Cost Optimization Scheme for Low Voltage Wire Harness of Automobile

Automobile wire harness is the assembly of automobile power and signal transmission and distribution system, the network main body of automobile circuit, and the connecting parts and the carrier of each part in automobile circuit. This paper briefly introduces the typical cost optimization scheme of automobile low-voltage wiring harness in the process of synchronous development and design, analyzes its feasibility and reliability, and shares the competitiveness that can contribute to the cost in design.

1 Introduction

As the central nervous system of the vehicle electrical system, automotive wiring loom products are an important part of the vehicle cost. At the initial stage of design, the direction, layout and positioning point distribution of the wiring harness have been designed through 3D digital simulation. Under the condition of fully simulating the actual loading state, the interference between the wiring harness and various electrical devices or pipelines has been avoided, thus reducing the man-hours for restructuring or reworking the wiring harness products in the later loading process and invisibly reducing the cost of the wiring harness products. In the design process, after fully analyzing the electrical principle of the whole vehicle, combined with the load of various electrical appliances, the assembly steps of the whole vehicle and the needs of after-sales maintenance, the wire diameter, direction and length of each wire, where to branch and where to go out, etc. are calculated most reasonably, which can save parts to the maximum extent and reduce the cost of wire harness products. This paper will share the cost competitiveness of wire harness products in design optimization.

2 Overview of wire harness products

Automobile wire harness is the assembly of automobile power and signal transmission and distribution system, the network main body of automobile circuit, and the connecting parts and the carrier of each part in automobile circuit. If the car is compared to the human body, the car engine is the heart and the ECU is the brain, then the car wire harness is the blood vessel and the nerve, which shows the importance of the car wire harness for the normal and stable operation of the car circuit.

In order to ensure that the electrical equipment of the whole vehicle can maintain reliable connection under normal use conditions, wires, sheaths and terminals with different specifications, colors and temperature resistance grades are used for all the electrical equipment of the whole vehicle, and the wires required by the whole vehicle are connected and integrated through reasonable wiring and full consideration of the needs of assembly and maintenance, and then bundled together through positioning pieces, protective tubes and other components according to reasonable technology, thus forming a wiring harness.

The wire harness consists of wires, sheaths, terminals, fuses, relays and other parts that can play the roles of insulation, protection, fixation and sealing.

Different from modern automatic production technology, automobile wire harness products are special products with intensive management, labor and parts. The processes that can realize automatic technology are limited, and there are high requirements for process control ability, quality assurance ability and operator skills.

With the continuous improvement of automobile electronic function configuration, consumers' requirements for the safety, comfort and handling of the whole vehicle are also increasing. In order to meet the preferences of different consumer groups for the functions of automobile electrical appliances, automobile manufacturers generally design vehicles with different electrical appliances for different consumer classes, so that the types of wiring harness products supporting them also increase. Take a series of cars with good sales volume and good reputation in the domestic market as an example. This car can be equipped with five gasoline engines, namely GW4G15F, GW4B15A, GW4D15D, GW4C20B and GW4N20, and there are as many as 13 kinds of engine and transmission harnesses, plus the door harness, dashboard and console harness, frame harness, front cabin harness and cockpit harness with different electrical functions, which can be installed by consumers themselves. It can be seen that the types of wiring harness products are closely related to the electrical configuration of the whole vehicle. The richer the functional configuration of electrical appliances, the more variety of supporting wiring harness products. In addition, the variety and small batch of commercial vehicle wiring harness products is another major feature.

At present, the mainstream automobile manufacturers in the world are mainly divided into three series: American series represented by the United States (mainly in North America), European series represented by Germany (mainly in Europe) and Japanese and Korean series represented by Japan and South Korea (mainly in Japan and South Korea). In addition to the above three mainstream car series, the automobile manufacturing industry in Britain, France, Italy and other countries also has considerable brand awareness in the world. The whole vehicle of each department has formed a system, so the matching parts naturally form a system, and the harness products are no exception. The parts used in the harness products are different with different car systems. There are more than 20 kinds of components that make up the product entity of the wire harness, such as sheaths, terminals, wires, positioning parts, rain plugs, fuse boxes, relays, rubber parts, pipes, adhesive tapes and foam strips, among which the materials of the components used are different according to different parts.

Generally speaking, the automatic coverage rate of vehicle wiring harness products in batch processing is less than 50%, which determines its labor-intensive product characteristics.

The processing technology of wire harness products mainly includes blanking, crimping, welding, insulation, sub-packaging and assembly, in which the automatic coverage of sub-packaging and assembly processes is less than 10%, which undoubtedly becomes the bottleneck of the development of wire harness industry today.

