Optimization of injection parameters for mechanical properties of specimens with weld line of polypropylene using Taguchi method

This study optimized effect of injection parameters and weld line on the mechanical properties of polypropylene (PP) moldings. The mold with an insert was designed to create weld line in the experimental specimen. Melt temperature, packing pressure and injection pressure were investigated to study their effects on the mechanical strength of specimens with/without weld lines. Taguchi's L₉ (3³) orthogonal array design was employed for the experimental plan. Mechanical properties such as maximum tensile load, extension at break and charpy impact strength (notched) of the specimens were measured. Signal to noise ratio for mechanical properties of PP using Taguchi method was calculated and effect of the injection parameters and weld line on mechanical properties was determined using the analysis of variance (ANOVA). Linear models were also created by using regression analysis. The most important parameter affecting the maximum tensile load and the extension at break (for specimen without/with weld line) was injection pressure and melt temperature, and for charpy impact strength (notched) (without/with weld line) was melt temperature and injection pressure, respectively.     

Influence of injection parameters and mold materials on mechanical properties of ABS in plastic injection molding

This study optimized effect of injection parameters such as melt temperature, packing pressure, cooling time and injection pressure on the mechanical properties of Acrylonitrile–Butadiene–Styrene (ABS) moldings. Mold materials having two different thermal conductivities, 191 W/mK for aluminum 2000 series and 50 W/mK for AISI 1020 at 25 °C were selected to use in experimental studies. Taguchi's L₉(3⁴) orthogonal array design was employed for the experimental plan. Mechanical properties of ABS specimens such as elasticity module, tensile strength and tensile strain at yield, tensile strain at break, flexural modules and izod impact strength (notched) were measured by using some test methods. Signal to noise ratio for mechanical properties of ABS using the Taguchi method was calculated and effect of the parameters on mechanical properties was determined using the analysis of variance. Linear mechanical models were also created by using regression analysis.     

Structure and mechanical properties of polystyrene foams made through microcellular injection molding via control mechanisms of gas counter pressure and mold temperature

In this study we developed a foaming control system using Gas Counter Pressure (GCP) combined with mold temperature control in the microcellular foaming (MuCell) process. The effects of the skin thickness, cell size, and cell morphology resulting from the three control mechanisms (including GCP control alone, mold temperature control alone, and GCP combined with mold temperature control) and process parameters on the mechanical properties of foamed polymer were investigated. In addition, the mechanical properties of foamed specimens molded from these three control mechanisms were also compared. It was found that skin thickness, cell size, and cell shape had significant influences on the mechanical properties of specimens depending on the molding conditions of gas counter pressure, holding time, and mold temperature. By increasing gas counter pressure, holding time, and decreasing the mold temperature, the tensile strength increased. In addition, by increasing gas counter pressure, holding time, and mold temperature alone, impact strength decreased. But, there were no clear relationships for processing parameters when GCP combined with dynamic mold temperature control was used because the effects of the skin thickness, cell size, and cell shape on the impact strength were unclear. Under experimental condition at mold temperature of 60 °C combined with appropriate GCP control system, better tensile strength and impact performance were achieved and specimens with thin skin, small and uniform cell size as well as better surface quality were produced.     

Effect of cavity surface coating on mold temperature variation and the quality of injection molded parts

Suiting for high gloss surface of injection molded parts free of painting is a great concern from both environment and cost effective considerations. As a result, variable mold temperature controls to achieve the mentioned goal have been paid great attentions. In this study, TiN and Teflon of various thicknesses were coated on the cavity surface of a tensile bar mold designed with double gate. During the injection molding process, melt–mold interface temperature was analyzed and simulated. In a regular injection molding of ABS resin using P20 as the mold material, the initial melt temperature may drop from 240 °C to about 65 °C after 0.01 s of contact with the cavity surface when the coolant temperature is 60 °C. For a TiN surface coating of 4 µm, the interface contact temperature was raised to 73.6 °C. For a Teflon coating of 22 µm, the contact surface temperature is as high as 100 °C initially (about 25 °C higher) and remains above 80 °C for about 0.4 s. Teflon coating on the cavity surface eliminates the weld-line marks, improves part surface smoothness and results in better tensile strength for weld line than TiN coating. Moreover, the cooling time was almost not affected. When surface coating is combined with infrared heating, not only the tensile strengths of the weld line were further enhanced but also the heating rate at mold surface is enhanced.     

