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plastic hybrids another option for car makers
Metal/plastic hvbrids STRONG, lightweight automotive parts can be produced by injection moulding reinforced plastic around a metal insert, says Bayer. The process is cost effective for complex parts which can be produced cheaply by injection moulding. In the continuing search for ways to achieve optimum functional efficiency while reducing costs and weight, one problem facing automotive designers is how to reduce the weight of load-bearing structural components. The simplest way to reduce the weight of load bearing metal profiles is to reduce their section thickness, but this can often lower the strength of the part and lead to bending or buckling of the component under excessive load. Stronger metals solve the strength problem but reduce ductility and weldability, while redesigning or supporting the part often leads to an unwanted increase in weight. And yet relatively minor forces are sufficient to keep such metal profiles ‘in shape’ while at the same time significantly increasing their load bearing capacity, according to Bayer. For example, injection moulding plastic supports in an ‘x’ pattern ribbing into a metal profile increases the load bearing properties of the metal quite considerably. Bayer’s metal/plastic composite process is based on established methods and materials. The metal insert is produced by conventional stamping and bending, and its geometry reflects the principal load acting
another oPtion for car makers
The metal/plastic composite production process for a car door: open injection moulding tool; prepositioned metal insert; and finished composite.
on the component. Holes are formed in the metal at the points where interconnection is required between the metal and plastic. The metal used depends on the demands which will be placed on the final component. Corrosion-protected steel or aluminium is a popular choice, usually in the form of thin-section high strength sheet. The plastic component is a glass fibre reinforced plastic, Bayer’s impact modified, glass reinforced polyamide 6, Durethan BKV. The properties of this material are said to make it ideal for this application, such as a good stiffness and toughness even at low temperatures, low internal stress when moulded around metal parts, excellent flow characteristics, and impact, noise and vibration damping properties. The metal section is placed in the open mould cavity, held in position by fasteners. Sensors monitor the position of the insert and stop the mould from closing if it is not in the right place. When positioning is correct, the mould is closed and the injection moulding cycle starts. The finished part is removed from the mould
at the end of the usual cycle time. The insert does not have to be made from one piece of metal. Individual sections can be placed in the mould and then joined together by moulding resin around the prefabricated interlocking points or be means of clinching integrated into the mould. This enables the type and thicknesses of the metal sheet to be varied, and eliminates the need for welding, reducing the outlay on tooling and the amount of assembly work required. Metal/plastic components are also good from the point of view of recycling as the physical characteristics of the two materials are very different. In addition, recycling is made easier by the fact that the metal and plastic are only interlocked by shape. It only takes a few seconds to break the composite into mall pieces using a conventional hammer mill, Afterwards the two materials can be separated by means of a screen and a magnetic separator. Test specimens made from the recycled plastic are said to display mechanical properties similar to those of virgin resin.
High mechanical properties combined with a large number of functions make instrument panel supports ideal candidates for production as a metal/ plastic hybrid. A prototype cross-car beam developed in the USA by General Motors, Delphi and Bayer Corp achieved a 10% reduction in component and investment costs and a 40% reduction in weight compared with a steel instrument panel support. Other potential applications for metal/plastic parts include front end structures, both modular integrated front ends and bumper support beams, and in a door design comprising a high load bearing interior structure. The door module makes it possible to integrate many different functions such as the wing mirror mounting, the housings for the loudspeaker and the lock, and the map pocket. Automotive seats are another potential application. The Mercedes-Benz Viano features separate individually adjustable seats with integral safety belts and a composite seat back which consists of a metal profile and a plastic shell. Bob Pugh, Bayer plc; tel: + 44- 1564- 779126; fax: + 44- 1564- 777496.
Reinforced Phstics April 1997
another oPtion for car makers
The metal/plastic composite production process for a car door: open injection moulding tool; prepositioned metal insert; and finished composite.
on the component. Holes are formed in the metal at the points where interconnection is required between the metal and plastic. The metal used depends on the demands which will be placed on the final component. Corrosion-protected steel or aluminium is a popular choice, usually in the form of thin-section high strength sheet. The plastic component is a glass fibre reinforced plastic, Bayer’s impact modified, glass reinforced polyamide 6, Durethan BKV. The properties of this material are said to make it ideal for this application, such as a good stiffness and toughness even at low temperatures, low internal stress when moulded around metal parts, excellent flow characteristics, and impact, noise and vibration damping properties. The metal section is placed in the open mould cavity, held in position by fasteners. Sensors monitor the position of the insert and stop the mould from closing if it is not in the right place. When positioning is correct, the mould is closed and the injection moulding cycle starts. The finished part is removed from the mould
at the end of the usual cycle time. The insert does not have to be made from one piece of metal. Individual sections can be placed in the mould and then joined together by moulding resin around the prefabricated interlocking points or be means of clinching integrated into the mould. This enables the type and thicknesses of the metal sheet to be varied, and eliminates the need for welding, reducing the outlay on tooling and the amount of assembly work required. Metal/plastic components are also good from the point of view of recycling as the physical characteristics of the two materials are very different. In addition, recycling is made easier by the fact that the metal and plastic are only interlocked by shape. It only takes a few seconds to break the composite into mall pieces using a conventional hammer mill, Afterwards the two materials can be separated by means of a screen and a magnetic separator. Test specimens made from the recycled plastic are said to display mechanical properties similar to those of virgin resin.
High mechanical properties combined with a large number of functions make instrument panel supports ideal candidates for production as a metal/ plastic hybrid. A prototype cross-car beam developed in the USA by General Motors, Delphi and Bayer Corp achieved a 10% reduction in component and investment costs and a 40% reduction in weight compared with a steel instrument panel support. Other potential applications for metal/plastic parts include front end structures, both modular integrated front ends and bumper support beams, and in a door design comprising a high load bearing interior structure. The door module makes it possible to integrate many different functions such as the wing mirror mounting, the housings for the loudspeaker and the lock, and the map pocket. Automotive seats are another potential application. The Mercedes-Benz Viano features separate individually adjustable seats with integral safety belts and a composite seat back which consists of a metal profile and a plastic shell. Bob Pugh, Bayer plc; tel: + 44- 1564- 779126; fax: + 44- 1564- 777496.
Reinforced Phstics April 1997