3. Quality Functional Deployment (QFD)

• Basically this relates the customer requirements (i.e., product specifications) to the product design parameters (i.e., final designs) mathematically. The result is a mathematically driven product redesign.

• Also known as House of Quality

• Advantages,

reduction of the product design time

cost reduction

exposes design trade-offs early

provides written documentation of design decisions

design errors and corrections reduced

provides clarity for decisions

• STEP 1: Voice of the Customer

Identify the customers needs, wants and requirements, also known as the Voice Of the Customer (VOX).

This ensures that the product design decisions are based on the customer and not just on the perceived customer needs.

this should involve all groups in a company that get any feedback from customers. Special programs may also be set up to poll customers.

the relative value that customers place on these items should also be identified.

• STEP 2: Customer Requirements Refinement

take customer requirements and expand it to more specific points.

this can be done with a What-to-How technique.

for each requirement ask “What must be accomplished?”, “How will this be accomplished?”

a chart can be constructed,

 

The how list should be expanded until each point is a measurable quantity (called the final-product-control-characteristic)

• Step 3: Begin Laying out the Planning Matrix

 

• ************ INCLUDE FIGURE FROM pg 76 Eureka, W.E., “Quality Functional Deployment Simplified”, Technical Report, American Supplier Institute, Michigan, 1987.

 

• STEP 4: Fill out the Correlation Matrix to determine how factors relate,

relate positive changes to any one of the Control Characteristics to the others. In this case 1 is a very negative effect, up to 4 which is a very positive effect. Unrelated factors have no entry.

If too many, or too few of these spots are filled, the customer requirements should be reexamined for accuracy, etc.

The product and process should be reconsidered if in general there are more negative than positive effects.

 

STEP 5: Complete the relationship matrix and importance rating values.

The relationships between the “WHATS” and “HOWS” are made in this matrix by assigning weights. For example 0-9 where 0 is none and 9 in very strong.

The column values are then summed to give an importance rating

This should result in a few clearly important features, and a few that are clearly not important.

 

STEP 6: Customer Importance Rating and Market Evaluations

The opinions of the customer (as collected in step 1) are quantified in terms of importance of the requirements “WHAT”s, these numbers are entered in the customer importance rating column.

The overall ratings for the competitors products, as well as yours are ranked for each requirement “WHAT” as poor to good. These values are derived from information gathered in step 1, and entered in the Market Evaluations column.

these sections will clearly identify the strengths and weaknesses of the product within the consumers objectives and compared to the competition.

if these values have a reasonable distribution, the customer requirements should be reexamined.

 

• STEP 7: Control Characteristics Competitive Evaluation

Competitors products, and the internal product are compared technically. The performance criteria are done in terms of the Final Product Control Characteristics.

Values are entered in the Control Characteristics Competitive Evaluation section of the chart, and are ranked good to poor.

when these numbers are compared to the numbers in the Importance rating row, the technical deficiencies of the product, and it’s importance are clear.

 

• STEP 8: Evaluate the Chart

the chart at this point contains enough information to do some critical evaluations.

the control characteristics competitive evaluation, and the importance rating should indicate candidates for change. Primarily a high importance rating, where the competitors product is rated better.

the candidates selected should be checked to see how the correlate to the Customer Importance Rating and market evaluations. If the choice is not considered important to the customer, or less important then consider it less important. (Use the planning matrix to find effects).

If any of the customer requirements are unanswered, then the requirements/control characteristics list must be reconsidered.

STEP 9: Develop new target values

using current implemented design parameters, and the relative importance exposed in the last step, new target values should be selected.

the values determined for the competitors products should be used as well as in-house data for the product.

a separate sheet, or document may be used here because descriptions may become bulky.

STEP 10: Technical Difficulty

considering the target values and previous production performance, the difficulty of achieving the target value should be estimated.

a ranking for this is entered in the “Degree of Technical Difficulty” row.

 

• STEP 11: Deployment Selection

quality has a cost, and at this point the cost/benefit trade-off is made.

one or more factors can be selected. If there are not a few clear choices, the process should be reexamined

the main objectives here are to select the elements with the lowest technical difficulties, but the greatest importance ratings

this decision will be slightly arbitrary, but it should not be far outside of what the chart suggests.

• STEP 12: Deployment Matrices

for each control characteristic selected in the last step a deployment matrix is developed

the top of the matrix is developed using factors discussed in development of the planning matrix

the relationship between testable components and the “WHAT”s of durability are put here.

the control characteristics measured for all products, and the target values are positioned below.

the bottom matrix is system components that can be affected by design. On the left are the systems they affect, and the components in those systems. On the right are the measurable variables, and in the center are the locations to track the relative quality of the components.

 

• STEP 13: Design and test

the deployment matrix is used to do design work, test the results, and compare them to the target values

• Note that this process is involved, and will require some period of time, but will improve competitiveness of products.

3.1 References

3.1 Ullman, D.G., The Mechanical Design Process, McGraw-Hill, 1997.

 

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