Future research directions in the machining of Inconel 718

Inconel 718 is the most popular nickel-based superalloy, extensively used in aerospace, automotive and energy industries owing to its extraordinary thermomechanical properties. It is also notoriously a difficult-to-cut material, due to its short tool life and low productivity in machining operations. Despite significant progress in cutting tool technologies, the machining of Inconel 718 is still considered a grand challenge.This paper provides a comprehensive review of recent advances in machining Inconel 718. The progress in cutting tools’ materials, coatings, geometries and surface texturing for machining Inconel 718 is reviewed. The investigation is focused on the most adopted tool materials for machining of Inconel 718, namely Cubic Boron Nitrides (CBNs), ceramics and coated carbides. The thermal conductivity of cutting tool materials has been identified as a major parameter of interest. Process control, based on sensor data for monitoring the machining of Inconel 718 alloy and detecting surface anomalies and tool wear are reviewed and discussed. This has been identified as the major step towards realising real-time control for machining safety critical Inconel 718 components. Recent advances in various processes, e.g. turning, milling and drilling for machining Inconel 718 are investigated and discussed. Recent studies related to machining additively manufactured Inconel 718 are also discussed and compared with the wrought alloy. Finally, the state of current research is established, and future research directions proposed.<br/

Comparison of Flank Super Abrasive Machining vs. Flank Milling on Inconel® 718 Surfaces

Thermoresistant superalloys present many challenges in terms of machinability, which leads to finding new alternatives to conventional manufacturing processes. In order to face this issue, super abrasive machining (SAM) is presented as a solution due to the fact that it combines the advantages of the use of grinding tools with milling feed rates. This technique is commonly used for finishing operations. Nevertheless, this work analyses the feasibility of this technique for roughing operations. In order to verify the adequacy of this new technique as an alternative to conventional process for roughing operations, five slots were performed in Inconel (R) 718 using flank SAM and flank milling. The results showed that flank SAM implies a suitable and controllable process to improve the manufacture of high added value components made by nickel-based superalloys in terms of roughness, microhardness, white layer, and residual stresses.The authors wish to acknowledge the financial support received from the Spanish Ministry of Economy and Competitiveness with the project TURBO (DPI2013-46164-C2-1-R), grant number [BES-2014-068874], to HAZITEK program from the Department of Economic Development and Infrastructures of the Basque Government and from FEDER funds, related to the HEMATEX project and Vice-chancellor of Innovation, Social Compromise and Cultural Action from UPV/EHU (the Bizialab program from the Basque Government). Finally, thanks are also addressed to Spanish Project MINECO DPI2016-74845-R and RTC-2014-1861-4

Mathematical Modeling for Radial Overcut on Electrical Discharge Machining of Incoloy 800 by Response Surface Methodology

AbstractIn the present study, Response surface methodology is applied for prediction of radial overcut in die sinking electrical discharge machining (EDM) process for Incoloy 800 superalloy with copper electrode. The current, pulse-ontime, pulse-off time and voltage are considered as input process parameters to study the ROC. The experiments were planned as per central composite design (CCD) method. After conducting 30 experiments, a mathematical model was developed to correlate the influences of these machining parameters and ROC. The significant coefficients were obtained by performing ANOVA at 5% level of significance. From the obtained results,It was found that current and voltage have significant effect on the radial overcut. The predicted results based on developed models are found to be in good agreement with the The predicted values match the experimental results reasonably well with the coefficient of determination 0.9699 for ROC

Experimental investigation on low-frequency vibration assisted micro-WEDM of Inconel 718

AbstractThe micro-wire electric discharge machining (micro-WEDM) has emerged as the popular micromachining processes for fabrication of micro-features. However, the low machining rate and poor surface finish are restricting wide applications of this process. Therefore, in this study, an attempt was made to improve machining rate of micro-WEDM with low-frequency workpiece vibration assistance. The gap voltage, capacitance, feed rate and vibrational frequency were chosen as control factors, whereas, the material removal rate (MRR) and kerf width were selected as performance measures while fabricating microchannels in Inconel 718. It was observed that in micro-WEDM, the capacitance is the most significant factor affecting both MRR and kerf width. It was witnessed that the low-frequency workpiece vibration improves the performance of micro-WEDM by improving the MRR due to enhanced flushing conditions and reduced electrode-workpiece adhesion

Effect of Cutting Parameters on Micro Drilling Characteristics of Incoloy 825

The study focuses on the micro drilling of Incoloy 825 alloy under flood cutting condition. Micro drilling on nickel based superalloy is very challenging process due to the material properties, operating conditions, low thermal conductivity and high quality requirements. Due to low thermal conductivity of material heat is concentrated near tool tip and unable to dissipate for which tool wear occurs. The current study described the machinability of Incoloy 825 in micro drilling operation and also the effect of spindle rpm and feed rate on thrust force, torque, radial component force, tangential component forces, oversize diameter and white layer thickness. The current study investigates the influence of micro drilling parameters on surface profile and circumferential damage of micro holes (in terms of damaged layer thickness). ANSYS simulation was carried out to theoretically determine and evaluated necessary data like equivalent stress and deformation. Statistical analysis was also carried out to develop predictive models for various output characteristics

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

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

Investigation of productivity, energy efficiency, quality and cost for laser drilling

