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Research Papers

Obtaining a Relationship Between Process Parameters and Fracture Characteristics for Hybrid $CO2$ Laser∕Waterjet Machining of Ceramics

[+] Author and Article Information
Dinesh Kalyanasundaram1

Laboratory for Lasers, MEMS and Nanotechnology, Department of Mechanical Engineering, Iowa State University, Ames, IA 50014kdinesh@iastate.edu

Pranav Shrotriya, Pal Molian

Laboratory for Lasers, MEMS and Nanotechnology, Department of Mechanical Engineering, Iowa State University, Ames, IA 50014

1

Corresponding author.

J. Eng. Mater. Technol 131(1), 011005 (Dec 17, 2008) (10 pages) doi:10.1115/1.3026547 History: Received March 21, 2008; Revised August 09, 2008; Published December 17, 2008

Abstract

A combined experimental and analytical approach is undertaken to identify the relationship between process parameters and fracture behavior in the cutting of a $1mm$ thick alumina samples by a hybrid $CO2$ laser∕waterjet (LWJ) manufacturing process. In LWJ machining, a $200W$ power laser was used for local heating followed by waterjet quenching of the sample surface leading to thermal shock fracture in the heated zone. Experimental results indicate three characteristic fracture responses: scribing, controlled separation, and uncontrolled fracture. A Green’s function based approach is used to develop an analytical solution for temperatures and stress fields generated in the workpiece during laser heating and subsequent waterjet quenching along the machining path. Temperature distribution was experimentally measured using thermocouples and compared with analytical predictions in order to validate the model assumptions. Computed thermal stress fields are utilized to determine the stress intensity factor and energy release rate for different configurations of cracks that caused scribing or separation of the workpiece. Calculated crack driving forces are compared with fracture toughness and critical energy release rates to predict the equilibrium crack length for scribed samples and the process parameters associated with transition from scribing to separation. Both of these predictions are in good agreement with experimental observations. An empirical parameter is developed to identify the transition from controlled separation to uncontrolled cracking because the equilibrium crack length based analysis is unable to predict this transition. Finally, the analytical model and empirical parameter are utilized to create a map that relates the process parameters to the fracture behavior of alumina samples.

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Figures

Figure 1

Schematic representation of the laser∕waterjet system

Figure 2

Schematic representation of the fixture with the workpiece in position during machining. Inset shows the thermocouple measurement points for recording the temperature history.

Figure 3

Orientation of the axes with respect to the workpiece. The y-axis represents the cutting direction.

Figure 4

(a) Plane strain cracking and (b) crack channeling

Figure 5

(a) Photographs of scribing, (b) controlled, and (c) uncontrolled fracture

Figure 6

(a) LWJ cutting of alumina for different spot sizes at 2.07MPa of water pressure and (b) LWJ cutting results at 2.07MPa of water pressure

Figure 7

SEM image of dye penetration in broken scribed specimens: (a) low line energy scribing and (b) high line energy scribing

Figure 8

Comparison of experimental measurements and numerical prediction of temperature during LWJ machining: (a) temperature measured at 1mm from the cutting path (◇ and ◻ markers) and numerical predictions for three different conditions (curves A, B, and C); and (b) measured temperature (◇ and ◻ markers) and numerical predictions (curve A) at a 2mm offset from the cutting path

Figure 9

(a) Temperature plot at x=0m, and y=0.004m at various line energies and (b) stress plot at x=0m, and y=0.004m at various z with the inset showing the stress across the thickness

Figure 10

KI at various a∕w (a≡crack length and w≡thickness) ratios

Figure 11

G curve at various a∕w (a≡crack length and w≡thickness) ratios

Figure 12

Minimum energy release rates plotted as a function of line energy for a spot size of 0.6mm

Figure 13

Graph relating process parameters and fracture characteristics (27)

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