Mark Jolly

Finite element investigations upon the influence of pocket die designs on metal flow in aluminium extrusion. Part I. Effect of pocket angle and volume on metal flow

Abstract In extrusion die design, it has become increasingly common to use “pocket” technology to balance the metal flow. The balance of metal flow is particularly important for multiple cavity dies or sections with varying thickness in order to maintain a uniform velocity profile across the face of the die and thus minimise distortion of the extrudate. However, the fundamental understandings of pocket design are currently very limited. In this study, results are presented from a series of pocket designs that were modelled using finite element method (FEM) to systematically investigate the influence of the pocket design parameters on the metal flow. In part I of this study, the effects of pocket angle and size on metal flow were investigated and it is shown that pocket angle plays an important role influencing metal flow velocity, whilst pocket volume has much less effect on velocity. The investigation is mainly focused on developing a qualitative understanding of pocket designs.

Finite element modelling investigations upon the influence of pocket die designs on metal flow in aluminium extrusion: Part II. Effect of pocket geometry configurations on metal flow

Abstract The effects of geometry and offset of pocket on flow velocity were modelled and the metal flow behaviour was investigated. FEM results show that different geometry configurations have different effects on metal flow velocity and conical pockets have the largest effect on increasing the flow velocity. The metal flow patterns and velocity profile around pockets have been illustrated. Although step(s) reduce the volume of dead metal zone and the pocket size of conventional square pockets, this does not change the metal flow velocity significantly. Offsets in the pocket have an effect on velocity, causing bending of the extrudates.

Modelling of the investment casting process

Abstract The aim of this paper is to present the modelling work carried for the FOCAST project in order to acquire a better understanding of the physical phenomena which control the investment casting processes. The paper will first present the general approach used by the authors. Then, for each process stage studied, the models used and their hypotheses are presented and discussed. The parameters needed for the modelling are also listed. From these models, and using simulation packages, numerical simulations have been carried out. The results obtained are presented, with a special focus on the comparison with experimental results where available.

Casting simulation: How well do reality and virtual casting match? State of the art review

Over the last ten years or so many man-hours have been dedicated to developing methods for simulating the casting process. The majority of the methods developed have been devised by a combination of computer, mathematics and materials specialists with little or no knowledge of foundries and foundrymen. As a result of this it would appear that although there are many software packages for the foundryman to use there still exist fundamental misunderstandings as to their usefulness and suitability within the foundry. This paper is an update review and aims to identify how well current software packages are progressing towards their target of predicting casting defects. The relationships between physical phenomena, practical defects and software capability are presented. Some discussion of the use of criterion functions is also presented. Finally issues arising from the postprocessing of results are discussed, as the presentation of the results to the layperson in simulation techniques is possibly one of the most important aspects in influencing the adoption of this type of software in the foundry community.

Finite element modelling simulation of transverse welding phenomenon in aluminium extrusion process

Transverse welds occur in the billet-to-billet extrusion process, which is often used in modern aluminium extrusion plants for the purpose of continuous production. The transverse weld introduces a discontinuity at the weld interface in the extruded product and in many structural applications. This is not acceptable because it can severely reduce the strength and is detrimental to the quality of the extruded product. For this reason the length of transverse weld material needs to be cut out of the extrusion. But this then decreases the overall yield of the product and so the transverse weld length should, therefore, be kept as minimum as possible. The experimental studies carried out in the past mainly concentrated on the quality and strength of the extruded products containing a weld interface. The behaviour of metal flow and the factors affecting the transverse weld length have not been systematically studied. Currently, the transverse welding pattern and length of the extrudate containing a transverse weld are determined purely by experience and simple empirical models. In this study, the formation and metal flow behaviour of transverse welds in the aluminium extrusion process were investigated using the finite element modelling (FEM) simulation technique. It was shown that inhomogeneous metal flow occurred and a transverse welding pattern was revealed. The design parameters influencing the transverse weld length were also investigated and discussed. This study concentrated on improving the understanding of the behaviour and the formation mechanisms of transverse welds with the aim of providing general guidance for the aluminium extrusion industry in minimising the transverse weld length of the extrudate.

