OPTIMUM DESIGN OF PROCESS CONDITIONS TO MINIMIZE RESIDUAL STRESSES IN INJECTION-MOLDED PARTS

Abstract This paper describes the development of geometry-based indices that predict sink mark depth in injection molded parts. Plastic part designers need such indices to incorporate manufacturability concerns at the conceptual stage of design. These indices apply to several form features so engineers do not have to check different design rules for each geometry element. First, we propose a geometry-based sink index that can be used to predict sink mark depth as a function of process conditions such as packing pressure. Next, we explain how this relationship is identified through experiments. We also describe HyperDesign/Plastics, a Macintosh-based design aid that incorporates the sink index.

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Effect of process conditions on birefringence development in injection-molded parts. I. Numerical analysis

Journal of Applied Polymer Science ◽

10.1002/app.1995.070551306 ◽

1995 ◽

Vol 55 (13) ◽

pp. 1757-1769 ◽

Cited By ~ 14

Author(s):

Shia Chung Chen ◽

Yung Cheng Chen

Keyword(s):

Numerical Analysis ◽

Process Conditions ◽

Molded Parts ◽

Injection Molded

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Thermal Stresses in Nonlinearly Viscoelastic Solids

Journal of Applied Mechanics ◽

10.1115/1.2899506 ◽

1992 ◽

Vol 59 (2S) ◽

pp. S43-S49 ◽

Cited By ~ 10

Author(s):

Giancarlo U. Losi ◽

Wolfgang G. Knauss

Keyword(s):

Glass Transition ◽

Residual Stresses ◽

Free Volume ◽

Thermal Stresses ◽

Morphological Changes ◽

Polymer Chains ◽

Transition Range ◽

Rheological Models ◽

Molded Parts ◽

Injection Molded

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

International Polymer Processing ◽

10.3139/217.920060 ◽

1992 ◽

Vol 7 (1) ◽

pp. 60-70 ◽

Cited By ~ 37

Author(s):

K. K. Kabanemi ◽

M. J. Crochet

Keyword(s):

Residual Stresses ◽

Molded Parts ◽

Injection Molded

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Correlation Between Mechanical Properties in Standard Test Specimens and Injection Molded Thin-Wall Parts

Volume 1: Processing ◽

10.1115/msec2013-1032 ◽

2013 ◽

Author(s):

Laurentiu I. Sandu ◽

Felicia Stan ◽

Catalin Fetecau

Keyword(s):

Mechanical Properties ◽

Elastic Modulus ◽

Yield Strength ◽

Injection Molding ◽

Process Conditions ◽

Thin Wall ◽

Optimal Process ◽

Melt Temperature ◽

Molded Parts ◽

Injection Molded

In this paper, we investigated the effect of injection molding parameters on the mechanical properties of thin-wall injection molded parts. A four-factor (melt temperature, mold temperature, injection speed and packing pressure) and three-level fractional experimental design was performed to investigate the influence of each factor on the mechanical properties and determine the optimal process conditions that maximize the mechanical properties of the part using the signal-to-noise (S/N) ratio response. The mechanical properties (e.g., elastic modulus, yield strength and strain at break) were measured by tensile tests at room temperature, at a crosshead speed of 5 mm/min, and compared with those of the injection-molded specimens. The experimental results showed that the tensile properties were highly dependent on the injection molding parameters, regardless of the type of the specimens. The values of Young modulus and yield strength of the injection-molded specimens were lower than those of the injection-molded parts, while the elongation at break was considerably lower for the injection-molded parts. The optimal process conditions were strongly dependent on the measured performance quantities (elastic modulus, yield strength and strain at break).

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