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Research Papers

Effect of Tool Wear on Hole Quality in Drilling of Carbon Fiber Reinforced Plastic–Titanium Alloy Stacks Using Tungsten Carbide and Polycrystalline Diamond Tools

[+] Author and Article Information
D. Kim

School of Engineering and Computer Science,
Washington State University,
Vancouver, WA 98686

A. Beal

Epic,
Verona, WI 53593

P. Kwon

Department of Mechanical Engineering,
Michigan State University,
East Lansing, MI 48824

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received December 22, 2014; final manuscript received July 3, 2015; published online October 1, 2015. Assoc. Editor: Guillaume Fromentin.

J. Manuf. Sci. Eng 138(3), 031006 (Oct 01, 2015) Paper No: MANU-14-1701; doi: 10.1115/1.4031052 History: Received December 22, 2014; Revised July 03, 2015

This paper reviews the nature of hole defects and postulates the cause of hole defects resulting from the drilling process of carbon fiber reinforced plastic–titanium alloy stacked panels (CFRP–Ti stacks) using tungsten carbide (WC) and polycrystalline diamond (PCD) twist drills. The parameters that describe the hole quality of the CFRP–Ti stacks include CFRP entry hole delamination, hole diameter and roundness, inner hole surface roughness, CFRP hole profile, CFRP–Ti interplate damage, and Ti exit burr. They are caused by heat generation during drilling as well as hot Ti chips and adhesion, Ti burr formation, tool instability, and tool geometry change due to tool wear. For the WC drills, large flank wear and margin wear occurred at the high spindle speed condition, resulting in a reduction of the hole size and an increase of the hole roundness and CFRP–Ti interface damage. At the low spindle speed condition, tool geometry was changed due to the large edge rounding. This resulted in large fiber pull-out at the CFRP hole surface. Ti entry burrs caused damage associated with fiber removal and matrix discoloring at the bottom of the CFRP panel and this interplate damage was observed to increase with tool wear. When compared with the WC tool at the same speed condition, the PCD drill maintained relatively small hole defects under all parameters.

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Figures

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Fig. 1

Force signal profile and maximum drilling forces versus number of holes drilled by the different tool types and conditions (a) maximum thrust and (b) maximum torque

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Fig. 2

SEM images for WC and PCD drills for various holes in CFRP/Ti stacks [9] (a) WC, high spindle speed condition, (b) WC, low spindle speed condition, and (c) PCD, low spindle speed condition

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Fig. 3

Photos of (a) experimental setup and (b) PCD and WC twist drills

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Fig. 4

The hole quality features and their measurement of the CFRP–Ti stacks focused for this study (a) schematics of the hole quality features, (b) CFRP hole entry delamination length measurement, (c) definition of roundness, and (d) photo of CFRP hole exit damage

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Fig. 5

Maximum entry delamination max length over the CFRP holes

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Fig. 6

Hole profiles for various hole numbers made by WC and PCD drills

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Fig. 7

Midpoint hole diameter and roundness versus hole number for CFRP plates (fresh tool diameter = 9.525 mm or the dotted lines) (a) CFRP-hole diameter and (b) CFRP-roundness

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Fig. 8

Midpoint hole diameter and roundness versus hole number for Ti plates (tool diameter = 9.525 mm): (a) Ti-hole diameter and (b) Ti-roundness

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Fig. 9

Damage at CFRP/Ti interface (a) SEM picture of CFRP hole exit damage and a CFRP exit hole thermal–mechanical damage measurement example, (b) cross section of Ti entry burr (white: Ti, black: bakelite mount)

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Fig. 10

CFRP exit hole damage, (a) discoloration and mechanical damages at CFRP exit holes by WC drill in the high-speed condition, (b) discoloration and mechanical damages at CFRP exit holes by WC drill in the low-speed condition, and discoloration and mechanical damages at CFRP exit holes by PCD drill in the low-speed condition

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Fig. 11

Ti entry burr height for WC drills and PCD drill

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Fig. 12

CFRP Ra and Rt for 20 hole intervals

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Fig. 13

SEM images of uncut fibers, fiber pullout, and surface scratches in CFRP hole and surface scratches of Ti hole: (a) CFRP uncut fibers, (b) CFRP fiber pullout, (c) CFRP surface scratches, and (d)Ti hole surface

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Fig. 14

Ti exit burr height versus hole number

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