Warpage behavior

To catch the warpage behavior and its behavior, we performed the experimental investigation. The... 

The warpage behavior in this sequential overmolding probably results from thermal residual stresses. In Fig. 11(a), when the width of 2 shot is small... 

Fig. 4. Warpage behavior of 2 shot with a plastic F shot in the presence of a runner system (a) display the 2 shot only, (b) display and 2 shots simultaneously (width of 2 shot x=2 mm, Enlarge 12 times)...

Fig. 6. Warpage behaviors definition for Inward or Outward from experimental study (a) A>B is Outward, (b) A

Fig. 7. Warpage behavior for a single shot experimental result shows it is inward.

Fig. 10. Warpage behavior in different 2"" shot width in the F shot material F shot material is PMMA, and 2 shot is PC.

Fig. 11. Thermal residual stresses after 2 shot Warpage behavior in different F shot thickness (a)F shot is ABS width=2.0 mm, 2" shot is PC with width=0.25 mm, (b)...

In recent years, lots of plastic parts are made of fiber-reinforced engineering materials for increasing its meehanieal properties, snch as strength and durability. However, these mechanical properties of fiber-reinforc plastie parts highly depend on its fiber orientation, which determines the fiber-indnced anisotropic mechanical properties. Since the flow induced fiber orientation is complex 3D behavior, the final properties of injected parts calculated from fiber orientation also become very complicated. Thus, a 3D injection molding simulation technique is adopted in this research and is capable of simulating the fiber orientation and the anisotropic warpage behavior. 

In order to validate all the simulation results, a ribbed flat plate with different gate positions is conducted to examine the effect of fibers with various design consideration on injected parts both numerically and experimentally. Fmthermore, the warpage behavior affected by gate positions can also be examined fi om experiment and simulation results. 

In this paper, we have developed a true 3D numerical approach for the simulation of flow-induced residual stress. By solving the primitive variables Navier-Stoke equations and constitutive equation of viscoealstic behavior, we can correctly predict the first normal difference, the second normal difference and flow-induced residual Von Mises stress, which are essential to have accurate predicting physical properties of the finished parts, such as warpage behavior and optical properties. By the results of our numerical approach > we can expect to have more accurate analysis of warpage. 

The silicone semi-IPN structure imparts unique behavior to thermoplastic composites without affecting mechanical strength and stifihess. Apart from the direct effects associated with the incorporation of thermoset character into a thermoplastic, the structure has particular value by functioning as (1) a nonmigrating internal lubricant, (2) a shrinkage and warpage modifier, (3) a fiow modifier, and (4) a release agent. As a polymer-polymer composite,... 

For example, the calculation of shrinkage and warpage in (long) fiber-rein-forced plastics can be worked out ahead of time and the data can be provided to the processor as well as the structural component development engineers. The same applies to improved integration of anisotropic and viscoelastic material behavior. The generation and expansion of FE calculation models (with rational... 

Uniform wall thickness throughout the entire part will ensure more uniform shrinkage behavior during molding, which decreases warpage and residual stress. Whenever possible, thicker part sections should be cored, the thinnest wall sections should be no less than 40% of the thickest wall sections in the part, and parts should be gated to fill from thicker sections into thinner sections. 

Representative behavior is also presented in Figure 3.7. It is observed that Zyx relaxes faster than t c — Zyy. Furthermore, it is known that as yo increases the time for Zyx and N to relax to zero is shorter. After relaxation is complete, the stress growth and relaxation experiment are repeated as shown in Figure 3.7, and it is observed that the behavior is repeatable. Although the stresses relax within 2.0 s, higher molecular weight polymers may take 10 to 20 s before the stresses completely relax. Residual stresses in an injection-molded part can lead to the warpage of parts. 

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