快速成形中切片位置和切片厚度的选择

减小尺寸误差、提高表面质量是快速成形的重要目标。本文通过比较切片层上表面L1 1、中间截面L1 0．5和下表面L1的轮廓环数,正确选择切片位置,减小小特征遗失引起的误差;分析了成形制件典型表面直线边和曲线边的表面轮廓算术平均偏差Ra,根据Ra反求出最佳烧结层厚,并进一步给出了CAD模型切片厚度的选取方法。     

Performance evaluation experiments on a laser spot triangulation probe

Laser triangulation probes are increasingly used for dimensional measurements in a variety of applications. At the National Institute of Standards and Technology, we have recently explored the use of laser spot triangulation probes to determine dimensional features such as height and width of channels in a fuel cell plate. To assess the suitability of the probes for performing these dimensional measurements, we designed several experiments that highlighted different error sources in the probes. This report is a summary of those experiments. Numerous studies have been reported in the literature on error sources in laser triangulation probes utilizing artifacts of varying shape (form), color, reflectivity, surface finish, etc. However, our experiments are targeted towards establishing bounds on errors when measuring simple linear dimensions such as height and width on prismatic objects of a single color and material. Our scope is indeed narrow, but intentionally so; it is our objective to highlight the influence of a number of “hidden performance attributes” [1] that impact accuracy of even simple linear dimensional measurements so that it may be of use to others who perform similar measurements.     

Path planning effect for the accuracy of rapid prototyping system

Stereolithography (SL) is one of the rapid prototyping (RP) systems that use liquid photopolymer resin as the raw material for building prototypes. The photopolymer type of the RP system employs lasers to selectively expose the surface of the liquid resin. The absorbance of energy leads to photo-polymerization that transfers the liquid resin into solid. Subsequently, the phenomenon of volume shrinkage is unavoidable, and the curl distortion changes with the different laser scan paths, even affecting the geometric profile of the final-parts. The volume shrinkage and curl distortion are the major causes that lead to poor accuracy of the built prototype. In order to understand and improve the curl distortion and the geometric profile, so as to find a simple and suitable laser scan path. This paper first of all uses simulation and experiment to explore the deformation and shrinkage during the process of photo-polymerization while the liquid resin uses a laser beam to carry out single line scanning or single layer scanning in liquid free surface, and further understands the final change of geometric profile. Secondly, it investigates into the curl distortion and changes of geometric profile occurred in the three-dimensional part by different scan paths. Finally, a simple, proper, and effective laser scan path planning is suggested to decrease the curl distortion, and promote the dimension accuracy and the profile of the final-parts. Besides, this paper also mentions the feasibility of multi-optical processing.     

影响金属零件激光快速成型质量的因素分析

本文通过实验等方法对影响金属零件激光快速成型质量的主要因素进行了研究,并提出了相应的解决方法。金属零件的质量评价主要包括三个方面:尺寸精度、机械性能以及表面粗糙度。光斑直径、搭接率和数控装置的运动精度是影响尺寸精度的主要因素;机械性能中的抗拉强度受填充模式的影响较小,显微硬度与激光功率和扫描速度有很大关系,激光功率和扫描速度越大,零件显微硬度越高;表面粗糙度与激光功率、扫描速度、搭接率、切片层厚及被加工面的倾斜角度都有很大的关系。     

激光快速成型软件系统开发的关键技术

本文详细论述了在VC.net2003环境下激光快速成型软件系统开发过程中的主要关键技术.给出了软件开发过程中所需的点、线、面、环和向量的数据结构;利用OpenGL完成立体模型的显示和控制的方法;切片与轮廓整理以及填充算法中的关键技术.实践证明:本文所述关键技术是可行的,并能提高成型件的加工质量和加工效率.     

