Читать книгу Welding Metallurgy - Sindo Kou - Страница 77

Many computer models have been developed to study 2D heat flow [44–49] and 3D heat flow [24, 50–61] during welding. Kou and Le [24] developed a 3D (x, y, z) finite‐difference computer model to study heat flow and solidification in welding. All Rosenthal's assumptions were dropped. Figure 2.24 shows the calculated results of Kou and Le [24] for the GTAW of 3.2‐mm‐thick sheets of 6061 aluminum alloy. The agreement with observed fusion boundaries and thermal cycles is good.

Figure 2.24 Computer simulation of GTAW of 3.2‐mm‐thick 6061 Al, 110 A, 10 V, and 4.23 mm/s: (a) fusion boundaries and isotherms; (b) thermal cycles.

Source: Kou and Le [24]. © TMS.

Figure 2.25 shows the results of computer simulation of Kou and Le [24] on the effect of the power density distribution of the heat source on the weld shape. Under the same heat input and welding speed, weld penetration decreases with decreasing power density of the heat source. In the computer simulation, the power density distribution at the workpiece surface is approximated by the following Gaussian distribution:

(2.12)

where q is the power density, Q the rate of heat transfer from the heat source to the workpiece, r is the radial distance at the workpiece surface from the centerline of the heat source, and a is the effective radius of the heat source. As shown previously in Figure 2.13, the measured power density distribution is close to a Gaussian distribution.

Figure 2.25 Effect of power density distribution on weld shape in GTAW of 3.2‐mm 6061 aluminum with 880 W and 4.23 mm/s.

Source: Kou and Le [24]. © TMS.