Investigation of the effects of cryogenic machining on surface integrity in CNC end milling of Ti–6Al–4V titanium alloy

Abstract

This paper presents the first comprehensive investigations on the effects of cryogenic cooling using liquid nitrogen on surface integrity of Ti-6Al-4V titanium alloy workpiece in end milling operations.Titanium is classified as a notoriously difficult-to-machine material, where its machining is characterised by poor surface integrity and short tool life. Increasing productivity, whilst meeting surface integrity requirements for aerospace and medical titanium-based components has always been a challenge in machining operations. Cryogenic machining using super cold liquid nitrogen at -197°C is a method to facilitate heat dissipation from the cutting zone and reduce the chemical affinity of workpiece and cutting tool materials and therefore improving machinability. Since milling is one of the major machining operations for aerospace components, this study is concentrated on cryogenic milling. The effects of cryogenic cooling on surface integrity are compared to conventional dry and flood cooling in end milling Ti-6Al-4V titanium alloy. A series of machining experiments were conducted at various combinations of cutting parameters. Surface roughness and microscopic surface integrity were investigated and subsurface microhardness was measured for each sample.The analysis indicated that cryogenic cooling has resulted in up to 39% and 31% lower surface roughness when compared to dry and flood cooling methods respectively. Furthermore, microscopic surface defects were significantly reduced as a result of cryogenic. The investigations indicated that cryogenic cooling considerably improves surface integrity in end milling of Ti-6Al-4V.

Influence of cutting environments on surface integrity and power consumption of austenitic stainless steel

“…9 the surface roughness increases when increasing the feed per tooth. This result is in agreement with previous research and is probably due to the fact that as the feed is increased the thickness of the chip also increases resulting in an increase of cutting forces [8,13,14].…”

“…When analyzing the results corresponding to a cryogenic cutting environment it can be observed that an increase of 50% of the cutting speed (from 105 m/min to 157 m/min) produced an increase of 4% on the surface roughness (from 1.180 μm to 1.229 μm), as previously mentioned probably due to a possible increase on the materials hardness as an effect of using super cold liquid nitrogen [8]. As the increased in roughness was so small (4%), we can consider a neglected influence of the cutting speed when machining in a cryogenic environment under this cutting speed and feed per tooth under study as a difference of almost 20% between the minimum and the maximum value of roughness was obtained when measuring the roughness of each trial.…”

“…The stainless steel has been defined as a difficult-to-machine ferrous alloy [8], basically due to its low thermal conductivity, where the heat generated during the cutting process concentrates in the cutting zone producing diffusion as main tool wear mechanisms as well as Built Up Edge (BUE) formation, this last increases the machining instability producing chipping on the cutting edge and poor surface quality.…”

Experimental study on chip deformation of Ti-6Al-4V titanium alloy in cryogenic cutting

“…The results indicated that the cryogenic cutting showed better performances than dry and wet cutting by reducing the tool wear and improving the surface integrity and the chip breakability. Shokrani et al [11] investigated the influence of cutting parameters and cooling conditions on surface roughness, surface integrity, and microhardness of titanium alloy in end milling operations. It was found that cryogenic cooling could reduce the surface roughness by 39 and 31% when compared to dry and flood cooling methods, respectively.…”

Evaluation of a Novel Controlled Cutting Fluid Impinging Supply System When Machining Titanium Alloys

“…The high working hardening affinity of titanium alloys can also promote high cutting forces and temperatures, leading to tool notching and excessive tool wear [5]. Without a cutting fluid, titanium alloys are more prone to forming oxides in atmospheric environments, which can also negatively affect their mechanical properties, causing embrittlement and reduced alloy fatigue strength [6][7][8]. Mineral oil-based, semi-synthetic and synthetic cutting fluids are traditionally employed due to their chemical stability.…”