In many companies, product and process design are fragmented and difficult to manage and coordinate. CAD/CAE tools automate the design and development process but, in many cases, cause the rapid proliferation of designs without regard to the impact on the rest of the organization. While these tools are to varying degrees integrated, often these systems will be used to create an item’s geometry on paper to communicate with other functional areas of a company.
One survey indicated that the typical company re-creates an item’s geometry five or more times in such areas as customer proposals or marketing specifications; conceptual design; detail design; finite element analysis; other engineering analysis; detail drafting; fabrication or assembly sketches; workcell device programming; tooling and fixture design; and training and service manuals. Each time part geometry or product design information is independently maintained in a separate system or independently created on paper, another source of redundant design information is created that needs to be managed.
Non-integrated systems also require additional effort to transfer data from one system to another. This allows errors to creep into the process, and data can be mis-handled or lost. Delays are inherent in this process and extra effort is required to coordinate activities.
Technology and information integration represent one dimension of overcoming these traditional problems. Integrated design and manufacturing automation systems and databases are the basis for the Engineering blueprint of the future. This will allow manufacturers to cost-effectively improve product and process design while facilitating the integration of design activities with the production process.
Product and process design will be greatly enhanced through the use of integrated databases and information systems to maintain and optimize use of design information. Product and process design information must be treated more as a corporate-wide resource. This information must be stored and maintained in a logical, consistent, non-redundant and usable manner. There must be a shift to definition-oriented design information that can directly drive downstream processes with little or no human interpretation and planning. Current standards such as IGES need to be improved upon so that this data can be readily accessed and used without regard to technical constraints.
Evolving standards such as the Standard for the Exchange of Product Model Data (STEP) will provide a more complete set of product data in a neutral format. This design information must be distributed to workstations, controllers, and other systems as required for use. Changes to product and process design data must be managed in accord with the company’s data access and configuration management procedures.
By focusing on maintaining product and process design information electronically, paper-based representations of this data can be minimized. As paper drawings are avoided, there will be reduced manual handling and storage of documents, reduced time to access the most current design of a part, and prevention of errors from avoiding the use of outdated drawing information. Design and administrative activities can be streamlined. When design information is maintained electronically, it can be readily analyzed and designs improved so that more mature and producible designs are developed more quickly. Most importantly, this is the basis for definition-oriented designs.
However, maintaining definition-oriented product and process design information electronically requires a number of supporting technologies. Further, these islands of technology must be linked physically, organizationally and electronically to achieve this integration of data. These technologies include the following:
When these technologies and integration concepts are effectively used, they will improve communication of product and process design within the engineering function, across the enterprise and externally with suppliers and customers.
Computer Aided Design and Engineering (CAD/CAE) systems are the key to developing and maintaining product design information electronically. Two dimension (2-D) systems, oriented to drafting, maintain relationships of lines, arcs, and circles electronically. The output of these systems requires human interpretation to obtain meaningful information. However, as CAD systems move toward solids, feature-based and parametric representation of items, this design information can be more meaningfully used without the same level of human interpretation.
One basis for this design approach is to maintain a complete three dimensional solid model of each finished and in-process part in a product definition data base. A rigorous representation of each part’s boundaries avoids the ambiguities in a 2-D and 3-D representation of a part. As parts and products become more and more complex, traditional 2-D and 3-D representations, even with hidden line removal, become difficult to understand and interpret. Solids modeling enhances visualization and communication of the design intent. Solids modeling with the evolution toward product or assembly modeling provides a more useful mechanism to represent how parts are put together to form assemblies. Newer solids modeling systems provide a complete definition of part geometry, topology and tolerances. This complete definition coupled with features representation provide information that can be more readily interpreted and used by downstream automated processes in manufacturing.
Features-based representation of design information and parametric design can enhance and augment solids-based representation of the design. Specification of features (e.g., holes, counter-bored holes, threads, pockets, slots, notches, cut-outs, bosses, fillets, chamfers, ribs, flanges, etc.) or design primitives can simplify the creation of the design. Designing based on the geometric abstractions inherent in solid modeling’s constructive solids geometry (CSG) or boundary representation (B-Rep) approaches is a more artificial and difficult to master process than specifying features. With a features-based approach, a part’s design then comprises a basic shape and a hierarchy of features and associated attributes. Feature attributes include dimensions and tolerances. Other information can be associated with individual features to provide design guidance such as design rules, restrictions, producibility indexes, costs, and process requirements.
