–
Analysis of the effect of draft angle and surface roughness on ejection forces in micro injection molding
MACIARIELLO Francesco, LUCCHETTA Giovanni, SORGATO Marco
download PDFAbstract. Minimizing ejection forces is a crucial challenge in micro injection molding to prevent component damage during demolding. This research investigates the effects and interactions of draft angle, surface roughness, mold temperature, and holding pressure on the ejection force in a small, box-shaped component made from polypropylene (PP) and cyclic olefin copolymer (COC). A piezoelectric force sensor, integrated into the ejection tray of the mold, was used to measure the peak ejection force. The results indicate a significant influence of polymer type on ejection force, with PP exhibiting a 26% lower peak ejection force than COC. The draft angle consistently reduced demolding forces. Strong interactions were observed between mold temperature, surface roughness, and polymer type. Specifically, an increase in mold temperature led to an 88% increase in ejection force for COC, while resulting in a 63% decrease for PP. For PP, the optimal ejection force was measured at a surface roughness (Sa) of 0.095 µm, while for COC, a continuous decrease in ejection force was measured with decreasing surface roughness.
Keywords
Micro Injection Molding, Draft Angle, Surface Roughness, Ejection Force, Demolding
Published online 4/24/2024, 9 pages
Copyright © 2024 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA
Citation: MACIARIELLO Francesco, LUCCHETTA Giovanni, SORGATO Marco, Analysis of the effect of draft angle and surface roughness on ejection forces in micro injection molding, Materials Research Proceedings, Vol. 41, pp 2686-2694, 2024
DOI: https://doi.org/10.21741/9781644903131-294
The article was published as article 294 of the book Material Forming
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
References
[1] K. D. Delaney, G. Bissacco, D. Kennedy, A Structured Review and Classification of Demolding Issues and Proven Solutions, Int. Polym. Process. 27 (2012) 77-90. https://doi.org/10.3139/217.2514
[2] C. A. Griffiths, S. S. Dimov, E. B. Brousseau, C. Chouquet, J. Gavillet, and S. Bigot, Investigation of surface treatment effects in micro-injection-moulding, Int. J. Adv. Manuf. Technol. 47 (2010) 99–110. https://doi.org/10.1007/s00170-009-2000-4
[3] O. M. Bataineh, B. E. Klamecki, Prediction of local part-mold and ejection force in injection molding, J. Manuf. Sci. Eng. 127 (2005) 598–604. https://doi.org/10.1115/1.1951785
[4] J. Zhao, R. H. Mayes, G. Chen, P. S. Chan, Z. J. Xiong, Polymer micromould design and micromoulding process, Plast. Rubber Compos. 32 (2003) 240–247. https://doi.org/10.1179/146580103225002614
[5] J. Giboz, T. Copponnex, P. Mélé, Microinjection molding of thermoplastic polymers: A review, J. Micromech. Microeng. 17 (2007) R96. https://doi.org/10.1088/0960-1317/17/6/R02
[6] M. Sorgato, D. Masato, G. Lucchetta, Effects of machined cavity texture on ejection force in micro injection molding, Precis. Eng. 50 (2017) 440–448. https://doi.org/10.1016/j.precisioneng.2017.06.019
[7] P. Parenti, D. Masato, M. Sorgato, G. Lucchetta, M. Annoni, Surface footprint in molds micromilling and effect on part demoldability in micro injection molding, J. Manuf. Process. 29 (2017) 160–174. https://doi.org/10.1016/j.jmapro.2017.05.024
[8] A. J. Pontes, A. S. Pouzada, Ejection force in tubular injection moldings. Part I: Effect of processing conditions, Polym. Eng. Sci. 44 (2004) 891–897. https://doi.org/10.1002/pen.20080
[9] K. Shen, L.-M. Chen, L. Jiang, Calculation of ejection force of hollow, thin walled, and injection moulded cones, Plast. Rubber Compos. 28 (1999) 341-345. https://doi.org/10.1179/146580199101540493
[10] M. S. Correia, A. S. Miranda, M. C. Oliveira, C. A. Capela, A. S. Pouzada, Analysis of friction in the ejection of thermoplastic mouldings, Int. J. Adv. Manuf. Technol. 59 (2012) 977–986. https://doi.org/10.1007/s00170-011-3573-2
[11] T. Sasaki, N. Koga, K. Shirai, Y. Kobayashi, A. Toyoshima, An experimental study on ejection forces of injection molding, Prec. Eng. 24 (2000) 270-273. https://doi.org/10.1016/S0141-6359(99)00039-2
[12] C. A. Griffiths, S. S. Dimov, S. G. Scholz, G. Tosello, A. Rees, Influence of injection and cavity pressure on the demoulding force in micro-injection moulding, J. Manuf. Sci. Eng. 136 (2014) 1087-1357. https://doi.org/10.1115/1.4026983
[13] N. Bhagavatula, D. Michalski, B. Lilly, and G. Glozer, Modelling and verification of ejection forces in thermoplastic injection moulding, Model. Simul. Mat. Sci. Eng. 12 (2004) S239. https://doi.org/10.1088/0965-0393/12/3/S12
[14] A. Gopanna, S. P. Thomas, K. P. Rajan, R. Rajan, E. Rainosalo, J. Zavašnik, M. Chavali, Investigation of mechanical, dynamic mechanical, rheological and morphological properties of blends based on polypropylene (PP) and cyclic olefin copolymer (COC), Eur. Polym. J. 108 (2018) 439–451. https://doi.org/10.1016/j.eurpolymj.2018.09.030
[15] S. Kwak, T. Kim, S. Park, and K. Lee, Layout and sizing of ejector pins for injection mould design using the wavelet transform, Proc. Inst. Mech. Eng., Part B 217 (2003) 463-473. https://doi.org/10.1243/095440503321628143
[16] Z. Wang, K.S. Lee, J.Y.H. Fuh, Z. Li, Y.F. Zhang, A.Y.C. Nee, D.C.H. Yang, Optimum ejector system design for plastic injection mould, Int. J. Comput. Appl. Technol. 9 (1996) 211-218. https://doi.org/10.1504/IJMPT.1996.036339
[17] A. S. Pouzada, E. C. Ferreira, and A. J. Pontes, Friction properties of moulding thermoplastics, Polym. Test. 25 (2006) 1017–1023 https://doi.org/10.1016/j.polymertesting.2006.06.009
[18] S. J. A. Rizvi, Effect of injection molding parameters on crystallinity and mechanical properties of isotactic polypropylene, International Journal of Plastics Technology, 21 (2017) 404–426. https://doi.org/10.1007/s12588-017-9194-3
