What is Statistical Process Control?

Statistical Process Control (SPC) is a standardized method in industry used to effectively measure and control quality during production and manufacturing processes. This methodology was designed by industrial engineer William Shewart prior to World War II after he considered the notion that a production process could be in statistical control.

SPC was created partially in response to weapons facilities seeking an efficient way to monitor the quality of products. Due to its increased popularity and wide-spread usage in Japanese manufacturing companies following the war, SPC was adopted by American industry where it quickly gained acceptance as one of the most important tools of quality in many industries.

Quality data is collected in the form of readings from numerous machines or product and process measurements by hand or calibrated instruments. Upon successful collection of data, the results are used to monitor a process while evaluating and controlling the quality of products. This is done on a control chart with pre-determined control limits determined by process capability and specification limits determined by the needs of the customer.

Data that remains inside the control limits indicates that everything is operating according to quality standards. There are two types of variation in the data. One is common-cause variation which is normal in manufacturing processes and is expected as a natural part of the process.

The other is special-cause variation and this indicates that product variation is most likely due to an assignable cause such as a shift in the process, tool adjustments, machine damage or a change in the measurement system. If any special causes are identified, appropriate action is taken to return the process to a state of statistical process control.

Why is it important to our customers?

By following strict statistical procedures, Kamet’s SPC program is able to ensure the highest quality standards as an effective method to drive continuous improvement which brings value to the customer. In the midst of increasing competition and raw material costs, it is critical to abide by a program of continuous improvement in order to satisfy quality and efficiency standards while reducing costs in the process by producing better parts and reducing scrap.

The establishment of a robust SPC capability program means that quality is essentially built in to our products through process assurance. By addressing any special causes, trends or shifts in the process, we can assure we are producing parts that meet the customer’s requirements.

How can we use it internally to improve efficiencies?

Through process monitoring, operators are able to detect process changes and existing trends before they end up as non-conforming material. When an out-of-control process is detected, we immediately investigate the root cause and provide a corrective action to ensure that future production jobs are in statistical control. Instead of waiting for inspection to identify quality issues, we aim to use quality controls to prevent rather than react to vital quality issues. SPC allows us to uncover possible hidden factors in the process and instantly react to process changes in order to make decisions on the shop floor that affect overall efficiency and productivity through every step of the manufacturing process.