功能梯度材料零件激光快速成型的实现方法

本文利用激光直接制造技术(DLF-Direct Laser Faberication),从软件控制的角度,论述了功能梯度材料零件激光加工的总体思路和实现方法.说明了一维功能梯度材料零件中的平面和曲面的扫描路径规划方法的不同之处;一维和二维功能梯度材料零件加工实现过程中的关键技术,例如一维功能梯度材料零件的不同材料含量随层数变化的计算方法,二维梯度材料的切片层厚计算方法等等.     

对CAD模型直接分层的方法研究

提出了直接对CAD实体模型进行分层处理以获取快速原型层片数据的方法,该方法无须进行从CAD到STL的数据转换,从而在根本上避免了由数据模型转换所引起的误差,且无需进行STL文件拓扑信息的提取及其错误的修复,极大地提高了快速原型的精度。     

Online assessment of power transmission belt geometry by using laser triangulation and profile parameterisation

We present a method that enables an automated assessment of the geometrical dimensions of power transmission belts and the detection of surface defects and small deviations from the ideal shape that are difficult to detect with a visual inspection. The method is based on the acquisition of belt surface profiles using a laser triangulation and automated profile assessment based on a custom-developed algorithm. The algorithm uses a novel approach to profile segmentation, featuring a template that defines the expected profile shape in advance and so, allows a faster implementation of the algorithm. It enables an automated calculation of the basic geometrical dimensions, which define the profile shape in the technical drawing and are important for online quality control in the production line. A macrolanguage was developed for a rapid and flexible definition of the mathematical operations used in the calculation of the profile's dimensions and thus, an adaptation to the requirements of a particular application. We demonstrate the use of the automatic belt profile geometry assessment on randomly chosen samples.     

面向快速成形技术的彩色模型计算机描述方法研究

介绍了适合于快速成形的彩色模型的定义,分析了彩色模型色彩分布的两种不同形式,并以STL文件为基础给出了相应的计算机描述方法。     

High accuracy profile measurement of quasi-conical mirror surfaces by laser autocollimation

A method is described for measuring the profile of a quasi-conical mirror surface along one of its axial generators. A laser beam is made to scan the surface and the variation in reflected beam angle is measured by autocollimation. Integrating the angle with respect to distance along the generator gives the profile height to within ±5 nm. The method has application to the metrology of X-ray microscope reflecting objectives     

Positional correction algorithm of a laser galvanometric scanning system used in rapid prototyping manufacturing

The laser galvanometric scanning technique has brought rapid prototyping manufacturing into a new era. However, a number of errors severely affect the prototyping accuracy of the work piece. This paper gives a detailed analysis of the errors involved in the galvanometric scanning system used in rapid prototyping manufacturing. A positional correction algorithm has been developed to rectify the errors to meet the precision requirements of the processing. Experimental results based on a selective laser stinting (SLS) machine prove the efficiency of the positional correction algorithm.     

Influence of measured objects parameters on CMM touch trigger probe accuracy of probing

Influence of the measured objects parameters on coordinate measuring machine (CMM) touch trigger probe inaccuracy of probing is investigated. Factors such as material stiffness of measured workpiece, its surface shape and roughness are taken into consideration. The measuring method out off CMM, based on a rotary table and a reference axis is applied for tests. The concept is based on measurements of the distance between reference and triggering points in various directions. The reference points are established by the rotation of a precise rotary table. The statistical analysis of variance and regression is applied for data analysis.     

运用快速成型技术的人工骨骼实体模型重建

将快速成型技术运用于骨骼实体模型的三维重建研究中,以人体下肢股骨近端为例,通过对原始CT图像数据进行阈值分割,提取股骨近端轮廓曲线,拟合成数字模型.利用快速成型机可以将股骨近端的数字模型实体化,得到与实际骨骼拟合程度较高的实体模型.     

