The u-chart is a control chart that is used to monitor the number of defects in a process. A u-chart is a type of statistical control chart used in quality control. It is also known as a Defects per Unit Control Chart. It measures the number of defects or nonconformities in a process. The u-chart is designed specifically for defect monitoring when the number of units produced is not constant and the size of each unit varies. The u-chart provides a method for calculating the average number of defects per unit and determining whether the process is under control or needs to be improved. The u-chart, by tracking the number of defects over time, assists organizations in identifying patterns and trends and taking corrective action to improve their processes and reduce defects.
Example:
Assume a manufacturing company makes various sizes of wooden boxes. They want to keep track of the number of defects (such as cracks or knots in the wood) in each box produced. They can use a u-chart to accomplish this.
Here’s how it works:
For each production run, the company randomly selects a sample of boxes and counts the number of defects in each box.
For each sample, the average number of defects per box is calculated and plotted on the u-chart.
Control limits are calculated and plotted on a graph. These limits help determine whether the process is under control (producing boxes with an acceptable level of defects) or if it needs to be improved.
The company continues to collect data and plot the average number of defects per box on the u-chart. If the process is under control, the number of defects should be kept within acceptable limits. If the number of defects exceeds the control limits, the company can investigate and make improvements to its process.
Using a u-chart, the company can track the number of defects in their boxes over time and take corrective action to improve their process and reduce defects.
