Can Plastic really replace Metal?

EMS Chemie answers some important questions of metal replacement.

Q) What are the main drivers behind Metal Replacement with Plastics?
A) Cost savings can be achieved in all market segments. In the automotive industry the constant drive towards weight savings, reduction of CO2 emissions and fuel consumption are ever present. The main product range available from EMSGRIVORY in the field of metal replacement is Grivory GV, a semi-crystalline polyamide with partially aromatic content and Grivory HT, a hightemperature resistant polyamide based on
polyphthalamide (PPA).

Q) What are the main challenges when substituting metal components with plastic?
A) In nearly all cases a metal component design is far away from an optimised plastic solution. The challenges are design variations and design methodology. Therefore, a reduction of wall section thickness is normally required and can be reinforced by the addition of rib patterns. Feeding points and flow lengths for the polymer also need to be studied. Compensation for material shrinkage and orientation of reinforcement fibre to prevent distortion when moulded are critical considerations, whilst keeping the overall packaging space fixed due to mating components and fixing methods.

Q) What advantages can be achieved with die-cast metal substitution vs plastic?
A) As mentioned, cost and weight savings are usually the targets. Additionally components made of Grivory are ready-to-use once they leave the injection-moulding machine. This means that complex and expensive mechanical post treatments; to remove flash, to achieve the necessary tolerances or smooth surfaces are no longer required. In comparison to die-cast metals, the use of Grivory materials ensures a longer mould working life, another factor which allows costs to be saved. Other benefits such as functional integration, a high-quality surface finish, the ability to mould in colour or acoustic properties may be the deciding factors vs a metal component design.

Q) What are the most common diffculties when trying to substitute metal with plastic?
A) Metal die cast parts are generally a higher E-Modulus than that of a plastic component, and also the thermal behaviour under load over time is different vs plastic. Therefore, it is important to understand the limitations with plastic designs to meet the necessary stress requirements and to prevent sink or void issues. The correct tool design and material, gating system and size, cooling channels, venting and processing parameters have a major influence over the
manufacturability, repeatability and overall integrity of the plastic component. It is important all influencing factors are optimised for the application.

Q) What are the critical factors for successful metal substitution?
a) EMS-GRIVORY is able to offer its customers a service package that covers the entire development process, from the initial concept to serial production. Using CAE (Computer Aided Engineering) to make design proposals before tool manufacture helps to prevent expensive mistakes. Theoretical methods such as calculations with finite elements, moldflow studies or rheological simulations are critical tools for optimising the plastic design solution.

Q) What new material developments can EMS offer for metal replacement?
A) EMS Grivory has developed a new group of long fibre materials for light-weight construction: Grivory XL (Xtra Light). This new generation of high-performance polyamides offers extraordinary stiffness combined with low density. The stiffness of the Grivory XL products allows thinner walled components and correspondingly shorter cycle times to be achieved. Due to the high E-modulus, Grivory XL grades show even further reduced creep deformation. This means these new Grivory XL materials have creep deformation values which are significantly lower than those of zinc die-cast metals.


Author
EMS Chemie (UK) Ltd

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