Rupert Soar

Characterisation of aluminium alloy 6061 for the ultrasonic consolidation process

Ultrasonic consolidation (UC) is a freeform fabrication technique developed for the layered fabrication of metal parts. The process uses a high intensity ultrasonic energy source to induce combined static and oscillating shear forces within layers of metal foil to produce solid-state bonds. This paper will consider control parameter optimisation and surface preparation issues, for the production of aluminium alloy 6061 specimens. It will assess weld quality through both mechanical testing and optical observation. Aluminium 6061 specimens were successfully welded by the UC machine using both unprepared and surface prepared foils. In the unprepared specimens, thick oxide films exist along the whole specimen length of the weld interface. Results showed that the dynamic interfacial stresses, generated under UC conditions, compact the oxide layer to form brittle, ceramic bonds at the weld interface. A simple cleaning procedure increased metallurgical bonds, within the weld interface, by up to 45%. A general process window was produced for 6061 alloy based on a combination of the peel test data and microstructural analysis.

A model for weld strength in ultrasonically consolidated components

Abstract Ultrasonic consolidation (UC) is a solid freeform fabrication technique developed for the manufacture of metal parts. The mechanisms by which bonds are formed, during the UC process, are based on a combination of the surface effect and the volume effect. Based on the outcomes of peel tests and microstructural analysis, this paper will consider the influence of these two phenomena on the weld strength of specimens. A model is presented to describe how calculations for weld strength may be derived on the basis of the theory of surface and volume effects. Through the application of the model, it was possible to demonstrate that the weld strength may be 7 per cent greater than the tensile strength of the base metal. The identification of the phenomena and the development of a model for weld strength have led to the modification and production of an enhanced test procedure which is described in this paper.

Smart structure sensors based on embedded fibre Bragg grating arrays in aluminium alloy matrix by ultrasonic consolidation

Smart structure sensors based on embedded fibre Bragg grating (FBG) arrays in aluminium alloy matrix by ultrasonic consolidation (UC) technique have been proposed and demonstrated successfully. The temperature, loading and bending responses of the embedded FBG arrays have been systematically characterized. The embedded FBGs exhibit an average temperature sensitivity of ~36 pm °C-1, which is three times higher than that of normal FBGs, a bending sensitivity of 0.73 nm/m-1 and a loading responsivity of ~0.1 nm kg-1 within the dynamic range from 0 kg to 3 kg. These initial experimental results clearly demonstrate that the UC produced metal matrix structures can be embedded with FBG sensor arrays to become smart structures with capabilities to monitor the structure operation and health conditions in applications.

Characterization of Process for Embedding SiC Fibers in Al 6061 O Matrix Through Ultrasonic Consolidation

In this paper, continuous SiC fibers were embedded in an Al 6061 O matrix through ultrasonic consolidation at room temperature. The optimum embedding parameters were determined through peel tests and metallographic analysis. The influence of the embedded fiber volume fraction and base metal thickness on the interface bond strength was studied, and the fiber/matrix bond strength was tested through fiber pullout test. The results showed that embedding ≥0.8% volume fraction of SiC fiber in a 6061 O matrix could significantly increase and even its interfacial strength, but there is a threshold for embedded fiber volume fraction at specific parameters, over which the plastic flow and friction may be insufficient to have a strong bond at foil/foil interfaces between fibers. The study also showed that base metal thickness did not have significant influence on the interfacial strength with an exception of samples with a base metal thickness of 500 μm. Based on the results, it was proposed that microfriction at consolidation interfaces plays an important role for joint formation, and localized plastic flow around fibers is important to have fibers fully and safely embedded.

Surface temperature of tools during the high-pressure die casting of aluminium:

Abstract The objective of this work was to determine the temperature experienced within a pressure die-casting tool during aluminium part production. It was important to determine the temperature profile of the production process so that an accurate thermal cycle could later be simulated. The research overcame several challenges of this aggressive environment to show that the surface temperature of a die could be obtained from an H13 steel tool running on an aluminium pressure die-casting machine. The results show that the surface of a typical aluminium pressure die-casting tool heats to 400–450°C within approximately 1 s and cools to 150–200°C within approximately 20 s.

Analysis of cooling channels performance

The die casting industry is under increasing pressure to improve production rates to enable greater productivity. Employing conformal cooling channels could potentially improve a die performance through the reduction of solidification times. The paper reviews simulated solidification results from a traditional cooling channel design and a conformal cooling channel design. The paper continues by describing the construction of bonded laminate insert with integrated cooling channels. Casting trials were conducted using the inserts to validate the simulated results. Work to date has demonstrated the ability to manufacture laminate inserts quickly, the accuracy of finite element analysis and the importance of designing conformal cooling channels.

Implications of solid freeform fabrication on acoustic absorbers

Purpose – Limitations in traditional manufacturing methods currently employed in the production of acoustic devices, restricts the development of design led performance improvements. These devices are used to control sound energy and are commonly employed for tailoring room acoustics. solid freeform fabrication allows the production of acoustic structures more complex than traditionally manufactured devices. This paper aims to focus on a novel absorber based on destructive interference, considering performance, design and manufacture.Design/methodology/approach – Selective laser sintering has been used in the investigation of the performance and manufacturing possibilities and limitations of a novel destructive interference absorber. Validation of the absorber performance is benchmarked against a conventional resonant absorber and compared to published results. The implications for acoustic devise design, the advances and limitations in manufacture using solid freeform fabrication techniques and potential...

Bio-inspired emergent construction

The huge termite mounds of Macrotermitinae are a perfect example of the emergence of vastly complex structures through the principles of self-organisation. Previous models of this construction behaviour have been somewhat lacking when describing individual responses and in modelling physical constraints. Here we present a simple 3D individual-based stimulus-response model, focusing on construction of the royal chamber and trail galleries. We show how simple response-threshold functions can be combined with pheromone templates and stigmergic mechanisms to mirror experimental work and provide an explanation for behavioural patterns.

Design limits of unbonded laminate tooling for pressure die-casting

Abstract This paper describes a new concept for the construction of prototype tooling specifically for pressure die-casting. The tools are made by clamping together laser-cut profiles in H13 tool steel sheet. The result of this endeavour has been the creation of a low cost, flexible, scalable and robust tooling system for design validation that allows multiple design iterations to be examined on the actual pressure die-casting equipment used in the production environment. Work to date has shown that relatively large up-standing features can withstand the forces of molten metal during injection.

Freeform Construction Application Research

The level of automation technology and processes control, within the construction sector, faces unique challenges if it is to catch up with automotive and aerospace applications. The construction industry has problems relating to health and safety, environmental legislation and traditional methods of procurement. These are compounded by diminishing skills in the labour force. One way to address these issues is by increased automation and integration of design, modelling and process control. Digital Fabrication has demonstrated the feasibility of the integration of design and component production on a large scale. Freeform Construction builds on Digital Fabrication by integrating the control of final material deposition. This paper reports on recent meetings held with industrialists to gauge their perceptions of the technology and encourage discourse to identify both applications and opportunities for the wider research community. Examples of digital fabrication in construction are discussed. Freeform Construction is defined and potential applications are presented. An example of physical model generation from construction CAD software is described.