Preparation and properties on the graphite/polypropylene composite bipolar plates with a 304 stainless steel by compression molding for PEM fuel cell

Graphite/polymer composites have high corrosion resistance, low contact resistance and low fabrication cost but low cell efficiency and mechanical strength. This study examined the electrical and mechanical properties of graphite/polypropylene composite bipolar plates. Carbon nanotubes (CNTs) were used to improve the electrical properties of the graphite/PP composites. Although the electrical properties increased when excess conducting filler was added to the composite, the mechanical strength decreased significantly. 304 stainless steel (304 SS) plates with different thicknesses were used as the support material of a graphite/PP composite bipolar plate. The 304 SS-supported graphite/PP composite bipolar plate had an optimum CNTs/graphite/PP composite composition of 1.2, 83 and 17 wt.%, respectively. The flexural strength of the 304 SS-supported graphite/PP composites increased from 35 to 58 MPa with increasing 304 SS thickness from 0.5 to 1 mm. The power density of the graphite bipolar plate and 304 SS-supported graphite/PP composite bipolar plate were 968 and 877 mW cm⁻², respectively. The 304 SS complemented the mechanical strength of the graphite/PP composite bipolar plate as well as the cell efficiency.     

Investigation on the weldline strength of thin-wall injection molded ABS parts

It is well known that the weldline reduces the mechanical performance of the conventional injection molded parts. Yet, systematic researches and reports on weldline strength of thin-wall molded parts are still insufficient. This study investigates the influence of processing conditions on the weldline strength of thin-wall Acrylonitrile Butadiene Styrene Copolymer (ABS) parts. The relevant parameters include melt temperature, mold temperature, injection speed and packing pressure. Tensile tests on specimens of different thickness (1.0, 1.2 and 2.5 mm) are conducted. Comparisons on tensile strength for single-gate molded specimens (without weldline) with those of double-gate molded specimens (with weldline) are presented. From the experimental results, it was found that weldline specimens molded at higher melt temperature, higher mold temperature, faster injection speed and lower packing pressure would result in better mechanical strengths. Higher melt and mold temperatures not only lower the residual stress but also help the diffusion of molecular chains leading to a higher degree of surface bonding at the weldline interface. On the other hand, high packing pressure leads to higher residual stress formation and reduces the molecular bonding rate. In addition, part thickness also exhibits significant effect on weldline strength. A regression analysis combined with fitting model seems to correlate process conditions and weldline strength reduction quite well.     

Mechanical property variation within Inconel 82/182 dissimilar metal weld between low alloy steel and 316 stainless steel

In several locations of pressurized water reactors, dissimilar metal welds using Inconel welding wires are used to join the low alloy steel components to stainless-steel pipes. Because of the existence of different materials and chemistry variation within welds, mechanical properties, such as tensile and fracture properties, are expected to show spatial variation. For design and integrity assessment of the dissimilar welds, these variations should be evaluated. In this study, dissimilar metal welds composed of low alloy steel, Inconel 82/182 weld, and stainless steel were prepared by gas tungsten arc welding and shielded metal arc welding techniques. Microstructures were observed using optical and electron microscopes. Typical dendrite structures were observed in Inconel 82/182 welds. Tensile tests using standard and mini-sized specimens and micro-hardness tests were conducted to measure the variation in strength along the thickness of the weld as well as across the weld. In addition, fracture toughness specimens were taken at the bottom, middle, and top of the welds and tested to evaluate the spatial variation along the thickness. It was found that while the strength is about 50–70 MPa greater at the bottom of the weld than at the top of the weld, fracture toughness values at the top of the weld are about 70% greater than those at the bottom of the weld.     

Induction heating with the ring effect for injection molding plates

Induction heating in injection molding has the advantages of rapid heating, reduced cycle time, and improved product quality. In this research, using both experiment and simulation, externally wrapped coil induction heating was applied to verify the heating capacity of a pair of mold plates. By applying different coil designs and mold gap, the effect of the externally wrapped coil induction heating was evaluated. Results showed that when a serial coil was used as an inductor, the heating rate reached 8.0 °C/s. From an initial mold temperature of 40 °C, after 15 s heating, the mold surface temperature reached 159.9 °C with the serial coil. The parallel coil shows a better heating uniformity but its heating rate is far lower than the serial coil. For the serial coil, the temperature distribution between the core and cavity plate are almost the same. The heating rate increases from 4.9 °C/s to 10.6 °C/s when the inductor design is changed from 5 turns to 7 turns. After 15 s heating, the temperature at point T2 increases from 40 °C to 166.7 °C and 106.1 °C with a mold gap of 1 mm, and 6 mm, respectively.     

