粉末注射成型最佳粉末装载量的确定方法研究

分析了不同粉末装载量下。喂料内黏结剂和粉末分布情况,估算出一晦界粉末装载量值;通过对同一配方黏结剂,不同粉末装载量的喂料,以及在转矩流变仪中混料过程的研究及毛细管流变仪中表观黏度的测定。得出最佳粉末装载量的试验值。试验结果表明,最佳粉末装载量试验值比估算值小约2％,本文中的方法可以作为最佳粉末装载量的简易测定方法。     

A rapid and precision hot embossing of LGP micro-arch lens array inside core microgrooves: simulation and experiment

The hot embossing needs the heat preservation for precision micro-forming, thus leading to inefficiency. A hot embossing of polymer micro-arch lens array in half molten is proposed for the application of light guide plate (LGP). It only performs a thermal deformation for micron-scale surface layer to be squeezed into core microgrooves. First, the micro-optic illumination of LGP was analyzed to design the micro-arch lens array; then the micro-grinding was employed to machine smooth microgrooves on ceramic core die; finally, the hot embossing experiments were conducted to adjust the thermal and structural parameters for modeling micro-arch height. It is shown that the micro-arch lens array may be rapidly and precisely formed inside the core microgrooves in half molten. The micro-arch height reaches 22 μm at a loading time of 5 s. The loading temperature and the core microgroove angle greatly influence the micro-arch height. The parameterized model of micro-arch height and radius may be used to optimize the hot embossing variables and the core microgroove parameters. The LGP patterned with the micro-arch lens array increases the irradiance intensity by 16% and its uniformity by 210% compared with smooth one, respectively.     

TiH2粉注射成形用新型粘结剂的研制及其性能

研发了一种适合TiH2粉注射成形用新型石蜡基粘结剂,对粘结剂组元间的相容性进行了计算,并分析了该粘结剂的流变性能和脱脂性能。结果表明:该新型粘结剂各组元相容性好,能够与TiH2粉实现良好混合,装载量(体积分数)达到70%以上;粘结剂流变性能佳且稳定,在注射温度为160℃和剪切速率为125s-1的条件下,黏度为0.081Pa.s,粘流活化能为36.85kJ.mol-1;与常规石蜡基粘接剂相比,在同样工艺条件下使用正庚烷脱脂时相同时间下脱脂率提高20%～30%;脱脂坯缺陷少、保形性好;与原料粉相比,经过热脱脂后坯样的碳含量仅增加了0.02%,氧和氮含量均降低。     

Small-hole arrays of ceramic material manufactured by micro powder injection molding

Ceramic substrate with three kinds of small-hole arrays (the minimum diameter is 400?μm) was manufactured by micro powder injection molding. The homogeneity, thermal, and rheological properties of the feedstock was characterized by means of SEM, Archimedes method, TGA, DSC, and capillary rheometer, respectively. The feedstock has good uniformity and the viscosity of feedstock accords with the pseudo-plastic behavior which is suitable for micro powder injection molding. The test results also show that the linear shrinkage of small holes is lower than the substrate which is important to mold design and size contraction of the sample. Moreover, the porosity of the sintered substrate is lower than that of the thin wall between two neighborhood small holes. Good surface roughness of the sintered samples is obtained by using sub-micron ZrO₂ powder which is even lower than molded surface. The relative density and hardness of the ceramic substrate with small-hole arrays sintered under 1,500°C for 2?h is 98.3% and 13.68?GPa, respectively.     

