Laser powder bed fusion additive manufacturing of NiTi shape memory alloys: a review

NiTi alloys have drawn significant attentions in biomedical and aerospace fields due to their unique shape memory effect(SME), superelasticity(SE), damping characteristics, high corrosion resistance, and good biocompatibility. Because of the unsatisfying processabilities and manufacturing requirements of complex NiTi components, additive manufacturing technology, especially laser powder bed fusion(LPBF), is appropriate for fabricating NiTi products. This paper comprehensively summarizes recent r...     

Advances in polishing of internal structures on parts made by laser-based powder bed fusion

The internal structures of metallic products are important in realizing functional applications. Considering the manufacturing of inner structures, laser-based powder bed fusion (L-PBF) is an attractive approach because its layering principle enables the fabrication of parts with customized interior structures. However, the inferior surface quality of L-PBF components hinders its productization progress seriously. In this article, process, basic forms, and applications relevant to L-PBF internal structures are reviewed comprehensively. The causes of poor surface quality and differences in the microstructure and property of the surface features of L-PBF inner structures are presented to provide a perspective of their surface characteristics. Various polishing technologies for L-PBF components with inner structures are presented, whereas their strengths and weaknesses are summarized along with a discussion on the challenges and prospects for improving the interior surface quality of L-PBF parts.     

Influence of scan strategy and process parameters on microstructure and its optimization in additively manufactured nickel alloy 625 via laser powder bed fusion

Automated systems based on programmable logic controllers (PLC) are still applied in discrete event systems (DES) for controlling and monitoring of industrial processes signals. PLC-based control systems are characterized for having physical input and output signals coming from and going to sensors and actuators, respectively, which they are in direct contact with the production or manufacturing process. The input subsystem to PLC consists of sensor-wiring-physical inputs module, and it can present two kinds of faults: short circuit or open circuit, in one or more signals of the process physical inputs, which it causes faults in the control and/or in the control algorithms behavior. Ladder diagram (LD) is one of the five programming languages supported by the International Electrotechnical Commission (IEC) through the IEC-61131-3 standard, and it remains being used at industry for control algorithm design of PLC-based systems. This paper proposes the simulation and validation of control algorithms developed in LD by using Petri Nets (PN) in order to deal with the possible fault options (short circuit and/or open circuit) in the physical inputs subsystem of a PLC-based control system. One control algorithms in LD have been analyzed in order to show the advantages of the proposed approach.     

Orientation effect of electropolishing characteristics of 316L stainless steel fabricated by laser powder bed fusion

Frontiers of Mechanical Engineering - 3D metal printing process has attracted increasing attention in recent years due to advantages, such as flexibility and rapid prototyping. This study aims to...     

Rapid in situ alloying of CoCrFeMnNi high-entropy alloy from elemental feedstock toward high-throughput synthesis via laser powder bed fusion

High-entropy alloys (HEAs) are considered alternatives to traditional structural materials because of their superior mechanical, physical, and chemical properties. However, alloy composition combinations are too numerous to explore. Finding a rapid synthesis method to accelerate the development of HEA bulks is imperative. Existing in situ synthesis methods based on additive manufacturing are insufficient for efficiently controlling the uniformity and accuracy of components. In this work, laser powder bed fusion (L-PBF) is adopted for the in situ synthesis of equiatomic CoCrFeMnNi HEA from elemental powder mixtures. High composition accuracy is achieved in parallel with ensuring internal density. The L-PBF-based process parameters are optimized; and two different methods, namely, a multi-melting process and homogenization heat treatment, are adopted to address the problem of incompletely melted Cr particles in the single-melted samples. X-ray diffraction indicates that HEA microstructure can be obtained from elemental powders via L-PBF. In the triple-melted samples, a strong crystallographic texture can be observed through electron backscatter diffraction, with a maximum polar density of 9.92 and a high ultimate tensile strength (UTS) of (735.3 ± 14.1) MPa. The homogenization heat-treated samples appear more like coarse equiaxed grains, with a UTS of (650.8 ± 16.1) MPa and an elongation of (40.2% ± 1.3%). Cellular substructures are also observed in the triple-melted samples, but not in the homogenization heat-treated samples. The differences in mechanical properties primarily originate from the changes in strengthening mechanism. The even and flat fractographic morphologies of the homogenization heat-treated samples represent a more uniform internal microstructure that is different from the complex morphologies of the triple-melted samples. Relative to the multi-melted samples, the homogenization heat-treated samples exhibit better processability, with a smaller composition deviation, i.e., ≤ 0.32 at.%. The two methods presented in this study are expected to have considerable potential for developing HEAs with high composition accuracy and composition flexibility.     

激光选区烧结中铺粉过程分析

在激光选区烧结(SLS)过程中,铺粉对烧结成形的顺利进行和烧结成形质量都具有重要的影响,为此,对辊式铺粉过程进行了深入分析,并且用数学方法对铺粉过程进行了描述.在分析的基础上,还提出影响铺粉过程的主要参数,结合实验和分析手段研究了这些参数对铺粉过程的影响规律,并给出参数的优化组合.     

