Injection-molded Parts Research Articles

Effects of dynamic mold temperature control on melt pressure, cellular structure, and mechanical properties of microcellular injection-molded parts: An experimental study

In this work, the effects of dynamic mold temperature control (DMTC) on melt pressure, cellular structure, and mechanical properties of microcellular injection molding (MIM)-molded parts are investigated experimentally. It is found that with the increase of the mold temperature, the duration of foaming pressure in the cooling stage increases. Meanwhile, the average cell diameter and cell diameter dispersion increases as well as the cell density decreases in MIM molded parts. The turning point of mold temperature after which the foaming pressure in the cooling stage and the cellular structure in MIM molded parts generate a significant change is around the glass transition temperature of the used plastic material. Under DMTC conditions, with the increase of mold temperature, the tensile strength, flexural strength, and impact strength of MIM molded specimens of single gate without weld line change a little, while the tensile strength, flexural strength of MIM molded specimens of double gates with weld line increase obviously. When the mold temperature increases to 120°C and over, the tensile strength, flexural strength of MIM molded specimens of double gates with weld line reach an equivalent level of specimens of single gate without weld line.

Process porosity and mechanical performance of fused filament fabricated 316L stainless steel

PurposeThis study aims to investigate the correlation between build orientation characteristics, part porosity and mechanical properties of the fused filament fabrication (FFF) process to provide insight into pore formation mechanisms and to establish guidelines for optimal process configurations.Design/methodology/approachMicro computed tomography and metallographic sections provide the basis for a correlation between porosity and extrusion path. Using the correlations found in this study, the way to improve printing strategies and filament properties can be deduced directly from an analysis of the print path and the final influence on mechanical performance.FindingsWith metal-FFF 3D printing technology, near-dense parts (0.5 Vol.%) can be fabricated. The pore architecture is strongly connected to the build direction and print strategy with parallel, elongated pore channels. Mechanical values of FFF samples are similar to metal injection-molded (MIM) parts, except the elongation to fracture. The high difference of yield strength of sintered samples compared to laser powder bed fusion (LPBF) samples can be attributed to the finer grains and a Hall–Petch hardening effect. The conclusions derived from this study are that the presented process is capable of producing comparable part qualities compared to MIM samples, with higher build rates in comparison to LPBF processes.Originality/value316L stainless steel was successfully manufactured via FFF. This paper also addresses the effects of scanning strategies on the resulting porosity and proposes improvements to reduce residual porosity, thus increasing the mechanical performance in the future.

Injection mold design of reverse engineering using injection molding analysis and machine learning

Plastic composites are used in vehicle components to improve fuel efficiency. Thus, the warpage of injection-molded plastic parts has become a quality issue. Factors, such as product shape and thickness, resin, and other injection molding conditions, can be modified to improve the warpage problem. However, if these factors are set with no possible adjustments, reverse engineering may be required. Reverse engineering is a difficult process that requires many trials and errors; thus, it is only used as a last resort. With respect to the warpage issue, reverse engineering considers the following: (1) Predicting and (2) modeling the warpage in opposite directions. Autodesk Moldflow Insight accommodates these key considerations, but many researchers are reluctant to use it. Although existing injectionmolding analysis programs are mainly used to predict qualitative results, computer-aided engineering (CAE) for reverse engineering requires quantitative analysis. Hence, the considerations are different from the existing analyses. An error in warpage prediction may lead to a costly mold modification because of the molds' complex structures. Quantitative warpage prediction for reverse engineering depends on process variables; thus, understanding how warpages are affected by uncertain process variables is important to improve the reliability of reverse engineering. Moreover, even if appropriate process variables are set, they cannot be applied due to tolerance in lengths. For this reason, mold shrinkage must be identified before designing a mold. This study conducted injection molding analysis for a radiator tank that uses glass fiber-reinforced plastic using Autodesk Moldflow Insight 2018.2. Data for warpage prediction were generated in accordance with five process variables to identify the relationship between the level of warpage and process variables. CAE also showed the level of mold shrinkage that can reduce warpage. In addition, a predictive model was created using the multilayer perceptron (MLP)- supervised learning technique, which is a deep learning method for artificial neural networks. The predictive model was compared with typical regression models, such as polynomial regression (also known as response surface model), EDT and RBF, to determine the optimal approximation model. The real modeling time for a radiator tank product is 1 h, but the MLP approximation model required only 1 min and 8 s to perform 8530 iterations with a similar reliability.

