镍基合金粉末的选择性激光烧结试验研究

分析了金属粉末选择性激光烧结的工艺特点 ,通过镍基合金粉末 F1 0 5的系列选择性激光烧结试验及其产物的微观结构分析 ,研究了金属粉末在激光作用下的熔凝过程以及各烧结参数对其熔凝过程的影响 ;对镍基 F1 0 5合金粉末的激光烧结工艺进行了初步优化 ,通过多层烧结试验对获得的烧结工艺进行了试验验证。研究结果表明 ,采用优化工艺制备的烧结制件内部组织主要由大量微米量级的等轴晶与少量枝晶组成 ,结构致密。     

Direct Selective Laser Sintering of Hard Metal Powders: Experimental Study and Simulation

Direct selective laser sintering (SLS) technology can be used to produce 3D hard metal functional parts from commercial available powders. Unlike conventional sintering, it does not require dedicated tools, such as dies. Hence, total production time and cost can be reduced. The large shape freedom offered by such a process makes the use of, for example, sintered carbides components viable in domains where they were not applied before. Successful results have been obtained in the production of sintered carbide or hard metal parts through SLS. The investigation focuses on tungsten carbide–cobalt (WC-Co) powder mixture. This material is characterised by its high mechanical properties and its high wear resistance and is widely used in the field of cutting tools. This paper is devoted to the experimental study and the simulation of direct selective laser sintering of WC-Co hard metal powders.     

Study on direct fabrication of ceramic shell mold with slurry-based ceramic laser fusion and ceramic laser sintering

Through studying the porosity of the ceramic parts fabricated with slurry-based rapid prototyping process of ceramic laser fusion and ceramic laser sintering, the feasibility of directly fabricating ceramic shell mold was investigated in this paper. Although the total porosity of the fusion part was low, microcracks led to low strength, which was hardly enhanced by post-treatment of infiltration. On the other hand, by adjusting the slurry formulation and varying the laser scanning energy, the open porosity of the sintered part was over 90?vol.% of the total porosity. High open porosity resulted in good permeability, which is one of the important characteristics of the ceramic shell mold for investment casting. To verify the feasibility of producing casting part with ceramic shell molds fabricated by the processes of ceramic laser fusion and ceramic laser sintering, the casting process was conducted to obtain the casting parts.     

一种微机械制造的新方法

提出对金属粉末直接进行选择性激光烧结制作微型机械;论述了激光烧结系统的原理及其硬件环境;用微细镍基合金粉末Ｎｉ３５和铜粉进行了实验,把镍粉、铜粉选择性烧结在一个微型机械中,并给出实验结果的扫描电镜显微照片,为进一步在微型机械中进行多种材料的集成式提供参考。     

Determining the effects of thermal conductivity on epoxy molds using profiled cooling channels with metal inserts

Polymer injection molds are generally manufactured with metallic materials, such as tool steel, which provide reliable working of molds and extended service life. The manufacture of injection molds with steel is a prolonged process because of the strength of steel. For a short prototype production run, one of the suitable choices could be the use of aluminum-filled epoxy material, which can produce a functional mold in a short time as compared with a conventionally machined tool. Aluminum-filled epoxy tooling is a good choice for short production runs for engineering applications, yet works best for relatively simple shapes. The advantages in relation to the fabrication of injection molds with epoxy-based materials include time saving in producing the mold, epoxy curing at ambient temperature, and ease of machining and post processing. Nevertheless, one major drawback of epoxy material is its poor thermal conductivity, which results in a relatively longer cooling time for epoxy injection molds. This study investigates some of the innovative ideas for enhancing the thermal conductivity for epoxy molds. The basic concept behind these ideas was to embed a highly thermally conductive metal insert within the mold between cavities with an innovative design of cooling channels called profiled cooling channels. This technique will increase the effective thermal conductivity of the epoxy mold, leading to the reduction in cooling time for the injection molded polymer part. Experimental analysis conducted in the current study also verified that the mold with profiled cooling channels and embedded metal insert has significantly reduced the cooling time.     

