A Process Control Plan (PCP) is a critical component of the control phase in the DMAIC (Define, Measure, Analyze, Improve, Control) process in lean Six Sigma. It is a document that outlines the steps that will be taken to monitor and control the process to ensure that it remains under control and that the improvements made during the previous phases are sustained. In this article, we will provide a detailed overview of how to develop a Process Control Plan for lean Six Sigma.

Identify the Key Process Inputs and Outputs

The first step in developing a Process Control Plan is to identify the key process inputs and outputs. This involves understanding the process and identifying the factors that impact its performance. The following are some of the key inputs and outputs that should be identified:

a. Input Factors: Input factors are the variables that impact the process inputs. These can include things like raw materials, equipment, and labor.

b. Output Factors: Output factors are the variables that impact the process outputs. These can include things like the quality of the product or service, the cycle time, and the cost.

Define the Critical to Quality (CTQ) Metrics

The next step in developing a Process Control Plan is to define the Critical to Quality (CTQ) metrics. These are the metrics that are most important to the customer and to the success of the process. The CTQ metrics should be defined based on the outputs identified in the previous step.

Establish the Process Control Limits

The next step is to establish the Process Control Limits. The Control Limits are the ranges that define the acceptable variation for the process. These can be determined using statistical analysis of the process data collected during the Measure phase. The Upper Control Limit (UCL) and Lower Control Limit (LCL) define the upper and lower boundaries of the Control Limits.

Define the Sampling Plan

The Sampling Plan is the strategy that defines the frequency and method of data collection. The Sampling Plan should be based on the CTQ metrics and the Process Control Limits. It should be designed to detect any variation in the process that may cause defects. The following are some of the key elements of a Sampling Plan:

a. Sampling Frequency: The Sampling Frequency defines how often data will be collected. This can vary based on the CTQ metrics and the stability of the process.

b. Sample Size: The Sample Size is the number of units that will be measured during each sampling event. This can also vary based on the CTQ metrics and the stability of the process.

c. Sampling Method: The Sampling Method defines how the data will be collected. This can include things like random sampling, stratified sampling, or continuous sampling.

Develop the Process Control Charts

The Process Control Charts are a critical component of the Process Control Plan. They provide a visual representation of the process performance over time. The Control Charts should be based on the CTQ metrics and the Process Control Limits. There are several types of Control Charts, including:

a. Variable Control Charts: Variable Control Charts are used to monitor continuous data, such as the weight of a product or the time it takes to complete a task.

b. Attribute Control Charts: Attribute Control Charts are used to monitor discrete data, such as the number of defects or the number of non-conformities.

Define the Response Plan

The Response Plan is the strategy that defines the actions that will be taken if the process goes out of control. This plan should be developed based on the Process Control Charts and the CTQ metrics. The Response Plan should include the following elements:

a. Criteria for Action: The Criteria for Action defines the thresholds that will trigger a response. This can include things like the number of consecutive points outside the Control Limits or the number of points near the Control Limits.

b. Actions to Take: The Actions to Take define the specific steps that will be taken if the Criteria for Action are met. This can include things like identifying the root cause of the issue, implementing corrective actions, and initiating a review of the process.

c. Individuals Responsible: The Individuals Responsible define the people who are responsible for taking action if the process goes out of control. This can include things like the process owner, the team leader, and the quality control manager.

Develop the Contingency Plan

The Contingency Plan is the strategy that defines the actions that will be taken if there is a problem with the process inputs. This plan should be developed based on the input factors identified in step one. The Contingency Plan should include the following elements:

a. Criteria for Action: The Criteria for Action defines the thresholds that will trigger a response. This can include things like a change in the quality of the raw materials or a change in the supplier.

b. Actions to Take: The Actions to Take define the specific steps that will be taken if the Criteria for Action are met. This can include things like identifying a new supplier, implementing a new inspection process, or modifying the process to accommodate the new inputs.

c. Individuals Responsible: The Individuals Responsible define the people who are responsible for taking action if there is a problem with the process inputs. This can include things like the supply chain manager, the purchasing manager, and the quality control manager.

Define the Roles and Responsibilities

The Roles and Responsibilities section of the Process Control Plan defines the people who are responsible for the different aspects of the plan. This section should include the following:

a. Process Owner: The Process Owner is the person who is responsible for the overall performance of the process.

b. Quality Control Manager: The Quality Control Manager is responsible for ensuring that the process is performed correctly and that the outputs meet the required quality standards.

c. Team Leader: The Team Leader is responsible for overseeing the implementation of the Process Control Plan.

d. Sampling Technician: The Sampling Technician is responsible for collecting data according to the Sampling Plan.

e. Data Analyst: The Data Analyst is responsible for analyzing the data and updating the Control Charts.

Establish the Communication Plan

The Communication Plan defines the stakeholders who will be informed of the results of the Process Control Plan. This can include internal stakeholders, such as management and employees, as well as external stakeholders, such as customers and suppliers. The Communication Plan should include the following elements:

a. Frequency of Communication: The Frequency of Communication defines how often the stakeholders will be updated on the process performance.

b. Method of Communication: The Method of Communication defines how the stakeholders will be informed of the process performance. This can include things like email, meetings, or reports.

c. Key Metrics: The Key Metrics define the metrics that will be communicated to the stakeholders. This can include things like the CTQ metrics and the Process Control Charts.

Conclusion

Developing a Process Control Plan is a critical component of the control phase in the DMAIC process. It involves identifying the key process inputs and outputs, defining the Critical to Quality (CTQ) metrics, establishing the Process Control Limits, defining the Sampling Plan, developing the Process Control Charts, defining the Response Plan, developing the Contingency Plan, defining the Roles and Responsibilities, and establishing the Communication Plan. By effectively developing a Process Control Plan, organizations can ensure that their processes are under control and that the improvements made during the DMAIC process are sustained.