A. Sherlock

Biological analogies in manufacturing

Abstract Biological organisms and manufacturing facilities are both examples of complex systems that exist in changing environments. It may be that some of the lessons that have been learned from nature are applicable to engineering. The purpose of this paper is to examine analogies from nature and to discuss their relevance to engineering systems. In particular systems that exhibit emergent behaviours or are subject to evolutionary forces are studied.

A voxel-based representation for evolutionary shape optimization

A voxel-based shape representation when integrated with an evolutionary algorithm offers a number of potential advantages for shape optimization. Topology need not be predefined, geometric constraints are easily imposed and, with adequate resolution, any shape can be approximated to arbitrary accuracy. However, lack of boundary smoothness, length of chromosome, and inclusion of small holes in the final shape have been stated as problems with this representation. This paper describes two experiments performed in an attempt to address some of these problems. First, a design problem with only a small computational cost of evaluating candidate shapes was used as a testbed for designing genetic operators for this shape representation. Second, these operators were refined for a design problem using a more costly finite element evaluation. It was concluded that the voxel representation can, with careful design of genetic operators, be useful in shape optimization.

A Voxel-Based Representation for the Evolutionary Shape Optimisation of a Simplified Beam: A Case-Study of a Problem-Centred Approach to Genetic Operator Design

This paper examines a voxel (N-dimcnsional pixel) based representation for shape optimisation problems, and shows that although a basic genetic algorithm performed poorly on a simplified beam design problem, the use of three domain specific operators improved performance greatly. Additionally, the use of a ‘directed smoothing’ operator that preferentially adds material to high stress areas was examined and found to assist evolutionary search. This paper demonstrates how domain knowledge and an understanding of how genetic algorithms work can be used to inform the design of suitable operators.

Real-time parameterization of electrochemical machining by ultrasound measurement of the interelectrode gap

Abstract This paper discusses the development of an ultrasound technique that enables the continuous, uninterrupted collection of time-resolved data for dissolution valency, interelectrode gap, and overpotential during electrochemical machining (ECM). These parameters, in combination with the dissolution current, give insight into the ECM process. The accuracy and expediency of this approach has been established using results collected from the ECM of the stainless steel SS410. The enhanced accuracy and resolution offered by this approach has been demonstrated through comparison with established current-time and interelectrode gap-time analysis methods. This superiority has been explained both in terms of the relative accuracy of the analysis methods and the removal of the requirement for the approximation of constant-valency machining. The resulting current-overpotential relationships are sufficiently accurate to give insight into the ECM dissolution characteristics of the steel, as well as providing an improved parameter base essential for increasingly accurate simulation of the ECM process and tool design techniques.

Two-dimensional tool design for two-dimensional equilibrium electrochemical machining die-sinking using a numerical method

Abstract Electrochemical machining (ECM) can be defined as controlled electrolytic anodic erosion. ECM can machine hard alloys and metals with tools of softer metals, without affecting either workpiece microstructure or surface properties. There is no tool wear owing to a lack of tool/workpiece contact. The ECM medium between the tool and workpiece is electrically conductive, causing the finished workpiece geometry to vary from the tool and not to become a direct inverse of the tool shape. The characteristics of the workpiece material can also affect shape transfer, increasing the difficulty of designing and simulating ECM tools. At present, ECM tool design in industry is a trial-and-error process that can be prohibitively time-consuming. Automated design and simulation procedures are, therefore, desirable. This paper describes a computational approach to ECM tool design for two-dimensional cases based on the solution of a set of ordinary differential equations in a basis function format that are based on the electric field during the ECM process. This method has a number of advantages. It allows for the use of geometric representations of the tool and workpiece, such as B-Splines and Bèzier curves. This enables easy integration with most current computer-aided design software. It is also possible more easily to design and simulate tools for non-ideal machining conditions, where parameters such as electrolyte conductivity vary with the ECM cell. Above all, this method can design tools directly for the ECM process, given a particular workpiece shape without iterative methods. Computational trials have been carried out and compared with the results of an experimentally validated model. These showed that the method was effective for tool design under ideal machining conditions and was easier to use for non-ideal condition modelling.

A Voxel Based Approach to Evolutionary Shape Optimisation

Shape optimisation is a hard problem from the field of Mechanical Engineering with the potential for significant cost savings if successfully performed. In the past, evolutionary optimisation approaches have proved successful. In those studies, a form of the shape was assumed, and its parameters optimised. An alternative is a voxel (N-dimensional pixel) based representation, which makes no such assumptions about the form of the solution, and allows the user to add domain knowledge if desired. This paper outlines a preliminary investigation into this approach and shows that the objections to this approach in the literature can be overcome if care is taken over the design of the operators.

Recognising 3D products and sourcing part documentation with scanned data

Searching databases of 3D models is a crucial yet difficult problem that has been studied by the academic community for a considerable time. A useful and robust method for finding engineering parts remains difficult however. Previous work typically describes finding the best match in a single search. Work described in this paper uses scanning techniques allied to shape similarity measures to produce a system that successfully allows search by browsing. We also describe some new shape descriptors and methods of identifying and dealing with chirality. The technique is evaluated in the context of the part search applications. The use of the techniques is applied to large (80,000+parts) databases of real world engineering components in use in automotive and aerospace companies. The methods employed are applicable to a wide range of scenarios in engineering, as well as the arts, archaeology, medicine and commerce.