In Situ Digital Image Correlation Observations of Laser Forming

Herman Fidder,Jeff Th M De Hosson,Václav Ocelík,Joris P J Admiraal

doi:10.3390/met10010017

Herman Fidder, Jeff Th M De Hosson + Show 2 more

Open Access

https://doi.org/10.3390/met10010017

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Abstract

In this study experimental and modelling methods are used to examine the microstructural and bending responses of laser-formed commercially pure titanium grade 2. The in situ bending angle response is measured for different processing parameters utilizing 3D digital image correlation. The microstructural changes are observed using electron backscatter diffraction. Finite element modelling is used to analyse the heat transfer and temperature field inside the material. It has been proven that the laser bending process is not only controlled by processing parameters such as laser power and laser beam scanning speed, but also by surface absorption. Grain size appears to have no influence on the final bending angle, however, sandblasted samples showed a considerably higher final bending angle. Experimental and simulation results suggest that the laser power has a larger influence on the final bending angle than that of the laser transverse speed. The microstructure of the laser heat-affected zone consists of small refined grains at the top layer followed by large elongated grains. Deformation mechanisms such as slip and twinning were observed in the heat-affected zone, where their distribution depends on particular processing parameters.

Highlights

Laser forming (LF) was first reported in the 1980s within the ship building industry using flat steel plates which has been formed into three-dimensional shapes as reported by [1,2]
The movement of the markers placed on the sample and basement during laser forming is recorded in situ as illustrated on a single frame image in Figure 2, which is at the free end of the sample
15 itthe is shown boundary is in agreement with the depth of the α to β phase transformation line determined by the that the maximum temperature achieved depends on the scanning speed and the laser power

Summary

Introduction

Laser forming (LF) was first reported in the 1980s within the ship building industry using flat steel plates which has been formed into three-dimensional shapes as reported by [1,2]. The bending model of [5] only takes into account laser power, sample thickness and beam scanning velocity. The model of [13] takes into account the flow stress at the heated region as variable with the entire equation appearing as a cube root Both above mentioned approaches deal with the final bending angle observed after processing by a laser beam. Some experiments were repeated 5–6 times with the same laser power and laser scanning speed to estimate the variation in the final bending angle with position on the sample. The highest possible power setting used was ~1000 W before the onset of melting of the surface Other processing parameters such as scanning speed and beam diameter have been selected to achieve TGM conditions in all experiments. It was empirically calibrated with the experimental data by observing the first melting features in the centre of the laser track

Experimental Results

Aramis

Bending angle of multiple overlapping different laser powers at

Conclusions