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QUALITY FUNCTION DEPLOYMENT (QFD): INTEGRATION OF LOGISTICS REQUIREMENTS INTO MAINSTREAM SYSTEM DESIGN Dinesh Verma Rajesh Chilakapati Benjamin S. Blanchard Systems Engineering Design Laboratory (SEDL) Industrial and Systems Engineering, Virginia Tech Blacksburg, Virginia 24061 ABSTRACT Numerous references make a case for the integration of logistics-related activities within the system engineering process. This is consistent with good system engineering practice and with concurrent and simultan
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    QUALITY FUNCTION DEPLOYMENT (QFD): INTEGRATION OF LOGISTICSREQUIREMENTS INTO MAINSTREAM SYSTEM DESIGN  Dinesh Verma Rajesh Chilakapati Benjamin S. Blanchard  Systems Engineering Design Laboratory (SEDL)Industrial and Systems Engineering, Virginia TechBlacksburg, Virginia 24061  ABSTRACT  Numerous references make a case for the integration of logistics-related activities within the system engineering process. This is consistent with good system engineering practice and with concurrent and simultaneous engineering concepts. For the effective and efficient design and  development of systems (products or processes) which are responsive to requirements and competitivein a global economy, this integration must evolve from the nascent stages of system design. Quality Function Deployment (QFD) is a design method which can facilitate this objective.This paper reviews the QFD method, the underlying process and elemental activities, and finally discusses opportunities for logistics engineers to contribute to, and integrate with, the mainstream system design activity. An illustrative QFD matrix is used to depict this integration. Introduction And Background The Quality Function Deployment (QFD) methodwas developed at the Kobe Shipyard of MitsubishiHeavy Industries, Ltd., and has evolved considerablysince. QFD facilitates translation of a prioritized set of subjective customer requirements into a set of system-level requirements during system conceptual design. Asimilar approach may be used to subsequently translatesystem-level requirements into a more detailed set of requirements at each stage of the design anddevelopment process.The sequence of activities which constitute theQFD method are shown in Figure 1. Further, a QFDmatrix, shown in Figure 2, serves as an excellentframework for the coordinated accomplishment of theseactivities and for the representation and analysis of information involved in the implementation of the QFDmethod.As a general quality tool (in the TQM context), theQFD matrix is often called the “House of Quality”[HAU88]. In the context of system engineering, QFDfacilitates a strong correlation between customerrequirements and design requirements, and the inclusionof supportability requirements within the spectrum of design requirements. As such, the method goes a longway in making the customer an integral part of earlydesign synthesis, analysis, and evaluation activities. The QFD Process Identification of a functional need is a primaryinput to the QFD process as shown in Figure 1. It isessential that the need be stated in functional terms toavoid premature commitment to a concept orconfiguration [VER94]. Methods such as customersurveys, interviews, trend analysis, and competitionanalysis are often used to facilitate identification of avalid need. Organizations which can identify andexploit a not-so-obvious need often gain a strategicheadstart over the competition. Activities whichcomprise the QFD method are discussed in thefollowing subsections. These discussions are conductedin the context of the QFD process shown in Figure 1and the QFD matrix shown in Figure 2.1. Need analysis and identification of customerrequirements . As a first step, the functional needis analyzed and translated into more specificcustomer requirements to better understand theperceived deficiency. In essence, the purpose of this step is to capture the “Voice of the Customer”.Reference to the “customer” includes not only theend-users, but also the applicable regulations andstandards, the intermediate distributors, installers,retailers, and the maintainers. As such, this is thefirst significant opportunity to integrate logisticsrequirements and issues into the mainstream designand development process.    Figure 1. The Quality Function Deployment (QFD) process. Properly developed checklists and taxonomies canhelp ensure a comprehensive and completeidentification of customer requirements. Further,consistent and concise translation of the need intocustomer requirements ensures uniformity of effort,and better understanding and communicationbetween members of a design team. Thecustomer’s language is often qualitative andsubjective which imparts vagueness andimprecision to this phase of system design. Vermahas addressed this imprecision through the use of linguistic variables and a linguistic scale [VER94].He uses concepts from fuzzy set theory tomanipulate this imprecise and vague information.Often the customer requirements are generatedthrough a brainstorming exercise by members of the design team. This approach suffers from anumber of crucial drawbacks. More likely thannot, this process “captures” the “Voice of theCompany” or “The Voice of the Team Leader”rather than the all-important “Voice of theCustomer”. Such practices can lead to poorreception of the ultimate product in themarketplace. Byrne and Barlow [BYR93] havereviewed user brainstorming procedures that can beemployed to elucidate customer requirementswithout the interference of internal opinions.Once identified, similar customer requirements areclassified into groups and sub-groups. Thisdevelops into a hierarchy of customer requirements,from the most abstract to the most specific. Thenumber of classification levels depends uponsystem complexity or the extent of detail beingrepresented.2. Importance of customer requirements . Selectedrequirements often impact each other adversely.For instance, a customer may desire ease whileopening and closing a car door, but at the sametime want power windows. Power windowsincrease the weight of the door and this correlatesnegatively with the ease of closing or opening it.To overcome such conflicts, requirements areassigned priorities. It is essential that prioritiesreflect preferences of the customers. There areseveral approaches to prioritizing customerrequirements. These approaches range from directindication by the customer to usage of theanalytical hierarchy process [ARM94] and cost andtechnical factors [WAS93].Three or five level priority scales are often used[GUI93; ZUL90; SLA90; HAU88]. While mostapplications utilize a simple numerical scale forpriorities, linguistic scales (utilizing concepts fromfuzzy set theory) have also been developed andapplied [VER94; WAS93a; MAS93]. 