点溶接機電極の先端部の温度上昇の実測と計算

Abstract

The maximum temperature rise in electrode tip is estimated from the measured heat input to the electrode during one spot welding. It reaches as high as about 700°C for ordinary spot welding conditions of steel plates of 0.8-3.2 mm thickness.For calculation the electrode cross section is assumed constant along the electrode length, and the effect of wave form of heat flow from the tip is investigated. Q in Table 1 is the measured heat input to each side of the electrode per one welding under the conditions shown in the table. θ2 in the table shows the calculated results using the equation (9) under the following assumption, i.e. the heat flow wave form is taken as Fig. 11(a), heat flow time TH is assumed as equal to current flow time T0 shown in the table, the cross section of the electrode is taken as S2 corresponding to the root diameter of the electrode.Fig.14 shows the temperature distribution curves along the length when a constant heat H=1000 cal/cm2 sec flows in from the electrode tip for the duration TH=0.25, 0.5, 1.0, 1.5sec. Curves A-D show the temperature rise when the distance x0 of cooling end from the tip is infinity and A, B'-E' for x0=1 cm. For the calculation of the effect of cooling water, it is assumed that equation (33) holds, according to the model shown in Fig. 13 (h is taken as 1 for Fig. 14 and 18).Heat flow time TH is divided into two parts as shown in Fig.17 and the temperature at the moment C is calculated as the sum of the parts. Temperature due to the part AB is calculated using equation (49), T1 being time constant defined as in equation (43) and the period of BC is chosen far longer than time constant T2.It is easily shown that the magnitude of temperature fluctuation at a point I cm distant from the tip is negligible when intermittent heat input cycle is less than 1 sec/spot and we see that the cooling effect of cooling water is only effective to reduce the average temperature rise in the electrode under intermittent welding.Table 3 shows the temperature rise at the tip for cyclic heat flow from the tip for various combinations of x0, h, TH and Tw (i.e. cyclic period). The value shows the temperature at the moment C in Fig. 19 for H=1000 cal/cm2 sec.Fig.2, 4 shows the oscillogram of the temperature rise at 2 mm distant from the tip (Fig.1). Electrode pressure is also shown in Fig.2.