Experimental and numerical investigation of the weld repair of superplastic forming dies

Superplastic forming process (SPF) is an advanced process conducted at high temperature using moderate strain rates, typically used for shaping TA6V sheets for aerospace applications. Thermomechanical stresses on the forming dies due to successive forming cycles may result in the early degradation and even fracture of SPF tools through fatigue crack propagation. To reduce cost and extend service life, dies are generally weld-repaired and subsequently re-used in the typical severe conditions of SPF. The implementation of robust, easy processing welding techniques resulting in high quality repair able to sustain cumulative thermomechanical stresses is of utmost concern to SPF parts manufacturers. The paper focuses on the development of an automated TIG technique to weld repair high nickel, high chromium heat resistant alloys based on a complementary approach including thermal instrumentation, numerical simulation using SysweldTM and metallurgical investigation; this former being performed on either as-received, repaired and repaired plus damaged materials.