Densification of alumina components via indirect selective laser sintering combined with isostatic pressing

To improve the final density of ceramic parts via indirect selective laser sintering (SLS), cold/hot isostatic pressing (CIP/HIP) technologies were introduced into the process. The proposed approach in the present study combined spray drying with mechanical mixing by which we prepared a kind of compound powder consisting of polyvinyl alcohol (PVA, 1.5 wt%), epoxy resin E06 (8 wt%), and alumina so as to get a good fluidity for SLS. At the first step, SLS parts reached the highest relative density of about 32 % when the laser energy density was 0.094 J/mm², which facilitated the next operation and improvement of final density. Then, a soft polymer canning was prepared for CIP around the surface of SLS alumina ceramic parts using pre-vulcanized natural rubber latex RTV-2, gelation and film. Following that, we experimented on different CIP maximum pressure which had different effects on densification of SLS alumina parts, the whole process in CIP was divided into three stages of I, II, and III. Based on thermal gravity curve of epoxy resin E06, ignoring the impacts of the only 1.5 wt% PVA on degreasing, green bodies were degreased and furnace-sintered. Finally, the relative density of alumina parts reached 95.94 % after HIP process. Field emission scanning electron microscopy was used to analyze the densification evolvement in each stage of process and the fracture mechanism. The study showed a positive and practical approach to manufacture ceramic matrix and ceramic components with complex shape by indirect SLS technology.     

Process development for green part printing using binder jetting additive manufacturing

Originally developed decades ago, the binder jetting additive manufacturing (BJ-AM) process possesses various advantages compared to other additive manufacturing (AM) technologies such as broad material compatibility and technological expandability. However, the adoption of BJ-AM has been limited by the lack of knowledge with the fundamental understanding of the process principles and characteristics, as well as the relatively few systematic design guideline that are available. In this work, the process design considerations for BJ-AM in green part fabrication were discussed in detail in order to provide a comprehensive perspective of the design for additive manufacturing for the process. Various process factors, including binder saturation, in-process drying, powder spreading, powder feedstock characteristics, binder characteristics and post-process curing, could significantly affect the printing quality of the green parts such as geometrical accuracy and part integrity. For powder feedstock with low flowability, even though process parameters could be optimized to partially offset the printing feasibility issue, the qualities of the green parts will be intrinsically limited due to the existence of large internal voids that are inaccessible to the binder. In addition, during the process development, the balanced combination between the saturation level and in-process drying is of critical importance in the quality control of the green parts.     

Selective laser melting W–10 wt.% Cu composite powders

Tungsten–Copper (W–Cu) alloys are promising materials for electrical and thermal applications. However, its forming method still remains limited in conventional powder metallurgy technique which is not suitable for manufacturing parts with intricate shapes. In this work, selective laser melting technology was introduced for fabricating W–10 wt.% Cu alloys parts. The morphological feature of a single molten track was analyzed. The results show that liquid phase sintering with complete melting of the binder (Cu), but nonmelting of the structural metal (W), acts as the main mechanism in this process. The melting conditions of single layers in different processing parameters were investigated. The results show that a moderate melting zone can be acquired from an established process map. Moreover, investigations on multilayers forming show that the final density increases with the decrease of scan speed until it reaches a plateau due to the insufficient rearrangement in liquid phase sintering and the balling effect.     

Experimental analysis and numerical simulation of sintered micro-fluidic devices using powder hot embossing process

For the past 2 years, interest in manufacturing technologies based on micro-fluidic systems has been continuously increasing. Today, micro-fluidic systems are used in numerous biomedical and pharmaceutical applications. Micro-fluidics cannot be thought about separately without advances in micro- and nano-fabrication. Investigations based on experiments, finite element modelling and simulations of powder hot embossing process (PHE) were performed to optimise the sintering step and processing parameters of micro-fluidic components. The model pertaining to thermo-elasto-viscoplastic behaviour was identified for 316L stainless steel powders. In this regard, different material properties such as sintering stress, bulk, and shearing viscosities were identified by inverse analysis from present dilatometer measurements using beam-bending and free sintering tests. The identification of materials was performed for various powder volume loadings and kinetic rates for different 316L elaborated feedstock, and the parameters were obtained as functions of relative density. The initial inhomogeneity due to the PHE process has been taken into account in the sintering simulation, as it affects the final shrinkage of the sintered components. The solid-state sintering simulations were investigated for various final sintering temperatures and kinetic rates to obtain high and homogeneous relative density distributions, achieve isotropic shrinkage and optimise the sintering process parameters. The numerical simulations were realised based on the identified parameters on a 3D micro-structured specimen with an associated rectangular plate support elaborated by PHE; this allowed a comparison between the numerical predictions and the experimental results for the sintering stage. The finite element simulation results of the sintering stage with a micro-fluidic structured component at a high final temperature (1360 °C) are in excellent agreement with the results of the experiments. The comparison of the simulation and experimental results validated the identified and implemented physical model and proposed methodologies.     

