Functional Integration with Air Ducts
Clips, straps and cable feed-throughs are usually welded on to air ducts in automobile engine compartments. Two new process variations eliminate the welding step and thus help to reduce manufacturing costs.
Simplification of assembly and functional integration are playing an increasingly important role for air ducts in automobile engine compartments. Clips are used to attach other components to the ducts, while straps fasten the ducts to the engine or body. Such functional elements have in the past been fastened to the ducts by hot plate welding, for instance. Unfortunately, however, this process has disadvantages: if the temperature window is not maintained exactly, material properties degraded and a poor weld bond results. A number of additional process steps and the necessity of purchasing additional equipment increase costs.
For this reason, Röchling Automotive, Mannheim, now offers two alternatives for bonding the functional elements to the ducts: overmoulding in a separate mould and integration during blow moulding. Straps, clips and other similar items are incorporated into the component quickly, with favourable economics, a strong bond and a good appearance. A report on this by Marco Barbolini, Product Manager at Röchling, appears in the current issue of Kunststoffe.
When overmoulding, a blow-moulded duct is placed in a special injection mould and straps are moulded on. Compared to hot tool welding, the reliability of the process is considerably greater, because the processing temperature can be controlled very accurately. The injection moulded material melts the surface of the duct, producing a firm bond between the strap and duct. In addition, overmoulding provides a great deal of design freedom; even complex shapes are possible.
In the second process variation, the functional elements are moulded on directly in the blow mould before the blow-moulded part cools. Adhesion is improved, since the more intense mixing in the incompletely cooled material produces more complex interlocking and greater adhesive forces. The visual appearance of the functional elements is very good and the reliability of the process is even higher, because there is no need to transfer the part between moulds. This leads to a shorter cycle time and lower costs. However, the more complex design of the combination blow mould/injection mould permits only a limited number of functional elements.
While moulding on directly in the blow mould represents a considerably higher degree of automation and fewer process steps, overmoulding in a second mould permits more complex duct geometries and greater flexibility. Compared to conventional manufacturing processes, both process variations yield a better bond between the duct and fastening element, and improve the economics of the production process.