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Research Papers

On the Geometrical Accuracy of High Aspect Ratio Micromilled Pins

[+] Author and Article Information
Paolo Parenti

Department of Mechanical Engineering,
Politecnico di Milano,
via La Masa 1,
Milan 20156, Italy
e-mail: paolo.parenti@polimi.it

Luca Pagani

EPSRC Centre for Innovative Manufacturing
in Advanced Metrology,
Centre for Precision Technologies (CPT),
University of Huddersfield,
Huddersfield, HD13DH, UK

Massimiliano Annoni, Bianca Maria Colosimo, Quirico Semeraro

Department of Mechanical Engineering,
Politecnico di Milano,
via La Masa 1,
Milan 20156, Italy

1Corresponding author.

Manuscript received February 19, 2016; final manuscript received October 17, 2016; published online November 10, 2016. Assoc. Editor: Laine Mears.

J. Manuf. Sci. Eng 139(5), 051002 (Nov 10, 2016) (14 pages) Paper No: MANU-16-1117; doi: 10.1115/1.4035035 History: Received February 19, 2016; Revised October 17, 2016

Geometrical accuracy of microfeatures in micromilling is strictly related with the choice of cutting parameters. Their correct selection is a challenging task in particular when the target feature geometry is a high aspect ratio feature with tight tolerance requirements. Metallic micromilled pins are adopted in many different industrial applications as in the micromold technology field, in the microelectromechanical systems, and in the biomedical devices and their geometrical accuracy represents a fundamental property for their functionality. This work outlines the connection between the achieved geometrical accuracy and the micromilling parameters and cutting strategies on pins with diameter = 100 μm and height = 2 mm (i.e., aspect ratio = 20). Pin geometrical error features are extracted from three-dimensional optical measurements and then correlated with cutting parameters to support machining process setup. A proper fitting based on Chebyshev functions is applied and a statistical analysis assesses the importance of each deviation component in relation to the imposed cutting conditions. The proposed methodology fills the specific lack in the literature domain about micropin machining and can easily extend to different types of geometrical microfeatures. Finally, correlation between part geometrical errors and machining forces is analyzed. Cutting force analysis is adopted in conventional machining for implementing online geometrical errors assessment or compensation methods. However, this study confirms that the applicability of this approach in high aspect ratio pin micromilling is prevented from the predominant scale-effects and the large part bending that generates a low direct correlation between forces and part geometrical errors.

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Figures

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Fig. 1

Machined pin and fixture geometry (a), radial and axial engagement (b), and top view trajectory (c)

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Fig. 2

Tool engagement (a) top view and (b) detail of end contact point

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Fig. 3

Machined pins and 3D point cloud acquired by focus variation microscope ((a) real pin test #42, (b) microscope acquisition of test #39, and (c) real pin of test #30)

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Fig. 4

Pin truncation planes (a), inclination angles definition (b) and least squares cylinder-gray approximating the pin cloud-blue (c)

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Fig. 5

Cluster dendrograms of the main angle γi—main effect plot of all the downmilling tests

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Fig. 6

Chebyshev fitting on pin #1 (a) and pin #46 (b)

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Fig. 7

Procedure to generate the 3D cutting force map

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Fig. 8

Peak detection (a) and smoothing on cutting forces maxima (b) during test #1

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Fig. 9

3D cutting force map: smoothed FR maxima during test #1 (a) and geometry patches used for computing the correlation (b)

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Fig. 10

Correlation index between FR, FT, FN and geometry of the pin

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