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Title:Vpliv parametrov mehanske obdelave na površinsko poroznost zaprto-celičnih aluminijastih pen : doktorska disertacija
Authors:ID Razboršek, Boštjan (Author)
ID Ficko, Mirko (Mentor) More about this mentor... New window
ID Vesenjak, Matej (Comentor)
Files:.pdf DOK_Razborsek_Bostjan_2023.pdf (14,14 MB)
MD5: C84E655D595D2B26D915C04E7670B32D
 
Language:Slovenian
Work type:Doctoral dissertation
Typology:2.08 - Doctoral Dissertation
Organization:FS - Faculty of Mechanical Engineering
Abstract:Aluminijeve pene se še uveljavljajo na področju modernega inženirstva. Uporabljajo se tam, kjer se zahtevajo lahke konstrukcije, ki morajo prenašati mehanske in termične obremenitve ali imeti sposobnost absorpcije udarne energije. Elementi iz aluminijevih pen, npr. kompozitni sendvič paneli, imajo običajno porozno jedro, ki ga obdaja tanka plast neporozne zunanje površine. Ta plast bistveno vpliva na mehanske lastnosti elementa, ima pa tudi funkcijo zaščite notranjosti pred vplivi okolice. Mehanska obdelava z odrezovanjem povzroči deformacijo zunanje neporozne površine, kar ima praviloma za posledico zmanjšanje trdnostnih lastnosti in izpostavljenost notranje strukture vplivom iz okolice. V disertaciji je opisana mehanska obdelava z odrezovanjem in preoblikovanjem različnih vzorcev zaprto-celičnih aluminijevih pen. V prvem delu so bili izvedeni mehanski postopki obdelave struženja, rezkanja, vrtanja in enotočkovnega inkrementalnega preoblikovanja vzorcev penjenih v kalup. Ti vzorci so imeli porozno jedro in tanko plast zunanje neporozne površine. Z odrezovanjem je bila ta plast odstranjena, s čimer so bile zmanjšane tlačne lastnosti, obdelana površina je postala porozna ter mersko nenatančna. Boljši rezultati so bili doseženi s postopkom enotočkovnega inkrementalnega preoblikovanja. S tem postopkom so bile na površini, brez porušitve, izdelane enostavne oblike kot so žlebovi, utori itd. V drugem delu so bile izvedene raziskave inkrementalnega preoblikovanja in tornega valjanja vzorcev štirih različnih aluminijevih pen, s porozno zunanjo površino. Vzorci so se razlikovali po gostoti, velikosti celic in metalurški sestavi. Izdelani so bili na tračni žagi z minimalno deformacijo površine. Za obdelavo s preoblikovanjem je bilo uporabljeno orodje iz karbidne trdine, ki je delovalo s čelnim ali bočnim delom. Vsak vzorec je bil obdelan s točno določenimi pogoji obdelave (globino preoblikovanja, podajalno hitrostjo in številom vrtljajev orodja). Obdelana površina je bila naknadno obarvana, za doseganje boljšega kontrasta med poroznim in neporoznim delom površine. Izdelane so bile digitalne fotografije obdelane površine in analizirane s pomočjo programske opreme ter pragovnega algoritma. Za vsak vzorec je bila glede na referenčne, neobdelane vzorce, izračunana sprememba površinske pozornosti. S pomočjo metode odzivnih površin je bil določen vpliv parametrov obdelave na poroznost obdelane površine. Iz rezultatov preizkusov je bilo ugotovljeno, da ima število vrtljajev največji, podajalna hitrost po najmanjši vpliv na zmanjšanje površinske poroznosti. V nadaljevanju so bile izmerjene in analizirane obdelovalne sile ter debelina sloja deformirane površine. Izvedeni so bili tlačni preizkusi obdelanih vzorcev, s katerimi je bil določen vpliv obdelane površine na tlačno trdnost, ki predstavlja področje konstantne napetosti v - diagramu. Tlačne lastnosti obdelanih vzorcev, katerim je bila zaradi deformacije površine zmanjšana površinska poroznost, so se bistveno povečale. Ugotovljeno je bilo, da je debelina deformirane površine odvisna od preoblikovalnih lastnosti materiala aluminijevih pen. Pri vzorcih z višjo stopnjo čistosti aluminija je bila deformirana plast debelejša, kar je, dokazano s preizkusi, pomenilo višjo stopnjo tlačne trdnosti. S celotno raziskavo je bilo ugotovljeno ter dokazano, da je elementom, izdelanim s postopki odvzemanja materiala, mogoče povečati tlačno trdnost ter zmanjšati zarezne učinke, z naknadnimi preoblikovalnimi postopki kot sta inkrementalno preoblikovanje in torno valjanje. Takšno kombinacijo obdelovalnih postopkov, ki se lahko izvajajo na istem stroju, je smiselno uporabiti pri maloserijski proizvodnji izdelkov, pri čemer se kot surovec uporabijo palice, bloki ali pločevina iz aluminijaste pene.
Keywords:aluminijeva pena, zaprto-celična pena, mehanska obdelave, površinska poroznost, inkrementalno preoblikovanje, torno valjanje, mehanske lastnosti
Place of publishing:Maribor
Place of performance:Maribor
Publisher:[B. Razboršek]
Year of publishing:2023
Number of pages:XII, 138 str.
PID:20.500.12556/DKUM-83334 New window
UDC:621.7/.9-4:669.71-4-026.747(043.3)
COBISS.SI-ID:151180547 New window
Publication date in DKUM:04.05.2023
Views:663
Downloads:54
Metadata:XML DC-XML DC-RDF
Categories:KTFMB - FS
:
RAZBORŠEK, Boštjan, 2023, Vpliv parametrov mehanske obdelave na površinsko poroznost zaprto-celičnih aluminijastih pen : doktorska disertacija [online]. Doctoral dissertation. Maribor : B. Razboršek. [Accessed 13 April 2025]. Retrieved from: https://dk.um.si/IzpisGradiva.php?lang=eng&id=83334
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License:CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Link:http://creativecommons.org/licenses/by-nc-nd/4.0/
Description:The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.
Licensing start date:26.10.2022