Laser drilling is a high speed, non-contact advanced machining process and has proven to be an important industrial process for producing cooling holes in various aeroengine components; in particular high-pressure turbine blades, combustor liners and nozzle guide vanes. However, an increase in the number of cooling holes demands the need for effective utilisation of laser drilling process capability. Material removal rate (MRR), specific energy consumption (SEC), hole taper and the drilling cost are the basic performance indicators to meet this goal. Hence, this research aims to examine the laser drilling process in terms of the mentioned performance measures. Taking into account the significance of material removal quantity, energy efficiency, product quality and manufacturing cost, this study is performed in the form of an experimental investigation for three laser drilling processes, namely, single-pulse drilling, percussion and trepanning. Two different laser drilling setups were prepared to produce holes in Inconel 718 superalloy sheets using flashlamp-pumped Nd:YAG laser and Quasi-CW fibre laser. This research contributes to an evaluation of the influence of laser drilling process parameters on the MRR, SEC, hole quality and drilling cost. Moreover, the performance of laser drilling methods has been compared in relation to the selected performance measures. To further understand the significance of laser sources, the performance of laser drilling was compared for the mentioned drilling setups. This research also introduced a detailed cost analysis to explore the economic implications of the laser drilling process. In addition, optimal drilling conditions were determined aiming to maximise the MRR and minimise hole taper and drilling cost.Manufacturin

Laser powder bed fusion of INCONEL® 718: optimization of process parameters and residual stress analysis before and after heat treatment

Metals Additive Manufacturing (AM) is a “flourishing” technology, developing fast and successfully. Laser Powder Bed Fusion (LPBF) is among the most used metals AM processes in industry. Inconel® 718 (IN718) is a nickel-based superalloy that maintains its exceptional properties at high and low temperatures, thereby, it is a material commonly used to fabricate high performance components. The purpose of this work is to study the residual stress (RS) evolution of IN718 parts fabricated by LPBF, before and after heat treatment. Firstly, specimens with different combinations of parameters were fabricated to select the optimal LPBF process parameters. With the results from that part of the work, the influence of the individual process parameters on the porosity was studied. Then, new specimens were fabricated with the selected parameters and the RS analyzed by the hole-drilling strain-gage method, in as-built, solution annealed (SA) and SA plus double-aged (DA) conditions. It was concluded that increasing the scanning speed contributes to the reduction of the porosity. Also, for lower scanning speeds, 400 mm/s and lower, a hatching distance of 0.13 mm was defined as optimal. For higher scanning speeds, 600 and 800 mm/s, no relevant influence of the hatching distance, from 0.05 to 0.11 mm, on the porosity was observed. Laser power and layer thickness were not studied. Larger pores were found in specimens with higher porosity. Also, the specimens with higher porosity presented irregular pores and with lower porosity presented spherical-like pores. Regarding the RS evolution, as-built top surface presented uniform RS distribution of approximately 400 MPa. Lateral surface presented anisotropic distribution, with RS magnitudes of 600 to 800 MPa in build direction and 200 to 300 MPa horizontally. After the SA heat treatment, the RS decrease greatly to values between 50 – 200 MPa. Series of carbides were found at the grain boundaries, which were attributed as the cause for oscillations in the RS profile. SA plus DA condition presented RS between 10 to 50 MPa. Heat-treated specimens revealed compressive RS at immediately near the surface.A fabricação aditiva (FA) de metais é uma tecnologia “florescente”, em rápido desenvolvimento e com sucesso. Fusão a laser em leito de pó (LPBF) está entre os processos de FA de metais mais usados na indústria. Inconel® 718 é uma superliga à base de Nickel, que mantém as suas propriedades excecionais a altas e baixas temperaturas, desse modo, é comummente usada para produzir componentes de alto desempenho. O objetivo deste trabalho é estudar a evolução das tensões residuais (TR) de partes produzidas por LPBF, antes e pós tratamento térmico. Primeiramente, produziram-se amostras com diferentes combinações de parâmetros do processo LPBF para selecionar os melhores parâmetros. Com os resultados obtidos dessa parte do trabalho, foi estudada a influência na porosidade dos diferentes parâmetros. Então, produziram-se novas amostras com os parâmetros selecionados e foram analisadas as TR pelo método do furo cego incremental, nas condições: “as-built”, recozido (SA) e SA mais envelhecimento duplo (DA). Concluiu-se que o aumento da velocidade de varredura contribuí para a redução da porosidade. Também, para velocidades mais baixas, 400 mm/s e abaixo, a distância entre passagens de 0.13 mm foi definida como ótima. Para velocidades mais altas, 600 mm/s e 800 mm/s, a influência da distância entre passagens, de 0.05 a 0.11 mm, na porosidade é desprezível. A potência do laser e a espessura das camadas não foram estudados. Poros maiores foram observados nas amostras com maior porosidade. Também, as amostras com maior porosidade exibiram poros irregulares, e com menor porosidade poros esféricos. Em relação à evolução das TR, a face superior “as-built” apresentou uma distribuição das TR uniforme de aproximadamente 400 MPa. A face lateral apresentou distribuição anisotrópica, com TR entre 600 e 800 MPa na direção de deposição, e entre 200 e 300 MPa horizontalmente. Nas amostras SA, as TR reduziram substancialmente para valores entre 50 e 200 MPa. Foram detetados conjuntos de carbonetos, aos quais se atribuiu a ocorrência de oscilações no perfil das TR. A condição SA mais DA apresentou TR entre 10 e 50 MPa. As amostras tratadas termicamente revelaram TR à compressão bem próximo da superfície