Plasmaterm (Romania)

The cooling system is a critical element in tooling for hot stamping high-strength aluminium alloys, for which very high quenching rates are required to ensure a supersaturated solid solution state in formed parts. To enhance cooling, ducts within the tools should be close and conformal to the surface die profile. Currently, ducts with curved profiles are made by drilling short straight lengths in die segments which are clamped together to form a complete die, which is expensive and hard to achieve the shape of duct with best cooling performance. To address these disadvantages, a novel method which enables efficient manufacture of conformal cooling systems by embedding a network of tubular cooling ducts within a cast matrix is presented in this paper. The feasibility of the proposed method of making ducts in the hot stamping die is demonstrated. Both experimental and computer-based die quenching tests using heated aluminium test pieces were undertaken to determine the cooling performance of a laboratory-scale tool set with cooling ducts. Simulations using the validated FE model were performed to investigate the effects of cross-sectional geometry, material and duct layout, on the quenching performance of the tools. It was found that ducts made of mild steel perform sufficiently well to make the use of high conductivity copper unnecessary. For a flat die surface, square section ducts provided highest cooling rates in comparison with circular and diagonal ones. The uniformity of die temperature increases with the decreased distance between neighbouring ducts, which indicates that a minimal gap is recommended without deteriorating tool strength. The developed tooling technology has the potential to provide a low-cost, highly efficient method of making conformal cooling ducts because the hot stamping die of high-strength aluminium alloy panels requires larger dimension, greater complexity and higher quenching rates.

Abstract Continuing the author’s efforts to outline the possible changes in surface engineering in the next decades, the present trends in materials science are analysed. The criteria considered in this analysis are connected to the imperatives of sustainable development, energy and environment. A comparison between the applications of new, non-conventional materials and those of ‘classical’ ones leads to the conclusion that for the next 20–30 years the most efficient way to preserve our ‘global assets’ is to reduce the specific materials and energy consumption by increased performance and more rational orientation in demand. Surface engineering is an efficient way to approach this target as it helps to find optimum combination between the bulk and surface properties. A brief analysis of the wide-spread and emerging surface engineering technologies helps to outline what reasonably may be expected in the next 25–30 years in the related field. The importance of more ‘common’ engineering solutions is emphasis...

Abstract The development of low temperature nitriding treatments to enhance wear resistance over the past 40 years is reviewed. The progress achieved is illustrated with evidence from extensive laboratory investigations and industrial trials on textile machine components and other parts. It is demonstrated that small additions of an oxidising component to gaseous nitrocarburising or plasma nitriding/nitrocarburising atmospheres have a beneficial effect on layer formation and on the wear properties of the treated components. The presence of oxygen increases layer formation rates and stabilises the ϵ-compound layer. The role of oxygen on surface activation is important for chromium containing steels but also on plain carbon or alloyed steels and to neutralise the passivating effect of finishing procedures. Applying a post-oxidation step after nitrocarburising can significantly increase the corrosion resistance of the surface but close control of gas composition and treatment parameters is necessary.