Production strategies

Production strategies can be divided into three main categories:

Tightening within torque limits: this is the easiest tightening method, it is enough applying torque within the limits.

Torque vs. Time
A
Upper torque limit

B
Nominal

C
Lower torque limit
Tightening within torque and angle limits: this is a more reliable way to tighten, because an additional information (angle) is used during the tightening process.

Torque vs. Angle
A
Upper torque limit

B
Nominal

C
Lower torque limit
D
Lower angle limit
E
Upper angle limit

Using this method, it is possible to detect potential problems on the joint (refer to the following examples):

Torque is correct, but angle is too small:

Misalignment problem
The hole is not completely threaded (or it is not deep enough)
The bolt is stopped by oil in a dead hole
There is dirt in the threads
The threads are damaged
The screw is already tightened

Angle is correct, but torque is too low:

The thread may be stripped out
The screw is too soft (tightened over yield)
Unexpected low µ (friction coefficient)

Tightening with torque and additional angle rotation (torque + angle): the bolt is first tightened to a certain torque and then it is further tightened to a specific angle. The goal is to stress the bolt over the yield point. Even with differences in the angle, the torque (causing clamping force) is quite reliable. Sometimes the joint is specially designed and the analysis of the joint helps making sure that strain is far away from the breaking point.

Torque vs. Angle

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