Establishing a rapid cooling complex mold design for the quality improvement of microcellular injection molding

Abstract

Injection molding is one of the most widely‐used processes for the production of plastic parts, due to the utilization of diverse materials, the complex product‐shape moldability, and the rapid mass production. In relation to the environmental issues, light‐weight technology and green molding solutions are becoming more important. Microcellular injection molding technology is one of the green molding solutions for saving materials, as well as reducing the weight of molded parts. However, the molding process brings about some defects, including a sliver flow mark on the surface and uneven mechanical properties that are caused by the uneven cell size and their distribution within the part. Dynamic molding temperature control technology seems to be an effective way of improving the product quality. Until recently, there has been very little discussion about high‐efficiency cooling methods. A new complex mold for a cooling system has been designed. The basis cooling ability of different materials was investigated. The complex mold design has a faster cooling rate, and it has a greater surface temperature uniformity. This cooling technology was used to improve the quality of microcellular injection molded parts, which improves the glossy finish by about 73%. The results show that the faster cooling rate brings about the more uniform cell size with higher cell density from 9.43E+11 to 1.92E+12 cells/cm3. Otherwise, the cell size reduced from 192.92 to 84.97 μm.

The Microcellular Structure of Injection Molded Thick-Walled Parts as Observed by In-Line Monitoring

“…Polymers and Fillers Molded Part Thickness, mm [4,7,8,11,13,16,22,23] PP GF20; PP/LDPE blends; PP + GF + Talc; PP-TPU; PP CF20; PP CF30; PP + EPDM + TALC 2.4-4.0 [6,9,15,17] PA66 GF 30 1.5-4.0 [7,24] PLA/PHBV; PLA/PTFE (fibril) 3.3-4.0 [10,12] PC; PC/ABS 1.7-4.0 [14,25] PS 3.0…”

Using P(Pressure)-T(Temperature) Path to Control the Foaming Cell Sizes in Microcellular Injection Molding Process

“…This design enables the cooling rate control varying from 0.8 °C/s to10.9 °C/s in the mold temperature range of 90 °C to 120 °C. The molded part geometry and the associated mold cooling inert block are illustrated in Figure 4 [ 26 ]. Details have been described earlier [ 26 ].…”

“…Foaming after melting filling plays a significant role in packing function leading to shrinkage reduction, warpage minimization, and elimination of sink marks, etc. The process characteristics and molded part properties have been studied earlier [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Despite its advantage, MuCell also faces technology challenges that hinder its wide application.…”

“…Systematic studies of gas counter-pressure effect on the MuCell process and conventional injection were carried out by Chen et al [ 22 , 24 , 26 , 27 , 28 ]. The use of gas counter-pressure (GCP) at the melt front during the filling process can suppress the fountain flow effect and minimize the foaming bubbles being drawn to the part surface.…”

“…In this study, a new concept of P(pressure)-T(temperature) (P-T) path control was employed for foaming control of MuCell parts ( Figure 2 ). Most earlier studies on foaming control were conducted either by varying mold cavity temperatures [ 14 , 15 , 16 , 17 , 26 ] or by varying pressure alone [ 23 , 24 ] at a fixed mold temperature. Our study proposed an approach of sequential and/or simultaneous combined control of both pressure and temperature.…”