Margaret Lucas

Influence of ultrasonics on upsetting of a model paste

This paper describes a preliminary study of the influence of ultrasonics on the boundary conditions associated with the equipment walls in a soft solid forming operation using Plasticine as a material model. A detailed finite element analysis is described involving the upsetting of a cylindrical specimen between two parallel rigid dies with kinematics and ultrasonic oscillatory loading conditions. A series of squeeze flow experiments has been conducted to validate the finite element models. The oscillation parameters were measured using a 3D laser Doppler vibrometer to complement the measurement of reaction forces.

Enhanced vibration performance of ultrasonic block horns

Block horns are tuned components designed to vibrate in a longitudinal mode at a low ultrasonic frequency. Reliable performance of such horns is normally associated with the amplitude of vibration, uniformity of vibration amplitude at the working surface and the avoidance of modal participation by non-tuned modes at the operating frequency. In order to maximise vibration amplitude uniformity, standard slotting configurations are included in the horn design. However, defining a slotted block geometry which guarantees sufficient tuned frequency isolation from nearby modes as well as high amplitude and amplitude uniformity, is not straightforward. This paper discusses horn configurations which satisfy these criteria and investigates the design requirements of block horns which operate as intermediate components in ultrasonic systems, where the block horn dominates the vibration behaviour of the system. The importance of mode shape characterisation is discussed and modes are classified using experimental data from 3D laser Doppler vibrometer measurements and finite element analysis. In particular, the role of additional fine slots and castellations are studied with reference to two distinct ultrasonic applications involving a similar block horn.

Breath sounds, asthma, and the mobile phone

The sounds generated by breathing in asthma are widely accepted as an indicator of disease activity. We have investigated the use of a mobile phone and electronic signal transfer by e-mail and voice mail to study tracheal breath sounds in individuals with normal lung function and patients with chronic or exercise-induced asthma. Spectrograms from patients with active asthma and impaired lung function were significantly different from people without asthma (p<0.0001). Our results suggest that mobile phone recordings clearly discriminate tracheal breath sounds in asthma and could be a non-invasive method of monitoring airway diseases.

Vibration sensitivity in the design of ultrasonic forming dies

Radially oscillating dies can be designed for reducing friction forces in metal forming processes. Cylindrical dies are prone to reliability problems due to the inherent dense modal activity close to the tuned operating mode. The determination of die vibration behaviour is critical to successful die design and a validated vibration characterisation strategy is therefore proposed. This paper discusses the adaptation of vibration analysis techniques to ultrasonic modal parameter estimation and proposes a redesign strategy based on sensitivity analysis. The result is a design procedure for improved vibration control of an ultrasonic metal forming process.

Design and characterisation of ultrasonic cutting tools

Cutting of food products and other materials with ultrasonically assisted tools has demonstrated significant benefits including reduced wastage and improved cut quality. However, the success of the technology relies on careful design of the ultrasonically excited tools and transmission components. In this paper, the different challenges of tool design are discussed with reference to two cutting devices. The studies demonstrate that accurate characterisation of the vibration behaviour of the tool and an understanding of the effects and limitations on vibration responses of design modifications, allows tool performance to be enhanced in the design.

Modelling wall boundary conditions in an elasto-viscoplastic material forming process

Abstract The numerical simulation of a hot metal or soft material processing operation, for optimising the design and operating variables, critically depends on the boundary conditions associated with the walls of the equipment. With advancements in finite element methods, more accurate determination of the field variables governing material flow in forming processes involving complex interfacial boundary conditions and realistic material constitutive models has become feasible. This paper describes a finite element study of the effect of wall boundary conditions on the upsetting of plasticine as a model for hot metal. The wall boundary and intrinsic flow characteristics for the model material are then used to investigate the effects of introducing a vibration assisted tooling method. The aim was to modify the wall boundary conditions in a way that reduced the forming force. A comparison between experimental and computed results, for the relationship between the forming force and tool displacement and for flow visualisation, demonstrate very close agreement. If deformation is performed under superimposed vibration, the mean stress necessary to maintain plastic flow decreases appreciably in comparison with that for purely static deformation, and this decrease is accurately predicted by the FE models.

Research applications and opportunities in power ultrasonics

Abstract The first applications in power ultrasonics were largely focused on ultrasonic cleaning baths, which rely on generating inertial cavitation, and the incorporation of ultrasonic excitation in manufacturing processes such as joining of plastics and metals. Since the early days of power ultrasonics there has been a rapid growth in the number of applications, and the diversified range of applications, from microwelding to ultrasonic osteotomy, has been made possible by a combination of advances in experimental techniques for characterizing low ultrasonic frequency vibrations and acoustics, and advances in computational modelling. This article highlights just some of the research in power ultrasonics that aims to exploit the benefits of low ultrasonic frequency high ultrasonic amplitude vibrations. This article reports current research and suggests future opportunities in three different application areas that have seen significant recent advances: joining and shaping of metals, surgical devices, and cavitation cells.

Automatic wheeze detection based on auditory modelling

Abstract Automatic wheeze detection has several potential benefits compared with reliance on human auscultation: it is experience independent, an automated historical record can easily be kept, and it allows quantification of wheeze severity. Previous attempts to detect wheezes automatically have had partial success but have not been reliable enough to become widely accepted as a useful tool. In this paper an improved algorithm for automatic wheeze detection based on auditory modelling is developed, called the frequency- and duration-dependent threshold algorithm. The mean frequency and duration of each wheeze component are obtained automatically. The detected wheezes are marked on a spectrogram. In the new algorithm, the concept of a frequency- and duration-dependent threshold for wheeze detection is introduced. Another departure from previous work is that the threshold is based not on global power but on power corresponding to a particular frequency range. The algorithm has been tested on 36 subjects, 11 of whom exhibited characteristics of wheeze. The results show a marked improvement in the accuracy of wheeze detection when compared with previous algorithms.

Temperature Effects in Ultrasonic Cutting of Natural Materials

This paper investigates the relationship between ultrasonic cutting parameters and temperature around the cutting site for wood and bone, with the aim of reducing thermal damage in natural materials. Two ultrasonic cutting blades, tuned at two different frequencies but with identical cutting edge and surface profiles, are used in the experiments. Temperature is monitored close to the cutting site and the effects of applied load and blade tip vibration velocity are studied. Results indicate that ultrasonic cutting blade design can incorporate cutting parameters to reduce or eliminate thermal damage in these natural materials without using an additional blade cooling system.

A finite element model of ultrasonic extrusion

Since the 1950s researchers have carried out investigations into the effects of applying ultrasonic excitation to metals undergoing elastic and plastic deformation. Experiments have been conducted where ultrasonic excitation is superimposed in complex metalworking operations such as wire drawing and extrusion, to identify the benefits of ultrasonic vibrations. This study presents a finite element analysis of ultrasonic excitation applied to the extrusion of a cylindrical aluminium bar. The effects of friction on the extrusion load are reported for the two excitation configurations of radially and axially applied ultrasonic vibrations and the results are compared with experimental data reported in the literature.