Integration of Design and Process Planning

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In Concurrent Engineering, augmented effort is invested in the integration of the different engineering processes applied in the manufacturing cycle of a product. In CE, emphasis is put on a simultaneous execution of shared tasks by separate departments, and - more important - on the control of co-operative decision making. Therefore, it is important to understand the need for interaction and communication between the diverse disciplines involved in the product development cycle. As a matter of fact, the possibility of communication is based on both the availability and the accessibility of coherent information. Instead of merely exchanging data, it is desired to have access to meaningful representations of the existing product data, reflecting the current state of design. Access to significant historical data may also be of significant help. If this data is available (in a so-called product information structure), it can be used as a basis for the control of the design and engineering processes, including the required communication.

Working with design teams brings forward the need for planning of the design, engineering and communication processes as part of the manufacturing cycle. This stresses the need for an overall product information structure that can be used as a basis for the control of the realisation process of a product through its entire life cycle, from functional requirement specification, until final disposal. This primarily implies that a model of the product life cycle is required. It will be obvious that the mutual influence of the product information structure, the product life cycle model and product information management is substantial. It is described that the combination of these three models in one overall product information structure offers significant advantages.

Reference model

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In order to be able to deal with different views on a manufacturing system, the system is introduced by means of a reference model. A reference model represents a system as an organisation in terms of its structure of relatively independent, interacting components, and in terms of the globally defined tasks of these components [Biemans, 1989]. The manufacturing engineering reference model proposed in the present context is shown in the figure.

This manufacturing engineering reference model is based on the manufacturing planning & control reference model introduced by Arentsen [1995]. However, adaptations have been made, in order to emphasise the equivalent importance of products, orders and resources in the entire manufacturing cycle.

Company Management is concerned with the control of customer orders. It is responsible for the strategic decisions concerning the range of products which will be produced and the processes and resources which are required to this end.

Product Engineering refers to all the engineering activities related to the product life cycle of a specific type of product. It is concerned with the design and development of a product and its variants, starting from functional requirements up to final recycling/disposal.

Order Engineering addresses those activities that relate a customer order to a specific (variant of a) product. It is the task of Order Engineering to compose production orders and to decide when given batches of products must be processed and with which resources. The objective of Order Engineering is the in-time execution of the production orders.

Resource Engineering refers to all the life cycle aspects of the resources which are required for the execution of the production activities. It therefore includes the specification, design, development, acquisition, preparation, use and maintenance of the resources of a company.

Production is concerned with the actual execution of the plans generated by the engineering tasks. From production, information is fed back to the engineering tasks.

In the manufacturing engineering reference model, Information Management is discerned as the kernel. This illustrates the opinion that the availability and accessibility of information is preferred over sheer data exchange.

The fact that Information Management takes a central role in the reference model indicates a changed view of manufacturing engineers upon the position of information in a company. Information becomes the pivot of the design, engineering and planning activities.

Traditionally, information is administered and controlled by the departments that have the knowledge to generate the information. If a certain department has finished its tasks, i.e., it has generated all the required information, this information is transferred to the next department. Gradually, the insight has been gained that the information that is transferred actually correlates more to the processes in the departments than to the objects that the information bears reference to.

Each department generates huge amounts of data, and makes myriad decisions in order to be able to transfer the required information to the next department. It is clear that this may lead to very complex and uncontrollable flows of information. Moreover, feedback and bilateral interdepartmental communication may result in even more complex relations (See figure a).

In order to keep track of documents establishing all the information of a product through its entire life cycle, Product Data Management (PDM) systems have been developed. These systems are used to archive, manage, retrieve and exchange documents reflecting product information. It is clear, that the task of these systems is mainly administrative, i.e., the documents are treated as entities without internal structure.

This situation may change considerably, if the information generated by different departments is attached to an overall model representing the product information, including all its manufacturing aspects (See figure b). In this way, the focus is put on the product information in support of the control of the manufacturing processes. This seems a rather subtle change, however, it has a number of drastic consequences. Instead of moving product data around, the information that is generated in the engineering and planning processes is attached to a widely accessible model of the product, being the product information structure.

This approach has a number of considerable advantages. Because of the fact that product information is available to all the departments during the entire life cycle, all the phases of this life cycle can be taken into account at any time during the manufacturing cycle. Furthermore, the transparency of the product data allows easier version control and variant control, which can be the basis for improved configuration management. However, the most important benefit of an overall product information structure is that it always represents the current state of the product in evolution.

Consequently, it is immediately clear which department is working on what aspect of the product, and apart from the design history, the entire manufacturing history may be available.

The advantages that have been substantiated here for the use of a product information structure also yield for the structuring of information concerning the resources and the orders. If the management of information concerning orders, products and resources is organised in Information Management as shown in the figure, the interrelations between the three information structures are even more advantageous.

In this way, e.g. information about the current occupation and condition of all the resources (concerning both their capabilities and their capacities) is easier available, and can therefore serve as a foundation for the decisions that have to be taken during product development. The other way round, product development can also influence the evolution of the available resources over time.

This implies that not only the integration of the tasks concerned with product development separately can be achieved, but that the integration of tasks encompassing order engineering, product engineering and resource engineering becomes possible as well. Especially when applying the Concurrent Engineering principles, the simultaneous development of products and the related processes can be realised much easier. In that case, departments can base their work on up-to-date information on product types and resources. Furthermore, more accurate quotations and estimates for lead times can be generated, based on the actual order information. The advantages mentioned in the above mainly arise from improved information handling, that is, the complex information flows in a company are looked upon in a more systematic and transparently structured manner.

The result of the availability of well-structured information management functionality is the ability to control the processes that are used to generate the information. As mentioned above, product data management systems possess merely administrative functionality. Therefore, they cannot keep pace with the actual state of affairs - by definition. They merely can record what has happened; however, in using information management as a kernel for the control of information processes, the information management system can be used as a basis to initiate, accompany, control and evaluate the development cycle by actuating the manufacturing processes.

It is important to notice that this is not only applicable to the development cycle of a product, but to resources and orders as well. The simultaneous control of product, resource and order engineering offers considerable advantages. For example, during order definition in an engineer-to-order environment, cost estimations can be generated by initiating specific processes in product engineering (e.g. process planning) and order engineering (e.g. capacity planning) at different levels of aggregation.

Contact

Eric Lutters

University of Twente

Department of Mechanical Engineering

Design, Production and Management group

P.O. Box 217

7500 AE Enschede

The Netherlands