WEB-BASED COLLABORATIVE ENGINEERING OF CAST PRODUCTS B. Ravi Mechanical Engineering Department Indian Institute of Technology, Bombay Phone: (+91-22) 576 7510 E-mail:
[email protected] Milind Akarte Production Engineering Department SGGS College of Engineering and Technology, Nanded Phone: (+91-2462) 29302 E-mail:
[email protected] Abstract: Cast products used in automobile, machine tools and other applications continue to have significant tooling costs, lead-time for delivery and rejections at finishing stage. To minimize these problems, product manufacturability issues must be considered early – during the design stage itself. We present an innovative framework called WebICE (for Web-based Integrated Casting Engineering) to enable data exchange and collaborative engineering between product, tooling and foundry engineers. The casting project information is stored on a web-server using an XML-based Casting Data Markup Language. Project team members can simultaneously access the data, view the solid models and suggest modifications from any location worldwide. The use of standard browsers coupled with an intuitive and context-sensitive user interface is expected to lower the entry barriers usually associated with high-end CAD/PDM systems and extend its use to even small and medium firms in remote areas. Keywords: Casting, Computer-Aided Design, Collaborative Engineering, Design for Manufacture, Internet, Product Data Management, World Wide Web, XML.
1. Introduction During the final manufacturing stage, it is easy to identify quality problems, but difficult to fix them. On the other hand, during early design stages, it is easy to fix the problems by simple modifications to product design, but quite difficult to predict their occurrence in the first place. The above is very much true in casting domain. Cast components are used in a large number of applications including transportation (automobiles, aerospace, railways), farming and mining, machine tools and plant machinery, municipal castings (pipes, joints, pumps and valves) and electrical equipment (motors and generators). It takes several weeks to develop the tooling and complete the trials for a new casting. Still, it is not unusual to find 5% or more rejections during machining stage, holding up production schedules. For example, the aluminum alloy valve casting shown in Figure 1, is produced in a permanent mold (gravity diecasting process) and suffers from a sizable shrinkage cavity in the middle region. It is easy to reason out that the defect is caused due to high heat concentration (thick section) and poor heat transfer (several cores meeting near the region). However such reasoning is too late, since significant costs would have already been committed to tooling production and shop-floor trials. If known earlier, the designer might have reduced the section thickness and reduced or relocated the holes, while conforming to functional requirements. To minimize if not avoid such problems, the product engineer must be able to assess the effect of a given design (geometry, material, process and quality specifications) on manufacturability (quality and cost). A few techniques for Design for Manufacturability (DFM) are already available: process simulation, manufacturing cost estimation and features-based DFM guidelines.
a
b Fig.1 Aluminum valve (a) shrinkage porosity defect, (b) prediction by process simulation.
Process simulation enables virtual manufacturing try-out for predicting potential problems without wasting actual material or energy. It however, requires the tooling models (die, mold, etc.) and sufficient domain knowledge for setting up the boundary conditions as well as interpreting the results. Most simulation programs are also expensive and computation-intensive. Cost estimation programs require considerable effort in setting up and maintaining the database of cost factors. The DFM guidelines are specific to the manufacturing process and available in the form of illustrations, empirical equations, graphs and tables [Bralla, 1988]. They are easy to apply, and enable avoiding common pitfalls. There is no quantitative feedback. Moreover, guidelines may conflict with each other and the designer may find it difficult to decide which one to apply. Thus the above techniques are useful only for preliminary evaluation and improvement with respect to manufacturability. It is still necessary to consult the manufacturing engineers before freezing the design, especially if it involves a new combination of geometric features, materials and processes. Concurrent engineering provides a systematic approach to integrated design of products and related processes including manufacturing and support [Brookes, 1996]. The success of this approach depends on the extent of information exchanged between the groups. If they are located far apart (an increasing trend with global manufacturing), then face-to-face interaction becomes difficult. This can be overcome to some extent by Product Data Management systems, which enable storing, retrieving and exchanging information between team members over an electronic network. Several commercial PDM systems are available today [Miller, 1997]. However, most of them are based on the bill of material concept and can not be linked to DFM programs. They also require extensive customizing and mainly useful when deployed on a local area network within an organization. Internet and World Wide Web technology are increasingly being used to share and exchange product information between the design team members from any location worldwide. Standard browsers – ubiquitous and inexpensive – are becoming the most preferred front-ends to obtain a uniform user interface irrespective of computing platforms. The web servers handle the client requests for library, directory, document or utility programs. An example of a web-based application for casting includes the casting defect analysis system [Spada, 1998]. The most common language employed for formatting the content for display purpose is the Hyper Text Markup Language or HTML. But this can not be ‘understood’ by computer programs for higher level purposes (such as calculations based on data in a web page). To overcome this limitation, eXtensible Markup Language or XML has been developed [World Wide Web Consortium, 2000]. This is a platformindependent meta-language that permits definition of domain-specific tags, allowing the data to become selfdescribing. A few XML-compatible database formats such as Material and Property Data Markup Language [MatML, 2001] are being developed, but no casting applications have been reported so far. As seen from the above, castability assessment during early design stage enables prediction and prevention of potential problems. This requires engineering software application as well as feedback of tooling and foundry engineers, who in turn need access to product information irrespective of their location. The use of advanced computer and communication tools adds a new dimension to concurrent product development and this new approach is referred as collaborative engineering.
