Lighter Through Foaming
Thermoplastic polymers can be foamed physically or chemically. The aim here is to achieve a weight reduction in the component. Many thermoplastic polymers are suitable for the foaming process. The specialists of AKRO-PLASTIC recommend our carbon fiber reinforced compounds - ICF compounds.
In the development of technical compounds for lightweight construction and especially for the foaming process, the focus is not on absolute weight reduction, but rather on combining maximum weight savings with the best possible preservation of mechanical properties. Furthermore, compounds developed specifically for the foaming process are characterized by very good surfaces and a uniform microcellular foam structure.
The lightest polymers of AKRO-PLASTIC
Carbon-fibre-reinforced compounds drastically reduce the weight of high-strength components.
AKRO-PLASTIC has developed new ways to incorporate dry, conditioned carbon-fibre fabrics into a polymer melt in a manner which enhances the added value.
This involves shredding the fabrics in a multiple-step process so that they can be gravimetrically dosed on an extruder, like conventional cut-carbon fibres.
Tensile testing shows that even at higher temperatures, approximately the same strengths can be achieved with lighter ICF compounds from AKRO-PLASTIC than with significantly higher glass-fibre reinforcement.
Using ICF polymers will be the perfect choice to achive the best results when foaming thermoplastic polymers.
Foaming of Thermoplastic Polymers
In its search for weight-saving potentials, the plastics industry is continuously finding new solutions. By adding a chemically coupled polypropylene, and after moisture absorption, a newly developed polyamide blend (PA+PP) from AKRO-PLASTIC GmbH in Niederzissen, Germany, exhibits the same strength as a standard polyamide. Depending on application and the degree of reinforcement, the blends already save 7-10 % of density compared with standard polyamides, and have a better flowability. In order to reduce component weight even more, one approach is to charge the melt with a chemical or physical foaming agent.
Advantages of foamed parts made from thermoplastic polymers:
• weight reduction/material saving
• reduction of sink marks
• reduction of warpage
• realisation of parts with greater wall thicknesses
• increase of the stiffness-to-weight ratio
Process variant of thermoplastic foam injection molding
Core-Back Injection Molding is a process variant of thermoplastic foam injection molding which can be combined with chemical or physical blowing agents. In this process, foaming of the thermoplastic melt is achieved by increasing the base wall thickness of the component.
The process begins after the cavity has been filled completely (full shot). After a short delay time where a compact boundary layer has formed, mold opens by means of precision opening until the desired opening stroke has been reached. During the opening a pressure drop takes place in the cavity and the gas can escape from the plastic melt and thus expand. Due to the defined mold opening, the plastic does not lose contact with the mold wall during expansion, allowing the foam structure to form inside. The foaming process causes the wall thickness of the component to increase continuously during the opening until the desired opening stroke is reached. This is followed by the standard residual cooling time, then the mold opens, and the component is demolded.
Integral foams are produced in the Core-Back Injection Molding process. These are characterized by a compact, solid skin layer followed by a porous, flexible foam structure inside the component. The density of the material thus decreases continuously from the outside to the inside. For this reason, the process is used primarily in the field of lightweight construction, e.g., for beams, underbody panels, etc. In this area, it can provide high cycle time reductions as well as weight savings in the order of 30 % and more. However, it requires a holistic approach - design / material / manufacturing technology - and requires additional machine equipment -> precision control for the clamping unit.
(Source: thermoPre symposium 2019 "From fiber to component").
A 300 t ENGEL victory injection molding machine in the technical center of AKRO-PLASTIC is equipped with a precission opening control system. So far, we have successfully sampled different components using this process. In a cooperation with the company Arburg, for example, we were able to produce demonstrator components with integral foams, which have both a good foam structure and surface quality with weight reductions of 55 - 60 %.
Lighter Through Foaming
Chemical Foaming Process
In chemical foaming, the foaming agent is mixed with the granules in the form of a masterbatch or powder.
Chemical foaming = injection molding with blowing agent.
During processing and under the melting conditions, the blowing agent is formed in the plasticizing unit. Here it dissolves in the melt and foams the plastic during processing after pressure is relieved. Chemical foaming offers the flexibility to use the process on conventional injection molding machines. Another advantage of this masterbatch solution is the ability to use specially adapted blowing agents for the polymer to be processed.
The part is completely filled, compacted and the shut-off nozzle is closed without a holding pressure phase, so that the machine can already start the next metering. This process achieves a weight reduction of 4% compared to the standard process without blowing agent.
The mechanical properties of the parts remain virtually identical. The advantage of this process is that the components can be produced with virtually no warpage, since the holding pressure is maintained by the blowing agent in the compound itself and is therefore equally effective everywhere.
The part is not completely filled, the complete filling of the cavity is achieved by the expansion of the blowing agent in the melt. Weight reductions of 5 to 15% are possible with the short-shot process.