scholarly journals Study on the Mechanism of the Packing Process and Sink Mark in External Gas-Assisted Injection Molding

2014 ◽  
Vol 6 ◽  
pp. 853142
Author(s):  
Shaofei Jiang ◽  
Jinlong Tao ◽  
Jiquan Li
Keyword(s):  
Injection Molding ◽  
Interaction Mechanism ◽  
Interface Morphology ◽  
Simulation Process ◽  
Condensate Layer ◽  
Fluent Software ◽  
Packing Process ◽  
Sink Marks ◽  
Plastic Parts ◽  
Sink Mark

External gas-assisted injection molding (EGAIM) technology can be applied to effectively reduce the sink marks generated from the shrinkage of plastic parts. In this paper, the interaction mechanism of gas and melting during the EGAIM stage was discussed. The causes of the sink marks on plastic parts as well as the influence of gas-melting interaction on the sink marks were analyzed. A corresponding physical model was established. Using plastic plate parts with stiffeners, for example, the EGAIM process was one-parameter simulated using Fluent software. The sink marks on the stiffeners, the interface morphology between the condensate layer and the gas, and other parameters were obtained. The effectiveness of the model, as well as the simulation process, was confirmed by experiment.

Effect of gas counter pressure on shrinkage and residual stress for injection molding process

2017 ◽  
Vol 37 (5) ◽  
pp. 505-520 ◽  
Author(s):  
Wen-Ren Jong ◽  
Shyh-Shin Hwang ◽  
Ming-Chieh Tsai ◽  
Chien-Chou Wu ◽  
Chi-Hung Kao ◽  
...  
Keyword(s):  
Residual Stress ◽  
Injection Molding ◽  
Flow Direction ◽  
Injection Molding Process ◽  
Molding Process ◽  
Daily Lives ◽  
Counter Pressure ◽  
Packing Pressure ◽  
Sink Marks ◽  
Feedback Data

Abstract Plastic products are common in contemporary daily lives. In the plastics industry, the injection molding process is advantageous for features such as mass production and stable quality. The problem, however, is that the melt will be affected by the residual stress and shrinkage generated in the process of filling and cooling; hence, defects such as warping, deformation, and sink marks will occur. In order to reduce product deformation and shrinkage during the process of molding, the screw of the injection molding machine will start the packing stage when filling is completed, which continuously pushes the melt into the cavity, thus making up for product shrinkage and improving their appearance, quality, and strength. If the packing pressure is too high, however, the internal residual stress will increase accordingly. This study set out to apply gas counter pressure (GCP) in the injection molding process. By importing gas through the ends of the cavity, the melt was exposed to a melt front pressure, which, together with the packing pressure from the screw, is supposed to reduce product shrinkage. The aim was to investigate the impacts of GCP on the process parameters via the changes in machine feedback data, such as pressure and the remaining injection resin. This study also used a relatively thin plate-shaped product and measurements, such as the photoelastic effect and luminance meter, to probe into the impacts of GCP on product residual stress, while a relatively thick paper-clip-shaped product was used to see the impacts of GCP on shrinkage in thick parts. According to the experimental results, the addition of GCP resulted in increased filling volume, improvement of product weight and stability, and effective reduction of section shrinkage, which was most obvious at the point closest to the gas entrance. The shrinkage of the sections parallel and vertical to the flow direction was proved to be reduced by 32% and 16%, respectively. Moreover, observations made via the polarizing stress viewer and luminance meter showed that the internal residual stress of a product could be effectively reduced by a proper amount of GCP.

Geometry-Based Index for Predicting Sink Mark in Plastic Parts

1991 ◽  
Author(s):  
Kurt Beiter ◽  
Kosuke Ishii ◽  
Lee Hornberger
Keyword(s):  
Process Conditions ◽  
Plastic Part ◽  
Design Rules ◽  
Packing Pressure ◽  
Molded Parts ◽  
Injection Molded ◽  
Form Features ◽  
Plastic Parts ◽  
Sink Mark

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.

