Papers by Keyword: Process Modelling

Abstract: The growing use of composite materials has generated interest in improving and optimising composite manufacturing processes such as Liquid Composite Moulding (LCM). In LCM, dry preforms are placed in a mould and impregnated with the matrix material. The efficiency of filling the moulds can be improved by using Computational Fluid Dynamics (CFD) filling simulations during the design of the mould. As part of an on-going effort to develop a CFD tool for the simulation of LCM processes, a volume averaged energy balance equation has been derived and implemented in a custom OpenFOAM solver. The energy balance is implemented in a custom OpenFOAM solver with and without the pressure terms for comparison with results from RTM experiments. It is found that the pressure terms do not significantly influence the results for LCM processes.

Abstract: Roll bonding is a joining-by-forming process to permanently join two or more layers of different materials by hot or cold rolling. One of the typical industrial applications is aluminium sheets for heat exchangers in automobiles. During roll bonding the layers are fed into the rolling stand with parallel surfaces. Due to the plastic deformation in the roll gap metallic bonds between the layers are achieved. Several theoretical models have been published to describe the process, e.g. Zhang & Bay. These models have mostly been developed for cold rolling and describe the bond strength based on surface enlargement, contact pressure and flow stress. Since these models are developed for cold rolling, they are not temperature depending. Heat exchange is usually neglected and de-bonding after the roll gap is not accounted for. However, for hot roll bonding the above mentioned assumptions do not hold true. To understand the mechanisms of hot roll bonding industrial and laboratory scale investigations have previously been conducted. Based on the findings a FE framework for hot roll bonding was developed. This FE framework accounts for the possibility of de-bonding after the roll gap but is restricted to isothermal conditions. However, for a roll bonding simulation it is essential to take the temperature influence into consideration. Therefore, this paper presents an extended version of the FE framework which accounts for temperature dependent material flow, compatible definition of thermal & mechanical interactions and bonding status related heat exchange. To verify the new features of the extended FE framework a roll bonding test case is employed. Mechanical and thermal interactions as well as the current flow stress are calculated in subroutines in order to enable a fully coupled thermal stress simulation. The results show that with this extended FE framework the influence of non-isothermal conditions on material flow and bonding status as well as the feedback effects of bonding status to heat exchange have been successfully integrated in hot roll bonding simulations. This fully coupled thermal stress simulation is the first step towards multi-pass roll bonding simulations.

Abstract: Hot forming of metals is important to achieve the desired shape and properties of products. The change in process behavior and final properties of materials during processing is essential for the design of new processes and products. Finite-element-software (FE-software) is nowadays widely used in industry to design and optimize hot forming processes. These FE codes need a proper description of the material behavior being developed for specific processes.In this paper the capability of a recently developed one-point-model will be discussed to predict material behavior for the carbon steel (C-steel) family. In detail, the following topics will be discussed: (i) description of the material behavior in varying processes, (ii) definition of material properties depending on alloying content, (iii) capability to describe whole alloy families, (iv) adjusting the model parameters by a small number of experiments.

Abstract: Modelling of the lapping process proves a complex undertaking because of the different forms of the abrasive particles in the working area, the wide dispersion of their dimensions, the modifications of their shape and dimensions during processing. The paper proposes the spherical model of the abrasive grain, based on the known fact that a good quality of the processed surfaces requires compact grains, with a dimensional ratio as close as possible to 1:1:1. Based on the adopted model the distribution of tensions at the grain-workpiece contact is determined, as well as the penetration depths of the abrasive grains into the workpiece and the transfer object, respectively. For this certain initial conditions are necessary, like Hertzian contact between the abrasive grain and the processed surface and the neglecting of strain hardening. Taking into consideration the known fact that only the large abrasive grains participate in the actual cutting process while the rest remain suspended in the gap between workpiece and tool, as well as their dimensional distribution and concentration in the lapping slurry, the volume of abrasive material required for processing was determined by statistical methods.

