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Industrial Processes

Simultaneous engineering

   
 
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SESAME is a software package that combines the functions of computer-aided design (CAD), process planning and manufacture for the production of engineering components. It handles all stages from conceptual design through to the production of numerical code for cutting machines. Advantages include a feature-based design system which is more intuitive than traditional CAD programs, and rapid feedback from process planning to design ('simultaneous engineering'), to ensure that the final design can be manufactured without unnecessary difficulty. Software based on SESAME modules is already being marketed by the lead partner.

The manufacturing industry is moving away from mass production towards customised manufacture of relatively small batches of specialised goods. For companies to compete in this fast-changing market, they will have to drastically reduce their investment of time and money in product design and development. The ideal solution would be a single computer system to handle all processes from conceptual design through to the manufacture of the product.
In this project, a team of academic and industrial partners has come close to realising this ideal. SESAME - Simultaneous Engineering System for Applications in Mechanical Engineering - is a software package that combines the functions of computer-aided design (CAD), process planning (CAPP) and manufacture (CAM).
Traditionally, the design of a component is finished before it is passed to the process planning department. If the part poses difficulties in manufacture, it is sent back to be redesigned. In SESAME, the manufacturing processes are planned as the design proceeds (hence 'simultaneous engineering'), so that problems can be solved as they arise. As a result, the designer can be confident that the component can be manufactured without problems.
SESAME consists of two main parts - a feature-based design system and a CAPP-CAM system.

Feature-based design

An engineering component can be thought of as built up from a number of design features, each of which has a function. A feature may be a slot, a drilled and threaded hole, a bearing seat, a flange, and so on. Research by the SESAME team has focussed on features which are so-called 'two-and-a-half-dimensional', that is, prismatic or rotational in form and produced on milling or drilling machines or lathes. In SESAME, the component is assumed to start out as a block, or a casting, in which features are formed by cutting away material. Each feature then corresponds to a volume to be removed by one or more actions of the appropriate cutting machine.
Features are defined not only in terms of their size and shape, but also their tolerances, surface finish and interdependency with other features. As each feature is treated as a conceptual whole, rather than a collection of lines and surfaces, it is relatively simple to alter a design. Features can be freely moved, resized or exchanged, and the program will modify its internal model to accommodate the changes.
In contrast, conventional CAD programs represent components as assemblies of simple geometrical shapes such as cubes, cylinders and cones. It can be very difficult to alter the design, because these shapes are purely descriptive and have no functional significance.
The designer builds a complete design for the component by selecting and specifying features on the screen. SESAME contains a pre-defined library of primitive features (such as slots and holes) and standard engineering features (corresponding to ISO specifications, such as threaded holes or circlip grooves). User-defined features which are particular to the industry or the company (sheet metal features, for example, are quite different to those in solid components), may be easily created and added to the pre-defined library. The designer can modify the design at will and experiment with different solutions, viewing the result on the screen each time.

Process planning

When the design is ready, the specification is passed to the CAPP-CAM system. Here it may be processed by up to three different modules.
The most innovative is the automatic process planner. It first checks if the design is realisable, by looking for geometric inconsistencies such as intersecting features, obstructions, inaccessible voids, disconnected parts, and so on. It also ensures that there is sufficient room for the machine tools to move in and out. Next, each design feature is assigned to one or more manufacturing features, building up a network of all possible manufacturing processes. Each feature has a corresponding microcycle, which is the sequence of machine operations required to execute the feature. The microcycle chosen depends on the specified dimensions, tolerance and surface finish, as well as implicit considerations, such as the proximity of features to each other. Any problems arising at this stage are automatically referred back to the designer.
Once all possible processing paths have been mapped out, the best solution is chosen by a genetic algorithm. In a process analogous to biological evolution, a number of possible solutions are bred together to produce offspring which are in turn used to produce the next generation. At each stage the best solutions, defined by lowest manufacturing cost, are selected for breeding. The result is the most economical process for manufacturing the component.
If the user prefers, or if the automatic process planner is unable to produce a complete plan, the interactive feature planner can be brought into play. Here, the user constructs the manufacturing plan by guiding SESAME in selecting manufacturing options where more than one process is available.
If need be, a third module, the manual feature planner, can be used for fine-tuning the manufacturing plan. It is essentially a traditional CAM system, in which the process plan can be altered by the user. Operations can be added, deleted or modified as required.
Finally, whichever module it comes from, the process plan is automatically translated into numerical control (NC) code used to give explicit instructions to the machine tools to make the component.

Ideal for small companies

SESAME is capable of supplying cost-effective solutions for one-off designs or small numbers of products. It is ideal for small companies who cannot afford a specialised CAPP department, and lack the resources to capture manufacturing know-how with conventional software tools. It should be particularly useful in the automotive and aircraft industries and for the manufacture of machine tools.
The Italian machine-tool manufacturers Spring were the end-users for SESAME, supplying specifications for features and testing the complete system. The University of Edinburgh designed the automatic process planner, while the University of Hannover developed the interactive feature planner. Project manager Strässle produced the feature-based design system and the NC system.
Although SESAME has been a success in its own right, the development of a marketable system has been hampered by the loss of a crucial software component which has been withdrawn by its US suppliers. Strässle has, however, used the feature-based design system of SESAME in their Feature M package (part of its Konsys 2000 suite), with pre-defined libraries of primitive, functional and industry standard features. In addition, the system enables the user to easily define new features to supplement the pre-defined library. A sheet metal working module is also available.

 

 

Project Title:  
Simultaneous engineering system for applications in mechanical engineering

Programmes:
Industrial and Materials Technologies (BRITE-EURAM/CRAFT/SMT)

Contract Reference: BE-4539

Cordis DatabaseFor more information on this project,
go to the CORDIS Database Record

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