مدل فعالیت و سیستم به کمک کامپیوتر برای تعیین برنامه ریزی فرایند ورق فلز

This paper focuses on the problem of choosing the manufacturing route and characteristics in sheet metal processes, a very important element in computer aided process planning (CAPP) systems. At present, decisions concerning the operations, die, machine and process parameters used in sheet metal are based on experience. One of the objectives of this work has been to develop an activity model to help define sheet metal processes. This activity model allows focusing on the second objective, which is to implement a computer aided system to select and define the parameters of the process definition in the case of drawing operations with sheet metal. The result is the selection of parameters related to the operations chosen, the kinds of operations, the sequence of these operations and the lay-out die dimensions for the product. A range of parts were evaluated. They were chosen because they were considered to be representative cases. The results obtained by the system are compared with the values proposed in reference manuals, and by experienced experts. The work has served to determine how to adjust the computer aided system. Applying the method helps to make the right decisions about the sheet metal operations related to drawing processes. The experiments have led to a reduction in processing times.

Process planning is the act of preparing detailed operating instructions for turning an engineering design into an end product, i.e. the part. This implies the need to translate the design specifications of a part into the required manufacturing operating instructions, to convert it from the raw material to the part in its final state [1]. There is a great deal of manufacturing data involved in process planning, such as the identification of machines, tools, flanging, parameters selection for the process, operations, etc. [2]. All of this data has to be evaluated in order to select the sequence of operations that will make up what is known as the sheet route. The sequence is generally made to conform with particular objectives, such as, for example, the shortest time and/or the minimum cost. Process planning requires many kinds of human abilities, which should be present in the process planner [1]. The traditional approach to resolving the process planning task is the one commonly used in a manufacturing company; the plans are handed over to the manufacturing process experts who then specify the procedures to make the product. The process planners, using their experience and knowledge, generate instructions for manufacturing the products based on the design specifications and the available installations and operators. The fact that there are few experienced process planners and that, when faced with the same problem, different process planners would probably come up with different plans is an indication of the heterogeneity that exists in process planning [1]. Consistent and correct planning requires two things: knowledge of manufacturing processes and experience [3]. This has led to the development of computer aided process planning (CAPP) systems, which are becoming more and more important in this field. The most maturely developed area so far has been focused on machining applications. Research and development in manufacture applications such as heat treatment, forging, injection moulding, and sheet metal manufacture is still premature, and the reported systems for sheet metal manufacture rely on a high level of interaction from the expert who provides the decision-making at different stages of planning [4]. Sheet metal components are widely used in various industries like aerospace, electronics, machine tools, refrigeration and air conditioning, etc., and they form a significant part of manufacturing activity. Sheet metal components are important not only from a functional point of view, but also from an aesthetic point of view, since they are used as enclosures to cover products and are visible to the outside world. These components vary in size, shape and complexity. Therefore, sheet metal processes receive a lot of attention and are widely used by the metal working industries [3]. The manufacturing processes required for sheet metal components are identified by analyzing the component layout, and then design information is manually translated into manufacturing information [5]. To overcome inherent difficulties and limitations associated with human beings, research work is progressing into the area of automatic transformation of design information into manufacturing information through feature recognition [3]. The main aim of this research is to develop a computer aided system for sheet metal manufacture. The purpose of the system developed is to calculate the manufacturing parameters needed for drawing components to be produced. The idea is not to replace the role of expert process planners, but instead, to provide a tool to assist them to be more efficient and consistent in their work. This project was set up in collaboration with a manufacturing company. In the company sheet metal forming processes such as bending and drawing are used to manufacture some components. Further development of these processes will allow the user to enter the product data as a feature for simple sheet metal components. Future developments in the system will make it capable of coping with the remaining, more complex components and possibly of being modified for prismatic and other rotational parts. The initial stage of the research was conducted on-site at the company, in order to understand the manufacturing processes and process planning tasks, and to find out the user requirements for computer aided process planning functions. The second stage was to develop the first iteration of the computer aided system. The underlying methodology can also be tailored to general sheet metal fabrication. The goal of this work is to contribute to developing a tool to help the planning process applied to sheet metal processes. This work focuses on drawing processes. The work helps the engineer to decide on manufacturing parameters such as the operations sequence and the die dimensions for a drawing sheet metal process. This work is based on the knowledge obtained from the collaboration with the enterprises. The future proposal will be a tool which is capable of defining a route sheet without depending on the sheet metal processes it is considering. The work will cover different processes such as flanging, blending, punching, trimming, drawing, etc. The integration of future recognition starting on CAD systems is necessary. There has been no work which covers this so far. However, to obtain this goal the research should start with a more concrete objective, which is presented in this paper.

This paper is a contribution to the subject of process planning. The initial approach of the paper is focused on drawing operations in sheet metal processes. A new computer system to help process planning has been developed based on the latest software engineering technology and a comprehensive literature survey as well as research into the requirements and experience of professional users. The incorporation of many planners’ knowledge into the computer system has made the developed system more competent than those that only use one or a few people's knowledge. The system has been tested with typical data provided by the collaborators and the results obtained and feedback received from engineers in the company has shown that the system is much quicker, more efficient and consistent in producing sheet metal fabrication process plans than existing systems reviewed. The system is flexible and generic as it can be adapted to the customer's needs without making many changes to the code. The system has an intuitive and user-friendly interface. It should be noted that although the number of forming processes available in the system is limited, further development of the system will include other types of forming processes. The future addition of a standalone feature modeller will allow a different and more graphical method of entering component information input into to the system. It will also allow the user to make quick and easy alterations. Finally, as it is already mentioned in this article, the study has certain limitations that must be taken into account. First of all, in the field of sheet metal processes there are many kinds of operations and the study has focused on drawing operations. Secondly, the computer system is applied to rotational part with one geometrical drawing. Thirdly, it is impossible to ensure that an application can provide the solution in all practical cases. It would be of considerable interest to continue these studies, not only in relation to the remaining geometry, but also to other existing kinds of sheet metal operations. However, it is believed that by carefully selecting the pieces used in the design of the system, it has obtained, for drawing operations, excellent results in the vast majority of cases studied. The methodology followed here is perfectly applicable to the majority of the sheet metal processes and, consequently, the effort required for continued study in this area is now greatly reduced.