The lightweight equipment container system (LGS)

Functional integration as a lightweight construction approach

Rail vehicles and some commercial vehicles have various equipment containers on the roof and in the underfloor area, which contain a wide variety of assemblies (air conditioning, electrics, pneumatics, etc.). Conventional equipment containers are manufactured using the differential frame construction method. This means that a, usually welded, rigid tubular frame absorbs all the forces acting on it (acceleration and deceleration loads, as well as crash loads) and transfers them to the vehicle via the connection points. One consequence of this is that the planking of the container primarily provides weight. Due to the requirements for dust and water tightness, as well as protection against accessibility, it is not possible to remove the sheet metal planking or replace it with lighter textiles.

In the joint project LGS - modular lightweight equipment container system, TGM Lightweight Solutions GmbH has found an alternative construction method with the hybrid shear panel design, which makes it possible to integrate the planking to absorb the forces. This makes it possible to downsize the frame, resulting in a weight reduction of up to 20%.

Aircraft construction shear panel design for container system

In order to integrate the cladding into the load-bearing structure, the shear panel construction method, which is known from aircraft construction, is used. Figuratively speaking, a shear panel can be imagined as the substitution of the diagonal members of a truss by metal sheets. A flexible frame is used in the main load direction, which is filled with shear bays. The frame is therefore mainly subjected to longitudinal forces instead of bending moments.

The advantage of such a design is that the shear panel is subjected to buckling rigidity that is several times higher than the bending rigidity of a conventional frame. This means that the frame can be made significantly slimmer.

Topology-optimized nodes, laser welding and modularity for maximum efficiency

The prerequisite for load transmission by shear bays is a frame consisting of bars that are usually arranged at right angles but mounted on pivot bearings so that only the normal forces are transmitted.

TGM's topology-optimized corner connectors meet this requirement without having to provide actual rotatability. This is achieved by creating stiffness corridors during topology optimization. The iterative removal of material during optimization enables an optimum compromise between bending capacity in the main load direction and stiffness orthogonal to it.

Generative manufacturing processes such as selective laser melting make it possible to produce corner connectors without losing lightweight construction potential due to manufacturing restrictions. Alternatively, node structures were developed using conventional construction methods, which still enable a high degree of lightweight construction at lower costs.

Laser welding is used as the joining method. The general advantages of laser welding also apply to this design. For example, the continuous, high-quality weld seam ensures that the container is leak-proof and that forces are applied and transmitted evenly. The lower, concentrated energy input into the components compared to other welding processes enables the use of thinner sheet thicknesses. The riveting process also offers an alternative here.

Another weight advantage results from the modular design of the equipment container. On the one hand, this applies to the individual container, which can be designed for a wide range of sizes and load weights without great effort. On the other hand, several containers can be combined in a global approach, eliminating duplicate structures and increasing the weight potential to over 20%.

Patented appliance container offers major cost and energy savings

The lightweight equipment container system is patented thanks to its innovative design. For customers who rely on this lightweight container, there are significant energy and therefore cost savings over the service life of the rail vehicle. The German Aerospace Center puts the reduction in energy requirements at up to 22.0 kWh/100 km for a weight saving of one ton.

The greatest savings can be achieved in suburban and regional areas. As several equipment containers are usually used per vehicle, this effect is multiplied and the ecological footprint is further reduced.