An Analysis of the Effect of Laser Beam Geometry on Laser Transformation Hardening

Abstract

The effect of transformation hardening depends upon both heating and cooling rates. It is desirable to have a slow heating rate and a rapid cooling rate to achieve full transformation. To date laser transformation hardening has been carried out using circular or rectangular beams which result in rapid heating and cooling. Although the use of different beam intensity distributions within the circular or rectangular laser beams has been studied to improve the process, no other beam geometries have been investigated so far for transformation hardening. This paper presents an investigation into the effects of different laser beam geometries in transformation hardening. Finite element modeling technique has been used to simulate the steady state and transient effects of moving beams in transformation hardening of EN 43A steel. The results are compared with experimental data. The work shows that neither of the two commonly used beams, circular and rectangular, are optimum beam shapes for transformation hardening. The homogenization temperature exceeds the melting point for these beam shapes for the usual laser scanning speeds and power density. Triangular beam geometry has been shown to produce the best thermal history to achieve better transformation and highest hardness due to slower heating without sacrificing the processing rate and hardening depths.

Laser heating of a moving slab: Influence of laser intensity parameter and scanning speed on temperature field and melt size

“…They adapted two criteria to predict the quantity of the laser cutting operation. The effect of laser beam geometry on laser transformation hardening was investigated by Safdar et al [6]. They showed that none of the circular and rectangular beams had optimum shapes for transformation hardening; however, triangular beam geometry was shown to produce the best thermal history for achieving transformation hardening.…”

Laser surface hardening of 42CrMo cast steel for obtaining a wide and uniform hardened layer by shaped beams

“…Safdar et al [16] have reported that both the heating and cooling rates influence the outcome of hardening achieved during LSH and that higher hardness was observed with lower heating rates. Obviously, the result here is different; the possible reason is the heating rate and peak temperature both being high enough in the case of shaped beam 2, as shown in Fig.…”

Laser Heating and the Phase Change Process

“…Equation [13] is the solution of the temperature distribution in an infinite solid due to the quantity of heat Q instantaneously generated at t ¼ 0 at a point (x 0 , y 0 , z 0 ). However, if this solution is introduced for an instantaneous source of heat in a substance lying in the plane z ¼ 0 and in the absence of radiation heat loss from the surface, the solution yields:…”

“…Considerable research studies were carried out to examine laser melting of metallic surfaces (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). As the heating duration or the intensity of the laser beam increases, phase change takes place at the irradiated surface.…”