A visual mold with variotherm system for weld line study in micro injection molding

In order to study the weld line developing process and its influence on mechanical properties in micro injection molding, a visual mold with variotherm system mold was designed and fabricated. In this mold, a visualization design and a rapid heating/cooling system were integrated, and specimens with different cross section shape and micro dimensions could be molded for weld line study. The building process for the visual and variotherm mold was presented and the experiments were executed. The specimens for weld line study of micro injection molding were produced applying different processing parameters. A problem of flash in molded specimens needs to be solved.     

A variotherm mold for micro metal injection molding

In this paper, a variotherm mold was designed and fabricated for the production of 316L stainless steel microstructures by micro metal injection molding (MIM). The variotherm mold incorporated a rapid heating/cooling system, vacuum unit, hot sprue and cavity pressure transducer. The design of the variotherm mold and the process cycle of MIM using the variotherm mold were described. Experiments were conducted to evaluate the molded microstructures produced using variotherm mold and conventional mold. The experiments showed that microstructures of higher aspect ratio such as 60 m × height 191 m and 40 m × height 174 m microstructures could be injection molded with complete filling and demolded successfully using the variotherm mold. Molded microstructures with dimensions of 60 m × height 191 m were successfully debound and sintered without visual defects.     

Microfluidic phase change valve with a two-level cooling/heating system

A phase change (PC) microvalve with an integrated two-level cooling/heating system is developed for microfluidic applications in this article. This PC microvalve utilizes the liquid–solid PC of a small portion of the working medium in a microchannel to switch on/off the flow in the microchannel. The size of the working medium for the PC microvalve is 5-mm long, 50-μm high, and 80-μm wide (50 μm × 80 μm is the cross-sectional area of the channel) in this study. The switch is actuated by using a two-level cooling/heating system integrated on the chip. The first-level cooling/heating unit keeps the working medium in the valve area in the temperature range of supercooling state. Based on the supercooling state, the second-level cooling/heating unit either heats up or cools down the medium in the valve area to trigger its PC between liquid and solid for valving purposes. The proposed microfluidic PC microvalve is characterized experimentally in microfluidic chips. The thermal impact of one PC microvalve in one particular microchannel on its adjacent channels is discussed by establishing a preliminary analytical model and a numerical model. In addition to no leakage and no moving element, this PC microvalve with a two-level cooling/heating system can achieve a very short cooling time (i.e., 2.72 s).     

Research on optimization design of the heating/cooling channels for rapid heat cycle molding based on response surface methodology and constrained particle swarm optimization

The aim of this work is to optimize the layout of the heating/cooling channels for rapid heat cycle molding with hot medium heating and coolant cooling by using response surface methodology and optimization technique. By means of a Box–Behnken experiment design technique, an experiment matrix with three factors and three levels was designed. The design variables including the diameter of the heating/cooling channels, distances from the wall of heating/cooling channel to the cavity surface and between the adjacent heating/cooling channels were used to describe the layout and shape of the heating/cooling channels. The heating efficiency, standard deviation of the cavity surface temperature and the maximum von-mises stress were considered as the model variables. Thermal response and structural strength analyses of the mold based on FEM were conducted to acquire the objective variables for combination of process parameters. Some mathematical models of response surface were created by the mixed regression model and response surface method. The analysis of variance (ANOVA) method was used to check the accuracy of the developed mathematical models. With these mathematical models, the layout of the heating/cooling channels was then optimized to minimize the required heating time within reasonable temperature distribution and structural strength of the cavity by coupling the developed response surface (RS) models with the particle swarm optimization (PSO) method.     

Single step cell lysis/PCR detection of Escherichia coli in an independently controllable silicon microreactor

Our studies describe a novel microreactor capable of single step microbial assays involving cell lysis and DNA amplification. The device with an integrated platinum heater and temperature sensor, was fabricated using conventional silicon fabrication technologies and then anodically bonded to a Pyrex lid. Finite element analysis (FEA) and experiments have shown that the temperature uniformity in the microreactor reaction cavity is homogeneous and that the microreactor is capable of fast thermal cycling with heating and cooling rates of 11 and 2.7 °C/s, respectively. The microreactor has novel design features, such as a thermal isolation channel which eliminates thermal cross talk and an inlet/outlet port designed for ease of use. The fabricated microreactor was successfully characterised using a multifunction microbial assay involving cell lysis and PCR in a single step. An assay time of 32 min was achieved.     

