Publication: Eklemeli imalat ile üretilen paslanmaz çelik malzemelerin dik kesilmesinde plastik deformasyon davranışının incelenmesi
Abstract
Eklemeli imalat, geleneksel imalat yöntemleriyle imal edilmesi zor veya mümkün olmayan geometrideki parçaların imalatının yanı sıra hızlı prototip üretimini de mümkün kılan bir imalat yöntemidir. Birçok farklı eklemeli imalat yöntemi mevcut olsa da bunlar arasında en yaygın olanı toz yatağında ergitme prensibiyle çalışan seçici lazerle ergitme (SLE) yöntemidir. Geleneksel 316L malzemenin mikroyapısını eş eksenli belirgin sınırlara sahip taneler oluşturmaktadır. SLE yöntemiyle imal edilen 316L malzemenin mikroyapısını ise inşa düzleminde ergime havuzları ve tarama düzleminde ise tarama izleri oluşmaktadır. Ayrıca bu yapıların iç kısımlarında mikron ve nano boyutlarında alt taneler yanı sıra dentrit yapıların düzensiz varlıkları malzemenin anizotropik bir mikroyapıya sahip olmasına neden olmaktadır. Nitekim bu tez çalışmasında olduğu gibi talaşlı imalat ikincil işlemi uygulanan SLE malzemelerin plastik deformasyon davranışları incelenirken anizotropi nedeniyle geleneksel malzemelerden farklılıklarına dikkat edilmelidir. Dolayısıyla SLE malzemenin talaşlı imalat, yüzey bütünlüğü ve anizotropi ilişkisinin plastik deformasyon davranışının iyi anlaşılması açısından değerlendirilmesi ve sonuçların geleneksel malzeme ile kıyaslanması, ürünün kullanım performansı açısından önemlidir. Bu tez çalışmasında SLE 316L malzemesinin dik kesilmesinde farklı kesme hızları, farklı kesici takım geometrileri ve sıvı azot ile kriyojenik soğutmanın malzemenin işlenebilirliğine etkileri incelenmiştir. SLE malzemenin işlenmesinde geleneksele kıyasla daha fazla kesme kuvveti gerektiği ve takım aşınmasının daha fazla olduğu tespit edilmiştir. Kesici takım geometrisinin SLE malzemenin mikroyapısında etkilenmiş katman kalınlığı ve anizotropiyi doğrudan etkilediği görülmüştür. Aynı kesme parametre ve koşullarında geleneksel malzemenin deformasyon hızı SLE malzemeye göre daha yüksek hesaplanarak malzeme farklığının etkisi ortaya konulmuştur.
Additive manufacturing is a manufacturing method that enables rapid prototyping as well as the production of parts with geometries that are difficult or impossible to manufacture with traditional manufacturing methods. Although there are many different additive manufacturing methods, the most common of these is the selective laser melting (SLM) method, which works on the principle of melting in a powder bed. The microstructure of the wrought 316L material consists of equiaxed grains with distinct boundaries. The microstructure of the SLM 316L material consists of melting pools in the built plane and scanning traces in the scan plane. In addition, the irregular presence of micron and nano-sized subgrains as well as dendritic structures in the inner parts of these structures cause the material to have an anisotropic microstructure. In fact, when examining the effect of machining as a post process on the plastic deformation behavior of SLM materials, attention should be paid to their differences from wrought materials due to anisotropy. Therefore, evaluating the relationship between machining, surface integrity and anisotropy of SLM material in terms of understanding the plastic deformation behavior and comparing the results with wrought materials is important in terms of the product's usage performance. In this thesis, the effects of different cutting speeds, different cutting tool geometries and cryogenic cooling with liquid nitrogen on the machinability were investigated in the orthogonal cutting of SLM 316L material. It was determined that more cutting force was required and tool wear was higher in the machining of SLM material compared to wrought. It was observed that the cutting tool geometry directly affected the layer thickness and anisotropy in the microstructure of SLM material. The strain rate of the wrought material was calculated higher than the SLM material under the same cutting parameters and conditions, and the effect of the material difference was revealed.
Additive manufacturing is a manufacturing method that enables rapid prototyping as well as the production of parts with geometries that are difficult or impossible to manufacture with traditional manufacturing methods. Although there are many different additive manufacturing methods, the most common of these is the selective laser melting (SLM) method, which works on the principle of melting in a powder bed. The microstructure of the wrought 316L material consists of equiaxed grains with distinct boundaries. The microstructure of the SLM 316L material consists of melting pools in the built plane and scanning traces in the scan plane. In addition, the irregular presence of micron and nano-sized subgrains as well as dendritic structures in the inner parts of these structures cause the material to have an anisotropic microstructure. In fact, when examining the effect of machining as a post process on the plastic deformation behavior of SLM materials, attention should be paid to their differences from wrought materials due to anisotropy. Therefore, evaluating the relationship between machining, surface integrity and anisotropy of SLM material in terms of understanding the plastic deformation behavior and comparing the results with wrought materials is important in terms of the product's usage performance. In this thesis, the effects of different cutting speeds, different cutting tool geometries and cryogenic cooling with liquid nitrogen on the machinability were investigated in the orthogonal cutting of SLM 316L material. It was determined that more cutting force was required and tool wear was higher in the machining of SLM material compared to wrought. It was observed that the cutting tool geometry directly affected the layer thickness and anisotropy in the microstructure of SLM material. The strain rate of the wrought material was calculated higher than the SLM material under the same cutting parameters and conditions, and the effect of the material difference was revealed.