PSI - Issue 19

M. Duchet et al. / Procedia Structural Integrity 19 (2019) 585–594 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Secondly, taking as reference a study made on a real application in the framework of S-in motion® solutions, a rear multi-link subframe (Fig. 14), replacing High Strength Low Alloyed steels (tensile strength in a range 280-420 MPa) by a combination of AHSS steels (tensile strength in a range 590-1000 MPa) and design adjustments allows to achieve almost 6 kg of mass reduction. From the initial mass of the component 28.6 kg, the introduction of AHSS having lower thicknesses as well as the integration of design modifications permit to reduce the total mass down to 22.7 kg . The additional cost induces by grades replacement does not exceed 0.62 € per kg saved according to an accurate cost evaluation.

Fig. 14: lightweight steel solution of a rear multi-links subframe by intensive introduction of AHSS grades.

Regarding this application, 8.5 meters of GMA welds are needed to assembly the components. Thanks to the help of our partner Improvalue, the cost of each solution has been precisely evaluated integrating all categories of cost (investment amortization, manpower, overhead, mark- up, charges…). The additional induced cost is reported according to the weld length to be reinforced. For a shot-peening post-treatment, the component being entirely put into a closed chamber of a shoot-peener, the cost is independent of the weld length but is counted for an entire part. It is reminded that we have arbitrary limited the cost of the weight saving to 3 € / kg saved as eligible in the automotive industry. The results are provided in Table 1 applied to rear multi-link subframe. The eligible costs are framed in green. For example, concerning TIG remelting, the maximal length of welds that can be reinforced is 2.55 m. Above, additional cost is higher than 3€ / kg saved. Then t he application of reinforcement solution should be used locally on specific welds when necessary. Post-treatments like TIG remelting or transversal oscillating welding could then be limited by their cost. On the other hand, shot-peening remains a cost-effective solution for the treatment of whole part, allowing also possible extra weight saving or solving fatigue issue on parent material.

Table 1. Evaluation of the additional costs generated by reinforcement solution for a total length of GMAW up to 8.5 meters for the rear multi-links subframe (Fig. 14).

Post-treated GMAW length [m] Cost vs process [€/kg saved]

0 0.85 1.7 2.55 3.4 4.25 5.1 5.95 6.8 7.65 8.5

TIG robot 0.62 1.41 2.19 2.98 3.77 4.56 5.34 6.13 6.92 7.70 8.49 Trans. osc. robot 0.62 1.03 1.44 1.86 2.27 2.68 3.09 3.51 3.92 4.33 4.75 Shot peening 0.62 1.44