Advanced machining of miniature unmanned aircraft vehicle components using nanostructured cutting tools

Abstract

The advanced machining of components used in miniature unmanned aircraft vehicles is the focus of this study. The finite element method (FEM) is used to predict forces and temperatures using cutting tool inserts with a thin nanostructured film of high integrity. Similarity models are used to validate the finite element results and to understand the influence of micromachining parameters on cutting temperatures generated when machining Al 380-0 alloy. The predicted results are compared to experimental forces and temperatures using a three-dimensional piezoelectric function dynamometer and a short-range infra-red wavelength thermal camera. Nanostructured thin layer coatings lower machining forces and temperatures, which are validated through FEM predictions and experimental observations. The experimental results suggest that increasing the cutting tool’s rake angle at higher depths of cut will reduce cutting temperatures, which are predicted using the similarity models for micromachining.

Similarity and difference in machining at mixed scales using nanostructured coated tools milling hypoeutectoid carbon steel

“…This is also the reason why coatings appear to have little impact on the tool life since tool wear is due to the lack of mechanical strength of the cutting edge rather than by thermal effects. 10,11 This re-iterates the fact that microtool coatings do not need to resist high temperatures but should be designed to improve the mechanical strength of the cutting edge.…”

“…The inertial terms plus internal forces are equal to the external forces plus internal forces acting on and within the body of elements ³ , , , where N a,j denotes shape functions of repeated indices, the comma representing a partial differentiation with respect to spatial coordinate(s), and P i,j is the nominal "Piola-Kirchhoff" stress tensor for the matrix of elements. 10,11…”

“…The following sections describe the calculation of forces and temperatures in micromilling of AISI SAE 1020 hypoeutectoid steel (~0.2 wt.% carbon in iron) using methods described in references. [10][11][12]22,24,28,29…”

“…28,29 The measurement of cutting temperature at the microscale was measured using the Fluke model Ti 45 infra-red (IR) thermal imaging camera. 11 The camera measures temperatures to 1200°C using a 1024 × 786-pixel resolution grating and a thermal sensitivity of 50 mK (spatial resolution ~0.8 mRad and 1200:1 distance to spot). The camera was connected to the computer through a composite video card, while an Osprey capture card was used to freeze dynamic thermal images.…”

“…10 Conventional milling tools are designed with slenderness ratios (l/d ~ 2-3), which prevents bending, whereas microtools are susceptible to bending because their diameters are only a few hundred microns. 11 During macroscale cutting, the leading tool edge encounters bulk material (composite structures), and therefore, avoids contact with hard particles, while a microcutting edge encounters individual grains ensuring contact with soft and hard particles. 12 The results of Ikawa et al 13 suggest that there is a critical minimum depth of cut below which chips do not form.…”