Secondary language

Language:English
Title:The influence of mechanical machining parameters on the surface porosity of a closed-cell aluminium foams
Abstract:Aluminium foams are one of the materials, which are gaining popularity in modern engineering. They are used where lightweight structures are required to carry mechanical and thermal loads or have the capacity to absorb impact energy. Aluminium foam elements generally have a porous core surrounded by a thin, non-porous outer layer. This layer significantly affects the mechanical properties of the element and has the function of protecting against internal corrosion. Mechanical processing by cutting deforms non-porous layer, which leads to a reduction in strength properties and exposure to internal corrosion. The dissertation describes the mechanical processing of different types of closed-cell aluminium foam. In the first part, mechanical processes such as turning, milling, drilling, and single-point incremental forming of samples foamed in moulds were performed. These samples had a porous core and a thin layer of an outer non-porous surface. Better results were obtained using the single-point incremental forming process. With this process, simple shapes such as grooves, slots, etc. could be produced without collapsing the homogeneity of the surface. In the second part, incremental forming and friction rolling studies were conducted on four different aluminium foam samples, with porous outer surfaces. The samples specimens, which differed in density, cell size, and metallurgical composition, were fabricated using a band saw with minimal surface deformation. A carbide tool was used for the forming process. Each sample was machined with the front and side of the tool using well-defined machining parameters (deformation depth, feed rate, and spindle speed). The treated surface was stained for better contrast between the porous and non-porous parts of the surface. High-resolution digital photographs of the treated surfaces were taken and analysed using image segmentation with multispectral thresholding algorithms. The change in surface porosity was calculated for each sample and the influence of the selected machining parameters was determined using the surface response methodology. From the test results, it was found that spindle speed had the greatest effect and the feed rate had the least effect on the reduction of surface porosity. Then, the machining forces and the thickness of the deformed surface were measured and evaluated. Quasi-static compression tests were performed on the treated samples, and the influence of the treated surface on the constant compressive strength in - diagram, was determined. It was found that the thickness of the deformed surface depends on the deformability properties of the aluminium foam. Samples with a higher purity of aluminium, the deformed layer was thicker, which, as the tests showed, meant a higher compressive strength. During the study, it was found that the compressive strength of elements produced with material removal processes, can be significantly increased by subsequent forming processes, such as incremental forming and friction rolling. The use of such a combination of machining processes, carried out on the same CNC machine is useful in small-batch production, where semi-finished products such as blocks, bars and sheets of aluminium foam can be used.
Keywords:aluminium foam, closed-cell foam, machining, surface porosity, friction stir incremental forming, friction rolling, mechanical properties


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