Coarse filters for shape matching

This article describes the coarse shape filters that support the 3D, Internet-based search engine ShapeSifter, which aims to locate parts already in production that have a shape similar to a desired new part. The search engine analyzes the target model's shape characteristics and performs a similarity match on the database's contents. Our main challenge is identifying shape metrics that produce effective characterizations of 3D models for similarity comparison. We focus on using three novel convex hull-based indices to carry out a preliminary coarse filtering of candidates prior to more detailed analysis. We also describe the crucial role played by two databases of benchmark objects. Unlike other shape-matching systems, we chose ShapeSifter's architecture (multistep query), 3D representation (triangulated mesh), and implementation (Java3D) to allow deployment online once it matures     

Factors affecting user performance in haptic assembly

Current computer-aided assembly systems provide engineers with a variety of spatial snapping and alignment techniques for interactively defining the positions and attachments of components. With the advent of haptics and its integration into virtual assembly systems, users now have the potential advantage of tactile information. This paper reports research that aims to quantify how the provision of haptic feedback in an assembly system can affect user performance. To investigate human–computer interaction processes in assembly modeling, performance of a peg-in-hole manipulation was studied to determine the extent to which haptics and stereovision may impact on task completion time. The results support two important conclusions: first, it is apparent that small (i.e. visually insignificant) assembly features (e.g. chamfers) affect the overall task completion at times only when haptic feedback is provided; and second, that the difference is approximately similar to the values reported for equivalent real world peg-in-hole assembly tasks.     

Identification of formation stages in a polymeric foam customised by sonication via electrical resistivity measurements

The polymerisation reactions associated with foam formation have distinct stages (i.e. nucleation, growth, packing, stiffening, solidification) some of which are known to be more sensitive to external inputs than others. Consequently, precise detection of the start and end points of each of the polymerisation stages would enable the fine control of material properties such as porosity in solid foams. The development of such process control can only be pursued if those sensitive stages can be clearly distinguished during the manufacture process. This paper reports how an electrical resistivity tracking method was used to assess the differences in the foaming processes when ultrasound was irradiated to polymeric melts undergoing foaming with the aim of tailoring the architecture of the final solid matrix. The electrical resistivity tracking method is also appraised with regard to its suitability to accurately identify the formation stages in the foam.     

Grain boundary precipitation in Inconel 718 and ATI 718Plus

Grain boundary precipitates in Inconel 718 and ATI 718Plus are important to control during hot working processes, since they can control the grain size. Precipitating excessive or insufficient amounts can be detrimental to the final component. Therefore, it is important for manufacturers to understand the formation and kinetics of grain boundary precipitation and the effect this has on mechanical properties. This review considers the background of grain boundary precipitation, including the effect of the thermal stability of γ′ and γ^″ phases. In addition, the effect of stress on the grain boundary phases and their precipitation kinetics in different conditions are also included. Also, the impact of grain boundary precipitation on the mechanical properties is explored.

This review was submitted as part of the 2017 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged     

Commercial and business issues in the e-sourcing and reuse of mechanical components

Currently, tens of thousands of mechanical components that are produced worldwide are specified by 3D CAD models held in the archives of individual manufacturing companies. Emerging technologies from a number of research projects suggest it will soon be feasible to conduct global ‘shape’ searches on these collections. In principle such “3D-search engines” could revolutionise the sourcing of mechanical components and enable a vigorous market for the resale of existing production tooling. The commercial and business aspects of this emerging technology (i.e. 3D e-Sourcing) are studied in this paper. State-of-the-art part-sourcing is outlined and estimates of the potential benefits of reuse are discussed. The paper then outlines ownership issues of CAD/CAM data and tooling, and identifies barriers, both technical and business, to forms of 3D e-Sourcing which would enable secondary use. The paper identifies the ability to prohibit the physical production of publicly circulated 3D models as key to the viability of this trading system. Consequently the paper concludes with details of a proposed “3D model public licence” which is specifically designed to protect the IP of manufacturers while allowing 3D search engines to index components.     

