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Reduce defects with control plan and PFMEA

A control plan is a living document that helps you to set the plan to control the products you make and the processes used during the manufacturing of those products. Control plan involves the product and process description and characteristics which are important to ensure the quality of the final product.

All these characteristics are important part of PFMEA for the detection and prevention controls and that means these two documents have to be used together.  Due to the fact it is a supplement to the PFMEA and not a replacement, everything what is written in the control plan must be shown on the PFMEA. It explains the why and what of the process and product controls, whilst the control plan describes how they should be implemented, how often, how many and the action plans when needed.

For example, the molding process and injection the plastic for a simple transparent ruler. For the customer is important the overall size of the ruler. In case of the ruler is too small or too large, it will be defective. The PFMEA for the ruler will name all various failure modes with the effects of the failures and their causes. Also it will list the controls for prevention and detection.

Process and results

Prevention controls are focused on the process and detection controls are focused on the results of the process. In this example, the prevention control can be montoring of the machine setting and the detection control is measuring the size of the ruler.

The control plan should give more information about the product and process characteristics and connect the controls to the process and product itself. In our case the machine settings would be a process characteristic and the lenght of the ruler would be a product characteristic. The control plan includes the process and product specifications (e.g. shot size - 5 grams, ruler lenght - 30 centimeters), measurement techniques (machine display, calipers) and the sample sizes and inspection frequencies (once per shift, five pieces per hour).

In the control plan are included also the control methods (machine setting check sheet and statistical process control chart) and reaction plans. In reaction plans you should find the instructions and steps regarding how to react to a failure (quarantine the product since the last inspection and notify the supervisor).

The control plan gives detailed instructions to the employees about how to implement the controls defined in the PFMEA, ensuring alignment between the PFMEA, the shop floor and proper execution of the controls.

To save the money for the organization is controlling the process characteristics more important than controlling the product characteristics. This is how the control plan pairs with the PFMEA: They identify the prevention controls and implement them by monitoring the process itself.

In this example, if the relationships between the machine settings, other process inputs and the product characteristics were completely understood, any defective products could be avoided. This is a method how to reach zero defects and also the cost reduction.

Control plans, in conjunction with PFMEA, can be used to prevent problems and save organizations money by identifying prevention controls and ensuring their successful implementation.

 

Author: Jana Loskotova