Recent advances and current developments of molten pool temperature measurement for laser additive manufacturing processes

Background: Molten pool temperature in Laser Additive Manufacturing (LAM) will affect powder efficiency, structural compositions of reactants and products in the molten pool, thus determining the microstructure evolutions and mechanical properties of the final part. An interest in molten pool temperature measurement has been around for a long time since the appearance of LAM. However, a comprehensive summary of the existing methods and their applications does not exist in the literature. Objective: The state-of-the-art of the existed devices and methods for molten pool temperature measurement in various of LAM processes is reviewed in this paper. Methods: The existing temperature measurement methods for molten pool monitoring in LAM processes are discussed. For each method, the existed patents, detailed procedures, advantages and disadvantages, specific applications are specified. In the end, comparisons among the current temperature measurement techniques are made according to data accuracy, operation complexity and cost of implementation. Results: Four methods are currently being used for the molten pool temperature measurement in LAM processes, including (i) Thermocouples, (ii) Infrared pyrometers, (iii) Infrared cameras, and (iv) Charge-coupled-device cameras. Conclusion: Different measurement methods represent different characteristics of the signal, and each has merits and defects. Selecting suitable measurement method according to different process characteristics will be helpful to achieve a preferable and more convincing results.  .