Evolution of stresses in metal injection molding parts during sintering

The evolution of stresses due to inhomogeneity in metal injection molding （MIM） parts during sintering was investigated. The sintering model of porous materials during densification process was developed based on the continuum mechanics and thermal elasto-viseoplastic constitutive law. Model parameters were identified from the dilatometer sintering experiment. The real density distribution of green body was measured by X-ray computed tomography （CT）, which was regarded as the initial condition of sintering model. Numerical calculation of the above sintering model was carried out with the finite element soRware Abaqus, through the user-defined material mechanical behavior （UMAT）. The calculation results showed that shrinkages of low density regions were faster than those of high density regions during sintering, which led to internal stresses. Compressive stresses existed in high density regions and tensile stresses existed in low density regions. The densification of local regions depended on not only the initial density, but also the evolution of stresses during the sintering stage.

Effects of the Water-Cement Ratio and the Molding Temperature on the Hydration Heat of Cement

The effects of the water-cement ratio and the molding temperature on the hydration heat of cement were investigated with semi-adiabatic calorimetry.The specimens were prepared with water-cement ratios of 0.31,0.38,and 0.45,and the molding temperature was specified at 10 and 20℃.The experimental results show that,as the water-binder ratio increases,the value of the second temperature peak on the temperature curve of the cement paste decreases,and the age at which the peak appears is delayed.The higher the water-cement ratio,the higher the hydration heat release in the early period of cement hydration,but this trend reverses in the late period.There are intersection points of the total hydration heat curve of the cement pastes under the influence of the water-cement ratio,and this law can be observed at both molding temperatures.With the increase in the molding temperature,the age of the second temperature peak on the temperature curve of the cement paste will advance,but the temperature peak will decrease.The higher the molding temperature,the earlier the acceleration period of the cement hydration began,and the larger the hydration heat of the cement in the early stage,but the smaller the total heat in the late period.A subsection function calculation model of the hydration heat,which was based on the existing models,was proposed in order to predict the heat of the hydration of the concrete.

Dependence of Lower Molding Temperature Limit and Molding Time on Molding Mechanism in Dental Thermoforming

Effectiveness and safety of a sports mouthguard depend on its thickness and material, and the thermoforming process affects these. The purpose of this study was to clarify the effects of differences in molding mechanisms on the lower molding temperature limit and molding time in dental thermoforming. Ethylene vinyl acetate resin mouthguard sheet and two thermoforming machines;vacuum blower molding machine and vacuum ejector/pressure molding machine were used. The molding pressures for suction molding were −0.018 MPa for vacuum blower molding and −0.090 MPa for vacuum ejector molding, and for pressure molding was set to 0.090 MPa or 0.450 MPa. Based on the manufacturer’s standard molding temperature of 95˚C, the molding temperature was lowered in 2.5˚C increments to determine the lower molding temperature limit at which no molding defects occurred. In order to investigate the difference in molding time depending on the molding mechanism, the duration of molding pressure was adjusted in each molding machine, and the molding time required to obtain a sample without molding defects was measured. The molding time of each molding machine were compared using one-way analysis of variance. The lower molding temperature limit was 90.0˚C for the vacuum blower machine, 77.5˚C for the vacuum ejector machine, 77.5˚C for the pressure molding machine at 0.090 MPa, and 67.5˚C for the pressure molding machine at 0.45 MPa. The lower molding temperature limit was higher for lower absolute values of molding pressure. The molding time was shorter for pressure molding than for suction molding. Significant differences were observed between all conditions except between the pressure molding machine at 0.090 MPa and 0.45 MPa (P < 0.01). A comparison of the differences in lower molding temperature limit and molding time due to molding mechanisms in dental thermoforming revealed that the lower molding temperature limit depends on the molding pressure and that the molding time is longer for suction molding than for pressure molding.

Non-Darcy Flow in Molding Sands

Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.

Effect of film types on thermal response,cellular structure,forming defects and mechanical properties of combined in-mold decoration and microcellular injection molding parts

Different types of polymer films were used in the combined in-mold decoration and microcellular injection molding(IMD/MIM)process.The multiphase fluid-solid coupled heat transfer model was established to study the thermal response at the melt filling stage in the IMD/MIM process.It was found that the temperature distributed asymmetrically along the thickness direction due to the changed heat transfer coefficient of the melt on the film side.When polyethylene terephthalate(PET)films were applied,the temperature of the melt-film interface increased faster and to be higher at the end of melt filling stage in comparison with the application of polycarbonate(PC)and thermoplastic polyurethane(TPU)films.And the effects of film types on the cellular structure,forming defects and mechanical properties of IMD/MIM parts were also studied experimentally.The results showed that the film types had no obvious effect on the cells size in the transition layer and the mechanical properties of the parts.Under certain film thickness,the offset distance of core layer was the largest with PET film used,while the offset distance was the smallest with TPU film used.And similar results were found for the warpage of the parts.However,an exactly opposite change occurred for the thickness of film-side transition layer and the bubble marks on the surface of the parts.

