28-12-2012, 06:07 PM
cZone (HAZ) in Laser Machining
Review on Heat Affected.pdf (Size: 95.21 KB / Downloads: 143)
Abstract.
Laser machining being a non-contact process possesses several advantages such as no tool wear or damage and no contact force induced problems. Laser cutting involves thermal process and it does not depend on the strength and hardness of the work piece, thus making it ideal for cutting non-homogeneous material. In this research work several papers related to the heat affected zone (HAZ) of laser machining of CFRP and GFRP are reviewed. It was found that laser parameters such as specific laser energy, laser power, repetition rate, work piece temperature determine the extent of HAZ. In CFRP HAZ in perpendicular laser grooving is much higher than that in parallel grooving. Presence of nitrogen jet decreases the work piece temperature leading to lower HAZ. Observations of the HAZ area of CFRP material revealed fiber swelling of 50 or 60% and fibers near the top are seen to curl up. In case of GFRP charred black material called shell and melted glass fibers are observed in the HAZ. It is also observed that the extent of HAZ affect the static tensile and bending strengths of CFRP. Tensile strength reduces linearly as HAZ increases. A comparison of laser cutting on CFRP using three types of laser is also presented here. Nd:YAG laser cutting on CFRP at optimized parameters has produced least HAZ and highest bending strength
Introduction
Laser machining being a non-contact process possesses several advantages such as no tool wear or damage and no contact-force- induced problems. Contact processes are accompanied by crack or mechanical degradation of the material being machined. Laser cutting involves thermal process and it does not depend on the strength and hardness of the work piece, thus making it ideal for cutting non-homogeneous material. Laser delivers high power-density beam which upon impact on the work piece is converted into heat. As the impact zone is very small very high temperature capable of melting or volatilizing the material can be attained. This leads to material removal. Laser cutting can be optimized by adjusting several parameters. Laser drilling which is a non-contact process produce small holes in various materials having high degree of precision and reproducibility. Due to the anisotropic nature of composites distorted holes and HAZ may result. In this work, papers involving HAZ formed due to laser machining were reviewed.
Literature Review
A lot of researches were undertaken regarding the heat affected zone (HAZ) in laser cutting. Hocheng and Pan represented HAZ by sectional area [1]. They used unidirectional carbon/PEEK composite with 60% fiber volume fraction for laser cutting. Carbon dioxide laser was employed. For cooling, a jet of liquid nitrogen (N2) with 100kPa and 200kPa was utilized. It also created an inert atmosphere to carry out the laser cutting.
Conclusions
Several articles regarding the heat affected zone (HAZ) in laser machining were reviewed. The parameters affecting the extent of HAZ are observed. HAZ is affected by parameters such as specific laser energy, repetition rate, nitrogen jet. Several mathematical models were reviewed. Matrix volatilization and fiber swelling are apparent in the region near the laser drilled hole which form HAZ. Mechanism for fiber swelling in carbon fibers was also reviewed. Several magnitudes for extent of HAZ has been discussed. The extent of HAZ in laser cutting influences mechanical properties [7].