In order to improve the forming precision of the wire arc additive manufacturing part

the section contour of the three-dimensional（ 3D） model needs to be offset by a certain width

in the offset process

the contour loop will be self-intersected. Aiming at the self-intersection of offset contour

the self-intersection point of offset contour is obtained by using the optimized strictly monotone chain（ SMC） intersection algorithm

which improves the efficiency of finding the intersection point; vector method is used to distinguish invalid rings

which improves the removal efficiency of invalid rings. The validity of the algorithm is validated by model slicing and arc welding forming experiments. The experiments show that the self-intersection processing algorithm reduces the waste of materials and improves the surface dimension precision of the parts.