Hybrid injection-molding/thermoforming process to make complex automotive components

SpriForm Cooperative Project is a multiyear project to develop a hybrid injection-molding/thermoforming process for making complex components from fiber-reinforced composite materials has been completed by a German partnership that comprises Audi AG, Bond-Laminates, Institute for Composite Materials, Jacob Plastics Group, Lanxess and KraussMaffei. The SpriForm project's main goals were to develop a process and material handling technology for the organic sheets and to optimize the trimming of geometrically complex components. It also focused on simulating the all-plastic hybrid components. To select the most suitable options for making each part from the large number of available materials and production solutions, costs and number of units of each component must be calculated, and its potential for being constructed entirely from an all-plastic lightweight material must be evaluated. The partners launched the project because of the growing importance of fiber-reinforced composite technology in lightweight automotive construction and the continuing increase in the proportion of plastics used as automotive materials. It was funded in part by the German Federal Ministry of Education and Research. The SpriForm production process creates lightweight, crash-resistant automotive components by combining thermoplastic injection-molded parts with thermoformed parts made of continuous fiber-reinforced thermoplastic sheets. Typical applications include seat shells and backs, instrument panel carriers, box covers, side impact protection pieces, and semi-structural parts. The project's aim was to unite the benefits of both processes in a single manufacturing process. The sheets' reinforcing fiber is impregnated with a polyamide (PA) matrix. The sheet for an automotive component that must withstand the impact of a crash consists of six 0.5 mm fiber layers and a PA6 matrix. In a fully automated SpriForm production cell, individual sheets are created with thermoforming, pre-heated by an infrared oven, inserted by robots into an injection mold, and fixed in place by hydraulic needles. At the same time, a finished part on the other side of the mold is removed. The newly inserted sheet is formed and back-injected with ribs. Its edges are then fully overmolded. The molds were constructed by Georg Kaufmann Formenbau AG, a project partner. KraussMaffei�s injection molding compounder was applied to the production cell, so that fiber content and length can be adjusted as each part requires. KraussMaffei's FiberForm process, which is based on SpriForm, offers short cycle times for a fully automated cell. As with typical injection molding, the cycle times (determined primarily by the cooling time required in the mold) are around 60 seconds each. Like the standard thermoforming process, FiberForm can be easily automated and combined with other manufacturing processes. Fiber composite technology is set to become a very important component in lightweight automotive construction and the proportion of plastics as an automotive material will continue to increase. The costs and unit numbers of each component must therefore be evaluated in regard to lightweight construction potential in order to select the most suitable options from the large number of materials and production solutions. The new SpriForm thermoforming injection moulding process is ideal not only for lightweight structural components used particularly in the automotive industry, but can also potentially suit applications in the aircraft, leisure craft and agricultural machinery industries. The new hybrid thermoforming injection moulding process combines the advantages of thermoplastic injection moulding and thermoforming of continuous fibre-reinforced, semi-finished products (organic sheets) for applications in structural lightweight components.

KraussMaffei has proven expertise in the whole fibre composite process chain and its specialized processes. These include:
LFI moulding : Has just two process steps. The first step takes place in the mixing head. Glass fibre from a roving is chopped, the PUR components are mixed, the fibres are wetted and the mix is poured into the open mould. The second process step is post-mould processing. Materials processed in LFI moulding are polyurethanes (PUR) and glass, carbon, sisal or flax fibres. Fibre length can be 12-100 mm. A typical application is the production of instrument panel substrates and other parts for automotive interiors.
The LFI-PUR process: Glassfibre rovings are chopped to a set length in a chopper immediately upstream of the mixing head. They are wetted with the PUR reaction system in the mixing head. The mix is discharged into the open mould, the mould closes and the part is shaped under pressure, causing the fibres and the PUR matrix to bond into a high-strength composite. Characteristic of LFI parts are high strength and low thermal expansion. Fibre length and concentration can be varied during pouring to locate strength and stiffness as required, by adjusting fibre concentrations and/or fibre length. Benefits include:
� Cost savings by eliminating logistics of an intermediate product, very little trimming waste
� Combine with honeycomb-core moulding
� Vary fibre content and length to locate strength and stiffness as required
� Combine with surface enhancement, e.g., in mould coating, films and fabrics
Long Fiber Injection Moulding: Economical production of bodywork for commercial vehicles. Shorter cycles for lower unit cost. Bodywork elements are produced by back foaming a thermoformed film with glass fibre-reinforced PUR. The film itself meets the criteria for a Class A surface, so no painting is required. One current application is producing engine covers in a very stable process with shorter cycle times than other processes. Increased productivity reduces the unit cost.
