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.     

Visibility-based conformal cooling channel generation for rapid tooling

In plastic injection moulding process, cooling channel design is an essential factor that affects the quality of the moulded parts and the productivity of the process. Non-uniform cooling or long cooling cycle time would result if a poorly designed cooling channel is adopted. Due to limitations of traditional machining processes, the cooling channel is usually formed from straight-line drilled holes and only simple shapes are allowed, regardless of the shape complexity of the part being moulded. With the advent of rapid tooling technology, cooling channels in complex shapes can now be possible. However, there are not many design methodologies for supporting this type of cooling channel. In this paper, a methodology called visibility-based cooling channel generation is proposed for automatic preliminary cooling channel design for rapid tooling. The cooling process between a mould surface and a cooling channel is considered analogous to whether they can be visible from each other. Without loss of generality, the mould surface is approximated by a polyhedral terrain and is normally offset. A number of point light sources together that can illuminate the whole polyhedral terrain are assigned to suitable terrain offset vertices. A cooling channel is then generated by connecting all the assigned light sources. When comparing the conventional verification and redesign methods by melt flow analysis, computer-aided design and, a better design of cooling channel for its mould surface results in a short time independent of the experience of mould engineer.     

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.     

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.     

Study on the bimodal filler influence on the effective thermal conductivity of thermal conductive adhesive

The thermal management for electronics systems becomes more crucial to the overall system performance as the packaging density becomes much higher and the IC power increases at the same time. Thermal conductive adhesives (TCAs) have been widely adopted in electronics systems. As an epoxy matrix with conductive fillers, it is essential to figure out the effective thermal conductivity of this composite material. In the present paper, a parameterized cubic cell model (CCM) is developed and then implemented by the finite element method to investigate the effects of the bimodal fillers on the effective thermal conductivity. In addition, a series of bimodal TCA samples are prepared and the thermal conductivities in the in-plane and vertical directions are measured experimentally. An obvious anisotropy with respect to the thermal conductivities has been observed for the bimodal filler loading under consideration. A good agreement between the numerical results and the experimental data is obtained.     

Optimal design of thermal loaded composites filled with curvilinear fibers

The problem of optimal design of shape and orientation of fibers in composite material, leading to the local inhomogeneity of its parameters, is considered in this paper. The paper concerns the problem of curvilinear fibers arrangement in the composite material, so that the structural element made from this material can fulfill the requirements imposed on its thermal properties. An equivalent homogeneous orthotropic model of the composite is utilized for this purpose and next, basing on this model, the attempt is taken to determine the most profitable orientation and arrangement of fibers in the layers of the composite in order to obtain the desired behavior of structure. To solve this problem, the optimization method based on evolutionary algorithm is applied, and it is supplemented with finite element method for heat transfer analysis.     

A novel approach to realize the local precise variotherm process in micro injection molding

Variotherm is special mould temperature controlling concept which realizes the rapid heating/cooling of mould during material processing in order to extend the freezing time of materials. A novel variotherm concept based on silicon wafer combined with micro electric resistance heating structures is purposed and prototyped in this study. The manufacture process of this variotherm unit was introduced and its heating/cooling performance was tested and analyzed by thermal graphic method, which indicate that the new variotherm concept has excellent thermal control efficiency and precise temperature distributions.     

Multi-objective robust design of helical milling hole quality on AISI H13 hardened steel by normalized normal constraint coupled with robust parameter design

Helical milling is a hole-making process which has been applied in hardened materials. Due to the difficulties on achieving high-quality boreholes in these materials, the influence of noise factors, and multi-quality performance outcomes, this work aims the multi-objective robust design of hole quality on AISI H13 hardened steel. Experiments were carried out through a central composite design considering process and noise factors. The process factors were the axial and tangential feed per tooth of the helix, and the cutting velocity. The noise factors considered were the tool overhang length, the material hardness and the borehole height of measurement. Response models were obtained through response surface methodology for roughness and roundness outcomes. The models presented good explanation of data variability and good prediction capability. Mean and variance models were derived through robust parameter design for all responses. Similarity analysis through cluster analysis was performed, and average surface roughness and total roundness were selected to multi-objective optimization. Mean square error optimization was performed to achieve bias and variance minimization. Multi-objective optimization through normalized normal constraint was performed to achieve a robust Pareto set for the hole quality outcomes. The normalized normal constraint optimization results outperformed the results of other methods in terms of evenness of the Pareto solutions and number of Pareto optimal solutions. The most compromise solution was selected considering the lowest Euclidian distance to the utopia point in the normalized space. Individual and moving range control charts were used to confirm the robustness achievement with regard to noise factors in the most compromise Pareto optimal solution. The methodology applied for robust modelling and optimization of helical milling of AISI H13 hardened steel was confirmed and may be applied to other manufacturing processes.     

