Fabrication of Biomedical Prototypes with Locally Controlled Properties Using FDM

Biomedical structures have complex geometries and mechanical behaviors, and are difficult to manufacture using traditional machining processes. This paper reports a study of fabrication of biomedical structures using fused deposition modelling (FDM) processes. The theoretical and experimental analyses of mechanical behaviours of FDM prototypes were carried out to establish the constitutive models. A new set of equations is proposed to calculate the elastic constants of FDM structures as functions of the constituent properties and geometric characteristics, taking into account of imperfect bonding among filaments and void geometries. The manufacturing parameters of deposition orientation and density are modeled for fabrication of prototypes with functionally graded properties. Examples are included to illustrate the fabrication of bone structures with locally controlled properties.     

Additive Manufacturing of PLA and CF/PLA Binding Layer Specimens via Fused Deposition Modeling

As one of the most popular additive manufacturing techniques, fused deposition modeling (FDM) is successfully applied in aerospace, automotive, architecture, and other fields to fabricate thermoplastic parts. Unfortunately, as a result of the limited nature of the mechanical properties and mass in raw materials, there is a pressing need to improve mechanical properties and reduce weight for FDM parts. Therefore, this paper presents an experiment of a special polylactic acid (PLA) and carbon fiber (CF)/PLA-laminated experimental specimen fabricated using the FDM process. The mechanical properties and mass analysis of the new composites for the PLA and CF/PLA binding layer specimen are investigated experimentally. Through the experimental analysis, one can conclude that the mass of laminated specimen is lighter than the CF/PLA specimen, and the tensile and flexural mechanical properties are higher than the pure PLA specimen.     

Development of a hybrid rapid prototyping system using low-cost fused deposition modeling and five-axis machining

Currently, two major processes are being used to produce prototypes, namely machining and rapid prototyping. Machining is generally more accurate and precise, but it is difficult to produce objects with certain complicated features. In contrast, rapid prototyping can produce objects with complicated features, which allows materials to be used more efficiently. However, due to the uneven shrinkage and residual stresses within rapid prototyping products, their accuracy is usually uncertain. This study attempts to integrate these two manufacturing processes and develop a hybrid rapid prototyping system in order to overcome the disadvantages associated with each process and to develop new applications. Fused deposition modeling (FDM) was used as the rapid prototyping process in this work. A spindle and a low-cost FDM extruder were designed to be placed on each end of a rotary axis in a five-axis machine tool. The proposed design allows the rotation of the axis on the five-axis machine to switch between machining and FDM, thus achieving the advantage of reducing costs for extra actuators without sacrificing working space. The case studies demonstrated that the proposed hybrid system can build FDM objects without using support materials and produce FDM parts with metal embedded to increase the stiffness. The system can also conduct five-axis machining on a completed FDM part or trim the freeform surface fabricated by FDM to achieve more accurate dimensions or better surface finish.     

FDM打印壳体类产品单螺旋快速成型方法

随着人们对小批量、个性化产品需求的增加,FDM打印技术因可直接快速制造所需产品得以迅速发展。但是打印一些特殊产品时,特别是壳体类的产品,当采用常规方式逐层叠加打印时,打印头会不断的非挤出移动、非连续Z轴变化等,进行不必要的打印动作并造成打印缺陷。提出一种FDM打印产品单螺旋快速成型方法,通过切片处理技术,解决上述问题。     

Development of a mobile fused deposition modeling system with enhanced manufacturing flexibility

Development of a flexible and mobile fused deposition modeling (FDM) system from an existing FDM system to enable deposition of material on virtually any surface without being confined to a build chamber is described. Flexibility of the system was demonstrated by depositing ABS on different surfaces, and simple pull tests were performed to determine bonding strength between the deposited materials. To develop the flexible FDM system, a Stratasys FDM 3000 machine was used and modified by reversing the z stage and attaching the x-y table controlling the FDM head to the bottom of the z stage. In this new configuration, the z stage transports the x-y table vertically, and the x-y table controls the x-y motion of the FDM dispensing head, which is exposed at the bottom of the machine. The mean of the absolute value of the difference between 49 part dimensions (based on 20 part features) measured on a modified Grimm test part (n = 5) was ∼0.44 mm for parts fabricated using the developed flexible FDM system, while a mean of ∼0.11 mm was measured using parts produced by the commercial system (n = 5). The dimensional accuracy of the flexible system was comparable but expectedly larger than the commercial system, due to the configuration of the flexible FDM system with the x-y table attached at the bottom of the z stage. There are many possible design improvements particularly focused on reducing deflections in the mechanical components that can be explored and implemented to improve the overall dimensional accuracy of the flexible system, but these investigations are left for future research. Instead, manufacturing flexibility of this new configuration was demonstrated by successfully building a cylinder on flat and 3D cupped surfaces, including building a horizontally oriented cylinder on a wall by orienting the FDM system in the horizontal position. Pull tests were performed and showed that bonding strength for the cylinders built on flat surfaces compared favorably to a glued part (3.06 ± 1.38 MPa for the specimens manufactured with the flexible FDM system compared with 2.00 ± 1.06 MPa for the glued specimens). Additional flexibility was demonstrated by printing directly on a complex curved surface, thus illustrating the possibilities for using AM (a traditional 2D layer-stacking processing technique) in conformal printing applications. It is concluded that this new machine can provide enormous flexibility in freeform manufacturing with applications in part repair, 3D conformal adhesive dispensing, and a number of applications where the removal of the size constraints imposed by the build chamber enables one to deposit new arbitrary features directly on existing parts.     

