Zr基非晶合金微热压印实验研究

利用微正挤压试验,研究了Zr65Cu17.5Al7.5Ni10非晶合金试样在不同温度和挤压速度下的微热压印过程,分析影响微流槽填充成形的工艺因素,利用泊肃叶公式找到描述微流槽热压印过程的工艺参数方程。结果表明,热压印过程受温度、挤压速率、槽宽等因素的影响,进而可以得到最佳的工艺参数范围;用泊肃叶公式能够较好的描述微流槽填充过程,并可以得到包含微热压工艺参数的方程,结合一些假设,可以解释某些实验现象并指导工艺参数的设定。     

Preventing non-uniform shrinkage in open-die hot embossing of PMMA microstructures

The quality of a product made by hot embossing is affected by its cooling shrinkage. The special pressure-specific volume–temperature characteristics of polymer are such that the specific volume of polymer varies with pressure during cooling. Therefore, the shrinkage of polymer depends on the embossing pressure. This paper analyzes, both analytically and numerically, the pressure distributions on the surface of polymer during hot embossing process. The results indicate that a higher embossing pressure results in more uniform shrinkage in the elastically deformed state during cooling.     

Finite element simulation and experimental investigation of forming micro-gear with Zr–Cu–Ni–Al bulk metallic glass

Bulk metallic glasses exhibit some unique physical properties as compared to their corresponding crystalline alloys. Due to the superplasticity by behaving like a Newtonian fluid in their supercooled liquid region, the bulk metallic glasses can be used to make high strength microparts by net-shape forming. In this paper, the compressive tests of Zr–Cu–Ni–Al metallic glass are performed with different strain rates at a temperature of 683 K. According to the experimental results, the forming evolution of a metallic glass micro-gear is simulated using a finite element simulation software DEFORM 3D, and the forming load is predicted at different processing parameters. Meanwhile, the filling stages of bulk metallic glass in the micro-gear mold cavity are investigated by finite element simulation and experiment. The predicted workpiece geometry shows good agreement with experimental result. The forming experiments for micro-gear of Zr–Cu–Ni–Al metallic glass are carried out by hot embossing process, and the amorphous micro-gears are obtained successfully. It is found that the finite element simulation results are in reasonable agreement with the experimental observation.     

Superplastic micro-forming with a fine grained Zn–22Al eutectoid alloy using hot embossing technology

A novel micro-forming method, combining a metal's superplastic behavior with hot embossing technology, has been developed for manufacturing micro components from a fine-grained Zn–22Al eutectoid alloy. The forging characteristics of this alloy have also been studied using a Gleeble simulation machine.

Experimental results indicated that neither fiber-flow lines nor internal cracks could be observed when the fine-grained Zn–22Al eutectoid alloy was forged at a temperature range from 150 to 200 °C under a compressive strain rate range from 0.6 to 0.006 s⁻¹. A good dimensional accuracy for a mini compound spur gear was obtained by using hot embossing technology. Finally, a 5:1 mini reduction gear train was assembled. Its rotational motion was very continuous and smooth, indicating that the micro-forming method is a suitable technology for manufacturing micro metal components for Micro Electro Mechanical Systems (MEMS).     

Fabrication of aspheric surface using ultraprecision cutting and BMG molding

A new process to replicate an aspheric lens is presented in this study. A mold of oxygen free copper (OFC) is fabricated using ultraprecision machining, which is a popular material for machining due to its good machinability. But OFC has a very low hardness of 1.606 GPa, it is not suitable for the subsequent molding process. Then, this OFC mold (known as the first mold) is used to hot emboss on Mg₅₈Cu₃₁Y₁₁ amorphous alloy to form a secondary mold which is one kind of metallic glass. The hardness of the secondary mold is as high as 3.445 GPa, whereas the glass transition temperature (T_g) of the Mg₅₈Cu₃₁Y₁₁ metallic glass is as low as 413 K (140 °C), at which the Mg₅₈Cu₃₁Y₁₁ metallic glass shows a good glass-forming ability (GFA). In order to perform superplastic microforming, the working temperature must be close to the glass temperature around 413 K. Therefore, in this study, the temperatures of the hot embossing experiments to fabricate the secondary mold are set at 423 K (150 °C). It shows experimentally that the working temperature is dependent on the applied stress level. Since the Mg₅₈Cu₃₁Y₁₁ metallic glass has superplastic property at the supercooled liquid region, it can be easily formed by the master die. This embossing process on the Mg₅₈Cu₃₁Y₁₁ metallic glass makes molding process faster and more diverse applications. Next, the secondary mold is used to emboss on polymethylmethacrylate (PMMA) sheets for replication process. The Mg₅₈Cu₃₁Y₁₁ metallic glass is not only a good material for hot embossing process to fabricate micro-structure directly, but also an excellent fast-molding material for hot embossing process. It is expected that the machining processes described in this paper could be applied to the related fields to fabricate precision components required of micro, sub-micro, or nano order of dimensional accuracy.     