A study of spray strategies on improvement of engine performance and emissions reduction characteristics in a DME fueled diesel engine

This paper investigated the impact of injection angle and advance injection timing on combustion, emission, and performance characteristics in a dimethyl ether (DME) fueled compression ignition engine through experimentation on spray behaviors and the use of numerical methods. To achieve this aim, a visualization system and two injectors with different injection angles were used to analyze spray characteristics. The combustion, emission, and performance characteristics were analyzed by numerical methods using a detailed chemical kinetic DME oxidation model. Each of five injection angles and timings were selected to examine the effect of injection angle and timing. It was revealed that the injected spray with narrow injection angles was impinged on the bottom wall after the SOI of BTDC 60°, and most of the fuel spray and evaporation with the wide injection angles had a distribution at the crevice region when the injection timing was advanced. In addition, NO_x emissions at the SOI of BTDC 20° and TDC had higher values, and the soot emission quantities were extremely small. The narrow injection angles had good performance at the advanced injection timing, and the injection timing over a range of BTDC 40-20° showed superiority in performance characteristics.     

Flow visualization and film cooling effectiveness measurements around shaped holes with compound angle orientations

Experimental results are presented which describe film cooling performance around shaped holes with compound angle orientations. The shaped hole has a 15° forward expansion with an inclination angle of 35°, but the orientation angles vary from 0° to 30° and 60°. The blowing ratios considered are 0.5, 1.0 and 2.0. Flow visualizations are performed using an aerosol seeding method for single enlarged shaped hole to investigate the interaction between the mainstream and the injectant at the hole exit plane. The adiabatic film cooling effectiveness distributions are measured for a single row of seven shaped holes using the thermochromic liquid crystal technique. Flow visualization reveals the occurrence of hot crossflow ingestion into the film hole at the hole exit plane at a large orientation angle such as 60°. Shaped holes with simple angle injection do not provide substantial improvement in the film cooling performance compared to round holes. However, shaped holes with compound angle injection exhibit improved film cooling effectiveness up to 55% in comparison with round hole data at high blowing ratios.     

Effect of decoration film on mold surface temperature during in-mold decoration injection molding process

In-mold decoration (IMD) during injection molding is a relatively new injection molding technique and has been employed for plastic products to improve surface quality and achieving colorful surface design, etc. During IMD processing, the film is preformed as the shape of mold cavity and attached to one side of the mold wall (usually cavity surface), then molten polymer is filled into the cavity. Heat transfer toward the mold cavity side during molding IMD part is significantly retarded because the film is much less thermal conductive than metal mold. To investigate the effect of film on temperature field, polycarbonate (PC) was injection molded under various conditions including coolant temperature, melt temperature, film material and film thickness. Simulations were also conducted to evaluate the melt–film interface temperature and its influence from film initial temperature and film thermal properties. For PC film, it was found that the heat transfer retardation results in the mold temperature drop in cavity surface and the maximum temperature drop as compared to that of conventional injection molding without film may be as high as 17.7 °C. For PET film, this maximum mold temperature drop is about 13 °C. As PC film thickness increases, the retardation-induced mold temperature difference also increases. The initial film temperature (30 °C and 95 °C) may affect the melt–film interface temperature at the contact instant of melt and film by about 12 °C to 17 °C. When thermal conductivity of film increases from 0.1 W/(m–k) to 0.2 W/(m–k), melt–film interface temperature may vary by 22.9 °C. The simulated mold temperature field showed reasonable agreement with experimental results.     

