Over the years, spotweld representation for crash and NVH applications have evolved from a crude to a detailed modeling resulting in reduced pre-processing effort while greatly enhancing the accuracy of numerical models. Here is link that gives a brief overview of spotwelding process in LS-DYNA. Please note that the document is over 2 years old and has not been updated since. Please refer to the latest LS-DYNA keyword and theory manual for more information.
Additional information compiled by Mr. Jim Day: Spotwelds