Direct slicing and G-code contour for rapid prototyping machine of UV resin spray using PowerSOLUTION macro commands

Rapid prototyping processes produce parts layer by layer directly from 3D CAD models. An important technique is required to slice the geometric model of a part into layers and to generate a motion code of the cross-sectional contour. Several slicing methods are available, such as slicing from sterolithgraphy (STL) files, tolerate-error slicing, adaptive slicing, direct slicing, and, adaptive and direct slicing. This paper proposes direct slicing from 3D CAD models and generating a G-code contour of each layer using PowerSOLUTION software (Delcam International, Birmingham, UK). PowerSOLUTION includes two main modules: PowerSHAPE is used to build 3D CAD models and PowerMILL is used to produce G-Code tool paths. It provides macro language, picture files and cutting paths for secondary development work.The authors used macro commands to write an interface generating direct slicing from 3D CAD models and G-code contours for all layers. Most well-known controllers in the market accept the G-Code. Therefore, it is easier to apply this scheme in a CNC-machining center to produce rapid prototyping such as laminated object manufacturing (LOM) for complex geometries. The interface was successfully applied the interface to the UV resin spray rapid prototyping (UVRS-RP) machine that was developed to produce RP.     

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     

Direct Slicing from AutoCAD Solid Models for Rapid Prototyping

To meet the requirement of faster and precise slicing in rapid prototyping, a direct slicing approach from AutoCAD solid models is proposed. The sliced layers are saved in ASCII DXF files. Lines, arcs and circles are used to describe the section contours. This approach can be used in stereolithography, selective laser sintering, fused deposition modelling, and other rapid prototyping processes, e.g. laminated object manufactu-ing.     

Machine path generation using direct slicing from design-by-feature solid model for rapid prototyping

This paper explains a new machine path generating system that its output is compatible with different rapid prototyping processes. The basis of this system is direct slicing from design-by-feature solid model. Slicing a computer-aided design (CAD) model through intersecting the model with the XY-plane at each Z increment is a well-known method of path generation. Slicing a CAD model is currently conducted through stereolithography (STL) file slicing, direct slicing, and additive direct slicing. A direct slicing approach inside a design-by-feature solid modeler is proposed. Autodesk Inventor solid modeler, as a design-by-feature solid modeler, is used for 3D solid modeling. The proposed system is implemented by Visual Basic codes inside Inventor. In this approach, first protrusion and subtractive features that form a model are extracted. Then, the intersection of each feature and the XY-plane is identified. Then, the internal and external loops are found. Depending on the specific rapid prototyping (RP) process requirements, internal or external hatch are also computed, respectively. Finally, a continuous path in required format is generated. The system reported in this paper has been successfully tested on several complex 3D models created in Inventor. The system offers customized output for different RP processes that need external or internal hatch pattern. The proposed approach for generating RP machine path through feature recognition inside design-by-feature solid modeler overcomes with the problems that are caused by imperfect STL files. Also, this system is capable of generating code compatible with major rapid prototyping processes.     

Recommended slicing positions for adaptive direct slicing by image processing technique

Build time and accuracy are two contradicting issues that have been a major concern in rapid prototyping, and have led to the development of many slicing approaches including those applying adaptive slicing, direct slicing, and adaptive direct slicing concepts. Presented in this paper is an approach for adaptive direct slicing that applies image processing technique to determine appropriate thickness for each sliced layer and to recommend slicing positions on a 3D CAD model. Two orthogonal views of a model are captured and converted to be edge images before being analyzed, and based on the surface complexity on the two edge images, slicing positions are recommended. These positions are passed to the CAD software for slicing activities. This adaptive direct slicing approach has been implemented on LabVIEW platform and compared with uniform direct slicing approach and uniform cusp height approach. The results show that this slicing approach improved slicing performance by reducing the number of layer which has a direct impact on build time while maintaining surface quality at the same level as the thin uniform direct slicing. Since its inputs are the images of a CAD model instead of the model itself, this adaptive direct slicing supports any CAD software.     

Dexel-Based Direct Slicing of Multi-Material Assemblies

Slicing is an important procedure in rapid prototyping (RP) pre-processing, and can be grouped into two categories: direct slicing and adaptive slicing. At present, investigations into the use of both direct and adaptive slicing methods are taking place. However, not many direct slicing approaches have been reported in the literature. The methods are also restricted to some solids in CSG or some CAD systems. Also, approaches on adaptive slicing are too complicated. The method proposed in this paper employs dexel encoding for direct slicing multi-material (MM) assemblies in RP. One advantage of using a dexel model is that Boolean operations can be performed simply on 1D line segments. Dexels can also be easily converted to tool paths in RP machines. Compared to the ray representation of CSG trees, dexel models can be extended to represent MM assemblies with material properties. Therefore, the method has high potential for direct slicing. In this paper, traditional dexel models are first extended for rapid manufacturing single solid and MM assemblies. Compared to other adaptive slicing approaches, a much more efficient and simple dexel model, for adaptive refinement in the building direction is then developed. To further improve the surface finish, a layerwise refinement approach is also discussed. Finally, the computational complexity of the proposed method is studied.     

