FASTENER QUALITY MEASURED IN PPM
How do you report your internal or external reject rate? Chances are you use a metric called PPM or Parts Per Million. In other words, PPM is a measurement of number of rejected parts for every one-million parts produced (internal metric) or shipped (external metric). By stating reject rate in terms of a generally accepted ratio you can compare your performance across your suppliers, customers, and internally using a common measurement. PPM is an automotive methodology that has carried into most industries as a generally accepted method of measuring reject rate.
To add perspective, if your unit of measurement was distance, a reject rate of 1 PPM, or part-per-million, means you had a reject of one inch for every 16 miles produced. Put in terms of time, 1 PPM rejected means you had a reject of one second every 12 days. These are small amounts of rejects. You may have been told by a supplier that their reject rate is less than one percent. Pretty good, right? Well 1% rejects equal 10,000 PPM. Conversely, 1 PPM equal .0001%. These numbers are pretty big, or pretty small depending on your perspective.
In the world of high-volume fastener production and distribution, the industry acceptable reject rate is 200 PPM. This means a customer can expect a 200 PPM reject rate or better with fasteners made with normal methods of high-volume production, which includes heading, threading, heat treatment, coating, and packaging. Most customer applications can accommodate 200 PPM without a problem. In terms of real numbers, a shipment of 250,000 screws may have up to 50 defects, and this is normal.
Sometimes customer’s applications require “zero defects” with fasteners due to a critical application or highly automated assembly process. This is achievable in high volume fastener production by adding an optical sorting process as the last operation prior to packaging. Optical sorting uses digital cameras to 100% inspect each fastener at a high speed for the important characteristics as defined by the customer. The good news is optical sorting will result in a normal PPM of 20 or better, which is considered zero defect. The bad news is that optical sorting costs extra. The actual cost depends on your supplier.
PPM is not a good method for measuring reject rate if the total amount produce is low. For example, if you produce 1,000 pieces per year of a specialty item and you tried to measure your reject performance in terms of PPM, one reject results in 1,000 PPM. A big number that does not give an accurate feel for your reject rate. One bad part per year and PPM is blown out of the water. So, the best use of PPM for measuring and comparing reject rates is for high volume production or distribution.
FIELD FASTENER PPM PERFORMANCE
In 2022 Field Fastener achieved an excellent external reject rate of 161 PPM. Here is the math on this: Field Fastener shipped 1.7 billion parts to its customers in 2022. Field’s customers rejected 278 k parts. Field manages tens of thousands of parts sourced from a thousand suppliers and shipped to over 750 customers. We use our robust systems and processes to minimize the effects of these many variables to deliver part quality our customers can count on.
Even more impressive, Field shipped an automotive customer over 20 million parts in 2022 with a total of 13 parts rejected. This calculates to a PPM of <1. This amazing quality level was achieved by controlled manufacturing processes, high quality suppliers, and optical sorting. This goes to prove that “zero defect” is achievable if you put the appropriate controls in place.
To learn more about Field Fastener’s approach to fastener quality metrics contact us today!
We would love to discuss this or any other fastener topic with you.
"Quality is never an unintentional outcome. It requires focus and effort in the development and monitoring of your processes. One of the ways we achieve high quality in our products is by leaning on suppliers that share that same philosophy. Defective Parts Per Million (DPPM) is one of the metrics we measure performance by in our supply base. In 2022, Field Fasteners not only met our expectations, but exceeded them with a performance level of 43 DPPM while providing us over 15 million parts. Thanks for the fantastic year!"
Sr. Director, Supplier Development
Leading Rail Car Manufacturer