QFD, FMEA, and Poka-Yoke for Enhanced Product Quality
Understanding Quality Function Deployment (QFD)
Quality Function Deployment (QFD) involves a thorough study to assess the product aspects that customers value most. Market studies are conducted to capture the “voice of the customer,” which includes:
- Basic Characteristics: What customers explicitly state they want in the product.
- Minimum Requirements: What customers expect but may not explicitly state (assumed features).
- Amazing Features: What customers don’t articulate but would be delighted to have (latent desires).
The design department then takes on the challenge of translating these desired features into reality. Thanks to QFD, organizations can achieve several benefits:
- Knowing customer requirements and desires for the product.
- Reducing product development time.
- Reducing customer complaints.
- Removing features that do not add value to the product.
The core of QFD is establishing the strength of the relationship between customer wants (the “Whats”) and the technical characteristics of the product (the “Hows”). The relationship matrix helps visualize how product characteristics meet the quality requirements expressed by the customer.
Key Elements for QFD Development
- Involvement of relevant departments.
- Clear function definition.
- Adequate training for participants.
- A dedicated working group.
- A facilitator or moderator.
Types of Relationships in QFD
Within the QFD matrix, relationships between technical characteristics can be:
- Negative: Improving one characteristic negatively impacts another (potential trade-offs).
- Positive: Improving one characteristic positively impacts another (synergies).
Phases of Quality Function Deployment
- Product Planning (House of Quality): Relates customer needs to product characteristics. Defines what needs to be achieved.
- Component Development: Deploys critical product characteristics to component-level specifications. Defines how each component contributes.
- Process Planning: Identifies key processes required to achieve component specifications. Defines how to produce it.
- Production Planning (Process Control): Establishes process control methods and quality checks. Defines how to produce consistently with quality.
Failure Mode and Effects Analysis (FMEA) Explained
Failure Mode and Effects Analysis (FMEA) is a systematic technique for taking proactive action to eliminate potential failures before they occur. FMEA analyzes how a process or product might fail and identifies the potential effects of those failures.
Types of FMEA
- Design FMEA (DFMEA): Performed on the product design and its components. Its purpose is to detect potential failures related to the design before the product is finalized.
- Process FMEA (PFMEA): Examines potential failures in the manufacturing or assembly process. Its goal is to predict and prevent process-related failures before they affect the product or reach the customer.
Steps for Conducting an FMEA
- Assemble a cross-functional working group.
- Define the scope:
- For a process: Decompose it into phases, indicating the function of each.
- For a product: Identify all components and define the function of each.
- Identify potential failure modes for each step/component.
- Identify the potential effects of each failure mode.
- Analyze the potential causes of each failure mode.
- Identify existing control systems (prevention and detection).
- Assign valuation indices (Severity, Occurrence, Detection) for each failure mode to calculate the Risk Priority Number (RPN).
- Develop and prioritize improvement actions for high-risk failure modes.
- Review, implement actions, and monitor the effectiveness of the FMEA.
FMEA Considerations and Limitations
FMEA allows teams to foresee the ways in which a product or process might fail. However, conducting a detailed FMEA for every single component or process step is often not economically viable. Therefore, it’s crucial to select the most critical elements (based on risk, complexity, or past issues) for FMEA application.
Implementing Poka-Yoke (Mistake-Proofing)
Poka-Yoke, a Japanese term meaning “mistake-proofing” or “error-proofing,” is a technique focused on designing processes so that mistakes are impossible or immediately detected. Its primary goal is to eliminate defects by preventing errors or correcting them as they happen.
It involves designing systems, machines, tools, and processes in such a way that human errors are minimized or prevented. Another aim is to achieve one hundred percent inspection implicitly within operations. There are two main approaches to achieve this:
- (a) Prevention: Make it physically impossible to make a human error (e.g., designing parts that only fit together in the correct orientation, using connectors that respect polarity).
- (b) Detection: Use sensors or devices to detect an error if it occurs (e.g., presence sensors, dimensional checks, counters).
Poka-Yoke Methods: Control and Warning
Poka-Yoke devices often operate using two primary methods:
- Control Method: Systems that automatically stop the process or machine when an error is detected, preventing the defect from moving forward.
- Warning Method: Systems that alert the worker (e.g., through visual or acoustic signals) when an error occurs, prompting corrective action.