Warpage Prediction of RHCM Crystalline Parts Based on Multi-Layers

Abstract

Warpage is a typical defect for injection-molded parts, especially for crystalline parts molded by rapid heat cycle molding (RHCM). In this paper, a prediction method is proposed for predicting the warpage of crystalline parts molded by the RHCM process. Multi-layer models were established to predict warpage with the same thicknesses as the skin-core structures in the molded parts. Warpages were defined as the deformations calculated by the multi-layer models. The deformations were solved using the classical laminated plate theory by Abaqus. A model was introduced to describe the elastic modulus with the influence of temperature and crystallinity. The simulation process was divided into two procedures, before ejection and after ejection. Thermal stresses and thermal strains were simulated, respectively, in the procedure before ejection and after ejection. The prediction results were compared with the experimental results, which showed that the average errors between predicted warpage and average experimental warpage are, respectively, 7.0%, 3.5%, and 4.4% in conventional injection molding (CIM), in RHCM under a 60 °C heating mold (RHCM60), and in RHCM under a 90 °C heating mold (RHCM90).

Potential of Rapid Tooling in Rapid Heat Cycle Molding: A Review

“…As a result, to improve part quality and reduce molding cycle time, a dynamic mold temperature control system for rapid heating and cooling of the mold is required [ 80 , 83 , 87 ]. As shown in Figure 2 , after the gate is solidified, the mold is cooled down rapidly by water to solidify and demold the polymer part [ 88 ]. However, in the CIM, the mold temperature control technique uses a concurrent cooling method, where a constant-temperature coolant circulates in a cooling channel to cool the mold and polymer melt [ 80 , 89 , 90 ].…”

“…Warpage is one of the defects that cannot be solved using RHCM. Li et al [ 88 ] investigated a method for predicting the warpage of crystalline parts molded using the RHCM process. To predict warpage, multilayer models with the same thicknesses as the skin–core structures in the molded parts were developed.…”

“…On the basis of the results from the previous researchers [ 48 , 88 ], it can be said that the application of RHCM in CIM has a big impact on the molded part. Previous studies used the same mold insert for both molding processes.…”

“…The heating and cooling system designs of electric heating molds are critical for RHCM with electric heating because they directly affect the heating/cooling efficiency and temperature uniformity, which have a decisive influence on the molding cycle and part quality [ 127 ]. Electric heating in RHCM can be accomplished through the deployment of electrical heating rods and cooling tunnels in the stationary mold, which can be rapidly heated via electric heating prior to filling and cooled via circulating water after filling [ 50 , 88 ]. In another study, Wang et al [ 54 ] investigated the thermal response of the electric heating with the deployment of a cartridge heater in rapid heat cycle molding, as well as its impact on the surface appearance and tensile strength of the molded part.…”

Reducing the Burn Marks on Injection-Molded Parts by External Gas-Assisted Injection Molding

“…Injection molding is one of the most important mass production methods of plastic parts [ 1 , 2 , 3 ]. However, some defects commonly appear in injection-molded parts, such as flashes [ 4 ], warpage [ 5 ], weld lines [ 6 ], burn marks [ 7 ], sink marks [ 8 ], etc. Of the aforementioned defects, a burn mark is a kind of surface defect that shows a dark or black character in certain places on the part surface.…”