Sink Marks Research Articles

Optimization of Process Parameters of Injection Moldings for Plastic Pallets Manufacturing Industry

Plastics have been heavily used in industries like automobile, manufacturing, electrical and electronics industry all over the world. Injection molding is one of the ways to process plastics polymers. However, one of the difficulties they have to face is to set the optimal parameter for the injection molding process. Incorrect parameter selection can lead to parts defects such as warpage, shrinkage, sink marks, weld marks and so on. In this study, the optimal process parameter of injection molding for manufacturing of plastic pallets which is used for warehousing was determined by the orthogonal array of Taguchi’s L9 which has 3 factors and 3 levels for each factor, experimental design, and Regression Analysis. The three main parameters such as Mold temperature, holding pressure and charging speed were choosen to study their effect on the Compressive strength. S/N ratios were utilized for determining the optimal set of parameters. According to the results, 230 °C of mold temperature, 98 RPM of charging speed, 25 MPa of Holding pressure make the products in the shape and proportion of the product satisfactory. Statically the most significant parameters were found to be as mold temperature and Charging speed for the Polypropylene moldings, respectively. Holding pressure had the least effect on the compressive strength of PP material. After the degree of significance of the studied process parameters was determined, the linear Regression model was generated and was shown to be an effective predictive tool for Compressive strength.

Applicability of Microcellular Injection Molding Process

Microcellular injection molding is relatively new and progressive technology for production of lightweight constructions. The weight reduction, elimination of sink marks, internal stresses and deformation of products are the main advantages of this unconventional technology. On the other hand, decrease in mechanical properties and poor surface quality are the application restrictions. There are several aspects affecting formation of microcellular structure and final properties of injection molded products. As a one of the most important aspects there is used material. Therefore, the main goal of this article was investigation the influence of different types of thermoplastic materials on the microcellular structure formation and mechanical properties of products. Further, the influence of holding pressure on products quality was also evaluated.

Influence of dynamic temperature control on the injection molding process of plastic components

Conventional injection molding (CIM) technology has been largely used to produce plastic parts, mainly on automotive industry, due to high production ratios, constricted dimensional tolerances production, and low labor costs. Nowadays, industry has been demanding for thinner and lighter molded parts production, with better mechanical properties. Low mold temperatures (≈60ºC) are used to decrease the cycle molding time and process final costs. However, the fast cooling of parts can easily result in surface defects, such as weld lines, sink marks, or warpage. To avoid such defects and eliminate the need for secondary operations (additional operating costs), a dynamic mold heating and cooling control technology known as Rapid Heating and Cooling Molding (RHCM) can be employed. Based on RHCM, this study compared the efficiency of using heating rods, water flow, and external infrared heating systems to investigate the effect of dynamic temperature control on the injection molding process. An experimental injection mold was manufactured and used for the studies under controlled conditions to produce standard tensile and flexure specimens. The effect of process parameters, geometry of the runner system, location of the injection point, and other relevant settings was considered. From this study, new insights were obtained regarding the industrial application of RHCM as well as the degree of efficiency of different design solutions for the RHCM process.

Exploring Micro-focus X-ray computed tomography for metal injection moulded green parts

Metal injection moulding (MIM) involves mass production of simple to intricate near-net shape parts at a relatively low cost by blending metal powders of defined characteristics with a polymeric binder system. The blend, popularly known as a feedstock, is injected into a mould cavity of a desired shape to form a green part. Most defects such as cracks, sink marks and voids manifest during the injection stage of the process. Internal cracks and voids are impossible to visualise after injection moulding. Micro-focus X-ray computed tomography (µXCT) is one of the techniques that can be used to evaluate and characterise such defective features. μXCT is a non-destructive method that uses penetrating X-ray radiation to probe objects or samples and create a complete virtual 3D representation of the object to visualise the internal structures and morphologies such as porosity, voids, cracks and inclusions as well as their location and their distribution in 3D. This work is intended to explore the µXCT approach MIM green parts and characterise the internal defects. The samples were scanned at 135 keV and 100 µA for X-ray penetration and contrast while placed onto a rotating sample manipulator which facilitated scanning through 360°. The samples were then reconstructed and further analysed for volume (3D) graphics.

