Manufactured products often contain orifices and cavities or other hollow parts that result from the manufacturing process and/or that are designed into the product for various purposes, such as weight reduction. Automotive vehicles, for example, include several such orifices and cavities throughout the vehicle, including in the vehicle's structural pillars and in the sheet metal of the vehicle doors. It is often desirable to seal such orifices and cavities so as to minimise noise, vibrations, fumes, dirt, water and the like from passing from one area to another within the vehicle by means of sealing members or baffle elements built into the orifice or cavity. Likewise, such members or elements often fulfill an additional task of reinforcing the hollow structure of the manufactured product, e.g. automotive part, so much that it becomes more resistant to mechanical stress but still maintains the low weight advantage of the hollow structure.
Such elements used for sealing, baffling or reinforcing often consist of a carrier, made of plastic, metal, or another rigid material, and one or more layers of a thermoplastic material attached to it which is able to expand its volume when heat or another physical or chemical form of energy is applied. With such a design, it is possible to insert the baffle or reinforcement element into the hollow part of the structure during the manufacture process but also to leave the inner walls of the structure still accessible (or the cavities passable) by e.g. a liquid. For example, during the manufacture process of a vehicle, the hollow parts of a metal frame can still be largely covered by an electrocoating liquid while the baffle or reinforcement elements are already inserted, and afterwards during a heat treatment step, the expandable thermoplastic material layers of the baffle or reinforcement expand to close the cavities as intended.
The development of such baffles or reinforcement elements has led to highly advanced systems, where the expandable material is able to increase its volume by up to 2000% or more, forming a foam-like structure filling the cavities and adhering to the walls of the structure intended to be sealed, baffled, or reinforced. Especially in automotive manufacturing, this has led to considerable weight reduction and excellent dampening of noise or vibrations in the car body.
With advanced materials that are able to expand even more, it is possible to reduce initial material mass and therefore contribute further to weight reduction and cost efficiency.
However, increasingly small portions of expandable material can also cause problems in manufacturing of the baffle or reinforcement elements. As such elements (or at least the expandable material layers) are normally produced by injection molding or extrusion, the feeding of very small sections gives rise to higher processing demands, such as higher injection pressures, or causes quality issues, such as flashing, short shots (incompletely molded parts) or material degradation.
It is thus desirable to obtain a way of manufacturing baffle or reinforcement elements with less initial mass of expandable material, but without the problems connected to very small initial volumes of that material.