A range of hybrid solutions combine metals and engineering plastics to be used in high-load bearing (semi-) closed structures, either with rib or hollow, are targeted at automotive usage.

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 and Metal Assembling (PMA), and Metal and 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 and 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, leading the way to a number of high-end applications replacing expensive aluminium or pure steel components while also minimizing the number of jointing and assembly steps.

Potential automotive applications - Rhodia sees a wide range of automotive applications for these three technologies, from structural front ends and instrument panel carriers to highly integrated door modules as well as seat shells and an array of smaller applications, such as brake pedals.

As far as front ends are concerned, MOM, MGAIM, MWAIM can be of help for car manufacturers in their pedestrian protection concern.

In fact, the stiffness of such potential solutions is so improved that it provides the opportunity to redesign the part and reduce its size, creating thus a free space between the engine hood and the upper beam of the front end.

This hollow space can then be optimized to smoothen the impact on pedestrian upper-leg.

Application development expertise - Rhodia supports its customers worldwide through eight technical application development centers with comprehensive material advice, process optimization for injection molding, as well as component testing.

Component testing alternatives span from thermal aging in (hot) air and liquid media to fatigue and resonance trials used to determine/review the long-term and reliable function performance of parts at typical operating conditions under vibration.

Facilities for pulse pressure, leakage and highly dynamic burst pressure tests are available for components with media-carrying sealed hollow sections or integrated channels.

To optimize part geometry and the injection molding process, Rhodia offers computer-assisted simulations of static and dynamic loads as well as mold flow analyses.

The results of these examinations provide valuable input for part and mold design, particularly regarding gating style and gate location(s).

Benefits include shorter cycle times as well as high strength, high dimensional stability and dimensional accuracy of mouldings in series production.

Rhodia Engineering Plastics, headquartered in Lyon, France, is the world wide specialist in polyamide engineering thermoplastic materials.

The company has a sales network that spans the world, with manufacturing plants and technical development centres in Europe, North America, South America and Asia.

Rhodia is one of the world's leading manufacturers of specialty chemicals.

Providing a wide range of innovative products and services to the consumer care, food, industrial care, pharmaceuticals, agrochemicals, automotive, electronics and fibers markets, Rhodia offers its customers tailor-made solutions based on the cross-fertilization of technologies, people and expertise.

Rhodia subscribes to the principles of Sustainable Development communicating its commitments and performance openly with stakeholders.