Bringing a process under control

Process control charts identify special-causes of variation that need to eliminated to bring the process under control, so the results are predictable and can be used to determine the ability of a process to meet customer specifications.

  1. Open the file Copper.xlsx.

    The worksheet is open with some of the data hidden. We will use the additional hidden data later in this tutorial.

  2. On the Analyse-it ribbon tab, in the Statistical Analyses group, click Process Control, and then click Xbar-R.
    The analysis task pane opens.
  3. In the Process drop-down list, select Copper.
  4. In the Sample size group, select the Subgroup by identifier variable option.
  5. In the Id drop-down list, select Date.
  6. Click Calculate.
    The results are calculated and the analysis report opens.

During the installation period of a new automated colorimeter for controlling the copper content in the plating process control charts can be used to identify special-causes of variation that need to eliminated to make the process perform predictably. The Xbar and R charts plot the mean and range of the copper concentration in the plating pool respectively.

Xbar-R control chart(click to enlarge)
Inspecting the plots you can see special-cause variation is present in the process:
  • There is a point dated the 03/01 on the R chart with high variation.
  • There are 2 further points dated the 11/01 and 13/02 on the Xbar chart.