Product design data such as features, dimensions, tolerances, finishes, etc., can be associated with specific manufacturing processes (e.g., a hole to a drilling operation) and even a specific piece of equipment. This capability will allow design tools to provide producibility guidance directly to the designer while the product or part is being developed. It also re-orients the designer from thinking in terms of just part geometry to also thinking in terms of manufacturing processes and, therefore, costs and quality implications associated with the part design. This type of definition-oriented design information will then facilitate generative process planning and computer-aided manufacturing.
A valuable aspect of modern CAD systems are their ability to not only render the design, but to capture its intent. The concept of capturing design intent is based on incorporating engineering knowledge into a model by establishing and preserving certain geometrical relationships. The wall thickness of a pressure vessel, for example, should be proportional to its surface area, and should remain so even its size changes. Parametric design allows a standard geometry to be specified once for an approved group of parts. By establishing one or more dimensions or characteristics as variable parameters with mathematical relationships to other dimensions, features or characteristics, multiple parts or assemblies can be readily specified by only varying these parameters while maintaining overall geometric and mathematical relationships. This approach provides variation with a minimum of design effort and process capability.
CAE also provides tools to help improve the maturity of the design by simulating the design and avoiding or minimizing the need to build and test prototypes. Finite element analysis as well as other engineering analysis tools can be used for testing loads and stresses, heat transfer, fluid flow, kinematics, circuit output and timing, and assembly interaction. By simulating important characteristics electronically, the design can be debugged and precious development time reduced. Newer analysis tools go a step further through design optimization capabilities. The designer specifies basic part geometry and geometry details that an optimization program is allowed to manipulate. By then stating design parameters such as weight requirements and required loads, the program will manipulate the part geometry to optimize meeting the requirements.
Reliability and maintainability are increasingly important considerations in product design as customers are increasingly considering the life cycle costs of a product. Tools are emerging to simulate product operating cycles, heat build-up, and wear, all significant factors in product failure. Solids modeling can be used to model accessibility to components and assemblies in products and systems for maintenance purposes and indicate more optimum approaches to designing the product for service and maintenance. As these tools are refined and merged with design tools, the designer will be in a better position to consider the life cycle costs in the design of products.
Artificial intelligence and, in particular, knowledge-based engineering systems provide a capability to define rules for effective product and process design in an integrated manner. Design rules can include producibility guidance to more effectively mesh the product design with the company’s process capabilities. Expert and knowledge-based engineering systems have already been developed to help configure complex products such as computer systems as well as design products such as turbine engine blades. This configuration guidance can be extended to help design products to order from basic, pre-designed product modules quickly and inexpensively.
Assembly Modeling
Solids modeling, features and attribute relationships can be the basis for more complete product definition. In addition to rigorously defining geometry and topology of individual parts, product assemblies can be defined through solids modeling by defining the:
This approach can yield a complete definition of the product’s geometry and topology at any level in the product structure.
Since the relationship of a product’s parts is a logical one maintained by the information system rather than a fixed physical relationship as represented on a drawing, it is possible to readily maintain more than one relationship. This will allow different views of part relationships in assemblies to correspond to the various departmental needs (e.g., engineering and manufacturing product structures), while maintaining rigor and consistency of the product’s definition through this single data base. Thus, this one logical data base can support product and process design requirements as well as maintain part relationships to serve as a manufacturing bill of materials for MRP II. An integrated approach to developing, organizing and maintaining part and product definition data facilitates the design process, makes design data more readily usable and enhances integration with process requirements.
