Special Section Papers

Green-State Micromilling of Additive Manufactured AISI316 L

[+] Author and Article Information
Sandeep Kuriakose

Department of Mechanical Engineering,
Politecnico di Milano,
Milan 20156, Italy
e-mail: sandeep.kuriakose@polimi.it

Paolo Parenti, Salvatore Cataldo, Massimiliano Annoni

Department of Mechanical Engineering,
Politecnico di Milano,
Milan 20156, Italy

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO-AND NANO-MANUFACTURING. Manuscript received November 12, 2018; final manuscript received February 26, 2019; published online April 11, 2019. Assoc. Editor: Martin Jun.

J. Micro Nano-Manuf 7(1), 010904 (Apr 11, 2019) (7 pages) Paper No: JMNM-18-1052; doi: 10.1115/1.4042977 History: Received November 12, 2018; Revised February 26, 2019

Additive manufacturing (AM) of metal offers matchless design sovereignty to manufacture metallic microcomponents from a wide range of materials. Green-state micromilling is a promising method that can be integrated into the AM of metallic feedstock microcomponents in typical extrusion-based AM methods for compensating the inability to generate microfeatures. The integration enables the manufacturing of complex geometries, the generation of good surface quality, and can provide exceptional flexibility to new product shapes. This work is a micromachinability study of AISI316 L feedstock components produced by extrusion-based AM where the effects of workpiece temperature and the typical micromilling parameters such as cutting speed, feed per tooth, axial depth of cut, and air supply are studied. Edge integrity and surface roughness of the machined slots, as well as cutting forces, are analyzed using three-dimensional microscopy and piezoelectric force sensor, respectively. Green-state micromilling results were satisfying with good produced quality. The micromilling of heated workpieces (45 °C), with external air supply for debris removal, showed the best surface quality with surface roughness values that reached around Sa = 1.5 μm, much smaller than the average metal particles size. Minimum tendency to borders breakage was showed but in some cases microcutting was responsible of the generation of surface defects imputable to lack of adhesion of deposited layers. Despite this fact, the integrability of micromilling into extrusion-based AM cycles of metallic feedstock is confirmed.

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Fig. 1

Prototype extrusion AM machine and milling setup

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Fig. 2

Workpiece preparation: (a) strategy used for AM, (b) workpiece produced by AM in green-state, and (c) AM workpiece after face milling and side milling operations

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Fig. 3

Schematic diagram of feedstock micromilling

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Fig. 4

(a) Cutting force signals set 2 (Tair = 5, TWP = 22.5, ap =0.5). (b) and (c) Main effect plots set 1 and set 2.

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Fig. 5

Root-mean-square force value during heated and cold workpiece condition, sets 4 (left) and 5 (right)

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Fig. 6

Optical microscope images of experiment: (a) set 1 and (b) set 2

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Fig. 7

Optical microscopic analysis on set 3: (a) experiment without air supply and (b) experiment with air supply

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Fig. 8

Main effect plot of Sa surface roughness: (fz, vc, and slot measured position)

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Fig. 9

Box plots comparison of roughness analysis for milling experiment on workpiece at hot (45 °C) and cold (22.5 °C) state

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Fig. 10

The scanning electron microscope image of the workpiece in brown state (left) and microstructure showing porosity reduction by sintering (right)

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Fig. 11

Box plot comparison of roughness analysis for green, brown, and sintered states

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Fig. 12

Corner radius measurement of the top edges of the slots (sintered)

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Fig. 13

Scanning electron microscope image of breakage of the slot edges (first), chamfer formation from the shape of milling cutter (second), and cross-sectional view showing chamfer formation (third)



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