Injection molding with an additive manufactured tool

This study examines the viability of using additively manufactured injection molding tools for short run proof‐of‐concept plastic parts by assessing the quantity and quality of molded parts. Prototyping injection molded parts traditionally can be very expensive, but with improved additive manufacturing materials and techniques such costs could be reduced. To prove this, plastic tools were made by using PolyJet and Fused Deposition Modeling out of Digital ABS, FullCure 720, and ULTEM 1010 materials in this study. The test tools were then compared to the standard P20 metal tool by molding acetal, polycarbonate (PC), and polypropylene (PP) in each tool type. The molded parts were analyzed for processing effects on part shrink, physical, and mechanical properties. Testing concluded that parts molded with additively manufactured tools performed comparably to parts made on a P20 tool. However, the quantity of satisfactory parts molded in acetal and PC were consistent with the literature at 10–100 parts. Conversely, molding in PP suggested that processing with additive manufactured tools could exceed 250 parts. POLYM. ENG. SCI., 59:1911–1918, 2019. © 2019 Society of Plastics Engineers

Tie-Bar Elongation Based Filling-To-Packing Switchover Control and Prediction of Injection Molding Quality.

Filling-to-packing switchover (also called V/P switchover) is critical for assuring injection molding quality. An improper V/P switchover setting may result in various defects of injection-molded parts, such as excessive residual stress, flash, short shot, and warpage, etc. To enhance a consistent molding quality, recent V/P switchover approaches adopt cavity pressure profiles requiring sensors embedded in mold cavities, which is invasive to mold cavities and more expensive. Instead of using cavity pressure sensors, by working with the most popular screw position switchover control, this study hereby proposes a novel approach of tuning V/P switchover timing using a tie-bar elongation profile. In this investigation, a dumbbell testing specimen mold is applied to verify the feasibility of the method proposed. The results show that the mold filling and packing stages can be observed along the tie-bar elongation profile, detected by mounting strain gauges on the tie bars. Also, the characteristics of the cavity pressure are similar to those of the tie-bar elongation profile under a proper clamping force condition. Moreover, the varying process parameter settings which include injection speed, V/P switchover point, and holding pressure, can be reflected in these profiles. By extracting their characteristics, the application of the V/P switchover is proved to be realistic. This research conducted an experiment to verify the proposed V/P switchover decision method based on the tie-bar elongation profile. The result showed that the fluctuation of the part’s weight corresponding to a slight change of the barrel’s temperature from 210 °C to 215 °C can be successfully controlled with this method. Besides, the maximum clamping force increment extracted from the tie-bar elongation profile was found to be a good indicator for online monitoring of the reground material variation.

“Improving the impact strength of PLA and its blends with PHA in fused layer modelling ”

Abstract Poly-(lactic acid) (PLA) is one of the most popular thermoplastics for fused layer modelling (FLM). Due to its semi-crystalline nature, the influences of printing parameters on the properties of the printed part are more complicated than with amorphous thermoplastics like acrylonitrile-butadiene-styrene (ABS). In present study, the influence of the process parameters, such as temperature of the plate as well as printing angle used for the three-dimensional printing process was studied in the case of virgin PLA. In addition, PLA was mixed with an amorphous polyhydroxyalkanoate (PHA) copolymer with the aim to improve its impact properties. Mechanical performance of virgin PLA and its PLA/PHA blend prepared by 3D printing method was compared with the mechanical performance of the parts produced by injection moulding. Small and wide angle X-ray measurements were performed in order to study the influence of the crystal morphology on the mechanics of PLA and PLA/PHA 3D printed as well as injection moulded parts. The PLA/PHA parts produced by 3D printing showed higher impact strength and notched impact strength values than injection moulded parts.

