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Design for Manufacturing

Product and process simplification are probably the two most useful concepts for designing. Simple systems are faster and cost less than more complicated ones. The lead times are shorter than that of more complicated systems because unnecessarily complex products or processes are more difficult to understand, modify, and control. The cumulative impact of complexity may not be seen until an extended period has passed and failures begin to occur in the field. There are two initiatives or programs useful for reducing complexity. Design for manufacturing (DFM) is used to reduce product design complexity, and Lean methods are used to simplify process complexity. There are strong analogies between the two initiatives.

In the mid-1980s, DFM was popularized through the work of Dewhurst and Boothroyd, two resident professors at the University of Rhode Island. Their work was a modification of classic value engineering. In value engineering, a product design is broken into its components, their assembly operations, and the elemental work tasks of each operation. Using value engineering, the standard cost of all components and the standard work tasks needed to produce a product is estimated. Using this initial analysis,

TABLE 4.7

Ten Steps to Implement Design for Manufacturing

Step

1. Simplify through elimination of unnecessary components.

2. Use standardized materials, components, and procedures where possible.

3. Combine several functions into one component.

4. Eliminate different materials.

5. Eliminate screws, fasteners, adhesives, and secondary operations.

6. Ensure components can be easily aligned to allow vertical assembly.

7. Ensure assembly operations are visible and easy to perform.

8. Mistake-proof assembly operations to prevent misalignment and assembly errors.

9. Ensure products are easy to disassemble, service, maintain, and dispose.

10. Ensure products are easy to test and analyze.

the value engineering team attempts to reduce the product’s complexity through the elimination or combination of components to reduce assembly time and materials cost. In this value engineering analysis, design alternatives are compared to the current baseline design relative to features, functions, costs, and time to assemble. The goal is to reduce the number of components and materials, the standard time to assemble one unit, as well as the per-unit cost. Published case studies have consistently shown reductions in component count that exceed 50% using DFM methods. There are also corresponding reductions in standard cost, the number of required suppliers, inventory investment, and time.

Table 4.7 lists ten steps to implement DFM. The first is simplification of a design through the elimination of unnecessary components, which also eliminates their assembly time and cost. Simplification includes the elimination of unnecessary features and functions, combining features and functions or components, and reducing assembly and inspection operations. If several components are combined into fewer components, there will be fewer assembly operations. The number of different materials should also be reduced, if possible, to enable combining product features and functions. An example is molding several components that use the same material (e.g., a type of polymer or plastic) into a single part. Because screws, fasteners, adhesives, and secondary operations increase cost and lead time, they should be eliminated if possible.

The product or service should also be designed for easy assembly. Components should be aligned to allow vertical assembly by robots or machines. Standardized materials, components, and procedures should also be used whenever possible. Standardized components and procedures also enable easier assembly of the product or deployment of the service, resulting in fewer mistakes. Standardization enables multiple sourcing of components by purchasing and lower costs.

Product quality is also improved when assembly operations are visible and easy to perform by workers or machines. As an example, imagine trying to assemble two components without being able to clearly see the assembly operation because it is hidden. Assembly operations that remain after implementing steps one through eight should be mistake-proofed to prevent errors. Products should be easy to disassemble and serviced at remote locations. At the end of their useful life, disposal should be inexpensive and safe. Finally, new products and services should be easy to test and analyze, both during assembly and at a remote location.

The deliverables or milestones from designing products or services are listed in Table 4.8. This is a generic list, and different industries may have more of these deliverables or fewer. These are incorporated into the five phases that were shown in Figure 4.1. These will be discussed in the following sections.

TABLE 4.8

Design Deliverables

Deliverables

1. Marketing strategy and voice of the customer

11. Prototype build

2. Product/process data

12. Engineering drawings and specifications

3. Product reliability studies

13. Equipment and tooling requirements with manufacturing

4. Design goals

14. Testing requirements

5. Preliminary bill of materials and process flow chart

15. Packaging specifications

6. Preliminary list of special characteristics

16. Process instructions

7. Design failure mode and effects analysis (DFMEA)

17. Measurements systems analysis

8. Design for manufacturability applications

18. Preliminary process capability study plan

9. Design verification

19. Production trial run with manufacturing

10. Design reviews

20. Customer production part approval

 
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