Real-time heat input monitoring towards robust GMA brazing

Abstract

Gas metal arc (GMA) brazing of thin sheets requires active control of heat input, filler alloy deposition and temperature field on sheet surface. A novel attempt is presented here for a rapid synchronous real-time monitoring of current and voltage transients, filler alloy depositions and temperature field using, respectively, a high-frequency recorder, high-speed videography and two thermal infrared cameras during GMA brazing of galvanized steel sheets. For heat inputs from 100 to 200 J mm −1 , the peak temperature varied from 1500 to 1700 K. The high-speed videography showed consistent filler deposition and bead profile. The methodology and results presented here depict a promising resource for real-time monitoring and feedback control of GMA brazing.

Real-time monitoring of temperature field, metal transfer and cooling rate during gas metal arc-directed energy deposition

“…The melt pool, the partially melted zone and the solidified deposit are referred to as the regions depicting temperatures beyond 1812 K, between 1812 and 1758 K and between 1758 and 1273 K, respectively. It is noteworthy that the two-colour camera (TC-1) is able to record down to 1273 K [6,17].…”

“…A comparison of the corresponding images between Figure 4(a-i) and Figure 5(a-i) shows the variations in the melt pool sizes and peak temperature to be around ±3 mm and ±10%, respectively. A fair identification of the melt pool boundary from the mono-colour IR camera is notable as the thermal images are processed using a single emissivity value [4][5][6]. Although the twocolour cameras can provide a more accurate real-time temperature field, it is more expensive than monocolour camera and a real-time monitoring of melt pool sizes using a mono-colour IR camera is therefore promising for GMA-DED.…”

“…Appropriate monitoring and control of the arc power and metal transfer are needed to build defect-free parts in GMA-DED [4,5]. Although significant efforts are reported for real-time monitoring of arc welding processes [6][7][8][9], similar attempts are yet scarce for GMA-DED [4,5].…”

“…A twocolour thermal camera measures the spectral intensities at two different wavelengths within a narrow range of wavelength bands and can directly estimate the actual temperature irrespective of variations in emissivity values over the radiating surface [13][14][15][16][17][18]. The two-colour thermal cameras are recently used for monitoring melt pool surface temperature for GMA brazing [6], GMAW [14] and GTAW [15] processes. The use of thermal cameras for process monitoring is just started for metal additive manufacturing processes.…”

“…The real-time monitoring of the melt pool and dynamic metal transfer using a high-speed video camera at frame rates ranging from 1 to 5 kHz has helped to achieve process stability in GTAW [22], GMAW [23][24][25][26], plasma arc (PA) assisted GMAW [27] and GMA brazing [6]. Similar efforts are also evolving for gas tungsten arc-directed energy deposition (GTA-DED) [28] and GMA-DED [29][30][31] and plasma arcdirected energy deposition (PA-DED) [32].…”