1. Laser Hardening of Grey Cast Iron using a High Power Diode Laser
E. Kennedy, G. Byrne, R. Byrne
The Process ●
Rapid cooling by conduction causes self-quenching to form hard martensite on surface
Thermal hardening process where high intensity laser radiation heats the workpiece surface above a critical transformation temperature ●
108
Shock Hardening
Drilling
Laser
W/mm2
106
Cutting
Melting
Vaporisation
104
Welding
Irradiance
x 50
Heating
102
Alloying
Laser beam
Transformation Hardening
Hardened layer in cast iron
Cladding
100
10-8
10-6
10-4
10-2
100 s
102
Interaction time t
Hardened track
Component
Fig.2 Interaction time vs. irradiance for a number of common laser applications
Fig.1 Schematic of laser hardening process
Thermodynamic modeling
Experimental Work
Aim: To create a tool for predicting the outputs from the laser hardening process using a high power diode laser, for a given set of input parameters ●
Heat transfer problem:
Aim: To validate the thermal model and to determine the link between wear resistance of the hardened surface and its material properties
Samples of cast iron laser hardened using a range of processing conditions and output characteristics such as hardness profile measured ●
Heat flow in 3 dimensions
Moving heat source =
Variable thermal properties
Transient heat conduction
Heat transfer solution:
Finite element method used to solve (ABAQUS) ●
Fig.4 High power diode laser hardening at UCD
Abrasive and erosive wear resistance of laser hardened surface experimentally determined ●
Hardness Profile for Laser Hardened Cast Iron Sample
(HRC)
Hardness
Fig.3 Visualisation of FEM model using ABAQUS software
(µm) ●
Heating and cooling rate of various points within the solid calculated
Results compared with published metallurgical data to predict resulting surface structures and characteristics
Depth below surface ●
Fig.5 Typical plot of hardness vs. hardened depth in laser hardening of cast iron