激光直接烧结成形多层金属薄壁件的温度场有限元模拟

为掌握多层粉末烧结过程中激光熔池的加热冷却规律以及各烧结层之间的相互影响,综合考虑热传导、热辐射和热对流以及材料的高度非线性,基于ANSYS平台建立了多层金属薄壁件的三维温度场有限元模型,利用APDL语言编程实现模拟中激光热源的移动,采用"单元生死"技术描述粉末材料动态增长过程。模拟结果表明:在现有工艺参数下,烧结获得的熔深在0.15mm以上,熔宽在0.61mm左右,烧结成形件与基体以及层层之间搭接牢固;成形件中,与x方向的热梯度相比,z方向热梯度占绝对优势,这说明成形件在冷却过程中热量的散失以堆积方向为主。将模拟结果与实验结果进行了对比,实验结果较好地验证了模拟结果。     

Rapid casting of turbine blades with abnormal film cooling holes using integral ceramic casting molds

Film cooling is an important cooling method to decrease the turbine blade surface temperature, and its average cooling efficiency is mainly dependent on the cooling structures of internal passageways and the shapes of film cooling holes. Compared with standard cylindrical film cooling holes, abnormal film cooling holes have higher average cooling efficiency. But it is difficult to manufacture these holes using traditional machining methods. In this paper, a novel process was developed to fabricate turbine blades with abnormal film cooling holes by combining stereolithography (SL) technology with gelcasting technology. To decrease the drying shrinkage, the freeze-drying technique was applied to treat the wet ceramic casting mold green body surrounded by the SL mold, and the proper sintering process parameters were determined for lowering the sintered shrinkage. Finally, the integral ceramic casting mold was obtained, and a turbine blade with converging–diverging film cooling holes was rapidly cast to verify the feasibility of the proposed process.     

PA6粉末选区激光烧结多层应力分析

选区激光烧结成型过程中,激光束扫描时反复的加热、冷却带来不均匀的热应力,影响烧结过程和烧结件的质量。基于弹性变形原理,利用单轴应力作用下的变形梁的挠曲和应变与应力之间的关系,来分析烧结过程中的应力以及不同烧结层之间的相互影响,结果表明,在每个单层烧结时,烧结应力主要集中在烧结层的上表面和下表面的两端,且呈现为拉应力;在多层烧结时,烧结的热载荷对紧邻已熔接层的应力有直接影响,随着烧结层数增加,新烧结层对已熔接层的热影响逐渐减小,对应的随着温度变化较小,已熔接层的应力也较小且保持较低水平。     

变模温注塑热响应模拟与模具结构优化

变模温注塑可根据不同工艺阶段的特点和要求,随时调整模具温度。在塑料熔体充模过程中,如果模具表面温度保持在塑料玻璃化转变温度以上,可以彻底解决常规注塑工艺存在的熔接痕、喷射痕、流动痕、翘曲和浮纤等缺陷。同时在冷却阶段,通过快速冷却已赋形的塑料熔体,以减小注塑成型周期。从而在不影响注塑生产效率的基础上,提升注塑件的品质。基于这种思想,在深入研究变模温注塑工艺原理的基础上,提出一套新的利用蒸汽辅助加热的模具温度控制方法,制定其工艺流程,并构建相应的动态模温控制装置和系统。通过研究蒸汽辅助加热变模温注塑模具的结构特点,提出了4种不同的模具设计方案,利用有限元软件ANSYS构建了变模温注塑模具传热分析模型,分别对变模温注塑工艺的加热、冷却过程进行温度响应模拟。以减小成型周期和提高温度均匀性为目标,对模具设计方案进行优化分析。将模拟分析获得的结果应用于平板电视机面板的注塑生产,验证分析结果的有效性。     

