A computer-aided EDM electrode design system for mold manufacturing

A large number of EDM electrodes are used in plastic injection mold manufacturing. However, electrode design is very time-consuming. This paper introduces a computer-aided electrode design system for plastic injection mold manufacturing. An algorithm to detect sharp corner uncut for electrode design is introduced in the paper. Through this algorithm, sharp corner uncut can be detected by calculating the surface angles at their common edges. Using this system, when electrode boundaries are identified either by the user or through detected sharp corner edges, the electrode tool, its holder and a working coordinate system (WCS) for electrode setting are created automatically. The system has been tested and has proved to be able to shorten the electrode design lead-time significantly.     

基于流动平衡的注塑模浇口位置优化设计

注塑成型可以制作大量具有高精度和复杂型腔形状的制件,其中注塑模浇1：2位置的设定是整个模具设计中关键的一步,它决定了聚合物流动方向和流动平衡性。文中通过引入等效流长的概念,建立了浇口位置优化问题。采用遗传算法自动搜索最佳浇1：2位置,使得不同流动路径的等效流长差异的算术平均值最小,从而得到平衡流动。算例表明,该法可以快捷地得到优化的浇1：2位置。     

THREE-DIMENSIONAL TRANSIENT MOLD COOLING ANALYSIS BASED ON GALERKIN FINITE ELEMENT FORMULATION WITH A MATRIX-FREE CONJUGATE GRADIENT TECHNIQUE

A methodology is presented to simulate the three-dimensional heat transfer within a mold during the injection molding process. The mold cooling analysis assists cooling channel design and paves the way for part shrinkage and warpage analysis. The transient temperature distributions in the mold and the polymer part are simultaneously computed by Galerkin Finite Element Method (GFEM) using a matrix-free Jacobi Conjugate Gradient (JCG) scheme. The numerical method presented here is efficient and has shown to require a fraction of the memory and computing time required by conventional methods. The matrix-free algorithm is initially validated using an injection mold designed to produce a plaque with a molded-in hole. Subsequently, the method is further applied to a representative automotive plastic component.     

Rapid manufacturing of plastic aspheric optical lens

This paper presents a new process to rapid manufacture the plastic aspheric optical lens. A bridge tooling was developed for fabricating the mold inserts of an aspheric lens using silicone rubber materials. Epoxy‐based composites were used to fabricate mold inserts of an aspheric optical lens. Z‐axis shrinkage error was investigated after plastic injection molding and compensated to the designed aspheric lens. In comparison with conventional method for fabricating a pair of mold inserts of a new plastic lens, a cost reduction of 75.02% and a time saving of 77.78% can be achieved. The deformation improvement percentage is about 92.48%. This technology can be used to compensate the z‐axis deformation efficiently due to shrinkage error of plastics in molding aspheric lens. Aspheric optical lens can be produced rapidly and cost‐effectively.     

基于转写技术的微针阵列制备与强度特性测试

为达到低成本、批量化制备微针阵列的目的,提出了一种分别制备微针针尖模具和微针立柱模具的微针模具制备方法.制备微针针尖硅模具是采用湿法刻蚀方法,SU-8微针的立柱部分则采用套刻工艺制备.以此模具为母版,采用聚二甲基硅氧烷(PDMS)二次转写技术获得PDMS二次母版.以PDMS母版为模具,分别用浇铸法制备了3种不同聚合物材料(左旋聚乳酸(PLLA),聚苯乙烯(PS),透明质酸(HA))的微针阵列;还以PDMS母版为模具,用电铸法制备了金属Ni微针阵列.该微针阵列的密度约为300根针/cm2.对制备的4种微针进行力学特性测试,实验结果表明,加工出的微针有足够的力学强度,可用于无痛注射.     

工艺参数对高光注射成型制品复制率的影响

以自主开发的车载高光蓝牙外壳模具和温控辅助装置为基础,研究了工艺因素对高光注射成型制品复制率的影响。结果表明,高光成型制品复制率随着模具温度的升高而准线性增大;模温设定条件下,保压压力对制件复制率的影响最大,其次是保压时间,冷却时间影响最小,熔体温度和注射压力的影响以塑料热变形温度为分界点,当模温低于该温度时注射压力的影响较大,反之则相反;随着模温逐步升高,熔体温度和注射压力对制品复制率影响小幅度增大,保压压力、保压时间和冷却时间的影响呈倒"V"型小幅度波动,且均在塑料热变形温度附近达极小值。     

A cost‐effective approach for rapid manufacturing a low pressure wax injection mold with high surface finish and high dimensional accuracy

Investment casting process is considered as an economic method for mass production of metal parts. Improvement of mold surface quality and geometric accuracy in the fused deposition rapid tooling is a major concern. In this paper, a new technique is proposed for rapid manufacturing a low pressure wax injection mold with high surface finish and high dimensional accuracy. Wax patterns produced from this mold have not only better dimensional accuracy but also better surface finish. The average relative error of dimension of wax patterns can be reduced from 1.76% to 0.66%. Surface roughness improvement rate of wax patterns of up to 85.71% can be achieved. Advantages of this technique include low manufacturing cost, simple manufacturing process and flexible process capability.     