Finite element simulations and experimental studies on inhomogeneous metal flow in aluminium extrusions with three-dimensional complex geometries

Abstract Aluminium extrusions with complex geometries are simulated in three-dimensions using the finite element method (FEM) and experiments were also carried out to investigate the behaviour of metal flow, exit velocities, and heat transfer for a simple channel and a more complex geometry profile. This study clearly shows that with both designed extrusions, at the initial stage of extrusion the metal flow is inhomogeneous, and even a slight inhomogeneity of metal flow can significantly affect the final geometry of extrudates. Both the FEM and experiment demonstrated that the extrudates are bent and twisted for a complex extrusion profile. The complex distortion patterns were analysed in detail and related to their cause: inhomogeneous flow behaviour. The inhomogeneous flow pattern for a complex geometry profile was also revealed through FEM. The factors which could influence the quantitative results of the FEM were also discussed.

Advanced Casting Methodologies: Investment Casting, Centrifugal Casting, Squeeze Casting, Metal Spinning, and Batch Casting

This chapter explores various advanced casting techniques. One such technique is investment casting, a process that came about as a result of the demand for complex geometry components in high-temperature capability materials in the first half of the twentieth century for use in aircraft engines. Such components could not be formed or would be too expensive to produce using the more common processes, such as forging or machining. The industry has developed rapidly since then, encompassing everything from the jewelry market to the aerospace field. Castings from a few grams to several hundred kilograms in weight can be produced using investment casting. Centrifugal casting is a technique in which liquid metal is poured into a rotating mold. The centrifugal force induced by the spinning causes the melt to be thrown against the inner mold wall, and rotation is maintained until the metal solidifies from the outer to the inner diameter of the casting.

Effect of moisture upon mechanical properties of ceramic moulds during high pressure steam dewaxing

Abstract Investment casting research is being carried out by the University of Birmingham, sponsored by EPSRC and a consortium of industrial companies. The programme is aimed at developing a fundamental understanding of the process, with a view to routinely producing sound, net shape castings. A key stage within the investment process is that involving the removal of wax from the unfired ceramic shell. This important process is carried out within the confines of a sealed pressure vessel, more commonly referred to as a Boilerclave (trademark, Leeds and Bradford Boiler Co. Ltd, UK) with external pressure gauges as the only indication of what is actually happening inside the cavity. The dewaxstage is a key stage in the process as wax needs to be removed from a weakceramic shell system without cracking or dimensional alteration, which would be reflected in outoftolerance casting scrap. Owing to the nature of the process, wax removal is probably the least understood or controlled aspect of the whole investment sequence. The following paper is the third in a series which contain results obtained at the University of Birmingham using a specially instrumented stream autoclave which allows visual data capture, thermal and steam pressure profiles within the chamber and thermal instrumentation of waxes and shells to be obtained. The results of simple conductivity calculations and experimentation to determine the effect of moisture upon the strength of ceramic shells will be presented and the strengthening role of wax penetration into the primary coat of the ceramic shell during dewax will be investigated.

Developing Fiber and Mineral Based Composite Materials from Paper Manufacturing By-Products

Developing valuable materials from the by-products of paper industry can help to address some environmental and economic issues associated with traditional synthetic composites. Particularly, the management of paper mill sludge (PMS) waste remains an economic and environmental challenge for the pulp and paper industry. 11 million tons of PMS is generated annually in Europe from the wastewater treatment (WWT) process of paper mills. PMS is mostly used in low value applications. However, PMS contains fibers and minerals with physio-chemical properties that exhibit a high potential to substitute some conventional materials in other industries. The research presented in this paper aims to explore new directions for further investigation on PMS material applications by reviewing the literature on PMS materials and subsequently characterizing sludge from 6 different mills. The study shows the technical feasibility, opportunities and technological readiness of fiber and mineral based composites obtained from PMS, such as; cementitious products, polymer reinforcement and fiberboards.

Road-Mapping Towards a Sustainable Lower Energy Foundry

Sustainable development is about reaching a balance between economic, social, and environmental goals, as well as people’s participation in the planning process in order to gain their input and support. For a foundry, sustainable development means adoption of strategy and actions that contribute to higher yield with a minimum environmental impact. This new approach forces foundries to change their behavior. Management should include new issues and develop innovative methods, practices and technologies striving for solving problem of shortages of resources in particular energy. Hence, its realization requires updating existing production models. The main message of sustainability for foundries is to expand the range of analysis and focusing on processes. Lean thinking offers numerous opportunities for more efficient resources utilization. Here some energy saving methods toward a more efficient and a sustainable foundry are briefly discussed.