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.     

Part Orientation in Stereolithography

Rapid prototyping (RP) machines reduce the lead time and cost of new products by automating the prototype manufacturing phase of the product development process. However, it is necessary for operators to orientate the prototype correctly in the RP machine to obtain the best trade-off between time, cost, and accuracy. The purpose of this work is to produce a decision-support tool to help RP users in this task. The tool is aimed at stereolithography which is the most widely adopted RP technology. The tool is a feature-based system produced using an object-orientated programming language and a solid modelling CAD environment. Cost, time, problematic features, optimally orientated features, overhanging area, and support volume are considered when recommending a build direction to the user. Three sample parts were used to illustrate the performance of the system. The system yielded the best surface finish and correctly highlighted several problem features.     

SLS成形件的收缩模型和翘曲模型

快速成形的精度是快速成形技术发展和扩大其应用领域的关键,工艺误差是影响成形精度的关系之一,而成形件收缩和翘曲对其工艺精度起决定性的作用,通过建立SLS成形过程的收缩模型研究了SLS加工中成形件的收缩形式以及收缩规律,同时研究了收缩的不均匀性所引起的翘曲,建立了成形件的翘曲模型,发现烧结收缩与烧结程度密切相关,翘曲量与烧结收缩率成正比,与零件线尺寸成正比,这些研究结果为克服SLS加工收缩引起的误差和收缩补偿提供了依据,为减少翘曲变形提供了一种方法。     

控制FDM成型制件误差的方法研究

快速制模是快速成型的主要应用之一,但成型件的精度难以达到快速制模对原型或型芯尺寸精度和表面精度的要求.系统分析了熔融堆积成型( FDM)工艺成型精度的影响因素,分析产生误差的根源及作用机理.针对FDM产生的误差,通过定性和定量分析,提出减小误差的途径和方法,并通过实例验证了解决翘曲变形和尺寸精度问题的方法,提高了原型的精度,对熔融堆积成型工艺精度的提高具有实际的参考价值.     

Experimental analysis of properties of materials for rapid prototyping

Rapid prototyping (RP) can substantially shorten the time and reduce the cost of developing a new product from the initial idea to production. Rapid prototyping can help in recognizing the basic defects whose subsequent correction may prove very expensive, especially if they have already been made when the product is ready for production. There are also many restrictions of RP procedures, primarily in the number of available materials and their properties, which may differ significantly from the properties of end product materials. In this work, based on the stipulated standards of the 3D printing machines (ZPrinter 310 Plus) and the hybrid Polyjet technique (Objet Eden 330), adequate test specimens were made. Furthermore, with adequate equipment, we carried out the analysis of the dimensions, roughness of surfaces, and mechanical properties of prototype test specimens. Then, based on the data obtained by testing of properties, we provided a critical commentary regarding the data stipulated by their producers.     

选区电化学沉积快速成型轨迹规划

数控选区电化学沉积快速成型是将快速成型技术与电化学沉积技术相结合的一种新型快速成型方法。为保证数控选区电化学沉积快速成型的零件精度,提出了一种基于电化学沉积技术的快速成型工艺的路径生成算法。结合该成型工艺的特点,分析了快速成型领域常用的几种扫描方式,轨迹规划方案分为STL切片处理、轮廓偏置、轮廓填充、数控加工代码生成四个过程,提出了平行交错往复间隙填充法。实验表明该轨迹规划能够达到选区电化学沉积快速成型的要求,制造出高精度、高表明光洁度的零件。     

A New Slicing Procedure for Rapid Prototyping Systems

The current slicing rule of most rapid prototyping (RP) systems cannot ensure unilateral tolerances on the whole prototype and often results in problems of overcut and undercut on the same part. This drawback leads to unsatisfactory precision of the part in post processing. In order to reduce the above problems, a new slicing method is proposed in this paper. Based on the geometry information in a stereolithography (STL) file, an algorithm is developed. The appropriate slicing rule is selected according to the inner product of the normal vector and working direction of the part, together with the function of the part to be manufactured. The STL file is cut into 2D sections and an accurate contour is calculated. After the slicing computation, an appropriate working path is produced. The rules proposed in this paper have been verified. This work contributes to the improvement of slicing rules in existing RP systems, especially in systems using uniform thickness slicing. It also improves manufacturing efficiency and working tolerances.     

