As a core component of the automotive electrical system, the terminal crimping quality of the vehicle wiring harness directly affects the stability and safety of the vehicle's electrical connections. During production, terminal crimping requires multi-dimensional testing and strict control to ensure a secure mechanical connection and reliable electrical performance. The following analysis focuses on three aspects: testing methods, process control, and defect prevention.
Visual inspection is the first hurdle in controlling terminal crimping quality. Visually inspecting the crimped area or using a magnifying glass, it must be ensured that the terminal completely covers the wire insulation and conductor, with no excessive conductor exposure or uncovered insulation. The terminal surface should be free of cracks, deformation, rust, or plating peeling; the plating should be uniform and continuous. The insulation layer should be free of damage, scratches, or deformation caused by excessive compression, and should fit tightly against the crimped area without significant gaps. Furthermore, the crimped area should have a regular geometric shape, such as a circle or hexagon, without twisting, skewing, or asymmetry. These details directly reflect the standardization of the crimping process; any visual defects may lead to poor contact or insufficient mechanical strength.
Dimensional accuracy is a core indicator of terminal crimping quality. The crimping height and width must be measured using a dedicated gauge or projector, with errors typically controlled within ±0.1mm. The conductor extending from the terminal tail should be uniform in length, generally 0.8-1.2mm; excessive length may cause a short circuit, while insufficient length may result in poor contact. The conductor must be centered in the terminal crimping groove, with an offset not exceeding 10% of the terminal width to avoid eccentric crimping and insufficient contact area. The insulation layer must be pressed into the terminal's insulation crimping area, with a pressing depth covering at least 80% of the insulation crimping area to ensure reliable mechanical fixation. Strict control of these dimensional parameters is fundamental to ensuring crimping strength and electrical performance.
Electrical performance testing is a crucial step in verifying terminal crimping quality. For different conductor specifications, crimping resistance or voltage drop tests are required. For conductors of 6 square millimeters and below, the resistance between the terminal and conductor is measured using a dry resistance test method, and the resistance of the reference sample must be subtracted to calculate the actual crimping resistance. For conductors larger than 6 square millimeters, a voltage drop test is performed, measuring the voltage drop at the crimping point under a specific current. These tests accurately reflect the contact resistance of the crimped joint. Excessive resistance can lead to overheating or even ablation, severely affecting the stability of the electrical system.
Tension testing is a direct means of evaluating the mechanical strength of terminal crimps. Using specialized equipment, a tensile force is applied along the axial direction of the conductor to detect the separation force between the terminal and the conductor. Different conductor specifications correspond to different tensile force standards, generally requiring a minimum of 50N to ensure reliable connection under vehicle vibration or external forces. Tensile testing not only verifies the robustness of the crimping process but also identifies potential material defects or process problems, such as terminal cracks or conductor detachment.
Cross-sectional analysis is the ultimate method for in-depth evaluation of crimp quality. Crimped cross-sectional samples are prepared through cutting, polishing, and staining, and the microstructure of the crimped joint is observed using an electron microscope. Key parameters tested include crimp height, width, support angle, and burr height to ensure compliance with design requirements. For example, the maximum angle between the conductor crimp tangent and the vertical line should not exceed 30°, the support height should be greater than or equal to 1/4 of the material thickness, and the burr height should be less than or equal to one terminal material thickness. Cross-sectional analysis can detect defects invisible to the naked eye, such as incompletely closed crimping flanges and thinning of the bottom material, providing a basis for process improvement.
Process control and defect prevention are fundamental to ensuring terminal crimping quality. Standardized operating procedures must be established, with strict control at every stage, from mold management and equipment debugging to personnel training. Molds need regular maintenance to prevent wear and tear that could lead to dimensional deviations in crimping; equipment requires CPK analysis to ensure process stability; and operators must undergo qualification and certification to improve crimping consistency. Simultaneously, a raw material approval process must be established, conducting full-size and full-performance verification of key materials such as wires and terminals to prevent poor crimping due to material issues.
The inspection and control of vehicle wiring harness terminal crimping quality must be integrated throughout the entire production process. Through multi-dimensional verification including visual inspection, dimensional measurement, electrical performance testing, tensile testing, and cross-sectional analysis, combined with strict process control and defect prevention measures, it is possible to ensure that every crimp meets design requirements, providing a reliable guarantee for the stable operation of the entire vehicle's electrical system.