Replication quality of micro structures in injection moulded thin wall parts using rapid tooling moulds

Injection moulding of micro structured polymer parts is often limited due to the replication quality of the structured surfaces. To enhance the replication quality process parameters, e.g., pressure, temperature or injection velocity, are adapted. Here, the mould temperature is the most important factor. This paper investigates the influence of the mould temperature on the replication of micro structured surfaces using amorphous and semi-crystalline polymers. Using rapid tooling moulds and a dynamic tempering system allows mould temperatures about the solidification temperatures during injection and a sufficient cooling for save ejection of the part. The results reveal that for amorphous polymers the mould temperature should be above the glass transition temperature for high replication quality. For semi-crystalline polymers the high cooling velocity seems to inhibit the crystallization process and this leads to a sufficiently low viscosity to achieve high replication quality.     

微流控PCR装置中温度控制技术评述

在微流控PCR装置中,温度直接影响PCR扩增结果,精确控制温度是微流控PCR的一个关键问题。温度控制包括系统加热方式和冷却方式,温度的测量和控制算法。加热和冷却有多种不同的实现方式,控制算法基本采用PID算法。总结了微流控PCR温度控制系统的加热方式、冷却方式和测量方式,并比较了各种方法的优缺点。     

结晶器变形计算机数据采集系统的建立

连铸过程中,结晶器铜管在热力载荷作用下,易发生机械变形。使用PCLD-789D型放大器、PCL-818L型数据采集板以及VISIDAQ应用软件设计了一套针对测量结晶器铜管变形的、完整的多输入通道的计算机数据采集系统,并对不同加热制度下的铜管应变进行了测量。结果显示,测量的铜壁变形与计算值吻合良好,证明开发的计算机采集系统可以用来对拉坯过程中的铜管应变动态监控,以便于随时调整工艺参数,避免事故的发生。     

Design of particle-reinforced polyurethane mould materials for soft tooling process using evolutionary multi-objective optimization algorithms

Polyurethane is used for making mould in soft tooling (ST) process for producing wax/plastic components. These wax components are later used as pattern in investment casting process. Due to low thermal conductivity of polyurethane, cooling time in ST process is long. To reduce the cooling time, thermal conductive fillers are incorporated into polyurethane to make composite mould material. However, addition of fillers affects various properties of the ST process, such as stiffness of the mould box, rendering flow-ability of melt mould material, etc. In the present work, multi-objective optimization of various conflicting objectives (namely maximization of equivalent thermal conductivity, minimization of effective modulus of elasticity, and minimization of equivalent viscosity) of composite material are conducted using evolutionary algorithms (EAs) in order to design particle-reinforced polyurethane composites by finding the optimal values of design parameters. The design parameters include volume fraction of filler content, size and shape factor of filler particle, etc. The Pareto-optimal front is targeted by solving the corresponding multi-objective problem using the NSGA-II procedure. Then, suitable multi-criterion decision-making techniques are employed to select one or a small set of the optimal solution(s) of design parameter(s) based on the higher level information of the ST process for industrial applications. Finally, the experimental study with a typical real industrial application demonstrates that the obtained optimal design parameters significantly reduce the cooling time in soft tooling process keeping other processing advantages.     

一种卡类终端的热保护算法设计

随着手持终端或者微型卡类电子终端功能的增强,其功耗也增大,造成单位面积发热情况严重,甚至影响到终端功能的正常使用或者损坏.因此在该类电子终端的设计中,控制其终端发热和有效散热,使元件温度不超过规定的最高安全温度,成为需解决的关键问题.区别于硬件优化以实现终端有效散热的传统手段,一种基于软件实现的热保护算法,可以在不改动PCB布局情况下解决终端设备发热问题,且相较而言比硬件优化的方式节约生产的成本和时间.     

