V. • . a Srlmvasan. G.W. Fischerb "Centro Inc., North Liberty, IA 52317 bDepartment of Industrial Engineering, The University of Iowa...
V. • . a Srlmvasan. G.W. Fischerb "Centro Inc., North Liberty, IA 52317 bDepartment of Industrial Engineering, The University of Iowa, Iowa City, IA 52245-1527
Abstract
Computer Integrated Manufacturing (CIM) is considered to be a strategy for planning, implementing, and integrating many functions in a manufacturing organization. A concurrent engineering design environment encourages multi-disciplinary communication of design ideas very early in the design cycle. A contemporary approach to realize the benefits of concurrent engineering design uses automated computer systems and a plethora of computer aided engineering tools. Methods are needed to integrate these tools, as most of them are stand-alone software tools that do not communicate to each other effectively. This paper presents a methodology that can integrate an advanced CAD software and a process planning software. A milling application example is used to demonstrate how the primary machining parameters can be calculated and directly imported to the CAD software, thus creating a seamless preparation of the NC part program.
Keywords: CAPP, CAD/CAM, CIM, Process Planning, Concurrent Engineering, Machinability Data
1. Introduction
The need for the availability of knowledge to the designer from different functional perspectives is of paramount importance in arriving at an optimized design of any product. A concurrent engineering design environment encourages multi- disciplinary communication of design ideas very early in the design cycle and provides a mechanism to make such knowledge available to the designer. A contemporary approach to realize the benefits of a concurrent engineering design uses a plethora of computer aided engineering tools. These tools have been developed, through a major investment of time and money, but are only usable in a specific computer environment. The costs for software vendors and internal developers to rewrite their application programs and support several versions are usually prohibitive. This paper presents a methodology that can integrate an advanced CAD software and a process planning (CAM) software. A milling application example is used to demonstrate how the primary machining parameters can be calculated and directly imported to the CAD software, thus creating a seamless preparation of an NC part program. Section 2 of the paper stresses the need for making knowledge available to the designer from several functional perspectives. Section 3 presents the proposed methodology and its advantages. The specifics of the integration are discussed by means of an example in Section 4. Conclusions are outlined in Section 5.
2. Knowledge and the design process
Ideally, the designer wants to arrive at a product design that optimally satisfies all design constraints while minimizing lead- from different design perspectives, such as dynamics, maintainability, structural analysis, and reliability. These analyses satisfy product related design decisions. Process related design decisions involve selecting the most appropriate manufacturing process, and optimizing the process parameters for the chosen manufacturing process (e.g., optimizing speed, feed, and depth of cut for a milling process). In order to perform the daunting task of optimizing the product design parameters, the designer needs access to tools that can effectively provide information on the various perspectives. The research effort at the Center for Computer Aided Design (CCAD), The University of Iowa, is an excellent example of an effective integrated computer-based environment that can support a concurrent engineering design process[l]. Fig. 1 shows an illustration of the different perspectives of product design that can be considered in the CCAD system.
The research presented in this paper describes an attempt to develop an Integrated Concurrent Engineering Environment (ICEE) that can support the analysis of product design from several design perspectives, e.g., dynamics, maintainability, structural analysis, reliability, and manufacturability. Manufacturing planning analyses are very critical to successful production of a product. It is reasonable to believe that computer aided tools that analyze design from the manufacturing perspective will soon become a necessary part of any concurrent engineering design environment. The methodology described here provides the designer with knowledge about a particular manufacturing process by means of interfacing a milling process planning software with an existing, state-of-the-art, 3D CAD modeler.
3. Proposed methodology and its advantages
Almost all of today's concurrent engineering efforts use automated engineering tools distributed throughout an organization's design development teams. In contrast to the concurrent engineering philosophy, these distributed Computer Aided Engineering (CAE) tools have a tendency to form a fragmented and sequential design environment rather than an integrated and simultaneous design environment. The reasons for such a fragmented design environment involving CAE tools is presented next.
3.1. Reasons and sources off ragmentation
Much research, with the ultimate goal of automating some aspect of contemporary concurrent engineering, exists. These efforts usually result in a CAE tool that can automate a particular function in the design process. However these tools are mostly stand-alone software tools with little or no scope for successful integration with other tools in an integrated design environment. Such fragmentation created among the CAE tools exists with regard to multiple perspectives. One source of this fragmentation stems from the internal design data formats and data content inherent in CAE tools. The methodology adopted by each CAE tool in storing, processing, and manipulating design data is often unique and the data formats created are proprietary to the CAE tool vendor. Therefore, the simultaneous sharing of product/process design data and information among distributed CAE tools becomes difficult, if not impossible. Use of standard file formats that can be interpreted and processed by multiple CAE tools is one approach to solving this fragmentation problem. Examples of common standard data exchange formats are IGES and DXF. Even though standard file formats may provide a solution to the design data formatting problem, the problem of different data content among CAE tools still persists. For example, a manufacturing process planning CAE tool manipulates and processes completely different information than a reliability analysis CAE tool. Therefore, even if a standard data file format is used, design data would continue to be fragmented as it would prove impossible for the reliability analysis tool to completely process the design data supplied by the manufacturing process planning tool and vice versa. In an attempt to provide a solution to this fragmented data content problem, the PDES/STEP standard has been developed by the International Standards organization (ISO)[2]. However, the PDES/STEP standard is not yet mature enough to be accepted in the industry, and until it is, the data fragmentation problem among distributed CAE tools will continue to exist. The inability of many CAE tools installed in design environments to communicate with one another forms yet another source of fragmentation among distributed CAE tools. Even if a CAE tool is able to completely understand and process all of the design data supplied by other CAE tools, design data must still be physically transferred between the applications. Hence, a communication medium must exist among CAE tools in order to have an integrated design environment. Unless an automated common communication medium over which a set of CAE tools can communicate exists, a fragmented, sequential design environment will remain. Ideally, to form a concurrent engineering design environment, CAE tools need to satisfy the following requirements[3]. 1. All tools should share the same data management facilities. 2. All tools should directly interact at the data processing level. 3. All tools should be alerted to incremental changes in design data. 4. All tools should have a common system level user interface.
3.2. Direct Interfacing
Even though numerous research efforts are underway to make the CAE tools satisfy the requirements outlined above, it will take significant time before such tools become a reality. However, it cannot be denied that individual CAE tools are robust by themselves and fulfill very effectively the function for which they are created. Hence it is a loss that such effective tools are in isolation and cannot effectively communicate with each other. When analyzing the design of a product to make process related design decisions, a particular manufacturing process needs to be selected from a set of competing manufacturing processes that satisfy a prescribed set of constraints. The constraints can either be cost driven or production driven. Although CAE tools do exist for performing the computer aided design of the product, these tools do not completely support the analysis of the suitability of a process from, say, a cost perspective. Such an analysis, for the operation being considered, could involve selecting the appropriate machine tool, cutting tools, and primary process parameters, such as feed, speed and depth of cut. However, tools that let the designer perform process analysis often have primitive modeling capabilities. Increasingly, it is felt among manufacturing software users that some amount of insight and provision for access should be provided to the database and implementation strategy of commercial CAD/CAM systems. This is because process planning is such a complex task that no universal solution can satisfy the needs of all users. Therefore, the next best option is to provide them some kind of access to the database of the CAD models that will enable them to write their own code to be interfaced with the CAD modeler. Fig. 2 shows such an environment where individual tools can be interfaced with a CAD modeler having interfacing capabilities. The question of what type of CAD modeler and what types of process planning tools need to be interfaced needs further discussion. Even though
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