Laser heat treating makes use of the laser energy to rapidly and efficiently heat a selected area of the surface of a metal component above the transformational temperature. The thermal mass of the component is all that is required to achieve quenching. In other words, a rapid quench necessary for hardening is achieved by removal of the laser energy via conduction. This occurs after turning off the laser or movement of the laser beam over the component’s surface. Rapid heat removal is achieved by the thermal mass of the component acting as a heat-sink. This heat removal rate is typically much higher than those associated with traditional methods and therefore can achieve a higher case hardness.
The major advantage of diode laser surface hardening is the high processing speed with precise case-depths resulting in negligible distortion. Laser surface transformation hardening not only increases the wear resistance; but, under certain conditions, the fatigue strength is also increased due to the compressive stresses induced on the work piece surface. This is especially true of powder metal parts and high torque parts such as cams, cranks, and couplings.
All heat treatable materials can be laser case hardened without liquid based quenchants. The low distortion is what makes the process a clear winner over traditional heat treating methods such as flame, RF-induction, furnace, carbonizing, and nitriding processes. Flame hardening has poor reproducibility, poor quench, and large distortions. Induction hardening requires precise controls over inductor placement, quenchant chemistries and flow, and still produces large distortions due to large thermal penetration. Furnace, carbonizing and nitriding processes are all inherently non-localized and therefore are distortion risks.
Advantages of laser hardening
Selective hardening both in depth and location
Low or negligible distortion
No post processing is required
Precision heating and control
Highly directional heating via line of site heat treatment
Process speeds typically 3 times the rate of induction
Environmentally friendly dry process requiring no quench oil or fluids
Process does not require absorbent coatings