Problem

When using an electric screwdriver to tighten bolts, the actual torque can overshoot the preset value—known as torque overshoot or over-torque. This risks stretching or breaking the bolt, degrading joint quality and increasing scrap and rework.

Root-Cause Analysis

All AC electric nutrunners on the market can exhibit torque overshoot; the phenomenon is not brand-specific. Two main factors drive it:

1. Joint stiffness (hard vs. soft)

• Hard joint: Target torque is reached within 30° after the seating point.

• Soft joint: Target torque is reached after ≥ 720° (2 turns) beyond the seating point.

• Neutral joint: Falls between the two.
  The stiffer the joint, the faster torque rises, making overshoot more likely.

2. Tool speed
   High nutrunner RPM shortens the reaction window for the controller to stop the motor, amplifying overshoot on hard joints.

Solutions

Address the issue from two angles:

1. Modify the joint (when design allows)
   Convert the joint toward a softer characteristic—e.g., longer clamp length, compliant gasket—to absorb energy more gradually and eliminate overshoot.

   
   

2. Optimize tool parameters (when joint cannot be changed)

• Reduce final tightening speed (RPM).

• Implement a two-step strategy: high speed to seating point, then low-speed “creep” to final torque.

• Adjust torque ramp slope for a softer approach.
  These parameter tweaks can be applied without lengthening cycle time, even on fast-paced production lines.