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INTRODUCTION
In the past, products have been designed that could not be produced.
Products have been released for production that could only be made to work
in the model shop when prototypes were built and adjusted by highly skilled
technicians. Effective product development must go beyond the traditional
steps of acquiring and implementing product and process design technology
as the solution. It must address management practices to consider customer
needs, designing those requirements into the product, and then ensuring
that both the factory and the virtual factory (the company's suppliers)
have the capability to effectively produce the product.
Products are initially conceptualized to provide a particular capability
and meet identified performance objectives and specifications. Given these
specifications, a product can be designed in many different ways. The designer's
objective must be to optimize the product design with the production system.
A company's production system includes its suppliers, material handling
systems, manufacturing processes, labor force capabilities and distribution
systems.
Generally, the designer works within the context of an existing production
system that can only be minimally modified. However in some cases, the production
system will be designed or redesigned in conjunction with the design of
the product. When design engineers and manufacturing engineers work together
to design and rationalize both the product and production and support processes,
it is known as integrated product and process design. The designer's consideration
of design for manufacturability, cost, reliability and maintainability is
the starting point for integrated product development.
A designer's primary objective is to design a functioning product within
given economic and schedule constraints. However, research has shown that
decisions made during the design period determine 70% of the product's costs
while decisions made during production only account for 20% of the product's
costs. Further, decisions made in the first 5% of product design could determine
the vast majority of the product's cost, quality and manufacturability characteristics.
This indicates the great leverage that DFM can have on a company's success
and profitability.
However, the application of DFM must consider the overall design economics.
It must balance the effort and cost associated with development and refinement
of the design to the cost and quality leverage that can be achieved. In
other words, greater effort to optimize a products design can be justified
with higher value or higher volume products.
Design effectiveness is improved and integration facilitated when:
- Fewer active parts are utilized through standardization, simplification
and group technology retrieval of information related to existing or preferred
products and processes.
- Producibility is improved through incorporation of DFM practices.
- Design alternatives are evaluated and design tools are used to develop
a more mature and producible design before release for production.
- Product and process design includes a framework
to balance product quality with design effort and product robustness.
SIMPLIFICATION AND STANDARDIZATION
As a design is being developed from the conceptual level to the detailed
level, a physical and functional requirement envelope is defined in which
a part must fit and perform. Within the constraints of this envelope, a
designer must design or select a part or assembly for use. A designer may
have many alternative ways to design a part to meet requirements within
this envelope.
While the design of a custom part or selection of a new part may be the
most optimal approach to meet product requirements from the designer's point
of view, it may not be the best overall approach for the company. Product
cost and quality may be negatively affected by the proliferation of specialized
items that require specialized capabilities or prevent efficient manufacture
and procurement.
Minimizing the number of active or approved parts through standardization
not only simplifies product design, but can also result in operational efficiencies
and lower inventories. A formal policy of parts standardization and emphasis
on use of parts from an approved parts list (APL) for certain commodities
provides management direction to the designer.
Group technology (GT) and Component Supplier
Management (CSM) systems can facilitate standardization through retrieval
of a similar part's design to consider for use or as a basis for
developing a new design. By providing a classification structure to store
and retrieve design information, an engineer can avoid "re-inventing the
wheel" and the design function can evolve toward the use of standards. CSM
systems maintain information about approved parts and suppliers and
provide easy access and cross reference to this information.
The engineer would determine the characteristics of the
item that is needed and identify similar parts that are available through
retrieval. One of these parts may function equally as well or there may
be a non-critical specification (e.g., tolerance, finish, dimension, etc.)
on an existing part that could be changed to suit both needs. If the existing
designs were not satisfactory, the design data could be used to facilitate
the design of a new part, particularly with computer-aided design tools.
This approach can be extended to identify existing tooling and fixtures
which also might be used, avoiding additional re-design.
In addition to
standardization, simplification of part and product designs also offers
significant opportunities to reduce costs and improve quality. Designers
need to evaluate if there is an easier way to accomplish the part
function. DFM tools and principles provide a structured approach to
seeking simplified designs. Product complexity can be further reduced by
utilizing a modular building block approach to assembling products.
Through standard product modules, a wide variety of products can be
assembled from a more limited number of modules, thereby simplifying the
design and manufacturing process. By simplifying and standardizing
designs, establishing design retrieval mechanisms, and embedding preferred
manufacturing processes in the preferred part list, design and production
efficiencies are enhanced.
