A trend chart, also known as a run chart, is a graphical representation of a data series over time. It is a powerful tool for quality control, process improvement, and project management. In the context of the Measure phase of DMAIC and lean six sigma, a trend chart is used to monitor and track the performance of a process or system over time. This article will explain how to create a trend chart, how to interpret the results, and how to use the chart to improve the process.

Creating a Trend Chart

The first step in creating a trend chart is to collect the data. The data can be collected manually or automatically, depending on the process being measured. Once the data has been collected, it should be organized into a time series, with the oldest data at the bottom and the most recent data at the top.

Next, the data should be plotted on a graph with time on the x-axis and the process variable on the y-axis. The process variable can be any measurable quantity, such as cycle time, defect rate, or customer satisfaction score. The chart should be labeled with a title, axis labels, and a legend if necessary.

Interpreting the Results

Once the trend chart has been created, it can be used to monitor and track the performance of the process. There are several key features of a trend chart that can be used to interpret the results.

First, the chart should be examined for any obvious patterns or trends. For example, is the process variable increasing, decreasing, or staying the same over time? Are there any seasonal or cyclical patterns in the data? These patterns can provide valuable insights into the process and help identify areas for improvement.

Second, the chart should be examined for any unusual or out-of-control points. These are data points that fall outside the normal range of variation and may indicate a problem with the process. Common types of out-of-control points include spikes, shifts, and trends. When an out-of-control point is detected, it is important to investigate the cause and take corrective action.

Finally, the chart should be used to calculate key performance indicators (KPIs) for the process. These can include averages, standard deviations, and other statistical measures. By tracking these KPIs over time, it is possible to monitor the performance of the process and identify opportunities for improvement.

Using the Trend Chart to Improve the Process

Once the trend chart has been created and the results have been interpreted, it can be used to improve the process. There are several key steps involved in this process.

First, the chart should be reviewed regularly to monitor the performance of the process. This can be done on a daily, weekly, or monthly basis, depending on the process being measured.

Second, any out-of-control points or unusual patterns should be investigated to identify the cause. This may involve collecting additional data, analyzing the process, or conducting experiments.

Third, corrective action should be taken to address the problem. This may involve changing the process, updating procedures, or training employees.

Fourth, the chart should be updated to reflect the new performance of the process. This will allow the team to monitor the effectiveness of the corrective action and ensure that the process is continuing to improve.

Fifth, the team should celebrate successes and recognize improvements. This will help maintain the motivation of the team and encourage them to continue to improve the process.

Case Study: Using a Trend Chart to Improve a Manufacturing Process

A manufacturer of automotive parts was experiencing a high defect rate in one of its production lines. The company decided to use a trend chart to monitor the defect rate over time and identify opportunities for improvement.

The company collected data on the defect rate for each shift and organized it into a time series. The data was plotted on a trend chart with time on the x-axis and the defect rate on the y-axis. The chart showed that the defect rate was highly variable and had several spikes and trends.

The company used the trend chart to identify several opportunities for improvement. First, they identified several shifts that had consistently high defect rates and began to investigate the causes. They found that one of the machines on the production line was not functioning properly and was causing defects. They replaced the machine and the defect rate immediately decreased.

Second, they identified several types of defects that were occurring more frequently than others. They began to investigate the causes of these defects and found that they were related to the training and skills of the operators. They implemented a training program for the operators and the defect rate for these types of defects decreased.

Finally, they used the trend chart to monitor the effectiveness of the corrective actions. The chart showed a steady decrease in the defect rate over time, indicating that the corrective actions were effective.

In this case, the trend chart was a valuable tool for improving the manufacturing process. It allowed the company to identify opportunities for improvement, investigate the causes of defects, and monitor the effectiveness of corrective actions. By using the trend chart to monitor the performance of the process, the company was able to reduce the defect rate and improve the quality of their products.

Conclusion

A trend chart is a valuable tool for monitoring and improving the performance of a process. It allows teams to track the performance of a process over time, identify trends and patterns, and monitor key performance indicators. By using a trend chart as part of the Measure phase of DMAIC and lean six sigma, teams can identify opportunities for improvement, investigate the causes of problems, and take corrective action. In addition, trend charts can be used to monitor the effectiveness of corrective actions and ensure that the process is continuing to improve.

When creating a trend chart, it is important to collect and organize the data, plot the data on a graph, and interpret the results. By examining the patterns, out-of-control points, and KPIs in the chart, teams can gain valuable insights into the process and identify opportunities for improvement.

In summary, a trend chart is a simple but powerful tool that can help teams improve the performance of a process. By using a trend chart as part of the Measure phase of DMAIC and lean six sigma, teams can monitor the performance of a process, identify opportunities for improvement, and take corrective action.