Laser Transmission Welding Of Thermopastic Polyurethane Films

With the advantages of excellent mechanical properties and good biocompatibilities,the Thermoplastic Polyurethane(TPU) film is substituting for the Polyvinyl Chloride(PVC)film,becoming the first choice of making medicine products such as fluid conveying pipes,urethral catheter,ice bags and so on.Laser transmission welding(LTW) as a untouchable joining method can satisfy the strict requirement about neatness in the process of making medical products.Accordingly,the investigation about LTW of TPU films has good application value,and also have important significance to understand the theory of LTWUsing the method of experiment and numerical simulation,this thesis carries systematical studies of LTW of TPU films.First of all,0.12mm thickness TPU films are welded using contour welding.The effect of main welding parameters including focal distance,laser average power, welding speed on welding quality is investigated.The results show that LTW is suitable for welding TPU films,and welding strength is higher than parent material’s.Using Clearweld(?) Resins,the color of welding seam is similar to parent material’s,and colorless welding is obtained.Adjusting welding speed and fixing the laser average power,parameter window for LTW of TPU films is obtained.The results show that with the matching of laser average power and welding speed,the welding speed can be increased by the premise of guarantee of weld seam quality.Secondly, based on the investigation of contour welding,mask welding is investigated.The study shows that at the laser average power of 2.3W,the welding speed of 100 mm/min,the seam width is consistent with the size of the mask;using the same width mask,with the increasing of the laser average power,the welding morphology changed,but the width of the welding doesn’t increase remarkably.And coaxial visual sensing technology is used in monitoring the laser welding process.Monitored results show that there is liquid flow in the molten pool which is not in a quasi-steady state. This study will lay a foundation for the analysis of the weld defects.Thirdly,A 3-D thermal model based on the finite element theory is implemented to simulate the temperature field on LTW of TPU films by means of the software ANSYS.With the ANSYS parametric design language APDL,a moving heat source is applied,and the distribution of the temperature field is gained.Effect of process parameters,including laser average power,welding speed on the welding result is investigated,and the calculated melting width is obtained.The results show that with increasing of laser average power,the maximum temperature and the melt width increases;with increasing of welding speed,the maximum temperature and the melt width decreases.Very good agreement is achieved between the calculated values and the measured values.It shows that the model is reliable.This study will lay a foundation for optimizing process parameters.