Customer requirements

Reduced unsprung weight, whilst meeting stress requirements against benchmark current design loading
Weldable using existing production processes
Cost to be commercially viable at an increased sales price-point for benefits shown
Shaped tubing to optimise swing arm constraints, stiffness and loading identified during the design/FEA phase of the CENEX project in the UK.
Recyclable and repairable.

Project solution and benefits

2 materials options initially identified : air-hardening 631 and 853 steels
Air hardening steels like 631 can be TIG or MIG welded. After cooling in air without stress-relieving, these can reach weld zone yield strength in excess of 800 MPa.
Weight reduction on the “631” tube diagonals due to higher strength compared to existing steel = 35% (0.60 kg). Unit weight reduction for the lower wishbone (after re-design) was in excess of 20% including suspension joints, bushes etc.
Shaping of the 631 and 853 tubes reflects the practical layout needed during welding of the wishbone in production, but retains the ideal stiffness from the design phase.
The use of “butted” 853 tubing could provide a further weight saving c. 0.3kg for a premium up-grade option. Yield strength rises to over 1000 MPa, probably the highest strength steel in commercial use for steel fabrications, whilst butted tubes allow lower wall thickness in the sections with lower loads.

Weight savings c 31% were realised in the suspension tubular parts� whilst becoming more streamlined on the front suspension.

Phase 2 of the project on the chassis also achieved impressive targets � a 15% reduction in weight and a 33% increase in torsional rigidity for the unpanelled chassis. The chassis was also subjected to a frontal crash test, which demonstrated progressive deformation offering improved crash protection for the driver/passenger.

Contact for a PDF version of the final report to CENEX.

Delta Motorsport – design engineering
Penso – finite element analysis
Westfield Sportscars – specialist UK Sports car maker