The manufacturing and replication of microfluidic mould inserts by the hot embossing process

In this paper, the manufacturing of metallic microfluidic mould inserts is studied based on the hot embossing process. The feedstocks are prepared and analysed. The quality of the feedstock resulting from the mixing process is found to depend on numerous parameters, such as the mixing time, the mixing temperature, the shear rate and the powder loading. The present mixing study is conducted with copper powders. The thermal and rheological properties of the selected feedstock under various mixing conditions are determined and used to establish the necessary conditions for mixing, hot embossing and debinding to obtain the copper microfluidic mould inserts. Sintering at different temperatures is conducted under vacuum. The effects of the sintering temperatures are evaluated based on the sintered microstructures. In this work, the dimensional variations in the microfluidic samples, in particular the dimensional shrinkage, global warpage and surface roughness at each stage of the process, are quantified and compared in detail.     

基于数值模拟的多模腔熔料填充流动平衡工艺优化

采用热流道系统的多模腔精密注射成型熔料的平衡填充过程较普通冷流道复杂。利用数值模拟对热流道板的温度场分布进行分析,优化热流道板的结构,获得较为合理的温度场分布,从而改善多腔注射模的平衡填充效果,提高制品质量和尺寸精度。     

鲨鱼皮微结构微电铸复制工艺研究

选择鲨鱼皮表面微结构作为复制模板,利用热压法制备PMMA阴模板,以导电化处理后的PMMA阴模板作为电铸电极,电铸形成仿鲨鱼皮铜模具。对比分析不同电流密度和占空比下铜模具的表面形貌和疏水性能。结果表明,占空比为40%及电流密度为4 A/dm2时,微电铸形成的铜模具表面鲨鱼皮微结构较清晰,槽宽变形量为4.4%,最大接触角可达116°,具有较好的疏水性能。     

Influence of Liquid Film Characteristics on Hot Cracking Initiation in Al-Cu Alloys at the End of Solidification

In this study, Al-4Cu alloy specimens with spherical grains and liquid films were obtained by isothermal reheating treatment. The hot cracking of the solidification process was determined using a modified constrained rod casting experimental apparatus, and the effect of liquid film characteristics at the end of solidification on hot cracking initiation of Al-4Cu alloys was systematically investigated by combining molecular dynamics simulations and other methods. With the extension of soaking time, the liquid fraction (liquid film fraction at the end of solidification) and grain shape factor increased with higher isothermal reheating temperatures. Additionally, the widened filling channel decreased the hot cracking initiation temperature and the critical hot cracking shrinkage stress was found to increase, thus reducing the hot cracking severity in Al-4Cu alloys. Molecular dynamics simulations revealed that with the extension of soaking time, the composition of the liquid film changed at different isothermal reheating temperatures, but the short-range structure and atomic ordering of the liquid film remained the same. The activity of the liquid film increased in equilibrium, leading to a decrease in viscosity and an increase in fluidity, which contributed to the filling behaviour. After isothermal reheating at 640 °C for 60 min, the liquid fraction reached the maximum, and the viscosity of the liquid film was the minimum. In addition, almost no hot cracks were found.     

Ti-3.0Al-3.7Cr-2.0Fe-0.1B钛合金的热压缩行为(英文)

利用Gleeble-1500D热模拟试验机对低成本钛合金Ti-3.0Al-3.7Cr-2.0Fe-0.1B的热压缩行为进行研究。采用的应变速率分别为0.01、0.1、1.0和10s1,选用的温度分别为800、850、900和950°C,试样的变形量最大为70%。结果表明:峰值流变应力随着温度的增加和应变速率的降低而降低;根据Arrhenius公式获得该合金在本实验条件下的本构方程为ε=6.1×1012[sinh(0.0113044σ)]3.35×exp(-261719.8/RT),并得到了该合金的加工图。当应变速率大于等于1.0s1时,合金内发生动态再结晶现象,且应变速率越大动态再结晶现象越明显。     

Characterization of hot deformation and microstructure evolution of a new metastable β titanium alloy