A process for solvent welded rapid prototype tooling

Rapid prototyping is widely seen as an effective tool for compressing time to market for new products. The typical process followed by industrial and mechanical design groups is to model a new product in a CAD system, rapidly prototype the component parts, use the parts as patterns for RTV silicone molds, and then cast polyurethane prototype parts from the molds. These prototype components are an integral part of the simultaneous engineering process. With prototype components, engineers are able to design, implement, test, and refine the assembly systems for a product while production tooling for the components is being made. In this paper, we describe an experimental rapid prototyping process, known as solvent welding freeform fabrication (SWIFT), that is very well suited to the production of short to medium run tooling. The advantage of the process is that it is very fast and inexpensive relative to the traditional RTV silicone mold making process. The process also produces ABS or polystyrene molds which last considerably longer than RTV silicone molds. Process development details are provided in the paper and its application to a power tool component is described.     

固化冷却过程中复合材料参数对其应变的影响

为有效降低某复合材料固化冷却过程中的应变水平,以某圆柱形复合材料为例,利用有限元分析软件MSC Nastran,研究固化冷却过程中复合材料参数对其应变的影响.计算得到复合材料最大von Mises应变值和分布位置,分析弹性模量、泊松比、线膨胀系数、密度等参数对其应变的影响.     

不确定因素下建筑集群冷热电联供系统多目标优化

为降低建筑楼宇的能源消耗,研究建筑集群中的多个建筑楼宇共享冷热电联供系统、热能存储装置以及电池时的能源调度优化问题.考虑到建筑楼宇的能源需求和能源价格具有随机性,并且每个建筑楼宇以各自的费用最小化为目标,从随机规划和多目标的角度,建立建筑集群供能系统的两阶段多目标随机规划模型.为了提高模型的求解效率,提出将线性规划松弛与Benders分解算法相结合,从而获得建筑楼宇共享能源系统的Pareto最优解集.算例分析中通过CPLEX软件求解,对比分析不同随机因素对最优化建筑集群供能系统总费用以及建筑楼宇各自费用的影响程度,结果表明了所提出算法的有效性以及所构建的模型可以有效提高最优化决策的准确性.     

A computer-aided design system for framed-mould in autoclave processing

The general computer-aided design (CAD) software cannot meet the mould design requirement of the autoclave process for composites, because many parameters such as temperature and pressure should be considered in the mould design process, in addition to the material and geometry of the part. A framed-mould computer-aided design system (FMCAD) used in the autoclave moulding process is proposed in this paper. A function model of the software is presented, in which influence factors such as part structure, mould structure, and process parameters are considered; a design model of the software is established using object oriented (0-0) technology to integrate the stiffness calculation, temperature field calculation, and deformation field calculation of mould in the design, and in the design model, a hybrid model of mould based on calculation feature and form feature is presented to support those calculations. A prototype system is developed, in which a mould design process wizard is built to integrate the input information, calculation, analysis, data storage, display, and design results of mould design. Finally, three design examples are used to verify the prototype.     

柔性结构机器人优化设计

本文提出了柔性结构机器人优化设计问题.将机器人结构重量函数和弹性变形能函数采用线性加权组合成多目标函数,并取精度、应力、驱动力矩等限制条件作为约束方程进行优化.其优化解确定了具有一定结构柔性和最轻结构重量的柔性结构机器人各臂的最佳横截面相对几何尺寸参数.     

Multi-objective concurrent topology optimization of thermoelastic structures composed of homogeneous porous material

The present paper studies multi-objective design of lightweight thermoelastic structure composed of homogeneous porous material. The concurrent optimization model is applied to design the topologies of light weight structures and of the material microstructure. The multi-objective optimization formulation attempts to find minimum structural compliance under only mechanical loads and minimum thermal expansion of the surfaces we are interested in under only thermo loads. The proposed optimization model is applied to a sandwich elliptically curved shell structure, an axisymmetric structure and a 3D structure. The advantage of the concurrent optimization model to single scale topology optimization model in improving the multi-objective performances of the thermoelastic structures is investigated. The influences of available material volume fraction and weighting coefficients are also discussed. Numerical examples demonstrate that the porous material is conducive to enhance the multi-objective performance of the thermoelastic structures in some cases, especially when lightweight structure is emphasized. An “optimal” material volume fraction is observed in some numerical examples.     

