Development of experimental method for in situ distortion and temperature measurements during the laser powder bed fusion additive manufacturing process

Measurements of the temperature and distortion evolution during laser powder bed fusion (LPBF) are taken as a function of time. In situ measurements have proven vital to the development and validation of FE (finite element) models for alternate forms of additive manufacturing. Due to powder obscuring all but the top layer of the part in LPBF, many non-contact measurement techniques used for in situ measurement of additive manufacturing processes are impossible. Therefore, an enclosed instrumented system is designed to allow for the in situ measurement of temperature and distortion in an LPBF machine without the need for altering the machine or the build process. By instrumenting a substrate from underneath, the spread powder does not affect measurements. Default processing parameters for the EOS M280 machine prescribe a rotating scan pattern of 67° for each layer. One test is completed using the default rotating scan pattern and a second is completed using a constant scan pattern. Experimental observations for the build geometry tested showed that for Inconel® 718 and a constant scan pattern produce results in a 37.6% increase in distortion as compared with a rotated scan pattern. The in situ measurements also show that the thermal cycles caused by the processing of a layer can impact the distortion accumulated during the deposition of the previous layers. The amount of distortion built per layer between the rotating and constant scan pattern cases highlights inter-layer effects not previously discovered in LPBF. The demonstrated inter-layer effects in the LPBF process should be considered in the development of thermo-mechanical models of the LPBF process.