Study On Additive Manufacturing Technology Based On The Principle Of Stationary Shoulder Friction Stir Welding

Additive manufacturing is a kind of emerging technology which is rapid developed and attracts widespread attention, because of its advantage of low cost and high efficiency, especially in the field of complex structures and small volume production. Laser, electron beam and arc additive manufacturing are used to additive metal material, which have their own advantage, scope and limitations, especially in the field of the light alloy additive manufacturing. Friction stir additive manufacturing(FSAM) technology comes into being with the unique advantages in light alloy material, but it still has some problems, such as the low material utilization rate and the large machining allowance. Therefore, it is necessary to develop a solid state additive manufacturing technology without margin. A new way based on the principle of stationary shoulder friction stir welding(SSFSW) is proposed in this paper, which aluminum alloy additive manufacturing can be achieved by using the solid state SSFSW method which is green and friendly to the environmental. The stationary shoulder friction stir additive manufacturing system including the stationary shoulder system, forming tools and special fixtures was designed. It achieves additive manufacturing without margin in 2024-T4 aluminum alloy by using self-designed additive manufacturing system and the formation of material is well, which proves the feasibility of stationary shoulder friction stir additive manufacturing(SSFSAM). With the increase of the number of the additiving layers, the effective additiving width and the additiving ratio reduces slightly, the effective material utilization increase, the total height of additiving material appears non-linear growth.The factors affected the stationary shoulder friction stir additive manufacturing were studied systematically in this paper. The result shown that the combination of the forming tool with a tapered thread stirring pin and a roll stationary shoulder is conducive to additiving forming. The width of additived material area and the height of interface migration decrease with the travel speed increasing and it increase with the rotational speed increasing. The depth of interface migration gradually increases with the travel speed increasing and it decreases with the rotational speed increasing by single layer additive manufacturing. When the rotational speed is 600 rpm and the travel speed is 30mm/min, the formation of the additived material is better, in which,there is no defect, the height of interface migration is smaller and the width of additived material area is larger. The additived material area generates defects easily with larger additivd material thickness. When the additivd material thickness is 3 mm and the length of the stirred pin is 4 mm; the additived material area is good without defect in surface. Additiving direction including the positive direction and the reverse direction have little effect on the formation of the additiving material area during the process of multilayer additive manufacturing. The constraint state of material has an important role to additiving formation by using the stationary shoulder friction stir additive manufacturing. The constraint of wide sheet is not conducive to additiving formation, because of large deformation and easily producing defects in additived material area. Additived material area does not easily deform during additive manufacturing with a narrow constraint, the process is stable and it is conducive to the control and prediction of additiving material shape. In order to achieve additiving manufacturing without allowance, the width of the sheet should be minimized.Meanwhile, the microstructure and properties of the bulk aluminum material gained by stationary shoulder friction stir additive manufacturing were studied.Hardness tests show that the hardness in the advance side is slightly higher than the return side. The hardness in the top layer is harder than the bottom. The hardness at the same horizontal position distribute relatively uniform, however hardness gradient exists in the vertical direction. Tensile tests showed that the level tensile strength is quite different at the different thickness position; tensile strength at the top layer is higher than the bottom. Tensile strength at the bottom gradually decreases with the increasing of the additiving layer numbers, and finally it gets stabilized. The tensile properties of the additiving material in the thickness direction are anisotropy.