Articles

Today’s quality professionals are expected to improve quality while simultaneously reducing manufacturing costs. However, traditional SPC tools don’t provide clear insight into which process improvement efforts will bring the largest bottom-line savings. New SPC technologies are available that uncover, measure, and prioritize improvement efforts based on which processes have the potential for greatest cost reduction.

TRADITIONAL PROCESS IMPROVEMENT ANALYSIS

A longstanding practice in the quality field is to rely upon two capability indices – Cpk and Cp – to prioritize process improvement activities. Figure 1 (right) shows a report that ranks variables of three separate parts from lowest to highest Cpk and calculates the difference between the Cp and Cpk – a difference indicating that a process is off target and that a process shift could improve process capability. The report highlights those cases where the lowest Cpk and/or largest differential between Cp and Cpk indicate variability or off-target data. Based on this approach alone, one would most likely focus efforts on the processes that influence the width, length, and hardness variables.

COST-BASED PROCESS IMPROVEMENT ANALYSIS

The traditional analysis, however, does not give quality teams any information regarding the cost savings that could come from improving those processes. This is significant because the amount of savings obtained from changing a process’ capability differs depending upon the expense involved in scrapping or reworking the parts, or the varying cost of the product materials or ingredients. In order to prioritize optimization activities based on potential savings, the material and production costs must be included in the analysis. Adding this cost information empowers quality professionals to prioritize and report on the twin executive goals of quality improvement and cost reduction.

WinSPC software’s new Cost Inspector™ provides an intuitive way to integrate cost with capability to calculate savings from process improvement. Figure 2 shows the Cost Inspector visualization of the fill weight variable listed in Figure 1. The cost of product give-away and the current data distribution are used to determine the optimal mean – that is, the target value that will produce the greatest savings. The Cost Inspector quantifies the amount saved by shifting the process to optimal, as well as the savings possible from reducing variability in the process.

PRIORITIZE AND REPORT BASED ON SAVINGS

By integrating cost information with process capability analysis, a new way to prioritize and report on process improvement becomes possible. The report in Figure 3, created using a standard template in WinSPC, evaluates the same parts and variables as in Figure 1, but ranks them based on potential cost reduction. The report highlights the cost savings potential of shifting each process to optimal and reducing variation. Using this cost-based approach, different priorities emerge. The report reveals that the single greatest cost savings does not come from altering the processes impacting length, width or height, but from shifting the process affecting fill weight – a variable that wasn’t flagged for attention using traditional capability measures. And once the job of improving the targeted process is complete, reporting on the project’s success won’t be based upon Cpk alone. This new approach enables quality professionals to provide outcome reports to executives in terms that everyone appreciates: dollars saved.