Six Sigma

Both DFMEA and PFMEA have similar principles and follow identical steps. Both involve identifying potential failures, their impact, and corrective measures to be taken for reducing or eliminating these potential failures.

However, DFMEA and PFMEA differ in a few aspects, such as their focus and the stage in which these two analyses are done.

DFMEA focuses on potential failures related to product design changes. The main focus is on finding potential failures that can result in malfunctions and safety hazards while using the product. It is also applied to identify potential causes that may curtail the life of the product. It  must be conducted throughout the entire design process, starting at the preliminary design as soon as the design concept has been selected to the production.

PFMEA focus on potential failures associated with processes and changes to them. The main focus is on finding potential failures related to a process that can affect the quality of a product or cause safety or environmental hazards and result in customer dissatisfaction. It is also applied to identify potential causes that reduce the reliability of the process.

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Description

Focus
  • DFMEA: On potential failures related to product design changes
  • PFMEA: On potential failures associated with processes and changes to them
Stage

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The Y-shaped matrix is a matrix diagram that relates three sets of elements where one set is related to the other two sets in a circular manner. . It can be formed by bending the columns of sets A and B in the T-matrix in such a way that there is an interrelation between the elements of these two sets.Y shaped matrix

Fig: A Y-shaped matrix that summarizes the requirements for different models of photocopiers


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Matrix diagrams can be sorted into several types depending on the number of data sets being compared.

  • L-shaped Relates two sets of elements to one another or a single set of elements to itself.
  • T-shaped Relates three sets of elements where there is no relation between the two sets that are related to a common set.
  • Y-shaped Relates three sets of elements where one set is related to the other two sets in a circular manner.
  • C-shaped relates three sets of elements simultaneously.
  • X-shaped relates four sets of elements.
  • Roof-shaped relates one set of elements to itself.

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A matrix diagram, also called a matrix chart, is a management and planning tool used for identifying relationships between two to four groups of elements or among elements in a single group. The elements in different groups are placed in rows and columns and relationships among them are analyzed by the team. Symbols indicating the strength of the relationships are then entered in the cell where the row and column of the two elements intersect. If there is no relationship, then it is left blank. Because matrix diagrams help you analyze data, they are also extensively used in the Measure and Analyze phases of the DMAIC methodology.

  • Relationships among different sets of items by comparing them, especially many-to-many relationships among them instead of one-to-one relationships.
  • The strength of the relationship between different sets of items qualitatively.
  • And, the success of a process that generates one set of items from another set of items.

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In the previous topic, you created a tree diagram. Key issues identified must also be sorted in the order of their importance. A prioritization matrix helps determine the order for dealing with different issues or selecting solutions according to their relative importance. In this topic, you will create a prioritization matrix to identify crucial issues that require immediate attention.

You must prioritize key issues identified according to their importance to determine which issues or solutions are the most critical and need to be addressed first. Using a prioritization matrix, you can determine such crucial areas where Six Sigma projects need be implemented to improve your business processes.

What are Prioritization Matrices?

A prioritization matrix is a tool used for determining the most important issues or solutions. This tool can be used for any prioritization activity. In a Six Sigma project, it can be used for filtering or prioritizing either causes or solutions. For example, the cause-and-effect matrix is a prioritization matrix used for prioritizing causes, while the criteria-based matrix is used for prioritizing solutions.

Whatever the matrix, the procedure used for prioritization is the same. The Six Sigma team identifies different criteria to be used for measuring different solutions. The relative importance of each criterion is determined and a numerical value indicating the weight of each criterion is entered in a column. Ratings are then assigned to the solutions against different criteria. The different solutions are scored against the identified criteria. Each rating is then multiplied by the criteria weights to obtain the weighted scores. The weighted scores are then added to find the cumulative value. The option with the highest total value is regarded as the option with the highest priority.

Prioritization Matrix

Fig: A sample prioritization matrix

What are the use of Prioritization Matrices?

  • Prioritizing complex issues involving several criteria against which the issues are assessed.
  • Assigning scores to the criteria or issues when data is available.
  • Choosing key areas to be focused upon immediately.
  • And, garnering team support and approval of crucial issues.

How to Create a Prioritization Matrix?

