## 4 Discussion  
Microscopic examinations of cross sections of embedded weld inserts before REW verified a complete filling of the undercut with reinforcing fibres and matrix for both types of weld inserts. Furthermore, the weld inserts are well positioned with the shank tip protruding from the laminate to enable the subsequent welding process. Thus, the selected process parameters for process-integrated embedding of weld inserts into TPC (cf. Table 1) could be confirmed as suitable for further investigations. The developed technology can be applied to other types of TPC in terms of matrix material as well as architecture and material of the reinforcement. For this purpose, the process parameters such as the heating temperature of the TPC sheet and the mould temperature need to be adjusted accordingly.  
For an application of the developed technology, especially in series production, the joint strength of the embedded weld inserts and the TPC component must be high enough to provide reliable handling of the component up to the final part assembly by REW. Due to the larger undercut, the measured ultimate push-out load of type A with 1.7 kN is higher than type B with 0.8 kN. For the further handling process, the push-out loads are considered high enough for both types of weld inserts.  
For the subsequent welding process, suitable process parameters were determined by numeric welding simulations, which were verified by the analysis of etched microsections. The shape and diameter of the weld nuggets were within the range predicted by the numeric simulation. With these types of welding simulations, a prediction of suitable process parameters can be obtained rapidly for applications with alternative materials or sheet thicknesses. In this context, the short welding times of 40 ms are particularly notable, which promise efficient processing.  
In chisel tests, a sufficient strength of the welded joints could be determined, as the failure mode matched the aspier failure for REW, which is unbuttoning of the weld nugget from the steel sheet or unbuttoning of the TPC. Tensile test using a weld stud welded on the head of the insert to transfer the tensile load will be carried out in order to quantify the ultimate strength of the weld nugget between the insert and the steel sheet.  
The ultimate shear load of the welded joints is higher for weld insert type A (3.7 kN) as compared to type B (3.0 kN). This is due to the significantly smaller countersunk head of type B compared to the head geometry of type A that protrudes from the composite surface as a disturbing contour. The load bearing capacity could be further increased by adjusting the head geometry, for example by increasing the head thickness. This could change the failure behaviour under shear load to a laminate bearing before element pull-out of the TPC. In addition, cross-tension tests will be carried out for further evaluation of the load bearing capability.  
It could be shown that high-quality joints can be achieved with the developed technology. This provides the opportunity to use conventional spot-welding guns in established metal-oriented processes for TPC as well. Compared to other technologies using weld inserts (such as [14]), the proposed approach allows the embedding of the weld insert during composite component manufacture without an additional process. Thereby the embedding of the weld insert does not require the preparation of a pre-hole in the TPC. For these reasons, the developed technology offers an excellent opportunity to integrate TPC into steel dominated multi-material systems. Of particular interest are fields of application where resistance spot welding is already implemented in series production, such as in the automotive industry.