Micromachining porous alumina ceramic for high quality trimming of turbine blade cores via double femtosecond laser scanning

Turbine blade cores are made of porous alumina ceramic and determine the molding accuracy of the cavity of turbine blades, which strongly affect thermal diffusion performance and service life of turbine engines. To get a high quality ceramic core, accurate trimming for a preliminarily processed core is needed and therefore, micromachining porous alumina ceramic, which differs from general alumina substrates, is crucial. This paper dealt with a processing technology for the special material via double femtosecond laser scanning. The materials ablation threshold was firstly determined through parameter fitting and then this material was machined at a combination of different laser processing parameters. Considering the produced debris blocks the lasers further propagation into the material, double femtosecond laser scanning was newly proposed and experimentally verified with the comparison of gas jet assist and underwater laser processing ways. The removal profiles of the machined material were characterized in terms of cutting width, cutting depth, deviation of linearity and surface morphology, which exhibited high dependence on the femtosecond laser processing parameters. The optimal laser operating window was identified and high quality laser cutting of the porous alumina ceramic was demonstrated. The developed processing technology has potential application in trimming for ceramic casting cores. In addition, it might also give a novel view for high quality laser micromachining another materials.     

Microstructure and properties evolution of silicon-based ceramic cores fabricated by 3D printing with stair-stepping effect control

A ceramic core is the key component in the manufacture of the hollow turbine blades of aeroengines. Compared with the traditional injection molding method, 3D printing is more suitable for manufacturing ceramic cores with a complex geometry at high precision. However, the stair-stepping effect is inevitable in the 3D printing process and affects the surface roughness and strength of the ceramic core. In this study, to explore the influence of nano-silica content on the microstructure and properties of the ceramic core, silicon-based ceramic cores were fabricated with the addition of nano-silica powder by digital light processing and subsequent sintering at 1200 °C. The results showed that the apparent porosity and pore size of the ceramic core gradually decreased as both the nano-silica powder content and bulk density increased. Meanwhile, the printing interlayer spacing was significantly reduced, resulting in a low surface roughness, high flexural strength, and creep-resistance. To simulate the entire casting process of a superalloy blade, the thermal deformation behavior of the ceramic core was observed by heating and cooling cycles performed in a thermal dilatometer at 1540 °C. The total linear shrinkage decreased as the nano-silica powder content increased, which was mainly due to the phase transformation of cristobalite and the densification of the ceramic core sintered at 1200 °C. The low surface roughness and linear shrinkage as well as high flexural strength of the ceramic core can contribute to the excellent quality of cast superalloy blades.     

基于工况识别的注塑过程产品质量预测方法

针对多工况注塑过程的在线质量预测问题,考虑了过程数据高维、耦合、非线性等特点,采用拉普拉斯特征映射(LE)方法实现过程数据的非线性降维;在低维特征空间中采用Mean Shift聚类算法完成样本的工况聚类,以便注塑过程的工况分析和知识挖掘;同时运用Mean Shift原理,提出一种新样本的在线工况识别方法;最后应用基于混合粒子群(PSO)参数寻优的偏最小二乘支持向量机(PLS-LSSVM)方法,建立了多工况注塑过程的产品质量软测量模型。实验结果表明,相较于PLS-LSSVM方法,本文方法的预测精度和泛化性能均有明显提高,可为实际注塑企业提供一种效果良好的多工况产品质量在线预测方法。     

基于PLC的注塑机多段温度控制系统设计

为保证注塑机注塑质量和加工精度,应对注塑机料筒温度进行精确控制,因此设计了基于可编程控制器(PLC)为核心控制器的注塑机温度控制系统。首先介绍了注塑机结构和注塑工艺流程,以PLC、触摸屏为控制器核心设计了注塑机硬件系统。采用热电偶传感器采集各段温度并传送到PLC中,通过比例积分微分(PID)智能控制算法完成温度的闭环精确控制。结果表明:基于PLC的注塑机PID多段温度控制系统能够实现温度的精确控制,温度误差能控制在±0.3℃以内;该控制系统完全满足注塑工艺要求,能够显著提高注塑机的自动化程度。     

A real‐time process optimization system for injection molding

The proposed real‐time intelligent model for the injection molding process control consists of the initial parameters setting and online defects correction. First, preliminary optimization based on a simplified simulation model is used for the initial setting. This simplified model adopts a geometric approximation of the original part by a rectangular edge‐gated plate. Then, the molding trial will be run on the molding machine by using the initial process parameters. And a fuzzy inference model based on expert knowledge is developed for correcting defects during the molding trial. This defects correction procedure will be repeated until the part quality is found satisfactory. A corresponding intelligent system has been developed that is integrated with the injection machine by communicating with the controller. The system can be used to optimize process parameters real time. Experimental studies have been carried out for verification. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers.     

