The 9th and 10th of May were conference days at the Kilometro Rosso in Bergamo: more specifically, we talked about thermal fatigue, a complex multi-faceted phenomenon which affects the operators in the die-casting industry.
The event was organised by the Die-Casting Technical Committee of the AIM (Italian Metallurgical Association) which, since it was founded almost 20 years ago, has often promoted similar initiatives availing itself of the availability and – as illustrated on the event brochure – the “tenacity” of the aforementioned Committee members, always ready to give their time to promoting the dissemination of concepts and experiences.The goal of this two-days conference was to examine the vast topic of thermal fatigue from all possible points of view, providing insights to discuss consolidated issues with a more technical and unusual approach.
In this context, TAG contributed with two interventions on the topics discussed by our CEO Antonino Silipigni and the laboratory manager Michele Bosisio: the first speech focused on optimising the placement of the impression in the mould, the second on the plasma nitriding of die-casting mould cavities.
TECHNICAL TWEAKS FOR THE OPTIMISATION OF DIE-CASTING MOULDS
With this first presentation, TAG intended to provide evidence of the extensive experience gained over many years of work in the industry to the attendees: it is fairly obvious, in fact, that the end customer will always attempt to prolong the life of a mould as long as possible, but some factors that can prove to be crucial are often overlooked.
In first place it is necessary to carefully choose the most suitable steel for the production of the mould, according to the reference standards; secondly, the impression must be studied and designed in detail, then it should be placed parallel to the fibres and be obtained near the cortical area of the bar, in order to exploit the best reduction/compression ratio deriving from the manufacturing process.
Particular attention must also be paid to the performing of mechanical machining: if this is not performed to top workmanship standards it can alter and harden the cortical area of the material, making it more sensitive to breakage. An in depth study was carried out by TAG on this topic, in collaboration with the Fraunhofer Institute (Aachen, Germany) to describe the most recurring cases and the precautions to be considered in order to avoid similar problems.
Last but not least, the heat treatment of the moulds must be carried out paying great attention to the cooling phase, which must be controlled in order to achieve the best structural characteristics: the systems installed at TAG provide an optimal control of all the process parameters aimed at guaranteeing the best performances possible.
PLASMA NITRIDING OF DIE-CASTING MOULDS
The second speech focused on a mould processing system that can guarantee an extension of their useful life, with effective reduction of thermo-mechanical traction stress generated by the flow of liquid aluminium during the injection phase: ionic nitriding.
In fact, when the cavity section of the mould is enriched superficially with atomic nitrogen during the nitriding process, a compression layer is created in the material which helps the increase in wear and fatigue resistance. This prevents the propagation of thermal fatigue cracks and, more generally, leads to an improvement in the performance of the mould.
Still talking about ionic nitriding treatments, T-OXI® oxidation is a process that has been developed in TAG and that makes it possible to achieve significant benefits. This is basically a combined process of plasma nitriding and controlled-potential oxidation, preceded by a conditioning process that makes the surface of the parts active, boosting the diffusion of the oxide layer.
The oxide layer on the surface of the mould is applied to protect the cavity of the mould from direct contact with the melted alloy during the operating phases, reducing erosion, corrosion and bonding.
The modern ionic nitriding plant systems installed at TAG make it possible to carry out this treatment with more accurate control over each parameter, so as to regulate the depth of the diffusion of the nitrogen in the matrix and obtain the desired thickness of the oxidised layer. For further details, the two papers presented during the conference are