Study on high-speed grinding mechanisms for quality and process efficiency

This paper focuses on the mechanism of high-speed grinding to achieve quality and efficiency for ceramics. The criterion of the brittle–ductile removal transition of ceramics is calculated and analyzed. The effects of the wheel velocity on the specific grinding forces, energy, and specific material removal rates were investigated. The influence of the wheel velocity on the surface integrity was studied in the terms of surface roughness by a 3D optical profilometer, scanning electron microscopy, respectively. The ductile removal mechanism of brittle material was validated experimentally. High quality and efficiency of grinding for SiC can been attained with high-speed grinding due to the understanding of the characteristics and mechanism for ductile grinding of brittle materials with high-speed grinding. Furthermore, based on the high-performance grinding mechanism, reasonable definitions on high-speed grinding are proposed.     

PLC在荧光粉表面处理系统中的应用

采用OMRON CQM1H系列PLC实现对荧光粉表面处理系统的监测和控制。本文详细介绍了系统的结构及硬件和软件的设计。     

流化床干燥过程的数学模型及其应用

通过对流化床干燥过程的机理分析,建立了流化床干燥过程简化的数学模型。并应用于聚氯乙烯的干燥,其结果表明该模型简化合理,计算结果可靠,与实际基本相符。     

Multisensor data fusion via Gaussian process models for dimensional and geometric verification

An increasing amount of commercial measurement instruments implementing a wide range of measurement technologies is rapidly becoming available for dimensional and geometric verification. Multiple solutions are often acquired within the shop-floor with the aim of providing alternatives to cover a wider array of measurement needs, thus overcoming the limitations of individual instruments and technologies.In such scenarios, multisensor data fusion aims at going one step further by seeking original and different ways to analyze and combine multiple measurement datasets taken from the same measurand, in order to produce synergistic effects and ultimately obtain overall better measurement results.In this work an original approach to multisensor data fusion is presented, based on the development of Gaussian process models (the technique also known as kriging), starting from point sets acquired from multiple instruments. The approach is illustrated and validated through the application to a simulated test case and two real-life industrial metrology scenarios involving structured light scanners and coordinate measurement machines.The results show that not only the proposed approach allows for obtaining final measurement results whose metrological quality transcends that of the original single-sensor datasets, but also it allows to better characterize metrological performance and potential sources of measurement error originated from within each individual sensor.     

Tribo-electrification mechanisms for self-mated carbon steels in dry severe wear process

The tribo-electrification mechanisms and wear behavior are investigated for self-mated metal pairs of iron and carbon steels (0.2% C, 0.45% C, 0.7% C) under the dry severe wear condition in the reciprocating friction tester. Results show that with increasing the carbon percentage of the steels, the formation mechanism of the wear particle varies from the macro-asperity removal of the slip-tongue to the micro-asperity removal of the wedge. Meanwhile, the variation of tribo-electrification with the sliding time appears to be more serious. The polarity of tribo-electrification is significantly influenced by the difference between the wear losses of the plate and pin specimens. This means the tribo-electrification is mainly caused by the effect of the material transfer for self-mated carbon steels. Under the higher surface hardness, the mean amplitude of the friction coefficient is decreased and the mean amplitude of tribo-electrification is increased. Results also show that the mean amplitude of tribo-electrification for self-mated carbon steels is linearly proportional to the electric resistivity and the relative wear rate, but inversely to the dynamic real contact area.     

基于多方法融合的服务设计过程优化

为提高服务设计的质量和效率,提出了多方法融合的服务设计过程模型.基于设计思维5阶段模型分析了服务设计过程特征,构建了服务设计阶段流程.应用QFD分析了利益相关者需求及系统要素,定义待解决问题及其权重,依据服务问题特征将问题定义为2种类型,并通过TRIZ构思设计概念.在此基础上,基于情感层次理论完成设计概念,并实现了原型可视化展示.在测试评价阶段,通过确定服务属性评价标准及方法,对用户进行测试,获取了用户反馈信息,进而评估服务系统的可行性.通过整合可行的设计概念形成完整设计方案,并由服务蓝图等工具交付,为后续方案实施提供依据.最终通过实例验证了该模型的有效性,为服务设计实践提供参考.     

Fabrication of micro spur gears by step powder extrusion of Zn-22wt%Al powder without sintering process

Micro spur gears were fabricated using the LIGA process and step powder extrusion without sintering. It is important to manufacture micro dies with high aspect ratios and determine the appropriate extrusion conditions for the micro-forming process. Micro-extrusion dies with close tolerance and long bearing length were produced by the LIGA process. Superplastic Zn-22wt%Al powders can deform under low stresses and exhibit a good micro-formability (average strain rate: 10^?3s^?1; constant temperature: 250°C). These powders were compacted to a cylinder (diameter: 3 mm; height: 10 mm) under 10kN compressive force, and sintered at 350°C for two hours. Micro spur gear shafts were not produced upon extrusion because of the high working pressure on the die surface. For the reduction of the forming load, step powder extrusion was carried out on the compacted powder without a sintering process, but controlling the temperature dwelling period. This process has succeeded in fabricating micro-gear shafts.     

聚氯乙烯粉料输送控制系统

本文介绍了聚氯乙烯粉料输送控制系统的构成；PLC在控制系统中的应用以及PLC应用程序的编制。     

粉末包套挤压非稳态流动过程的数值模拟

为研究金属粉末压制成形致密化机理 ,采用国外MSC .SoftwareCooperation公司的MSC .Marc软件 ,模拟金属粉末包套挤压锥形变形区形成阶段的变形过程 ,获得了金属粉末包套挤压的变形规律 ,以及变形过程中相对密度的分布。     

球形硅微粉生产线自动化系统

介绍了基于西门子WINCC及S7—300PLC的一套自动化系统的硬件、控制功能、人机界面等。该系统应用于球形硅微粉年产千吨新工艺。