The effect of process parameters during the insertion phase of robotic friction stir welding on axial force

To establish a reference for developing an automated insertion strategy based on axial force, as well as an active axial force control strategy during the insertion stage for robot friction stir welding. This research specifically focuses on the insertion phase of stationary shoulder friction stir welding using the 6061-T6 aluminum alloy. It investigates the effects of various parameters, including spindle rotation speed, insertion depth of the stirring pin, insertion speed, and spindle insertion angle, on the axial force experienced during the insertion phase. The experiments were conducted using a ZK3000-500-A industrial robot equipped with a static shoulder friction stir welding spindle system. The axial force was measured using a force transducer and data acquisition system, recording real-time force signals throughout the welding process. The methodology involves varying the insertion depth from 7 to 11 mm, spindle rotation speed from 1000 to 3000 rpm, insertion speed from 10 to 50 mm/min, and spindle insertion angles of 0°, 2.5°, and 5°. The welding process parameters were systematically varied while keeping other conditions constant to isolate the effect of each parameter. The results indicate that the robotic friction stir welding insertion process can be divided into four distinct stages: initial rise, transition, secondary rise, and stabilization. Furthermore, the change in the axial force value exhibits an approximately linear relationship with the insertion depth. It was observed that the axial force increased linearly with increasing insertion depth during the stable stage. Higher spindle speed results in an earlier initiation and termination of the transition stage. Among the investigated parameters, the insertion speed has the most significant impact on the trend of the axial force change. A higher spindle speed not only facilitated a quicker insertion but also resulted in a more rapid initial force increase. Specifically, a higher insertion speed leads to an increased rate of force increase, a decreased stabilized value, and a shorter transition time. On the other hand, the spindle insertion angle does not exert a significant influence on the trend of the force change. This study establishes a basis for future enhancements in force control strategies.