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

David Tormey,M. Mahmood Ali,Richard Sherlock,Foram Dave,Alistair Mcilhagger

doi:10.3389/fmats.2021.737689

David Tormey, M. Mahmood Ali + Show 3 more

Open Access

https://doi.org/10.3389/fmats.2021.737689

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Abstract

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 (&gt;1 wt%) appear to be more difficult to weld.

Highlights

Laser processing technology has become well established, playing a crucial role in solving several challenging manufacturing issues for about 4 decades (Purtonen et al, 2014)
The Laser transmission welding (LTW) in lap geometry involves two dissimilar materials: the top layer is transparent or semi-transparent which allows the laser beam propagation to the bottom layer which is absorptive in nature and the energy coming from the laser beam is absorbed and converted into heat
The weld width (WW) and depth of absorptive layer (DA) are more sensitive in the lower power range, but the depth of transmissive layer (DT) is more sensitive in the higher power range

Summary

Introduction

Laser processing technology has become well established, playing a crucial role in solving several challenging manufacturing issues for about 4 decades (Purtonen et al, 2014). There are several types of laser welding categorized on the basis of laser source (solid-state, gas, diode, fibre), temporal characteristics (continuous, pulsed); material geometry, (butt, corner, edge, lap, T-joint), laser-material interaction (direct, surface heating, through transmission), and mode of laser beam delivery (contour, simultaneous, quasi-simultaneous, masked) (Grewell et al, 2003; Grewell and Benatar, 2007; Troughton, 2008; Tres, 2017; Dave et al, 2021). Local temperatures in excess of the degradation temperature of one or other of the constituent materials can result in contamination of the weld zone and poor joint characteristics

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