Ultra-Precision Machining

Precision Beyond Imagination

Unlike conventional machining, ultra-precision machining can handle difficult-to-cut and emerging materials with incredible tolerances and surface quality. It opens new opportunities to various industries by allowing full 3-D feature generation with less than 100s of nanometer form accuracy and single/sub-nanometer surface quality. Feasibility of unrealistic machining quality removes typical machining challenges, which leads to a new manufacturing paradigm called MFD (Manufacturing for Design).

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Ultra-Precision Machining of Single Crystal Sapphire

 

Research team: Suk Bum Kwon, Aditya Nagaraj

Single crystalline sapphire (Al2O3) is a ceramic material commonly used in various advanced engineering applications due to it’s excellent mechanical, chemical and thermal properties. Sapphire is commonly used as the base material for precision products, such as precision lenses, electronic substrates and laser diodes which require an ultrafine surface with extremely small tolerances. Due to the pronounced brittleness and hardness exhibited by sapphire, there are many difficulties are encountered during processing. Ultra-precision machining (UPM) has been suggested as one way to precisely process sapphire. By using ultra-precision machining with the depth of cut of a few nanometers, the extremely fine machined surface can be obtained. At this scale, sapphire transitions from a brittle material response and exhibits plastic deformation and ductile material removal. This phenomenon is called the ductile-brittle transition and it shows an anisotropic trend due to the hexagonal symmetry of the sapphire unit cell. The ductile-brittle transition phenomenon, which occurs during UPM is still in a veil because exact mechanisms are not yet fully understood. This research aims to discover and visualize the mechanism of ductile-brittle transition during the UPM of single-crystal sapphire based on the slip and fracture system activation hypothesis. Further, this hypothesis will be used to predict the point where the ductile-brittle transition begins in terms of cutting direction and depth of cut.

Crack Removal

Research team: Suk Bum Kwon, Aditya Nagaraj

Machining of single-crystalline ceramics is a time-consuming process due to the small amount of material removed in each pass owing to the susceptibility of ceramics to fracture. Conventionally, machining of ceramics has been carried out through the process of grinding. One of the major limitations of grinding is the inability to produce full 3D features and shapes. To overcome this, ultra-precision machining (UPM) is used where the material is removed at the sub-micron scale using 3 – 5 axis CNC machines. In UPM, the material removal rate is very low due to the small area of engagement between the tool and work-piece. This research aims to improve the throughput of the UPM process by studying fracture in ceramics during machining and removing surface cracks by subsequent machining operations over the cracked areas.

Error Identification

Research team: Sangjin Maeng, Qidi Chen

Geometric errors on the axis and induced by tool setting are inevitable on machine tools. The error degrades the form accuracy of machined parts. Especially, the error on an ultra-precision machine tool,which has machining accuracy under one μm, generates “relatively” worse machining quality than conventional machining tools. To improve the accuracy of machining, error sources have to be analyzed and compensated. The aim of the study is to identify geometric errors of the ultra-precision machine tool.