<p>This study investigates a new method for enhancing the mechanical performance of clinched joints by filling the residual cavity with structural epoxy adhesive. Two adhesives (3M 07333 and Betamate 2098) with different Young’s moduli and multiple fill volumes were examined to determine how adhesive properties and cavity filling influence joint behaviour. Single-lap shear tests showed that adhesive filling increases peak force compared to unfilled joints, with the higher-modulus adhesive providing the largest improvement. Reducing the fill volume led to proportional reductions in shear strength, demonstrating that the joint response can be tuned through controlled cavity filling. In head-tension loading, adhesive filling increased peak force relative to unfilled joints, although variations in fill volume produced no significant change. All shear specimens failed by neck fracture, while cross-tension specimens consistently failed by pull-out, indicating that the adhesive modifies load capacity but not failure mode. The results demonstrate that cavity filling is an effective post-process reinforcement strategy that allows targeted adaptation of clinched joint behaviour without modifying the clinching process or geometry.</p>