The hot deformation characteristics of as-forged Ti?3.5Al?5Mo?6V?3Cr?2Sn?0.5Fe?0.1B?0.1C alloy within a temperature range from 750 to 910 °C and a strain rate range from 0.001 to 1 s^?1 were investigated by hot compression tests. The stress?strain curves show that the flow stress decreases with the increase of temperature and the decrease of strain rate. The microstructure is sensitive to deformation parameters. The dynamic recrystallization (DRX) grains appear while the temperature reaches 790 °C at a constant strain rate of 0.001 s^?1 and strain rate is not higher than 0.1 s^?1 at a constant temperature of 910 °C. The work-hardening rate θ is calculated and it is found that DRX prefers to happen at high temperature and low strain rate. The constitutive equation and processing map were obtained. The average activation energy of the alloy is 242.78 kJ/mol and there are few unstable regions on the processing map, which indicates excellent hot workability. At the strain rate of 0.1 s^?1, the stress?strain curves show an abnormal shape where there are two stress peaks simultaneously. This can be attributed to the alternation of hardening effect, which results from the continuous dynamic recrystallization (CDRX) and the rotation of DRX grains, and dynamic softening mechanism.     

120°模具室温ECAP制备工业纯钛的压缩变形本构关系

在Gleeble-1500热模拟机上对120°模具室温Bc方式ECAP变形8道次制备的平均晶粒尺寸约为200 nm的工业纯钛进行等温变速压缩实验,研究超细晶工业纯钛在变形温度为298~673 K和应变速率为1×10-4~1×100s-1条件下的流变应力行为。结果表明:变形温度和应变速率均对流变应力具有显著影响,峰值应力随变形温度的升高和应变速率的降低而降低;流变应力在变形初期随应变的增加而增大,出现峰值后逐渐趋于平稳,呈现稳态流变特征。采用双曲正弦模型确定了超细晶工业纯钛的变形激活能Q=104.46 kJ/mol和应力指数n=23,建立了相应的变形本构关系。     

Enhanced machining of micron-scale features in microchip molding masters by CNC milling

An improved approach for the generation of aluminum masters used in the replication of polymer-based microfluidic devices is proposed. It is commonly assumed that conventional computer numerical controlled (CNC)-milling yields insufficient specifications for use in micro-milling. As molding masters suitable for microfluidic device replication require features whose dimensions are on the order of tens to hundreds of microns, the previous limitations of CNC-milling include machining tolerances that exceed 25% of the machined feature and inability to mill intersecting features. Here, we present several novel and advanced machining techniques to overcome existing limitations of a CNC-milling based approach. To achieve microfeatures with tolerances up to a factor of ten better than expected from the CNC-mill used, external calibration and measurement of the milling process was employed. To reduce the unwanted volume occurring from two intersecting features, 102 μm dia. high-density micrograin carbon endmills were used with all milling steps externally calibrated and measured. To generate masters with abutting features of different widths, keyway slots were milled into the master that could accommodate various size molding master keys. In addition to adding flexibility to the downstream embossing step, the use of keys eliminated dead-volume effects. A variety of molding masters have been machined and characterized in this work. Taken together, these approaches illustrate that conventional CNC-milling using equipment commonly found in university machine shops is a viable alternative to other more expensive master generation processes. Molding masters can be machined to yield high aspect ratio microfeatures with a tolerance of ±4 μm, and these masters can then be used in conjunction with casting or hot embossing to produce polymer microchip platforms suitable for analytical use.     

35% SiC_p/2024A1复合材料的热变形行为(英文)

采用Gleeble-1500D热模拟试验机,对35%SiCp/2024A1复合材料在温度350~500°C、应变速率0.01~10s-1的条件下进行热压缩试验,研究该复合材料的热变形行为与热加工特征,建立热变形本构方程和加工图。结果表明,35%SiCp/2024A1复合材料的流变应力随着温度的升高而降低,随着应变速率的增大而升高,说明该复合材料是正应变速率敏感材料,其热压缩变形时的流变应力可采用Zener-Hollomon参数的双曲正弦形式来描述;在本实验条件下平均热变形激活能为225.4 kJ/mol。为了证实其潜在的可加工性,对加工图中的稳定区和失稳区进行标识,并通过微观组织得到验证。综合考虑热加工图和显微组织,得到变形温度500°C、应变速率0.1~1 s-1是复合材料适宜的热变形条件。     

Numerical simulation and its application ofrheological forming of titanium alloy vane disk

The hot rheological forming method was proposed to form the second titanium alloy vane disk. The hot rheological forming process of the TC 11 titanium vane disk under a certain temperature and different strain rates was investigated by using the bulk forming software of DEFORM 3D. A series of results including temperature field, equivalent strain distribution, load-stroke curve and rheology procedure were obtained by this finite element method. The rheological forming characteristics were well realized and the forming parameters were determined. The results and analysis show that with decreasing strain rate, the metal flow more equably and the filling of the vane shape is also better. Moreover, the mechanical properties and microstructures of the products produced by this new technique are improved evidently compared with that produced by traditional method.     