This paper presents an innovative framework to enable web-based data exchange and collaborative engineering between product, tooling and foundry engineers. The system is named WebICE (web-based Integrated Casting Engineering). The backbone of the system is an XML-compatible self-describing Casting Data Markup Language (CDML), which facilitates modeling the essential information exchanged between product, tooling and foundry engineers. Important features of CDML and WebICE framework are discussed next. 2. CDML Structure The Casting Data Markup Language (CDML) has been developed with the following objectives: 1. 2. 3. 4. 5. 6.
Enable a modular and systematic approach to casting product data management. Capture essential information exchanged between product, tooling and foundry engineers. Provide a structure for linking image and solid model files. Facilitate quick searching and identification of any desired item of information. Enable linking libraries of alternative options as well as design/analysis functions. Easily extensible by including additional information, without affecting existing functions.
The CDML structure comprises a tree and several data blocks. The CDML tree represents the hierarchical (parent-child-grandchild) relationship between different data blocks, represented by nodes in the CDML tree. The data block files are linked to the tree through an indexing scheme. Other files, containing images and solid models are hyper-linked to the respective data blocks. A complete set of files including CDML tree, data blocks, images and solid models defines the casting project database for a given product. A new casting project can be initiated starting from a default database. A library of alternative options (for the data blocks) and application programs are also linked to the CDML structure (Figure 2).
Root node
Node
Image
BMP, GIF, JPG
-- --- --- --
3D Model
STL, DXF, IGES
Library
Alternative Options
Data block
Functions
Application Program.
Tree
Figure 2. CDML comprises a tree of nodes linked to data blocks. 3. WebICE System The WebICE framework has been designed to enable creating, viewing, modifying and updating casting project data over the Internet from any location worldwide. WebICE uses a two-tier client-server architecture, in which the clients (engineers) interact with a central server (where project files are stored) through standard web browsers. Key features of the WebICE architecture include the following. • • • • • •
Casting project information management: Provides an environment to create, view, modify and update information related to casting project. Libraries: Enables creation and linking of library options (materials, processes and other items) that can be viewed and copied to current project. Decision support: Provides a suitable mechanism to link and execute functions for analyzing and/or updating casting project information. Collaboration: Enables team-members to simultaneously access the project data from any location worldwide. Installation and platform: The system runs from standard web browsers from Windows PC or Unix workstations and requires minimal installation procedures at the user end. User interface: The user interface is easy-to-use (minimal buttons and icons) and does not require any training or technical support.
•
Real-time interaction: The user need not wait for more than few second for any task, especially for viewing the desired information, even with standard modems that have a low bandwidth.