FDM成形件精度预测模型的建立

熔融沉积成形(FDM)是快速成型(RP)最有发展前途的工艺之一,掌握提高成形件精度的控制方法是推广其应用的重要途径。在分析FDM成形件精度影响因素的基础上,提出应用误差反向传播(BP)神经网络建立预测精度模型的方法。将主要影响因素作为BP神经网络模型的输入参数,并根据最小预测误差选择输入层和中间层的维数,确定了BP模型结构。利用多组实验数据进行模型训练,建立了BP神经网络模型。模型预测与实验测量的对比结果表明,模型的预测误差在6%以内,具有很高的预测精度,可以指导实际应用。     

A BOM Oriented Class-Based Storage Assignment in an Automated Storage/Retrieval System

A solid laser-diode plotter (SLP) system is one of the commer-cial rapid prototyping (RP) systems developed and marketed in Japan. In the SLP system, two semiconductor lasers are employed instead of a UV laser or a diode-pumped solid state laser, as used in the stereolithography process to cure a specially designed photopolymer. An ascending platform is used to build the suspended solid model, and only a small amount of resin is cured in a thin layer on a plate of glass just below the last layer built. Hence, the SLP system is a low-cost RP system and is well suited for educational purposes, because a high-power laser is not involved and only a small amount of resin is used. However, the over-curing of the overhanging area is a processing problem in the ascending platform method, because the built part is suspended. In order to reduce the over-curing of the SLP parts, the Taguchi method was employed to analyse the processing parameters. The effect of the processing parameters on the over-curing was investigated and presented. The results show that the over-curing of the SLP parts was reduced about 40% using the optima processing parameters as analysed by the Taguchi method.     

典型大尺寸薄壁快速成型件的加工方法

在快速成型机加工大尺寸、薄壁零件时,快速成型机的激光功率、加工中的零件的受力情况和零件的支撑工艺都会影响到零件最终精度。结合在实际加工原型件中遇到的具体问题,进行了加工工艺方法的研究和解决,以便更有效地缩短产品的研发周期,提高产品质量和缩减产品的成本。     

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.     

Rapid prototyping in the development of optical pickup unit

Rapid prototyping (RP) has already proven itself in the electronics industry as a method for shortening the product development time cycle. In the development of the optical pickup unit (OPU), extremely high precision is needed to make a functional model. Very often, in the design phase of the product development cycle, the prototype of the OPU is machined from a single piece of aluminium block to make the working sample. In this project, a comparison of the machined aluminium sample, RP samples from various RP processes and that moulded out from the injection moulding machine is made on surface finishing as well as dimensional accuracy. Finally, a comparison of tooling cost, piece part cost and lead time of obtaining the parts is also discussed on the different prototyping and manufacturing processes.     

Determination of optimal build direction in rapid prototyping with variable slicing

Several important factors must be taken into consideration in order to maximize the efficiency of rapid prototyping (RP) processes. The ability to select the optimal orientation of the build direction is one of the most critical factors in using RP processes, since it affects part quality, build time, and part cost. This study aims to determine the optimal build-up direction when a part is built with the variable layer thickness for different RP systems. The average weighted surface roughness (AWSR) that is generated from the stair stepping effect, the build time, and the part cost using the variable layer thickness are all considered in the process. Using the multi-attribute decision-making method, the best orientation is determined among the orientation candidates chosen from the convex hull of a model. The validity of the algorithm is illustrated by an example. The algorithm can help RP users select the best build-up direction of the part and create an efficient process planning.     

<Emphasis Type="Bold">Curl Distortion Analysis During Photopolymerisation of Stereolithography Using Dynamic Finite Element Method</Emphasis>

Stereolithography is one of the rapid prototyping processes which uses a photopolymer as the raw material to build prototypes. The photopolymer absorbs energy by selective laser exposure. The curing effect starts when the absorbing energy exceeds a critical value, and the process is called photopolymerisation. The photopolymerisation changes the phase from liquid to solid. The cured volume can expand and then shrink on cooling. The process parameters such as the scanning speed, scanning path, scanning pitch, and the slicing thickness, lead to different shrinkage and curl distortion, so, the photopolymerisation process is a dynamic material behaviour. In this study, a dynamic finite element simulation code has been developed to simulate the photopolymerisation process. The simulated result for a suspended beam which corresponds to the process parameters shows that a short raster causes less curl distortion than a long raster. The experimental result agrees very well with the simulated result.     

