Rhodia Engineering Plastics introduces new plastic-metal hybrid materials for high-load bearing semi-structural components

Lyon, France, April 19, 2004 – Rhodia Engineering Plastics has developed a range of hybrid solutions that combine metals and engineering plastics to be used in high-load bearing (semi-) structural components. These closed structures, either with rib or hollow, are targeted especially at automotive applications, where they bring benefits such as potential parts integration, depth, weight and size reduction, cost savings, enhanced energy absorption, and added-value appearance.

While existing open rib designs, where thin metallic sections are moulded over with thermoplastic ribs, provide a good strength-to-cost ratio, their effective mechanical strength and stiffness is highly dependent on the direction of the applied load. This typically results in complex mold requirements, which must be met by means of sophisticated hot runner technology and/or the use of very low-viscosity resins. Furthermore, the open rib approach cannot be used for applications that need to be safely protected from dirt and water penetration.

In contrast, Rhodia’s closed rib and related hollow designs have a more balanced profile of high stiffness and strength regardless of the load direction, that is in both tensile stress and in compression areas. In addition, the hollow sections may be used to integrate other functions. Rhodia has been investigating three different closed hybrid technologies – Metal Over Molding (MOM), Plastic & Metal Assembling (PMA), and Metal & Gas or Water Assisted Injection Molding (MGAIM or MWAIM) – each providing a number of distinct advantages depending on the specific application requirements. In each case, Rhodia’s TECHNYL STAR™ polyamide technology helps to enable the fluidity and processability for these closed hybrid technology alternatives to succeed.

Metal Over Molding (MOM)

In MOM, one or more metal inserts are directly molded over with an engineering thermoplastic resin. The final reinforcing design is then created in a second step by one or several plastic covers assembled on the existing metal-plastic structure. The resulting hollow section(s) within the structure can serve to integrate cables, flow channels or fluid containers, As one potential application example, a structure of this type would eliminate the need for a separate cooling water expansion tank in automotive front-ends. While MOM components will be somewhat heavier than open rib designs, this is counterbalanced by their superior load-bearing, energy absorption and integration capabilities. MOM is one solution to improve energy absorption, or to redesign classical parts -- reducing their size while keeping the same energy absorption. The time and cost for the additional injection mold and the jointing process is counterbalanced by reduced mold complexity, lower injection pressures, and reduced mold wear.

Plastics and Metal Assembling (PMA)

PMA also involves two process steps, by combining a rigid, ribbed injection molded plastic part with a metal section by means of clips, rivets and/or ultrasonic welding.

Again, this requires additional capital expenditure, but the space within the final product provides significant potential for cost and weight savings, and functional part consolidation. The mechanical strength compares well with that of open rib structures at lower overall costs.

Metal & Gas or Water Assisted Injection Molding (MGAIM or MWAIM)

In MGAIM or MWAIN, the complete hybrid component is manufactured in a single integrated process, by over-moulding a metal part and then coring the plastic material by use of the gas or water assisted technique. The result is a very stiff and lightweight, energy absorbing structure with outstanding surface appearance (no sink marks). The cored-out sections lend themselves to functional integration. Gas and water assisted injection molding involve some additional cost, but are state-of-the-art, and the mold technology is even simpler yet. In particular, the freedom of design offered by MGAIM and MWAIN clearly exceeds that of any deep-drawing metal,

Reader enquiries

Rhodia Engineering Plastics
Avenue Ramboz
F-69192 Saint-Fons Cedex
France

+33 4 72 89 27 53

christine.bourguignon@​eu.rhodia.com

www.rhodia-ep.com