Ensure Your Process Reaches Its Full Potential With SPC

For a process to be successful, variation must be controlled, and deviations must be corrected appropriately. The consequences of failing to react (or overreacting) to a deviation can result in a defect or waste, causing your process to be unsuccessful and likely costing you time and money, as well. 

To ensure that your product meets customer needs and delivers the desired results, you need a means of monitoring and controlling the process. Statistical Process Control (SPC) is an effective quality control method designed to ensure the process at hand operates at its peak. To better understand how SPC coincides with Six Sigma, we’ll take a look at its history, purposes, benefits, and tools of implementation.

Defining Statistical Process Control 

SPC is a means to measure and control quality for manufacturing processes. Data regarding quality is tracked during the manufacturing process alongside control limits. Control limits are defined by the voice of the process and past performance. 

The purpose of control limits is to facilitate the identification of variations. Some minor variation may be acceptable if it falls within the control limits. Otherwise, it likely points to a quality issue and possible defect. 

How SPC Came to Be

SPC as we know it today took shape in the early 20th century. Dr. Walter Shewhart first worked with the concepts in the 1920s and developed the control chart at this time. The chart was developed in response to two common sources of variation: Common Cause and Special Cause. Common Cause can also be defined as stable chance or fluctuation and is the result of unknown factors. Special Cause variation is the result of specific factors and is unstable in nature. Control charts provided for the plotting of data related to variation as well as the identification of Common Cause and Special Cause variation. 

Control charts enjoyed a huge wave of popularity during World War II. Quality and stabilization were of the utmost importance for the manufacturing of military weapons and ammunition. After WWII, Dr. W. Edwards Deming furthered developed SPC and promoted Shewart’s ideas. A champion of continual improvement, Deming is credited with introducing the modern day concept of SPC to Japan in 1950 while visiting the country to deliver a speech on statistical product administration. The control chart later became an integral part of Japan’s manufacturing industry. 

Today, SPC and its related techniques are core components of Six Sigma. As a tool, SPC facilitates the reduction of variation and augmentation of quality. What has made SPC such a success for industries across the world is its ability to be implemented in real-time. Process owners must track data while the process is taking place to avoid excessive variation and defects. Steps can be taken immediately to correct any causes of failure. SPC is commonly used in the food and tech industries. 

Interested in learning more about Statistical Process Control? Check out NWCPE’s two-day workshop , which provides participants with an intuitive understanding of SPC theory and practical knowledge regarding control chart mechanics. 

The Benefits of SPC for Process Owners

SPC has benefits to offer any individual who works with processes.  It provides an appropriate means to determine the stability and success of processes. A stable and successful process delivers a product that satisfies customers time and time again. 

SPC can also be used to: 

• Determine the cause of failure
• Take action to correct causes of failure
• Control processes in real-time
• Determine the stability of processes
• Identify sources of variation
• Ensure the success of quality improvement efforts

To reap the most benefits of SPC, take special care during data collection. Any data which will help monitor the process should be collected. The overall objective is to gather data which will confirm the stability and success of the process in question. The measurement process can then be determined and affirmed. 

Become a master of measurement, control, and quality by earning your Six Sigma Belt . NWPCE offers certifications for Yellow, Green, and Black Belts as well as personalized consulting services. 

Control Charts: The Essential Tool for SPC Implementation

The control chart is the right-hand man of SPC as it allows for the study of process development over time. It is also one of the seven essential tools for quality control, the other six being:

• The cause and effect diagram
• The check sheet
• The histogram
• The pareto chart
• The scatter diagram
• The stratification technique

Every control chart should include control limits, performance data, and a center line (the average of plotted samples. Before using the control chart, you must also identify the best time period to gather and plot related data. 

With the control chart, you should be able to monitor the process’s capability and maintain overall control with data and control limits. 

While we often think of control charts as a tool for identifying when to take action, they also help us to determine when it’s best to maintain a hands-off approach. Too much corrective action and over adjustment can be seen as a form of waste when it does not address the cause of failure. 

The Plan-Do-Check-Act Cycle (PDCA), or Deming Cycle,  can also be used in conjunction with SPC. This cycle is used during the change management process. PDCA is defined as follows:

• Plan the change
• Do and test the change
• Check the results
• Act based on the results

As with the control chart, the PDCA cycle highlights the importance of taking a measured approach to corrective action and adjustments. 

To discover the way to continual improvement through Six Sigma, check out our recent article, “ How to Foster Continual Improvement with the PDCA Cycle .”