Thermoviscoelastic Calculation of Residual Stresses and Residual Shapes of Injection Molded Parts**

Three different rheological models are applied to the study of transient and residual thermal stresses in amorphous polymers cooled across the glass transition. The models differ mainly in their treatments of the nonequilibrium (time-dependent) portion of the morphological changes in the polymer and their influence on the relaxation process. The interstitial volume between polymer chains (free volume) is found to play an important role in the residual stresses; they are affected by the relative time scale of thermal diffusion and thermoviscoelastic relaxation/creep. This result has implications for injection molded parts of different section dimensions and for extrusion products. This fact must also be accounted for in determining the thermomechanicalproperties in the glass transition range. The step cooling ofPVAc spheres (1 and 20 mm dia.) and a cylinder (20 mm dia.) have been considered; most of the results presented apply to the sphere(s). Residual stresses can vary by as much as 100percent depending on whether the interstitial molecular (free) volume is counted or not. It is also demonstrated that residual stresses can be higher than an elastic analysis based on the glassy properties would suggest; thus the “stressfree temperature” is found to be significantly above the glass transition.

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Analysis of polymer crystallization and residual stresses in injection molded parts

International Journal of Precision Engineering and Manufacturing ◽

10.1007/s12541-013-0309-2 ◽

2014 ◽

Vol 15 (1) ◽

pp. 89-96 ◽

Cited By ~ 21

Author(s):

Roberto Spina ◽

Marcel Spekowius ◽

Rainer Dahlmann ◽

Christian Hopmann

Keyword(s):

Residual Stresses ◽

Polymer Crystallization ◽

Molded Parts ◽

Injection Molded

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ELIMINATING FLOW INDUCED BIREFRINGENCE AND MINIMIZING THERMALLY INDUCED RESIDUAL STRESSES IN INJECTION MOLDED PARTS*

Polymer-Plastics Technology and Engineering ◽

10.1081/ppt-100002072 ◽

2001 ◽

Vol 40 (4) ◽

pp. 491-503 ◽

Cited By ~ 27

Author(s):

Ming Chen ◽

Donggang Yao ◽

Byung Kim

Keyword(s):

Residual Stresses ◽

Thermally Induced ◽

Molded Parts ◽

Injection Molded

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Shrinkage, warpage and residual stresses of injection molded parts

10.1063/1.5084847 ◽

2019 ◽

Author(s):

Tristan Koslowski ◽

Christian Bonten

Keyword(s):

Residual Stresses ◽

Molded Parts ◽

Injection Molded

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Comparative Analysis of Different Methods in Residual Stress Measurement for Polymeric Parts

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.837.175 ◽

2013 ◽

Vol 837 ◽

pp. 175-178

Author(s):

Alexandra Raicu

Keyword(s):

Residual Stress ◽

Residual Stresses ◽

Stress Measurement ◽

Polymeric Materials ◽

Injection Molding Process ◽

Uniform Temperature ◽

Molding Process ◽

Molded Parts ◽

Injection Molded ◽

Technological Constraints

This paper presents the measurements of the residual stresses for polymeric parts using different methods. The residual stresses are usually introduced during manufacturing and are caused by processes such as molding. In order to optimize injection molding process with polymeric material, it is important to predict the internal stress development during molding. The residual stresses are caused mainly by non-uniform temperature profile in the cavity during filling, packing and cooling stages. This research offers information and a methodology which may be applied in practical conditions for a large number of parts manufactured from the different polymeric materials and for several technological constraints. The author confirmed that all this methods which measure the residual stresses can be applied to injection molded parts.

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A Study on the Birefringence Measurement in Injection Molded Parts Using Two Different Laser Sources and R-G-B Separation of White Light

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.326-328.187 ◽

2006 ◽

Vol 326-328 ◽

pp. 187-190

Author(s):

Jong Sun Kim ◽

Chul Jin Hwang ◽

Kyung Hwan Yoon

Keyword(s):

White Light ◽

Low Cost ◽

Main Idea ◽

Injection Molding Process ◽

Molding Process ◽

Laser Method ◽

High Productivity ◽

Molded Parts ◽

Injection Molded ◽

Plastic Parts

Recently, injection molded plastic optical products are widely used in many fields, because injection molding process has advantages of low cost and high productivity. However, there remains residual birefringence and residual stresses originated from flow history and differential cooling. The present study focused on developing a technique to measure the birefringence in transparent injection-molded optical plastic parts using two methods as follows: (i) the two colored laser method, (ii) the R-G-B separation method of white light. The main idea of both methods came from the fact that more information can be obtained from the distribution of retardation caused by different wavelengths. The comparison between two methods is demonstrated for the same sample of which retardation is up to 850 nm.

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Silane-Functionalized Sheep Wool Fibers from Dairy Industry Waste for the Development of Plasticized PLA Composites with Maleinized Linseed Oil for Injection-Molded Parts

Polymers ◽

10.3390/polym12112523 ◽

2020 ◽

Vol 12 (11) ◽

pp. 2523

Author(s):

Franciszek Pawlak ◽

Miguel Aldas ◽

Francisco Parres ◽

Juan López-Martínez ◽

Marina Patricia Arrieta

Keyword(s):

Linseed Oil ◽

Microstructural Analysis ◽

Dairy Industry ◽

Poly Lactic Acid ◽

Industry Waste ◽

Wool Fibers ◽

Molded Parts ◽

Silane Modification ◽

Injection Molded ◽

Sheep Wool

Poly(lactic acid) (PLA) was plasticized with maleinized linseed oil (MLO) and further reinforced with sheep wool fibers recovered from the dairy industry. The wool fibers were firstly functionalized with 1 and 2.5 phr of tris(2-methoxyethoxy)(vinyl) (TVS) silane coupling agent and were further used in 1, 5, and 10 phr to reinforce the PLA/MLO matrix. Then, the composite materials were processed by extrusion, followed by injection-molding processes. The mechanical, thermal, microstructural, and surface properties were assessed. While the addition of untreated wool fibers to the plasticized PLA/MLO matrix caused a general decrease in the mechanical properties, the TVS treatment was able to slightly compensate for such mechanical losses. Additionally, a shift in cold crystallization and a decrease in the degree of crystallization were observed due to the fiber silane modification. The microstructural analysis confirmed enhanced interaction between silane-modified fibers and the polymeric matrix. The inclusion of the fiber into the PLA/MLO matrix made the obtained material more hydrophobic, while the yellowish color of the material increased with the fiber content.

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