In industrial assembly, bolt tightening is a common operation, but the technical depth behind it goes far beyond imagination. Especially when dealing with different joint characteristics, the choice of tightening strategy is crucial. Compared to rigid joints, "soft joints" made of plastics, composite materials, and thin-walled sheet metals present more diverse and challenging defects that directly affect product reliability, safety, and service life.

Three Core Defects and Challenges in Soft Joint Tightening

Due to their inherent characteristics, soft joint materials introduce unique uncertainties during bolt tightening. The main defect impacts are manifested in three aspects:

1. Material "Collapse" Leading to Premature Torque Decay

When tightening plastic parts or certain composite materials, the most obvious problem is "unable to reach target torque." This occurs because after the bolt head or nut contacts the workpiece, the continued rotation is not entirely converted into bolt elongation (i.e., clamping force), but partially used to compress the soft material itself. Once the applied force exceeds the material's rigidity limit, the material undergoes plastic deformation or even "collapse." At this point, although the torque meets the standard, the actual clamping force is far below the design value, creating a "false torque" phenomenon with weak connection.

2. Potential Risks in Sheet Metal Parts

To fully utilize bolt strength, modern assembly processes often use the "yield tightening method" (i.e., torque-angle method), stretching the bolt to its yield point to obtain maximum and stable clamping force. However, when tightening soft joints like sheet metals, this efficient process may fail. Because the stiffness of sheet metal is much lower than high-strength bolts, before the bolt reaches its yield point, the clamped sheet metal may already experience permanent indentation or deformation. This not only fails to achieve the expected clamping force but may also damage the structural integrity of the connected parts.

3. Torque Decay Caused by Material Creep

Another "invisible killer" in soft joint tightening is material creep. Even if the ideal clamping force is achieved at the moment of assembly, under continuous stress, plastics or composite materials will slowly deform over time (creep). This deformation reduces bolt elongation, causing clamping force to decrease - known as "torque decay." This decay is dynamic and may worsen during vehicle operation, equipment vibration, or temperature changes, ultimately leading to connection loosening, abnormal noise, or even failure.

In summary, the core of soft joint tightening problems is ultimately "how to ensure long-term stable residual torque (clamping force)." Traditional torque control methods can no longer cope with these complex challenges.

Facing the diversity of soft joints, the advantage of intelligent tightening systems lies in their focus not just on the "final torque" point, but on monitoring the entire tightening process curve and dynamically adjusting strategies to ensure result reliability.

Core Solution: Diverse Tightening Strategies to Ensure Residual Torque

Torque-Angle Monitoring Method: The Golden Rule for Soft Joints

This is the most commonly used and effective strategy for dealing with soft joints. The system first applies a lower initial torque to snug the bolt to the workpiece surface, eliminating gaps. Then, it drives the bolt to rotate a preset angle.

Advantages: This method directly controls the bolt elongation, which is directly related to clamping force. It effectively avoids the influence of material stiffness differences on torque readings. Regardless of material compression, the bolt elongation is determined, thus ensuring consistent clamping force. Smart tools simultaneously monitor torque values during this process as auxiliary quality judgment. If torque is abnormally high or low, it is judged as faulty.

The tightening defects of soft joints expose the limitations of traditional torque methods. In an era pursuing lightweight and wide application of new materials, the key to ensuring connection reliability has shifted from controlling the process parameter of "torque" to ensuring the final result of "residual torque/clamping force."

Through process monitoring, data analysis, and dynamic adjustment capabilities, smart tightening tools upgrade tightening from a simple "operation" to a traceable, optimizable, and predictable "intelligent assembly."