Yield Point
This strategy guides the operator in tightening a joint to its yield point.
Parameter | Description |
|---|---|
Required tag number | A specific number must be written in the TAG of the end fitting tool. |
Name | Name of the tightening program. |
Program start | Torque value from which the tightening operation starts. |
Torque min | Lower torque limit. |
Torque max | Higher torque limit. |
Maximum torque limit | If the torque applied reaches this limit, the message Change screw is shown on the wrench display. |
Target torque | The torque target. |
Trigger torque | Torque value from which the angle measurement starts (usually set to 50% of the Target torque). |
Angle min | Lower angle limit. |
Angle max | Higher angle limit. |
Target angle | Angle value (measured from the detected yield point) that the tightening operation must reach in order to stop. Target angle must be > 0. |
Torque units | This parameter is not editable. |
Angle limit for rehit | If the Torque min value is reached within the specified angle, the message Joint already tightened is shown on the wrench display. |
Stop condition | Select between Torque peak and Angle peak. |
Linear slope coefficient | Coefficient that defines the joint stiffness in the linear part of the curve. The coefficient is meant as torque/angle slope and it is measured in Nm/°. Default value: 0.5. Minimum value: 0.1 (also suitable for very soft joints with a ration less than 0.1). If the selected unit of measurement is different from Nm, the Linear slope coefficient must always be converted into Nm/°. |
Torque correction coefficient | When extensions are used, the wrench measurement might be compensated to show a more accurate torque value. To calculate the correction coefficient, please refer to How to calculate the Torque Correction Coefficient. When extensions are not used, Torque correction coefficient = 1. |
Angle correction | When extensions cause additional wrench bending, the wrench angle measurement can be compensated to show a more accurate angle value. When extensions are not used, Angle correction = 0. |
Batch size | Number of tightenings the batch will perform. |
Max consecutive NOK | Number of accepted consecutive NOK to have an OK result. |
End cycle time | Starts when the torque goes below the Program start after reaching the 3rd percentage. |
Ratchet time | Starts when the torque goes below the Program start without reaching the 3rd percentage value. This allows the operator to release the torque for a while and recharge during the tightening operation. |
A | Torque max | E | Angle min |
B | Torque min | F | Target angle |
C | Torque trigger | G | Angle max |
D | Program start | H | Yield point |
The Target angle is measured from the detected yield point, while the Angle min and the Angle max are measured from the Trigger torque.
Define the torque limits to get and OK result.
Torque results:
If the yield point is detected and Target angle (measured from the detected yield point) is reached, the torque result is taken at Target angle.
If the operator stops the tightening after the yield point but before reaching Target angle, the torque result is the maximum measured torque.
If the torque exceeds the Maximum torque limit value, the yield point is no longer detected and the torque result is the maximum measured torque.
During the tightening operation, LEDs, buzzer and vibration are activated as follows:
LEDs
LEDs:
White LED: activated when the torque value goes over the smartHEAD's Min load value.
First, second and third radial gradient LEDs turn green in sequence when the three thresholds defined for the tool in use are reached.
For further information, refer to Tool LEDs.All three radial gradient LEDs green: torque between Torque min and Torque max.
All three radial gradient LEDs red: torque over Torque max.
Buzzer:
The beep starts when the torque goes over the Program start value; the signal increases when the Target angle is reached after detecting the yield point.
Vibration:
Starts when the Target angle is reached after detecting the yield point.
At the end of the test operation, LEDs, buzzer and vibration are activated as follows:
LEDs:
LEDs behave according to the configuration of Result Indicator and Duration defined for the tool in use.
For further information, refer to Tool LEDs.
Buzzer
Two beeps indicate the end of the operation; if the final result is in the red area, the signal in continuous.
To stop the buzzer, start a new tightening operation or press a button on the tool controller.
Vibration:
Stays active until the torque applied is released.
In the configuration of the Yield Point strategy, there is one advanced parameter: the Linear slope coefficient. This coefficient defines the joint stiffness in the linear part of the curve. The coefficient is meant as torque/angle slope, and it is measured in Nm/°. The minimum value is 0.1, which suits also very soft joints with a ratio smaller than 0.1. The default value is 0.5.
The Linear slope coefficient can be calculated experimentally for each single joint (only after running a trial test to get data for calculating it) as follows:
= Linear slope coefficient
If the measuring unit selected for the operation is different from Nm, the Linear slope coefficient must be converted into Nm/°.
For instance, for a joint with a stiffness of 0.6 lbf*ft/°, since 1 lbf*ft = 1.3558 Nm, the Linear slope coefficient must be converted as follows:
0.6 lbf*ft/° → 0.6x1.3558 = 0.81 Nm/°
