Planeness of upper ring surface of nether frame carbody of grab

Residual plastic strain method is applied to the planeness prediction of the upper ring surface of gragb nether frame carbody where welds are distributed in spatial. For most of welds lie on the above of the gravity, the structure is bending toward bottom after welding. It is reasonable welding bottom plate welds and upper plate welds by turns to decrease of the welding deformation. Residual plastic strain method cannot consider the effect of the welding sequences on the welding deformation. But the effect of parts of welds on the structure can be individualy analyzed by residual plastic strain method. Calculation of the main circle welds showed that it is profit for decreasing the plane degree by welding the circle welds in segments and by turns. The predicted plane degree of the upper ring surface of grag nether frame carbody is 0.68 mm. It seems not easy to meet the demand of 0.5 mm. Welding circles in segments or diminishing the size of welds are suggested to decrease the planeess of the upper ring surface.