Process error-proofing design in automobile wiring harness manufacturing

1 Error-proofing design for wire cutting and crimping process (MES system error-proofing)

The wire cutting and crimping process is the most automated process in the manufacturing of automotive wiring harnesses. Most of the wiring harness factories in China use automated wire cutting and crimping equipment for operation. Therefore, the wire cutting and crimping process is a process with a low probability of manufacturing errors. Common manufacturing errors are incorrect use of wires, terminals, waterproof plugs, incorrect wire lengths, and incorrect crimping dies, resulting in incorrect crimping standards, which lead to semi-finished products being returned for repair or scrapped. Factories using the wiring harness MES system usually use material and mold barcode scanning confirmation when switching different kanbans to prevent errors. Scanning errors will cause sound and image alarms, which can effectively prevent the incorrect use of materials, as shown in Figure 1: MES scanning material confirmation; for factories with low manufacturing capabilities, they can control the secondary inspection of kanban materials by quality inspectors during the first product inspection. This error prevention method cannot completely eliminate the occurrence of errors.

The phenomenon of using the wrong wire mainly occurs when employees are tired or the work pace is fast. Therefore, when arranging the wire cache storage rack, wires with similar wire colors, wire diameters, and wire types must be stored in different rack addresses to prevent operators from taking the wrong wires. For example, 0.35FLRY-B red/blue wire and 0.35FLRY-B red/purple wire; 0.5AVSS yellow wire and 0.5AVSS yellow/white wire are stored in different cache racks. The material labels on the racks are eye-catching and can be effectively identified. As shown in Figure 2: The wire storage rack marks the wires that have been cut, crimped, and bundled. The wrong kanban number labels are affixed to the entire batch, resulting in the use of the wrong semi-finished material in the subsequent process. The reason is that after the operator prints the semi-finished wire labels in batches, there is no self-inspection label or reprint label after switching the production kanban. Therefore, when compiling the wire bundling protection process card, indicate the kanban label as the inspection content, and prohibit batch printing of semi-finished product labels. The wire length error in the tangent crimping process board is caused by the operator's error in inputting the tangent length in the automatic machine ACM program, which causes the input of wrong data. The most fundamental error prevention method is to use the MES system and the automatic offline crimping machine ACM system to establish data communication. After loading the board, the board process length, left and right stripping lengths, and crimping parameter data are automatically communicated to the automatic machine ACM software system without manual intervention. Secondly, according to the parameters of the operation process card, strengthen the frequency of self-inspection and quality inspection to prevent batch errors to the greatest extent (some wire harness factories have developed their own CUTTING system and better docking with MSE)!

2. Error-proofing design for semi-automatic crimping process (CFM pressure monitoring system error-proofing)

For some extreme wire harnesses, which are too short or cannot be crimped by automatic machines due to compression, riveting, or waterproof plugs, they can only be crimped manually by semi-automatic machines.

The automation level is low. This process is dominated by manual work, including manual bolt threading, heat shrink tubing, closed-end PVC tubes, wire binding, single-wire manual crimping terminals, combined wire crimping nodes, ultrasonic welding nodes, etc. It is also a process with many manufacturing errors. Even in factories that use the MES system, this process is a relatively weak link in the MES system's error-proofing design. If each operation is designed in the MES system, there will be multiple links of semi-finished materials waiting for turnover, which will increase the complexity of manufacturing, seriously affect the improvement of production efficiency and increase the intensity of MES system process maintenance, resulting in system maintenance errors and delayed process data updates. Through reasonable process error-proofing design and the application of error-proofing tooling, production and manufacturing errors can be effectively prevented.

Regarding the crimping quality, the terminal machine can be equipped with a pressure monitoring system CFM and a terminal section analysis system to handle unqualified crimping in a timely manner.

First-article inspection, including cross-section analysis, tensile testing, and voltage drop testing of the terminals, is also an important way to ensure crimping quality and effectively prevent poor batch crimping.