3 wire harness product cost composition

The cost of wire harness products consists of fixed costs and variable costs, including material costs, working hours, burning costs, manufacturing costs, management fees, financial costs, sales costs, mold sharing costs, development costs, etc. Compared with fixed costs such as working hours, manufacturing costs, financial costs and management costs, variable costs such as material costs account for a higher proportion in wire harness products. In order to meet the fierce demand of terminal competitive sales and end users for high cost performance of vehicles, OEMs constantly put forward new requirements for the cost contribution of parts suppliers, which is directly reflected in the unit price of product supply. Faced with the requirements of quality assurance and price reduction of the whole vehicle factory, parts suppliers achieve the goal of cost reduction through a series of cost optimization activities such as improving workers' labor efficiency, VA\VE, improving automation rate and optimizing procurement resources. The following will analyze the competitiveness of cost contribution from the design aspect.

4 Typical design optimization scheme

4.1 Optimization principle

Realize the reliability of wire harness products under the condition of optimal economy.

4.2 Optimization scheme

4.2.1 Localization of imported parts and components

Localization of imported parts is a common way for harness suppliers to reduce the cost of harness products. With the globalization of auto parts procurement, the price difference between imported parts and domestic parts is no longer more than 50%, but it has always maintained a price difference of 10%~35%. Although the key electrical components used in wire harness, such as ABS, SRS, ECU and BCM, are still monopolized by international auto parts giants such as APTIV, BOSCH, SIEMENS and TE with their high-end technical advantages, some parts suppliers for non-key electrical parts are widely distributed, and this part of the parts is also the focus of localization. Generally speaking, the procurement cost of imported parts in vehicle wiring harness products accounts for 20%~40% of the material cost, and the material cost accounts for 65%~85% of the vehicle wiring harness cost. Then, the localization of non-critical parts can reduce the cost of vehicle wiring harness products by 1.3%~11.9%. From the data point of view, the absolute value of cost reduction is considerable, but it is insufficient in some aspects when it is really implemented.

First of all, the localization of parts needs to be completed with the cooperation of automakers, wire harness suppliers and parts suppliers. After the development of domestic parts is completed, the parts supplier needs to conduct self-inspection. After the self-inspection is qualified, the harness manufacturer needs to fully match the data and test the domestic parts according to industry standards or customer standards. After the above inspection and test are completed, the vehicle manufacturer is required to carry out on-site assembly and road driving test on the domestic parts. After all the above tests are completed and qualified, they can be put into production after small batch and batch trial loading. The whole development and test cycle lasts from a few months to a year. During this period, close communication and full cooperation among the three parties are needed, which are indispensable.

Secondly, at present, many domestic parts suppliers still have a lot of room for improvement in the development ability of composite structure and small-size series parts. The most common problem of domestic parts is specious. Although it meets the requirements of appearance and structure, there are still some deficiencies in reliability, which requires automakers and wire harness suppliers to assist domestic parts suppliers to improve their development capabilities and design verification capabilities.

Thirdly, insufficient supply stability is another common problem of domestic parts. Apart from the purchasing resources of raw materials, the machining accuracy of parts molds, the production process control ability and quality assurance ability of parts suppliers are also important factors that cause this problem. This also requires OEMs and wiring harness suppliers to continuously improve their process control ability and quality assurance ability through process evaluation of parts suppliers.

4.2.2 Harness Structure Optimization

Through the continuous production efficiency improvement activities of the automobile factory, "parts pre-assembly" is more and more applied to the assembly line. For example, the engine, dashboard, front and rear bumpers, doors and other parts have been assembled and supplied to the automobile factory under the assembly line, which improves the production rhythm of the automobile factory and reduces the risk of damage caused by interference with too many other parts during the assembly process.

After adopting the optimization scheme of splitting the main harness, it has the following advantages.

1) Judging from the claims and fault information fed back from the after-sales market over the years, the claims and faults of harness products are mostly in the engine compartment with harsh working environment, while the number of claims for harness products in the cab is relatively small. Using the main harness with optimized front structure is not conducive to the maintenance and replacement of the line. After the main harness is divided into three parts: engine compartment harness, instrument panel harness and body harness, the man-hours used for after-sales maintenance and the maintenance cost of end users can be greatly shortened.

2) By implementing the "parts pre-assembly" scheme, the production and assembly time of wire harness suppliers can be reduced, and at the same time, the loading efficiency of the automobile factory in the assembly line can be improved.

3) After the main harness is split, there are many kinds of harness products, which improves the flexibility of production organization, logistics management efficiency and parts delivery rate of the whole vehicle factory.