Determination of the flow stress and thermal properties of ceramic powder feedstock in ceramic injection molding

To simulate numerically the material behavior of a ceramic powder feedstock that consist of a two-phase mixture of zirconia powder and polymer binder, a material model is needed that incorporates the change in volume fraction and temperature dependency of viscosity. Heat transfer occurs between the feedstock and the mold during ceramic injection molding (CIM). The feedstock is heavily influenced by thermal properties such as thermal conductivity and specific heat. In this study, three models are proposed to explain the material and thermal properties: a rigid-plastic flow stress model that is dependent on volume fraction and viscosity, a thermal conductivity model, and a specific heat model as a function of temperature. The material parameters in each model are obtained by using the optimization method. Error functions are defined as the differences between the experimental measurements and numerical simulation results. The parameters are determined by minimizing the error functions. The confirmation simulation for each model is conducted by applying cases that are not directly used in the optimization. The results of the confirmation simulation tend to follow the experimental results well, with correlation coefficients exceeding 0.92. The numerical simulation of the CIM process with the determined parameters is compared with the flow behavior of an actual CIM process. Simulation results, such as flow pattern and direction, are in good agreement with the measured feedstock behavior. Therefore, the method for determining the material parameters of the proposed models is feasible.     

NBR Powder Modified Phenolic Resin Composite: Influence of Graphite on Tribological and Thermal Properties

The incorporation of graphite as a solid lubricant in the formulation of brake friction material is well-recognized practice. However, achieving the desired level of performances using graphite is still a significant challenge, due to difficulty in dispersion and loading of graphite in composite materials. The present investigation was aimed at identifying the effect of graphite loading on the tribological and thermal properties of a composite made from phenolic resin modified with powdered acrylonitrile butadiene rubber (NBR). Five composites were prepared with different proportions of graphite (0–40 phr) to the phenolic resin. Thermogravimetric analysis (TGA) and thermal conductivity measurements were carried out to demonstrate the thermal stability and thermal conductivity behaviors. Both the thermal stability and thermal conductivity were found to increase with an increase in graphite content. On the other hand, the tribological properties were found to be optimum at a definite loading of graphite (30 phr). The change in surface morphology of these composites was studied before and after the friction test and correlated with the tribological properties. This investigation provides guidelines for achieving a high-performance composite using graphite for brake friction materials.     

Microstructural evolvement and formation of selective laser melting W–Ni–Cu composite powder

W–Ni–Cu alloy (90 wt% W, 7.5 wt% Ni, and 2.5 wt% Cu) parts were successfully fabricated via selective laser melting method. Phases, microstructure, compositions, and laser forming parameters of laser melted samples were investigated. It was found that the W–Ni–Cu powder system was based on the mechanism of liquid solidification. This process was realized through full melting of W, Ni, and Cu particles under high laser energy input. However, using relatively lower energy input, particle bonding was realized through liquid phase sintering with complete melting of Ni–Cu acting as binder and nonmelting of W acting as structure. Due to the Ni–Cu solid solution phase that appeared in a wide range from 1,084 to 1,455 °C, a coherent matrix interface can be observed after solidification. The microhardness of laser-fabricated specimens varied with different powder layer thicknesses, resulting from the laser-treated condition and ability of trapped air in the loose powder bed to escape. The metallurgical mechanisms were also addressed.     

