I. Choosing the right screw and matching the substrate to prevent slippage from the source
1. Select the appropriate screw according to the material type
Plastic parts (e.g., ABS, PP, PC): Use self-tapping screws with pointed tails or multi-threaded screws to reduce cutting force and prevent hole wall cracking.
Thin metal plates (e.g., steel plates, aluminum plates): Use self-tapping screws with thread forming, which rely on extrusion to form internal threads and improve connection strength.
Hard/thick metals: Use self-tapping screws with thread cutting edges at the end to reduce screwing resistance.
Scenarios where pre-drilling is not required: Use self-drilling self-tapping screws (drill-tail screws) directly, which integrate drilling and fastening functions.
2. Control the pre-drilled hole size
Too small a hole diameter → high screwing resistance, easy stripping; Too large a hole diameter → insufficient engagement. Recommended pilot hole diameter is 70%~90% of the screw's nominal diameter, adjusted according to material hardness.
Reference standard: GB/T GB/T 43655-2024 clearly specifies the bottom hole and torque parameters for different sheet metals.
3. Ensure sufficient engagement length
The effective number of thread engagement turns should be ≥ 3 turns; otherwise, shear force concentration can easily lead to stripping.
For light metals such as aluminum alloys, it is recommended to increase the thread hole depth to improve shear strength.
II. Scientifically set the tightening process to avoid "torque overload"
1. Reasonably set the target torque
Too high torque → stripping; too low torque → loosening
Target torque calculation formula (based on GB/T 43655-2024):
MA = Ms + k×(MO - Ms)
Where: MA is the target torque, Ms is the contact torque, MO is the breaking torque, and k takes a value of 0.3~0.5
2. Staged speed control (five-stage tightening strategy)
Using a smart electric screwdriver to perform the following steps significantly reduces the risk of stripping:
Cap recognition stage: Speed < 100 rpm, to prevent floating or misalignment
Thread recognition stage: 200~300 rpm, to avoid misalignment
High-speed screwing in: Plastic parts no more than 600 rpm, aluminum parts no more than 80% of the process speed
Fitting stage: Reduce to 100~200 rpm to ensure accurate fit
Final tightening stage: 10~50 rpm low-speed tightening to prevent torque overshoot
3. Avoid "torque overshoot"
During high-speed rotation, the tool has large inertia, and torque may continue to be applied even after power is cut off, which can easily cause stripping.
Solution: Use a servo electric screwdriver with angle monitoring and stripping detection functions to judge abnormalities in real time.
III. Standardized operation and tool selection to eliminate human error
1. Keep screwing in vertically
Tilted installation will cause the thread to be stressed on one side, with local stress exceeding the standard, causing thread breakage.
Make sure the screwdriver head and screw are coaxial to avoid skewing.
2. Select appropriate Tools
Disable pneumatic screwdrivers: Uncontrollable speed, prone to impact and stripping.
Recommended: Smart electric screwdrivers: Torque, speed, and angle can be set; data traceability is supported; suitable for precision assembly.
3. Avoid repeated disassembly and assembly.
Self-tapping screws in plastic generally only support up to 8 disassembly and assembly cycles. After repeated use, the threads are ineffective, and new parts should be replaced.
IV. Strengthen incoming material and process quality control
1. Inspect screw quality.
Threads should be complete, burr-free, without reverse taper, and without cracks. Major diameter, minor diameter, and pitch should conform to standards (e.g., GB/T). (845-2017) Moderate hardness to avoid brittle fracture or deformation.
2. Verify workpiece strength.
Manually test the breaking torque of key parts to confirm they can withstand the set assembly torque.
Compare with qualified benchmark parts and analyze differences (e.g., material, wall thickness, hole diameter).
3. Use anti-slip measures.
Use threadlocker (e.g., Loctite 243) at key connections.
Add spring washers or toothed washers to improve anti-loosening performance.