Algorithms for the physical rendering and assembly of octree models

Hierarchical decomposition techniques are well established for the representation of 2D images, the calculation of distance maps, and the modelling of volume data. However, recent work has suggested that their use can be extended to the manufacture of physical objects for low cost prototyping and visualization. This paper details various decomposition and assembly planning routines created to support this process. Specifically the decomposition methods are described to generate octants appropriate for the physical assembly process. Having established methods for generating suitable octrees, three different algorithms for planning the assembly of octrees are presented. The comparative performance of these different approaches is discussed.     

Viewer-centered geometric feature recognition

Computer aided design (CAD) and computer aided manufacturing (CAM) systems are now indispensable tools for all stages of product development. The flexibility and ease of use of these systems has dramatically increased productivity and quality of product while reducing lead times. These advances have been largely achieved by automating individual tasks. At present, these islands of automation are poorly linked. One reason for this is that current computer systems are unable to extract geometric and topological information automatically from solid models that is relevant to the down-stream application. In other words, feature information.The objective of the research reported in this paper was to develop a more generic methodology than heretofore, in order to find the generic protrusion and depression features of a CAD model. The approach taken is one relying on a more human type of analysis, one that is viewer-centered as opposed to the object-centered approach of most previous research in this area. The viewer-centered approach to feature recognition described is based on a novel geometric probing or tomographic methodology. A five-step algorithm is described and then applied to a number of components by way of illustration.     

Morphological and biological characterization of density engineered foams fabricated by ultrasonic sonication

The successful manufacture of functionally tailored materials (e.g., density engineered foams) for advanced applications (e.g., structures or in bioengineering) requires an effective control over the process variables. In order to achieve this, density gradation needs to be represented and quantified. Current density measurement techniques offer information on bulk values, but neglect local position as valuable information (i.e., do not associate density scalar values with specific location, which is frequently critical when mechanical properties or functionalities have to be engineered). In this article, we present a method that characterizes the density gradation of engineered foams manufactured by the sonication technique, which allows the generation of sophisticated porous architectures beyond a simple linear gradient. A 3D data capture (μCT) and a flexible analysis software program (ImageJ) are used to obtain “global” density gradation values that can, ultimately, inform, control, and optimize the manufacture process. Polymeric foams, i.e., polyurethane (PU) foams, were used in this study as proof of concept. The measurements performed on the PU foams were validated by checking consistency in the results for both horizontal and vertical image slices. Biological characterization was done to assess the samples’ tailored structure viability as scaffolds for tissue engineering. The comparison between untreated and sonicated samples yielded a 12.7% of increment in living cell count adhered to the walls after treatment. The conclusions drawn from this study may inform the design and manufacture of density-engineered materials used in other fields (e.g., structural materials, optoelectronics, food technology, etc.)     

Optimizing tool selection

Selecting optimal cutting tools that can answer to the performance criteria of manufacturing economics (quality, productivity, cost, etc) is an important step in planning the manufacture of components. Achieving this, however, is difficult because of the many constraints involved in the tool selection process. This paper describes a method for determining a theoretical optimal combination of cutting tools given a set of 3D volumes or 2D profiles. Optimal tools are selected by considering residual material that is inaccessible to oversized cutters and the relative clearance rates of cutters that can access these regions of the selected machining features. The current implementation described does not give exact results because several machining parameters have been ignored during the selection process, such as tool path length, plunge rates, etc. However, the experimental studies carried out to verify the theoretical results suggest that while these factors may influence the absolute values calculated, in general, their influence on the relative ranking of the tools is insignificant. The results presented here suggest that the 'correct' combination of tools could significantly reduce machining times. Consequently, the paper concludes with a discussion of how modifications to typical tool path generation routines in commercial CAM systems could improve productivity.