Precision Analysis On 3-PRS Parallel Head Of Friction Stir Welding Machine

Friction Stir Welding(FSW) is a kind of solid state welding method invented late in the 20 th century, which is now widely applied in aerospace, automobile and shipping industries. But because of the heavy load during the process of FSW, the machine needs great stiffness, therefore the FSW devices are usually parallel machines.In this paper, the precision of 3-PRS parallel structured head which was designed for the FSW has been analyzed. The sdudy has been mainly focused on the structured errors which might appear during the manufacturing and installing processes, as well as the errors caused by the heavy loads while the thick plates welding processes.This paper has mainly focused on studies as follows:Firstly, the kinematics of 3-PRS mechanism has been studied. In the study the mathmatics model has been built and a way to depicting its orientation has been found,then the inverse solution has been obtained and based on this the forward solution has been obtained using numerical method.Secondly, the influence of the manufacturing and installing error on the precision of the tool has been studied. A 6-dof equivalent mechanism has been constructed to remove the constraints of the 3-PRS mechanism itself, all the manufacturing and installing factors that affects the precision of the machine tool have been found and how they should be expressed in the equivalent mechanism has been figured out, the influence of these errors on the tool has been studied by the forward simulating method.Thirdly, the static stiffness has been studied. The force analysis of the entire structure has been conducted, according to this the strut could be equivalent to two springs toward different directions, using the finite element method to calculate its stiffness,thus the deformation of the struts has been obtained and the machine tool deformation could be calculated under the constraint equation.Finally, the error analysis program, which was part of 3-PRS parallel machine designing software has been completed.This program was written in MATLABGUI,which consisted of two mainly parts,one is the deformation calculation of the machine tool under the effect of load, the other part is the manufacturing and installing error input and the interface of inverse/forward solution,which could calculate the position of the tool when there was structural error.Based on these program,an example has been given and the results has been compared with the simulation results,which proved the program stable and the results reliable.