Application Status and Prospect of Foaming Technology in Automobile Wire Harness

In recent years, the development of related technologies for polyurethane modification has become a research hotspot. Its purpose is to make the modified polyurethane have better mechanical properties, heat resistance, chemical resistance and other properties, and to make foaming technology more widely used in the field of automobile parts manufacturing.

Polyester was first synthesized by German chemist Otto Bayer and his colleagues in 1936 while studying the addition polymerization of isocyanate. Three major technological breakthroughs in the 20th century promoted the rapid development of industrial production of polyurethane. Polyurethane products can be widely used in light industry, petrochemical, electromechanical, automotive, energy, military construction and other fields.

1 The Processing Method of Polyurethane Material

Generally, RIM polyurethanes mainly include RIM, RRIM (Reinforced Reaction Injection Molding), SRIM, MC-RIM, GRIM and RIRIM(Rotary Injection RIM).

RIM refers to the process of ordinary unreinforced materials; RRIM mainly refers to the material or technological process prepared by mixing relatively short fibers or other reinforcing materials with the reaction material and then reacting with another component; SRIM refers to the material or technological process in which continuous long fibers are placed in the cavity in advance, and then the reaction liquid is injected into the cavity to pass through the fiber mat, which has been vigorously developed and popularized by Daimler, Ford and General Motors. MC-RIM refers to multi-component reaction injection molding, also known as "multi-stage injection RIM", that is, the materials of the skin and the central part are successively injected into the cavity; GRIM refers to thin-walled and hollow parts, which can save about 40% of raw materials; RIRM is called rotary reaction injection molding, which is characterized by no restriction on the viscosity of materials. There are two injection modes: one is rotary injection mixing mode with small holes as injection ports, and the other is rotary plane jet mixing mode with gaps as injection ports.

2 The Characteristics of RIM Processing Technology

1. It is easy to realize accurate measurement, with good mixing and process controllability. The raw materials used in the formula are all low viscosity liquids, and the circulating pressure of the equipment is relatively low.

2. The molding process is simple, the production efficiency is high, the raw materials are uniformly collided and mixed in an instant, and the production man-hour of a single product is relatively short. Compared with traditional polyurethane production, it has obvious advantages.

3. The energy consumption is correspondingly less, and the liquid raw material system only needs a lower heating temperature, without reusing high-temperature baking or melting raw materials. The system is exothermic during the reaction and curing, the working temperature of the mold is low, and the requirement for input energy such as electricity is low, so there is no need for secondary high-temperature heating of raw materials, and the production is not energy intensive.

4. Because the cavity pressure in the reaction process is relatively low, the pressure only needs no high-pressure mode-locking system, which can save the energy consumption of the mode-locking system of the equipment and simplify the structure of the equipment. The lower cavity pressure also makes it easy to choose the mold material, usually aluminum, epoxy resin and other materials can be competent, and the lower mold cost can be obtained.

5.RIM process can adapt to the parts with complex appearance, and the design freedom of parts is high. One of the benefits that can be obtained from lower cavity pressure is that the mold can be designed into a solid parting structure, so that it can cope with the more complex product structure. In addition, the characteristics of the three-dimensional parting structure can easily design the mold of the insert structure. Structural reinforced reaction injection mold can be produced by adding specific reinforcing materials into liquid raw materials.

6. The range of mechanical properties of products is wide, the adjustable range of formula is large, and the freedom of raw material selection is large. Besides common polyurethane and polyurea, it can also be applied to the processing and molding of epoxy resin, nylon, dicyclopentadiene, polyester and other materials.

7. By applying in-mold coating technology, the surface treatment process can be completed at one time without additional painting treatment, thus simplifying the processing technology and reducing the manufacturing cost.

3 Application Status and Methods of Polyurethane in automotive wiring harness

In recent years, the automobile industry in China has developed rapidly, and polyurethane, as one of the polymer materials, has been widely used in automobile parts.

In automotive wire harness products, the main function of the wiring loom guide groove is to ensure that the wire harness is safely protected in the narrow and irregular hidden space of the car and fixed with the car body. In places with relatively low ambient temperature requirements, such as the passenger compartment area, high polymer plastic is used as the material of the wire harness guide groove. In harsh environments with high temperature and vibration, such as engine room, materials with high temperature resistance, such as nylon reinforced with glass fiber, should be selected.

The traditional engine wiring harness is protected by bellows. The wiring harness designed by this design has the characteristics of low cost, simple and flexible manufacturing. However, the anti-corrosion and anti-fouling ability of the finished product line is poor, especially dust, oil and so on can easily penetrate into the wiring harness.

The harness formed by polyurethane foam has good guidance and convenient installation. Workers only need to get the harness and follow the molding direction and path, which can be installed in one step, and it is not easy to make mistakes. The harness made of polyurethane has many characteristics superior to the common harness, such as oil stain resistance, strong dust resistance, no noise after the harness is installed, and various irregular shapes can be made by free three-dimensional modeling according to the body space.

However, because the wire harness made of this material needs a large investment in fixed equipment in the early stage, many wire harness manufacturers do not adopt this method, and only a few high-end cars such as Mercedes-Benz and Audi's engine wire harnesses are used. However, in the case of a large and stable order, if the average cost and quality stability are to be calculated, then this kind of wire harness still has a good competitive advantage.

4 Outlook

Compared with the traditional injection molding process, RIM materials and processes have the advantages of low energy consumption, light weight, simple process, low mold and manufacturing cost, etc. Modern automobiles are designed to meet higher comfort requirements, and their functions are more and more complex, so the space left for wiring harness is narrower and more irregular. Traditional injection molding tools are more and more restricted in this respect, while polyurethane mold design is more flexible.

Reinforced reaction injection molding (RRIM) is a new type of reaction injection molding technology, which can prepare products with better mechanical properties by putting fibrous fillers such as glass fiber into the preheated mold.

Using the existing polyurethane equipment and materials to carry out the research work of polyurethane technology can optimize the manufacturing process of materials and improve the service performance of materials. In the future, technology should be further introduced into the manufacture of automotive wiring harness guide groove. Finally, enterprises can achieve the goal of reducing costs and improving market competitiveness.