Material flow influence on the quality of molded parts

This paper focuses on a new occurrence mechanism of the flow marks, which appear on the surface of injection-molded parts, through characterization of the part surface structure. Injection-molded parts involving long flow lengths can exhibit visible flow defects characterized by alternating glossy and dull bands on the polymer surface, which have approximately the same direction with the material flow front. These flow defects are considered to have strong negative effect on the appearance of the molded component and thus on the perceived quality. The reasons for the appearance of these stripes are not entirely clear. Defect flow marks (shiny areas) were cut from the molded part and analyzed using optical microscopy, Fourier transform infrared spectroscopy, laser Raman spectroscopy and scanning electron microscopy coupled with energy-dispersive X-ray (SEM/EDX) spectroscopy. Raman spectra detected differences between spectra of defect area and of the reference one. The EDX analysis revealed that the defect area contains slightly more quantity of talc (Mg and Si). This happened because of material flow morphology in the areas where the molded part presents ribs. The flow of melted resin through an enlargement (rib) results in a decrease in flow velocity, and consequently, a pressure rise will occur and it also involves a vortex development. Therefore, the shear stress in this area is higher than upstream and downstream ones, and it will cause a delay of the flow stream, a premature solidification of the melted resin and ribs flow marks occurrence.

Binder removal by a two-stage debinding process for powder injection molding Fe–50Ni alloy parts

Debinding is a critical process for injection molded green parts of soft magnetic materials. In case of incomplete binder removal, the residual impurities deteriorate the magnetic performance of the final components. On the other hand, binder decomposition reduces the structural strength of the green parts. Therefore, it is important to engineer an appropriate debinding cycle not only to ensure efficient binder removal but also to retain the structural strength of the parts. In this study, the two-stage debinding process is optimized focusing on the higher rate of binder removal to get defect-free parts. The feedstock of Fe–50Ni alloy with a multicomponent binder system was prepared followed by injection molding. In the first stage, the binder was removed by solvent debinding and in the second stage, thermal debinding was carried out. The various types of defects were observed during debinding process. It has been found that efficient solvent debinding extracted 98% binder whereas thermal debinding at a heating rate of 2 °C min−1 results in defect-free quality parts.

Effect of Melt Temperature on Weld Line Strength

This article deals with the influence of the melt temperature on weld line strength in injection-molded plastic parts. A special mold was created for this investigation to make specimens with a central weld line. The experimental material was polypropylene Sabic PP 90910. Its stress at break is around 16 MPa and its melting temperature is between 200°C and 260°C. In general, the presence of weld lines has a negative impact on mechanical properties. This investigation showed that the strength depends on the melt temperature (160–260°C in this case). Strength was measured using mechanical testing. It was found to increase with the melt temperature, up to 210°C. Above 210°C, degradation of the plastic led to decreasing strengths. A melt temperature range of 190–210°C is therefore optimal for this application. Shear forces and friction were found to play a great role, as they raise the melt temperature during molding. This was confirmed by mold-flow analysis. The melt temperature during molding was up to 18% higher than the initial melt temperature. This investigation has important consequences for the plastic industry. It is relevant to evaluations of the polymer matrix strength in composite materials and the strength of 3D printed parts with multiple weld lines.

Injection-molded parts of fully bio-based polyamide 1010 strengthened with waste derived slate fibers pretreated with glycidyl- and amino-silane coupling agents

Abstract Fully bio-based polyamide 1010 (PA1010) was melt-compounded with 15 wt% of slate fibers (SFs), which were obtained from wastes of the tile industry, and the resultant composites were shaped into parts by injection molding. The as-received fibers were first thermally treated and afterwards subjected to surface modification with glycidyl- and amino-silane coupling agents to improve the interfacial adhesion of the composites. The incorporation of both the glycidyl-silane slate fiber (G-SF) and amino-silane slate fiber (A-SF) remarkably improved the mechanical strength of PA1010, inducing a 3-fold increase in tensile modulus. The composite parts prepared with the silanized SFs also presented higher thermal stability and improved thermomechanical resistance. Water uptake was reduced below 1 wt%, encouragingly suggesting that the mechanical performance of the PA1010/SF composites would be scarcely affected by atmospheric humidity. G-SF was the most effective in strengthening PA1010. This improvement was ascribed to the higher reactivity of the cyclic anhydride in the coupled silane with the terminal hydroxyl groups of the biopolymer.