LFI In-mould Painting: High-strength parts with premium surfaces- a new approach to producing LFI parts with high-gloss painted surfaces. A paint layer is sprayed directly onto the surface of the mould. A spray mixing head then sprays a barrier coat on top of the paint. The LFI layer is poured into the mould, the mould is closed and clamped. The pressing step is the final stage in producing a high-strength, fibre-reinforced part with an outstanding high-gloss surface.
Modular shuttle mould carrier concept: Developed specially for the LFI process. This is the type of mould carrier used in producing the engine covers. To allow the pouring robot maximum freedom of movement, the lower half of the foam mould is run out of the mould carrier frame on a shuttle platen. A very stiff structure and a highly dynamic drive ensures that the mould closes quickly once the pour is completed, and before the chemical foaming and curing reaction gets under way.
LFI � Long Fiber Injection Moulding + honeycomb: for lightweight sandwich products, offers low weight and high stiffness. Fibre-reinforced outer layers and a lightweight core produce a part that can take the load. The LFI-PUR + honeycomb process produces functional elements for automotive interiors, such as rear shelves or car boot mats. The spacer layer of honeycomb-structure cardboard has a very low weight to area ratio. It is given a thin layer of glass fibre-reinforced PUR on both sides and pressed into the required shape to produce a finished part with very low weight and very high stiffness.
Fiber Composite Spraying: Cost-competitive production through far lower mould costs. This is a Three process step. The first step takes place in the 4-component mixing head:
glass fibre from a roving is chopped, the PUR components are mixed, the PUR mix is atomized, the fibres are blown into the spray jet and sprayed as a reinforcing layer. The second step is air curing, before the third post-processing step. FCS is optimal for polyurethane (PUR) plus glass or carbon fibres. Fibre lengths from 5 � 12 mm and fibre contents of 10 � 25% can be achieved. Benefits include:
� Only one mould half, no mould carrier required
� Moulds can be made of resin because thermal and mechanical loads are low
� Ideal for small series and/or large parts (low investment)
� Very high flexural elasticity modulus, low weight
� Sandwich structure with application-specific number of layers, layer thicknesses and materials (compact, foamed, filled, unfilled)
� Variable fibre content and length
� Combine with surface enhancement, eg, inmould coating, films and fabrics
RRIM - Reinforced Reaction Injection Moulding: Use fast-reacting systems for shorter cycles. This is a two process step. In the first process step, polyol � with glassfibre already added � is combined in the mixing head with isocyanate, poured into the mould and allowed to react. The second step is the minimal post-mould processing required. Materials processed in RRIM moulding are polyurethanes (PUR), glass and wollastonite. Fibre length is 0.2 � 0.5 mm. Typical applications are the production of door sills and front and rear spoilers. Benefits include
� Short cycles thanks to highly reactive components
� Paintable surfaces
� High heat resistance
� Excellent impact resistance
SRIM - Structural Reaction Injection Moulding: Standard system using preformed, endless-fibre mat for large-area parts. SRIM involves four process steps. The first process step is preforming and cutting the glass mats. These are then manually loaded into the mould. The third step is PUR pour into the open mould, which is then closed and clamped. The fourth step is post-mould processing. Materials processed in RRIM moulding are polyurethanes (PUR) and glassfibre. Initial fibre length is 50 mm. �. Typical applications are the production of door trim panels and many other parts for automotive interiors.
SCS - Structural Component Spraying: Offers low weight and high stiffness. SCS involves three process steps. In the first step, the preassembled sandwich part (glassfibre layer, spacer, glass mat) is sprayed with the reaction mix. The second step is loading the sandwich into the mould, which is then closed and clamped. The third step is post-mould processing. Materials processed in SCS spraying are polyurethanes (PUR), and glass, sisal or flax fibres. Initial fibre length is 50 mm. A typical application is the production of cargo mats and rear shelves for automotive interiors. Benefits offered
� Lightweight and high stiffness with the use of honeycomb core or similar spacers
� Economical use of PUR and uniform wetting
Resin Transfer Moulding: Vacuum-assisted in a closed mould, glassfibre content up to 70% by weight, for high-strength structural parts. RTM involves four processing steps. The first step is cutting the glass mat to size. These are then manually inserted into the mould. The third step is EP pour into the closed mould � if necessary vacuum-assisted. The fourth step is post-processing. Materials processed in RTM are epoxy resin (EP) and fibre. Initial fibre length is 50 mm. typical applications are the production of exterior parts for commercial vehicles, carbon fibre composites for the aviation industry and optical parts.