Quality Tools and Acceptance Sampling Concepts

Quality Management Tools and Techniques

Brainstorming

Brainstorming is based on the ideas and contributions of individuals and is used to define the causes of problems, take interim measures, and achieve innovative ideas. This mode can be:

• Structured: Each person in the group gives their idea in turn (e.g., in a circle).
• Unstructured: Free flow, where each person gives their idea when they think of it.

Cause-Effect Diagram (Ishikawa Fishbone)

This diagram is used to identify and sort all the causes of a problem to specify the source and fix it. Its use is widespread and helps to:

• Identify the true causes.
• Summarize existing relationships.
• Promote process improvement and foster creativity.
• Gain a more global perspective.
• Equalize members and help analyze and solve problems systematically.

Diagram of Dispersion (Correlation Scatter Plot)

This is a graphical tool for analyzing relationships between two variables. It is used to:

• Visualize the intensity of the relationship between the variables.
• Verify relations between two variables.
• Determine known values of variables difficult to measure.
• Ensure that measures correspond with the results.

Stratification

Stratification involves separating the data into groups or categories for analysis.

Flow Diagrams

Flow diagrams graphically describe the function and structure of processes and can be applied to any area or activity. To use them, the following steps are taken:

1. Identify the target.
2. Define the process and set its limits.
3. Determine the activities that comprise the process.
4. Represent the process graphically.

Concepts in Sampling Inspection

Advantages of Sampling Inspection

• Lower cost.
• Knowledge of risks.
• Less monotonous work.

Key Definitions

Batch

A homogeneous set of output units produced in a process.

Sample

A part of the lot on which the inspection is performed in order to assess the quality of the lot.

Unit of Product

The item inspected to determine if it is defective or valid.

Defective (Failing)

Any nonconformance or non-compliance of the unit from the specifications or requirements.

Number of Acceptance (A)

Determines the maximum number of defectives in the lot that could be successfully accepted.

Number of Rejection (R)

The same as the number of acceptance, but for rejection.

Lot Quality

The percentage of defectives present in a lot.

Acceptable Quality Level (AQL)

The maximum average value of defective units that the customer is willing to accept.

Quality Limits

The maximum percentage of defectives that can be admitted in an individual batch.

Factors for Choosing AQL

Factors include the type of defect, customer complaints, inspection costs, and performance of suppliers.

Stringency in Sampling Inspection

Inspections may be:

• Normal: This is the most commonly used level.
• Strict: Recommended when quality is poor; the acceptance criteria is more severe.
• Reduced: Applied after a number of standard inspections achieve consistently good quality.