Optimization of process parameters in plastic injection molding for minimizing the volumetric shrinkage and warpage using radial basis function (RBF) coupled with the k-fold cross validation technique

Abstract In this study, a multi-objective design optimization method based on a radial basis function (RBF) model was applied to minimize the volumetric shrinkage and warpage of hip liners as an injection-molded biomedical part. The hip liners included an ultrahigh molecular weight polyethylene (UHMWPE) liner and UHMWPE reinforced with a nano-hydroxyapatite (nHA) liner. The shrinkage and warpage values of the hip liners were generated by simulation of the injection molding process using Autodesk Moldflow. The RBF model was used to build an approximate function relationship between the objectives and the process parameters. The process parameters, including mold temperature, melt temperature, injection time, packing time, packing pressure, coolant temperature, and type of liner, were surveyed to find the interaction effects of them on the shrinkage and warpage of the liners. The results indicated that the addition of nHA helps the liners to obtain more dimensional stability. The model was validated by the k-fold cross validation technique. Finally, the model revealed the optimal process conditions to achieve the minimized shrinkage and warpage simultaneously for various weights.

Effects of heat energy on morphology and properties of selective inhibition sintered high density polyethylene

This study provides an account of comprehensive experimentation and mechanical characterisation of high density polyethylene (HDPE) parts that are fabricated through an additive manufacturing process called selective inhibition sintering (SIS). In this study, test specimens are fabricated by selective fusing of HDPE particles through controlled heating. Morphological studies and mechanical property evaluation of these specimens are carried out to assess the impact of energy on sintering of HDPE particles and structural integrity. Results indicate that, heat energy up to a threshold level of 28.48 J/mm2 results in superior fusion of the HDPE particles, and further increase causes degradation of the structure. Surface roughness, tensile and flexural properties of SIS parts are compared with those of injection moulded parts for assessing their suitability to engineering applications.

Comparison of similar injection moulded parts by a coordinate measuring machine

One of the biggest issues in measuring injection moulded parts by touch-probe coordinate measuring machine is the deformation of parts being measured. Even though the contact force rarely exceeds 200 mN, it can deform the part, or influence the fixture, thus introducing measurement error. In order to provide the most appropriate measurement method for the inspection of injection moulded part geometry, this paper combines two research topics: one is the comparison of measurement objects similar in shape—expensive brand name products with cheap no-name products, and another is the deformation analysis of the contact between the CMM touch-probe and flexible polymer parts which tend to deform when this type of measurement is used.

Steel mould surface improvement by robot fluid jet polishing and robot pad polishing for polymer optic production

In order to improve the quality of injection-moulded polymer optic parts, it is necessary to improve the quality of the respective steel moulds. For this reason, it is not only necessary to improve the surface roughness of the mould, but also its geometrical shape. The material removal obtained from robot pad polishing is too low. This makes a shape correction after the milling step a very prolonged process. The aim of this work is to use a polishing chain to improve the surface quality of steel samples in terms of shape deviation and surface roughness. This correction polishing chain uses the robot fluid jet polishing for the geometrical shape correction and afterwards the robot pad polishing for the improvement of the surface roughness. Due to the high material removal rates of the fluid jet polishing, it is possible to correct the geometrical shape of steel moulds very fast up to a certain deviation. The pad polishing process improves the surface roughness of the steel samples. A correction of the shape deviation of more than 80% with a RMS of approximately 8 nm was obtained.

Mechanical properties of 3D printed composites with ABS/ASA substrate and glass fiber inserts

3D printed specimens (ASTM D638 Type I) were manufactured from ABS and ASA material via additive manufacturing through material extrusion 3D printing (ME3DP). During manufacturing, the printing process has been paused, pre-impregnated biaxial or uniaxial glass fiber mesh has been placed onto the ABS/ASA substrate and then the printing process has been resumed. The obtained composite specimens have been subjected to tensile strength testing and results have been compared to those of specimens printed from homogenous material. The influence of raster angle, glass fiber direction and mesh density on resulting toughness has also been analyzed. It was found that inserting uniaxial glass fiber increases toughness of specimens in the axial direction, with a drop in layer adhesion if biaxial fiber is used. Test specimens manufactured with 30 uniaxial fiber strands embedded in a 0o raster angle 3D printed thermoplastic matrix match mechanical characteristics of injection-molded parts. The maximum mesh density without leading to delamination is one layer of glass fiber every two layers of thermoplastic matrix.

