The effects of developed selective laser melting strategies on titanium hybrid parts

Hagedorn-Hansen, Devon (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT:Additive manufacturing (AM) is gaining popularity in industries such as the aerospace, medical, and tool-and-die industries. One of the major challenges faced by additive manufacturing technology is the high costs involved. In the case of selective laser melting (SLM), a metal powder bed fusion technology, warping due to residual stress could lead to the part being scrapped. SLM can be compared to a repetitive laser welding process whereby hundreds of layers are welded together in a specific shape to produce a 3-dimensional geometry. During the SLM process a thermal heat sink effect takes place between the base plate and the previously consolidated layers. This results in extremely large directional thermal gradients, which act in the direction of the scan track. These high thermal gradients cause the build-up of residual stresses, which can cause part deformation. The stress built up by the thermal shrinkage of the solidified melt pool induces a tensile stress at the top surface of the SLM part. These tensile stresses cause the part to curl upward, which is usually restrained by the base plate being anchored to the machine with screws. Sometimes the stress is so great that the base plate still warps and the screws break or get elongated past their elastic limit. To reduce the costs involved with SLM a process chain with subtractive manufacturing (SM) and additive manufacturing processes has been suggested. Process chains can incorporate a combination of manufacturing technologies in order to produce a product in the most resource efficient manner. Components produced using a combination of SLM and conventional machining are referred to as hybrid parts if the SLM section is fused to the machined section. The problems associated with the SLM technology, such as geometric deviation (warping) and porosity, are still applicable to the production of hybrid components. The purpose of this study was to determine whether different laser scan strategies can be developed to reduce geometric deviation and porosity in titanium hybrid parts. A new method called Hatch Pattern Designing was developed to bypass the default hatch strategies used by the Concept Laser machine. A new scan strategy was developed and compared to the patented Concept Laser Island scan strategy. Using the new scanning strategy on the experimental samples resulted in less geometric deviation and less porosity than those produced using the Concept Laser M2 Cusing machine’s default scan strategy.

AFRIKAANSE OPSOMMING: Additive Manufacturing (AM) is besig om in gewildheid in bedrywe soos die Ruimte, mediese, en instrument-en-sterf nywerhede. Een van die groot uitdagings in die gesig gestaar deur toevoeging vervaardiging tegnologie is die hoë koste daaraan verbonde. In die geval van Selective Laser Melting (SLM), 'n metaal poeier bed fusie tegnologie, buiging as gevolg van residuele spanning kan lei tot die deel wees gesloop. SLM kan vergelyk word met 'n herhalende laser sweiswerk proses waardeur honderde lae saam in 'n spesifieke vorm van 'n 3-dimensionele meetkunde produseer gesweis. Gedurende die SLM proses neem 'n warm heat sink effek tussen die basisplaat en die voorheen gekonsolideer lae. Dit lei tot 'n baie groot directional termiese gradiënte wat optree in die rigting van die scan spoor. Hierdie hoë termiese gradiënte veroorsaak die opbou van die oorblywende spanning wat deel vervorming veroorsaak. Die spanning opgebou deur die hitte krimping van die gestolde smelt swembad veroorsaak 'n trekspanning aan die bokant oppervlak van die SLM deel. Hierdie trek spanning veroorsaak dat die deel te krul opwaarts wat gewoonlik opgehou deur die basisplaat word geanker aan die masjien met skroewe. Soms is die spanning is so groot dat die basisplaat nog warps en die skroewe te breek of te verleng verby hul elastisiteitsgrens. Om die betrokke met SLM koste van die gebruik van 'n hibriede proses ketting is voorgestel te verminder. Hybrid proses kettings inkorporeer 'n kombinasie van vervaardiging tegnologie om 'n produk in die mees hulpbron doeltreffende wyse te produseer. In hierdie geval is 'n kombinasie van subtraktiewe vervaardiging en toevoeging vervaardiging tegnologie gebruik sal word. Die probleme wat verband hou met die SLM tegnologie, soos geometriese afwyking (buiging) en porositeit, is steeds van toepassing op die produksie van hibriede komponente. Hierdie studie bepaal of verskillende laser scan strategieë ontwikkel kan word om meetkundige afwyking en porositeit in titanium baster dele verminder. 'N nuwe metode genoem Hatch Patroon ontwerp is ontwikkel om die verstek broei strategieë wat gebruik word deur die Concept Laser masjien te omseil. 'N Nuwe scan strategie is ontwikkel en in vergelyking met die gepatenteerde Concept Laser Island skandering strategie. Die gebruik van die nuwe skandering strategie op die eksperimentele monsters gelei tot minder geometriese afwyking en minder porositeit dan diegene wat met behulp van standaard scan strategie die Concept Laser M2 Cusing masjien se.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100926
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