To create a prioritization matrix for determining key areas where Six Sigma projects need be implemented first:

  1. Gather the team members required to participate in the exercise.
    1. It is not necessary to limit the team to only the project team members.
    2. Involve all stakeholders who would have influence on the items to be prioritized.
    3. Ideally, the size of the team should be around eight.
    4. Agree upon the scope and the duration of the exercise because there is a tendency to drift from the main subject of interest, which may consume more time.
  2. Identify criteria against which the items to be prioritized can be weighed. Select the criteria according to your business and the nature of the process.
  3. Assign weights to the criteria on a scale of 1 to 10.
    1. Use an ascending scale while assigning the weight. Usually, the higher the better.
    2. Draw consensus within the team on the weights.
  4. Assign ratings for each item to be prioritized against different criteria on a scale of 1 to 10. Alternatively, the team can also pick solutions one by one and gather votes for each criterion. Members who agree that a solution fits a particular criterion vote for it. Ensure that necessary information is available to the team before voting.
  5. Compute the total score for each item.
    1. Multiply the rating for an item by the weight.
    2. Add the total scores for each item.
  6. Continue doing this for every criterion of all the items.
  7. Shortlist the items with higher scores for implementation.

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An interrelationship digraph, also called a relations diagram or network diagram, is a tool that depicts relationships among different elements, areas, or processes through a network of boxes and arrows. It is usually used by Six Sigma teams to understand cause-and-effect relationships among different factors of a problem.

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The metrics of a Six Sigma project reflect customer needs and ensure that the internal metrics of the organization are achieved. The selection of project metrics is one of the crucial elements in the Define phase of the Six Sigma methodology.

Six Sigma project metrics can be categorized into primary metrics and secondary metrics.

Primary Metrics

A primary metric, also called a project CTQ, is a CTQ measure that is used to monitor project progression and success. It is the reference point throughout the Six Sigma project. Ideally, project CTQs should have direct impact on customers. For any Six Sigma project, the primary metrics should be:

  • Tied to the problem statement and objective of the project.
  • In possession of an operational definition.
  • Measurable, simple, and expressed in the form of an equation.
  • Aligned to business objectives.
  • Tracked on hourly, daily, weekly, and monthly basis.
  • Expressed graphically over time with a run chart, time series, or control chart.
  • And, validated with a Measurement Systems Analysis (MSA).

Some of the primary metrics of a Six Sigma project include customer satisfaction, on-time delivery of products, final product quality, and less costly products.

Secondary Metrics

A secondary metric, also known as a consequential metric, is a project metric that you do not want to sacrifice at the expense of primary improvements in a process. These metrics ensure that the process is improving and not shifting one metric at the expense of another. It means that the secondary metrics have a relationship with the primary metrics of a Six Sigma project. Therefore, the primary goal of a Six Sigma project will be to move the primary metrics, but ensure that secondary metrics do not deteriorate or stay constant. Some of the secondary metrics include cycle time, volume shipped, inspection data, and rework hours. These metrics should not be sacrificed to achieve the primary metrics such as customer satisfaction, on-time delivery of products, and final product quality.


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A project charter is a contract between a Six Sigma project team and a sponsor. It provides a clear, concise description of the business needs that the project is intended to address. Any changes to the critical elements of a project charter need prior approval from the sponsor and consensus from the team members.

A completed sample project charter is available for download.

Click here to download here

Project charter


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Six Sigma projects are primarily focused on customers. The other areas that Six Sigma projects focus on are:

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Some of the major attributes of CTQ include:

  • A single meaning for each metric across all geographic locations.
  • Defining the process owners who are responsible for tracking the CTQ.
  • Clearly defined defects and opportunities in the process.
  • A consistent measurement system to provide accurate and precise measurements.
  • And, it must be derived from the VOC so that it provides a strong linkage to the VOC.

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An affinity diagram is a tool that is used to organize a large number of ideas, opinions, and issues and group them based on their relationships. Affinity diagrams are generally used for categorizing ideas that are generated during brainstorming sessions and can be particularly useful for analyzing complex issues.
Affinity Diagrams
The steps for creating an affinity diagram can include:

  1. Generating ideas through brainstorming.
  2. Displaying the ideas randomly.
  3. Sorting the ideas into groups.
  4. Creating header cards for each group to capture the essential links among the ideas in each group.
  5. And, drawing the affinity diagram by writing the problem statement at the top and the headers with their respective groups of ideas below the problem statement.
  6. An affinity diagram helps in sorting and grouping customer requirements.

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To gather the VOC, effective methods for accurately capturing customer requirements are required. Several methods are available to capture the VOC.

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