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INTRODUCTION
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:
- CAD/CAE with solids modeling and features representation as the mechanism
for defining and maintaining product design information electronically
and extensive analysis and simulation of products early in the development
cycle
- Product data management to manage product data in digital form, provide
configuration management of this data, and facilitate the development process
workflow
- Automation of process design, process specification and manufacturing
planning through definition-oriented design information and tools such
as computer-aided process planning (CAPP) and workcell device programming
(e.g., NC, robotic, and computer-aided inspection and test equipment)
- Communications and data interchange of product
design information internally and externally with suppliers and
customers
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.
PRODUCT DESIGN
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.
Solids Modeling
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.
Analysis and Simulation
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.
Knowledge-Based Engineering
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:
- Instances or occurrences of each part in a hierarchical manner similar
to a bill of material structure
- The relative location of each instance or occurrence of the part in
terms of the part's x, y and z coordinates relative to the assembly's base
or reference point x, y and z coordinates
- For each instance or occurrence of a part, the part's orientation in
relation to the assembly's orientation
- Vectors or axes of rotation to describe
movement of parts within assemblies
This approach can yield a complete definition of the product's geometry
and topology at any level in the product structure.
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.
PRODUCT DATA MANAGEMENT
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
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.
PROCESS DESIGN
Product design must logically extend beyond part geometric information,
drawings and parts lists. It must include the design or specification of
manufacturing processes including:
- The specification, design and layout of production equipment and processes
- Process plans to define how the product will be manufactured with the
given production processes and capabilities
- Workcell device programming (e.g., NC, robotic, insertion equipment,
coordinate measuring machines, vision and computer-aided test equipment)
- Tool and fixture design
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.
DATA INTERCHANGE
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.
SUMMARY
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.
ABOUT THE AUTHOR
Kenneth A. Crow is President of DRM Associates,
a management consulting and education firm focusing on integrated product
development practices. He is a distinguished speaker and recognized expert
in the field of integrated product development. He has over twenty years
of experience consulting with major companies internationally in aerospace,
capital equipment, defense, high technology, medical equipment, and transportation
industries. He has provided guidance to executive management in formulating
a integrated product development program and reengineering the development
process as well as assisted product development teams applying IPD to specific
development projects.
He has written papers, contributed to books, and given many presentations
and seminars for professional associations, conferences, and manufacturing
clients on integrated product development, design for manufacturability,
design to cost, product development teams, QFD, and team building.
He is a certified New Product Development Professional. Among
many professional affiliations, he is past President and a founding member
of the Society of Concurrent Product Development and is a member of the Product
Development Management Association and the Engineering Management Society.
For further information, contact the author at DRM Associates, 2613 Via
Olivera, Palos Verdes, CA 90274, telephone (310) 377-5569, fax (310) 377-1315,
or email at KCrow@aol.com.
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