Study on the evaluation and compensating strategy for the wear damage of non-return valve during injection molding process

Injection molding (IM) is one of the most essential forming methods for plastics. However, some potential risks which influence part quality may occur in the molding process. A non-return valve (NRV) is a major component on the screw head whose function is to seal during the injection process to prevent the backflow of the melt. The NRV will wear in this process and cause fluctuations in parameters and quality but the wear states of NRVs cannot be monitored without the disassembly of the injection barrel. In this study, we proposed an optimization method to compensate for the wear damage of the NRVs. The V/P switchover point in each molding cycle was recalculated and output to stabilize the part quality. As a result, the wear damage of the NRV on the current machine was able to be predicted and the part quality could be initially optimized in the condition that the NRV had a degree of wear. The experimental results reveal that our proposed compensation algorithm can monitor the type of wear of NRV online, and at the same time, it can compensate the axial wear of NRV and finally improve the consistency of product weight, which established a fundamental for further research in the future.     

Optimization for Injection Molding Process Conditions of the Refrigeratory Top Cover Using Combination Method of Artificial Neural Network and Genetic Algorithms

The process conditions have important influence on final part quality in injection molding, and how to get optimum process conditions is the key to improving part quality. Sinkmarks on the surfaces of injection-molded parts is one of the problems that limit the overall success of injection molding technology, and the presence of sinkmarks significantly impairs the surface quality of injection molded parts. A combination method of artificial neural network and genetic algorithms is proposed to optimize the injection molding process, and the processing parameters of a refrigeratory top cover are optimized using the combining method to minimize the sinkmarks on the part. The results indicate the combining method is an effective tool for the process optimization of injection molding.     

微孔发泡模内表面装饰复合成型工艺参数对泡孔结构与力学性能影响

微孔发泡模内表面装饰复合成型工艺是高表观质量、轻量化塑料制品的重要成型方法,成型制品的泡孔结构与力学性能对其最终质量具有决定性影响。以典型拉伸样条为例,采用数值模拟的方法,通过对比分析不同工艺参数条件下平均气泡半径、密度和力学性能的变化规律,研究该工艺过程中主要工艺参数对泡孔结构及其力学性能的影响。结果表明,注射速率、熔体温度、超临界流体(SCF)质量分数、模具温度与充填/保压(V/P)切换时充填体积分别设置在50~80 cm~3/s、180℃、0.5%~0.8%、70℃以上与86%时,试样的泡孔结构分布和宏观力学性能最佳。通过工艺参数对泡孔结构和力学性能的影响规律研究,为优化复合成型工艺的工艺参数、获取高表观质量制品提供理论基础。     

Real‐time diagnosis of co‐injection molding using ultrasound

Co‐injection molding, also known as sandwich molding, is a process in which two or more polymers are laminated together in a mold cavity. Integrated ultrasonic sensors embedded into a mold insert of a co‐injection‐molding machine have been used for real‐time, nonintrusive, and nondestructive diagnosis of co‐injection‐molding processes. Diagnosis of core arrival, core flow speed, part solidification, part detachment from the mold, thickness of skin and core, and core length at the mold was demonstrated. It is found that core flow speed and peak cavity pressure monotonically increased and decreased with the core volume percentage, respectively. Thicknesses of the skin and core of the molded part were estimated using the presented ultrasonic technique during molding with an accuracy better than ±17%. In addition, the core length had correlation with core thickness, core flow speed, and peak cavity pressure. Among them, the core thickness measured by the ultrasonic technique had the better correlation. This technique enables process optimization, the maximum process efficiency, and in‐process quality assurance of the molded parts. POLYM. ENG. SCI., 47:1491–1500, 2007. © 2007 Society of Plastics Engineers     

注射成型氧化铝陶瓷工艺研究

研究了氧化铝陶瓷注射成型工艺过程,包括粘结剂的选择、粉末装载量的确定及热脱脂工艺的研究。探讨了注射压力、注射温度和模具温度等注射成型工艺参数对试样性能的影响,得到了一条优化的氧化铝注射成型工艺路线。     

精密注塑成型PVT最佳保压控制

阐述了PVT最佳保压控制的概念、基本原理及方法,并以精密塑料透镜注射成型为例,通过PVT状态图讨论注射成型工艺过程并制定工艺路线,选择注射-压缩工艺成型精密光学透镜,通过该工艺有效地解决了注塑中的应力问题,在制品的变形、尺寸精度及光学特性等方面大幅提高产品质量.     

低频振动场对HDPE性能的影响

利用低频熔体振动注射成型技术获得自增强高密度聚乙烯。实验结果表明,采用振动注射成型工艺,试样屈服拉伸强度由26.5MPa提高到36.1MPa;试样的芯层中可获取沿流动方向生成的串晶或行式排列的片晶结构;压力振动注射有利于分子在(110)晶面择优取向,使结晶更加完善;振动注射提高了试样的结晶度,芯层结晶度最大提高了10.2%。     

基于UG的空调面框注塑模设计

分析了形状较复杂、精度要求较高、模具设计制造困难的空调面框的结构,探讨了应用UG软件对空调面框塑料件成型工艺、浇注系统、成型零件结构及抽芯机构等进行设计的方法,在实际应用中对类似结构塑料件注塑模的设计有一定参考价值。     

