Application of optical sensor for arc welding

Summary

In CO₂ gas-shielded arc welding, spatter is scattered and adheres to the base metal surface. The main factors affecting any difference in the bonding force remain obscure. This paper examines the bonding force of spatter adhering to the surface of SS400 base metal (rolled steel sheets) under different temperature conditions in CO₂ gas-shielded arc welding using 1.2 mm dia. solid wire. The following four types of base metal surface condition were adopted:

Type 1: As-received surface covered with an oxide film;

Type 2: Ground surface machined with a plain grinder (R_max = 0.6 μm);

Type 3: Surface with fume adhering to the ground surface;

Type 4: Free-ground surface machined with a disc grinder (R_max = 7–16 μm).

The base metal was heated by a 14 mm dia. x 600 mm ceramic heater arranged on the back of the base metal. The bonding force was measured as the shearing force of the spatter. Some 400 spatter particles on each surface were examined. The particles mostly have diameters ranging between 0.4–1.4 mm.

At a base metal temperature below around 450 K, the spatter on the scaled surface is insufficiently hot to melt the base metal and cannot adhere by melting the base metal surface. The shear stress is mostly below around 40 MPa. Despite a rising base metal temperature, however, spatter removal is still possible at less than 300 MPa.

Fume on the surface or the surface roughness do not affect the bonding force as directly as scale on the surface. The temperature, however, affects the bonding force. At a base metal temperature below around 450 K, the bonding force is slightly smaller.

When spatter adheres to the surface, heat causes the microstructure to change with corresponding hardening. The spatter and HAZ of the base metal here show a slightly higher Vickers hardness value (some spatter particles having HV470) than the base metal hardness (HV156–165), although this depends on the surface conditions and temperature.