For waterproof plugs with similar or close colors, sizes and shapes, manual work is performed at different workstations through process arrangement, or the waterproof plugs are threaded by machine; each waterproof plug storage container is marked with eye-catching labels such as material number, description, picture, etc. for effective identification.

The complete and clear information on the kanban, wire information, and product project on each bundle of semi-finished wire labels can also effectively prevent the incorrect use of kanban wires. Semi-finished wires on the same kanban are centrally stored in cache racks, turnover carts, and turnover boxes with complete and easy-to-identify labels, which can also effectively prevent the incorrect use of kanban wires.

At the wire crimping (welding) station, the most common manufacturing errors are the wrong number of wires on the left and right sides or the wrong use of the kanban. Therefore, during the process design, two stations are assigned to perform the wire binding operation before wire crimping according to the wire binding kanban operation card. The semi-finished products after the wire binding operation are equipped with a unique wire binding semi-finished product identification card. Use error-proofing tooling to design wire binding wire isolation grooves or fixtures on the wire binding station workbench to effectively prevent wire binding operation errors and prevent the occurrence of multiple binding, missing binding, and wrong binding operation errors, as shown in Figure 4: wire binding separation groove. At the same time, strengthen the frequency of quality inspections at the beginning, middle, and end to minimize the occurrence of manufacturing errors.

Due to the particularity of ultrasonic welding joints, before welding, the wire combination on both sides of the welding joint is checked according to the process card and divided into kanban numbers. After the employees self-check and confirm that there are no errors, batch production operations can be carried out after the first piece inspection is qualified, so as to minimize the chance of incorrect welding. A common operational error is to take the wrong side of the wire binding semi-finished product, resulting in welding errors. When designing the process error prevention, the single-line kanban number of the wire binding semi-finished product combination must be indicated. The turnover box for storing the wire binding semi-finished product should be stored at a fixed address and location. There are turnover cards with logos, batches, and quantities in the turnover box. Depending on the project, the turnover box can be distinguished by different colors (blue, grass green, orange). As shown in Figure 5: Wire binding drawer semi-finished product box

3. Error-proofing design for pre-assembly process

The pre-assembly process of automobile wiring harness manufacturing includes two operation modes: centralized regional pre-assembly according to order batch and product model and online pre-assembly on the assembly line. If necessary, the two pre-assembly modes are mixed. Since there is basically no automated equipment operation in the pre-assembly process, it is a labor-intensive operation process. Therefore, this process is most commonly used through process error-proofing design and tooling error-proofing design. At the same time, the quality of process error-proofing design directly affects the assembly efficiency of the assembly line and the quality of the finished wiring harness. In the design process of the pre-installation process card, in addition to considering the time rhythm and operability of the pre-installation operation, it is more important to consider the process error-proofing design of the pre-installation operation. If the rubber parts need to be inserted in the pre-installation process card, the material number of the rubber parts and the threading direction must be indicated under the rubber parts, as shown in Figure 6: Rubber parts threading error-proofing.

For symmetrical sheaths with unclear self-locking features, be sure to indicate the threading space or special requirements on the pre-assembly process card. If necessary, attach a photo of the sheath to the pre-assembly process card to avoid incorrect threading in batches. Figure 7: Special sheath matching diagram

When preparing the pre-installation process card, for wires with the same color, wire diameter, terminals, and the same sheath on one end, both ends of one wire must be marked with a marker of the same color to prevent process errors, so as to avoid the other end of the wire being put into the wrong sheath or hole position, resulting in rework and repair.

The order of the wires on the kanban in the pre-installed material cable drum should be consistent with the threading order of the main sheath on the pre-installed process card, which can greatly improve the pre-installation speed of the operator and avoid threading misalignment. The pre-installation order of the sheath is marked on the pre-installation process card, and the pre-installation process card with a fixed version should adjust the pre-installation order according to the pre-installation operation situation to improve the convenience of workers' operation and improve labor efficiency.