Residual stresses and deformations in metal additive manufacturing (AM) are persistent challenges. In the present study, we present a computationally efficient thermomechanical finite element (FE) model to predict the temperature and stress/strains during the AM process. The model utilizes an analytical temperature approach to estimate thermal histories. Then, the thermal field is used as the input for subsequent mechanical calculation. The accuracy of the proposed model is carefully examined by comparing the predicted results with the reported data in the literature. The computed stresses and deformations demonstrate accurate trends. A numerical tool named AM-builder, which can automatically construct the thermomechanical FE model for AM simulations, is developed to enhance practicality. A complete simulation for building a lattice-solid structure is presented. Results show that the temperature and stress/strain evolutions are effectively captured. This work provides a valuable resource for guiding the AM experiments to optimize the residual stresses and deformations.