PRODUCT DESIGN GUIDELINES
A number of general design guidelines have been established to achieve
higher quality, lower cost, improved application of automation and better
maintainability. Examples of these
DFM guidelines
are as follows:
- Reduce the number of parts to minimize the opportunity for a defective
part or an assembly error, to decrease the total cost of fabricating and
assembling the product, and to improve the chance to automate the process
- Foolproof the assembly design (poka-yoke) so that the assembly process
is unambiguous
- Design verifiability into the product and its components to provide
a natural test or inspection of the item
- Avoid tight tolerances beyond the natural capability of the manufacturing
processes and design in the middle of a part's tolerance range
- Design "robustness" into products to compensate for uncertainty
in the product's manufacturing, testing and use
- Design for parts orientation and handling to minimize non-value-added
manual effort, to avoid ambiguity in orienting and merging parts, and to
facilitate automation
- Design for ease of assembly by utilizing simple patterns of movement
and minimizing fastening steps
- Utilize common parts and materials to facilitate design activities,
to minimize the amount of inventory in the system and to standardize handling
and assembly operations
- Design modular products to facilitate assembly with building block
components and sub-assemblies
- Design for ease of servicing the product
In addition to these guidelines, designers need to understand more about
their own company's production system, i.e., its capabilities and limitations,
in order to establish company-specific design rules to further guide and
optimize their product design to the company's production system. For example,
they need to understand the tolerance limitations of certain manufacturing
processes.
EVALUATION OF DESIGN ALTERNATIVES
With the traditional approach, the designer would develop an initial
concept and translate that into a product design, making minor modifications
as required to meet the specification. DFM requires that the designer start
the process by considering various design concept alternatives early in
the process. At this point, little has been invested in a design alternative
and much can be gained if a more effective design approach can be developed.
Only through consideration of more than one alternative is there any assurance
of moving toward an optimum design. Using some of the previous design rules
as a framework, the designer needs to creatively develop design alternatives.
Then alternatives are evaluated against DFM objectives.
Design automation tools can assist in the economic development of multiple
design alternatives as well as the evaluation of these alternatives. These
design tools include computer-aided design (CAD), computer-aided engineering
(CAE), solids modeling, finite element analysis, group technology (GT) and
computer-aided process planning (CAPP). CAD/CAE aid the designer in cost
effectively developing and analyzing design alternatives. CAD/CAE and expert
system tools can utilize manufacturing guidelines to develop producible
designs. Solids modeling helps the designer visualize the individual part;
understand part relationships, orientation and clearances during assembly;
and detect errors and assembly difficulties. Finite element analysis and
other design analysis tools can be used to assess the ability of the design
to meet functional requirements prior to manufacture as well as assess a
part's or product's robustness. Computer-aided process planning can be used
during the development of the product design to help the designer assess
the manufacturability of a design. Without CAPP, this level of manufacturing
assessment would not usually be performed until after the design was released
for production. However, the use of these design productivity tools must
be managed because they may create a temptation for the designer to exercise
too much creativity and design a slightly improved part rather than opt
for part standardization.
In addition to these design productivity tools, there are a variety of DFM
analysis tools to evaluate designs and suggest opportunities for improvement.
These can be used to analyze design symmetry; ease of part handling, feeding
and orientation; and the number of parts. They can also analyze assembly
operations, evaluate designs against design practices and analyze tolerancing
requirements.
Once the designer acquires a basic DFM background, the designer must learn
to work more closely with manufacturing engineers and others who can provide
him with feedback on DFM design issues. In summary, this design approach
and the supporting engineering tools should:
- Identify design alternatives and develop these alternatives economically
- Evaluate these alternatives against DFM objectives
- Establish standardized designs based on DFM principles which can be
readily retrieved for new products
- Utilize design reviews and include
participation of Manufacturing in the design process to evolve the
producibility guidelines
SUMMARY
Design for Manufacturability and Integrated Product Development may require
additional effort early in the design process. However, the integration
of product and process design through improved business practices, management
philosophies and technology tools will result in a more producible product
to better meet customer needs, a quicker and smoother transition to manufacturing,
and a lower total program/life cycle cost.
In an increasingly competitive world, product design and customer service
may be the ultimate way to distinguish a company's capabilities. Because
of the growing importance of product design, Design for Manufacturability
and Integrated Product Development concepts will be critical. It will be
the key to achieving and sustaining competitive advantage through the development
of high quality, highly functional products effectively manufactured through
the synergy of integrated product and process design.
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 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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