The New “Thermoplastic” T-RTM: Suitable For Mass Production In The Automotive Industry

 

KraussMaffei introduced thermoplastic resin transfer molding (T-RTM) technology at K 2016, which can produce mixed-material automotive prototypes made of fiber, plastic and metal in short cycle times. New metering systems enable just-in-time material supply, and near-net-shape production minimizes material waste and processing steps.

 

 

Zebra Appearance:

 

This roof shell frame for the Roding Roadster R1 sports car is a fiber-reinforced composite automotive structural component with metal inserts, which is created by KraussMaffei’s T-RTM process and the production process takes only a few minutes. It is worth noting that the process can process glass fiber (white) and carbon fiber at the same time. At the K 2016 exhibition, the KraussMaffei booth demonstrated the process of producing this component in a mass production environment several times a day.

 

Continuous fiber, short production cycle, welding and recycling capabilities – KraussMaffei’s T-RTM process combines the advantages of reaction processing equipment, thermoplastic materials and molding in transfer molding (i.e. “resin transfer molding”, referred to as “RTM“), and thus achieves the perfect integration of modern lightweight production. The system proves that it is feasible to reliably integrate metal carriers into T-RTM parts using automated production.

 

Focus On Mass Production

 

The following individual processing steps demonstrate the complexity of the process and the optimization of the cycle time:

 

➤ First, the four preformed components with aluminum and steel inserts are positioned on a ruler;

 

➤ Next, the steel insert is riveted to one of the preformed components;

 

➤ A handling robot then positions the aluminum bracket and the preassembled hybrid component into the T-RTM mold;

 

➤ Caprolactam is poured into the mold and then, where a chemical reaction occurs, the material solidifies into thermoplastic polyamide 6. After the reaction time has expired, the handling robot removes the finished component.

 

The so-called “near net shape” method allows the finished component to be close to its final shape, which means that no complex post-processing processes, such as milling edge areas, are necessary after molding.

 

Melting Materials On Demand

 

As a system supplier, KraussMaffei offers complete production cells, an important component of which is the new RimStar 8/8 T-RTM metering system:

 

➤ It enables the melting process to be carried out on demand;

 

➤ Material that only needs a few shots is usually melted at once, which minimizes thermal stress on the melt and prevents material aging of the two caprolactam components (caprolactam-based material and catalyst, or catalyst);

 

➤ It provides very precise temperature control from melting to injection into the cavity.

 

“These features together ensure a consistently higher product quality and are therefore suitable for large-scale production,” said Erich Fries, head of the Composites/Surface Technology business unit at KraussMaffei. The new metering system enables processing at temperatures of up to 180°C and is therefore very suitable for polyamide 6 (PA6).

 

 

 

Melting on demand: The new RimStar 8/8 T-RTM metering system enables the caprolactam component to be melted on demand

 

To meet the high temperature requirements, KraussMaffei has also optimized the design of some other products, including:

 

➤ MK 10-2K high-pressure pouring head: flow rate 100g/s, one-time pouring amount 250g;

 

➤ High-pressure pouring pump: In-house pump manufacturing capabilities enable KraussMaffei to customize pouring pumps;

 

➤ The compact FTR mold frame (clamping force 3800kN) ensures precise and space-saving operation of T-RTM molds.

 

Advantages For Fiber Content, Material Consumption and Post-mold Processing

 

T-RTM has many advantages over the well-known RTM processes with epoxy resins or polyurethanes (PUR):

 

➤ The low viscosity of only 5mPA·s (similar to water) allows the matrix material caprolactam to penetrate the fiber layer even at low pressure in the mold;

 

➤ For the application at the exhibition, a clamping force of about 3500kN is sufficient, which means lower investment costs and energy consumption;

 

➤ High flow rates allow the wall thickness to be minimized and fiber contents of up to about 60% can be allowed.

 

➤ A so-called “near net shape” approach reduces the consumption of expensive carbon fiber materials through close-to-contour production, thereby reducing material costs and minimizing post-mold processing steps. In addition, the multi-preform concept also helps to further reduce fiber waste and obtain a load-bearing fiber structure (local).

 

Compared to 3D network thermosets, these chain-structured thermoplastics have unique properties: they can be reheated and reshaped, making them weldable and recyclable. For example, the roof frame material can be re-crushed into pellets and, together with its fiber content, used to produce parts in injection molding.

 

High Impact Strength And More Ductile Fracture Characteristics

 

PA6’s mechanical properties are also very attractive for structural components. This thermoplastic has a higher impact strength and a more ductile fracture characteristic than thermosets, which means that the impact force can be absorbed by deformation of the material before breaking.

 

Compared with injection molding, a typical process for processing thermoplastics, the advantages of T-RTM are clearly reflected in the high fiber content and low viscosity, which allows the production of very thin-walled components.

 

“For the production of structural components, T-RTM is an effective supplement to the well-known RTM technology, and KraussMaffei can make full use of its extensive expertise in plastics processing. KraussMaffei is the only supplier on the market that can provide both metering and mixing technology and presses up to 1,000 tons, and can therefore promote the development of the entire system.” Fries said.

 

In addition to KraussMaffei, the development partners involved in the technical production demonstration of the roof shell frame of the Roding Roadster R1 are: Forward Engineering (component design and hybrid material concept), Alpex Technologies (T-RTM tool), Dieffenbacher (preforms and handling device), Saertex (fiber layer), Henkel (adhesive), Handtmann (aluminum insert), TUM/LCC (fiber selection) and Keller (extraction technology).