Mr. Anant Deshpande (View Profile)
Sr. Vice President
Laser Science Services (I) Pvt. Ltd.
Laser Heat Treatment / Laser Hardening
Heat treatment/hardening is very commonly done to improve strength and wear characteristics and extend the lifetime of steel parts which are subjected to wear and tear such as cutting tools, shaft , gear, etc.. There are various ways of increasing the hardness using conventional technique such flame hardening used for medium to large parts and Induction hardening . While the conventional hardening is very good and cost effective way if one wants to the complete hardening of the material and in bulk , however when it come to selective hardening and large parts , the cost of hardening by conventional way of hardening does have limitation . Moreover with the technology going towards green , Laser Hardening is widely now days used for such hardening application.
Its not that Laser were not used earlier , however the cost of Laser ( initial as well as operation cost ) being high and only Co2 Laser availability at higher power , did not make them a suitable choice for hardening until and unless critical and precise hardening is required. However with the change in technology and modern manufacturing the cost of Laser specially high power Diode laser and Fiber laser , has changed the game of Laser hardening . Direct diode , as well as fiber coupled Diode laser and fiber lasers are now available with power level from few 100W to 25KW or higher and optics giving spot size from 1mm to more than 90mm with suitable optics, thereby making them economic and viable for hardening process. Apart from power , coupling of laser to fibre and better absorption of Diode /fiber by base material ( refer graph 1) along with 5 axis Robotic system gives flexibly and thereby making it easier to do any component (3D) . This enables the laser to be readily applied for treating a wide range of part sizes and shapes without the need for special coils custom-designed for each part geometry as in Induction hardening.
Laser heat treating is a selective hardening technique in which a spatially beam of laser light is absorbed near the surface, causing rapid heating . The spot size of the laser beam defines the area of the surface which is hardened onto the surface area of material. . In Laser hardening usually no external quenching medium used, the bulk material acts as a heat sink. . Thus Laser hardening is faster , better and accurate with advantage such as selective area , short cycle time , no distortion , does not require any specific environment condition, temperature controlled and Clean and Green process i.e. no pollution of the surface ( no external media for quenching ) .
The Laser heat treatment set up typically includes a Laser ( Diode or Fiber or Disk ) along with beam shaping optics to provide the desired spot size , mounted on a 5 axis Robot with turn and tilt table along with rotary and fixture for holding the material to be heat treated . Normally for precise hardening a pyrometer is recommended in the set up.
Note that typically any material with the carbon content of more than 0.2% can be Laser hardened . The most common material such as low carbon, medium to high carbon steel , Alloy steel , stainless steels and cast irons can be hardened by the laser process ( except few ). The Laser hardening depth depends on the % of content of the carbon in the material. Note that the Laser penetration into the material is limited ( min 0.1 mm to max up 1.5 -2mm ). However there are various parameters such as micro structure of parts , homogeneity , grain size , hardiness of core and cleanness of part , while parameters such as travel speed, hardness requirement , power density , bulk material thickness plays important role in defining the laser hardening depth.
The various application for which Laser hardening is very widely used such as piston, piston rings, gear, shaft, metal springs, cutting tools , valves .molds and Cylinder for diesel locomotiv, many others.
If you have any queries regarding Laser Heat treatment / Hardening and other Laser applications and processes, please post your queries in the comment section below.
References 1. A. Kopel and W. Reitz, “Laser Surface Treatment,” Advanced Materials and Processes, ASM, October 1999