Friction and wear behaviour of rapid prototype parts by direct metal laser sintering

Abstract

Rapid prototyping and manufacturing (RP/M) is one of the proven tools for product development owing to its advantages such as short product cycle, high quality product and possibility of fabricating functionally gradient materials. Several RP/M techniques do exist. Among them, direct metal laser sintering (DMLS) method is quite popular as near net shape components with high dimensional accuracies can be manufactured. Meager information is available as regards the tribological behaviour of laser built parts, although this is vital in judging the suitability of built-up parts for applications where sliding is inevitable. In the light of the above, the present investigation is aimed at building parts by DMLS technique of RP/M using 50 μm iron powder and characterising its density, microstructure, microhardness, tensile strength, friction and wear behaviour under sliding conditions. The effect of laser speed on the above properties of built-up parts has been studied. The build layer thickness was maintained at 50 μm. Laser diameter of 0˙4 mm, laser power of 180 W and hatch spacing of 0˙2 mm were adopted. However, the laser speed was varied from 50 to 125 mm s^–1 in steps of 25 mm s^–1. Laser speed had a profound influence on density, microstructure, microhardness, tensile strength, friction and wear behaviour of built-up parts. Lesser laser speed resulted in higher density, microhardness, tensile strength and wear resistance while higher laser speed promoted lowering of coefficient of friction.     

粉末冶金技术的发展与贡献

粉末冶金是制造金属材料和金属零件的特殊技术。本文论述了粉末冶金各分支领域的发展,及应用各类粉末冶金制品对国民经济和科学技术的贡献,粉末冶金作为新材料技术,在研制新型结构材料和功能材料中起到重要作用。并介绍了粉末冶金新技术的发展概况。     

拉曼光谱法无损检验打印文件朱墨时序

打印字迹与印文形成先后顺序的检验是文件检验领域的难题之一,常见的显微镜检验法、机械法等检验方法,其检验结果易受检验人员的主观影响,准确率不够高,常常受到质疑。本文研究了运用Invia显微激光拉曼光谱仪对不同种类打印文件与不同种类印章盖印的样本进行检验,鉴别样本的朱墨时序。研究利用显微激光拉曼光谱测定朱墨时序样本中各部位的光谱,通过比对印字交叉部位与未交叉部位的字迹、印文的特征拉曼峰,判断打印文件的朱墨时序。实验结果表明,这是一种准确性高的无损检验方法,打印机的种类、印油种类、印油量及纸张对实验结果基本没有影响。直观的图谱及客观的数据更令人信服,对实践检验工作有重要指导意义。     

Robust generalized numerical inspection fixture for the metrology of compliant mechanical parts

Free-form non-rigid parts form the essence of today’s automotive and aerospace industries. These parts have different shapes in free state due to their dimensional and geometric variations, gravity and residual strains. For the geometric inspection of such compliant parts, special inspection fixtures are used in combination with coordinate measuring systems (CMM) and/or optical data acquisition devices (scanners). In our previous work, a general procedure was developed to eliminate the use of inspection fixtures. We measured the similarities between CAD model and scanned data by taking the advantage of the geodesic distance metric. Then, using finite element non-rigid registration, we deformed the CAD model into range data to find the geometric deviations. Here, we apply a new method to robustify the generalized numerical inspection fixture. We filter out points causing incoherent geodesic distances and demonstrate that our approach has several significant advantages, one being the ability to handle parts with missing range data. The other advantage of the method presented is its capacity to inspect parts with large deformations.     

高强螺栓实物拉伸试验夹具的研制及应用

在分析现有高强螺栓实物拉伸试验夹具优缺点的基础上,对新研制的高强螺栓实物拉伸试验夹具从材料选择到结构设计、锻造、机加工、热处理等方面,都进行了改进和完善。新研制的高强螺栓实物拉伸试验夹具自2011年4月投入使用至今,累计完成5000余件螺栓的实物拉伸试验,其主要部件夹具体、连接轴和平垫圈仍然保持良好,证明其具有很高的使用寿命,满足了高强螺栓的检测需求。     

Improved Bi-Criterion flexible registration for fixtureless inspection of compliant parts

Because of the effects of gravity and/or residual stress, some manufactured mechanical parts, such as sheet metals and skins, often have a significantly different shape in a free-state position as compared to their state-of-use position. These parts are described as compliant, flexible or nonrigid. Expensive specialized fixtures are currently used prior to performing geometrical inspection operations in order to maintain compliant parts in the state-of-use position. This paper introduces an automatic bi-criterion flexible registration method for the dimensional and geometric inspection of such parts. The proposed method deforms the data acquired via a non-contact scanner of a compliant part in a free-state position until it reaches the nominal CAD shape for inspection with conventional Computer-Aided Inspection (CAI) tools. In other words, the method neutralizes the deviations induced in a compliant part by the effects of gravity and residual stress, allowing the acquired data to be treated as if it were obtained from a rigid part, using already available conventional (rigid) CAI tools. A proposed algorithm based on the BOFR-2 (the 2nd version of a Bi-Objective Flexible Registration algorithm) method is validated against both virtual simulated and experimental real industrial case studies from the aerospace sector. The resulting cost reduction and agility increasing make this fixtureless method well adapted to the requirements of unit-batch production in the context of Industry 4.0.     