Influence of talc and rubber contents on surface replication of polypropylene injection molding application to automotive plastics

Abstract The influence of talc and rubber contents included in polypropylene (PP) on surface replication properties for microstructure was analyzed. By increasing the talc and rubber contents, surface replication on the injection-molded parts has been reduced. From the surface observation, an uneven microstructure surface was formed for a material containing talc during the shrinkage process. It was confirmed that if the PP resin contains talc, then the correlation between glossiness of the mold and glossiness of the molded product was lost and glossiness was decreased. On the contrary, as the rubber content increased, the replication properties improved. At the same time, generation of the streak pattern in the transferred area, which was generated in the base PP, decreased and glossiness increased. Moreover, the fine uneven structure of the nontransferred area, as observed in the talc-containing material, was not observed in the rubber-containing material.

Optimization of Fiber Orientation Model Parameters in the Presence of Flow-Fiber Coupling

In this paper, we propose a novel systematic procedure to minimize the discrepancy between the numerically predicted and the experimentally measured fiber orientation results on an injection-molded part. Fiber orientation model parameters are optimized simultaneously using Latin hypercube sampling and kriging-based adaptive surrogate modeling techniques. Via an adequate discrepancy measure, the optimized solution possesses correct skin–shell–core structure and global orientation evolution throughout the considered center-gated disk. Some non-trivial interaction between these parameters and flow-fiber coupling effects as well as their quantitative importance are illustrated. The parametric fine-tuning of orientation models mostly leads to a better agreement in the skin and shell regions, while the coupling effect via a fiber-dependent viscosity improves prediction in the core.

Effect of Chemical Modification on Mechanical Properties of Wood-Plastic Composite Injection-Molded Parts.

Wood chips from furniture-manufacturing byproducts, which do not include adhesive or paint in the waste wood, were used for the flouring process and chemical modification of wood flour (WF). After chemical modification, the WF was mixed with polypropylene through extrusion compounding and injection-molding to prepare wood-plastic composite (WPC) injection-molded specimens for the American Society for Testing and Materials. Static contact angle measurements and stereomicroscope observations were performed. In this study, it was confirmed that the impact strength was improved by up to 55.8% and the tensile strength by up to 33.8%. The flexural modulus decreased marginally. As a result of WF chemical modification, the measured contact angle of WPC increased, which means that the wettability of the WPC specimen surface decreased. In addition, it was observed through stereomicroscopy that the whitening of the surface of the WPC specimen improved.

Effect of glass fiber distributions on the mechanical and fracture behaviors of injection-molded glass fiber-filled polypropylene with 2-Hole Tension specimens

In this study, various fracture characteristics of plastic parts were experimentally investigated using newly designed specimens with 2 holes to observe the deformation and fracture behaviors of injection-molded plastic parts fabricated by short glass fiber (GF)-reinforced polypropylene (PP). This 2-hole tension (2HT) specimen affects the flow pattern of resin and the orientation of GF during the injection molding process, and various stress concentrations and distributions can be generated under a simple tensile load. The effects of rheological and mechanical variations of the resin on the deformation and fracture behavior of the test specimens were successfully investigated using the 2-hole tension specimens. In addition, it was confirmed that the non-uniform distribution of GF observed in the hole arrays region through the computed tomography (CT) scan is related to the crack propagation pathway, which ultimately affects the fracture behavior of the specimen.

Investigation of inserts surface structures on injection moulded parts

Nowadays, the surface quality of injection moulded products is becoming increasingly important to users. Due to increasing demands, engineers (especially in the automotive industry) creates structures on the surface of the parts that are close to the appearance of natural materials (e.g. leather, wood, etc.). These aspirations are not only aesthetically but functionally important. In order to create quality product, besides processing parameters, it is also crucial how to design the mould. However, it is important to know how the processing parameters affect the mould surface mapping. The preliminary objective is to investigate the effect of different macro-geometric structures created by cutting technology on the flow of polymer melt.