David Bould

An Investigation into plate deformation in flexographic printing

Abstract Deformation of the flexographic printing plate is an important factor in determining the quality of the printed image. A numerical model of the individual dots has been developed and used to examine the deformation of the plate under a range of printing conditions and image characteristics. Two mechanisms have been identified for the deformation of the image on the plate: expansion of the dot surface and dot barrelling. These results have been combined with those from an experimental study to apportion the dot gain due to ink spreading and physical deformation of the dot. The results have shown the low-coverage dots at high line rulings to be particularly affected by the effect of variation in the impression pressure. This has significant implications for the ability of the process to reproduce high-resolution images that combine both highlight and shadow regions successfully and consistently. Ink spreading has been identified as the major cause of dot gain, except at low coverages, where the deformation of the dots makes a significant contribution.

A novel variable selection approach based on co-linearity index to discover optimal process settings by analysing mixed data

Abstract In the last two decades the application of statistical techniques to process control has gained popularity due to the widespread adoption of quality management systems such as ISO9001. Demonstration of continual process improvement by monitoring process effectiveness has become an integral part of satisfying the requirements of clause 8 of the ISO9001:2008 standard. The process effectiveness is measured in terms of one or more process responses. Data driven approaches are often used to associate the variability in process responses with one or more process variables. However, traditional techniques become unpractical in the presence of large number of variables and noisy data sets. This paper extends the co-linearity index and penalty matrix approach (Ransing et al., 2013) for discovering noise free correlations between heterogeneous process variables and responses. Noise is removed by reducing the dimensionality of the variable space and using robust data pre-treatment methods which are more suitable in the presence of outliers and skewed distributions for process variables. Scaling factors have been proposed to balance variance contributions from response variables, quantitative and categorical variables. The proposed method allows process variables with skewed distribution to contribute more to the variance than Gaussian distributed variables so that these variables can be investigated further, if necessary. Correlations are visualised in a single plot and can be used in real industrial settings to assist process engineers in manufacturing diagnosis and root cause analysis. The applicability and validity of this novel method has been demonstrated through two industrial case studies.

Effect of impression pressure and anilox specification on solid and halftone density

Controlling the transfer of ink to the substrate is a key requirement of the flexographic printing process. Its ability to transfer ink from the image carrier to the substrate at low pressures enables the process to be used for the production of printed matter using pressure-sensitive materials. These can range from substrates where high pressures can damage surface structure (e.g. corrugated board), to specialist inks, which can be damaged by the high shearing action associated with other volume print processes. This paper evaluates the effect of pressure changes on print quality for different anilox specifications and line rulings on the plate. Data collected from an experimental print trial were used to quantify the effects of anilox roll specifications, dot pitch, and plate-to-substrate engagement on the reproduction of both a continuous ink film and the formation of discrete halftone dots. The ink-carrying volume of the cells of the anilox roll was shown to have the greatest influence on solid density (a parameter used as an indirect measure of ink film thickness) and halftone dot formation; however, the geometrical characteristics of the cells were also shown to have an effect. An initial increase in the pressure within the printing nip resulted in a significant rise in both solid density and tone gain (growth of the halftone dots) due to improved ink transfer from the plate to the substrate. Subsequent increases in pressure produced little further increase of solid density, indicating ink transfer had reached a plateau. The rate of increase of halftone density was found to be reduced as pressure increased, which was attributed to the ink approaching its maximum capability for spreading on the substrate.

Organisational Knowledge Management for Defect Reduction and Sustainable Development in Foundries

Despite many advances in the field of casting technologies the foundry industry still incurs significant losses due to the cost of scrap and rework with adverse effects on profitability and the environment. Approaches such as Six Sigma, DoE, FMEA are used by foundries to address quality issues. However these approaches lack support to manage the heterogeneous knowledge created during process improvement activities. The proposed revision of ISO9001:2015 quality standard puts emphasis on retaining organisational knowledge and its continual use in process improvement. In this paper a novel framework for creation, storage and reuse of product specific process knowledge is presented. The framework is reviewed taking into consideration theoretical perspectives of organisational knowledge management as well as addressing the challenges concerning its practical implementation. A knowledge repository concept is introduced to demonstrate how organisational knowledge can be effectively stored and reused for achieving continual process improvement and sustainable development.

On the optimisation of mechanical properties of PP moulded parts

An injection moulding study that utilised an L9 (34) Taguchi array to determine the optimal process condition of a semi-crystalline PP grade is discussed. This used a multipurpose tensile bar geometry with the objective to maximise the mechanical properties, i.e. tensile modulus and strength (ISO 527), flexural modulus (ISO 178) and Izod impact strength (ISO 180, unnotched). After determining the optimal process settings, analysis of variance (ANOVA) revealed that packing time (among injection time, melt temperature and packing pressure) was the most dominant process factor for all the measured mechanical properties.

Design and Optimization of a Vertical Axis Wind Turbine Housing to Standards

Optimization techniques have been used extensively over the last decades to assist in the design of steel structures. This paper describes the integrated use of a number of these techniques in the costing and design of a large-scale housing for a Vertical Axis Wind Turbine (VAWT) satisfying British Standards. The problem is complex with seven different wind loadings applied to an atypical geometry and as many as 1400 design variables. The housing is subject to displacement, stress and buckling constraints on each component. Ease of transportation and manufacturability are also considered in the design.