| Laser transmission welding(LTW) is an advanced welding technology for plastics. LTW is superior to traditional welding methods in many aspects. LTW process is a kind of flexible and efficient welding technology and through which micro-welding and the welding of part of dissimilar plastics can be fulfilled. Joints with high quality can be obtained via LTW——high strength, high precise formation, excellent sealing property and low residual stress in joints, etc. Nowadays, LTW is widely applied in industries. The fiberglass-doped plastics is a kind of composite material which is widely occupied in car industry, medicine,electronics,etc. After fiberglass doped, the physical and chemical properties of material are significantly improved but the welding property gets worse, too. In this paper, in order to research the transmission welding of fiberglass-doped plastics, the study on LTW of fiberglass doped Acrylonitrile- Styrene Copolymers(ASG) is carried out and the laser absorbent is developed for translucent plastics welding.For the joining of translucent and opaque ASG, the influence of parameters on welding quality is studied. The penetration and weld width linearly improves as line energy increases, approximatively, and the variation of penetration is more obvious. And the shear strength of joint improves firstly and then declines with the increase of line energy. For the joints welded under line energy between 0.75 to 1J/mm, the shear strength can be up to 18 MPa and partial fiberglass fractures during the shear test. And on the other hand, the penetration reduces and weld width widens along with the increases of laser spot diameter and the shear strength reaches 18 MPa when spot diameter is between 2.72-3.29 mm.An integrated parameter, Energy Density(Ep), namely the average heat input on unit area, is put forward and the mechanism of the influence of parameter on welding is figured out based on energy density. The effect rule of energy density on shear strength is obtained which indicates that shear strength promotes first and then drops with the increases of energy density. When energy density is between 0.275-0.371J/mm2, the peak welding temperature is 293.7oC and fusion time reaches 0.59 s, therefore, the bead is compact and free of defects because no decomposition occurs in welding process and the fusion time is relatively long. However, fake welding emerges under the condition that heat input is lower than 0.275J/mm2 because of low welding temperature and short fusion time. When energy density exceeds 0.4 J/mm2, the peak welding temperature over decomposition point of ASG, so porosity and decomposition hole comes into being and low strength joint is generated.Independently develop the laser absorbent, and through which complete the high quality welding of two ASG translucent plates. The appropriate thickness of absorbent layer is between 60 to 90 um, which is defined by experiment. And the result of research of ASG translucent welding shows that the shear strength of joint under optimized parameter reaches above 14 MPa which is as large as 77% of translucent-absorbing joint.The microstructure of translucent-absorbing and translucent-translucent welding beads is analyzed and studied. It is found that the bead can be divided into Weld Nugget Area and Plastic Remelting Area. The shape of Weld Nugget Area is ellipse, and in which the plastics is fully mixed together and the microstructure of it is tremendously different from base plastics. Plastic Remelting area is an elliptical ring domain outside of Weld Nugget Area and porosities appear under high heat input condition in this area and nevertheless, the microstructure of the area without porosities is almost same as base plastics. There is a clear boundary between two areas and much fiberglass gathers here. For the translucent-translucent bead, the microstructure of area near boundary shows an obvious hybrid characteristic. |
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