Study On Some Key Techniques Of FSW's Parallel Robot Based On Space Curve

Friction stir welding(FSW)is used widely as a high quality,high-efficiency,low cost and environment friendly welding method.FSW equipment is the carrier of the technology's development,the traditional friction stir welding equipments are designed mostly based on the long straight welding seam and the simple trajectory welding seam.Because welding equipment need the characteristics of strong rigidity,large torque and flexible multi-axis control when welding the space curve,the traditional tandem welding equipment showed lack of capacity in the welding of the space curved parts.However,the 3-TPT parallel robot developed by Northeastern University has advantages of high stiffness,high load capacity,high accuracy,good dynamic performance,large working space and so on,it can be very good to make up the disadvantages of tandem equipment in the FSW of space curve.In this paper,the 3-TPT parallel mechanism is re-designed,which can be transformed into a five degree of freedom parallel robot which has the ability of the space curve's FSW.In order to achieve the above objectives,this paper mainly carried out the following design and research:(1)The paper researched the welding process of FSW aiming at space curve welding in-depth,explored the difference between the technology and the simple welding process.It analyzed the stir-welding head's trajectory mainly and studied the relationship between the press amount and the shoulder radius and when welding space curve.In addition,the force model of the tool is established and the experimental verification is carried out.(2)According to FSW process requirements of the space curve,re-designed the 3-TPT parallel robot.It mainly includes the design and model building of the head's micro-motion mechanism,the design and model building of 2-DOF NC rotary table,and then combined the two designs with 3-TPT parallel mechanism to form a 5-DOF parallel friction stir welding robot.(3)The kinematics research of 5-DOF parallel friction stir welding robot is carried out.Changing the base coordinate,re-deduced the forward and inverse equations of robot kinematics,and then deduced the forward and inverse equations of 5-DOF parallel robot under the condition of adding 2-DOF NC rotary table.At last,this paper analyzed the correctness of the forward and inverse equations,and the result is correct.(4)Because of the large rigidity requirements of the friction stir welding,the stiffness and strength analysis of the 5-DOF parallel robot is carried out.Established the relationship between the force of each telescopic rod and the force of stir-welding head by vector method;using MATLAB to search the maximum force of telescopic rod when welding in the working space of the robot,and obtained the point.Finally the finite element analysis of the robot's main parts was carried out using the maximum force obtained.(5)In order to verify the selection principle of the technological parameters and the design principle of the shape and size of the mixing head is reasonable,this paper has designed a set of special fixture and manufactured and assembled it to carry out the experiment of FSW based on space curve.Installed the fixture of circular weld on a general friction stir welding machine to implement the FSW experiment of space circular weld,verified the performance of fixture designed in this paper,studied preliminary the welding process of space curve.