Study of selective laser melting (SLM) Inconel 718 part surface improvement by electrochemical polishing

The surface integrity of machined metal components is critical to their in-service functionality, longevity and overall performance. Surface defects induced by machining operations vary from the nano to macro scale, which cause microstructural, mechanical and chemical effects. Hence, they require advanced evaluation and post processing techniques. While surface integrity varies significantly across the range of machining processes, this paper explores the state-of-the-art of surface integrity research with an emphasis on their governing mechanisms and emerging evaluation approaches. In this review, removal mechanisms are grouped by their primary energy transfer mechanisms; mechanical, thermal and chemical based. Accordingly, the resultant multi-scale phenomena associated with metal machining are analyzed. The contribution of these material removal mechanisms to the workpiece surfaces/subsurface characteristics is reviewed. Post-processing options for the mitigation of induced surface defects are also discussed.

Surface integrity in metal machining - Part I: Fundamentals of surface characteristics and formation mechanisms

The research and application of high speed metal cutting (HSMC) is aimed at achieving higher productivity and improved surface quality. This paper reviews the advancements in HSMC with a focus on the material removal mechanism and machined surface integrity without considering the effect of cutting dynamics on the machining process. In addition, the variation of cutting force and cutting temperature as well as the tool wear behavior during HSMC are summarized. Through comparing with conventional machining (or called as normal speed machining), the advantages of HSMC are elaborated from the aspects of high material removal rate, good finished surface quality (except surface residual stress), low cutting force, and low cutting temperature. Meanwhile, the shortcomings of HSMC are presented from the aspects of high tool wear rate and tensile residual stress on finished surface. The variation of material dynamic properties at high cutting speeds is the underlying mechanism responsible for the transition of chip morphology and material removal mechanism. Less surface defects and lower surface roughness can be obtained at a specific range of high cutting speeds, which depends on the workpiece material and cutting conditions. The thorough review on pros and cons of HSMC can help to effectively utilize its advantages and circumvent its shortcomings. Furthermore, the challenges for advancing and future research directions of HSMC are highlighted. Particularly, to reveal the relationships among inherent attributes of workpiece materials, processing parameters during HSMC, and evolution of machined surface properties will be a potential breakthrough direction. Although the influence of cutting speed on the material removal mechanism and surface integrity has been studied extensively, it still requires more detailed investigations in the future with continuous increase in cutting speed and emergence of new engineering materials in industries.

Advancements in material removal mechanism and surface integrity of high speed metal cutting: A review

Ceramic cutting tools are widely used particularly in high-speed machining of difficult-to-machine materials. However, using cutting fluid with these ceramic tools significantly reduces tool life. Therefore, the inclusion of a cooling/lubrication method into the process to improve the machining performance of ceramic tools will make machining efficiency much more effective. The aim of this study is to analyze the effect of cutting parameters and cooling/lubricating conditions on tool wear and surface roughness in the milling of nickel-based Waspaloy with ceramic tools. The cutting tools selected for the study were Ti[C, N]-mixed alumina inserts (CC650), SiC whisker-reinforced alumina inserts (CC670) and alumina and SiAlON ceramic inserts (CC6060). The machining parameters comprised three different cooling/lubricating methods (dry, wet and MQL), three different cutting speeds (500, 600 and 700 m/min) and three different feed rates (0.02, 0.04 and 0.06 mm/rev). Analysis of variance was used to determine the effects of the machining parameters on tool wear and surface roughness. In addition, a regression analysis was conducted to identify the relationship between the dependent and independent variables. According to the experimental results, the minimum quantity lubrication method was identified as the best cooling method for minimum tool wear and surface roughness. In terms of ceramic grades, the SiAlON inserts provided better results in all experimental trials. The dominant wear types observed in all cutting tools were flank wear and notch wear.

Tool wear and surface roughness analysis in milling with ceramic tools of Waspaloy: a comparison of machining performance with different cooling methods

Multiscale simulation of grain refinement induced by dynamic recrystallization of Ti6Al4V alloy during high speed machining

A physically based constitutive model for predicting the surface integrity in machining of Waspaloy

The paper presents a deep experimental study on surface modifications induced by roller burnishing process of Ti6Al4V titanium alloy. The experimental campaign has been performed based on a design of experiments at varying lubrication/cooling strategies, roller geometry, coating, and burnishing speed. The overall surface integrity has been analyzed in terms of surface roughness, micro hardness, topography, microstructural changes, and tribological performance. The results allowed to better define the relationships within burnishing process parameters and the surface quality of the final component. In particular, the obtained evidences show that cryogenic cooling conditions and coating tools significantly improve the hardness of the final component while the MQL lubrication leads to superior surface roughness. Overall, the process always improves the wear resistance of the components with optimal results when cryogenic cooling and coated tools are employed. Thus, the outcomes of the extensive experimental campaign allow to define a combination of process parameters leading to improved Ti6Al4V surface quality.

Roller burnishing of Ti6Al4V under different cooling/lubrication conditions and tool design: effects on surface integrity

It has been well documented in the literature the importance of strict surface integrity checks upon performance and quality of machined components, especially for the safety critical components (e.g., aerospace) that work at cyclic high mechanical loads and elevated temperatures. In this field, Waspaloy, within the commercially available nickel-based superalloys, is extensively applied in different industries such as aircraft, chemical plant equipment, and petrochemical equipment. The main objective of this paper is to implement a reliable FE model, for dry orthogonal machining of Waspaloy, capable to predict microstructural changes and dynamic recrystallization during the cutting process. A user subroutine was implemented in FE code to simulate the dynamic recrystallization and consequently grain refinement and hardness variation on the machined surface and below it. Zener–Hollomon (Z-H) and Hall–Petch (H-P) equations were employed to, respectively, predict grain size and microhardness. In addition, depth of the affected layer was controlled using the critical strain equation. FE numerical model was properly calibrated using an iterative procedure based on the comparison between simulated and experimental results. Finally, very good agreement was found between experimental and simulated results of grain size, microhardness, depth of the affected layer, and other fundamental variables such as cutting forces, temperature, and chip morphology.

Sergio Rinaldi

Papers

A physically based constitutive model for predicting the surface integrity in machining of Waspaloy

Roller burnishing of Ti6Al4V under different cooling/lubrication conditions and tool design: effects on surface integrity

Finite element modeling of microstructural changes in Waspaloy dry machining

Modelling the effects of twinning and dislocation induced strengthening in orthogonal micro and macro cutting of commercially pure titanium

2D FE Prediction of Surface Alteration of Inconel 718 under Machining Condition