A hybrid of mode-pursuing sampling method and genetic algorithm for minimization of injection molding warpage

This paper presents a hybrid optimization method for minimizing the warpage of injection molded plastic parts. This proposed method combines a mode-pursuing sampling (MPS) method with a conventional global optimization algorithm, i.e. genetic algorithm, to search for the optimal injection molding process parameters. During optimization, Kriging surrogate modeling strategy is also exploited to substitute the computationally intensive Computer-Aided Engineering (CAE) simulation of injection molding process. With the application of genetic algorithm, the “likelihood-global optimums” are identified; and the MPS method generates and chooses new sample points in the neighborhood of the current “likelihood-global optimums”. By integrating the two algorithms, a new sampling guidance function is proposed, which can divert the search process towards the relatively unexplored region resulting in less likelihood of being trapped at the local minima. A case study of a food tray plastic part is presented, with the injection time, mold temperature, melt temperature and packing pressure selected as the design variables. This case study demonstrates that the proposed optimization method can effectively reduce the warpage in a computationally efficient manner.     

虚拟制造环境下成本评估技术

介绍了通过历史成本数据矩阵,寻求最小成本路径,估算最小成本和确定最优工艺路径的方法,为虚拟制造和产品设计提供了有效的决策工具。     

浅述精密注塑件的设计

简述了在模具设计前,设计塑料件的重要性,详细阐述了塑料件设计的壁厚、脱模角度、产品表面质量、分型面、模具结构可行性和浇注系统等要求的具体内容,总结了注塑件在结构、外观、模具制造工艺、注塑工艺等方面的一些注意事项。     

Cost estimation system for machined parts

Estimating the manufacturing cost of a machined part is a critical task with high importance to manufacturing firms. Accurate cost estimation is important for cost control, successful bidding for jobs, and maintaining a competitive position in the marketplace. There are three main approaches towards cost estimation: estimation based on past experience (variant cost estimation), estimation based on explicit cost computations, and parametric cost estimation. This paper presents a hybrid cost estimation system for rotational parts that uses a combination of the variant approach and explicit cost calculations. The variant approach is used to retrieve machining parameters from a database of past parameters. The explicit cost calculations are based on the part geometry, the cutting tools available and the machining parameters retrieved. The system presented calculates the time that a part needs to stay on the machine. This time, which includes processing, set-up (chucking and re-chucking) as well as tool changes, is used to find the machining cost.     

Optimization of injection flow rate to minimize micro/macro-voids formation in resin transfer molded composites

Resin transfer molding (RTM) has become one of the most widely used processes to manufacture medium size reinforced composite parts. To further enhance the process yield while ensuring the best possible quality of the produced parts, physically based optimization procedures have to be devised. The filling of the mold remains the limiting step of the whole process, and the reduction of the filling time has an important impact on the overall cost reduction. On the other hand, the injection cycle has to be appropriately carried out to ensure a proper fiber impregnation. Indeed, a partial fiber impregnation leads to the creation of micro-scopic and macro-scopic voids.In the present work, based on a double scale flow model and the capillary number Ca, an optimization algorithm is proposed to minimize the micro/macro-voids in RTM composite parts. The optimized injection flow rate ensures an optimum Ca at the flow front during part filling. The implemented algorithm allows the use of various constraints such as maximum capabilities of the injection equipment (i.e., maximum pressure or flow rate at the injection gates) or maximum velocity to avoid fiber washing. Bounded by these constraints, the optimization procedure is devised to handle any injection configuration (i.e., injection gates or vents locations) for two or three-dimensional parts. The numerical model is based on a mixed (FE/CV) formulation that uses non-conforming elements to ensure mass conservation. The proposed algorithm is tested for two and three-dimensional parts while emphasizing the important void reduction that results from the optimized injection cycle.     

