Nwabueze Emekwuru

Application of a moments spray model to solid cone diesel sprays

Discrete droplet models in which parcels of droplets are tracked in space in a Lagrangian framework have historically dominated the modelling of fuel sprays. These models are computationally expensive, as the chaotic motions of each droplet have to be predicted. A development of a spray model that captures the full polydisperse nature of spray flow without using droplet size classes has been presented in previous publications. In this paper, the model is applied to solid cone diesel sprays. The size information concerning the spray is obtained by calculating three moments of the droplet-size distribution function from transport equations and one moment from a Gamma size distribution function. The predictions from the model are compared with results from experiments, a discrete droplet model, and two moments-based models. These indicate that droplet break-up, collisions, penetration and sizes are successfully modelled.

Preliminary study of improving the speed and cost of diffusion bonding of metal sheets

Diffusion bonding may be used, with superplastic forming, to create a great range of cellular structured materials, with great potential for material efficiency, multi-functionality and lightweighting. However, this potential is generally considered to be constrained by the slowness (hours) of and the overall cost of achieving such solid-state bonds. The work described is part of the basis for the development of a process that can produce good diffusion bonds, in the commonly used titanium alloy Ti64 (Ti6Al4V), in less than 60 s. And so it has the capability of increasing the productivity for diffusion bonding. Localised direct heating can induce high levels of stress, and these thermal stresses can accelerate the diffusion bonding process. The equipment used involved induction heating and required no large (and expensive) hot presses or pressure vessels. Hence, machinery capital cost may be reduced. A sequence of numerical models was found useful to understand the effects of the process parameters on diffusion bonding. Finite element modelling looked at accelerating the collapse of the voids, determined by the relative flatness and roughness of the metallic sheets at different spatial wavelengths. It appears that the localised heating drives the diffusion bonding process in inducing significant stress levels, into the material to be bonded, and thus accelerates the collapse of voids and the achievement of intimate contact. Raising the temperature as much as possible assists the actual diffusion processes required for bonding to occur and is an important aspect of accelerating the process. Therefore, the increase in the rate of bonding and the lower cost of the equipment open up the possibility of much more affordable diffusion bonding and the production of material efficient and functionally useful cellular materials.

Numerical Study of Radiation and Temperature Phenomena for Improved Super-Plastic Sheet Metal Forming

In most super-plastic forming (SPF) investigations the focus is usually on the material aspects. In this paper the authors develop a model to improve the heat management of SPF. The model presented improved process possibilities. The improved design involves selective application of heat to the material. Final product shape can easily be controlled by accurate temperature control of the work piece. Numerical simulation has been carried out on various components including a ‘top hat shape‘ and a heat exchanger part. Simulation comparisons are made between selective heating and conventional processing, where all of the formed material is at the same temperature, and greater process efficiency of the selective heating approach is demonstrated.

Construction of next-generation superplastic forming using additive manufacturing and numerical techniques:

The superplastic forming process is used in a wide range of high-value-added manufacturing sectors to make lightweight, complex-shaped components for high-performance applications. Currently, it is a high-cost process, for example, the superplastic forming of titanium alloys involves a high-temperature furnace, costly (mould) tooling and has a high utilization of resources such as argon gas and energy. The authors of this article propose a prototype for next-generation superplastic forming laboratory equipment. The aim is to develop improved methods, particularly for heat management in the superplastic forming process, to allow a more widespread application of the process to manufacture lower cost products. The next-generation superplastic forming tool comprises a tool in the form of a hemispherical shell, pressure chamber with incorporated water cooling system and an infrared heating system. The construction, usability and suitability of the next-generation superplastic forming equipment have been proven by a series of physical experiments, and numerical simulations are performed and the results are presented and discussed in this article.