超大城市土地覆盖与热环境的随机森林回归模型研究

目前对于超大城市土地覆盖和热环境定量模型研究报道不足,这主要是因为大城市地表温度和地表生物物理组分之间存在复杂的潜在非线性关系,这使得准确评估城市热环境情况遇到了严峻的技术挑战。研究选取中外6个典型超大城市（北京、上海、广州、伦敦、纽约和东京）为研究对象,以Landsat遥感影像为主要数据源,利用单通道算法反演各城市地表温度,采用随机森林回归模型（RFR）建立土地覆盖类型与城市热环境定量关系模型（LCT）,综合分析城市土地覆盖因子与热环境间的多维定量关系。土地覆盖与地表温度的定量关系显示,城市地表热场的空间结构在很大程度上被下垫面用地类型所左右,不透水面会导致高温热场的聚集,而植被和水体则有降温作用。6个超大城市地表覆盖结构变化产生的升温/降温效应有所差异,北京、上海、纽约和东京等城市区域的植被和水体降温效应较广州和伦敦显著。基于随机森林回归方法建立了NDVI、MNDWI和NDISI等3种土地覆盖类型与城市热环境的综合定量关系模型（LCT）,模型得到的精度高于基于多元线性回归方法建立的模型。LCT＿RF模型的R2值在0.623～0.826之间,比LCT＿MLR模型高0.021～0.07...     

Actuator – sensor technology on “electronic grade” diamond films

 Thermal microheaters as used for example in thermal ink print heads contain a variety of materials, the heater itself is commonly based on refractory metals. Here, a novel concept based on diamond as a multifunctional material is proposed and demonstrated. In this concept, diamond serves as an insulating substrate, a metal-like heater and as a temperature sensor. Superheating of water could be achieved after 7.5 μs heating of a 60×60 μm element. Bubble nucleation was visualized using a high speed stroboscopic technique. The influence of the diamond thermal properties and geometry on the thermal response were investigated by dynamic 3D-simulations. Received: 29 June 1997 / Accepted: 12 November 1997     

一种微腔型PCR集成芯片的设计及其热分析

设计了一种新型的硅微聚合酶链式反应(PCR)芯片.该芯片采用掺杂半导体作为加热电阻来提高加热效率,改善反应腔内的温度均匀性.集成在芯片底部的Pt温度传感器与微加热器组成温度控制单元,为PCR反应过程提供所需的三种特定温度.此外,为了便于温度校准,设计了敞开式的反应腔,其容积约1.78 μL.采用集总参数法计算了芯片在加...     

变模温注射成型数值仿真

针对传统的恒定模温控制技术易导致塑件表面产生熔接痕、流动痕和凹陷等表面缺陷的问题,采用Moldex 3D对某典型型腔进行流动分析,预测模型中熔接痕产生的位置;利用该软件中的暂态冷却模块,采用改变冷却方式和注射时间的方法对普通冷却与变模温技术的保压和冷却效果进行对比.分析结果表明,变模温技术能在不影响生产效率的基础上,达到提升制品品质的目的.     

Modeling of multi-connected porous passageway for mould cooling

Cooling channel design in the plastic injection moulding process is of paramount importance to the performance of the mould, influencing the quality of the parts being produced and productivity of the process. However, cooling channel design is usually limited to relatively simple configurations as well as conventional machining processes, such as straight-line drilling, and milling, etc. The cooling performance may not meet the expectations of the mould engineers.This paper proposes an alternative design method for a conformal cooling passageway with multi-connected porous characteristics based on the duality principle. The proposed method can provide a more uniform cooling performance between the mould plate and the conformal cooling passageway than the existing conformal cooling channel design. Injection mould defects like warpage or hot spots can be avoided.In this study, a 3D mould plate model was offset negatively and the location of the proposed multi-connected porous cooling passageway was identified. The negatively offset model was decomposed into a finite number of cubical cells via the sub-boundary spatial enumerated cell decomposition. Then a duality relationship between the primal and the dual graphs was developed. This provided the preliminary layout of the multi-connected porous passageway for the coolant flow in multiple directions. The cooling channel axis design of the multi-connected porous passageway, illustrated by the skeleton from the dual graph, was created. Following a Boolean difference operation, the proposed multi-connected porous cooling passageway inside the mould plate was able to be generated and fabricated with the aid of rapid tooling technologies. A real-life case study for the design of a multi-connected porous cooling passageway was implemented and examined. The effects of coolant flow and cooling performances, analyzed by computational fluid dynamics simulation, were validated.     

