How do you audit a joint?

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At the end of a fastening process, it is important to be sure that the right amount of torque was left on the joint. Too much torque could weaken the structure of a joint, resulting in a fastener failure. Too little torque could make the joint come loose.

During the prototyping phase of a new product, auditing joints helps manufacturers fine tune the production process to deliver the best torque on their joints. Also during the production process, joint audits confirm the quality of the tightened joints.

Traditionally, this process was implemented with click wrenches to confirm that each joint had the minimum amount of torque required. This type of audit has a couple of problems. First, there is no way to know if a joint is over-torqued. Click wrenches would click when a minimum torque level is reached, but we cannot set an upper bound for torque. Also, we have no traceability. No torque value can be read from a click wrench, so no statistical evaluations can be done on the torque installed on the joints.

One way to overcome these issues is to use a dial indicating wrench or, even better, an electronic wrench that reads the peak torque. This is valuable information because we can know if the quality operator has over-torqued the joint. At the same time, it is not really telling us much about the amount of torque that was installed on the joint (or residual torque). If quality operators would be able to stop pulling the wrench as soon as the fasteners starts moving, they would read the residual torque of the joint. The problem here is that each operator has a different reaction time, so this auditing process would be completely operator-dependent.

The Atlas Copco STwrench has a patented algorithm that analyses in real time the joint behavior during a joint audit. The wrench vibrates when a residual torque point is detected in order to tell the operator to stop pulling. It reports both the residual torque point and the peak torque, so that manufactures can know how much torque was installed on their joints and be sure that the quality operators didn’t over-torque the joints. The STwrench makes the joint audit process completely error-proofed.

For more information or to request a demo, please visit our contact page to speak with a product expert.