Vacuum Infusion Molding Process Part 1:VIMP Based on a High-Permeable Medium

The visualization experiments were carried out to investigate the permeability of the high permeable medium (HPM) and the roles of the peel ply and the HPM in the mold filling.The influence of process parameters on mold filling is discussed.Furthermore,the whole vacuum infusion molding process (VIMP) procedure is introduced in detail taking the manufacture of a model boat for example.

Constitutive model and numerical simulation for injection molding of MgTiO_(3) ceramic parts

In order to predict the powder flow law of the injection molding process of MgTiO3 ceramic parts with complex structures,a constitutive model and numerical simulation method for MgTiO3 ceramic injection molding were established based on the Hunt method.The material parameters of MgTiO3 such as elastic modulus,Poisson ratio,glass transition temperature,thermal conductivity and specific heat capacity were measured.Based on the fitting curve and the material parameters measured,the cross-WLF viscosity model and P-V-T model required for MgTiO3 ceramic injection molding were optimized.Furthermore,the influence of process parameters on mold filling flow and distribution of parts defects was researched.It was found that the gate position,injection speed and melt temperature have greater influence on mold filling flow and the packing process has an obvious effect on parts’defects.On this basis,the MgTiO3 ceramic parts injection molding experiment verification was carried out.By comparing the experimental results with the simulated results,it is found that the deformation error is within 1.5%and the density error is within 1%.Therefore,this research provided theoretical guidance for the engineering application of MgTiO3 ceramic parts fabricated by injection molding.

Withdraw: Improvement on Adhesion Properties of Insert Injection Molding Composites: Effect of Inserted Parts, Adhesive Lengths and Injection Conditions

Short Retraction Notice The paper does not meet the standards of "Open Journal of Composite Materials". This article has been retracted to straighten the academic record. In making this decision the Editorial Board follows COPE's Retraction Guidelines. The aim is to promote the circulation of scientific research by offering an ideal research publication platform with due consideration of internationally accepted standards on publication ethics. The Editorial Board would like to extend its sincere apologies for any inconvenience this retraction may have caused. Editor guiding this retraction: Prof. Chengye Fan (EiC of OJCM) The full retraction notice in PDF is preceding the original paper, which is marked "Withdraw".

Vacuum Infusion Molding Process (Part 2 VIMP Based on Grooves)

The optimal parameters for flow grooves and supply grooves were determined by a series of experiments,and the influences of various molding conditions on the mold filling process were analyzed.Furthermore,the whole VIMP procedure based on grooves was introduced in detail taking the manufacture of a sandwich panel as an example.

Numerical Study on the Resin Transfer Molding Curing Process for Thick Composites Materials

The successful manufacture of thick composites is challenging since the highly exothermic nature of thermoset resins and limited temperature control make avoiding the onset of detrimental thermal gradients within the composite relatively difficult.This phenomenon is mainly caused by exothermic heat reactions.The so-called Michaud's model has been largely used in the literature to reduce the gap between experience and simulation with regard to the effective prediction of the temperature cycle in these processes.In this work,another solution is proposed to simulate the curing process for thick composites,namely preheating the resin to activate the curing reaction before resin injection into the mold.A good agreement between the experiment and the simulation is found.Moreover,in order to minimize the thermal gradient in the final composite,the thermophysical properties of the fiber and the torque(temperature,time)of the Plate have been varied leading to interesting results.

Numerical Simulation of Injection Molding of three-Dimensional Thin Parts

This paper is concerned with the numerical simulation of the injection mold filling process. A mathematical model based on generalized Hele-Shaw flow for an inelastic non-Newtonian fluid under nonisothermal conditions is used.A hybrid numerical scheme is employed.The numerical simulating re- sults,pressure and temperature profile,location of the melt fronts,are in a good agreement with the ex- perimental ones.

