Milling strategy induced shape deviation of thin-walled Ti-6Al-4V components

Delport, Lourens Daniel (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Titanium and its alloys possess favourable characteristics and are thus increasingly used in the aerospace, biomedical and automotive industries. Difficulties due to these favourable characteristics result in various problems with final components manufactured from titanium alloys. These problems lead to high amounts of material waste, long machining times, high costs and safety issues. One of these problems identified in the industry was the shape deviation of thin-walled Ti-6Al-4V aerospace components during the machining process. This shape deviation leads to decreased dimensional accuracy of the final component which leads to increased scrap. A study was conducted on simplified components in order to determine the effects of cutting speed and wall thickness on the shape deviation. The aim of this study is to investigate the effects of axial depth of cut (ap) on the shape deviation of the simplified thin-walled Ti-6Al-4V components, machining process time, tool wear and cost. The main research objective is to find a balance between low machining cost and low shape deviation. The chosen benchmark components were CNC milled at three different axial depths of cut. These depths were 8 mm, 5.33 mm and 4 mm. Experiments consisted of 5 components at each depth of cut resulting in a total of 15 parts. All other machining parameters were kept constant. The components were measured using a Coordinate Measurement Machine (CMM) in order to determine the amount of shape deviation. Tool wear was measured after each finished part on an optical microscope. It was determined that the axial depth of cut has no significant effect on the tool wear. The shape deviation was however affected significantly by the axial depth of cut. The ap of 5.33 mm had the lowest shape deviation values. The time increased linearly with a decrease in ap and similarly the machining cost as a result of the little effect on tool wear. Plotting the machining cost and the shape deviation on the same graph made it revealed a point where the best balance between cost/time and shape deviation can be determined. This point coincided with an ap value of approximately 5.9 mm. It can, therefore, be concluded that the ap of 5.33 mm is the closest to this point is, therefore, the best balance between cost/time and shape deviation.

AFRIKAANSE OPSOMMING: Titaan en sy allooie besit gunstige eienskappe en word dus toenemend gebruik in die lugvaart, biomediese en die motor-industrieë. Hierdie gunstige eienskappe lei egter tot verskeie probleme met finale komponente wat vervaardig is van Titaan allooie. Dit lei tot 'n hoë aantal afvalmateriaal, lang masjinering tye, hoë koste en veiligheids kwessies. Een van die probleme wat in die bedryf voorkom is vorm afwyking van dunwandige Ti-6Al-4V lugvaart komponente tydens die masjinering proses. Dit lei tot verminderde dimensionele akkuraatheid van die finale komponent wat lei tot verhoogde afval. Studies is op vereenvoudigde komponente uitgevoer ten einde die gevolge van snyspoed en wanddikte op die vorm afwyking te bepaal. Die doel van hierdie studie is om die gevolge van aksiale snitdiepte (ap) op die vorm afwyking van die vereenvoudigte dunwandige Ti-6Al-4V komponente, masjinering proses tyd, snybeitel leeftyd en koste te ondersoek. Die belangrikste navorsing doel is om 'n balans te vind tussen lae bewerking koste en lae vorm afwyking. Freeswerk van die gekose maatstaf komponente is by drie verskillende aksiale dieptes van snit uitgevoer. Hierdie snitdieptes was 8 mm, 5,33 mm en 4 mm. Eksperimente het bestaan uit 5 parte vir elke snitdiepte wat lei tot 'n totaal van 15 dele. Alle ander masjinering parameters is konstant gehou. Die komponente is gemeet met behulp van 'n Koördinaat Meet Masjien (KMM) om ten einde die vorm afwyking te bepaal. Snybeitel slytasie is gemeet na elke voltooide deel met 'n optiese mikroskoop. Daar is vasgestel dat die aksiale snitdiepte geen noemenswaardige uitwerking op die snybeitel slytasie het nie. Die vorm afwyking is egter beduidend beïnvloed deur die aksiale snitdiepte. Die ap van 5.33 mm het die laagste vorm afwyking waardes getoon. Die masjinerings tyd het lineêr toegeneem met 'n afname in ap en soortgelyk die bewerkingskoste as gevolg van die minimale uitwerking op snybeitel slytasie. Die bewerkingskoste en die vorm afwyking is op dieselfde grafiek geplot. Dit het 'n punt waar die beste balans tussen koste / tyd en vorm afwyking bepaal kan word aan die lig gebring. Hierdie punt is by 'n ap waarde van ongeveer 5.9 mm. Dit kan dus afgelei word dat die ap van 5.33 mm dus die beste balans tussen koste / tyd en vorm afwyking is in hierdie geval.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101005
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