Title: Effects of milling methods and cooling strategies on tool wear, chip morphology and surface roughness in high speed end-milling of Inconel-718

Authors: Anthony Chukwujekwu Okafor; Paras Mohan Jasra

Addresses: Computer Numeric Control and Virtual Manufacturing Laboratory, Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, 327 Toomey Hall, Rolla, MO-65409-0050, USA ' Computer Numeric Control and Virtual Manufacturing Laboratory, Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, 327 Toomey Hall, Rolla, MO-65409-0050, USA

Abstract: This paper presents the results of experimental investigation of the effects of milling methods (up-milling and down-milling) and cooling strategies [emulsion cooling, minimum quantity lubrication (MQL), cryogenic cooling using liquid nitrogen (LN₂) and combined (MQL + LN₂)] on flank wear, chip morphology and surface roughness in peripheral high speed end-milling of Inconel-718. The experimental results show that down-milling generated lower maximum flank wear than up-milling for all cooling strategies, thus improves machinability. MQL cooling with down-milling generated lowest maximum flank wear of 0.072 mm after eight passes and is recommended for machining Inconel-718, whereas LN₂ cooling with up-milling generated highest flank wear of 1.984 mm after first pass only. Tool wear mechanism in up-milling is adhesion and failure modes are chipping and plastic deformation, causing rapid tool wear, while abrasion is the tool wear mechanism under down-milling causing progressive tool wear. Also, emulsion up-milling generated lowest surface roughness of 0.29 μm, whereas emulsion, MQL and combined (MQL + LN₂) cooling strategies with down-milling generated equal and second lowest surface roughness of 0.34 μm. Results show that using MQL cooling under down-milling for machining Inconel-718 can lead to significant cost saving and sustainable machining.

Keywords: milling methods; cooling strategies; tool wear; chip morphology; surface roughness; Inconel 718; high speed end-milling; emulsion cooling; minimum quantity lubrication; cryogenic cooling; machining; machinability.

DOI: 10.1504/IJMMM.2019.098065

International Journal of Machining and Machinability of Materials, 2019 Vol.21 No.1/2, pp.3 - 42

Received: 24 Feb 2018
Accepted: 16 May 2018
Published online: 01 Mar 2019 *

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