In the filling stage of plastic injection molding

the energy equation is dominated by convection.The simulation of temperature with the classical Galerkin finite element method in a fixed element might be unstable and oscillatory if time step is unreasonable.To get the reliable solution

the algorithm must deal with both convection and conduction

which requires highly different time scales.For this reason

the energy equation was solved by an operator-splitting method. First

the convective part of the problem was solved

and then the conduction term and source term were solved.In this way

particularly effective numerical schemes were used.As this approach used sub-time steps for the convection term

which was much smaller than that for the conduction term

the unstable result caused by convection could be solved consequently.In addition

the lumped mass heat capacity matrix was used to deal with the transient item

which reduced non-physical oscillations that the consistent mass heat capacity matrix possibly led to.For the given examples

the simulation results illustrated that the scheme in this paper had better accuracy.