Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The purpose of this study is to investigate the machinability of commercially pure (CP)
titanium, manufactured using the press-and-sinter PM process.
To this end, CP titanium powder (-200 mesh) was compacted and sintered in vacuum
(10-4 torr) for two hours at 1200°C. Small cylindrical samples were compacted at
pressures varying from 350 to 600 MPa in order to determine the compressibility of the
powder. Following these tests, four larger stepped-cylinder samples were compacted at
pressures close to 400 MPa and sintered under similar conditions. These samples had
sintered densities varying between 3.82 and 4.41 g/cm3. They were used to evaluate the
machinability of the sintered titanium using face turning machining tests.
The samples were machined dry, using uncoated carbide (WC-Co) cutting tool. Cutting
speeds between 60-150 m/min were evaluated while keeping the feed rate and depth of
cut constant at 0.15 mm/rev and 0.5 mm, respectively. The final machined surface finish
and the tool wear experienced during the face turning machining tests were monitored in
order to evaluate PM titanium’s machining performance.
This study showed that it is possible to use the press-and-sinter PM process with CP
titanium powder, with a particle size of less than 75 μm (-200 mesh), to manufacture
sintered titanium. However, particle shape influences the compressibility of the powder
and pressing parts of larger volume, such as the machining test sample shape, is
challenging when using such small particle size powder. Processing conditions, such as
compaction pressure, sintering temperature and sintering time, influence the sintered
density.
Results from the machinability tests show that tool wear increases with a decrease in the
porosity of the sintered titanium. A more porous sintered material has both lower strength
and thermal conductivity. As these factors have opposing effects on the machinability of
materials, it is concluded that the strength of the sintered titanium has a stronger influence
on its machinability than the thermal conductivity.
The cutting tool wear was uniform but showed indications of crater wear. The machined
surface of the denser parts had minimal defects compared to less dense parts. Chip shape
is long for the dense parts, and spiral for the less dense parts. The chips formed were all
segmented, which is typical for titanium.
The machinability of the sintered CP titanium was compared to that of wrought titanium
alloys. As expected, it was found that the machinability of the sintered titanium was poor
in comparison. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie is om die masjineerbaarheid van kommersieel suiwer (KS)
titaan, wat deur die pers-en-sinter poeiermetallurgie (PM) metode vervaardig word, te
ondersoek.
Om hierdie doel te bereik, is KS titaan poeier (-200 ogiesdraad) gekompakteer en gesinter
in ‘n vakuum (10-4 torr) teen 1200°C vir 2 ure. Klein silindriese monsters is tussen drukke
van 350en 600 MPa gekompakteer om die samedrukbaarheid van die poeier te bepaal. Na
aanleiding van hierdie toetse, is vier groter trapvormige-silinder monsters by drukke naby
aan 400MPa gekompakteer en onder soortgelyke omstandighede gesinter. Hierdie
monsters het gesinterde digthede tussen 3.82 en 4.41 g/cm3 gehad. Hulle is gebruik om
die masjineerbaarheid van die gesinterde titaan te ondersoek deur middel van vlak-draai
masjineringstoetse.
Die monsters is sonder smeermiddel gemasjineer met onbedekte karbied (WC-Co)
snygereedskap. Snysnelhede tussen 60 – 150 m/min is geëvalueer terwyl die voertempo
en diepte van die snit konstant by 0.15 mm/rev en 0.5 mm, onderskeidelik, gehou is. Die
finale gemasjineerde oppervlak afwerking en gereedskapsslytasie tydens die vlak-draai
masjinering toets is van die faktore wat gemonitor is sodat PM titaan se optrede tydens
masjinering geëvalueer kan word.
Hierdie studie wys dat diepers-en-sinter metode wel met KS titaan poeier, met ‘n partikel
grootte van minder as 75 μm (-200 maas), gebruik kan word om gesinterde titaan te
vervaardig. Die partikelgrootte beïnvloed wel die samedrukbaarheid van die poeier. Die
samedrukking van parte met groter volume, soos bv die masjinerings toetsmonster, is
uitdagend wanneer klein partikelgrootte poeier gebruik word. Proses omstandighede, soos
kompaksie druk, sinteringstemperatuur en sinteringstyd, beïnvloed die gesinterde
digtheid.
Resultate van die masjineerbaarheidstoetse wys dat beitelslytasie toeneem met ‘n afname
in porositeit van die gesinterede titaan. ‘n Meer poreus gesinterde materiaal het beide laer
sterkte en termiese geleidingsvermoë. Aangesien hierdie faktore teenoorgestelde
uitwerkings op masjineerbaarheid het, word dit dan afgelei dat die sterkte van gesinterde
titaan ‘n groter invloed het op sy masjineerbaarheid as die termiese geleidingsvermoë.
Die beitel se slytasie is hoofsaahlik, maar het tekens van kraterslytasie getoon. Die
gemasjineerde oppervlak van die meer digte onderdele of toetsmonters het min gebreke
gehad in vergelyking met die minder digte dele. Die vorm van die spaanders is lank vir
digte parte, en spiraalvormig vir minder digte toetsmonsters. Die spaanders wat gevorm
het, was almal gesegmenteerd, wat tipies is vir titaan.
Die masjineerbaarheid van die gesinterde KS titaan is met dié van gesmede titaanallooie
vergelyk. Soos verwag is, is gevind dat die masjineerbaarheid van die gesinterde titaan in
vergelyking swak is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6852 |
| Date | 03 1900 |
| Creators | Sobiyi, Kehinde Kolawole |
| Contributors | Blaine, D. C., University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 100 p. : ill. |
| Rights | University of Stellenbosch |
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