Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The aerospace industry actively pursues innovation, especially in materials and their use in new
applications, to improve their aircraft as well as their competitive position. Ti-6Al-4V has been available
now for more than 50 years. Yet, in the new generation of aircraft using structural composites,
a dramatic increase in the proportion of Ti-6Al-4V will be seen along with emerging application in
automotive and chemical industries. This material possesses superior material properties compared to
conventional materials such as steel and aluminium, although it is at the expense of machinability.
Researchers are therefore actively searching for improved cutting technologies to improve production
rates for Ti-6Al-4V. At higher cutting speeds than the industry norm of 60 - 90 m/min, machining
becomes a challenge, resulting in low productivity on titanium parts.
The limiting factor in the machining of Ti-6Al-4V is high tool temperatures of the order of 1000oC, caused
by its resistance to absorb heat and good mechanical strength at elevated temperatures. The result is
extreme temperatures that are concentrated on the cutting edge of the tool. The challenge to improve
the tool life is therefore focused on removing heat from the insert. Liquid nitrogen was identified as a
good candidate as coolant with the additional advantage of being environmentally friendly.
The research presented investigates the use of a gravity feed enclosed liquid nitrogen cooling system to
improve the tool life of the cutting inserts. The liquid nitrogen is contained on the insert rake face by
means of a tool cap. To improve the effectiveness of the cooling method, a polycrystalline diamond
(PCD) insert was used. This insert has a considerably higher thermal conductivity that aids in cooling the
cutting edge. Tungsten carbide inserts are used for benchmark testing.
The round tungsten carbide inserts with conventional cooling performed exceptionally well for
machining titanium compared to square inserts, yielding exceptional tool life improvements while
significantly increasing the material removal rate.
Positive results were recorded with the liquid nitrogen cooling system when used with the
polycrystalline diamond cutting insert. A number of far reaching performance issues are identified
relating to the design of the tool cap that hindered clear scientific outputs. From a research perspective,
the project makes a contribution to the knowledge base in this field. Additionally a new approach in
cooling was investigated, resulting in clear indications of design changes required. / AFRIKAANSE OPSOMMING: Die lugvaart industrie streef aktief innovasie na, veral op die gebied van materiale en hul gebruike, om
hul vliegtuie en kompeterende posisie in die mark te verbeter. Ti-6Al-4V is al vir meer as 50 jaar
beskikbaar. ‘n Drastiese verhoging in die aanvraag na Ti-6Al-4V deur die lugvaart, motor en chemiese
industrieë word verwag wanneer die volgende geslag vliegtuie wat koolstofvesel as strukturele
materiaal begin gebruik, in produksie gaan. Die materiaal het beter materiaaleienskappe as
konvensionele materiale soos staal en aluminium, maar dit kom egter teen die prys van
masjieneerbaarheid. Ti-6Al-4V se masjienering bo die industrie norm van 60 – 90m/min is ‘n groot
uitdaging. Navorsers soek daarom deurentyd na verbeterde sny tegnologieë om die produksie tempo
van Ti-6Al-4V te verbeter.
Die beperkende faktor vir Ti-6Al-4V masjienering is die temperatuur wat genereer word. Die weerstand
van die materiaal om hitte te absorbeer en sy goeie meganiese eienskappe veroorsaak dat temperature
in die beitel 1000oC bereik. Hierdie temperature word egter op die snykant van die beitel gekonsentreer.
Die uitdaging is dus om hierdie temperature in die beitel te beheer. Vloeibare stikstof is geïdentifiseer as
‘n goeie kandidaat vir verkoeling met die bykomende voordeel dat dit omgewingsvriendelik is.
Die navorsing wat hier uiteengesit word, ondersoek die gebruik van ‘n geslote kamer
beitelverkoelingstelsel wat deur gravitasie met vloeibare stikstof voorsien word om die beitel leeftyd te
verbeter. Die oppervlak van die beitel word in hierdie konsep direk aan die vloeibare stikstof
blootgestel. Om die effektiwiteit van die stelsel te verbeter word van PCD beitels gebruik gemaak. Die
beitel se verbeterde hittegeleidingsvermoë help om die beitel se snykant koel te hou. Tungstenkarbied
beitels word gebruik om ‘n standaard te stel vir eksperimentele analise.
Die ronde tungstenkarbied beitels en konvensionele verkoeling het verstommend goed presteer vir
Ti-6A-4V masjienering in vergelyking met vierkantige beitels. Die materiaalverwyderingstempo is
aansienlik verhoog sonder om die beitel se leeftyd in te boet.
Positiewe resultate is waargeneem met die vloeibare stikstof sisteem saam met die PCD beitels. ‘n
Aantal verreikende uitdagings is geïdentifiseer wat suiwer wetenskaplike afleidings bemoeilik. Hierdie
probleme kan almal aan die ontwerp van die toerusting toegeskryf word. Die werk lewer egter steeds ‘n
bydrae tot die kennis in die veld. ‘n Bykomende benadering vir verkoeling is ondersoek wat duidelik
ontwerp-veranderings aandui.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/18058 |
| Date | 12 1900 |
| Creators | Koen, Devan |
| Contributors | Treurnicht, N. F., Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 85 p. : ill. |
| Rights | Stellenbosch University |
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