4S are mostly hand tools, operated by people, and the stability can not meet the consistency requirements of the machine. Tool matching: the tightening gun, sleeve, gun head and wrench are seriously worn, and it is estimated that they are still in use, and the 4S compression cost is very high. The car is assembled by assembly line, and the parts installed at each station are fixed, so the size of the wrench is completely matched with the screws. In this way, in the process of screwing the screw, the stress on the screw head is uniform and it is not easy to appear traces. In the production process of automobile factory, most screws are not tightened by hand. Most of them are made by robots. For the parts that need to be done manually, they use a sleeve with torque, as long as the specified force is reached. So there will be no common traces.

The tools used in the car factory are all equipped and the torque is calibrated! The trace left by the initial installation is very small, which will be different from the trace left by the subsequent disassembly! After the installation of the other screw, some screws were sealed by paint mist after passing through the painting workshop. There are two main tools used in automobile production line, one is electric torque wrench, and the other is servo motor torque wrench used for important safety components. The former controls the mechanical torque of the wrench, while the latter controls the rotational speed and torque of the wrench through the computer, even if the manipulator screws the screw. Therefore, the anti-corrosion coating needs to be repaired after the bolts are tightened, and some screws with torque requirements need to be marked with anti-loosening signs. So you can't see the traces of distortion.

There is no trace whether it is money or after painting, because the tools used are calibrated. The torque will not be too large or too small, and even the operators can only take up their posts through training. The factory uses torque wrenches and automatic air guns, not hand tools like screwdrivers or adjustable wrench that we usually see, but professional tools. When the tightening force reaches the set Newton, the inside of the tool begins to slide. When the car body is assembled in the welding workshop and then painted in the painting workshop, the paint will cover the screw marks. Naturally, there is no trace, but it is not absolutely invisible.