Simultaneous Computer-Aided Design of Rotational Plastic Parts

1993 ◽  
Author(s):  
Colin Chong ◽  
Kiyoshi Sogabe ◽  
Kosuke Ishii
Keyword(s):  
Injection Molding ◽  
Dynamic Characteristics ◽  
Computer Aided Design ◽  
Critical Speed ◽  
Dynamic Balance ◽  
Cad System ◽  
Compatibility Analysis ◽  
Computer Aided ◽  
Plastic Parts ◽  
Aided Design

Abstract This paper addresses the problem of balancing rotational plastic parts during the early stages of design. The study develops an interactive methodology that uses a solid modeling CAD system and considers injection molding concerns simultaneously with static and dynamic balance. The Transfer Matrix Method evaluates the dynamic characteristics by predicting the approximate critical speed of the part. Design Compatibility Analysis (DCA) checks for injection molding guidelines. Using these evaluation modules interactively, designers can develop a functional and manufacturable part quickly.

scholarly journals Molecular Dynamics Simulations on the Demolding Process for Nanostructures in Injection Molding

Micromachines ◽  
2019 ◽  
Vol 10 (10) ◽  
pp. 636 ◽  
Author(s):  
Can Weng ◽  
Dongjiao Yang ◽  
Mingyong Zhou
Keyword(s):  
Molecular Dynamics ◽  
Injection Molding ◽  
Molecular Dynamics Simulations ◽  
Interaction Mechanism ◽  
Mold Insert ◽  
Sharp Decrease ◽  
Average Density ◽  
Radius Of Gyration ◽  
Good Shape ◽  
Dynamics Simulations

Injection molding is one of the most potential techniques for fabricating polymeric products in large numbers. The filling process, but also the demolding process, influence the quality of injection-molded nanostructures. In this study, nano-cavities with different depth-to-width ratios (D/W) were built and molecular dynamics simulations on the demolding process were conducted. Conformation change and density distribution were analyzed. Interfacial adhesion was utilized to investigate the interaction mechanism between polypropylene (PP) and nickel mold insert. The results show that the separation would first happen at the shoulder of the nanostructures. Nanostructures and the whole PP layer are both stretched, resulting in a sharp decrease in average density after demolding. The largest increase in the radius of gyration and lowest velocity can be observed in 3:1 nanostructure during the separation. Deformation on nanostructure occurs, but nevertheless the whole structure is still in good shape. The adhesion energy gets higher with the increase of D/W. The demolding force increases quickly to the peak point and then gradually decreases to zero. The majority of the force comes from the adhesion and friction on the nanostructure due to the interfacial interaction.

scholarly journals Visualization of potential sink marks using thickness analysis of finely tessellated solid model

2018 ◽  
Vol 5 (4) ◽  
pp. 409-418
Author(s):  
Masatomo Inui ◽  
Shunsuke Onishi ◽  
Nobuyuki Umezu
Keyword(s):  
Thickness Distribution ◽  
Solid Model ◽  
Aesthetic Quality ◽  
Plastic Surface ◽  
Part Surface ◽  
Novel Method ◽  
Sink Marks ◽  
Automated Technique ◽  
The Aesthetic ◽  
Sink Mark

Abstract Sink marks are unwanted shallow depressions on the molded plastic surface caused by localized shrinkage during the hardening process of injection molding. Sink marks appearing in the exterior impair the aesthetic quality of the product. In this study, a novel method for extracting potential sink marks that can occur on the part surface is proposed. The thicker portion of the part shrinks with a greater amount than that of the thinner portion. This difference in the shrinkage amount is the main cause of the sink mark. In the plastic part design practice, engineers often check the thickness distribution to predict potential sink marks in the part surface. Our method can be considered as an automated technique of such manual inspection task. A polyhedral solid model of the part with sufficiently small triangles of nearly the same size is prepared. The amount of shrinkage at each polygon is estimated based on its thickness and the shrinkage ratio of the part. The developed algorithm extracts the potential sink marks by analyzing the shrinkage distribution on the part surface. Highlights A novel method for extracting potential sink marks on part surface is proposed. Polygons of input model are tessellated into a set of sufficiently small triangles. The shrinkage of each model polygon is estimated by using the thickness. Potential sink marks are extracted by analyzing the shrinkage distribution.

