Study On The Process Characteristics Of Titanium Alloy Laser Wire Additive Manufacturing In Vacuum

With the development of technological innovation and revolution around the world,additive manufacturing technology,as a technology that can promote manufacturing innovation,is a key research field and industry development direction.The development of additive manufacturing has also been carried out 20 years in China.The research of space metal additive manufacturing is one of the major strategic objectives of China's orbital space.But it is still in the primary research stage.In this paper,the manufacturing process of Ti-6Al-4V titanium alloy laser wire additive in vacuum was researched.And the laser metal wire additive manufacturing technology was taken as the research object,aiming at improving the forming quality and the performance of the formed parts.The successful development of the project will provide a key scientific foundation and important technical support for metal wire additive manufacturing.It also will provide theoretical basis and factual support for the realization of the space station's metal additive manufacturing.Firstly,some forming process problems of single-layer cladding bead,multi-layer thin-walled part,and multi-layer thin-walled box were studied.The circular laser spot and the good neutrality of wire are the premise of maintaining the directionless forming.When the wire melting transition is liquid bridge transition,forming stability is higher.Then,aiming at avoiding the problem of poor forming quality and stability of the forming multi-layer thin-walled part,it is proposed to form closed-type thin-walled parts.At the same time,the forming path during forming of multi-layer thin-walled box should meet the four sides of the box at an angle to the X-axis or Y-axis and the corners should be rounded.The forming stability and the surface quality of the formed part will be better in these conditions.Secondly,the influence of key forming factor(k= wire feeding speed/scanning speed),line energy(Q= laser power/scanning speed)on the size of single-layer cladding bead were studied.And the parameters range is also studied.It is found that the larger laser power and line energy,the process range become larger.When the value of key forming factor increases,both the height and width of cladding bead will increase.The line energy has little effect on the size of cladding bead.In addition,according to the forming size rule of single-layer cladding bead,the research on the forming size rule of multi-layer thin-walled part was carried out.It is found that for a multi-layer thin-walled part,the layer width will gradually increase with the number of layers increment in the first few layers except the second layer.And the layer width tends to be stable after some layers.Heat accumulation is much greater than other conditions when the inter-layer time is 1 s.The layer width of thin-walled parts is no obvious difference when the inter-layer times is bigger than 5 s.Finally,the microstructure of Ti-6Al-4V titanium alloy after laser wire additive manufacturing was analyzed.And heat treated was carried out to improve the surface microhardness.Most of the Ti-6Al-4V titanium alloy single-layer cladding bead is widmanstatten structure and basket-weave microstructure.With the increase of key forming factor,the size of ?' acicular microstructure decreases.With the increase of linear energy,the number of ?' acicular phase increases.The multi-layer thin-walled part has a large columnar ?-grain throughout the entire thin-walled cladding layer.The lower layer and the upper layer are mostly widmanstatten structure,while the middle layer is basket-weave microstructure.When the multi-layer thin-walled part is heat-treated,the microhardness of the thin-walled part is maximized by 930 ? solution and 500 ?/4 h aging.