Effect of surface microgeometry on pressure distribution and film thickness profile in circular contact under impact loading

The transient contact between a steel ball and a metal plate is studied experimentally. The main aim of this research is to reveal the impact prints and the indentation profiles of the contacting surfaces for different conditions of thermal treatment, roughness and lubrication. The impact test rig and the measuring devices that have been used to carry out the study are presented. A ballistic pendulum with a steel ball as contacting part frontally impacts the steel sample. Using auxiliary devices, the force, acceleration and total impact duration are simultaneously recorded. When the impact velocity is increased, the force, acceleration and impression diameter increase in all cases. The recorded values of force, acceleration and contact pressure are higher in the lubricated condition than for dry impact for the annealed steel samples used, while the impression diameter is smaller. Copyright © 2006 John Wiley & Sons, Ltd.     

射流电铸快速成型系统研究

将射流电铸与快速成型技术有机结合起来,发展了一种直接快速成型金属零件的新方法--射流电铸快速成型技术,并分析了其成型原理与系统结构组成特点.基于Windows平台,采用NC嵌入PC的结构模式构建了其计算机控制系统,对该控制系统的软硬件组成、结构和功能特点进行了分析和研究,并用研制开发的射流电铸快速成型设备直接快速成型了具有良好形状和尺寸精度的金属铜零件.     

A regression model for analysing the non-linearity of laser triangulation probes

A study on the non-linearity of laser triangulation probes is presented in this paper. The influences of design variables on non-linearity were studied by response surface methodology, and the significant factors were identified. A regression model was developed with which non-linearity can be conveniently evaluated in the design stage of laser triangulation probes. The sensitivities of non-linearity to the design variables are evaluated.     

Adaptive direct slicing of a commercial CAD model for use in rapid prototyping

Slicing a 3D graphic model into layers of 2D contour plots is an essential step for all rapid prototyping (RP) machines. Various methods are available, such as stereo lithography (STL) file slicing, direct slicing and adaptive direct slicing. Amongst these, adaptive direct slicing is the most advanced for its capability of adapting the slicing thickness according to the curvature of any contour. In this study, an adaptive direct slicing method complete with the algorithm for calculating the thickness of each layer is proposed. As an illustration of the method, the algorithm was programmed within the commercial CAD software package, PowerSHAPE. The method was shown to be fast and accurate in comparison with STL file slicing and direct slicing, which both used a constant layer thickness. An erratum to this article can be found at     

基于快速成型的CAD模型数据转换之对比

数据处理与转换是快速成型制造的一个预处理环节,其中数据格式的选择决定着数据处理的流程和方法。文中介绍了STL、IGES和STEP等快速成型技术常用数据接口类型,并基于Pro/E系统进行了CAD模型的数据转换实验,从转换数据量的大小和误差等方面对不同数据格式的转换效果进行了对比分析。     

Effect of crosslinking on the elasticity of polyelectrolyte multilayer films measured by colloidal probe AFM

A homemade colloidal probe atomic force microscope was used to perform nanoindentation with a spherical probe of 5 microm in diameter, at different approach velocities in order to extract the Young's modulus, E0, of poly(L-lysine)/hyaluronan (PLL/HA) films. This parameter is of prime importance to control cellular adhesion. The films were either kept in their native form or cross-linked with a mixture of 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide (EDC) and N-hydrosulfosuccinimide (sulfo-NHS), where the EDC concentration was varied from 1 up to 100 mg mL(-1) (approximately from 5 to 500 mM). A model based on Hertz mechanics was used to account for the interactions between film and probe. It is shown that the Young's modulus varies with the approach velocity for the native (PLL/HA) films, whereas for cross-linked ones, E0 is independent from the velocity over the whole range investigated. It is found that for native films, E0 takes a value of 3 kPa at low approach velocities, a velocity domain that should be relevant in cellular adhesion processes. The Young's modulus increases with the EDC concentration used to cross-link the films and levels off at a value of about 400 kPa for EDC concentrations exceeding 40 mg mL(-1). Thus, it is possible by crosslinking PLL/HA films to control their elastic properties with the aim to alter their behavior as to the cellular adhesion.     

EVA热熔胶厚度对LOM型快速成形件精度的影响和改进措施

在实验测试的基础上，对影响LOM型快速成形件精度的因素之一——热熔胶厚度场作了全面的分析，提出了提高LOM型快速成形精度的改进措施。