SLS激光功率与烧结件弹性模量关系研究

为了研究利用SLS加工力学性能变化的功能件,首先分析了SLS成型机的粉床预热温度场,根据拉伸试验设计试样尺寸,烧结出9种激光功率下的试样;其次根据静力学拉伸试验数据,计算出了各种试样的弹性模量值;最后推导出SLS成型机激光功率与烧结件弹性模量间的数学模型。     

基于零件切片的选择性激光烧结预热温度控制方法

选择性激光烧结(Selective laser sintering,SLS)系统是通过加支撑或采用人工调节预热温度的方法来减少成形件的翘曲变形,它劳动强度大、SLS材料浪费多、成形效率低,且预热温度难以精确控制。基于以上情况,提出一种新的控制方法,使预热温度能随零件断面几何形状的变化而自动调节。以华中科技大学开发的SLS设备为研究对象,验证这种新型控制方法的可行性。试验结果和实际应用表明:与原有控制方式比较,根据文中所提出的方法成形的零件表面质量、尺寸精度和形状精度等都有较大幅度改善,并且真正实现了SLS成形过程的自动化。     

尼龙6／铜复合粉末选区激光烧结工艺参数优化及力学性能研究

制备了不同铜粉含量（质量分数）的尼龙6机械混合复合粉末,对复合粉末进行激光烧结,利用扫描电镜对烧结件的形貌进行了表征,通过正交试验优化工艺参数,并研究了铜粉含量对烧结件力学性能的影响。结果表明,铜粉与尼龙表面黏结良好,铜粉均匀分布在尼龙基体中;随着铜粉含量增加,烧结件抗弯强度、抗拉强度显著提高,冲击强度逐渐降低;铜粉含量为50％时,烧结试样抗拉强度为43．28MPa,抗弯强度为77．66MPa,硬度为112HRL,分别比纯尼龙6提高了10．04％、59．27％和39．29％。     

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.     

不锈钢激光间接烧结粉末材料及其成型工艺研究

开发低成本,成型性好的材料对激光选择性烧结的应用具有重要的意义。本文研究了一种不绣钢间接烧结粉末材料,并对其工艺参数进行了优化,用此种材料在优化的工艺参数下制作出了复杂的三维零件。     

激光选区烧结超高分子量聚乙烯工艺及性能

研究了激光选区烧结(SLS)成型工艺中不同工艺参数以及后续热处理工艺对超高分子量聚乙烯(UHMWPE)材料成型性能的影响。通过调整扫描间距、激光功率、扫描速度等不同工艺参数,描述了SLS成型UHMWPE零件的致密度、拉伸强度以及断裂伸长率,并对热处理前后的SLS成型UHMWPE零件的力学性能进行了比较。结果显示,致密度、拉伸强度、断裂伸长率总体上与激光功率呈正相关关系,与扫描间距、扫描速度呈负相关关系。经热处理后,SLS成型UHMWPE零件的力学性能有明显提高,致密度达到95.12%,抗拉强度达到24.08 MPa,断裂伸长率达到334.82 MPa。实验结果表明:SLS成型UHMWPE零件与模塑成型UHMWPE零件性能尚有差距,仅优化成型工艺不足以得到理想性能,但经热处理后,零件性能基本满足使用要求。     

Towards selective laser sintering of objects with customized mechanical properties based on ANFIS predictions

Recently, the adaptive network-based fuzzy inference system (ANFIS) has been used extensively in modeling of manufacturing processes to save both optimization time and manufacturing costs. ANFIS is a powerful iterative tool for optimizing non-linear and multivariable manufacturing operations. In the present study, ANFIS is used to predict the optimum manufacturing parameters in selective laser sintering (SLS) of cement-filled polyamide 12 (PA12) composite. For this purpose, a set of cement-filled PA12 test specimens is manufactured by SLS technique with 8 different values of laser power (4.5–8 Watt) and 8 different weight fractions of white cement (5 %–40 %). Mechanical characterization of cement-filled PA12 is carried out to evaluate the ultimate tensile strength (UTS), compressive strength, and flexural properties. The experimental data are then divided into two groups; one group for training the ANFIS model and the other group for checking the validity of the identified model. The built ANFIS model was validated experimentally and comparison with experimental results revealed mean relative errors of 2.92 %, 3.84 %, 4.75 %, and 3.31 % in the predictions of UTS, compressive strength, flexural modulus, and flexural yield strength, respectively.

     

Fuzzy set based cost model of additive manufacturing with specific example of selective laser sintering

A fuzzy set based cost model for additive manufacturing is proposed. The model is illustrated through an example of selective laser sintering (SLS), a commonly used additive manufacturing (AM) process. Initially, a deterministic cost model is developed. It is then converted to a fuzzy set based model by considering uncertainty in build time estimation and cost components. For the specific case of SLS, a build time estimation procedure is developed as a part of the cost model. A method to evaluate the reliability of the cost estimate in AM and its significance is also introduced. The cost model is illustrated through two examples of products manufactured by SLS.

