This article applies to the glue-free bonding of the components made of thermoplastic, specifically techniques that use friction heat to plasticize and then join two surfaces. The featured technique is a friction (spin) welding process. Welding parameters were checked and presented. Spin welding is known to consist of four phases. Analytical calculations were made for the first step. They are focused on the changeability of welding parameters depending on weld velocity. In the next part of this article, calculations including the finite element method were performed, which provided additional data and visualization of the process, which were not available in analytical calculations. Results of both methods were compared. This made it possible to verify the correctness of theoretical calculations and exactness of FEM analysis.