3. Identification of design dependent parameters(DDPs).   Design dependent parameters or technicalperformance measures are engineeringcharacteristics under a designer’s control. Theseparameters are manipulated to directly orindirectlyinfluence customer requirements.   In thiscontext, customer requirements are often referredto as the set of “WHATs”, while design Identify and ClassifyCustomer Requirements   Identify Importance of Customer RequirementsIdentify Design DependentParametersCorrelate Requirementsand ParametersCheck Correlation GridBenchmark Customer Perceptions NEED Benchmark DesignDeendent Parameters Analyze Correlation Gridfor InconsistenciesDelineate DesignDependent Parameter Target Values andRelative Priorities    Figure 2. The QFD matrix or “house of quality”. 1   CustomerrequirementsDesign DependentParameters (DDPs)Importance ofcustomerrequirementsCorrelation MatrixBenchmarkingcustomerperceptions 123476109 This figure represents a “screen shot” from FuzzyQFD , a computer-based implementation of QFD incorporating fuzzy concepts andprinciples to better address design imprecision and vagueness. The computer model was developed within the Systems EngineeringDesign Laboratory at Virginia Tech. 1    set of “WHATs”, while design dependent parametersrepresent the set of “HOWs”. Accordingly to Sullivan[SUL86], “ These (engineering) characteristics are the product requirements that relate directly to thecustomer requirements and must be selectivelydeployed throughout the design, manufacturing,assembly, and service process to manifest themselves inthe final product performance and customer acceptance. ”The DDPs should be tangible, describe theproduct in measurable terms, and directly affectcustomer perceptions [HAU88]. DDPs guide theanalysis and evaluation of design concepts,configurations, and artifacts during the conceptual,preliminary, and detailed system design phases. Assuch, it is essential that all relevant DDPs beidentified. Once again, development of focusedchecklists and taxonomies facilitates this objective.A complete and comprehensive set of DDPsincludes not only performance related parameters,but also parameters which impact systemsupportability and cost.4. Correlation of customer requirements anddesign dependent parameters . This step of theQFD process involves populating the correlationmatrix within the “house of quality”. Each DDP isanalyzed in terms of the extent of its influence oncustomer requirements. Varying levels of thiscorrelation are represented in the correlationmatrix. Depending upon the extent of resolutionnecessary, three or five levels of correlation areused. Further, correlation between DDPs andcustomer requirements may be represented throughthe use of symbols as shown in Table 1. Table 1. Correlation between customerrequirements and parameters. CorrelationLabelCorrespondingIcon Very LowLowMediumHighVery High5. Check correlation matrix.   It is necessary at thisstage to conduct an examination of the correlationgrid before proceeding further. This examinationinvolves checking for: ã  Empty rows in the correlation matrix . Emptyrows in the correlation grid signifyunaddressed customer requirements. Inresponse, the set of design dependentparameters needs to be revisited and, if necessary, additional DDPs identified. ã  Empty columns in the correlation matrix .Empty columns in the correlation grid implyredundant or unnecessary system-level designrequirements. The design team may haveincluded design requirements which cannot betraced back to any customer requirement andcould potentially be dropped from furtherconsideration.The above two possibilities, and otherinconsistencies pertaining to customerrequirements, their importance and correlation withdesign dependent parameters, must be identifiedand discussed in terms of their implication onsystem design and development.6. Benchmarking customer requirements . A keyactivity involves identification of availablesystems/products capable of responding to thefunctional need (to whatever extent). Customerperceptions are then benchmarked relative to howwell these capabilities satisfy the initially specifiedset of requirements. The objective is to assess thestate-of-the-art from a customer perspective.It is important that members of the design anddevelopment team not influence this activity. Theirtechnical knowledge is likely to bias results[SLA90]. Benchmarking of customer perceptionsis facilitated through tools such as customersurveys, customer interviews, demonstrations,media information, and feedback from themarketing, sales and service organizations. Thepurpose of this effort is to “ highlight the absolutestrengths and weaknesses of the products in themarketplace and those areas of your products that require improvement  ” [SUL86]. This activityprovides invaluable insight into avenues wherecompetitive gains can be made most effectively.7. Technical assessment of design dependentparameters (DDPs). This activity involvesassessment of the competition from a technicalperspective. Designers and engineers activelyparticipate during this step in the QFD process.Cavanagh [CAV90] has identified somemethods and techniques to facilitate the effectiveaccomplishment of this step, to include: a) producttesting (baseline the system or product, competitivesystems or products, non-competitive but similarsystems or products), b) informal evaluations
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