1 |
Determining the Influence of the Type of Shielding Gas during Additive Manufacturing of an Aluminum Alloy by Monitoring the Process Qualitatively and Analyzing Process Byproducts QuantitativelyKleemeyer, Stefanie Desiree January 2021 (has links)
This thesis analyzes the influence of process gases on the formation and the characteristics of process byproducts that emerge during additive manufacturing of an aluminum alloy belonging to the 2000 series. In order to address the influence, four pure gases, argon, nitrogen, helium, and carbon dioxide, were used as a shielding gas on the same parameter sets. The interaction of the laser beam with the powder bed under each shielding condition was recorded by a camera. The humidity, particle size distribution, and chemistry of the spatters produced after each job was analyzed. The chemistry of small cylinders printed, was determined. The density of the produced cubic samples was determined following the Archimedes principle, as well as through the analysis of the cross-section. Lastly, the embedded and polished samples were etched, and the penetration depth of the laser was determined. Under argon and nitrogen shielding, the process looked the same and the produced spatters show similar results. Under helium shielding, less incandescent spatters were seen, and the particle size distribution is smaller than under argon or nitrogen. Carbon dioxide resulted in the highest number of incandescent particles and a change of the color of the rays from red to yellow. The chemical analysis shows that a slight increase of nitrogen in the spatters and the bulk material can be seen under nitrogen shielding. Oxygen and hydrogen content was sim- ilar under argon, nitrogen, and helium shielding. Carbon dioxide shielding resulted in the highest oxygen content in the spatter and the bulk material. The density is highest under helium shielding, and lowest under carbon dioxide shielding. Under argon and nitrogen shielding, the density was similar. The study concluded that the choice of a process gas is not an arbitrary one but should be selected with care. / Denna avhandling analyserar processgasernas påverkan på bildandet och egenskaperna hos process biprodukter som uppstår vid additiv tillverkning av en aluminiumlegering som tillhör 2000-serien. För att hantera inflytandet användes fyra rena gaser, argon, kväve, helium och koldioxid som skyddsgas på samma parameteruppsättningar. Interaktionen mellan laserstrålen och pulverbädden under varje skärmningsförhållande registrerades av en kamera. Fuktigheten, partikelstorleksfördelningen och kemin hos stänkarna som producerades efter varje jobb analyserades. Kemien hos de små cylindrarna som trycktes bestämdes. Densiteten hos de producerade kubikproven bestämdes enligt Archimedes princip, liksom genom analys av tvärsnittet. Slutligen etsades de inbäddade och polerade proverna och laserns penetrationsdjup bestämdes. Under argon- och kväveavskärmning såg processen likadan ut och de producerade stänkarna visar liknande resultat. Under heliumskärmning sågs mindre glödande stänk och partikelstorleksfördelningen är mindre än under argon eller kväve. Koldioxid resulterade i det högsta antalet glödande partiklar och en förändring av strålarnas färg från rött till gult. Den kemiska analysen visar att en liten ökning av kväve i stänkarna och bulkmaterialet kan ses under kväveavskärmning. Syre- och väteinnehållet var liknande under argon-, kväve- och heliumskärmning. Koldioxidavskärmning resulterade i det högsta syreinnehållet i stänk och bulkmaterial. Densiteten är högst under heliumskärmning och lägst under koldioxidskärmning. Under argon- och kväveavskärmning var densiteten densamma. Studien drog slutsatsen att valet av en processgas inte är godtyckligt utan bör väljas med omsorg.
|
2 |
Effect of conformal cooling in Additive Manufactured inserts on properties of high pressure die cast aluminum componentSevastopolev, Ruslan January 2020 (has links)
Additive manufacturing can bring several advantages in tooling applications especially hot working tooling as high pressure die casting. Printing of conformal cooling channels can lead to improved cooling and faster solidification, which, in turn, can possibly result in better quality of the cast part. However, few studies on advantages of additive manufactured tools in high pressure die casting are published.The aim of this study was to investigate and quantify the effect of conformal cooling on microstructure and mechanical properties of high pressure die cast aluminum alloy. Two tools each consisting of two die inserts were produced with and without conformal channels using additive manufacturing. Both tools were used in die casting of aluminum alloy. Aluminum specimens were then characterized microstructurally in light optical microscope for secondary arm spacing measurements and subjected to tensile and hardness testing. Cooling behavior of different inserts was studied with a thermal camera and by monitoring the temperature change of cooling oil during casting. Surface roughness of die inserts was measured with profilometer before and after casting.Thermal imaging of temperature as a function of time and temperature change of oil during casting cycle indicated that conformal insert had faster cooling and lower temperature compared to conventional insert. However, thermal imaging of temperature after each shot in a certain point of time showed higher maximum and minimum temperature on conformal die surface but no significant difference in normalized temperature gradient compared to the conventional insert.The average secondary dendrite arm spacing values were fairly similar for samples from conventional and conformal inserts, while more specimens from conventional insert demonstrated coarser structure. Slower cooling in conventional insert could result in the coarser secondary dendrite arm spacing.Tensile strength and hardness testing revealed no significant difference in mechanical properties of the specimens cast in conventional and conformal die inserts. However, reduced deviations in hardness was observed for samples cast with conformal insert. This is in agreement with secondary dendrite arm spacing measurements indicating improved cooling with conformal insert.Surface roughness measurement showed small wear of the inserts. More castings are needed to observe a possible difference in wear between the conventional and conformal inserts.Small observed differences in cooling rate and secondary arm spacing did not result in evident difference in mechanical properties of the aluminum alloy but the variation in properties were reduced for samples cast with conformal cooling. Future work may include more accurate measurement of cooling behavior with a thermocouple printed into the die insert, casting of thicker specimen for porosity evaluation and fatigue testing and longer casting series to evaluate the influence of conformal cooling on tool wear.
