In the multi-material lightweight design of structural components for the automotive industry, the joint between different materials plays a significant role in reducing vehicle weight without compromising performance or safety. Conventional technologies to mechanically join metals and carbon fibre reinforced polymers result in either drilling a hole in the composite material or increasing the weight of the part because of the fasteners employed. This work presents a new, simple, cost-efficient and non-weight penalizing mechanical joining technology for metal sheets and fibre reinforced polymer prepregs. It consists of a single-step punching process where the metallic sheet is completely perforated, but the prepreg is not. The punch pushes the carbon fibres through the hole in the metal sheet with no or minimal fibre breakage, generating a mechanical interlock which, in turn, increases the shear strength and absorbed energy of the co-cured joint.