Enhanced mechanical properties and corrosion behavior of polypropylene/multi-walled carbon nanotubes/carbon nanofibers nanocomposites for application in bipolar plates of proton exchange membrane fuel cells

Polypropylene (PP) nanocomposites with multi-walled carbon nanotubes (MWCNT) alone or combined with carbon nanofibers (CNF) at different loadings have been fabricated by melt mixing with a focus on their mechanical properties and corrosion resistance for bipolar plates applications in proton exchange membrane fuel cells (PEMFCs). The incorporation of up to 20 wt% MWCNT in the PP matrix produces enhancements of 71, 47, 56, and 30% in microhardness, elastic modulus, and tensile and flexural strength, respectively. Combined additions of MWCNT and CNF allow producing hybrid nanocomposites with increased strength than when neat MWCNT as reinforcement, preserving their processability even at a total filler content of up to 30 wt%. The measured values of i_corr in both PP/MWCNT and PP/MWCNT/CNF suggest a slow degradation rate in the PEMFC environment. Based on the US Department of Energy (DOE) targets, PP/20MWCNT, PP/21.5MWCNT, and PP/15MWCNT/15CNF nanocomposites are good candidates to produce bipolar plates for PEMFCs.     

Material characterisation and selection for the international research project “PRIMAVERA”

The international research project “PRIMAVERA” aims to develop a physically validated prediction model for the transition temperature shift dependence (ΔT_K) of VVER-400 weld metals versus neutron fluence after reactor pressure vessel annealing. The reactor pressure vessel of VVER type has several ring welds between the forgings, characterised by large overall dimensions, structural heterogeneity and mechanical properties variations. The weld metal is a mild low-alloy steel with rather complex structure depending on chemical composition, manufacturing technology and heat treatment and the selection of the weld sample is crucial for the success of the project. A weld with high phosphorus content manufactured following standard VVER-440/230 weld technology, has been identified and selected for the project. The detailed characterisation of the selected weld in the un-irradiated condition is the first phase of the research programme and is presented in this paper. Significant phosphorus content variations through the weld could be identified; from 0.022 to 0.044 wt%. Only small variations in mechanical properties were identified; a maximum of 13 °C difference in ductile to brittle transition temperature, mainly related to the distance to the fusion boundary and the base metal. The study also showed that testing of 14 Charpy specimens is sufficient for a correct evaluation of transition temperature. A larger number of tests are required for base metal compared with the weld metal.     

Three-dimensional numerical and experimental investigations on polymer rheology in meso-scale injection molding

Three-dimensional simulation and experimental investigation of polymer rheology in a miniature injection molding process is presented. The material used in the study is ABS plastic, Toyolac 250-X10 and tests are carried out at different temperatures of the molten thermoplastic which is injected into the mold cavity. FLUENT 6.3 software is used in the simulation to verify the viscosity model (Cross model) and the Volume of Fluid (VOF) method is applied for the melt front tracking. The model is validated by means of experiments performed by using Davenport High Shear Viscometer with injection nozzle. It has been observed that there exists an optimum combination of temperature viscosity and shear rate for the selected injection molding process. Accordingly, the temperature range 200–260 °C and shear rate 10²–10⁴ s^− 1 are found good for the process. The mold flow profiles for various temperatures and time steps are also presented. The experimental and the simulation results are in good conformity and the strength of FLUENT 6.3 in handling injection mold filling problems is proved to be excellent.     

Effect of weld angle and axial load on the creep failure behaviour of an internally pressurised thick walled CrMoV pipe weld

This paper describes the results of a finite element investigation of the effects of the weld interface angle and end load on the creep failure behaviour of an internally pressurised thick walled pipe weld, using a steady-state approach with an axisymmetric three-material weld model. The material properties used were those for a (1/2)Cr (1/2)Mo (1/4)V: 2(1/4)Cr 1Mo weldment service-exposed at 565°C but with data obtained at 640°C. The failure lives for each weld situation were predicted from the obtained peak rupture stresses, with a range of weld angles and axial loading. Although the effects are small, there are definite trends. The results obtained have shown that with low or moderate end load, there is a consistent increase in failure life with increasing weld angle. However, when the end load is high, the failure lives slightly reduce with increasing weld angle, θ, when θ>15°. The results presented are useful in the general understanding of the geometry/loading influence on the weld performance in power plant pipelines.     