基于3D CAD模型表面Z向特征曲线的自适应分层方法

为提高快速成形中3D CAD模型的分层效率和分层精度,定义了模型表面Z向特征曲线的概念及提取原则,建立了模型表面几何特征到层厚的直接映射关系,提出一种基于模型表面多处兴趣特征的快速自适应分层算法。该算法利用Z向特征曲线提取CAD模型表面的兴趣特征,通过特征曲线几何特征到层厚的直接映射关系快速确定分层点处的适应性层厚,整个层厚计算过程不存在冗余计算。结果表明,该算法能够高效地计算复杂形状3D模型在分层点处的最优层厚,实现3D模型的快速自适应分层。     

基于STL模型的轮廓线自适应分层方法研究

目前,大多数快速成型系统在表达CAD模型时仍采用STL模型。由于快速成型自身的特点,对STL模型进行分层处理是其必由之路。在分析了传统的STL模型分层方法的基础上,提出了一种基于STL模型的轮廓外形线自适应分层的方法,然后通过实例对该自适应分层方法进行了验证,证明了该方法的可行性和正确性。     

基于CNC的自适应直接分层制造方法研究

将RP技术的增材制造理念与数控铣削加工技术相结合,提出了基于CNC机床的金属零件分层制造方法。为解决等厚分层方法存在的缺陷,提出了基于相邻层面积变化比率和轮廓法向矢量的自适应直接分层算法,并在Pro/E软件平台上,利用Pro/TOOLKIT进行了系统的开发。该方法采用定厚板材作为造型材料,在等厚分层的基础上对分层板进行自适应分层切削,有利于保证成型精度和提高成型效率,为复杂形面功能零件的快速成型制造提供了一种有效的方法。     

Adaptive direct slicing with non-uniform cusp heights for rapid prototyping

Adaptive slicing varies layer thickness by taking the geometry change of the CAD model in the build direction into account to improve surface finish. Direct slicing generates exact slice contours from the original CAD model and avoids an intermediate representation, known as an STL file. At present, most direct slicing approaches are restricted to some CSG solids or some CAD systems. In this paper, an approach toward adaptive direct slicing with non-uniform cusp heights independent of CAD systems for rapid prototyping is presented. First the geometry model is imported into the adaptive direct slicing system from CAD systems using the standard STEP format. Using OpenGL graphics libraries, the solid model is then displayed and the user is prompted to specify the allowable cusp height for each highlighted surface. Lastly, the CAD model is sliced adaptively with different cusp heights (tolerance requirements) for different surfaces. With non-uniform cusp heights, adaptive slicing has a higher efficiency. Implementation details and results are also presented.     

一种基于STEP的CAD模型直接分层方法

提出了一种基于产品模型数据交换标准的3维计算机辅助设计实体模型直接分层方法,零件的原始计算机辅助设计模型以产品模型数据交换标准中性文件的格式输入分层系统,系统提取其几何拓扑信息并重建计算机内部几何模型。用户选择零件的制作方向并指定分层厚度后,系统自动对计算机辅助设计模型进行直接分层,分层结果可直接送到各种快速成型系统加工。基于产品模型数据交换标准的计算机辅助设计模型直接分层不依赖任何特定的计算机辅助设计系统,通用性、灵活性好,而且产品模型数据交换标准文件的数据量大大小于STL文件,有利于网络化设计与制造环境下的数据传输与交换。     

Improved intermediate point curve model for integrating reverse engineering and rapid prototyping

Direct integration of reverse engineering and rapid prototyping removes two intermediate steps of surface fitting from point cloud data and STL file generation from CAD models. Therefore errors introduced due to surface fitting and triangulations are eliminated and also the process of STL data validation and repair is avoided. Intermediate point based curve model (IPCM) method is one of the promising approaches for direct integration of reverse engineering and rapid prototyping however this approach has the limitation that it cannot handle objects, which result in multiple contoured slices. Moreover, IPCM based method is implemented with layers of constant thickness slices, and adaptive slicing with this method is not attempted. The present work is an attempt towards improving the capabilities of IPCM based method by overcoming the above-mentioned two limitations. The new system developed here has been tested on many parts, which demonstrates the capability of the proposed system. An erratum to this article can be found at     

