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Research Papers

# Force Modeling in Laser-Assisted Microgrooving Including the Effect of Machine Deflection

[+] Author and Article Information
Ramesh Singh, Shreyes N. Melkote

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405

J. Manuf. Sci. Eng 131(1), 011013 (Jan 23, 2009) (9 pages) doi:10.1115/1.3040076 History: Received July 24, 2007; Revised August 20, 2008; Published January 23, 2009

## Abstract

Laser assisted mechanical micromachining is a process that utilizes highly localized thermal softening of the material by continuous wave laser irradiation applied simultaneously and directly in front of a miniature cutting tool in order to produce micron scale three-dimensional features in difficult-to-machine materials. The hybrid process is characterized by lower cutting forces and deflections, fewer tool failures, and potentially higher material removal rates. The desktop-sized machine used to implement this process has a finite stiffness and deflects under the influence of the cutting forces. The deflections can be of the same order of magnitude as the depth of cut in some cases, thereby having a negative effect on the dimensional accuracy of the micromachined feature. As a result, selection of the laser and cutting parameters that yield the desired reduction in cutting forces and deflection, and consequently an improvement in dimensional accuracy, requires a reliable cutting force model. This paper describes a cutting force model for the laser-assisted microgrooving process. The model accounts for the effect of elastic deflection of the machine $X-Y$ stages on the forces and accuracy of the micromachined feature. The model combines an existing slip-line field based force model with a finite element based thermal model of laser heating and a constitutive material flow stress model to account for thermal softening. Experiments are carried out on H-13 steel (42 HRC (hardness measured on the Rockwell ‘C’ scale)) to validate the force model. The effects of process parameters, such as laser power and cutting speed, on the forces are also analyzed. The model captures the effect of thermal softening and indicates a 66% reduction in the shear flow stress at 35 W laser power. The cutting force and depth of cut prediction errors are less than 20% and 10%, respectively, for most of the cases examined.

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## Figures

Figure 1

Flowchart of force prediction methodology

Figure 2

Simulated temperature distribution in the material removal half plane (10 W laser power, Gaussian beam, 10 mm/min scan speed, and 110 μm spot size)

Figure 3

Location of material removal plane

Figure 4

Geometric model of the cutting process with an edge radius tool (17)

Figure 5

Image of the tool edge (top) and tool edge profile (bottom) extracted from it

Figure 6

Image of chip

Figure 7

Shear stress distribution in the material removal half plane (10 W laser power, 100 μm laser-tool distance, 110 μm laser spot size, and 10 mm/min cutting speed)

Figure 8

Flowchart for determining the equilibrium depth of cut and the equilibrium cutting and thrust forces

Figure 9

Picture (a) and schematic (b) of the LAMM setup for microgrooving

Figure 10

Experimental and predicted cutting forces for 10 mm/min cutting speed and no laser heating. The error bars represent the range of average force data from three replications of each test condition.

Figure 11

Experimental and predicted thrust forces for 10 mm/min cutting speed and no laser heating. The error bars represent the range of the average force data from three replications of each test condition.

Figure 12

Measured and predicted depths of cut. The error bars represent the range of the average depth of cut obtained in three replications of each test condition.

Figure 13

Measured and predicted cutting and thrust forces at 0 W and 35 W laser powers. The error bars represent the range of the average force data from three replications of each test condition.

Figure 16

Thrust forces at 25 μm nominal depth of cut, 50 mm/min cutting speed, and 0 W, 5 W, and 10 W laser powers. The error bars represent the range of the average force data from three replications of each test condition.

Figure 15

Cutting forces at 25 μm nominal depth of cut, 50 mm/min cutting speed, and 0 W, 5 W, and 10 W laser powers. The error bars represent the range of the average force data from three replications of each test condition.

Figure 14

Measured and predicted depths of cut at 0 W and 35 W laser powers. The error bars represent the range of the average depth of cut obtained in three replications of each test condition.

Figure 17

Measured and predicted cutting and thrust forces at 10 mm/min and 100 mm/min cutting speeds, 35 W laser power, and 25 μm nominal depth of cut. The error bars represent the range of the average force data from three replications of each test condition.

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