选择性激光烧结间接成型金属件及其在机械工业中的应用

快速成型的重要发展方向是快速制造。在各种利用快速成型制造金属功能件的方法中，选择性激光烧结间接法制造金属件是已商业化并在模具制造中广泛应用的方法。介绍了间接法的原理、所使用的覆膜金属粉末材料、成型工艺和后处理工艺，总结了该方法的应用现状。     

A study on compound contents for plastic injection molding products of metallic resin pigment

Injection molding process is widely used for producing most plastic products. In order to make a metal-colored plastic product especially in modern luxury home alliances, metallic pigments which are mixed to a basic resin material for injection molding are available. However, the process control for the metal-colored plastic product is extremely difficult due to non-uniform melt flow of the metallic resin pigments. To improve the process efficiency, a rapid mold cooling method by a compressed cryogenic fluid and electricity mold are also proposed to decrease undesired compound contents within a molded plastic product. In this study, a quality of the metal-colored plastic product is evaluated with process parameters; injection speed, injection pressure, and pigment contents, and an influence of the rapid cooling and heating system is demonstrated.

     

直接金属激光烧结成形的机理及实验研究

探讨了直接金属激光烧结成形机理，分析了烧结参数与激光输入能量之间关系。在室温惰性气体环境下，进行了不同匹配参数下314不锈钢金属粉末的直接激光烧结成形实验，测试了成形件的微观组织结构和机械性能，研究了工艺参数与直接金属激光烧结成形件的微观组织结构及宏观机械性能的关系。为制定合理的激光烧结工艺参数提供了依据。     

激光烧结金属粉末制造微型机械的研究

采用激光直接烧结微细金属粉末技术制造3维微型机械。分析了采用不同激光器进行烧结的优缺点,总结了多种工艺参数,包括激光功率密度、扫描速度、离焦量对烧结精度的影响,并给出部分烧结样件以及多种材料集成的扫描电镜显微照片,同时提出采用电子束烧结亚微米级粉末成形微米级3维微型机械的设想。     

基于Moldflow的魔方中心轴注射分析与优化设计

应用Moldflow软件对魔方中心轴的注射成型过程进行浇口位置、充填、冷却和翘曲等模拟分析。通过在不同注射工艺条件下进行对比分析,确定了注射的最佳工艺参数:充填时间为2 s,注射+冷却时间为8 s,模具温度为40℃,熔体温度为240℃,注射压力为100 MPa。应用UG软件建立了注射模具的实体模型,解决了传统注射模具设计方法存在设计周期长、成本高且质量难以保证等问题。     

汽车把手件气辅成型气指缺陷影响因素分析

在气体辅助成型工艺中,常常遇到一种缺陷是“气指”,气泡穿过气道形成指状分支,严重的“气指”会降低注塑件的强度,造成气辅成型技术的失败,或者不能发挥气辅成型技术的优势。为了消除或减少这种缺陷的产生,本文采用数值模拟方法和正交试验方法对气辅成型制品“气指”缺陷进行了研究。研究了对“气指”缺陷影响最重要的6个工艺参数：熔体短射量、气体注射延迟时间、气体注射压力 、模具温度、熔体温度以及气体注射时间对气辅成型制品“气指”缺陷的影响关系。结果表明,影响“气指”最重要的工艺参数依次是气体注射延迟时间、熔体温度和气体注射压力。因此优先选择合理的延时,熔体温度和注气压力参数尤为重要,为控制气指行为建议在相同熔体温度下适当延长气体注射延迟时间。     

Mold design and forming process parameters optimization for passenger vehicle front wing plate

The main objective of the present article is to solve the problems of poor molding quality, large warpage, inadequate cooling effect and unsuitable selection of process parameters, in the injection molding process for passenger vehicle front-end plastic wing plate. The thickness and parting surface of the vehicle front-end fender were determined, the injection mold and its cooling system were designed. The relevant process parameters, affecting the product molding quality, were tested, according to orthogonal experimental approach, while their influence on the warpage was obtained, by analyzing the data. Finally, the BP neural network of warpage model was established and globally optimized using genetic algorithm. The optimal parameter combination of the injection molding process was derived as: melt temperature 236 °C, mold temperature 51 °C, cooling time 32 s, packing pressure 97 MPa and packing time 16 s.