熔融沉积成型工艺参数及数控加工后处理对表面精度的影响

为了提高熔融沉积成型(Fused Deposition Modeling,FDM)成型件的表面质量,提出利用数控加工对FDM成型件进行表面加工的后处理方法,研究打印速度、挤出速度和分层厚度等工艺参数对成型件的成型误差和表面粗糙度的影响,在此基础上,研究数控加工对其加工误差和表面粗糙度的影响。结果表明:FDM成型件表面粗糙度较大,最大达到24.434μm,合理设置打印速度、挤出速度和分层厚度可以有效降低FDM成型件的成型误差;数控加工可以有效降低FDM成型件的表面粗糙度值,表面粗糙度降低到1.979~2.446μm。     

Study of compression properties of topologically optimized FDM made structured parts

Most rapid prototyping (RP) additive techniques are expensive and suffer from a lack of efficiency when massive products are to be manufactured. The authors propose to reduce the density of rapid prototyped parts, finding alternative building styles. Topologically optimized parts have been created with internal geometry, using a narrow-waisted structure that avoids the need for building supports. In order to characterise and study the behaviour of the obtained low density parts, an experimental plan has been designed and executed. The approach has been tested using a fused deposition modelling (FDM) machine, but it is of a general nature and can be applied to other layered manufacturing (LM) technologies that use supports, dealing with slow building of massive parts.     

FDM工艺精度分析与试验研究

熔融沉积成型技术的不断发展受到了各行各业的关注,在快速成型过程中的每一环节都会产生误差,这严重影响了产品的精度。通过对熔融沉积工艺流程进行介绍,分析了影响产品精度的多个因素并提出相应的解决方法。进一步将影响快速成型精度的喷头温度、扫描速度、分层厚度3个因素进行试验分析,得到了影响精度的主要因素,并结合实际经验进行对比分析,得出相关结论。对进一步研究熔融沉积成型技术工艺以及提高成型件的精度具有参考意义。     

Representation of surface roughness in fused deposition modeling

Most rapid prototyping (RP) technologies apply a layered manufacturing (LM) process to efficiently fabricate 3D physical models. However, a critical drawback that reduces the surface quality of the RP parts occurs by utilizing LM. Hence, topics related to surface roughness have been a key issue in RP. In this paper, a new approach to model surface roughness in fused deposition modeling (FDM) is proposed. Based on actual surface roughness distributions of FDM parts, a theoretical model to express surface roughness distribution according to changes in surface angle is presented by considering the main factors that crucially affect surface quality. The proposed expression is verified by implementation and comparison with empirical data. Also, the effectiveness of the main factors is analyzed and discussed.     

Quantitative analysis of a chemical treatment to reduce roughness of parts fabricated using fused deposition modeling

The surface finish of Fused Deposition Modeled (FDM) parts can be improved by performing chemical dipping based on immersion in a dimethylketone-water solution.The authors aim to gain a more in-depth knowledge of this process, by analyzing and comparing the mechanical properties and the surface quality of treated and untreated FDM parts. Tensile and bending mechanical properties have been investigated by designing and performing four Central Composite Designs (CCDs) of experiments, totalizing about two-hundred tests. The results have been verified by testing an FDM marine turbine blade employed to generate energy.     