Moulage par injection de poudres métalliques. Expérimentation,modélisation et simulation

Metal injection moulding. Experiment, modelling and simulation. The metal injection moulding process is used to produce small and complex metallic components. The first step is the injection of a mixture composed by a metallic powder and a thermoplastic binder. The binder is eliminated by a thermal or catalytic debinding. The last step is the sintering in order to obtain a part with the correct size and required mechanical properties. The metal injection moulding process is analysed using both experiments and computational modelling. A numerical approach for biphasic mixtures has been developed to analyse the flow of the feedstock during injection. The solution of the Navier–Stokes equations is made by an implicit finite element method. The mould filling simulation uses an Eulerian formulation with a VOF method. The simulation gives the density field in order to detect the segregation zones leading to an anisotropic shrinkage. The modelling of the solid state sintering is based on a viscoplastic model. The results obtained by experiments and numerical simulations are compared and reveal a good agreement. Furthermore, the components obtained after injection, debinding and sintering have the correct size and required mechanical properties.     

阵列式微流道的粉末微注射成形技术

作为一种近净成形技术,粉末微注射成形具有低成本、高精度、高效率的特点,在成形微小型复杂形状的零件方面优势突出。文中详述了粉末微注射成形制备工艺,采用纳米级粉末材料,通过优化成形参数,成功制备了满足实际使用要求的阵列式微流道零件,成形精度误差低,不超过1.5%,降低成本50%以上。此粉末微注射成形制备阵列式微流道技术对电子机械领域微小型电子元器件的设计和制造具有重要的借鉴意义。     

Effect of metal particle size and powder volume fraction on the filling performance of powder injection moulded parts with a microtextured surface

Metal injection moulding of miniaturized devices demands unique feedstock materials and mould designs with high dimensional accuracy. In this work, the influences of the powder size and powder content of 17–4 PH stainless steel feedstock and the influence of mould design on the successful production of micro-scaled structures were investigated. Ni mould inserts with high dimensional accuracy and texture sizes of 50–200 μm using a new microtexturing technique were manufactured. 17–4 PH stainless steel feedstocks with powder sizes (D₉₀) of 10 and 22 μm and powder contents of 60 and 65 vol.-% were compounded. The rheological properties of the obtained feedstocks were characterized with a capillary rheometer to assess their flowability. The results showed that 10 μm sized particles caused a slight but not significant increase in the viscosity. The highest viscosity increase occurred when the powder content increased from 60 to 65 vol.-%. Feedstocks with the 10 μm powder particles ensured complete filling within microtextures for all mould variations. However, when using feedstocks with 22 μm particles, the filling capabilities of the 50 and 100 μm microtextures decreased with increasing powder content. The shape retention was better for those micropillars produced with mould inserts with 200 μm cavities than for the micropillars replicated with the inserts having cavities of 50 and 100 μm. The results indicated that the proposed mould insert preparation technique opens new possibilities for mass production using the μMIM process to create micro-scaled components using feedstocks without nanoparticles.     

金属注射成形的数值模拟和高效算法

金属注射烧结成形的注射模拟不同于普通的塑料注射工艺。注入模具的是金属粉末和塑性流动剂构成的均匀混合喂料。除流动本构显著不同外，注射结果的匀质性分析是一项重要内容。混合理论的应用和高效显式算法的开发与研究，是解决这一问题的关键。对模拟结果与试验结果进行了比较和对照，验证了该方法的有效性。     

Effect of two different rubbers as secondary binders on the friction and wear characteristics of non-asbestos organic (NAO) brake friction materials

Binder provides structural integrity by holding all ingredients in the composition of a brake friction material. The modified binders have played a major role in improving the frictional performance and thermal resistance of the friction material. The present research work evaluates the influence of secondary binders (Nitrile Butadiene rubber (NBR) and Styrene Butadiene rubber (SBR)) on the tribological performance of the friction material using a full-scale inertia brake dynamometer as per JASO C406 standard. Three brake pads were developed by varying the type and composition of secondary rubber binder (5%NBR, 5%SBR and 2.5%NBR + 2.5%SBR) with rest of the ingredients kept unaltered. It was found that the quantity of SBR rubber powder present as secondary binder improved dry and wet recovery. Friction coefficient (μ) exhibited better stability during the fade with the inclusion of both the rubber powders. The friction material with the inclusion of both the NBR and SBR rubber powders exhibited overall better performance than compared to the inclusion of only one secondary binder rubber in the composition. The worn-out surface of the developed friction materials and the counter discs were characterised using FESEM.     