|
3 |
Investigating the effect of extending powder particle size distribution of Ti-6Al-4V produced by powder bed fusion laser beam process : Influence of process parameters on material integritySquillaci, Linda January 2023 (has links)
This thesis focuses on the topic of PBF-LB applied to titanium alloys. Of allalloys, an α + β is chosen, named Ti-6Al-4V. The selection of this particular alloy is driven by its current widespread use in many industrial applications where high strength coupled with low density are both desirable properties. For the last 50 years, parts made with this alloy have been cast or forged and then machined to achieve the final geometry. There is now an opportunity totransform this process chain by additive manufacturing, hence reducing material waste and achieving near net shape from powder feedstock. The process is summarised as follows: a laser selectively melts areas on a build plate where powder is pre-placed. Then a successive powder layer is spread and the process is repeated until completion. Upon removal of the part from the build plate, loose powder in the chamber is collected and recycled whenever possible. The design freedom provided by powder bed fusion methods enables production of intricate geometries and added functionality, despite the need for post-build consolidation and/or microstructural adjustments. Today’s fine and narrow powder cuts (e.g., 15-50μm) are designed to be coupled with low layer thicknesses (i.e., 30μm) to achieve smooth surfaces and high resolutions of small features e.g., internal cooling channels. However, costs associated with production of fine and narrow powder cuts are substantial as refinement of batches requires multiple sieving steps. In addition, resulting building times are considerably long (i.e., days), therefore a beneficial alternative could be that of exploring higher layer thicknesses together with wider and coarser powder cuts. The main idea of this work is to investigate the effects of employing a powder with a wider size distribution 15-90μm. The aim is to reduce the sievingrequired and consequently decrease the costs of developing and building parts made by PBF-LB. An extensive microstructural investigation is conducted on single tracks and cubes built with 27 different process parameter combinations, which also attempts to establish correlations between characteristics of tracks and responses measured in cubes. As a second step, the amount of residual porosity of asbuilt cubes is chosen as the discriminant for further mechanical testing of sub and super-β transus high-pressure heat treated material. / Den här avhandlingen fokuserar på additiv tillverkning av titanlegeringar med laser pulverbädd metoden. Den legering som främst är i fokus är Ti-6Al-4Vsom är en α+β legering. Anledningen till valet av denna titanlegering är att det är den vanligast förekommande titanlegeringen och att den används i ett antal olika industriella tillämpningar där hög styrka i kombination med låg vikt är önskvärda egenskaper. Under de senaste 50 åren har komponenter utav denna legering tillverkats med gjutning eller smide, följt av bearbetning till slutlig geometri. Med hjälp av additiv tillverkning finns nu en möjlighet att förändra tillverkningskedjan i vilket minskat materialspill och en mer nära-slutgeometri kan erhållas direkt genom användning av metallpulver som utgångsmaterial. Processen kan summeras enligt följande: en laser smälter ett förbestämt område på en byggplatta som täckts mer pulver. Därefter adderas ytterligare ett lager med metallpulver ovanpå, på vilket samma process sker igen, och igen osv, tills hela detaljen är färdigtillverkad. När detaljen ska tas loss ifrån byggplattan samlas det kvarvarande icke-smälta pulvret upp och återanvänds i så stor utsträckning som möjligt. Frihetsgraderna vid design i processen möjliggör tillverkning av komplexa geometrier och adderade funktionaliteter, även fast efterbehandling och/eller justeringar av mikrostrukturen kan behövas. Dagens smala pulverstorleksfördelning (tex 15-50μm) är avsedd att ge tunna lagertjocklekar (tex 30μm) för att åstadkomma en fin yta och hög upplösning av små geometrier, såsom exempelvis interna kylkanaler. Men kostnaderna som det innebär att framställa och sortera ut fina och smala kornstorleksfördelningarär avsevärd eftersom det innebär flera steg med silning. Vidare leder de tunnalagertjocklekarna till långa byggtider (typiskt dagar). Ett alternativ, som därför vore fördelaktigt, är att undersöka möjligheten med att bygga tjockare lager med en bredare och större pulverstorleksfördelning. Huvudfokuset i detta arbete fokuserar på att undersöka effekterna av att använda en bredare pulverpartikelstorleksfördelning 15-90μm, med syfte at minska silningsbehovet och därmed reducera kostnaden för att utveckla och tillverka detaljer med laser pulverbädd additiv tillverkning. En omfattande mikrostrukturundersökning har gjorts på enkelsträngar och kuber byggda med 27 olika processparameter-kombinationer, vilket samtidigt försöker identifiera korrelationer mellan enkelsträngarnas karaktäristik med resultaten uppmätta hos kuberna. I ett nästa steg har material, som tillverkats med processparametrar som renderade i minst/mest porer hos kuberna, mekaniskt provats efter att det högtrycksvärmebehandlats över- respektive under β-transus. / <p>Paper A is not included due to the copyright.</p><p>Paper B and C are to be submitted.</p>
|
Page generated in 0.0189 seconds