Case study: A tubular solution to lightweighting

Tata cuts chassis weight by 10%

All powertrain solutions demand that every part of the vehicle is as light as possible to maximise vehicle range, performance and efficiency. With its strict safety targets and narrow profit margins, an essential challenge of vehicle design is balancing weight with the performance of the materials and the cost of the process. Tata Steel’s total cost of ownership (TCO) concept studies can offer designers a solution to finding their preferred balance of the three. These studies quantify the TCO reduction potential that advanced steel solutions offer for specific automotive applications.

Following a customer request to propose affordable solutions to reduce the weight of a front chassis subframe, Tata Steel studied how replacing stamped and welded assemblies with a tubular intensive design could meet this objective. Tubular structures are more structurally efficient than welded stamped components and offer the possibility of part-count reduction, feature integration and improved joint configuration. Combined, these benefits can reduce both mass and cost. The resulting chassis design maximised these tubular benefits and ensured suitability for high-volume production.

Modelling

A conventional passenger car front subframe was selected as the baseline structure and Tata Steel engineers redesigned the structure using the company’s own tubes. These tubes were made from hot-rolled steel grades with gauges above 2.0mm, to prevent the need for galvanising and to avoid welding issues.

Different tubular processing solutions were considered, but hydroforming -pumping fluid into the metal at high pressure to force the tube to take the shape of the die - was selected, as this process can produce complex shape options whilst maintaining the required dimensional accuracy.

The tubular structure was designed using computer-aided design combinedwith Tata Steel’s bespoke Knowledge Based Engineering toolkit, which takes into account the ductility of the material to assess the hydroforming manufacturing feasibility, including assembly. All package constraints - the available space for the structure to avoid clashing with other critical areas such as the engine, wheel envelope and ground clearance - were maintained. Particular attention was given to the joint design, building on tubular joint design information generated by Tata Steel research and development, to ensure maximum stiffness in the final solution. Material selection was optimised between achieving best performance whilst ensuring the robust manufacturability of the tubular components during the hydroforming process.

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