Influence of hydrogen content on the tensile properties and fracture of austenitic stainless steel welds

This study evaluates the effects of internal hydrogen on the tensile properties and fracture behaviours of a tungsten inert gas (TIG) weld and an autogenous electron beam (EB) weld of a 304L steel tube. Tensile specimens were thermally charged with hydrogen gas to achieve three different levels of hydrogen in these materials. Metallographic examination revealed that the TIG weld contained skeletal and lathy ferrite, whilst the EB weld displayed a fine dispersion of skeletal and vermicular ferrite. Average volume fractions of ferrite in these welds were 8% and 1%, respectively. The tensile data showed that hydrogen increased the yield and tensile strength, and caused a significant loss in ductility, particularly for the TIG weld. Fractographic analysis revealed that hydrogen induced a change in the fracture mode of the welds and promoted cracking at or near ferrite–austenite interfaces. The TIG weld was found to exhibit a higher susceptibility to hydrogen embrittlement than that of the EB and base metal.     

Passive mold temperature control by a hybrid filming-microcellular injection molding processing

Microcellular injection molding (also known as Mucell process) with supercritical fluid (SCF) content is capable of producing parts with excellent dimensional stability while using less material, lower injection pressure, and achieving a shorter cycle time. However, most of microcellular processing studies were done on interior morphology, microstructure of the microcellular products, researches and reports on the splay-like appearance, or even a rougher swirl surface which is the restriction for the application of the microcellular injection molding are insufficient. This study investigates the influence of mold temperature on the surface roughness of Polyethylene terephthalate (PET)/Polycarbonate (PC) parts molded by hybrid filming–microcellular injection processing. The PET film is considered as a passive mold temperature controller because of its lower heat transfer coefficient (0.16 J/kg °C) compared with mold base steel of 31.5 J/kg °C. Temperature field changes of mold base caused by different film thickness (0.125 mm, 0.188 mm) were analyzed. The surface roughness of microcellular parts with/without film was measured by a 3D laser microscope. It was found that surface toughness decreases while film thickness increases with minimum surface roughness 1.8 μm. Compared with conventional mold temperature (60 °C), the hybrid molded parts with 0.125 mm film lowered surface roughness from 26 μm to 5.6 μm, to 1.8 μm of 0.188 mm film. And the hybrid processing also improved the uniformity of foamed parts surface quality by eliminating swirl and even surface roughness.     

含交叉裂隙类岩石试样物理力学特性试验及其RFPA模拟

为探究含交叉裂隙试样在单轴应力下的物理力学特性,制备了与岩石力学性质相似的类岩石材料,利用预制树脂片法模拟了不同倾角交叉裂隙的情况,对其进行了单轴压缩试验,同时利用RFPA软件对不同工况进行了数值模拟。结果表明,含交叉裂隙类岩石试样在单轴应力下主要有单一裂隙扩展模式、主裂纹扩展贯通模式、次生裂纹扩展贯通模式三种破坏模式;单一裂隙扩展模式与主裂纹扩展模式下,次生裂隙尖端产生剪破坏,主裂纹尖端产生拉破坏,而次生裂纹扩展模式下主裂纹尖端产生剪破坏,次生裂纹尖端产生拉破坏,最终产生的翼裂纹与反翼裂纹属于拉剪破坏;单轴应力下的含交叉裂隙试样应力-应变曲线经历弹性变形阶段、非线性变形阶段、残余变形阶段三个阶段;主裂纹倾角对含交叉裂隙试样的峰值强度起到控制性作用,而次生裂隙仅在主裂纹倾角为0°时对试样的峰值强度有较大影响。     

Analysis for diving regulator applying local heating mechanism of vapor chamber in insert molding process

This paper aims to use the local heating mechanism, along with the excellent thermal performance of vapor chamber, to analyze and enhance the strength of products formed after insert molding process. In the insert molding process, the metal insert is firstly placed into the mold, and then formed into an embedded plastic product named diving regulator by injection molding. These results indicate that, the product formed by the local heating mechanism of vapor chamber can reduce the weld line efficiency and achieve high strength, which passed the standard of 15.82 N-m torque test, with a yield rate up to 100%.     

Effect of hydrogen charging on the mechanical properties of advanced high strength steels

The present work investigates the influence of hydrogen on the mechanical properties of four multiphase high strength steels by means of tensile tests on notched samples. This was done by performing mechanical tests on both hydrogen charged and uncharged specimens at a cross-head displacement speed of 5 mm/min. A considerable hydrogen influence was observed, as the ductility dropped by 8–60%. In order to demonstrate the influence of diffusible hydrogen, some parameters in the experimental set-up were varied. After tensile tests, fractography was performed. It was found that hydrogen charging caused a change from ductile to transgranular cleavage failure near the notch with a transition zone to a fracture surface with ductile features near the centre.