The server side of WebICE mainly consists of databases in XML format and programs in PHP scripting language. The databases include the project database template, library database and user projects. Project database template consists of default CDML Tree and data blocks and is automatically copied into the user project while creating the new project. A library of cast metals and processes has been created; this facilitates selecting the appropriate metal or process and copying their values (properties and capabilities, respectively), avoiding manual input that may be prone to errors. User project database consists of various casting projects created by the users. Each project is unique in terms of its information content in CDML tree and data block and stored separately a with unique project name within the user directory created with login name. The client side user interface is based on standard web browsers such as Microsoft Internet Explorer (version 5 and above). It displays the CDML tree, current data file, and image model or results (Figure 3). A novel contextsensitive scheme eliminates the clutter of pull down menu and arrays of icons, usually associated with most CAD/PDM programs. In our approach, the user browses the CDML tree to view the type of results first (say, costs) and the relevant functions (estimate_cost) automatically appear for the user to compute or update the results. This also applies to the libraries: the user selects the node related to cast metal or process and the relevant library functions appear immediately. All these functions are coded using HTML, JavaScript and XMLDOM (Document Object Model) utilities. A special pair of programs has been developed to compress and upload a casting solid model and to automatically download, decompress and display the model. The models can be exported from any commercial solid modeling system in standard STL format and are compressed to less than 5% of their original size to reduce bandwidth requirements during uploading and downloading. The display program itself is automatically downloaded into the user’s computer and enables panning, zooming and turning the model in near-real time. 4. Case Study The WebICE system is primarily intended to promote interaction between casting project team members (product, tooling and foundry engineers). A demo version of the system has been implemented at http://www.metalcastingworld.com/intercat/cdml/. A sample session of a ductile iron automobile yoke casting is presented here to illustrate the application. Initiating a casting project: The user logs into the web site and starts a new project from a default CDML template. The WebICE interface comes up, showing the CDML tree, the nodes of which can be clicked to expand or collapse the tree and display the data file linked to the clicked node. Linking and viewing part model: The user can upload and link the part model (after compression) to the PRODUCT node in the tree. Now, any team member can view the part model by clicking the PRODUCT node and then the Display_Model function, which automatically downloads the part model and displays it in the main window [Figure 2]. The model can be rotated, zoomed and panned. Metal selection: The user browses through the CDML tree and selects the node corresponding to the CASTING MATERIAL. Its data block is immediately displayed in the data window. Clicking the Library function displays the list of ferrous and non-ferrous metals. The user selects ductile iron family, and the various options are displayed. The user can select an option, view its properties and copy the values to the current project. Clicking the Material_Selection function brings up two utilities. The first utility allows the user to specify a standard and view the equivalent standards for the metal [Figure 3]. The second utility short-lists the metals that have properties closest to the product requirements. The user clicks the Update function to save the metal data to the server. Any other user accessing the same database will also be able to view the latest data now. Preliminary cost estimation: The casting cost is estimated using the information available about the part size and geometric properties, materials, process plan and production requirements. This involves computation of metal costs, tooling costs (both permanent and dispensable), foundry costs (mainly labor, energy and overheads) and other costs (delivery, taxes, etc.). The user can interactively change design parameters (for example, eliminating a cored hole) and view its effect on total cost.
Fig. 3. WebICE system: (a) casting project database and solid model viewing, (b) material selection, (c) preliminary cost estimation, (d) product-process-producer compatibility evaluation. Process and Producer Evaluation: A multi-criteria based product-process-producer compatibility evaluation methodology has been developed and linked to the WebICE framework [Akarte 2002]. It uses a common set of criteria (objective and subjective type) to evaluate the compatibility between the product requirements and process or producer capability, and help identifying the design parameters that could be modified to improve the manufacturability. Initially, the user has to input the product requirements that includes minimum wall thickness, minimum core hole size, weight, maximum size, order quantity, dimensional tolerance, surface roughness, delivery frequency, etc. These are updated and saved to the web server using the ‘update’ function. Now, the ‘Screen’ function linked to the FOUNDRY node short-lists feasible alternatives from the metalprocess specific databases stored at the server. The user can select and copy one option from the displayed list of feasible alternatives and evaluates the option linked to PRODUCT_ANALYSIS node [Figure 4]. The above functions may be executed by any of the team members (product designer, tool maker or foundry engineer). The results can be updated on the server and are immediately visible to other team members who are accessing the same project. This enables feedback and suggestions to be considered and incorporated in the product design, and concurrent planning of respective activities. Since no specialized software (or even dedicated hardware) is required, the above approach is suitable to even small firms in remote areas. 5. Conclusion Product design for manufacturability, through collaborative engineering between project team members, has become necessary for early identification and prevention of potential problems. This requires on-line access to the latest data about the product and project by team members. We have developed and demonstrated such a system, called WebICE, for the casting domain. The system provides a virtual environment for casting life-cycle
engineers to simultaneously work on the same project irrespective of their physical location. It allows the engineers to initiate a project, select material and process, upload solid models, estimate the cost and evaluate the compatibility between product, process and producer. A standard browser serves as the user interface; no other special software is required. The system enables better quality assurance, lower tooling and production cost and shorter development time through early modifications to product, tooling or process parameters. This approach is expected to lower the entry barriers usually associated with high end engineering software systems and extend its reach to all firms irrespective of their size or location. References 1. 2. 3. 4. 5. 6. 7.
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