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The Nissan Murano hatchback door is a good example of what is feasible in thermoplastic composite materials, even for high-volume applications.
(Published on August-September 2005 – JEC Magazine #19)
BY KARL-HEINZ KALMBACH, PRODUCT MANAGER, QUADRANT PLASTIC COMPOSITES AG (QPC)
OEM Nissan, moulder Hitachi and material supplier Quadrant Plastic Composites (QPC) teamed up for this complex rear door application. In the development partnership, Nissan was responsible for design, specifications and economics. Hitachi, as a tier 1 supplier, handled the part development, all mouldings, assembly and logistics. QPC advised on materials for the inner part and provided CAD/ CAE, tooling and processing support. The development process was based on previous experience with DaimlerChrysler’s first A-Class model, which has a similar rear-door concept. The same material combination is used for Nissan’s Stagea and Infinity models.
Including that first DaimlerChrysler A-Class series, more than 1.7 million cars have already been equipped with this type of reardoor solution. The experience gained from all these applications has provided thorough knowledge on these hatchback doors.
Thermoplastic materials may be used for the same interior and exterior hatchback door functions achievable with steel applications, such as flip window, integrated rear lights, and wrap-around or inlay door construction. The level of integration is even higher with thermoplastic materials, which provide good electrical performance for electronic attachment parts and allow producing aerodynamic spoiler geometries in a single step, among many other things. The Nissan Murano’s complex interior and exterior shapes can be compression moulded and injection moulded in a single step, while a comparable metal part would require more individual manufacturing steps.
Inner part in thermoplastic composite
The inner structural part is made out of GMT/GMTex materials from Quadrant Plastic Composites. These guarantee a stiff, strong, lightweight and crashworthy solution, thanks to the glass-mat reinforcement and local weave inlay. The three-dimensional forming of these woven materials allows absorption of high loads, with long-fibre content in all critical areas of the part at the same time. Different weave-inlay orientations can be used to achieve tailored material properties. One-step forming of complex shapes without need for additional trimming is state of the art, thanks to the use of a flow-moulding process during compression moulding. GMT/GMTex processing gives competitive cycle times. Functional integration, e.g. screw domes or guiding, can be done in a single processing step. Thermoplastic materials are also used for mass-produced parts such as seats, instrument panel carriers, spare wheel wells, battery boxes, battery trays, door module carriers, underbody shields, pedestrian protection beams, bumper beams and front end carriers.
The Nissan Murano hatchback door
The Nissan Murano rear door system consists mainly of two large one-step-moulded parts: - an inner structural part that is compression moulded in GMT/ GMTex and - an outer part that is injection moulded in Noryl GTX. The pillar and lock area features some additional metal reinforcement. The hatchback door is quite large (~1600mm in Y direction, ~920mm in Z direction) compared to the conventional doors in this SUV market segment, and even more so compared to passenger cars. All attachment parts – hinges, wiring harnesses, lock, gas spring fixations, rubber stops, third stop light, rear window and licence lumps – are mounted onto the body-in-white of the rear door in a series of pre-assembly steps.
A high-flow GMT grade is used to achieve the good surface quality of the inner structural part. This also reduces added weight while improving the height-to-thickness ratio of the structural ribs. The surfaces that are visible in the passenger compartment have a grained surface and are painted in interior colour.
The outer panel is painted off-line in nine different body colours and glued in the border area to the inner part.
Different simulation tools were used during the development process to find the right parameters before prototyping. For the thermal elongation behaviour of inner and outer materials, no critical transitions were measured in the gap area. Therefore, the convex shape of the outer panel influences the behaviour in different temperature rates positively.
Using thermoplastic materials reduces the weight of each car by about 5 kg and provides a styling flexibility that is not possible with metal materials. Integrating components also reduces cost, compared to a steel solution with identical functions. The GMT/ GMTex materials used for the structural part ensure the crashworthiness of the rear door system.
Quadrant Plastic Composites
Quadrant Plastic Composites and its subsidiary Quadrant Natural Fiber Composites are worldwide leaders in the development, manufacturing and sales of glass-/natural-fibre reinforced polypropylene thermoplastic composites. The company’s strategic positioning allows it to supply the world’s major regional markets efficiently with its high-quality GMT, GMTexTM, SymaLITE and semi-finished products. QPC offers its customers industrial design capacities and CAD engineering resources, and works with compression moulders and part suppliers to provide support for global solutions, all the way from product design concept to market launch. QPC also develops concepts directly with system suppliers or automakers.