基于激光诱导化学液相沉积的快速成型方法

对当前常用的RP工艺,如立体光刻、分层实体制造、熔融挤压成型、选区激光烧结等的原理、工艺和优缺点进行了简单评述,认为上述工艺均存在一些固有缺陷,距离企业的需求(如金属模具直接成型等)还有比较大的差距。在介绍激光诱导化学液相沉积(LCLD)技术的基础上,本文提出了一种基于该技术的新型快速成型方法,给出了其成型系统原理图,并详细介绍了系统的工作过程。分析表明,该种RP系统能够较好地弥补现有系统的不足之处,具有极其广阔的应用前景。     

Effects of Powder Geometry and Composition in Coaxial Laser Deposition of 316L Steel for Rapid Prototyping

Multiple layer laser powder deposition has recently been applied to producing fully dense 3-D metallic engineering parts for rapid prototyping and tooling. To date, however, the process has been limited to using only gas-atomised, spherical powders. In this paper, the feasibility of using water-atomised powders is investigated, based on an experimental comparison of gas- and water- atomised powders in multiple layer, laser fused deposition of 316L stainless steel. The work shows that, despite much lower cost (approximately 25% of the pries of gas-atomised powders), the water-atomised, irregular powders have superior deposition quality in terms of surface finish, deposition uniformity, microstructures and bonding between layers, compared to the gas-atomised powders under the same processing conditions, although deposition rate is lower. Powder geometry and oxygen content differences of the two powders have been found to be the principal reasons for the observed effects. Theoretical analyses of the beam-material interaction processes and malt pool behaviour are presented to explain the observed phenomena. The results indicate that there are both functional and economic reasons for using water-atomised powders for this additive manufacturing application.     

A modelling framework for comparing the environmental and economic performance of WAAM-based integrated manufacturing and machining

Additive Manufacturing has proved to be suitable for supporting or even replacing traditional manufacturing approaches in some industrial contexts. Among the various processes that can be used to produce metal parts, Wire Arc Additive Manufacturing (WAAM) is known to be an economically convenient, welding-based direct energy deposition technique for large parts with reduced complexity. The present paper proposes a structured modelling framework to assess whether WAAM could successfully substitute machining processes. The costs, manufacturing times, energy demand and carbon footprint are considered. A case study is presented to clarify and demonstrate the applicability of the proposed methodology.     

Thermal spray shape deposition

This paper describes a new spray-forming process based on thermal spray shape deposition. Shape deposition processes build three-dimensional shapes by incremental material buildup of thin, planar crosssectional layers. These processes do not require preformed mandrels and can directly build three-dimensional structures of arbitrary geometric complexity. The basis for the thermal spray approach is to spray each layer using a disposable mask that has the shape of the current cross section. Masks can be produced from paper rolls, for example, with a CO₂ laser. In addition to applications for rapid prototyping, this approach makes possible the fabrication of composite structures and integrated electronic/mechanical assemblies that are not feasible with conventional manufacturing technologies.     

基于曲面分层的大型螺旋桨GMA增材制造

为了实现曲面复杂零件的高精度高效率增材制造,开发了高适应性的曲面分层算法.采用从空间角加权法向方向平移三角网格控制点的策略,生成与初始分层曲面等距的曲面簇,与模型求交运算,从而获得了每层曲面切片轮廓.在此基础上,使用基于体素化和曲面积分思想的曲面等距路径规划算法,获得了分层曲面上的等距轮廓偏置路径,保证了零件曲面轮廓的成形精度并进行了试验验证. 试验采用六轴机器人与旋倾变位机作为运动机构,使用熔化极气体保护电弧(gas metal arc,GMA)增材制造方法,在一个外径为0.2 m的圆柱金属管上,实际堆敷了直径1 m的扭转棱形螺旋桨.经过扫描检测和模型比对,得到桨叶的成形尺寸标准偏差为1.1 mm,最大偏差在3.0 mm以下.结果表明,对于特定曲面零件如螺旋桨的增材制造,曲面分层算法可以提高成形的效率和表面质量.     

基于CMT的钛合金电弧增材制造技术研究现状与展望

钛合金高强度、高耐热的特性决定了其在航空航天、船舶制造等领域的广泛应用,但由于钛合金的难加工性,使得传统锻造+机加的方式模具损耗严重、制造周期长。增材制造作为一种制造成本低、成形效率高的绿色化制造工艺,凭借其无需模具、直接成形的优势在钛合金制造领域受到国内外学者的广泛关注。电弧增材制造技术相较于其他增材工艺(如激光增材制造、电子束增材制造等)沉积效率更高,不受零件尺寸的限制,在大型和超大型结构件的制造中具有突出优势,其中基于冷金属过渡(Cold metal transfer,CMT)的电弧增材制造技术由于沉积过程更稳定、热输入量更低,已逐渐成为钛合金增材制造领域的研究热点。文中对基于冷金属过渡的钛合金电弧增材制造技术的研究现状进行综述,介绍钛合金打印件的微观组织和力学性能特征,总结分析了成形参数对打印件微观组织与力学性能的影响规律,并概述了形核条件调控、轧制和超声冲击等辅助技术对打印件微观组织与力学性能的影响机制,最后展望了钛合金CMT电弧增材制造的未来发展趋势。     

