By overmolding plastics and also metals, highly functional composite components, such as plug connectors can be produced. Plug connectors used in the automotive sector must meet high requirements. In addition to temperature fluctuations of 170 K, which in extreme cases can even occur several times a day, mechanical, electrical and chemical requirements must also be fulfilled. A fundamental requirement of the connector is tightness, which must be guaranteed over the entire product life cycle. A tight connector prevents the ingress of moisture and a wide variety of operating media such as lubricants and coolants. Penetrating media can lead to corrosion or a short circuit in internal metal contacts and consequently to failure of the connector. Currently, most of the plug connectors are made of short glass fiber reinforced polyamide (PA) materials, where the insert is made of PA 6 and the overmold out of PA 6.6. In order to improve the strength and, above all, the tightness between the components, so-called melt ribs are used. These are constructively attached elevations on the insert part, which partially melt during overmolding and mix with the overmolding material. The main target of this thesis was to investigate various geometry factors of the melt ribs in relation to the tightness of the connection, using statistical design of experiments. By using a special injection molding tool, it was possible to manufacture components - similar to a plug connector - with different melt rib geometries. After the inserts had been overmolded, the parts were investigated optically and for leaks, before and after a thermal aging procedure. Based on the optical investigations, geometric factors of the melt ribs could be determined, which led to an improved melting performance of the ribs. A direct correlation between melting performance and tightness could not be confirmed. However, one of the geometry factors could be linked to leaky components. It was also determined that severe damage to the melt ribs has a negative effect on the tightness. In addition to the geometry of the melt ribs, it was possible to define other factors that lead to an increased delamination between the insert and the overmold.