电真空高铝陶瓷管产品质量控制

热压铸成型是电真空高铝陶瓷管的传统成型工艺,提高产品合格率是提高生产效率的关键点,采用该工艺,产品合格率的高低受到原材料、配方、成型、排蜡工艺、烧成制度和磨加工工艺及现场管理等各个方面的影响。重点对热压铸成型工艺控制进行了论述,热压铸成型工艺用于中、低压领域的氧化铝陶瓷真空管的生产,具有潜力可挖。     

电风扇壳体多重倒扣成型注塑模具设计

针对某款落地电风扇后壳的结构特点,对此塑料产品的分型面做了合理设计。由于该产品内侧存在多个形状各异、方向不同的倒扣难以脱模,因此设计了四组斜导柱抽芯机构和四组斜顶机构组合的单型腔注塑模具,从而保证成型的同时能够顺利脱模。该壳体作为大众消费品有较高外观质量要求,因此采用侧浇口进浇以保证产品外观质量。对产品进行注塑模具设计的同时,利用CAE技术对所设计的注塑模具进行了注塑成型过程的模流分析,提高了注塑模具的设计效率、优化了模具的设计结构和注射成型工艺参数的设置,降低了模具制造成本。经验证,该模具结构可靠,运动顺畅,产品注塑成型效果良好,为类似结构特点模具的设计提供了良好的借鉴。     

Aetiology of Defects in Large Ceramic Moldings

This study is an attempt to identify the causes of defects that appear in large ceramic injection molded bodies after sintering. It asks the question: are such defects established at the injection molding stage or are they caused by the debinding process or by sintering? Moldings with ascending thickness were prepared using a mold cavity with replaceable tool faceplates. Control over pressure during solidification was compared by using conventional molding and a novel molding technique that uses an insulated sprue. The organic vehicle is polyoxymethylene, which can be displaced by catalytic degradation in the solid state. This is a shrinking unreacted core process with a clearly defined reaction boundary in which there is no provision for particle movement in the liquid state. This study tracks the development of defects at each stage and concludes that the defects apparent after sintering have their origin in injection molding, even though they do not mature until a later stage.     

基于响应面模型的注塑件精密成型工艺优化

为了提高注塑件品质,对注塑件进行了成型工艺优化。结合中心复合试验设计,采用Moldflow软件和响应面模型方法,拟合得到注塑件二阶响应面模型,由响应面模型获得成型最佳产品品质的工艺参数组合。采用Moldflow软件对该工艺参数组合进行了分析。结果表明:采用响应面模型预测与Moldflow软件分析得到的体积收缩率相差约0.185%,该二阶响应面模型具有较高预测精度;使用该方法极大地缩短了分析周期,降低了生产成本。     

基于时段过渡分析的多时段间歇过程质量预测(英文)

Batch processes are usually involved with multiple phases in the time domain and many researches on process monitoring as well as quality prediction have been done using phase information. However, few of them consider phase transitions, though they exit widely in batch processes and have non-ignorable impacts on product qualities. In the present work, a phase-based partial least squares (PLS) method utilizing transition information is proposed to give both online and offline quality predictions. First, batch processes are divided into several phases using regression parameters other than prior process knowledge. Then both steady phases and transitions which have great influences on qualities are identified as critical-to-quality phases using statistical methods. Finally, based on the analysis of different characteristics of transitions and steady phases, an integrated algorithm is developed for quality prediction. The application to an injection molding process shows the effectiveness of the proposed algorithm in comparison with the traditional MPLS method and the phase-based PLS method.     

Enhancing fracture strength of ceramic core using sodium silicate as the binder

Ceramic cores used in the casting must exhibit high heat resistance because they come in direct contact with molten metals. Therefore, in this study, ceramic cores with high heat resistance and fracture strength were fabricated using sodium silicate as the binder instead of a commonly used organic binder. In addition, the prepared ceramic core was coated with Si and Si-Na precursors as the inorganic binder to improve the firing strength of the ceramic core. The thermal stability and firing strength of the sample were investigated. The results revealed that the firing strength of the ceramic core was significantly improved up to 15.2 MPa owing to the formation of a glass phase between the ceramic particles, which was formed by the reaction of sodium silicate and the inorganic binder precursor. In addition, the core was completely decomposed in an NaOH solution at a relatively low temperature of 60°C, indicating the excellent elution properties of the sample. These results indicate that the method proposed in this study is suitable for the preparation of ceramic cores with high fracture strength and excellent elution behavior.     

基于矢量控制的全电动注塑机控制系统设计

根据全电动注塑机的工艺结构及对控制系统的要求,通过分析全电动注塑机的结构,在把矢量控制应用到永磁同步电机控制的基础上,提出了一种全电动注塑机控制系统的设计方案。经过分析和研究,表明该方案能够进一步提高全电动注塑机的精确控制能力,其稳定性好、可靠性高,能够较好地满足对全电动注塑机控制精度和稳定性的要求。