     

激光选区快速成型件后处理工艺的试验研究

快速成型技术就是直接根据CAD模型,快速生产样件或零件的成组技术总称[1],它是先进制造技术的重要组成部分.本文主要介绍了激光选区粉末烧结(SLS)技术的原理,并结合工业生产,研究了SLS快速成型件的后处理工艺,为激光选区粉末烧结快速成型技术的进一步应用打下了良好的基础.     

Ni60 A含量对激光再制造试件力学性能的影响

采用激光再制造技术在Q235基材上熔覆三种不同成分配比的304不锈钢粉末,分别为纯304不锈钢末,添加10％Ni60A的304不锈钢粉末,添加15％Ni60A的304不锈钢粉末,利用维氏显微硬度计研究熔覆层表面维氏显微硬度,利用万能试验机研究熔覆层拉伸力学性能。实验结果表明：添加了Ni60 A粉末的304不锈钢再制造试件由于发生了固溶强化,使得维氏显微硬度和抗拉强度显著增强,延伸率则有所下降,且随着Ni60 A含量的增加,效果更明显。     

SLS快速成形技术中激光加工参数对制件性能的影响

以AFS--320MZ快速成形机为例，研究了基于选择性激光烧结(SLS)快速成形制造中激光功率密度、扫描速度、扫描间距、扫描方式和铺粉密度等加工参数对制件性能的影响。     

Building Porous Biopolymeric Microstructures for Controlled Drug Delivery Devices Using Selective Laser Sintering

The capability to build parts with predetermined porous microstructure and dense walls using powdered biomaterials makes selective laser sintering (SLS), one of the more flexible rapid prototyping (RP) process, a strong candidate for building biodegradable controlled release drug delivery devices (DDD). The objective is to design a varying-porosity circular disc with outer region being denser acting as diffusion barrier region and inner more porous region acting as drug encapsulation region. This is to achieve a zero-order of release over a desired duration of time in drug administration.A key study in this paper was to determine the influence of critical SLS process parameters namely, laser power, laser scan speed and part bed temperature on dense wall formation and control of the porous microstructure of SLS-fabricated parts built with biomaterials. The physical characteristics of the fabricated devices were investigated through microstructure examination using the scanning electron microscope (SEM). Two biodegradable polymers, namely Polycaprolactone (PCL) and Poly (-L) Lactic Acid (PLLA), were investigated. For PCL varying-porosity disc, the laser power is set at 3 W (inner region) - 4 W (outer region), the scan speed at 5080 mm/s and the part bed temperature at 40°C. For Poly(-L) Lactic Acid (PLLA), the laser power is set at 12 W, the scan speed at 1270 mm/s and the part bed temperature at 60°C. With the set of SLS parameters tabulated for specific polymers, polymeric matrix with specific porosity can be fabricated as drug delivery devices.     

Determination of process parameters in stereolithography using neural network

For stereolithography process, accuracy of prototypes is related to laser power, scan speed, scan width, scan pattern, layer thickness, resin characteristics and etc. An accurate prototype is obtained by using appropriate process parameters. In order to determine these parameters, the stereolithography (SLA) machine using neural network was developed and efficiency of the developed SLA machine was compared with that of the traditional SLA. Optimum values for scan speed, hatching spacing and layer thickness improved the surface roughness and build time for the developed SLA.     

能量密度对激光选区熔化成形AlSi10Mg合金缺陷及力学性能的影响

分析了能量密度对激光选区熔化成形AlSi10Mg合金致密度的影响规律，并采用微纳CT检测结合EDS能谱分析的方法，统计了试样内部缺陷的类型和尺寸，分析了缺陷在试样三维层面上的分布规律及产生原因，得出了影响激光选区熔化成形AlSi10Mg合金致密度和内部缺陷的主要因素。结果表明，合适的激光能量输入是获得高致密度的关键，当激光能量密度处于47.62~50.00 J/mm³区间时，试样致密度最高，此时试样中夹杂缺陷消失，孔洞缺陷最大尺寸降至0.056 mm。孔洞缺陷产生原因主要与未熔粉体、空心粉及氧化物有关。在优选激光能量密度区间内成形的AlSi10Mg合金试样，其平均抗拉强度和伸长率分别在294 MPa和8.0%以上，优于铸造AlSi10Mg合金。     

Optimizing process parameters for selective laser sintering based on neural network and genetic algorithm

Selective laser sintering (SLS) is an attractive rapid prototyping (RP) technology capable of manufacturing parts from a variety of materials. However, the wider application of SLS has been limited, due to their accuracy. This paper presents an optimal method to determine the best processing parameter for SLS by minimizing the shrinkage. According to the nonlinear and multitudinous processing parameter feature of SLS, the theory and the algorithms of the neural network are applied for studying SLS process parameters. The process is modeled and described by neural network based on experiment. Moreover, the optimum process parameters, such as layer thickness, hatch spacing, laser power, scanning speed, work surroundings temperature, interval time, and scanning mode are obtained by adopting the genetic algorithm based on the neural network model. The optimum process parameters will be benefit for RP users in creating RP parts with a higher level of accuracy.     

