Quanren Zeng

Investigation into grindability of a superalloy and effects of grinding parameters on its surface integrity

GH4169 is comparatively a new superalloy mainly used as turbine components because of its outstanding combination properties such as high-temperature strength, thermal stability and wear resistance. But these also make it hard to cut, and its machined surface quality and integrity are particularly sensitive to the manufacturing process employed. The existing researches on machining-induced surface integrity and machinability of hard-to-cut materials are briefly reviewed; the effects of processing parameters on surface integrity for GH4169 components are studied in detail via orthogonal-designed external grinding experiment. The single-factorial plain grinding experiment was designed to further investigate the influence of depth of cut on the surface integrity characteristics. The surface roughness, residual stress distribution, microhardness profile and microstructural alteration within the subsurface were obtained and analyzed. It was shown that the surface integrity is susceptible to the magnitude of depth of cut, and the components ground with low depth of cut are of more acceptable surface quality with less variation in residual stress and microhardness within the machining-affected layer than those obtained with high depth of cut. No severe microstructural alteration or adverse surface cracking was discerned when the depth of cut is reasonably set.

Parameterised FE modelling of the surface-systems with coatings which considers the cracking of the coatings and influences of the case-hardening of the substrate

Accurately predicting the failure of multilayered surface systems, including coatings on tools or products, is of significance for all of the parties concerned within the chain of design, manufacturing and use of a product. Previous modeling work has, however, been focused largely on the effect of individual parameters rather than on the performance of a multilayered system as a whole. Design and manufacture of multilayered surface systems, currently, still relies largely on experiments and failure tests. A parameterized approach which considers geometrical, material, interfacial and loading variables, processing history, thermal effects, surface-failure modeling, etc. has therefore been developed to address the situation in order to be able to improve the efficiency and accuracy of the analysis and design of multilayered coating-systems. Material property values for the hardened case of the substrate are described with a function of the hardened depth and defined with a field method. Initial residual stresses calculated using a newly developed theoretical model are incorporated into the model as initial stress conditions. Thermo-mechanical coupled modeling is incorporated into the model so as to be able to consider temperature effects. These are associated with a cohesive-element modeling approach, which has been used to predict indentation-induced crack initiation and propagation within the coating layer. The comparison of experimental results with those of numerical modeling affords excellent agreement. The parameterized modeling method developed allows for the parameters to be changed easily during a series analysis. Combined with the capability of the prediction of cracking of the coatings, the developed method/model provides an efficient way for investigating the effects of these parameters on the behavior of multilayered systems, which is demonstrated by the analysis of three cases of the coated tool steels (H11): (i) a substrate without being pre-heat-treated; and (ii) two substrates with a shallow and a deep hardened-case, respectively, (both are treated by plasma-nitriding). The results showed that the case-hardening of a substrate has a significant influence on the performance of the surface system with coating, especially on its load-bearing capacity and the cracking of the coating.

Multiscale modelling of hybrid machining processes

The fundamentals of multiscale modeling, e.g., its concept, definition and categories, are reviewed and summarized in this chapter. Different multiscale modeling approaches or techniques, such as sequential multiscale modeling and concurrent multiscale modeling are introduced. Then, the modeling for assisted hybrid machining processes, especially for the laser-assisted machining (LAM), are illustrated. A case study for the modeling of LAM is also analyzed and discussed in detail. The chapter concludes with the future possibility and prospect of making use of multiscale modeling techniques to facilitate investigation into the hybrid machining processes or process chain.

Advancement in additive manufacturing & numerical modelling considerations of direct energy deposition process

The development speed and application range of the additive manufacturing (AM) processes, such as selective laser melting (SLM), laser metal deposition (LMD) or laser-engineering net shaping (LENS), are ever-increasing in modern advanced manufacturing field for rapid manufacturing, tooling repair or surface enhancement of the critical metal components. LMD is based on a kind of directed energy deposition (DED) technology which ejects a strand of metal powders into a moving molten pool caused by energy-intensive laser to finally generate the solid tracks on the workpiece surface. Accurate numerical modelling of LMD process is considered to be a big challenge due to the involvement of multiple phase changes and accompanied mass and heat flows. This paper overviewed the existing advancement of additive manufacturing, especially its sub-category relating to the DED. LMD process is analyzed in detail and subsequently broken down to facilitate the simulation of each physical stage involved in the whole process, including powder transportation and dynamics, micro-mechanical modelling, formation of deposited track and residual stress on the substrate. The proposed modelling considerations and a specific CFD model of powder feeding will assist in accurately simulating the DED process; it is particularly useful in the field of aerospace manufacturing which normally has demanding requirement on its products.