Digital Image Correlation for On-Line Wall Thickness Measurements in Thick Gauge Thermoforming

Abstract:

The homogeneity of the wall thickness (distribution) is considered to be the most critical parameter in the quality assessment of a thermoformed product. Numerous previous studies have characterized the thickness distribution by means of manual discrete tactile measurements. Such approach is slow, operator dependent and only gives results on specific points of the final product, resulting in complicated judgements on the causes of the thinning of the polymer sheet. This work presents a methodology to use digital image correlation (DIC) for on-line, full field wall thickness measurements of thick gauge thermoformed parts during and after thermoforming. Such technique offers the following advantages. Firstly, it provides the user with thickness results over a complete area instead of a discrete measuring point. Secondly, it allows on-line measurements so that a better insight can be obtained in the deformation mechanisms during the forming process. Finally, a correlation is made between each undeformed point in the base image and the same point in the deformed images during thermoforming, resulting in a full-field strain image where intermediate sheet thinning can be calculated. This makes it easier to determine a causal relation between thermoforming parameters and final thickness distribution of the product.

• Periodical: Key Engineering Materials (Volumes 554-557)
• Pages: 1583-1591
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.554-557.1583
• Online since: June 2013
• Authors: Bart van Mieghem, Pascal Lava, Dimitri Debruyne, Albert van Bael, Jan Ivens
• Keywords: Digital Image Correlation (DIC), Thermoforming, Wall Thickness

References

[1] R. McCool and P. J. Martin, The Role of Process Parameters in Determining Wall Thickness Distribution in Plug-Assisted Thermoforming, Polymer Engineering and Science, vol. 50, pp.1923-1934, 2010.

DOI: 10.1002/pen.21718

[2] J. K. Lee, T. L. Virkler, and C. E. Scott, Effects of rheological properties and processing parameters on ABS thermoforming, Polymer Engineering and Science, vol. 41, pp.240-261, 2001.

DOI: 10.1002/pen.10725

[3] A. Aroujalian, M. O. Ngadi, and J. P. Emond, Effect of processing parameters on compression resistance of plug-assist vacuum thermoformed container, Advances in Polymer Technology, vol. 16, pp.129-134, 1997.

DOI: 10.1002/(sici)1098-2329(199722)16:2<129::aid-adv5>3.0.co;2-w

[4] Z. Ayhan and Q. H. Zhang, Wall thickness distribution in thermoformed food containers produced by a Benco aseptic packaging machine, Polymer Engineering and Science, vol. 40, pp.1-10, 2000.

DOI: 10.1002/pen.11134

[5] P. Collins, E. M. A. Harkin-Jones, and P. J. Martin, The role of tool/sheet contact in plug-assisted thermoforming, International Polymer Processing, vol. 17, pp.361-369, 2002.

DOI: 10.3139/217.1702

[6] H. Hosseini, B. V. Berdyshev, and A. Mehrabani-Zeinabad, A solution for warpage in polymeric products by plug-assisted thermoforming, European Polymer Journal, vol. 42, pp.1836-1843, 2006.

DOI: 10.1016/j.eurpolymj.2006.03.020

[7] S. A. D. Wiesche, Industrial thermoforming simulation of automotive fuel tanks, Applied Thermal Engineering, vol. 24, pp.2391-2409, 2004.

DOI: 10.1016/j.applthermaleng.2004.03.003

[8] K. D. Fernholz and R. Wykoff, Impact of Cooling Method and Incoming Sheet Quality on Final Part Surface Quality in Thick Sheet Paint Film Thermoformed Parts, Polymer Engineering and Science, vol. 49, pp.137-147, 2009.

DOI: 10.1002/pen.21232

[9] F. Beilharz, C. Bonten, and P. Eyerer, Influence of processing conditions on the thermoformability of PP-sheet material, presented at the ANTEC, 2011.

[10] J. Jeswiet, F. Micari, G. Hirt, A. Bramley, J. Duflou, and J. Allwood, Asymmetric single point incremental forming of sheet metal, Cirp Annals-Manufacturing Technology, vol. 54, pp.623-649, 2005.

DOI: 10.1016/s0007-8506(07)60021-3

[11] A. Seefried and D. Drummer, The Effects of Radiation Cross-Linking and Process Parameters on the Behavior of Polyamide 12 in Vacuum Thermoforming, Polymer Engineering and Science, vol. 52, pp.884-892, 2012.

DOI: 10.1002/pen.22155

[12] Information on http://www.matchid.org

[13] P. Lava, S. Cooreman, S. Coppieters, M. De Strycker, and D. Debruyne, Assessment of measuring errors in DIC using deformation fields generated by plastic FEA, Optics and Lasers in Engineering, vol. 47, pp.747-753, 2009.

DOI: 10.1016/j.optlaseng.2009.03.007

[14] L. Stroebels, I. Current, J. Compton, and R. D. Zakia, Basic photographic materials and processes, 2 ed. Focal press, 2000.

[15] A. R. Greenleaf, Photographic optics. New York, The Macmillan Company, 1950.

[16] R. E. Jacobson, S. F. Ray, G. G. Attridge, and N. R. Axford, The Manual of Photography, Photographic and Digital Imaging, 9 ed., Focal Press, 2000.

[17] B. Pan, Z. X. Lu, and H. M. Xie, Mean intensity gradient: An effective global parameter for quality assessment of the speckle patterns used in digital image correlation, Optics and Lasers in Engineering, vol. 48, pp.469-477, 2010.

DOI: 10.1016/j.optlaseng.2009.08.010

[18] Accuform, T-SIM, version 4.7a, 2009.