Numerical Investigation of Temperature Distribution in Laser Assisted Metal Polymer (LAMP) Joining

Abstract

The need for lightweight components, reduced cost, and improved efficiency in modern manufacturing has led to increasing interest towards hybrid polymermetal components. This has necessitated the development of components with tailored properties for application in aerospace, energy generation, medical and electronics as well as for consumer goods. There is requirement to explore reliable joining methods for polymer - metal joining. Conventional polymer-metal joining techniques such as adhesive and mechanical joining have limited design and process flexibility. Ultrasonic and friction spot joining have not yet addressed the challenge of joining complex geometrical components and fusion for dissimilar materials with different melting points. Laser assisted metal to polymer (LAMP) joining is a modern technique which is not only fast, but highly reliable and flexible. Most thermoplastic polymers can be laser bonded to different types of ferrous and non ferrous metals. The joining process involves irradiation of a laser beam to the metal-polymer interface. High temperatures are produced in the interface between polymer and metal, which causes the polymer to melt and flow into the metal surface forming a bond. For the formation of a strong bond, it is important that the interface be exposed to sufficient heat to melt the polymer layer in order to form a close contact between the surfaces. Excessive heat could degrade the polymer while insufficient heat could lead to uneven melting. Delivery of the thermal energy by the laser beam is affected by process parameters such as laser beam power, scanning speed, absorptivity of the materials, and the contact pressure at the interface. To attain uniform temperature distribution and optimum amount of heat for proper melting of the polymer and good bond strength, a careful selection of the parameters involved is vital. Previous studies on optimization of joint characteristic in LAMP are not conclusive as the effects oflaserparametersontemperaturedistributionattheinterfaceduringthejoining process are yet to be investigated. This makes it difficult to predict the quality of joint expected from a set of parameters. In this work, a finite element model was developed to investigate the influence of laser parameters namely; the laser power, scan speed and beam spot size on temperature distribution at the interface during LAMP joining. This model was used to predict the depth and width of the molten zone, and temperature distribution within the heat-affected zone. Simulation runs were carried out for the joining of Polyethylene Terephthalate (PET) and stainless steel plate type (SUS304) materials. The model successfully predicted the bond width and depth of molten region of the polymer. The effects of laser parameters were investigated and results showed that increasing the laser power leads to increase in interface temperatures, while increasing the scan speed and spot diameter leads to decrease in maximum temperatures. In the range of parameters considered, optimal parameters for joining PET to SUS304 were laser power of 60 W, scan speed range of 20-35 mm/min and spot diameter of 4.5 mm. A comparison made between simulated data and experimental data on xx bond width showed a close agreement with a deviation of 3 %. This deviation was as a result of the assumptions made in the model.