A numerical simulation of the greenhouse microclimate

A numerical one-dimensional model was designed to simulate the diurnal changes of the greenhouse environment. The model takes into consideration a soil layer, a vegetation layer, an air layer and a cover. The thermal radiative, sensible, latent and conductive heat fluxes were modeled in each layer in terms of its unknown temperature and vapor pressure. The model was applied to the coastal region of Israel during the winter and summer seasons in order to assess the heating/cooling requirements of glass and polyethylene covered greenhouses.     

基于模糊控制的单片机式热保护器

针对电动机运行过程中因为绕组温度过高而影响绝缘性能的问题,设计了一种新型的基于模糊控制的单片机热保护器。通过分析和讨论各种标准和热过载模型,提出了最佳的可供单片机热保护器使用的热特性模型,即双时间常数的指数发热和冷却模型及其建模机理。针对电动机热保护器的延迟动作时间选取不准确的问题,利用模糊控制理论设计了热保护器的软件,提高了电动机热保护器的动作精度和可靠性。     

一种新型的比例-周期控温算法

提出了一种新型的比例-周期控温算法。控制器能自动辨识跟加热器功率有关的升温常数,结合实时的环境温度变化,动态地修改升温时间和降温时间,使受控件温度在设定的范围内波动。比例-周期控温算法综合考虑了环境和加热器对受控件的热影响,环境温度发生短时间的突变后,能够做出快速响应,从而取得较佳的控制效果。     

Investigating the role of metallic fillers in particulate reinforced flexible mould material composites using evolutionary algorithms

To reduce the cooling time in soft tooling (ST) process, high thermal conductive fillers (such as metallic filler) are included in flexible mould material. But addition of metallic fillers affects various properties of ST process and the influences may vary according to the types of materials used. Therefore, in order to investigate the role of various metallic fillers in particulate reinforced flexible mould material composites, multi-objective optimizations of maximizing equivalent thermal conductivity and minimizing effective modulus of elasticity of composite mould materials are conducted using evolutionary algorithms (EAs). Here we have adopted two EA-based algorithms namely NSGAII and SPEA2 in order to solve the present problem independently. Comparative study of the results reveals that NSGAII performs better over SPEA2 for investigating the role of metallic fillers in particulate reinforced flexible mould material composites. A recently proposed innovization procedure is also used to unveil salient properties associated with the obtained trade-off solutions. These solutions are analyzed to study the role of various parameters influencing the equivalent thermal conductivity and modulus of elasticity of the composite mould material. Based on the findings through investigations, the optimal selection of materials is suggested including the cost implication factor.     

A micromachined system for the separation of molecules using thermal field-flow fractionation method

All silicon-glass micromachined thermal field-flow fractionation (TFFF) microsystem has been developed and presented for the first time. The device consists of seven layers of double side, deep, selectively etched silicon and glass substrates, bonded anodically. The built-in fluidic heater and cooler allows producing the high thermal gradient. In the 30 μm deep, 2 mm wide and 50 mm long separation channel, the temperature gradient 1.5×10⁶ K/m has been obtained for relatively low heating agent temperature (343 K). The TFFF microsystem has been equipped with two integrated, three-electrodes conductivity detectors. Some basic separation properties have been evaluated for low concentrated KCl test samples in water. It has been found that retention time of 0.6 μl sample of 0.01 M KCl in water, for 293/321 K (cooling/heating agents) compared to 0.9×10⁶ K/m, is almost two times longer than it has been obtained in the device during the absence of the temperature gradient.