Optimization of a Composite Drive Shaft by Minimizaton of Sink Mark Defects in Injection Moulding Process

Optimization of a Composite Drive Shaft by Minimizaton of Sink Mark Defects in Injection Moulding Process

뮤셀공법을 이용한 In-Mold Type PAB Door 싱크마크 개선

뮤셀공법을 이용한 In-Mold Type PAB Door 싱크마크 개선

Study of the effects produced by ultrasonic vibration on AISI 1045 steel surface: surface residual stress and surface 3D morphology

Abstract Experiments for ultrasonic-assisted pulsed-laser surface irradiation and pulsed-laser surface irradiation were conducted based on an Nd:YAG pulsed-laser machine in order to study the effects produced by ultrasonic vibration on the AISI 1045 steel surface. In addition, the effects of the ultrasonic vibration on the AISI 1045 steel surface are discussed. The results show that larger tensile residual stress is induced at the pulsed-laser surface irradiation area, and the resultant surface 3D morphology is a noticeable sink mark owing to the temperature effect and the tensile residual stress effect. The surface integrity of AISI 1045 steel subjected to pulsed-laser surface irradiation can be improved with the aid of the extra acoustic field. The findings confirm that the acoustic field can be introduced to high-power laser processing technology to improve the surface integrity of the treated materials.

Preparation of Injection Moulding Processing for High Density Polyethylene via MoldFlow Advisor 2015 Simulation

Injection moulding simulation is one of the optimization methods which may reduce the cost due to the occurrence of defects. In order to utilise this method during the preparation of injection moulding for high density polyethylene, a processing verification through simulation and the validation through practical injection moulding needs to be conducted. In this research, Moldflow Advisor 2015 software was utilised to simulate the process while Nissei NP-7F machine was used for practical injection moulding experimentation. The criteria evaluation that was considered were filling time, time to reach ejection temperature, volumetric shrinkage, warpage, and sink marks. Through the simulation, the filling time was 3.232 seconds, the time to reach ejection temperature was 36.2 seconds, and the volumetric shrinkage was 17.69%. The warpage of 0.006 mm was also predicted in this simulation. While during practical injection moulding, the filling time was 3 seconds, the volumetric shrinkage was 16.6% and 0.07 mm warpage. Both simulation and practical results have no sink marks. Therefore, it can be concluded that the simulation process had provided a good prediction for practical injection moulding preparation. The findings of this research shall be beneficial by providing the manufacturing processing reference in related with injection moulding and high density polyethylene products.

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

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.

Optimization of Injection Molding Process to Minimize Weld-line and Sink-mark Defects Using Taguchi based Grey Relational Analysis

The study gives an insight of the material ABS stare UT-0510T material with MFI OF 16G/10MIN by conducting experiment on an injection molding machine. The part that is considered for this V3 window transparent used in air conditioners. This study is basically done to identify the effect of molding parameters on defects such as weld line and sink mark. The experiments have been performed by using L27 ORTHOGONAL ARRAY and these have been normalized by Grey relational analysis (GRA).The input variables are considered by using ANOVA. To determine optimal molding parameters Taguchi method constructed GRA was used. On these experiments we got optimized parameters which have reduced the weld-line width of 56.4% and sink mark depth of 68.9.

Gate Location and Injection Analysis of a Spur Gear

Injection moulding process is one of the common processes to produce plastic parts from simple to complicated parts. This paper focuses on the injection process analysis of a 25 tooth spur gear. Three runner system are proposed for the gear and each system will be analysed using Autodesk Simulation Moldflow Advisor. The most suitable design will then be chosen based on the results obtained from the simulation. The design undergoes cooling quality, sink mark, fill + pack, and warp analysis. Based on these analyses, Design 1 gave the better results compared to Design 2 and 3. From there, Design 1 runner system is chosen for the injection moulding mould which will be fabricated later in the research.

Injection mold design for a plastic component with blowing agent

Foam injection molding is a variant of conventional injection molding that uses a chemical blowing agent (CBA). The main advantages are the reduction of density and elimination of sink marks. On the other hand, the ever-increasing customer demands for quality and low cost have led to the requirement of best possible quality. Thus, mold designers are using Finite Element Method (FEM) for optimization. This work aims to design a mold for injection with CBA. The three-dimensional (3D) mold design process aims to predict problems that may occur in the mold and to present the advantages of injecting with CBA. The injected component is a high-density polyethylene (HDPE) pallet. The CBA enables obtaining parts with smaller warp in a shorter cycle, and in smaller injection machines. In addition, it was possible to save in raw material, with a considerable reduction of weight.

