Difference between Process Capability & Process Performance

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Introduction

Here you will learn the difference between process capability and process performance.

This is short and easy learn guide for such topics,

Process Capability

  • It is the 6б Range of inherent process variation of process.
  • Indices:
    • Cp -Process Capability 
    • Cpk – Process Capability Index
  • Also in capability study the Standard deviation (б) is calculated by Range method: R̅/d2

  • Capability is to be calculated for statistically stable process only.
  • Only common cause present in the process. Special cause should not be present.
  • Capability is calculated when the data is collected by subgroup wise.
  • Process capability is used when the process is ongoing and in statistically control condition.
  • Process capability is used when the process is ongoing and in statistically control condition.

Process Performance

  • It is the 6б Range of total Process variation of process.
  • Indices:
    • Pp-Process Performance
    • Ppk – Process Performance Index
  • So in performance study the Standard deviation (б) is calculated by RMS method:
  • Performance is to be calculated for statistically stable or unstable process.
  • Process may present both common cause and special cause.
  • Performance is calculated when continuous data or subgroup data is collected.
  • Process performance is used when the new process, during initial development or not under statistical control.
  • Process performance is used when the process is new, during initial development or not under statistical control.

Finally, for the statistically control process, as we calculate both Process Capability and Performance. Then observed that both value are close to each other, to learn more about Statistical Process control.

After calculation, If the values of Process Capability (Cp) and Process Performance (Pp) are not close to each other, so more difference in both values indicate that the special cause is present in the process.