Heat Treating

Lasers are an excellent heat source for hardening of metal

parts for preventing surface wear while preserving the

metallurgical properties of the base material. Formation

of a martensite layer  on the wear surface and

retention the ductility of the  base material for the

rest of the part can greatly increase the life and

performance of these parts.

Fiber lasers bring several advantages over

non-laser surface hardening technologies.

Fiber lasers are easy to set up and allow

precise control and stability of the

laser power minimizing part

distortion and eliminating the

need for a quenchant.

Laser heat treating, also known as laser hardening, is a surface modification process used to increase wear resistance or extend the lifetime for items ranging from household tools to parts in automobile manufacturing and tooling in heavy industry and transport sectors. Laser hardening is most commonly used for steel and cast iron materials. Lasers transform target areas on metal parts by controlled localized heating while preserving the metallurgical properties of the base material.

Absorption depends on the material type, carbon content, microstructure, surface condition, size and geometry and is typically restricted to surface layer. The depth of hardening ranges from
0.2–2.0 mm. The heated area can be controlled with beam shaping optics. As a result, laser heat treating provides manufacturers a precise and controlled process to modify their tooling and equipment for increased wear resistance.

 

cross-section of a laser hardened camshaft

Cross-section of a laser hardened camshaft

Laser Hardening with 6 kW IPG fiber laser, courtesy of Preco

 

Typical process speeds range from 10 to 150 cm per minute. Depth of hardening will decrease as speed increases. Achievable depth will depend on the make up of alloy. Typical width of pass values achievable with readily available equipment range from 0.5 mm to 5 cm. Smaller or larger values are possible with specialized setups. 

The choice of a mode of laser operation for surface hardening mainly depends on the part itself. Most hardening applications require CW beams, such as in track hardening of most industrial tools. Some intricate parts require pulsed lasers such as IPG's YLPN Mega Pulse ytterbium pulsed laser. 

Most near IR lasers can be used for hardening applications, as the main parameter required to harden the material to desired depth and hardness is the laser power. Iron based materials readily absorb 1 micron wavelength eliminating the need for pre-applying absorptive coatings to parts in the case of CO2 lasers.

 

IPG's diode lasers and high power fiber lasers are used for heat treating. Advantages include higher output powers, flexibility of fiber optic beam delivery, compact size, higher reliability due to hot redundancy and higher wall-plug efficiency exceeding that of kW class diode lasers.

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