高光注塑成型工艺控制试验

建立了制品对模具型腔复原性的宏观量化表征模型,以自主开发的车用高光蓝牙模具和温控辅助装置为试验基础,以制品质量、线收缩率、翘曲变形和沉降指数等为品质考核指标,采用试验生产与仿真分析相结合的方法对高光制品成型性能进行了试验研究。在考虑到各指标权重因素的同时,采用信噪比之望小特性理论实现了样本数据的归一化处理。得出了各考核参数相对于各个品质指标的影响趋势及影响显著性顺序,进而研究得出了相对于该高光制品的最佳成型工艺组合。     

Optimization of injection molding process parameters using sequential simplex algorithm

In this study warpage and shrinkage as defects in injection molding of plastic parts have been undertaken. MoldFlow software package has been used to simulate the molding experiments numerically. Plastic part used is an automotive ventiduct grid. The process optimization to minimize the above defects is carried out by sequential simplex method. Process design parameters are mold temperature, melt temperature, pressure switch-over, pack/holding pressure, packing time, and coolant inlet temperature. The output parameters aside from warpage and shrinkage consist of part weight, residual stresses, cycle time, and maximum bulk temperature. Results are correlated and interpreted with recommendations to be considered in such processes.     

工期不确定的模具车间柔性Flow-shop调度问题

由于模具制造属于非重复性单件订货生产,模具加工的任务工期具有较强的不确定性,导致生产调度混乱。为制定合理可行的生产调度方案,建立了任务工期离散概率模型,以最大完工时间的期望值最小为目标,建立不确定工期柔性Flow-shop调度模型;在遗传算法交叉、变异等操作中融入模拟退火操作,将遗传算法的全局搜索能力与模拟退火算法的良好局部搜索能力相结合,设计了不确定工期的柔性Flow-shop调度问题混合遗传模拟退火算法。利用混合遗传模拟退火算法对调度模型进行求解,通过仿真实验表明,该研究对于解决工期不确定的模具车间柔性Flow-shop调度问题是行之有效的。     

An industrial approach of laser polishing with different laser sources

Surface finishing of dies and molds is one of the most interesting applications of laser polishing process. Because of the variety of materials used in die and mold manufacturing, as well as the different surface topographies, in each case, it is necessary to use appropriate process parameters. The presented work focuses on the study of laser polishing process on three commonly used materials in the manufacture of dies and molds, such as tool steels AISI D2 and AISI P20, ductile cast iron GGG70L and LaserForm ST‐100, a specific material developed for plastic injection mold making. Experimental studies were carried out determining the influence of the energy density on the roughness reduction rate. A key point that has a direct impact on the resulting surface roughness is the initial surface finishing of the material before laser polishing. In order to determine the degree of influence, experimental studies were conducted on two steels, AISI H13 and AISI P20, which are typically used in mold making industry. The experimental tests showed that a random distribution of peaks and valleys allows more homogenous material melting and gives as result a smoother surface after laser polishing.     

基于特征的零件加工成本评价

提出了一种基于零件形状特征及特征间关系的成本评价方法。又根据不同加工方式建立了成本模型,并利用有向图来表示加工过程,把加工成本评价问题转化为最小路径问题求解。     

Nano-surface-finishing of permanent mold punch using magnetorheological fluid-based finishing processes

Various plastic products such as bottles’ plastic caps are manufactured through casting using permanent molds. To obtain the smooth surface on plastic caps during manufacturing, the required permanent mold die punch surface should be defect free and its roughness values in nanometer range. Two different magnetorheological (MR) fluid-based finishing processes are used for nano-surface-finishing of die punch. The MR ball end with solid rotating tool core is used to finish the flat surface, and a turning type MR finishing process is used for external circular surface of the present mold die punch. The material of the present permanent mold punch is P20 tool steel with hardness of 431 VHN. The final roughness values of flat and external circular surfaces of the present die punch are obtained as 30?nm and 80?nm from the initial values of 1080?nm and 630?nm in 120?min of finishing. The change in topography of the surface is observed using metallurgical microscope and mirror image test. The reduction in surface roughness at the nanolevel and microscopic improvement on the die punch surface have demonstrated the feasibility of present finishing processes to be useful in industries for manufacturing the smooth surface of bottles’ plastic caps.     

Optimal Burn-in Time to Minimize Cost for Products Sold Under Warranty

For products with an initially high failure rate, burn-in can be used to reduce the warranty cost. This paper examines the optimal burn-in time to achieve a trade-off between the reduction in the warranty cost and the increase in the manufacturing cost (as burn-in can be viewed as a part of the manufacturing process). Conditions for burn-in to be beneficial are derived for various warranty policies. A numerical example is presented.