Topic

The DfX concept

The meaning of the X in DfX

The electronics industry strives to meet four criteria when developing new products: quality, cost, performance and delivery. To remain successful these have to be achieved continually. Companies are now realising that in order to catch up with Far Eastern (and now Western) manufacturers, new tools and techniques must be used. Design for eXcellence is a philosophy that promotes rapid and successful products by encouraging communication and cooperation between the functional departments that are responsible for the design and manufacture of a product. Implementation of a successful DfX programme will decrease product development time, product cost and manufacturing cycle time while increasing product quality, reliability and ultimately, customer satisfaction.

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In 1982, NCR began a formal program on implementing design for manufacturability throughout its operation. By 1989, the program had been officially named as Design for Excellence (DfX). The company described DfX as:

“Continuous improvement in concurrent product and manufacturing process development to focus developers’ attention from the beginning on all key product lifecycle considerations such as customer requirements, quality, time to market, cost of ownership, and operational complexity.’’

 

There are two views on the meaning of the X in DfX:

Design for ‘X’. This suggests that the X is used as a variable term that can be substituted with, for example, Assembly, Cost, Environment, Fabrication, Manufacture, Obsolescence, Procurement, Reliability, Serviceability or Test.

Design for eXcellence. Suggests using all the ‘Design for’ methods to achieve excellence. As examples, the next section gives four interpretations of DfX including DfX as part of concurrent engineering and as part of a continuous improvement programme.

In reality, both meanings should be implied. The implementation of DfX will include whichever Design for ‘X’s the organisation feels are applicable. It should also be used as part of a programme or a design philosophy for achieving or striving for a level of product excellence.

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Interpretations of DfX

The term DfX has different meanings to different people. The differences reflect the individual’s position in an organisation and therefore exposure to it. Naturally, individual opinions are based on past experiences of the use of DfX, which can be good or bad.

Examples of perceptions of DfX are:

DfX as an organisation-wide culture

In order for a DfX programme to be implemented and propagated, there must be involvement from many departments within an organisation. These departments will ultimately report to representatives on the Board of Directors. It will be fruitless to ask employees from traditionally uninvolved departments to set aside time for product design reviews. Similarly, asking middle management to free employee time, with project timescales to adhere to and departmental deliverables to distribute, will have the same result.

Ideally, especially at the implementation stage, there should be a DfX champion reporting at Board level who can then influence other departments from the top down to allocate resources and time, and to integrate DfX into their regular work. If this finds strong resistance, as does any cultural change introduced, the champion will have to be highly persuasive and promote DfX at every opportunity. To aid in persuasion, the goals of DfX must be obvious and measurable to everyone, and the benefits must be justifiable. In order to be implemented properly, DfX must be part of the corporate culture, and it must have strong support from all levels of management.

For larger organisations where DfX is part of the culture, it may be sufficient for DfX engineers to report to respective functional managers (R & D, manufacturing or engineering managers).

DfX and Concurrent Engineering

Figure 1 and Figure 2 show the traditional sequential process of product development and the equivalent concurrent process. The savings in time and money are due to the reduction or elimination of product respins1 due to changes and corrections to the design from the manufacturing functions upstream. Concurrent engineering can be viewed as the simultaneous development of the whole design, its components and its assembly process and tooling requirements.

1 The term ‘respins’ refers to the reworking of a design appears to derive from the record industry and is quite common within the ASIC community.

 

Figure 1: Traditional sequential product development

Traditional sequential product development

Figure 2: Concurrent product development

Concurrent product development

DfX is a methodology that involves various groups with knowledge of different parts of the whole lifecycle of a product advising the Design Engineering functions during the design phase. This knowledge can take the form of guidelines that the designer will follow during design, or design review meetings with the field experts.

A typical electronic product development team may contain representatives from the following functions:

The DfX methods ensure the information released is correct or useful. Therefore, concurrent engineering and DfX used together reduce the development and production cycle and reduce product respins, low yields or high costs.

DfX and Continuous Improvement

DfX may be used as part of an organisation’s Continuous Improvement programme along with other tools that strive towards some defined goals such as achieving a ‘World Class’ organisation. DfX will decrease product development time, product cost and manufacturing cycle time while increasing product quality, reliability and customer satisfaction. It will decrease the overall cycle time required to get a product from concept to the customer, which is a critical success factor.

Exercise

Using any cross-departmental tools or methodologies within an organisation will incur problems. Think about some of these problems specifically when using DfX and how an organisation may lessen or prevent the problems.

Compare your answer with our comments.

 

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The benefits of using DfX

The majority of a product’s cost is committed at the design stage before the product is manufactured. There are many sources that quote 75–85% of the cost of a product is committed during the design and planning activities (Figure 3), whereas the actual amount spent only increases during production after the design has been accepted. Consideration of manufacturing and assembly problems at the product design stage is therefore the most cost effective way available for reducing assembly costs and increasing productivity.

