Core out geometries in water channels of water assisted injection moulded parts

Abstract

In water assisted injection moulded parts, structural ribs are usually designed to reinforce the parts as well as to serve as water channels. Water penetration in the channels results in improved mouldability and minimises sinkmarks. However, water leaves a rib core void, which reduces part rigidity. The present study examines the core out shapes of channels in water assisted injection moulded parts. The effects of channel geometry as well as processing conditions such as water injection delay time, water temperature, water pressure, etc., on the core out shapes were investigated. For the parameters selected, melt temperature, short shot size and water injection delay time were found to be the principal factors affecting the core out shapes of moulded parts. The core out geometries in water assisted injection moulded parts were compared with those in gas assisted injection moulded products. Water penetrated the parts with higher core out ratios, which are the ratios of the cross-sectional area of the water (gas) channel to the area of the water (gas) bubble in moulded parts, than gas. The core out geometry of water assisted injection moulded parts mainly resembles that of the water channel, while the void shape of gas assisted injection moulded parts tends to be more round shaped. Channels with ribs on top exhibited the highest bending strengths. Furthermore, a numerical simulation of the temperature distribution in the channels was completed to better interpret the water core out behaviour in water assisted injection moulded products.

Overview of the Experimental Trends in Water‐Assisted Injection Molding

“…Despite the advantages associated with WAIM process, the molding window and process control become more critical and difficult since additional processing parameters are involved, such as water pressure, water delay time, and water injection time. Water penetration length and residual wall thickness significantly affect the quality of WAIM parts, therefore many researchers have investigated the effects of processing parameters as well as water pin form and channel geometry on the penetration length and residual wall thickness distribution by experiments and achieved lots of research findings …”

Numerical simulation on residual wall thickness of tubes with dimensional transitions and curved sections in water‐assisted injection molding

“…Residual wall thickness significantly affects the strength of molded parts; so many researchers have investigated the size and distribution of the residual wall thickness by experiments, and achieved lots of research findings 4–8. On the other hand, the majority of current researches are mainly focused on experiments, while few scholars explain and verify experiments by numerical simulation methods.…”

An Experimental Study of the Water-Assisted Injection Molding of PA-6 Composites

“…Water-assisted injection molding can produce parts incorporating both thick and thin sections with less shrinkage and warpage and a better surface finish, but with a shorter cycle time. The water-assisted injection molding process can enable greater freedom of design, material savings, weight reduction, and cost savings in tooling and press capacity requirements [2][3][4]. Typical applications include tubes and rods, as well as large sheet-like structural parts with a built-in water channel network.…”

“…This report was carried out to study the water-assisted injection molding of glass fiberreinforced Nylon composites. Experiments were carried out on an 80 ton injection molding machine equipped with a water injection unit developed earlier in our laboratory [3,4]. A spiral cavity with a square cross-section was used for all experiments.…”