Genetic-algorithm-based multi-objective optimization of the build orientation in stereolithography

Build orientation is an important fabrication parameter in layer manufacturing (LM) since it affects the part fabrication accuracy, cost, and time. Despite its importance, orientation selection relies quite heavily on the experience and skill of the operator of the LM system, which does not guarantee optimality of the decision. In the present work, a decision support system that automates the orientation selection task is proposed. The proposed system utilizes genetic algorithms and multi-criteria optimization techniques for the definition of (near) optimum build orientation for parts fabricated with stereolithography. Build time, surface roughness, and post-processing time are considered as the main optimization criteria.     

碳化硅零件的激光选区烧结及反应烧结工艺

为了获得高密度、高性能、复杂结构的碳化硅陶瓷件,提出采用机械混合法制备含有黏结剂和乌洛托品固化剂的碳化硅复合粉体,对复合粉体进行激光选区烧结（SLS）形成陶瓷素坯,并对素坯进行气氛烧结和渗硅处理,使其与基体发生反应烧结,最终形成复杂陶瓷异形件。实验证明：若激光功率为8.0 W、扫描速率为2 000 mm/s、扫描间距为0.1 mm、单层厚度为0.15 mm,获得的 SLS 陶瓷样品密度和强度最好。对SLS试样进行合理的中温碳化和高温渗硅,所得碳化硅陶瓷烧结体的抗弯强度最高可达 81 MPa,相对密度大于86%。     

Empirical investigation of environmental characteristic of 3-D additive manufacturing process based on slice thickness and part orientation

The significant amount of research has been done in improving the mechanical properties (compressive strength), dimensional accuracy (length, height and width), and build time of the components manufactured from the additive manufacturing process. In contrast to this, the research in the optimization of environmental characteristic i.e. energy consumption for the additive manufacturing processes such as selective laser sintering (SLS), and selective laser melting (SLM) needs significant attention. These processes intakes the significant portion of input laser energy for driving the laser system, heating system and other machine components. With world moving towards globalization of additive manufacturing processes, the optimization of laser energy consumption thus become a necessity from productivity and as well as an environmental perspective. Therefore, the present work performs the empirical investigation by proposing the optimization framework in modelling of laser energy consumption of the SLS process. The experimental procedure involves the computation of energy consumption by measuring the total area of sintering. The optimization framework when applied on the experimental data generates the functional expression for laser energy consumption which suggests that the slice thickness is a vital parameter in optimizing it. The implications arising from the study is discussed.     

Effect of Heat Sink and Cooling Mediums on Ferrite Austenite Ratio and Distortion in Laser Welding of Duplex Stainless Steel 2205

In order to control the ferrite and austenite percentage in duplex stainless steel welding, many researchers try to change the laser welding parameters and cooling medium, but ignore to study the influence of heat sink e ect on weld strength. In this work, the e ect of aluminium heat sink and varying cooling medium on the laser welding of duplex stainless steel(DSS) 2205 is studied. The 2 mm thick DSS sheets welded with pulsed Nd: YAG laser welding machine by varying the cooling medium(air and oil) and an aluminium plate used as a heat sink. The welded specimens tested for tensile strength, micro-hardness, distortion, microstructure and radiography analysis. The faster cooling rate in the oil quenching process enhances the ferrite percentage compared with air-cooled samples. But the faster cooling rate in oil quenching leads to more distortion and using aluminium as a heat sink influenced positively the distortion to a small extent. The lower cooling rate in air quenching leads to a higher tensile strength of the welded specimen. The objective of this work is to analyse experimentally the e ect of cooling medium and heat sink in the mechanical and metallurgical properties of laser welded duplex stainless steel.     

Implementation of a Robot System for Sculptured Surface Cutting. Part 2. Finish Machining

Rapid prototyping plays an important role in product development. There are two ways to realise rapid prototyping: one is to develop new prototyping equipment such as stereolithography apparatus (SLA), selective laser sintering (SLS), etc., and the other is to improve existing CNC techniques. In this work, a robot system for rapid prototyping, which is an enhancement of the CNC based method, is presented. A robot arm holding a milling tool is used to machine the prototype of a solid model drawn using a commercial CAD system. In a previous paper, Part 1, a strategy using the robot for rough machining was discussed and then an automatic tool-path generation method using a grid height array was presented. As a verification of the proposed algorithm, a number of prototypes were produced, which demonstrated the feasibility and advantages of the algorithm. In this paper, Part 2, an approach to represent C-space by incorporating possible variations in tooling orientations is proposed. In order to reduce the error on complex surfaces resulting from undercut or overcut operations, a curvature-matching algorithm is also developed. Finally, experimental work using collsion-free planning for manipulator movement and stimulation for the curvature matching algorithm is carried out.