Abstract
When the characteristic structure size of the component is at the micron level, the internal crystal grains, grain boundaries, and pore defects of the component material with the same size at the micron level cannot be ignored, so the micro-sized component will show different physical properties from the macro-sized component, which is called size effect. Since the tool diameter of a micro-end mill is in the micron level, the micro-end mill will also show a significant size effect phenomenon. In addition, in the micro milling process, because the surface roughness that affects the performance and service life of micro parts is mainly influenced by the vibration of the micro-end mill, in order to enhance the machined surface quality, it is crucial to research the formation mechanism of surface topography in the micro milling process. In this paper, a comprehensive method is proposed to predict micro-end mill vibration, micro milling force, and surface roughness. At first, a size-dependent dynamic model of micro-end mill is presented based on the strain gradient elasticity theory (SGET). Secondly, considering the feedback of a micro-end mill vibration, the micro milling force model is presented and solved through the iterative method. Then the machined surface topography is simulated through the actual cutting edge trajectory considering the micro-end mill size-dependent vibration and material elastic recovery. The results show that the vibration of the micro-end mill will increase the micro milling force and surface roughness. In order to verify the accuracy and efficiency of the presented method, experiments are performed, and it is found that the predicted results are consistent with the experimental results.
Highlights
Micro products with micron level feature size and complex shapes is widely used in the fields of aerospace, defense science and biomedical science [1], and micro milling with the advantages of high machining precision and strong three-dimensional machining capability is the main process for processing micro products [2],[3]
Due to the minimum uncut chip thickness, the generation of surface roughness in micro milling process is divided into two types: when the actual uncut chip thickness is larger than the minimum uncut chip thickness, the workpiece material is cut by micro-end mill to form chip, and the machined surface topography can be described by the cutting edge trajectory; when the actual uncut chip thickness is less than the minimum uncut chip thickness, the workpiece undergoes extrusion deformation and partial elastic recovery without chip generation
(1) The size effect improves the stiffness of micro-end mill, so the vibration amplitude of microend mill calculated by strain gradient elasticity theory is lower than that calculated by traditional theory
Summary
Micro products with micron level feature size and complex shapes is widely used in the fields of aerospace, defense science and biomedical science [1], and micro milling with the advantages of high machining precision and strong three-dimensional machining capability is the main process for processing micro products [2],[3]. Scholars have systematically researched the machining mechanism of micro milling, the factors affecting the surface roughness, and the micro milling surface roughness prediction method. Since the vibration of micro-end mill is an important factor affecting the surface roughness in micro milling process, an accurate vibration model considering the size effect is the basis for predicting the surface roughness accurately. In order to obtain the required micro milling force and surface roughness, a comprehensive micro milling force prediction model and surface roughness prediction model considering size-dependent vibration of micro-end mill is proposed. The organizational of the paper is as follows: Section 2 proposes the mechanistic models of micro milling, including micro-end mill size-dependent vibration model, iterative micro milling force model and surface roughness prediction model.
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