Abstract: In the pursuit of producing high quality, low-cost composite aircraft structures, out-of-autoclave manufacturing processes for textile reinforcements are being simulated with increasing accuracy. This paper focuses on the continuum-based, finite element modelling of textile composites as they deform during the draping process. A non-orthogonal constitutive model tracks yarn orientations within a material subroutine developed for Abaqus/Explicit, resulting in the realistic determination of fabric shearing and material draw-in. Supplementary material characterisation was experimentally performed in order to define the tensile and non-linear shear behaviour accurately. The validity of the finite element model has been studied through comparison with similar research in the field and the experimental lay-up of carbon fibre textile reinforcement over a tool with double curvature geometry, showing good agreement.

Abstract: High quality and low variability in the properties of the products are the main goals in manufacturing. The quality of the product is verified by testing different properties. It can be improved with models developed for event prediction. This paper presents with application examples the modelling steps required for effective process modelling. First, the pre-processing and feature extraction phase are illustrated. The modelling phase concentrates especially on the heteroscedasticity problem that is commonly present in industrial applications. The process monitoring and control parameter optimization based on these models is presented, as well as the solution for the lack of observations for the dependent variable. Many of the developed models are in daily use in different process states in steel industry. They enable the design of new products and the analysis of the effects of different process parameters on variability reduction. The proposed methods are application independent.

Abstract: This paper collects the main methodologies and tools employed for predicting the surface roughness. The goal of this work is to provide compact and adequate information that could be useful in metal cutting industries to select the techniques and optimization tools that best suit to their needs and particular requirements. Each approach, with its advantages and disadvantages, is outlined and the present and future trends are discussed. As result, a quick guide for using practitioners of mentioned industrial sector is provided in form of tables that relate: machining parameters, cutting tool properties, workpiece properties and cutting phenomena with the different techniques and optimization tools usually employed to analyze the different parameters and phenomena involved in the process of surface roughness generation.

Abstract: The laser cladding process is based on the generation of a melt-pool in a substrate where a filler material is injected, generating a high quality clad with a minimum heat affected zone. This process is industrially used to generate coatings over wear or damaged surfaces, being an alternative to traditional deposition techniques. One of the most important aspects for its industrial application is to know the clad geometry in order to calculate the deposited layer thickness. This work presents a model in which, starting from the concentration of injected material and the melt-pool geometry, clad height is finally estimated. Both input variables are obtained by two previous validated models. On one hand, the melt pool is estimated by a thermal model based on the finite difference method, and on the other hand, concentration of injected material is provided by a particle concentration CFD model. This data is used in a mass balance over melt-pool area in order to estimate the deposited clad height.

Abstract: A study concerning the application of fiber laser to perforate thermoplastic pre-pregs is presented. An IPG fiber laser was used to drill arrays of holes in PEKK carbon-fiber composite pre-preg material. Perforated holes were of the order of 100μm. The effects of laser perforation process parameters including the number of pulses on the geometry of the resultant holes and the thermal damage to the matrix and fibres have been investigated. Dimensional analysis and experimental results have been used to construct the laser perforation process model. Keywords: Laser perforation; Fibre laser; Process modelling; Polymer matrix composites.

Abstract: The production of high-quality Ceramic-Matrix Composites often includes matrix deposition by Chemical Vapour Infiltration (CVI), a process which involves many phenomena such as gas transport, chemical reactions, and structural evolution of the preform. Control and optimization of this high-tech process are demanding for modelling tools. In this context, a numerical simulation of CVI in complex 3D images, acquired e.g. by X-ray Computerized Microtomography, has been developed. The approach addresses the two length scales which are inherent to a composite with woven textile reinforcement (i.e. inter- and intra-bundle), with two numerical tools. The small-scale program allows direct simulation of CVI in small intra-bundle pores. Effective laws for porosity, internal surface area and transport properties as infiltration proceeds are produced by averaging. They are an input for the next modelling step. The second code is a large-scale solver which accounts for the locally heterogeneous and anisotropic character of the pore space. Simulation of the infiltration of a whole composite material part is possible with this program. Validation of these tools on test cases, as well as some examples on actual materials, are shown and discussed.