Integrated hot-melt extrusion – injection molding continuous tablet manufacturing platform: Effects of critical process parameters and formulation attributes on product robustness and dimensional stability

This study provides a framework for robust tablet development using an integrated hot-melt extrusion-injection molding (IM) continuous manufacturing platform. Griseofulvin, maltodextrin, xylitol and lactose were employed as drug, carrier, plasticizer and reinforcing agent respectively. A pre-blended drug-excipient mixture was fed from a loss-in-weight feeder to a twin-screw extruder. The extrudate was subsequently injected directly into the integrated IM unit and molded into tablets. Tablets were stored in different storage conditions up to 20 weeks to monitor physical stability and were evaluated by polarized light microscopy, DSC, SEM, XRD and dissolution analysis. Optimized injection pressure provided robust tablet formulations. Tablets manufactured at low and high injection pressures exhibited the flaws of sink marks and flashing respectively. Higher solidification temperature during IM process reduced the thermal induced residual stress and prevented chipping and cracking issues. Polarized light microscopy revealed a homogeneous dispersion of crystalline griseofulvin in an amorphous matrix. DSC underpinned the effect of high tablet residual moisture on maltodextrin-xylitol phase separation that resulted in dimensional instability. Tablets with low residual moisture demonstrated long term dimensional stability. This study serves as a model for IM tablet formulations for mechanistic understanding of critical process parameters and formulation attributes required for optimal product performance.

A Formal Model for Verification of ZigBee Protocol for Secure Network Authentication

Objectives: This paper proposes data mining approach to detect the causes of sink marks, short shot, burn marks and flash in 25 ml container cap and control the injection molding process to produce defect free product by optimal setting of process parameters. Methods and Statistical Analysis: Neural Net, Naive Bayes classifier and rule induction techniques are implemented to build the data mining models on training dataset acquired during the injection molding of 25 ml container cap. Findings: Neural Net and Rule Induction Models outperformed over Naive Bayes model (80%) with prediction accuracies of 95% on test dataset. Rule Induction model detected that sink marks are caused by high molding temperature, low injection speed, nozzle temperature and injection time. Low injection pressure, barrel temperature and mould temperature are responsible for short shot to occur in the product. Flash is caused by high mould temperature. Applications/Improvements: The custom prediction for quality of the product for a specific parameter setting can be made by applying Neural Net and Rule Induction models in order to control the process to ensure defect free caps. This approach can be applied for other injection molded products manufactured from other plastic materials.

Data Mining Approach for Quality Prediction and Fault Diagnosis of Injection Molding Process

Objectives: To implement data mining approach to diagnose the causes of faults occurring in the injection molding product and to predict the quality of product for a particular setting of process parameters. Methods and Statistical Analysis: Decision Tree, k-Nearest Neighbor (k-NN) and Polynomial by Binomial classification techniques are used to build the data mining models by training them on dataset collected during the injection molding of a cap for 25 ml container. Findings: These models are evaluated on test dataset and their prediction accuracy is found to be 95%. Sink marks are caused by low injection speed, nozzle temperature and injection pressure. Low nozzle and mould temperatures and injection pressure resulted in short shot. High barrel temperature at Zone 2 and injection speed are responsible for burn marks in the product. Applications/Improvements: The higher prediction accuracy of these models is helpful in predicting the quality of product before its manufacture and thereby avoiding the production of defective parts. This approach can be further extended for injection molded parts made out of various plastic materials and process conditions.

Reduction of Sink Marks in Injection Overmolding Process of Metal-Plastic Parts

Metal-plastic parts with steel inserts prepared by overmolding technique showed several molding defects including sink marks. The depths of sink marks on overmolding metal-plastic parts prepared at two injection overmolding temperatures of 280 and 230 °C and the same packing pressure of 60 MPa were measured by contact profilometer. They reached the depths of 3.02 mm and 1.51 mm at the overmolding temperature of 280 and 230 °C respectively. These values were correlated with sink marks indexes simulated in Moldflow software at the same conditions. Based on the simulated and measured results the optimal process parameters with injection temperature of 200 °C and packing pressure of 25 MPa were proposed. Simulation showed a positive effect of optimized parameters on sink marks minimizations. Sink marks indexes decreased of 20 % and 53 % compared to injection molding temperatures of 230 and 280 °C respectively. Maximal depth of sinks marks decreased to the value of 1.00 mm at optimized injection overmolding process parameters.

