What are the common faults of automobile terminals?

What are the common faults of automobile terminals?

Poor contact of connector, short circuit between wires, open circuit, grounding, etc.

The causes are as follows:

1) Natural damage

The use of the wire harness has exceeded the service life, aging the wire, cracking the insulation layer, and significantly reducing the mechanical strength, resulting in short circuit, open circuit and grounding between the wires, resulting in burning out of the wire harness.

2) Damage to wire harness due to failure of electrical equipment

In case of overload, short circuit, grounding and other faults of electrical equipment, the wire harness may be damaged.

3) Human fault

When assembling or overhauling auto parts, metal objects crush the wire harness and break the insulation layer of the wire harness; The positive and negative leads of the battery are connected reversely; When repairing circuit faults, disorderly connecting and cutting wire bundles and wires can cause abnormal operation of electrical equipment.
automoblie terminal harness
The terminal crimping area usually refers to the area contained in the terminal material. If there is a gap, the area of the gap must be included. Whether the terminal crimping area is qualified mainly depends on two aspects: one is to calculate the compression ratio and the other is to calculate the compression ratio. Compression ratio: the compression ratio of terminal crimping area can be divided into three categories according to the industry, the first is automobile, the second is household appliances, and the third is electronics. Among them, the automotive standard is the most stringent, which needs to be controlled at 80% to 90%, that is, if the area of all copper wires of the terminal is expressed as 1, the area after crimping must be between 0.8 and 0.9. If the area after crimping is greater than 1, it means that the remaining area in the crimping area except 1 is the area of the gap. The standard compression ratio of household appliances is 70% to 90%, and that of electronics is usually controlled at about 85%, with a minimum of 70% and a maximum of 90%.

Compression ratio: the general compression ratio is between 15% and 20%. The crimping quality depends on the amount of compression, which is controlled by the crimping tool and the size of crimping pin and conductor section. Therefore, it is very important that the cross-sectional area of conductor used in mass production of terminal wire is the same as that used in crimping design confirmation. The verification of compression during mass production of terminal wires is verified by crimping samples with terminals, wires and crimping tools.
The detection of such standards needs to pass the terminal section analyzer.

Common terminal crimping standards include national standard QC / T 29106 technical conditions for automobile low voltage wire harness, American Automobile standard uscar 21 and Volkswagen standard VW 60330.

1、 QCT 29106-2014 technical conditions for automobile wire harness

The current domestic automobile harness standards are mainly QCT 29106-2014 technical conditions for automobile wire harness and enterprise standards of various enterprises. The test items probably include: inspection of crimping quality of terminal and wire or wire contact, waterproof performance of contact, high and low temperature resistance, damp and heat resistance, salt spray resistance and vibration resistance of harness. But this does not explain the compression ratio or compression ratio, only the section.

2、 Uscar 21 (2014)

Uscar 21 uses the compression ratio (Note: This is not the compression ratio).

Compression ratio: the reduction of cross-sectional area caused by crimping of terminals and wires.

Uscar 21 states:
When developing the crimping process, the first step to determine the core components and variables is to collect the terminal, crimping parts, conductor size, including (but not limited to) the following data. These crimping parameters will be limited by conductor parameters, terminal and crimping configuration.

• terminal wall thickness
• crimp wing length and width
• crimp wing features (stiffeners, guest slots, prints, etc.)
• alloy toughness and hardness (yield strength)
• coating type of crimping wing (tin, silver, etc.)
• number of single wires
• diameter of single (copper) wire
• core wire coating
• core wire alloy and elongation (copper, cold drawn copper, tempered copper, etc.)
• internal dimensions of crimped parts
O top arc radius
O top arc center distance
O inclination of guide surface
O cutting arc radius
O cutting width
O undercut platform
O hardness, polishing, plating, etc. of blade parts
1. The appropriate crimping size can be estimated through compression ratio analysis. The compression ratio can be calculated by a simple ratio from the (area) data obtained by finite element analysis or other methods. The compression ratio is 100 times 1 minus the ratio of the blade cavity area after crimping to the sum of the cross-sectional areas of terminals and wires before crimping.
Compression ratio% = 100 * (1-T / (at + AC))
T = area retained when crimping blade is closed
At = sectional area of terminal
AC = sectional area of conductor
Formula - Compressibility calculation formula
2. The compression ratio of good core wire and terminal starts from 15% to 20%. This standard requires that the continuous crimping height of three gears pass the electrical and mechanical performance test. Samples within this compression ratio range pass these tests most easily.
3. The crimping quality is related to the compression rate and is affected by the size of crimping blade, terminal wing and conductor cross-sectional area. Therefore, it is very important to record the cross-sectional area actually used by the conductor and make it consistent with the cross-sectional area used in the design of crimping verification. In the actual process, the compression ratio is affected by the size of the terminal, wire and crimping blade (usually represented by the blade number).
4. Other useful information can be calculated by the same calculation method, including the shape proportion of crimping and the clearance of blade. Crimping according to this compression ratio range will cause the terminal to bend slightly upward in core crimping, and this effect should be offset by the action of crimping die to ensure good connector matching. The product engineer of the harness supplier shall determine the (allowable) maximum terminal bending angle and torsion angle.
3、 VW 60300 (2013 Edition)
VW 60300 uses the compression ratio, which is specified by the change of strand cross-sectional area.
VW 60330 reads as follows:
Compression ratio
The degree of compression (compression ratio) can only be determined using microsections.
The manufacturer of contact elements (terminals) shall ensure good compressibility when observing the specified crimping dimensions. Good compression ratio is characterized by a fully filled crimping sleeve, in which the strands in the crimping area shall be fully compressed in a honeycomb structure.