Nonrigid geometric metrology using generalized numerical inspection fixtures

Freeform surfaces have become an integral part of the automobile and aerospace industries. The parts with a very thin wall in proportion to their size are referred to as nonrigid (or flexible) parts. Generally, for the geometric inspection of such flexible parts, special inspection fixtures, in combination with coordinate measuring systems (CMM), are used because these parts may have different shapes in a free state from the design model due to dimensional and geometric variations, gravity loads and residual strains. A general procedure to eliminate the use of inspection fixtures will be developed. Presented methodology is based on the fact that the interpoint geodesic distance between any two points of a shape remains unchangeable during isometric deformation. This study elaborates on the theory and general methods for the metrology of nonrigid parts. We will merge existing technologies in metric and computational geometry, statistics, and finite element method to develop a general approach to the geometrical inspection of nonrigid parts.     

机器视觉在工业测量中的应用与研究

基于普通双目视觉测量模型,针对视觉测量系统的关键技术-标定、特征提取、特征匹配,提出了一种实用的高精度摄像机标定方法,基于“多对一”的思想,讨论了一种改进的Hough变换方法;山外极约束理论,提出了一种基于角点的外极斜率特征匹配方法。实验证明.该方法能成功的应川于复杂零件的测量。     

Laser inspection: An automotive industry application

The inspection of parts is a difficult task to automate within the working environment of a factory. Such inspection may be used both for quality control and for purposes of identification. However some parts present special problems, such as those made from transparent or translucent materials. In this case, interpretation of the signal emitted by a low-power laser source facilitates the task of 100% parts inspection and detection of defects. This method has advantages both in cost, reliability and long life, in comparison with other possible solutions.     

On-line 3-D system for the inspection of deformable parts

In spite of the development of automated tolerance inspection systems for manufactured parts over the years, there are still processes that inevitably require manual intervention making full automation impossible in most cases; in particular when dealing with deformable parts. In most current industrial inspection systems, a deformable part under inspection must first be mechanically constrained on a rigid support or jig so as to be able to compare it with its nominal shape. This paper presents a new system to perform real-time surface inspection of deformable parts that does not require fixturing. Instead, the proposed system applies virtual forces to the part??s CAD model as if the part was installed in the fixturing device. Normally, a precise finite element method (FEM) simulation should be used to approximate the deformation that appends when the part is installed in the device. Even with a fast parallel computer, FEM is far from being real-time and cannot be used for on-line inspection. In the proposed system, a radial basis function approximation of the FEM simulation is trained off-line and used to speed-up the simulation by an order of magnitude. Experimental evaluation of the proposed system is presented for three plastic parts. Using the proposed scheme, an approximation of 0.25?mm compared with the real deformation was obtained. In this paper, statistical results are presented such as the average deviation, standard deviation, and processing time between the approximations obtained with the proposed method and with the finite element method applied to the full CAD model.     

特种设备检验检测技术应用效果研究——以物联网技术为例

近年来,随着我国社会发展进程逐步加快,国内科学技术得到了良好发展契机,这也为特种设备物联网技术的发展提供良好环境。特种设备在现代人们生产生活中扮演着重要角色,特种设备运行的安全性对于人们生活水平以及稳定社会的构建都具有重大影响,随着社会对特种设备重视程度的逐步提升,对于现阶段特种设备检验检测技术的要求也日益提升。因此,务必要对特种设备检验检测技术予以高度重视,加大对这一领域新技术、新手段的研究力度,以此来推进特种设备检验检测整体成效的进一步优化和提升。文章以物联网技术为切入点,对特种设备检验检测技术应用效果进行研究和分析,以供参考。     

Three-body impact wear study on conventional and new P/M + HIPed wear resistant materials

A new hammer-mill type impact wear testing facility was built for impact wear testing and characterization. Tests with the hammer-mill impact wear device were carried out on conventional wear resistant materials such as Mn-steels of different compositions, white cast iron, and on new P/M+HIPed wear resistant materials. To verify the validity in using this laboratory wear testing apparatus, wear behavior and worn surfaces obtained on conventional and new Mn-steels generated from this device were compared with wear phenomena and worn surfaces developed in industrial applications, i.e. from certain types of rock crushers. The strain hardening effect in different Mn-steel grades was studied first. Second, the wear resistance of materials with different properties was studied using two different grades of abrasive. With silica sand (high hardness, low compressive strength), conventional Mn-steel and white cast iron perform in a manner comparable with the P/M+HIPed materials. With volcanite sand (low hardness, very high compressive strength), the P/M+HIPed wear resistant materials appear to have the best wear resistance.     

