcement.
Open Access
Evaluating and controlling process variability in micro-injection moulding
(Springer Science Business Media, 2011-01-31T00:00:00Z) Attia, Usama M.; Alcock, Jeffrey R.
Microsystem technologies require relatively strict quality requirements. This is because their functionalities are usually dependent on stringent requirements of dimensions, masses or tolerances. When mass-producing micro-components, e.g. replication of disposable microfluidic diagnostics devices, the consistency of the produced components could be significantly affected by process variability. The variability could be associated with a specific process parameter or could be a result of process noise. This paper presents a methodology to assess and minimise process variability in micro-injection moulding, an example of well- established mass-production techniques for micro-components. A design-of- experiments approach was implemented, where five process parameters were investigated for possible effects on the process variability of two components. The variability was represented by the standard deviation of the replicated part mass. It was found that melt temperature was a significant source of variability in part mass for one of the components, whilst the other was affected by unsystematic variability. Optimisations tools such as response surfaces and desirability functions were implemented to minimise mass variability by more than 40%.
Open Access
An evaluation of process-parameter and part-geometry effects on the quality of filling in micro-injection moulding
(Springer Science Business Media, 2009-12-01T00:00:00Z) Attia, Usama M.; Alcock, Jeffrey R.
This paper addresses the use of micro-injection moulding for the fabrication of polymeric parts with microfeatures. Five separate parts with different micro- feature designs are moulded of Polymethylmethacrylate. The design-of-experiments approach is applied to correlate the quality of the parts to the processing parameters. Five processing parameters are investigated using a screening half- factorial experimentation plan to determine their possible effect on the filling quality of the moulded parts. The part mass is used as an output parameter to reflect the filling of the parts. The experiments showed that the holding pressure is the most significant processing parameter for all the different shapes. In addition, the experiments showed that the geometry of the parts plays a role in determining the significant processing parameters. For a more complex part, injection speed and mould temperature became statistically significant. A desirability function approach was successfully used to improve the filling quality of each part.