This product definition data base will not only provide geometric part information, but it can maintain information about the part’s (or assembly’s) various physical properties, functional characteristics, process requirements, cost, producibility, and design guidelines. Use of an integrated product definition data base allows an organization to concentrate its product data management efforts on this data base. Configuration management practices can be super-imposed on top of product data management functions. Access control to each element in the product definition data base can be specified. Read only access can be given to personnel not directly involved with the design, development and planning process. Creation and maintenance access can be given to the individuals responsible for product and process design.
Engineering changes can be facilitated with this configuration management and administrative control embedded within the system. CAE/ CAD tools will enable engineering changes to be more thoroughly developed and analyzed to better define change impact. Once a design has been created, it can be checked-out electronically to a workstation for engineering changes. When the changes have been made, it can be returned to the central database and placed in a queue for electronic approval by designated parties. In this manner, a Change Control Board (CCB) can even “convene” and provide individual member’s input electronically. In addition to supporting engineering analysis, information related to procurement, inventory, manufacturing and cost is available for members of the CCB to evaluate, designate the effectivity of the change and determine the disposition of existing items.
Product design must logically extend beyond part geometric information, drawings and parts lists. It must include the design or specification of manufacturing processes including:
These process design, development and workcell device programming tasks need to become linked to part or product design and development. CAD tools can work with part geometry and features to design or specify processes and workcell envelopes. Graphic production simulation tools can be used to test the resulting production system. Product definition, feature specification and group technology classification information drive computer-aided process planning. Part geometry maintained in CAD is also used to develop tool paths, other NC programs, electronic component insertion programs, and photomasks. This geometry also supports tool and fixture design. Functional characteristics, geometry, and specifications stored in the product definition data base can be used to derive automated test equipment programs and coordinate measurement equipment programs.
When product definition information is developed and released, process engineering information must be similarly developed and released in this type of integrated environment. This will assure that when a new part is introduced or an engineering change is made, that the electronic release for production includes the correct process plans, tool requirements and workcell device programs for the latest configuration and process capability. As computer-aided manufacturing technology is utilized and integrated with the product definition data base, part geometry and process information can be passed directly to production process equipment in DNC-fashion. The release procedures will include the electronic release of this information into appropriate libraries to download to workcell controllers or make available to manufacturing personnel on-line as required. The physical drawings, process plans and NC tapes will not need to be manually assembled and coordinated to support manufacture of an item.
Engineering and product definition information must be communicated and used across the enterprise. In addition, the use of Engineering information extends beyond the company’s facility. Engineering needs to exchange product definition and configuration data including part geometry and other textual information with suppliers and customers. Electronic Data Interchange (EDI) is a first step in the commercial world to utilize standards for ordering parts and material, but it lacks interchange of geometric information.
The Initial Graphics Exchange Specification (IGES) is the current standard for exchanging geometry data, but it does not contain all required digital product data and IGES translations may not provide a complete translation of geometric data. More comprehensive standards will be required. The Standard for the Exchange of Product Model Data (STEP) is an effort to establish product data standards related to physical design information (geometry, topology, tolerances, and form features, functional design information, product administrative information, and product life cycle information) (see STEP Parts). Establishing a single product data model with tools to provide ready access to this product data will enable direct use of this data and enable a move away from the traditional engineering drawing and other product documentation. This is intended as a successor to IGES and as a standard for a more complete definition of product information and, thereby, facilitate improved data interchange, communication and interpretation of product data.
These standards will not only allow paper drawings to be replaced with electronic representations, but will serve as a common digital product model to more readily communicate product data throughout the enterprise and to external organizations as required.
These design automation technologies are reasonably mature and can be effectively used to enhance product development. Prices are rapidly declining making these design automation tools more and more cost effective for smaller organizations. However, availability and effectiveness are not the critical issues. Generally, available technological capabilities exceed the ability of most organizations to effectively implement and use these technologies in an integrated, widespread way. The greatest challenges exist not in implementing technology, but in overcoming the organizational barriers and the resistance to changing the way things are done. This change will be essential for high levels of performance. Given the current state of product development practices and technology, more significant improvement opportunities exist with better process and organizational approaches. The engineering function needs to recognize this and, to increase performance, it must refocus its priorities from technology to improving the development process and integrating the functional organizations involved in product development in order to most cost effectively increase the overall performance of the enterprise.