薄膜拉伸机构关键零部件有限元分析研究

利用两种CAE分析软件,对新型薄膜主动预拉伸机构的的关键零部件,大胶辊和小胶辊进行有限元分析,得到了两者的共同点和区别。Pro/E的MECHANICA模块,由于其强大的网格划分能力,适用于分析结构复杂、受力较大的零件;而CosMosexpress具有界面简单,效率高的特点,适用于分析一般复杂的零件。二者都能通过新的可视化界面和分析报告,提供准确的分析结果。     

Fe-Mo-B预合金粉对温压铁基材料烧结硬化性能的影响

研究了Fe-Mo-B预合金粉的含量对温压铁基材料烧结硬化后试样的密度、尺寸精度、表观硬度和抗拉强度以及显微组织的影响。结果表明：混合粉中加入一定量的Fe-Mo-B预合金粉,利用温压工艺压制成形后烧结硬化,可有效提高试样的力学性能并可获得典型贝氏体组织。烧结试样密度最高为7．49g／cm^3,其相对密度为97．74％;表观硬度最高可达44HRC,抗拉强度为1434MPa。     

X射线安检设备智能控制与诊断系统设计

典型的X射线安检设备主要由X射线发生器、X射线线性阵列探测器、滚筒电机及传动装置、装有图像采集卡的PC及光触发传感器等组成，要实现各部分协调、高效的工作需设计一套完善的控制系统。依据X射线安检机各部分的工作原理及控制要求，制定了系统的控制方案，该控制系统方案已应用到沈阳地泰检测设备有限公司DEX9080B型X射线安检机上，经过2年多的运行，证明该系统运行稳定、响应速度快，具有良好的抗干扰性和实用价值。     

曲轴在线综合测量机的原理及组成

介绍了一种汽车曲轴在线多参数综合测量机,该机采用气电转换技术、信号调理电路及多路信号采集等方法,可自动完成曲轴终检工序47个参数的综合测量,其准确度误差<2μm。测量机所具有的专用测量系统与控制软件技术,实现了自动识别和处理零件的几何特征(如键槽、油孔等),具有自动调频、自动调零与校准、故障自检等功能。     

起重机械能耗检测与评价研究

指出了当前国内对起重机械的节能检验与测试研究工作刚刚有所起步,国外已进行了一些研究,但尚未对起重机械节能的检测方法和评价体系进行系统和全面研究的情况。分析了起重机节能研究现状,论述了起重机节能评价关键技术。     

基于可见光和热成像的风机叶片全周期无损检测综述

风机叶片在制造、服役和维修阶段的无损检测非常重要。叶片长期在高强度的风力载荷下工作,制造过程产生的任何微小缺陷将在服役中扩大,进一步威胁到风机的正常运行。因而,风机叶片的无损检测一直是工业界与学术界探索的难题。根据叶片视觉检测方法结合无人机技术应用、相关数据包括图像处理方法以及缺陷评判方法的智能程度等方面对前人以及作者所在课题组的前期工作进行综述、总结、分析与对比。目前,可见光视觉检测与红外热成像检测等以视觉为基础的检测手段满足了风机叶片在役运维时非接触、高效、低成本、安全等需求。视觉检测与无人机巡检技术相结合能最大程度的保证人员安全,同时克服了望远镜检测视野受限的难题。然而该检测手段在风机叶片巡检中目前尚存在缺陷定量难、内部缺陷识别率低等方面的不足。通过分析对比可见光检测与热成像检测技术,认为结合智能算法的无人机搭载双光融合检测手段未来有望于解决风机叶片检测中存在的不足。     

磁性零件在线式激光光电计数仪的设计

为实现对磁性零件的在线计数检测 ,开发了一种在线式磁性零件激光光电计数仪系统。采用激光光源 ,缩束光管 ,光束发散小 ,准直性好 ;采用对辊式自动排料机构和圆刷式梳料器 ,工件排列有序 ,下料速度快 ,解决了目前磁性零件大批量计数的问题。该计数仪具有计数准确、快速和适应多种规格产品计数的特点 ,对 3～ 10 0 m m和厚度 1～ 2 0 m m的零件均可进行计数 ,并且计数速度可达到 10 0 0件 /分以上 ,已应用于实际生产中。