Simulated Effect of Carbon Black on High Speed Laser Transmission Welding of Polypropylene With Low Line Energy

Laser welding is an important manufacturing tool for a wide variety of polymer products including consumer goods, automotive components and medical devices. The laser process parameters and polymer properties have a significant impact on weld quality. Due to higher heat density generated by the laser transmission welding (LTW) technique, defining a set of suitable parameters for LTW of thermoplastics and composites can be challenging. In this work the effect of carbon black along other control parameters has been investigated for high speed welding using a laser source of 980 nm wavelength with low line energy. In this work, the finite element method (FEM)-based software COMSOL Multiphysics is used to create a 3D transient thermal model for LTW of isotactic polypropylene (iPP) and its composites with carbon black (CB) of concentrations ranging from 0.5 wt% to 1.5 wt%. The design of experiments based on Box-Behnken design (BBD) is used to organize the simulation experiments and mathematical models are developed based on multiple curvilinear regression analysis on the simulation findings. Independent control variables include the laser power, welding speed, beam diameter, and carbon black content in the absorbent polymer. The maximum weld temperature, weld width, and weld depth within the transmissive and absorptive layers are considered as dependent response variables. Furthermore, sensitivity analysis is carried out to investigate the impact of carbon black along with other independent variables on the responses. The welding feasibility check was performed on the basis of melt and degradation temperature of the materials, and weld depths of transmissive and absorptive layers. It has been observed that the composites containing 0.5 wt% and 1 wt% of CB can be welded successfully with neat iPP. However, due to a degradation temperature problem, composites having a larger proportion of CB (>1 wt%) appear to be more difficult to weld.

An Integrated Hybrid Methodology for Estimation of Absorptivity and Interface Temperature in Laser Transmission Welding

This study reports a new hybrid integrated technique to predict the absorptivity of absorber and the interface temperature of the joint in laser transmission welding. The new approach is more robust as the numerical model is confirmed through experimental observations initially with weld width and further with surface temperature. Experiments are performed on a polycarbonate sheets with electrolytic iron powder (EIP) as an absorber. The surface temperature and weld width are measured from the experiments. A transient 3-D finite element-based numerical model is developed for heat transfer analysis. The variation of heat flux with stand-off distance is also considered to enhance the accuracy of the computed results. The absorptivity is tuned in the numerical model so that the numerical weld width is in close conjunction with the experimental weld width. The numerical model is validated by comparing the upper surface temperatures at the center, measured in the experiments using infrared thermography. The results indicate that the surface temperatures in the numerical model are in good agreement with experimental observations, and the average error is less than 6%. The interface temperatures are estimated after the validation of the numerical model.