4) After splitting the main wire harness, the risk of scraping and dragging caused by excessively long wires can be reduced during the turnover and transportation of the finished and semi-finished products of the wire harness. At the same time, it also faces the following challenges: ① After the main harness is split, the number of connection points between harnesses increases, which increases the risk points of harness product quality; ② After the main harness is split, there will be more connectors between harnesses, which will lead to an increase in the material cost of harness products.

The optimization of the harness structure ultimately depends on the collaborative cost between the OEM and the harness supplier.

4.2.3 Optimization of Conductor Types

At present, there are four kinds of wires used in the wire harness according to the requirements of customer standards, namely Japanese wires conforming to JASO standards, German wires conforming to VW or DIN standards, wires conforming to ISO6722 international standards and wires conforming to GB/T25085, among which Japanese and German wires are mostly used. By calculating the current carrying capacity, on the premise of meeting the use function, adding some specifications between some conductor specifications with large span or supplementing them with wires with different specifications that meet other standards, the cost of wire harness parts can be reduced and the weight of the whole vehicle can be contributed.

Although there are structural differences between German standard conductor and Japanese standard conductor with similar specifications, German standard conductor has advantages in cross-sectional area and conductor resistance, but the differences are not particularly obvious, while Japanese standard conductor has certain advantages in both external diameter and quality of finished products.

1) Difference in temperature rise and current curve between German standard conductor and Japanese standard conductor with similar specifications.

From the temperature rise and current curves of the two types of conductors, it can be seen that under the same temperature rise condition, the current carrying capacity of German standard conductor is slightly stronger than that of Japanese standard conductor. For example, when the temperature rises to 20℃, the difference of current carrying capacity between wires with different specifications is between 8.33% and 9.52%, and the lower the temperature rise, the smaller the difference of carrying capacity.

2) Difference in smoke generation time between German standard conductor and Japanese standard conductor with similar specifications.

From the smoke time curves of the two types of conductors, it can be seen that under the same overcurrent condition, the smoke time of German standard conductor is longer than that of Japanese standard conductor, and the smoke time difference between different specifications is between 13.79% and 17.44%. The smaller the overcurrent, the smaller the smoke time difference.

Based on the comparison of the indexes of the two types of conductors, under the premise of full design verification, adding some conductor specifications that meet the requirements of this type of conductor or using different specifications that meet other standards will have more room for the selection of conductor specifications and meet some requirements of cost and weight.

4.2.4 Sub-regional design of parts materials

Rising global energy prices have led to rising raw material prices. In this situation, it is particularly important to fully consider the performance of parts according to the different use areas of dry area and wet area, and use the most economical raw materials to improve the cost performance of parts and avoid excessive functions of parts.

1) The commonly used materials of connectors have been verified under practical application conditions.

2) The insulation layers made of different materials have different temperature resistance grades, and their raw material prices and processing technologies are also different.

3) The parts commonly used in the above wire harness products can be designed regionally according to different use areas, thus reducing the cost of raw materials.

4.2.5 Platform Design of Parts and Components

Platformization of parts, that is, improving the continuity and universality of parts, can effectively reduce the development cost and mold cost of parts, thus reducing the price of parts. When developing new models, many OEMs need to redevelop and design the necessary parts for special vehicles, such as car bodies and lamps. At the initial stage of design, other electrical components are mostly borrowed from the mature parts used in existing mass-produced models, that is, platform use. In this way, the development cost and mold cost of parts and components are greatly reduced, the development and procurement cycle of parts and components in new projects is shortened, the stability and reliability of parts and components quality are ensured, and the procurement cost and management cost of parts and components of the whole vehicle factory are reduced. In the same vehicle supply and demand chain, the fewer types of parts, the lower the procurement cost and management cost. It can be seen that the advantages of parts platformization are self-evident.

1) The sheaths are integrated according to the specifications of the matching terminals, and those with similar structures can be distinguished from the number of holes, color, limit, etc.

2) According to the matching mode, space and structure with the car body, the types of positioning parts can be integrated except special-shaped positioning parts and brackets.

3) The current load capacity of terminals of various specifications depends on the cross-sectional area of the wire to be crimped, the material and coating of the terminal.

5 Conclusion

This paper starts with the common optimization schemes in the design of automobile low-voltage wire harness products, and shares the competitiveness of some design optimization schemes on cost contribution. Of course, there are many ways to optimize the design cost, such as the application of smart electrical box and the use of multi-pin fuse, which can curb the cost of wiring harness to a certain extent. I hope that through the sharing of this article, I can contribute to the automobile industry and do my bit.