Date of Award
Open Access Thesis
The purpose of this study was to use non-standard Design of Experiments (DoE) inputs in Friction Stir Welding (FSW) to deduce relationships between various weld input and response variables. Typically, inputs for FSW DoE are tool rotational speed, welding speed and forge force. In this study, three different input factors were investigated: travel speed, thermal boundary conditions (TBC), and advance per revolution (APR). The experimental design included a full factorial with each factor at two levels plus two centerpoint runs. Response variables included weld temperature, microstructure, hardness, power, weld energy, and in plane forces.
An investigation of the effect of stationary shoulder (SS) FSW welds on the weld response variables was also undertaken. The weld parameters for the SS welds were: a rotation speed of 1000 rpm and 640 rpm, various Z-forces, 6.77 mm/s travel speed, and a Steel backplate. Comparison between properties and weld responses was made between stationary shoulder and otherwise similar conventional shoulder welds. The effects of Z-force on X-force and defect formation in stationary shoulder welding were also examined.
For the DoE study it was hypothesized that through the manipulation of the thermal boundary condition, tool travel speed, and tool rotational speed that weld process parameters could be influenced; the process parameters of focus being maximum weld temperature, weld torque, weld power, specific weld energy per unit length, and in-plane forces. The process parameters listed above provides one with an insight into the temperature of the weld, the time the weld spends at that temperature, and the effectiveness of the movement of welding material around the pin during the welding process. Knowledge of and control over the weld temperature, time at said temperature, and material movement provides one with knowledge and control over the material properties of an FSW weld.
The results of the DoE study demonstrate the following conclusions.
• Increasing the heat extraction rate through changing the TBC will: decrease maximum weld temperature, increase weld power, increase weld torque, and increase X-force. • Increasing the travel speed will: increase maximum weld temperature, increase weld power, decrease weld torque, and increase X-force. • Increasing the APR will: decrease the maximum weld temperature, decrease weld power, decrease weld torque, and decrease X-force.
For the stationary shoulder study it was hypothesized that manipulation of standard FSW process inputs forge force (Z-force), rotational speed, travel speed, and the shoulder diameter (which is a tool parameter)would demonstrate insights to and control over welding process parameters in SS welds. Also, that a comparison of similar conventional shoulder (CS) and stationary shoulder (SS) welds could be made.
The results of the SS study demonstrate the following conclusions. •
• For a given rotational and travel speed increasing the Z-force will decrease the surface area of surface breaking defects. • The majority of the heat input for the CS welds of this study does not stem from the rotating shoulder of the FSW tool. • Approximately 50% of the X-force in a SS weld is due to the pin. • Higher maximum weld temperature is achieved through higher rotational speed.• Greater weld torque is achieved through lower rotational speed, and increased Z-force. • Increased X-force occurs with higher Z-force and increased shoulder diameter.
Widejko, R.(2015). Design of Experiments Analysis of Non-Standard Inputs for the Optimization of Friction Stir Welding. (Master's thesis). Retrieved from http://scholarcommons.sc.edu/etd/3617