| Refill friction stir spot welding is a new spot welding method,which is widely used in industry.In this paper,the existing friction stir welding equipment was refitted,and the key parts and fixture of refill friction stir spot welding were designed and manufactured.The welding process experiment of 6061-T6 aluminum alloy with thickness of 2mm was carried out by using a self-designed welding tools.The influence of welding process parameters on the surface formation,microstructure and mechanical properties of joints was studied.The corresponding relationship between welding process parameters and process characteristic parameters was established,and the mechanism of the influence of welding process parameters on hook angle was revealed.In this paper,3Cr3Mo3W2V steel was selected to design a variety of welding tools independently.Firstly,two kinds of welding tools with different sizes were designed with spring as transmission device.After testing,it was found that the sleeve of small-sized welding tool was broken and the pin was bent,and the problem that the pin could not be refilled was found in the large-size welding tool.Therefore,it was improved on the original design and completely depended on the external mechanical structure.To realize the movement of the pin,a motion platform of the pin was designed,which completely relies on the external drive to realize the refilling reaction of the pin and realizing the refilling step.The motion platform of the pin is mainly composed of a mechanical frame,a moving plate and a driving device,and the relative movement of the pin and the sleeve can be realized through control to meet the welding requirements.In the aspect of equipment control system,the refill friction stir spot welding subprogram was added,the intelligent man-machine interface was created,the FX2N-10 GM positioning program was modified,and the coordinate monitoring window was established in the FX2N-20 GM module.through PLC + human-machine interface,the joint movement of sleeve and pin could be accurately controlled,and the original equipment was refitted,and the refill friction stir spot welding equipment was completed.The refill friction stir spot welding equipment built by ourselves was used to carry out the process test.Under the rotation speed of 1800 r / min,the pressing speed of 60 mm / min,and the pressing depth of 2.8mm,the macroscopic shape of the welding joint is great.The key hole is refilled evenly,and there is no obvious welding defect on the surface of the welding joint.The results show that the microstructure of the stirring zone is fine and dense under the action of extrusion and stirring of the pin.Under the action of welding thermal cycle and mechanical stirring,the grain size of the heat affected zone is different,and the grain size of the heat affected zone is relatively coarse.The hardness of the whole welding joint is "W" distribution,and the welding joint has obvious softening phenomenon.The maximum hardness of the stirring zone is 79 HV,which is 82.3% of the base metal.The lowest hardness of the boundary between the zone and the HAZ is 58 HV,which is 60.4% of the base metal hardness.The results show that there are three main fracture modes of welding joint: plug type fracture,interface fracture and base metal fracture.With the increase of rotation speed,pressing speed and depth of sleeve,the maximum shear resistance of joint increases at first and then decreases.In the process of micro analysis,the typical appearance hook of refill friction stir spot welding is also found.With the increase of welding rotation speed,the hook angle gradually increases,and the hook shape gradually changes from sharp "V" shape to wavy shape.With the increase of pressing depth,the hook angle gradually increases.With the increase of pressing speed,the hook angle gradually decreases.When the heat input is more,the hook angle is smaller,the effective bearing area is increased and the mechanical properties of the joint are strengthened. |
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