During the process of tightening bolts with an electric screwdriver, it is sometimes found that the torque applied to the bolt exceeds the set value significantly (over-torque), causing a torque overshoot problem. This torque overshoot may lead to bolts being stretched or even broken, affecting the quality of the tightening, increasing costs, and resulting in rework and waste. The main reasons for bolt tightening torque overshoot are the following two: first, whether the bolt joint has hard joint characteristics, and second, whether the rotational speed of the electric screwdriver is too high.

Analysis of the Causes of Excessive Torque

Currently, AC electric screwdrivers on the market all face the issue of torque overshoot during the tightening process, regardless of the brand. Other influencing factors are involved. Bolt joints can be categorized into hard joints and soft joints. A hard joint is one where the bolt or nut reaches the target torque within 30° of rotation after contact; a soft joint is one where the bolt or nut requires more than 2 full rotations (720°) to reach the target torque after contact. Joints that fall between these two are referred to as neutral joints.

Torque overshoot refers to the actual torque applied to the bolt exceeding the preset value, also known as over-torque. This problem is mainly influenced by the hardness of the joint and the rotational speed of the electric screwdriver. The harder the joint and the faster the tightening speed, the more likely torque overshoot will occur.

Solutions to the Problem of Excessive Torque

To address the issue of torque overshoot when using an electric screwdriver to quickly tighten hard joints, solutions must be implemented from two aspects: changing the hard characteristics of the bolt joint itself, and optimizing the program parameters of the electric screwdriver.

• Regarding the hard joint characteristics, one can modify the joint to be softer, thereby avoiding torque overshoot when using an electric screwdriver.

• If the joint must remain hard, reducing the tightening speed and torque without changing its characteristics can effectively solve the torque overshoot problem. This is especially useful in fast-paced production lines where cycle time cannot be compromised.