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Cryogenic Cutting of Titanium

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Gabriel Batistuta

on 20 May 2014

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Transcript of Cryogenic Cutting of Titanium

Cryogenic Cooling Technique In Titanium Alloys Machining
Coolant delivery techniques
Flood cooling: Poor penetration of the fluid at cutting interface, uneconomical and not environmentally friendly [1, 2].
Cryogenic cooling with liquid nitrogen (LN2): In cutting speed higher than 100 m/min, inadequate penetration of LN2 observed [3].
High pressure coolant: Higher consumption rate of the cutting fluid, high pressure delivery cost and system setup cost [1, 4].

ACF spray system
Pressure nozzle atomization and two-fluid nozzle or gas assisted atomization do not produce a narrow range of droplet sizes, resulting in difficult control for the droplet size distribution. Ultrasonic vibration creates quasimonodisperse sprays with easy control of the flow rate. This method can be made compact since no high pressure pump is required [6].

Photograph of the ACF spray unit [5]
High strength-to-weight ratio
High-temperature rate
Strong fracture and corrosion resistance

Aerospace industry
Medical devices and implants
Automobile industry
Sports equipments
Titanium alloys
Jet turbine blades made from Titanium alloy
Problem statement
High temperature developed in a more localized area during machining can not be immediately dissipate away from the tool-chip interface. It results in sever edge chipping and plastic deformation which ultimately shorten tool life and affect surface finish.

Effective cooling methods can significantly contribute to improve tool life by minimizing the friction and lowering the cutting temperature.

Effect of fluid concentration in Titanium machining
Issues in machining titanium alloys
Poor thermal conductivity
Thin produced chips cause a smaller tool-chip contact area
Chemically reactive with most tool materials at a cutting temperature of 500'C or above
The requirements for an effective cutting fluid application:

(1) the disturbance force due to the delivery of the cutting fluid to the cutting zone must be at least an order of magnitude less than the cutting forces.
(2) the cutting fluid must possess a good wettability to be able to penetrate into the cutting zone and lubricating property.
(3) the velocity of the droplets and the carrying air must be appropriate to effectively spread and wet the surface and simultaneously flush away chips from the cutting zone since micro-scale chips tend to stick to the cutting zone.

So an atomization-based cutting fluid (ACF) spray system required to deliver significantly small amount of cutting fluid in the form of small separated fluid droplets.
Schematic of an ACF spray system [5]
Fluid film formation and its penetration, cooling and lubrication characteristics of an ACF spray system are influenced by five specific system parameters:
1. Pressure level of the droplet carrier gas
2. Type of carrier gas
3. Fluid flow rate
4. Droplet impingement angle
5. Spray distance
ACF spray parameters in turning setup [5]
Front view of 2D cross-section of the nozzle unit [5]
The nozzle unit in the ACF spray system combines two nozzles of different sizes that are co-axially assembled.
To produce a focused and high-pressure fluid droplet jet, the pressurized gas is delivered through the gas nozzle that adds its momentum to the low-velocity fluid droplets.
In order to secure maximum fluid droplets coming with the pressured gas, Rukosuyev et al. [7] suggested that the gas nozzle outlet should be set inside with respect to the droplet nozzle outlet and the droplet nozzle should have a convergence slope.
At low Metal Working Fluid (MWF) concentration, a lack of the lubrication effect due to a smaller viscosity causes higher friction at the tool–chip interface resulting in severe chipping and tool nose/flank wear comparatively within a short machining time. In contrary, less amount of the cooling effect at high concentration increases cutting temperature and thus a faster thermal softening/chipping of the tool mate-rial and higher friction at the tool–chip–workpiece interaction zones resulting in early tool failure. The maximum tool life was found to be at the 10% MWF concentration [8].
Flood Cooling
Cryogenic cooling with liquid nitrogen
High pressure coolant
The effects of system parameters of atomization-based cutting fluid spray
Effects of nozzle geometry
The position of the nozzle with respect to the cutting zone is likely very critical for the system’s cooling and lubricating performance since the spray focuses at a specific point and then diverges.
It is preferable to have the high speed air jet pipe within the nozzle and a converging slope for the nozzle for better focusing of the spray [7].

Effects of mist and spray velocities
The mist velocity has a negative effect and the spray velocity a positive effect on the spray focusing [7].
Four different nozzle geometries [7]
Photograph of the spray at different nozzle geometries [7]

Wear at the tool rake and flank faces after 6 min for different concentration of the MWF [8].
Nozzle unit
[1] Nandy AK, Gowrishankar MC, Paul S. Some studies on high-pressure cooling in turning of Ti–6Al–4V. International Journal of Machine Tools and Manufacture 2009;49:182–98.

[2] Sun S, Brandt M, Dargusch MS. Machining Ti–6Al–4V alloy with cryogenic compressed air cooling. International Journal of Machine Tools and Manufacture 2010;50:933–42.

[3] K.A. Venugopal, S. Paul, A.B. Chattopadhyay, Growth of tool wear in turning of Ti–6Al–4V alloy under cryogenic cooling, Wear 262 (2007) 1071–1078.

[4] Pusavec F, Krajnik P, Kopac J. Transition to sustainable production – part I: application on machining technologies. Journal of Cleaner Production 2010;18:174–84.

[5] Chandra Nath, Shiv G. Kapoor, Richard E. DeVor, Anil K. Srivastava, Jon Iverson, Design and evaluation of an atomization-based cutting fluid spray system in turning of titanium alloy, Journal of Manufacturing Processes, Volume 14, Issue 4, October 2012, Pages 452-459, ISSN 1526-6125.

[6] Lacas, F., Versaevel, P., Scouflaire, P., and Coeur-July, G., 1994, “Design and performance of an ultrasonic atomization system for experimental combustion applications” Part. Part. Syst. Charact., 11(2), pp. 166-771.

[7] Rukosuyev M, Goo CS, Jun MBG. Understanding the effects of system parameters of an ultrasonic cutting fluid application system for micromachining. Journal of Manufacturing Processes 2010;12(2):92–8.

[8] Chandra Nath, Shiv G. Kapoor, Anil K. Srivastava, Jon Iverson, Effect of fluid concentration in titanium machining with an atomization-based cutting fluid (ACF) spray system, Journal of Manufacturing Processes, Volume 15, Issue 4, October 2013, Pages 419-425, ISSN 1526-6125.
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