Multi-objective optimal design of hybrid viscoelastic/composite sandwich beams by using the generalized differential quadrature method and the non-dominated sorting genetic algorithm II

In this study, the multi-objective optimal design of hybrid viscoelastic/composite sandwich beams for minimum weight and minimum vibration response is aimed. The equation of motion for linear vibrations of a multi-layer beam is derived by using the principle of virtual work in the most general form. These governing equations together with the boundary conditions are discretized by the generalized differential quadrature method (GDQM) in the frequency domain for the first time. Also, the time and temperature dependent properties of the viscoelastic materials are taken into consideration by a novel ten-parameter fractional derivative model that can realistically capture the response of these materials. The material variability is accounted for by letting an optimization algorithm choose a material freely out of four fiber-reinforced composite materials and five viscoelastic damping polymers for each layer. The design parameters, i.e., the orientation angles of the composites, layer thicknesses and the layer materials that give the set of optimal solutions, namely the Pareto frontier, is obtained for the three and nine-layered clamped-free sandwich beams by using a variant of the non-dominated sorting genetic algorithms (NSGA II).     

周期性复合材料单胞结构优化设计

提出了一种基于网格的周期性多孔复合材料单胞模拟方法,以孔洞的形状、大小、位置为优化变量,建立了以材料在某个方向上的导热性能最好为目标的两相材料单胞优化模型,并用遗传算法进行求解,数值结果验证了优化模型和优化算法的有效性,获得了多种最优单胞结构。     

Evolutionary operators for optimal gate location in liquid composite moulding

A multi-objective evolutionary algorithm is applied to the problem of optimal gate location in liquid composite moulding. The Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is implemented and the efficiency of different variation operators is assessed on a benchmark problem, i.e., a mould of simple geometry. Following this, the algorithm is applied to a more complex mould geometry with the best variation operators. It is shown that the sole use of mutation proved better in the case of a complex part, whereas crossover proved helpful only for a simpler geometry.     

甲酸钠/氧化铜复合相变材料的制备与热力学性能测试

配制了甲酸钠/氧化铜复合相变材料。通过恒温槽实验对比了甲酸钠,乙酸钠,丙酸钠以及氯化铵的性能,选择了性能最优的甲酸钠。通过配制不同浓度的甲酸钠溶液,对比其性能,发现29.4 wt%甲酸钠溶液的效果最好。为了优化溶液的导热性能,通过对比不同纯金属纳米材料和金属氧化物纳米材料的种类以及对比添加同种纳米材料不同的质量分数,发现添加0.5 wt%的氧化铜效果最优。通过Hot Disk和DSC实验对配方进行了导热值以及潜热值的测量,结果显示添加了纳米材料的配方其潜热为250.4 J/g,相变温度为-16℃,导热系数为1.078 W/（m·K）,比未添加的导热能力提高了9.66%。实验过程中未发生化学沉降等现象。     

Thermal-aware floorplanner for 3D IC,including TSVs,liquid microchannels and thermal domains optimization

3D stacked technology has emerged as an effective mechanism to overcome physical limits and communication delays found in 2D integration. However, 3D technology also presents several drawbacks that prevent its smooth application. Two of the major concerns are heat reduction and power density distribution. In our work, we propose a novel 3D thermal-aware floorplanner that includes: (1) an effective thermal-aware process with three different evolutionary algorithms that aim to solve the soft computing problem of optimizing the placement of functional units and through silicon vias, as well as the smooth inclusion of active cooling systems and new design strategies, (2) an approximated thermal model inside the optimization loop, (3) an optimizer for active cooling (liquid channels), and (4) a novel technique based on air channel placement designed to isolate thermal domains have been also proposed. The experimental work is conducted for a realistic many-core single-chip architecture based on the Niagara design. Results show promising improvements of the thermal and reliability metrics, and also show optimal scaling capabilities to target future-trend many-core systems.     

Estimation of constitutive parameters for powder pressing by inverse modelling

Powder metallurgy processes are used in many material technologies for manufacturing of a wide range of industrial parts. Products such as components for cars, cemented carbides and high-speed steels for mechanical cutting, magnets and soft magnetic materials, bearings and refractory metals are made from powder. These parts are manufactured by powder die pressing followed by sintering of the resulting green body in a furnace. Traditionally, experience-based methods have been used to design and adapt the processing variables for optimal performance. Cost savings can be made if the tool design can be based on reliable predictive numerical simulations of the powder compaction process. Computer modelling could aid process and design engineers in selecting and optimizing the best pressing route for many industrial components. The aim of the present work has been to develop an efficient way to determine the necessary constitutive model parameters of the numerical models by means of inverse modelling. An experiment for establishing input data to the inverse problem has been designed and validated. The objective function is formed based on the discrepancy in force–displacement data between the numerical model prediction and the experiment. Minimization of the objective function with respect to the material parameters is performed using an in-house optimization software shell which is built on a modified Nelder–Mead simplex method also known as the subplex method. The completed analyses show that the proposed approach can readily be used to determine material parameters.