     

Two-dimensional modeling of sintering of a powder layer on top of nonporous substrate

Selective laser sintering (SLS) of a two-component metal powder layer on the top of multiple sintered layers by a moving Gaussian laser beam is modeled. The loose metal powder layer is composed of a powder mixture with significantly different melting points. The physical model that accounts the shrinkage induced by melting is described by using a temperature-transforming model. The effects of the porosity and the thickness of the atop loose powder layer with different numbers of the existing sintered metal powder layers below on the sintering process are numerically investigated. The present work will provide a better understanding to simulate much more complicated three-dimensional SLS process.     

Two-dimensional modeling of sintering of a powder layer on top of nonporous substrate

Selective laser sintering (SLS) of a two-component metal powder layer on the top of multiple sintered layers by a moving Gaussian laser beam is modeled. The loose metal powder layer is composed of a powder mixture with significantly different melting points. The physical model that accounts the shrinkage induced by melting is described by using a temperature-transforming model. The effects of the porosity and the thickness of the atop loose powder layer with different numbers of the existing sintered metal powder layers below on the sintering process are numerically investigated. The present work will provide a better understanding to simulate much more complicated three-dimensional SLS process.     

Research on manufacturing Cu matrix Fe-Cu-Ni-C alloy composite parts by indirect selective laser sintering

The property of alloy parts can be adjusted conveniently if alloy element powders are used for manufacturing alloy parts by indirect selective laser sintering (SLS), but there have been no reports in this field. Fe, Cu, Ni, C composite powders of two compositions were obtained through a 3D blending way in this paper. Green parts of above composite powder were manufactured by indirect SLS. Then, Cu matrix Fe-Cu-Ni-C alloy composites were produced after green parts had been depolymerized, high temperature sintered and infiltrated by molten Cu. The post-processing of green parts, microstructure and mechanical properties of alloy composites were investigated. The results show: Ni, Cu and C diffuse into γ-Fe when green parts are being sintered at high temperature and the distributing non-uniformity of alloy elements is eliminated basically; at room temperature, alloy composite microstructures are composed of lower bainite, α-Cu precipitated out of γ-Fe and Fe-Ni after they have been solution treated at 930°C and held at 350°C for 1 h later; the yield strength of alloy composites is near to 400 MPa and the elongation is under 3%. It can be used for manufacturing injection mold or other functional parts by indirect SLS.     

Direct metal laser fabrication: machine development and experimental work

A novel modification of the freeform technique selective laser sintering machine via system integration to develop a direct metal laser fabrication machine suitable for both nonmetal and metal materials is put forward in this paper, the aim of which is to establish an experiment platform for studying the direct metal laser fabrication (DMLF) as a variant of selective laser sintering (SLS). The system integration of two machines is realized by use of the low-power SLS Machine (CO₂, 50 W) and high-power laser processing machine (CO₂, 2,000 W) in our institute after the improvement or rebuilding of light route system, functional units, machinery and electrical system, and control software in the primary SLS machine, which means that direct metal laser fabrication machine with the laser power up to 1,000 W has been developed successfully. Functional tests of two machines and DMLF experiments of a large number of metal powders including Cu-based mixture and 316L-based mixture of powder have been done in detail. The results show that the material suitable for direct metal laser fabrication machine ranges from nonmetal powders to metal powders, including polystyrene, polyamide, polycarbonate, sands, and a large number of metal powders. At the same time, the primary functions or performances of both low-power SLS Machine and high-power laser processing machine are preserved entirely. Metal samples based on copper and 316L powders can be fabricated with the relative density of about 80% and 100%, respectively, by use of developed DMLF machine. The macro appearance and microstructure and processing mechanisms of DMLF are analyzed minutely. The academic application of DMLF machine for metal powders with high melting point has been making its mark.