电子束应用于快速成型(RP)之初探

探讨将电子束的加工方法引进到快速成型技术中,用以替代SLS技术中的激光作为加工热源,以此去掉快速成型系统中激光扫描部分的机械传动部分,简化系统装置及控制系统的软件设计。     

A decision support system for the selection of a rapid prototyping process using the modified TOPSIS method

As a new technology that fabricates a three-dimensional (3D) physical model from computer-aided design (CAD) data using an additive process, rapid prototyping (RP) has been developed to reduce product development time and cost. Recently, many newly emerging techniques of RP have been commercialized worldwide. This paper deals with the selection of an optimal RP system that best suits the end use of a part by using multiple-attribute decision making and the test part designed with conjoint analysis to reflect users’ preference. Evaluation factors include only the major attributes that significantly affect the performance of an RP system such as accuracy, roughness, strength, elongation, part cost and build time. Crisp values such as accuracy and surface roughness are obtained with a new test part developed in this study. The part cost and build time are identified as falling within approximate ranges due to varying costs and many variable parameters. They are presented as linguistic values that can be described with triangular fuzzy numbers. Based on the evaluation values obtained, an appropriate RP process for a specific part application can be selected using a modified technique of order preference by a similarity to ideal solution (TOPIS) method given crisp data and linguistic variables as the alternatives of attributes. Finally, each attribute’s weight is assigned using a pairwise comparison matrix. Determined using these weights, the final ranking order aids in the selection of the RP system.     

The Application of the Skipped Layer Interior Method and Higher Depostition Height to Accelerate Fabrication Speed of the Model Maker Rapid Prototyping System

The Model Maker (MM) process is one of the jet deposition rapid prototyping (RP) systems that delivers material through a jet and deposits the liquefied material onto a platform to build a physical model. The fabrication speed of the MM model is extremely low because of the low deposition rate and cutting operation. In order to accelerate the fabrication speed of the MM, the line pitch of the MM processing parameters was reconfigured to increase the deposition rate and, hence, increase the deposition height. The cutting operation of the MM removes almost half of the deposited material because of the requirements of model accuracy and layer thickness. In order to reduce the amount of the removed material, a skipped layer interior method was employed. The reconfiguration of the line pitch to increase deposition height enabled more interior layers to be skipped and, hence, less deposited material was removed. Therefore, the fabrication speed was significantly accelerated. The results show that the average model printing time saved was around 40% for all layer thicknesses, while the model accuracy and the layer thickness were still the same as in the original MM process.     

一种提高快速成形系统精度的新切片算法

现有快速成型系统的切片规则不能保证整个原型件的单侧公差,从而影响了快速成型系统的成型精度。本文研究了一种基于STL文件几何信息切片的新规则,通过计算零件法矢量与快速成型加工方向的点积来选择合适的切片方法。实验证明:与传统切片规则相比,这种新切片规则有效地提高了快速成型系统、尤其是应用等厚度切片的快速成型系统的成型精度。     

Rapid prototyping fabrication and finite element evaluation of the three-dimensional medical pelvic model

This paper presents a non-uniform, periodic closed B-spline approximation algorithm for the fabrication of a medical pelvic model, based on rapid prototyping, and also gives the finite element evaluation of the pelvic model. Rapid prototyping (RP), when used in fabricating medical prosthesis, has a strict requirement for closeness and impermeability of STL files. Incorrect data structure in STL files will cause the subsequent slicing process not to proceed. The non-uniform periodic closed B-spline curve approximation method was applied to processing CT data. The precision and size of STL files was improved to optimize the RP model of the pelvis. Finally, the model of the pelvis was evaluated with the finite element method. Results suggest that a high similarity has been achieved in terms of shape, size and biomechanical properties of the pelvic model and the normal one, which validates our argument that rapid prototyping with non-uniform, periodic closed B-spline algorithm is suitable for the fabrication of a pelvic model, which will prove to be significant in the design of pelvic prostheses .     

半导体泵浦激光器在选区激光熔化工艺中的应用研究

选区激光熔化是新出现的能直接成型致密性接近100%终端金属产品的快速成型技术,该技术对成型能量源的要求严格。半导体泵浦激光器具有电光转换效率高、性能可靠、体积小巧、使用寿命长、输出光束质量好等优点。本文分析了选区激光熔化工艺对能量源的选用要求,对将半导体侧向泵浦Nd押YAG激光器应用于选区激光熔化工艺的可行性进行了评估,并通过实验进一步验证了评估结果。