All design engineers are faced with questions like “What torque is the correct torque?” and “How do I know my assemblers are achieving the correct torque?”. When Bossard engineers hear these questions we typically respond by asking “What clamp load are you trying to achieve?”. When asked, engineers usually reply with confused expressions, or the unveiling of a torque chart from engineering manuals or colleagues. There is no doubt time and effort went into these torque charts, but how does the testing to create the chart relate to the application the engineer is working on?
Bossard’s biggest piece of advice is to test, test, test! The approach that yields the most success and maximizes the strength of fasteners is to test the application until failure. Until you know the point that the current fastener fails, you are throwing darts at your target clamp load. In some instances, friction varies from lot to lot and can affect the clamp load enough resulting in loose fasteners. Testing until failure helps you achieve a baseline average of total fastener strength. This baseline encompasses friction and is incontestable. The only thing left for the engineer to decide is the percentage of the baseline that is needed for the application. Typically, 75% of the failure torque is used for assembly but there are times in critical applications that fasteners are needed to be pushed further.
When investigating current torque strategies at your company don’t be afraid of torque charts. They can often be used as a great starting point. When a clamp load needs to be met to hold something together, challenge the tightening strategy and test it to prove its validity. You will never regret testing the actual application.
Have more questions about clamp load and proper torque? Reach out to Bossard at ProvenProductivity@bossard.com to receive personalized advice from one of our Application Engineers!