Research On Finite Element Simulation Of Tricone Bit Legs Welding And Deformation Control

The roller bit consists of some parts,such as bit legs,cone,bearing,water hole and lubricant compensation system,which are directly welded by three bit legs assembled with roller cone.However,due to the uneven temperature distribution caused by electric arc,the weldment is locally heated to above the melting point temperature,and a large temperature gradient is formed at the weld and base metal.During the cooling process,the tooth palm shrinks and deforms due to stress,which is directly affects the structural quality and performance of the roller bit.Therefore,the research on the optimization of the welding of the bit legs deformation has important theoretical significance and engineering application prospects.In this paper,the key problems such as residual stress,deformation of bit legs and offset of journal face involved in bit legs welding are systematically studied.Based on thermal,elasticplastic theory and finite element theory,the finite element model of bit legs welding of roller bit is established with ABAQUS software as the platform and Python and Fortran language programming,and the temperature field,stress field and deformation results of bit legs welding are analyzed.The influence of welding is optimized from two aspects of welding sequence and constraint mode,and reasonable welding sequence and constraint mode are put forward,which provides a theoretical basis for the measures taken by roller bit companies to accurately control bit geometry parameters.especially bit diameter,in the bit welding process,and has certain practical value.The results are as follows:(1)The finite element model of bit legs welding is established,and the residual stress distribution and deformation law of bit legs welding of roller bit under the existing technology are analyzed.Specifically,there is a large residual stress between the external circular weld and the horizontal weld,and the offsets at the central nodes of the three journal surfaces were 1.44 mm,1.27 mm and 1.52 mm inward shrinkage.(2)Appropriate welding sequence can optimize the welding of bit legs.Scheme 2.which has the opposite welding sequence to the weld bead and the original process is superior to the original process in terms of residual stress and deformation after welding.The offsets at the central nodes of the three journal surfaces are respectively 1.42 mm,0.95 mm and 1.24 mm inward shrinkage,which are 1.3%,25.2% and 18.4% lower than those in the original process.(3)The constraint at the leg back greatly improves the welding deformation of the bit legs of the roller bit.But the residual stress increases obviously.Scheme I.which imposes restraints on the two sides of the leg back,the offsets at the central nodes of the three journal surfaces were respectively 0.90 mm,0.79 mm and 0.81 mm inward shrinkage,which are 37.5%,37.8%and 46.7% lower than those of the original process.The second scheme to impose restraints on the inner and outer part of the bit back,the offsets at the central nodes of the three journal surfaces were respectively 0.09 mm,0.24 mm and 0.23 mm outward expansion,which are reduced by 93.8%,81.1% and 84.9% respectively compared with the original process.(4)Although the constraint has no effect on the peak value of welding equivalent stress,the residual stress in all directions is increased in different degrees compared with the original process.However,excessive residual stress will shorten the service life of the drill bit and reduce the mechanical properties such as fatigue strength and stress corrosion of the drill bit.Therefore,it is the best control scheme to comprehensively adjust and control the deformation and take into account the influence of residual stress,use the welding sequence opposite to the original process in the same weld pass and impose restraints on both sides of the leg back.