Effect of Molding Technique That Move Model Position Just before Formation in Production of Laminated Mouthguard

Many molding techniques have been researched to ensure the thickness of custom mouthguards. The aim of this study was to clarify the effect on the thickness of a laminated mouthguard of a molding technique in which the model position is moved forward just before molding. Mouthguards were molded using a 3.0-mm-thick ethylene vinyl acetate mouthguard sheet and a pressure molding machine. The molding method was the normal molding method (condition C) and the molding technique (condition MP) in which the model position was moved 20 mm forward just before molding. Regarding the molding of the first layer (F) and the second layer (S), the following four molding methods based on the combination of conditions C and MP were compared;FC-SC, FC-SMP, FMP-SC, and FMP-SMP. Differences in mouthguard thickness due to molding conditions for the first and second layers were analyzed by two-way ANOVA and Bonferroni’s multiple comparison test. Significant differences were observed among all molding conditions on the labial surface, and the thicknesses were in the order FC-SC < FC-SMP < FMP-SC < FMP-SMP. FMP-SMP was 4.67 mm thick, which was 1.39 mm thicker than FC-SC. FC-SC was the thinnest at the cusp, and a significant difference was observed between other molding conditions. On the buccal side, significant differences were observed between all conditions except FC-SMP and FMP-SC, and the thicknesses were in the order FC-SC < FC-SMP, FMP-SC < FMP-SMP. The results of this study suggested that the labial and buccal sides of laminated mouthguards could be made 1.4 and 1.2 times thicker when a molding technique that moves the model position just before formation was used for the first and second layers. The reduction in thickness was suppressed by approximately 23.2% and approximately 10.7% on the labial and buccal sides, respectively, compared with the normal molding method.

Irregular initial solidification by mold thermal monitoring in the continuous casting of steels:A review

Occasional irregular initial solidification phenomena,including stickers,deep oscillation marks,depressions,and surface cracks of strand shells in continuous casting molds,are important limitations for developing the high-efficiency continuous casting of steels.The application of mold thermal monitoring(MTM) systems,which use thermocouples to detect and respond to temperature variations in molds,has become an effective method to address irregular initial solidification phenomena.Such systems are widely applied in numerous steel companies for sticker breakout prediction.However,monitoring the surface defects of strands remains immature.Hence,indepth research is necessary to utilize the potential advantages and comprehensive monitoring of MTM systems.This paper summarizes what is included in the irregular initial solidification phenomena and systematically reviews the current state of research on these phenomena by the MTM systems.Furthermore,the influences of mold slag behavior on monitoring these phenomena are analyzed.Finally,the remaining problems of the formation mechanisms and investigations of irregular initial solidification phenomena are discussed,and future research directions are proposed.

基于创新性内侧壁成型工艺的多光学通道微型碱金属原子气室

Existing microfabricated atomic vapor cells have only one optical channel,which is insufficient for supporting the multiple orthogonal beams required by atomic devices.In this study,we present a novel wafer-level manufacturing process for fabricating multi-optical-channel atomic vapor cells and an innovative method for batch processing the inner sidewalls of millimeter glass holes to meet optical channel requirements.Surface characterization and transmittance tests demonstrate that the processed inner sidewalls satisfy the criteria for an optical channel.In addition,the construction of an integrated processing platform enables multilayer non-isothermal anode bonding,the filling of inert gases,and the recovery and recycling of noble gases.Measurements of the absorption spectra and free-induction decay signals of xenon-129(^(129)Xe)and xenon-131(^(131)Xe)under different pump-probe schemes demonstrate the suitability of our vapor cell for use in atomic devices including atomic gyroscopes,dual-beam atomic magnetometers,and other optical/atomic devices.The proposed micromolding technology has broad application prospects in the field of optical-device processing.

Research Progress of Biomass Fuel Composite Molding Technology

At present, the technology of biomass fuel composite molding technique is relatively lagging in China, which brings several negative influences, such as high energy consumption, short service life of the equipment. The current situation of the biomass pellet fuel molding technology at home and abroad was introduced, and the development direction in China was put forward, which was of great significance for enhancing the level of pellet fuel molding technology in China.

Numerical simulation of nozzle structure to improve eccentric mold electromagnetic stirring in a round bloom mold

A three-dimensional mathematical model coupling electromagnetic,flow,heat transfer,and solidification has been developed to investigate the effect of eccentric mold electromagnetic stirring(EM-EMS)on the flow and heat transfer of molten steel in round blooms with different cross sections.The uneven distribution of the flow field caused by EM-EMS was improved by changing the straight submerged entry nozzle(SEN)to a four-port SEN.The symmetry index was determined by the velocity distributions on the left and right sides of the center cross section of mold electromagnetic stirring(M-EMS),which quantitatively evaluated the symmetry of EM-EMS on the flow field.In the presence of EM-EMS,the maximum temperature difference ofϕ500 mm andϕ650 mm round blooms between the inner and outer curves amounted to 63 and 26 K,respectively.The maximum distinction between the solidified shells in the inner and outer curves was 11.5 and 5.3 mm,respectively.After using the four-port SEN,the temperature and the shell distribution on the inner and outer curves for theϕ500 mm round bloom were almost the same.The symmetry indices ofϕ500 mm andϕ650 mm round blooms were increased from 0.55 and 0.70 to 0.77 and 0.87,respectively.The four-port SEN can be used to mitigate the negative impact of EM-EMS on the steel flow field.

