Six Steps is all it takes to ensure product success.
- Statement of Requirement for Fit, Form & Function
- Design Failure Modes & Effects Analysis (DFMEA)
- Design Validation for Performance, Value & Reliability
- Design for Assembly, Manufacture, Service, Safety and Cost
- Tolerance Specification based on Process Capability
- Estimating Product Quality & PPM at Design Stage
1. Statement of Requirement (SOR) for Fit, Form & Function:
Attention paid at the beginning of a product design, towards enumerating the product requirements in terms of Fit, Form and Function goes a long way in ensuring product acceptance, performance and delivery. Time well spent in documenting the capabilities and limitations of the proposed product, would ensure that the Voice of Customer, Marketing Strategies, Unique Selling Points, Performance Specifications and Acceptance Criteria are known and accepted by the cross-functional team comprising of Design, Manufacturing, Marketing, Sales, Finance, Quality and After-Sales-Service members. Sign off on the SOR indicates the acceptance and endorsement of the proposed design by all team members with their input given the priority as required. SOR is a live working document that is updated during the life of the product. Without this document and its acceptance by concurrent engineering team members, the product would go thro’ many design changes in the initial stages of the product development process that the goals could get compromised. In fact, prioritization of design objectives in consultation with the cross-functional team members assures timely development of the product with little scope for unpleasant surprises towards the end of the development cycle.
Structure of the Statement of Requirement could consist of Objectives, Fit Requirements, Form Specification and establishment of Functional criteria for product performance and acceptance. Additionally, Functional Test Criteria, Quality Acceptance Criteria, Voice of Customer, Scope of Product Usage, Limitations of Product proposed, Life & Reliability expectancy, Safety parameters, Sustainability Goals should form a part of the SOR.
2. Design Failure Modes & Effects Analysis (DFMEA)
Design criticality is captured by incorporating the DFMEA as a part of the product design process. This document forms the IPR of the organization. The design assumptions, verification, criticality assessment and considerations included in understanding and preventing failure modes in addition to the calculation of the Risk Priority Number (RPN) help ensure that all aspects of the product are considered and addressed. This reflects the strength of the design process and the ability to address potential threats to the product during and after launch. Needless to say, successful and careful assessement of the DFMEA assures the management on the product viability, reliability and life-time performance. This homework needs to be done by the design team in charge of the product design early in the design process leaving ample scope for improvement and update.
3. Design Validation for Performance, Value & Reliability
Validation of the Design at every stage of the product evolution is a necessity driven by competition, predatory pricing and enhanced customer satisfaction. Technologies such as Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) have matured for practical application to real-world problems. Post-processing of FE Stresses, Strains and computing Fatigue Life for analyses performed on the basis of the DFMEA document ensures that the objectives of Performance and Reliability are met. Design for Cost is an added responsibility of the Design Team to ensure that the product cost parameters are met. Targets for Cost Reduction, Value Addition & Value Engineering (VAVE) goals should be provided to the Design Team, and monitored, to achieve assured profitability.
4. Design for Assembly, Manufacture, Service, Safety and Cost
Design for Assembly (DFA) is a criteria that is sometimes overlooked or given lesser priority. However, it is a single important assessment that will influence product cost in terms of manufacturing stages, inspection time, assembly time and fitment issues that lead to wastage and re-work. Method of assembly, Interference check at extremes of tolerance variation, Sequence prioritization for efficiency and cycle time reduction, wrongful assembly check (including Poka Yoke) are some of the considerations that need to be addressed early on in the design process.
Design for Manufacture (DFM) considerations regarding tooling (such as Drill Depth to Diameter Ratio, Undercut, Draft among others). Design for Serviceablity, Safety and Cost are as important as product reliability for improved Customer Satisfaction.
5. Tolerance Specification based on Process Capability
Tolerancing of part features is an important part of the design process that usually is given least importance, until product sign-off. Design Engineers need to understand the process capability of the manufacturing processes (Cp, Cpk) and reflect the same in the selection of tolerances. If the process capability does not meet the tolerance criteria required, in addition to specifying the process capability required, it is the responsibility of the design team to justify the selection of tolerances. Least cost tolerancing should be the guiding principle in selection of tolerances without affecting Fit, Form and Functional specifications.
6. Estimating Product Quality & PPM at Design Stage
Tolerance Stack Up Analysis is a part of the Dimensional Management process that needs special emphasis before design drawing sign-off. By incorporating GD&T (Geometric Dimensioning & Tolerancing) and ensuring the correctness and compleness of the Drawing Specification, the pre-requisite to perform Tolerance Stack Up Analysis is ensured. 1-D, 2-D, or sometimes, 3D Tolerance Stack Up Analysis can be performed using CAD based tools by either manually or automatically selecting the Vector Loop. The process capability of the various processes can be attributed to the feature dimensions and their tolerances to perform what-if analysis of tolerance variations. Additionally, by specifying the assembly build criteria, the PPM based on control limits as against specification limits are known a priori, even before the first product build is completed. This ensures the identification of critical features and their required tolerance deviations that would permit achievement of PPM based on Sigma Levels. This provides the management a profitability dashboard to evaluate the pros and cons of making investments in new manufacturing lines and tooling depending on ROI calculations. Additionally, the Quality personnel can monitor critical processes based on these assessments and ensure that the SPC stays within limits as stipulated by design.
Now that we have completed the enumeration of the Six Steps in Product Design for Success, the design engineers have to ask themselves the following questions for continuous improvement in processes and products:
- Is this the best design that is possible to achieve for the cost provided?
- Is the design reliable?
- Have I given the best to the Company, Customer and Society?
- If I were to go about re-designing the product all over again, where would I start the correction process?
- Am I a good Corporate Citizen in delivering Sustainable Products and Technologies?