三维模型的适应性切片方法研究

阐述了一种基于STL文件进行自适应切片的有效方法，以减少台阶效应对成形零件各种性能的影响。利用零件STL文件中小三角片法向量，计算出各小单元层侧表面最大法向量，适应性地计算出在分层方向上每层切片的厚度，确保层与层之间的台阶效应在允许值范围内。利用STL小三角片数据反向求出其切片方向对应小单元层的法向量，提高了计算速度。对该方法在直接切片时的不足进行了分析，提出了精确性修正方案。     

快速成型技术中分层算法的研究综述

作为快速成型技术中必不可少的环节,根据对零件制造精度和装配要求及效率的侧重不同,多年来多种分层算法已被国内外学者开发出来。在同等加工条件下,根据加工精度要求和层厚变化的不同,将分层算法大致分为等层厚分层算法和适应性分层算法两类。从常用的立体光刻(STL)模型、原始计算机辅助设计(CAD)模型和点云数据3种数据模型入手,简述了两类分层算法的研究和发展;介绍了采用斜边的分层算法、基于区域划分的混合算法、曲面分层算法等先进分层算法;讨论了分层算法中待解决的问题:直接分层算法的文件格式标准和轮廓的精确拟合等问题。最后,总结得出了分层算法未来的研究方向和趋势。     

基于SLC数据模型的扫描工艺研究

介绍了快速成形加工中常用的SLC数据模型的构成,提出了SLC数据模型下快速成形扫描路径的生成算法以及数据点的排序方法。采用VC++编程实现了扫描路径的生成,并通过风机叶片和车标模型两个实例,分析了扫描路径生成过程中零件切层厚度、扫描间距对扫描路径长度的影响。     

An Effective Error-Tolerance Slicing Algorithm for STL Files

Although the STL (stereo lithography) file format is the de facto standard for the rapid prototyping industries, there are always some defects in STL files, many of which are difficult to correct. Instead of correcting the defects of bad STL files by a manual, interactive and complex approach with an STL file correction program, an error-tolerance slicing algorithm for STL files is proposed in this paper. With the detailed analysis of complex defects such as cracks and non-manifold facets, a complete topological structure for the facets model with defects is built and the layer is sliced effectively. The badly sliced contour is processed by crack-tracking and non-manifold facet travelling methods to obtain a correct contour in a relatively easy 2D way.     

Adaptive slicing of functionally graded material objects for rapid prototyping

Slicing is a fundamental process planning task and an important procedure in rapid prototyping. However, most research currently focuses on the slicing of homogeneous objects and few approaches for slicing of heterogeneous objects have been reported in the literature. In this article, we present an approach for adaptive slicing of functionally graded material objects. Unlike homogeneous objects, functionally graded material objects contain both geometry and material information. The layer thickness is computed by considering not only geometry but also material variation along the build direction. The continuous material distribution in each layer is discretised into step-wise gradings by subdividing the slice into sub-regions, which can be regarded as homogeneous material regions. An algorithm that summarised the slicing procedure is described and an example is also presented.     

基于STEP的非均匀自适应分层方法

现有的自适应分层方法，通常对整个零件采用同一个最大的尖顶高度要求，实际上，大多数零件由于表面的重要程度不同，而需要不同的尖顶高度要求。对零件的不同表面采用不同的尖顶高度要求，可以进一步提高自适应分层的效率。为此，提出了一种在CAD系统外直接对STEP标准CAD模型进行非均匀自适应分层的方法，CAD系统与分层系统之间的数据交换采用STEP中性文件的格式。选择好零件的制作方向后，用户可根据零件表面的重要程度指定不同的尖顶高度要求，然后系统自动对CAD模型进行自适应分层。最后给出了分层实例，并对结果进行分析。     

Developing a paving system for fabricating ultra-thin layers in ceramic laser rapid prototyping

“Step effect” is one of the major concerns for engineers because it affects the surface quality in layer manufacturing. Instead of constant thickness, adaptive slicing procedures use slices of variable thickness that are governed by the model geometry, manufacturing process, material, and rapid prototyping system. The RP system has the capability of fabricating the layer between a minimum and maximum thickness with certain intermediate thickness during the model making and is indispensable. Due to agglomeration of powder and upward deformation of the layer, the layer’s thickness in powder-based rapid prototyping processes is restricted. To improve surface quality, the current study constructs a paving system to minimize the layer thickness. Based on a wet process-ceramic laser rapid prototyping technique, a paving system, which can fabricate ultra-thin layers to a thickness of 20 μm and can achieve instant layer drying, was successfully constructed. A strategy of compensative layer was induced to improve accuracy of the Z-axis. Due to the ultra-thin layers, a plane surface finishing of R_z = 15∼24 μm was obtained.     

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 .