Analysis and optimization of stamping and forming process of bearing outer ring

To address the common issues of wrinkling,tearing,and uneven wall thickness in the actual sheet metal stamp-ing process of the outer ring of needle roller bearings,this study analyzes critical technical indicators such asforming limits,thickness distribution,and principal strains in the forming process in detail.Three-dimensionalmodels of the concave and convex dies were constructed.The effects of different process parameters,includingstamping speed,edge pressure,sheet metal thickness,and friction coefficient,on the quality of the forming partswere investigated by varying these parameters.Subsequently,the orthogonal experimental method was used todetermine an optimal experimental group from multiple sets of experiments.It was found that under the processparameters of a stamping speed of 3000 mm/s,edge pressure of 2000 N,sheet metal thickness of 0.9 mm,andfriction coefficient of 0.125,the forming quality of the outer ring of the bearing is ideal.

Elimination of cracks in stainless steel casings via 3D printed sand molds with an internal topology structure

The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects are prone to occur.This leads to an increase in the scrap rate of casings,causing significant resource wastage.Additionally,the presence of cracks poses a significant safety hazard after the casings are put into service.The generation of different types of crack defects in stainless steel casings is closely related to casting stress and the high-temperature concession of the sand mold.Therefore,the types and causes of cracks in stainless steel casing products,based on their structural characteristics,were systematically analyzed.Various sand molds with different internal topology designs were printed using the 3DP technology to investigate the impact of sand mold structures on high-temperature concession.The optimal sand mold structure was used to cast casings,and the crack suppression effect was verified by analyzing its eddy current testing results.The experimental results indicate that the skeleton structure has an excellent effect on suppressing cracks in the casing.This research holds important theoretical and engineering significance in improving the quality of casing castings and reducing production costs.

Curcuminoids Inhibit Botrytis cinerea and Colletotrichum gloeosporioides

The growth rate method was adopted to measure the inhibitory effect of curcumin,tetrahydrocurcumin,demethoxycurcumin,and bisdemethoxycurcumin on the mycelial growth of Botrytis cinerea and Colletotrichum gloeosporioides.The results showed that the four curcuminoids inhibited the mycelial growth of the two pathogens in a concentration-dependent manner.Bisdemethoxycurcumin at 600 mg/L exerted the strongest inhibitory effect on the mycelial growth of B.cinerea and C.gloeosporioides,with the relative inhibition rates of 98.19%and 100%,respectively;followed by demethoxycurcumin;curcumin exerted the worst inhibitory effect.Toxicity test results also showed that four curcuminoids all had a certain toxicity to B.cinerea and C.gloeosporioides,among which,bisdemethoxycurcumin exhibited the strongest toxicity,with the EC_(50)of 131.125 and 122.235 mg/L,respectively;while curcumin had the lowest toxicity,with the EC_(50)of 273.143 and 194.943 mg/L,respectively.

Management of Strawberry Grey Mold Disease Using Biocontrol Agents and Plant Extracts

Strawberry (Fragaria × ananassa Duch.) is a significant global soft fruit crop, prized for its nutrient content and pleasant flavor. However, diseases, particularly grey mold caused by Botrytis cinerea Pers. Fr. poses major constraints to strawberry production and productivity. Grey mold severely impacts fruit quality and quantity, diminishing market value. This study evaluated five B. cinerea isolates from various locations in the Ri-Bhoi district of Meghalaya. All isolates were pathogenic, with isolate SGM 2 identified as highly virulent. Host range studies showed the pathogen-producing symptoms in the fava bean pods, marigold, gerbera, and chrysanthemum flowers and in the fava bean, gerbera, and lettuce leaves. In vitro tests revealed that neem extract (15% w/v) achieved the highest mycelial growth inhibition at 76.66%, while black turmeric extract (5% w/v) had the lowest inhibition at 9.62%. Dual culture methods with bio-control agents indicated that Bacillus subtilis recorded the highest mean inhibition at 77.03%, while Pseudomonas fluorescens had the lowest at 20.36% against the two virulent isolates. Pot evaluations demonstrated that B. subtilis resulted in the lowest percent disease index at 20.59%, followed by neem extract at 23.31%, with the highest disease index in the control group at 42.51%. Additionally, B. subtilis significantly improved plant growth, yielding an average of 0.32 kg compared to 0.14 kg in the control. The promising results of B. subtilis and neem leaf extract from this study suggest their potential for eco-friendly managing grey mold in strawberries under field conditions.