How to implement SPC? | SPC Cycle


All are too confuse about the concept of Statistical process control (SPC) or how to perform the SPC, therefore here we take the look on SPC implementation through some steps. Here we discuss How to implement SPC? | SPC cycle.

Please refer below figure for better understanding of the SPC cycle, and further the same will be discussed in detail…

Steps-1: Measurement System

SPC implementation starts with the step of measurement system.

The collection of operations, procedures, gauges and other equipment, and person used to assign measure characteristics so the complete process is to obtain data by measurement is called the measurement system. First of all We have to define the measurement system for the collection of data. For deciding measuring instrument you should follow 1/10th Rule.

Step-2: Perform MSA

In this step we have to verify that our measurement system is acceptable or not. Therefore to verify the error in the measurement system we perform the Measurement system analysis (MSA) study. If data is variable then we have to perform the Gauge R & R study to Identify that error in our measurement system is acceptable or not.

Step-3: Take actions if error not acceptable

Take action base on the results we are getting from our Gauge R&R study

  • When repeatability is large compare to reproducibility
    • Instrument need maintenance
    • Redesign Gage for more rigidity
    • Improve location / clamping of gauging
    • Excessive within part variation
  • When reproducibility is large compare to repeatability
    • Training need to operator for better Gage measurement
    • Incremental division on instrument are not readable
    • Need fixture to provide consistency in Gage use.

If the measurement system is acceptable then further step applies.

Step-4: Data collection

Define strategy on Sample size, how many sample you have to check at define frequency. Select the sample size for inspection and subgroup wise data.

Step-5: Reaction Plan

Prepare and document the reaction plan for the abnormal data, and process correction. If the data found abnormal, which is out of specification, out of control then take action to control the data within specification and make process stable.

Step-6: Run chart

Use the run chart for data recording so that we can measure and verify our data for the ongoing process.

Step-7: Control plan and SOP

Make the standard operating procedure for how data is to be collected, Who collect data, Frequency for inspection, sampling plan, chart location etc. and document the same in control plan.


Calculate the control limit from chart data and monitored the process in control.


Verify the process is in control or not, interpret the process with the hep of data which is been collected.


Analyze the data to identify the source of variation and take action to correct. If process is not in control means the special cause is present in the process.


Define and implement the action for eliminating the root cause of special cause variation, and bring the process in control.

Step-12: Process Capability (Cp & Cpk)

Calculate the Process Capability (Cp & Cpk), so that we verify that

  • How good is the process
  • Is the process capable of meeting the specification
  • How to analyze the process


Interpret that the process capability (Cp & Cpk) is greater than 2, because if the process capability is greater than 2 then it is the Six sigma process.


If the Process capability is less than 2, then we have to identify the common cause present in the process and try to reduce the common cause variation by taking actions through project and management strategy, so that the process is capable.


If your process capability is >2, then the process is capable and only monitored the process further. Next focus on the other priority process.

The complete steps in SPC implementation cycle is covered. You can read the blog of AIAG.

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