The effect of billets extruded by a curved and flat-face die on the semisolid characteristics and tensile properties of thixoformed products

In this study, A356 aluminum billets in different extruded states are used as feedstock for the thixoforming. The extrusion billets were fabricated by a hot extrusion process through a flat-face and a curved die. After the induction reheating of the extrusion billets into a semisolid state, the microstructural evolution was thoroughly investigated. For the extrusion alloy by the flat-face die, there was a large variation in the average grain size (20 %) and the mean roundness (17 %) of equiaxed α-Al grains. This, together with evidence of elongated grains in the interior regions of the billet, indicated that a noticeably nonuniform globular microstructure had been obtained. In contrast, for the extrusion alloy through the curved die, the obtained globular microstructure was more uniform. There were slight variations of 5 % and 7 % in the average grain size and the mean roundness, respectively. By using the extrusion billets, some parts fabricated via the thixoforming process those underwent T6 heat treatment. The tensile test results for the fabricated parts showed that when the extrusion billet through the conventional flat-face die was used as the feedstock, there was a large scattering in the tensile properties throughout the part. In contrast, when the extruded billet through the curved die was used as the feedstock, limited variation was observed in the tensile properties.     

Role of elongational viscosity of feedstock in extrusion-based additive manufacturing of powder-binder mixtures

The 3D printing of metals and ceramics by the extrusion of a powder/thermoplastic binder feedstock is an extrusion-based additive manufacturing (EAM) techn     

Laser shock wave treatment of polycrystalline diamond tool and nanodiamond powder compact

Laser shock processing (LSP) of polycrystalline diamond (PCD) tools and nanodiamond powder compacts was conducted using a 1,064-nm Q-switched Nd:YAG laser at peak power densities in the range of 4 to 18 GW/cm² and pulse repetition rates of 1 to 10 Hz. The PCD tools were directly procured from the tool manufacturer while nanodiamond powder compacts were prepared in the laboratory by cold die press forming and annealing using a powder mixture of nanodiamond, 8 wt.% cobalt, and 10 wt.% agar–agar as the binder. The samples were characterized by Raman spectroscopy, scanning electron microscopy, micro-indentation, and optical profilometer. Results indicate that LSP induced diamond purification, inhomogeneity of phases in PCD, densification in nanodiamond compact, phase transition to various amounts of sp³ and sp² carbon forms, and an increase in hardness and surface roughness.     

CR 200J用树脂基摩擦材料的正交试验及多指标加权优选

为制备CR 200J用高耐磨树脂基摩擦材料,采用正交试验法设计不同含量的减摩组分(鳞片石墨、石油焦)与增摩组分(NFJ高温黏结剂、腰果壳油摩擦粉)的树脂基摩擦材料配方。通过热压成型法制备出样品,在制动压力0.8 MPa和转速3 300、4 200、5 400 r/min下测试试样的平均摩擦因数,并计算试样的体积磨损率、热衰退性能及对偶质量磨损。对试样的平均摩擦因数、体积磨损率、热衰退性能及对偶质量磨损进行极差分析及均一化处理,使用多指标权重优选了综合性能优异的配方。结果表明：鳞片石墨在高转速下对材料的平均摩擦因数起稳定作用及降低材料的热衰退性能,而石油焦在低速制动过程中可稳定材料的平均摩擦因数;NFJ高温黏结剂对材料的各项性能影响不显著,而腰果壳油摩擦粉在高转速下表现出优异的黏弹性,有利于提高材料的平均摩擦因数,降低材料的体积磨损率及对偶质量磨损。使用多指标权重优选得到较好的配方,其中鳞片石墨、石油焦、NFJ高温黏结剂、腰果壳油摩擦粉的质量分数分别为1%、4%、3%、6%。