Figure 3: The Lucas view of cost commitment

The Lucas view of cost commitment

Figure 4 shows an exponential-type increase in cost of product change. This change at the production stage will typically take the form of an ECO/ECN2. The cost of change to a product is high once in manufacturing, but the cost of change is even higher when it is in use. The graph does not show the effect of cost of change once the product has been delivered. It becomes more difficult to quantify due to the intangible nature of the cost. We have control over the processes within our own organisation. Unfortunately, this is not the case once the product has been delivered. Product recalls incur logistical costs, which are quantifiable, but subsequent loss of customer faith and lawsuits are not.

Figure 4: The cost impact of changing a product during each stage of a product's development

The cost impact of changing a product during each stage of a product's development
2 Engineering Change Order or Engineering Change Note/Notice. These are formal instructions from Design Engineering that have been approved by other groups such as Manufacturing and Quality. Good practice is to include on the ECO a statement of the cost implications of the change.

 

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History and development of DfX

The most common Design for Xs, and the foundation for Design for eXcellence, are Design for Assembly and (especially) Design for Manufacture. These were the first formal DfX methods used, and consequently form a large part of the development of DfX, and unfortunately, DfM has tended to become a catch-all term.

The first recognition of the importance of DfM came during World War II with the scarcity of resources and constant pressure on industry to build better weapons in the shortest possible turnaround time. Small, integrated, multi-disciplinary teams designed many of the successful weapons of that period.

After World War II, prosperity and the rapid industrial growth saw design and manufacturing segregated into distinct departments, resulting in a sequential product development environment with little attention to DfM.

In the late 1950s and early 1960s, organisations began to realise that the current design methodologies and paradigms were not applicable to the new style of automated manufacturing. In particular, robotic and reprogrammable manufacturing systems had many different concerns and requirements than those of previous years. From this, manufacturability and assemblability guidelines were formalised. One of the earliest works dealing exclusively with this topic was produced by General Electric and was called the Manufacturing Producibility Handbook.

Throughout the 1960s and 1970s, many companies realised the need to streamline their designs and processes for the evolving paradigm in manufacturing and did a lot of internal research independently. In the late 1970s, increasing global competition and the desire to reduce lead times led to the rediscovery of DfM. Some attempted to build inter-departmental design teams with representatives from both design and manufacturing departments. In these design projects, manufacturing engineers participated in the design process from the beginning and made suggestions about possible ways of improving manufacturability.

By the 1980s the concept of DfM and DfA was being embraced by many companies. During this time, many of the previously determined rules were being quantified and programmed into computers for automated analysis of designs. DfA is a product of the automation endeavours of the late seventies and early eighties when moves toward high levels of automated assembly highlighted deficiencies in current product design with respect to automation capability. The application of DfA to new products not only released benefits for the automated assembly processes but to manual assembly and assembly processes in general.

More recently, emphasis has been placed on designing not only for manufacture, but for the whole life of the product including: manufacture, service, repair, and, ultimately, disassembly and recyclability – in short, DfX. Throughout this entire evolution, however, the basic premise of designing a product for ease of assembly has been constantly updated as the methods and techniques of manufacturing have changed.

Levels of DfX analysis

Over time the DfX methods have grown in sophistication aided by the concurrent engineering philosophy and then the use of technology. There are generally three different levels of analysis:

The following of a general set of rules or guidelines. They may be based on an individual's experience or a formal checklist derived over time by an organisation’s engineers. These rules generally are not quantitative in nature and require a human to interpret and apply to each specific and unique case. While this is a much better case than just blindly starting each design from scratch, it does require some skill and knowledge on the part of the designer to interpret and apply the rules correctly.

The employment of a quantitative analysis of the design. Each part of the design is rated or scored with a numeric value depending on its manufacturability. In some organisations this is referred to as a Design Scorecard. The numbers are summed for the entire design and the resulting value is used as a guide to the overall quality of the design. The product is then redesigned, using the numerical values as a goal to be minimised. By concentrating on areas of the design that contribute heavily to the overall score, the effects of the redesign can be maximized. This again, however, requires much insight and knowledge on the part of the designer. Examples of this type are the Hitachi AEM, Lucas DfA and Boothroyd-Dewhurst’s DfMA.

The automation of the entire process. By using a computer, quantitative analysis can be applied to the design. The analysis engine is an expert or knowledge-based system that uses representations of the design rules gleaned from the respective experts. A system can be developed which can analyse a design and provide recommendations for redesign or suggest and rate alternative designs. These systems will alleviate the need to study and memorize guidelines and checklists, therefore allowing the designers to focus on the creative aspects of the design process.

Exercise

The methods used by design engineers to measure how manufacturable a product is have developed over time. Originally, the engineers would have used a binary system, which would have reported whether or not a given set of design attributes was manufacturable. This is the most basic - can you think of any others?

Show solution

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