Characteristics of Ni-Ir and Pt-Ir hard coatings surface treated by pulsed Nd:YAG laser

The subjects of the presented paper are to develop a laser surface treatment technology for the protective coatings of glass-molding dies and to better understand the interaction between laser beam and materials coated on the die surface. A variety of alloy films, including Ir-25 at.% Pt, Ir-50 at.% Pt, Ir-75 at.% Pt, Ir-25 at.% Ni, Ir-50 at.% Ni, and Ir-75 at.% Ni compositions are deposited by the ion source assisted magnetron sputtering system (ISAMSS). A Cr layer that functioned as a buffer layer is deposited between the alloy film and die surface. After an alloy film and the buffer Cr layer were sequentially coated on tungsten carbide (WC) surface, Nd:YAG laser was directly applied in the writing process. The temperature profile of the film stack structure is simulated by ANSYS software. The surface roughness was analyzed by atomic force microscopy (AFM) to compare the coating surface roughness before and after the laser surface treatments. The treated coatings for oxidation prevention test were examined by energy dispersive x-ray spectrometry (EDS). Nanoindentation instrument was performed to evaluate microhardness and reduced modulus of the coatings. The cross-sectional structures between the hard coating layer and buffer layer were also inspected by a scanning electron microscope (SEM). The Pt-Ir and Ni-Ir film coatings are unable to withstand the working temperature over 1500 °C, which is considered for quartz molding process and hot embossing process. The films showed high roughness, low microhardness and low reduced modulus because the film oxidation occurred in a high working temperature process.     

7150铝合金高温热压缩变形流变应力行为

在Gleeble-1500热模拟机上对7150铝合金进行高温热压缩实验,研究该合金在变形温度为300~450 ℃和应变速率为0.01～10 s~(-1) 条件下的流变应力行为.结果表明:流变应力在变形初期随着应变的增加而增大,出现峰值后逐渐趋于平稳;峰值应力随着温度的升高而减小,随着应变速率的增大而增大;可用包含Zener-Hollomon参数的Arrhenius双曲正弦关系来描述合金的热流变行为,其变形激活能为226.698 8 kJ/mol;随着温度的升高和应变速率的降低,合金中拉长的晶粒发生粗化,亚晶尺寸增大,再结晶晶粒在晶界交叉处出现并且晶粒数量逐渐增加;合金热压缩变形的主要软化机制由动态回复逐步转变为动态再结晶.     

Applicability of adhesive–embossing hybrid joining process to glass-fiber-reinforced plastic and metallic thin sheets

Adhesive–embossing hybrid joining process was applied to A2017P and three types of glass-fiber-reinforced plastic (GFRP) thin sheets. Optical microscopy shows that a sound A2017P–thermosetting GFRP hybrid joint without crack/delamination in the composite or adhesive failure can be produced by optimizing adhesive thickness, embossing stroke and embossing temperature. The results of tensile shear test indicate that the optimally hybrid-bonded A2017P–GFRP joint exhibits improved load carrying capability, slip displacement and better energy absorbing characteristics than the adhesively bonded joint when subjected to tensile loading. This investigation shows that the adhesive–embossing hybrid joining process is a competitive alternative joining method for the fabrication of ultra lightweight thermosetting GFRP-metal hybrid structures and has great potential for wider applications, which is attributed to its benefits in terms of joining properties, operation simplicity, weight-cost effectiveness and recyclability.     

浇注与铸型温度对6082铝合金热裂倾向的影响

研究了浇注温度和铸型温度对6082铝合金热裂倾向的影响。使用金相显微镜观察不同浇注条件下合金的组织发展,较高浇注温度时组织呈树枝状,较低浇注温度时组织呈蔷薇状枝晶。应用ADSTENFAN模拟软件对合金充型、凝固以及应力分布进行联动模拟。试验结果表明,通过采用降低浇注温度,提高合金凝固速率的方法可减少合金热裂倾向,且通过计算机模拟可准确认识热裂倾向大小及裂纹产生位置,为改善工艺参数,减少热裂倾向打下良好基础。     

热变形温度对纳米晶Nd-Fe-B磁体性能的影响

为了研究纳米晶Nd-Fe-B磁体的热变形机理,在不同温度下对快淬粉进行热压热变形处理.通过分析不同温度下热变形过程中应力和磁体应变的变化,以及磁性能和SEM测试,研究了温度对热变形磁体性能和微观结构的影响,分析了热变形过程的热变形机理.结果表明,纳米晶磁体存在最佳的热压温度和热变形温度.当热压温度为550℃,热变形温度...