scholarly journals Multiobjective Optimization Method for Polymer Injection Molding Based on a Genetic Algorithm

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Zhijun Yuan ◽  
Hui Wang ◽  
Xuebing Wei ◽  
Kui Yan ◽  
Cheng Gao
Keyword(s):  
Genetic Algorithm ◽  
Injection Molding ◽  
Multiobjective Optimization ◽  
Optimization Method ◽  
Optimal Combination ◽  
Cover Plate ◽  
Polymer Injection ◽  
Impact Parameters ◽  
Sink Marks ◽  
The Impact

To solve the quality problem of polymer injection parts, a quality prediction and multiobjective optimization method is established. In this method, the parameters that have an important effect on the part quality are selected using an orthogonal testing method, and then a central composite design experiment is performed using these parameters. A mathematical model considering an objective and impact factors is developed using the response surface method. The optimal combination of the impact parameters is determined using a multiobjective genetic algorithm. The injection molding of a typical interior trim part of a car, i.e., the seat belt cover plate, is used as an example to demonstrate the method. The two most troublesome problems in this process—the sink marks and warpage—are multiobjectively analyzed using the established method, and the optimal combination of impact parameters that minimized the defects is determined. The errors of the sink marks and warpage between the experimental and theoretical values were 7.95% and 0.2%, respectively. The optimized parameters were tested in actual injection molding. The results show that the shrinkage and warpage of the parts are obviously improved by optimization using the proposed method, allowing the parts to satisfy the requirements of assembly and appearance.

Quality Defects and Analysis of the Microfluidic Chip Injection Molding

2009 ◽  
Vol 628-629 ◽  
pp. 417-422 ◽  
Author(s):  
Ying Liu ◽  
M.C. Song ◽  
Min Jie Wang ◽  
C.Z. Zhang
Keyword(s):  
Quality Control ◽  
Injection Molding ◽  
Mass Production ◽  
Control Process ◽  
Parameter Design ◽  
Micro Channel ◽  
Microfluidic Chips ◽  
New Methods ◽  
Sink Mark ◽  
Stagnant Flow

Compared with hot embossing, microfluidic chips injection molding is higher efficiency process and more suitable for mass production, but the quality control for injection molding is much more complex. Experiments indicate that the incomplete replication of the micro-channel and the sink mark for microfluidic chips are the chief defects to the molding. Simulation and theoretical analysis show that the stagnant flow of the melt in micro-channel and the shrinkage difference of the chips in different directions are the main reasons for molding defect. A set of new methods that how to control process parameter, design mold, and select polymer material is proposed to reduce or avoid the defects.

Observation of Polypropylene (PP) Melt Flow on Macro and Micro Cavities during Filling Phase of Injection Molding

2011 ◽  
Vol 314-316 ◽  
pp. 1273-1277
Author(s):  
M. Azuddin ◽  
Z Taha ◽  
Imtiaz Ahmed Choudhury
Keyword(s):  
Injection Molding ◽  
High Speed ◽  
Electrical Discharge Machining ◽  
Mold Cavity ◽  
Melt Flow ◽  
Observation Window ◽  
Custom Made ◽  
Micro Parts ◽  
Filling Phase ◽  
Plastic Parts

The flow of plastic melt in macro and micro parts during the filling phase of injection molding is an interesting area to discover. The visualization technique is a common method used to understand the phenomena of polymer flow in mold cavity. Various shapes and sizes were fabricated on aluminum molds embedded with Polymethyl Methacrylate (PMMA) as observation window. Electrical discharge machining (EDM) and micro mechanical machining method were employed to fabricate plastic parts shape on aluminum mold cavity. This paper focuses and discusses in detail on the Polypropylene (PP) melt flow injected using a custom made vertical injection molding machine. The PP melt flow can be clearly seen through the PMMA window and captured using high speed camera. The captured images are then compared with result from commercially available plastic injection molding software, Autodesk MoldFlow. It was found that there is good agreement for macro plastic parts but not for the micro parts. It can be concluded that, the analysis software has less capability in predicting the flow of melt plastic in micro parts.

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