Crimping Quality Inspection of Connecting Wire Harness Terminals

This article mainly introduces the technical requirements, diagrams and test methods for terminal crimping quality, as well as graphic and text standards. It is recommended to bookmark the YAXUN wiring harness engineer website.

Conductor Crimping of Wire Harness Terminals:
Terminal crimping bell mouth: There are bell mouths at both ends of the conductor crimping area or near the end of the insulation. The length is between 0.1mm~1/5 the length of the crimping area.
Wire core fixation: All wire cores (conductors) are stored in the conductor crimping area. The wire core breakage meets the following criteria: no breakage for ≤20 cores, less than 5% for >20 cores, and no cores flying out.

Conductor crimping technology for wire harness terminals

The front core of the wire harness is exposed: the end of the wire core can be seen at the front of the conductor crimping area. The exposed length of the front core is between 0.5~1.5mm and does not affect the terminal fit.
Note: Not available with flag terminals.
Conductor crimping: The conductor crimping area is neatly crimped, and there are no problems such as core exposure or damage in the middle seam. Curl claw misalignment ≤0.3mn.

Insulation crimping technology for wire harness terminals

Insulation crimping of wire harness terminals
Insulation skin length: The insulation skin and wire core can be seen between the insulation crimping area and the conductor crimping area, and the insulation skin length is >1/3c~≤1C. Note: If the insulation length = 1C and it is in contact with the conductor crimping area, the wire core can be observed by pushing back the end of the insulation.

Insulation crimping: The insulation crimping area and the insulation skin match well, without deformation, and the curl claw misalignment is ≤0.3mm.

Technical requirements for front and rear burrs of crimped wiring harness terminals

Terminal deformation:
The terminal is bent upward and downward: the terminal mating area and the crimping area are straight, and the bending angle is ≤3°.
The terminal is bent left and right: the terminal mating area is aligned with the central axis of the crimping area, and the deviation angle is ≤5°.
Twist: The center seam of the insulation crimp is aligned with the axis of the conductor crimp, and the degree of twist should be ≤5°.

For the insulation bending fixed terminal, at a distance of 50mm from the conductor crimping area, perform an insulation bending test for five cycles (bending 45° → bending 90° in the opposite direction → reset, as one cycle) according to Figure 3. No pulling force is exerted on the lead during the test. After the test, the insulation crimping was good and the insulation skin did not come out from the insulation crimping area.
(2) Insulation crimping section
(3) Measurement method of crimping height and width: crimping width is measured with a caliper (accuracy: 1/100); crimping height is measured with a crimping height micrometer (accuracy: 1/1000), as shown in Figure 5.

Deformation problem of crimped wiring harness terminals

(4) Profile analysis method
• Use special cutting equipment to cut the conductor crimping area and insulation crimping area respectively according to Figure 6. When cutting, cut vertically and longitudinally in the middle of the crimping area, and avoid the grooves (reinforcing ribs) in the conductor crimping area.
• The cut section should be flat and without deformation, and the curl should not be opened.
• After cutting, polish the section to remove burrs. When polishing, be careful not to damage the section (such as curling, cracking, etc.).
• The polished section is coated with ferric chloride solution (content: 35%-45%) to clearly display the outline of the wire core and terminal wall.
• Use an electron microscope and calibrated profile analysis software to analyze and measure the relevant parameters of the profile.
Note: If the terminal is difficult to fix or cut, and problems such as cross-sectional deformation or curling occur during polishing, the terminal can be solidified in resin before polishing.

Insulation crimp profile requirements for crimped wiring harness terminals

(2) Tensile test method
• According to the test method in Figure 7, release the insulation crimping, remove the insulation about 200mm away from the conductor crimping area, and reversely weld the conductor end to the conductor to form a stretch ring.
• After fixing the terminal with a special clamp and keeping the lead and conductor crimping area in a straight state, conduct a tensile test on the tension ring.
• Explosive force should not be used during the test. The test can be carried out by a tensile testing machine, and the moving speed of the machine head is between 25-50mm/min. During the test, observe and record the maximum tensile force value of the conductor, which should comply with the regulations of its wire diameter.
• Double-wire compression should be tested on each conductor one by one.

Tensile strength requirements for crimped wiring harness terminals