Minimization of variation in volumetric shrinkage and deflection on injection molding of Bi-aspheric lens using numerical simulation

The profile of a bi-aspheric lens is such a way that the thickness narrows down from center to periphery (convex). Injection molding of these profiles has high shrinkage in localized areas, which results in internal voids or sink marks when the part gets cool down to room temperature. This paper deals with the influence of injection molding process parameters such as mold surface temperature, melt temperature, injection time, V/P Switch over by percentage volume filled, packing pressure, and packing duration on the volumetric shrinkage and deflection. The optimal molding parameters for minimum variation in volumetric shrinkage and deflection of bi-aspheric lens have been determined with the application of computer numerical simulation integrated with optimization. The real experimental work carried out with optimal molding parameters and found to have a shallow and steep surface profile accuracy of 0.14 and 1.57 mm, 21.38-45.66 and 12.28-26.90 μm, 41.56-157.33 and 41.56-157.33 nm towards Radii of curvatures (RoC), surface roughness (Ra) and waviness of the surface profiles (profile error Pt), respectively.

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

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.

Microscopic and mechanical properties of semi‐crystalline and amorphous polymeric parts produced by laser cutting

ABSTRACTMicroscopic and mechanical properties of polymeric parts are effective factors on their durability. Laser cutting is one of the most common methods for production of 2D polymeric parts. Experimental study of the mentioned properties of semi‐crystalline and amorphous polymeric parts after laser cutting is conducted in this research. Low density polyethylene (LDPE) and polystyrene (PS) are considered as semi‐crystalline and amorphous polymers, respectively. Laser power and cutting velocity were selected as input parameters of cutting process. According to microscopic observations, the microcracks, re‐solidified spots of molten material, and sink marks just appear in heat affected zone (HAZ) on amorphous polymer. Results also showed that the HAZ width and surface roughness values are smaller for semi‐crystalline polymer. For both polymers, decreasing of power and increasing of cutting velocity reduce the HAZ and surface roughness. In the case of mechanical properties, tensile strength of semi‐crystalline and amorphous polymers reduces after laser cutting. Results of experiments revealed that the extension of HAZ and deterioration of surface finish decrease tensile strength of parts. Therefore, lower power and higher cutting velocity condition is preferable for reaching the better mechanical properties. Furthermore, two separate mathematical models for each polymer are presented for prediction of tensile strength after laser cutting process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44179.

Study on reducing sink mark depth of a microcellular injection molded part with many reinforcing ribs

As a novel injection molding process, microcellular injection molding process has the characteristics of saving material, decreasing warpage and surface sink mark, improving dimensional accuracy, etc. But for the plastic part with thick reinforcing ribs, if selection of process parameters are not reasonable, foaming quality of melt will be affected and obvious sink mark defects will appear on the surface of plastic part. This paper selected a medical appliance shell with many reinforcing ribs as research object. Simulation experiments of microcellular injection molding process were performed by using orthogonal experiment method. The influence of different process parameters, such as mold cavity surface temperature, melt temperature, injection rate, cooling time, weight reduction ratio and supercritical fluid level, on the surface sink mark of microcellular injection molding part was studied by using signal-to-noise ratio analysis and analysis of variance . The results showed that mold cavity surface temperature was the most important influence factor on surface sink mark depth of microcellular injection molding part, followed by weight reduction ratio, cooling time, supercritical fluid level, injection rate and melt temperature. Meanwhile, the optimal combination of process parameters was obtained for minimizing sink mark depth of microcellular injection molding part. The average surface sink mark depth of microcellular injection molding part molded by using the optimized process parameters was only 2.62 µm, compared to 4.87 µm of average surface sink mark depth of microcellular injection molding part molded by using the process parameters before optimization, the average sink mark depth of microcellular injection molding part was reduced by 46.2%. Finally, the forming mechanism of sink mark of microcellular injection molding part at locations of reinforcing ribs was discussed, and the influence mechanism of different process parameters on surface sink mark defects of microcellular injection molding part was also analyzed.