Paper describes design for manufacturability in product development and provides DFMA guidelines.

DESIGN  FOR  MANUFACTURABILITY

Kenneth Crow
DRM Associates

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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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