The non-return valve is an essential component of an injection molding machine. In combination with locking and pressure ring it prevents the back-flowing of the mold via custom-fit locking in the injection and holding-pressure phases, while it opens in the plasticizing phase. In these processes the forces within the different components are extremely high –pressures of even more than 2400 bar may occur in the injection phase. Thus non-return valves are subject to highest stress – especially at the so-called wings. Therefore both hardness and ductility at the wing tips have to be especially high in order to obtain a satisfactory lifetime of the non-return valve.
The technology of laser alloying is developed at MATERIALS since more than 20 years: by investigating different alloy systems these alloys are realized by using a high-power laser to melt the surface of a metallic compound to a depth of several millimeters while additional alloying elements are added to the melt pool. After solidification a new alloy is created. This technology can be regarded as “miniature steelworks”. The only limitation of laser alloying is the restriction on simple and nearly even surfaces aside from the edges.
The insertion of certain elements (V, Nb, Ti) results in the formation of monocarbides after solidification with high hardness of up to 3000 HV. The resulting microstructure can be systematically influenced by the feed rate.
Distribution, size and morphology of the precipitated carbides depend on the nucleation during cooling of the melt, which is not only a function of concentration, but also of the melting pool temperature and the cooling rate. Thus the melting pool temperature can be increased by higher power density resulting in an increased cooling rate and decreased nucleation. Furthermore, when alloying vanadium the additional seeding of titanium produces nuclei of titanium carbide (TiC) that serve as additional growth nuclei for vanadium carbide VC. This increase in the number of nuclei results in smaller carbides with higher density.
Homogenization of the melt pool is achieved through strong convection. Since the flow of the melt pool always runs towards the direction of rising surface tension, the geometry of the melt pool can be influenced by the addition of surface-active substances.
In cooperation with Engel Austria GmbH laser alloying with VC as wear protection at the critical spots of non-return valves was brought into serial production readiness in a development process over several years. The alloying process of steel was optimized by using Vanadium, which brought a high wear resistance in combination with low brittleness and a minimized crack susceptibility during production process.
Due to the limitation of this technology to the application on nearly even surfaces aside from the edges laser alloying on non-return valves was realized in this case on the semi-finished product. After the alloying process the residual oversize is removed and the form of the wings finalized, resulting in maximum alloying depth at the wing tips.
After successful transformation into serial-production readiness various dimensions of non-return valves of Engel Austria GmbH have been alloyed for 20 years. This specific way of the local modification of material properties is patented and cannot be substituted up to date by any alternative technology.