*2.2. Measurement of Bead Geometry*

Macro cross-sectional inspection is a method to smoothly polish the surface of a welded part and perform a chemical solution treatment, to examine the structure, pore, penetration, HAZ and the like. Bead geometry measurements are made in all experiments and basically performed in BOP test, butt and fillet welding.

In this study, in order to analyze the effect of welding variables on the shape of the molten part shape, 9 measuring positions were selected, as shown in Figure 2.

**Figure 2.** Definition of measurement site on bead cross-section.

A description of the cross-sectional measurement positions of the melted zone and the heat-affected zone is as follows:


In this study, the size of welding specimen is 150 mm × 300 mm × 15mm. The laser power is stabilized at the center of the specimen; the sections from this location make it possible to show the representative section, as shown Figure 3. For measuring back-bead geometry, middle parts of horizontal axis of the experiment specimen were cut in 10 mm × 25 mm size, by a wire-cutting machine, and polished.

**Figure 3.** Welding specimen and coupon for cross-section observation.

To make the experiment specimen's bead geometry clearly visible, Nital (10% HNO3 and Ethanol) solution were applied for the etching of the cross-section of specimens. Moreover, an optical microscope system was used for accurate measurement of bead geometry and actually measured cross-sectional bead geometries. Figure 4 shows the digital electronic microscope with 2 Mega pixels and photographed at ×60 magnification, associated with bead geometry measurement. The shape of the bead cross-section, the penetration depth, bead width and height are measured by matching the 0.1 mm mesh of the optical camera with the image.

(a) Optical microscope equipment

(b) Bead geometry measurement

**Figure 4.** Equipment and method for measuring for bead geometry; (**a**) Optical microscope equipment, (**b**) Bead geometry measurement.
