Non-destructive optical testing of the products obtained using additive manufacturing

Developing of additive manufacturing and the use of additive technologies at all stages of the product life cycle entails the necessity of developing methods providing control of their characteristics. Here we consider application of the optical measurement procedures to the objects of complicated shape. Products manufactured by the methods of additive technologies may have defects such as delamination, starved joint, porosity, warp, stress-strain state, roughness, etc. We present the devices designed and developed on the principles of interference, structured light and holography at the «VNIIOFI» Federal State Unitary Enterprise to identify the defects in the products of additive technologies. The advantages and shortcomings of the interference microscope, scanner-profilometer, and shearograph are examined with regard to the control of the aforementioned types of geometric defects. The special feature of the contact-free methods is the possibility of control of different types of materials: metals and dielectrics, transparent, reflective, scattering and composite materials. The results of experimental study aimed at detection of the surface and subsurface defects are presented. Interferograms and results of phase reconstruction are presented both for reflective and transparent objects. Defects of the refractive index of the microcavity made of an optical fiber were detected. Metrological characteristics of optical devices for non-destructive testing of products are estimated. Standards for calibration and graduation of the optical devices considered in the study were manufactured and tested. The use of specially developed standards makes it possible to use these methods both for qualitative assessment of the objects of complicated shape and flaw detection and for quantitative estimation of their characteristics.

1. Aleshin N. P., Murashov V. V., Evgenov A. G., et al. The classification of flaws of metal materials synthesized by the selective laser melting method and the capabilities of nondestructive testing methods for their detection / Russ. J. nondestruct. Test. 2016. Vol. 52. N 1. P. 38 – 43.

2. Klein J., Stern M., Franchin G., et al. Additive Manufacturing of Optically Transparent Glass / 3D Printing and Additive Manufacturing. 2015. Vol. 2. N 3. P. 92 – 105.

3. Vishnyakov G., Levin G., Minaev V., Nekrasov N. Advanced method of phase shift measurement from variances of interferogram / Appl. Opt. 2015. Vol. 54. N 15. P. 4797 – 4804.

4. Levin G. G., Minaev V. L., Min’kov K. N., et al. Studying the Internal Structure of Microcavities by Means of Optical Tomography / Opt. Spectrosc. 2019. Vol. 129. N 3. P. 226 – 231.

5. Zhang Z. H. Review of single-shot 3D shape measurement by phase calculation-based fringe projection techniques / Opt. Lasers Eng. 2012. Vol. 50. N 8. P. 1097 – 1106.

6. Xie X., Xu N., Sun J., et al. Simultaneous measurement of deformation and the first derivative with spatial phase-shift digital shearography / Opt. Commun. 2013. Vol. 286. P. 277 – 281.