<p>The increasing application of tailor-welded blanks in automotive structures has emphasized the need for methods of material testing that offer analyses of the paired materials and weld seam, as well as fast production accompanying inspection. In conventional cupping tests, heterogeneous thickness distributions and asymmetric stiffness of tailor-welded blanks lead to non-uniform deformation and weld seam misalignment. This work presents a self-adjusting cupping test tool designed specifically for the evaluation of stretch formability of the weld seam of tailor-welded blanks composed of sheets of dissimilar thicknesses. The tool integrates an adaptive die mechanism capable of automatically compensating for the stepped geometry of the blank. This self-adjustment ensures uniform contact pressure between tool and blank and, thus, minimizes bending moments that can compromise test validity in conventional tool setups. Experimental investigations demonstrate that the self-adjusting die significantly improves deformation symmetry and provides more representative measurements of the cupping depth.</p>