The electrical systems of vehicles, such as automobiles and commercial vehicles, are intricate and continue to develop as manufacturers seek to provide more and more electrical capabilities to consumers. Early models of such vehicles had relatively few electrical systems, and many of these systems were relatively simple by today's standards. In contrast, modern electrical systems often involve numerous and complex subsystems, requiring substantial use of conductors and electronic devices for interconnecting components of the electrical systems.
As the demands on electrical systems have proliferated, manufacturers have sought to control the space occupied by conductors used in the electrical systems by bundling these conductors together into harnesses. A number of different types of protective coverings have been used, from relatively simple harness coverings, such as engineered tape, woven threading, nylon braiding, asphaltic loom material etc., used to bundle conductors together, to more complicated harness coverings, such as extruded plastic and metal sleeving/conduits. Overmolded polymers (in which a polymer is molded to wholly or partially encase the wire harness) are especially desirable for use as harness coverings because they provide advantages that are not available from the use of other types of harness coverings. For example, in addition to controlling and managing the routing of numerous conductors, overmolded polymers provide protection from damage to the bundled conductors that might otherwise result from salt corrosion, heat, vibration, water, and ultraviolet radiation.
These overmolded polymers must be shaped in accordance with a predetermined three-dimensional geometry, in order to fit properly in a vehicle. In the automotive and commercial vehicle industries, the overmolded polymer acts as a structural template for routing conductors and electronic devices through the desired parts of the vehicle. Spacing and volume considerations and potential paths between electrical subsystems are taken into account in determining the desired three-dimensional geometry for the harness coverings.
In order to create these overmolded harness coverings in a cost-effective manner, these coverings are often formed pursuant to injection molding. The mold generally includes two halves, i.e., a bottom half and a top half, defining a cavity therebetween that corresponds to a desired shape, and therefore, the exact configuration of the mold is important. One conventional injection molding technique is reaction injection molding (RIM). In accordance with this technique, two liquid components, generally a polyol and an isocyanate, are injected under pressure into the mold corresponding to the predetermined three-dimensional geometry of the harness covering. The liquids chemically react in the mold, i.e., the molecules of the components cross-link, to form a solid thermoset polymer, generally polyurethane.
The molds used in injection molding are often relatively expensive to manufacture. Generally, they are used to mass produce a high volume of identical parts and are less economical in low volume situations. Many molds are made of steel or aluminum to ensure a relatively long mold lifespan, but these materials may be relatively expensive and add to the cost of injection molding. Further, in the case of commercial vehicles, molds must be relatively large for the formation of large harnesses, which again adds to the cost of injection molding.
In addition, complex geometries often involve the use of molds having complex shapes, which further adds to the cost of molding. A three-dimensional mold is very expensive, and to create the three-dimensional geometries needed for the final harness covering shape, the mold becomes very complicated and costly to construct. Typically, the use of “actions,” such as inserts or slides, in the mold allows a complex shape to be molded and, after molding, for the mold halves to be separated. The use of “actions: generally increase the fabrication cost of a harness covering by increasing the amount and complexity of the mechanisms that need to be placed in the mold and by increasing the molding time.
After the two liquids are injected and mixed, the resulting mixture cures over time to form a strong protective covering that is relatively strong and lightweight. Generally, the covering cures sufficiently such that within a few minutes the harness can be removed from the mold, i.e., demolded, and handled without damage. The covering continues to cure over the next few hours and becomes increasingly rigid and solid. After curing is completed, the harness with covering is a rigid and geometrically stable structure.
A need exists for a less expensive system and method for forming a harness having a predetermined three-dimensional geometry. There is also a need for a system and method for forming a harness covering that does not require the use of a separate three-dimensional mold for each desired three-dimensional geometry and that avoids the need for expensive molds to form complex geometries. Further, there is a need for an economical system and method for forming large harness covering having a desired geometry through reaction injection molding for use in commercial vehicles.