An adaptive slicing approach to modelling cloud data for rapid prototyping

In this paper, an adaptive slicing method for modelling point cloud data is presented. A layer-based rapid prototyping (RP) model is directly constructed from arbitrarily scattered cloud data and fed to RP machines for fabrication. The emphasis is on how to control the thickness of each layer so that a user-specified shape error is met. Given a set of unorganised point cloud acquired by scanning a part, the first step is to segment the cloud data into a number of layers by slicing the point cloud along the part building direction (user-specified). Taking the first layer, the data points are projected onto a plane. These projected data points are then compressed and sorted to keep only the key feature points (FPs) using a reduction method based on linear correlation. The FPs are then used to construct a polygon approximation of the points. The maximum deviation of the points in the layer is then compared to the given shape error to decide whether to reduce or increase the layer thickness. This process is repeated until the maximum deviation is just below the given shape error and the first layer thus obtained. Subsequently, the remaining layers are obtained in the same manner. The algorithm has been implemented using VC++ and OpenGL. Testing results are very much satisfactory. Compared with traditional modelling methods, this method is highly automated and the generated layer-based model is highly efficient for RP manufacturing.     

激光辅助涂层技术和表面改性质量的研究概述

激光辅助涂层技术的目的是保护暴露的工业产品或易受化学损伤的部件和结构.概述了想要在材料表面的高性能和昂贵部件中权衡制造成本,主体部件可由更便宜的材料制成,通过涂覆技术以达到成本设计的最优化.重点综述了近年来激光辅助技术的研究进展.使用激光作为热源制造机械零件的一组革命性工艺,包括采用基于激光的工艺在所选区域上产生材料沉积以提供保护层和增强基材的耐腐蚀和耐磨性、传热和机械性能.迄今为止,已经引入和研究了多种激光辅助工艺,包括增材制造(AM)、激光表面合金化(LSA)、激光表面熔覆(LSC)、激光辅助等离子体喷涂(LPS)、激光化学气相沉积(LCVD)及其他多种激光辅助涂覆技术.重点归纳了涂覆过程中每种工艺的优势及限制其应用的缺点.对激光辅助涂层方法进行了分类,归纳了激光辅助涂覆方法,并对其进行了比较研究,用以提供更清晰的图片和选择合适的涂层技术,从而根据实际应用获得最理想的涂层设计方案.最后展望了通过发展更先进的技术和材料,可能会获得更高质量的保护性能.     

Surface modification of fused deposition modeling ABS to enable rapid prototyping of biomedical microdevices

Fused deposition modeling (FDM) using poly (acrylonitrile butadiene styrene) (ABS) has emerged as a powerful method in rapid prototyping. However, to date this technique has not been suitable for use in 3D printing of microdevices that interact with biological molecules and cells owing to its water permeability and biofouling nature. In this paper, a versatile method to modify surfaces of ABS fused deposition modeling rapid prototyped devices with microstructured features to render them water-impermeable, hydrophilic, and biocompatible is presented. An acetone-based sealing method is described that has a minimal effect on surface roughness and structural fidelity. Photo-induced graft polymerization of poly (ethylene glycol) functionalities onto the surface is used to increase the hydrophilicity of the ABS and increase resistance to non-specific protein adhesion. These surfaces have been characterized for their morphology, water contact angle and the adhesion of a model protein to demonstrate their improved biocompatibility. The proposed methods use cheap, safe, and widely available materials which should make the creation of biocompatible surfaces using FDM economical, fast, and expand the range of applications of this technique.     

Fabrication of curved micro structures on photoresist layer

A novel fabrication process for micro patterns with curvature was introduced. The curved structures were made by compensating rectangular micro structures with liquid photoresist layer. Because of the surface tension of the liquid in micro scale, various shapes of meniscus can be made on the micro channels. The micro channels were made on the silicon substrate in advance, and then the liquid layer was coated on the micro channels. From the nature of liquid behavior, the curved patterns with smooth surface are obtained, which cannot be made easily with the conventional mechanical machining, as well as with the microfabrication processes, such as wet and dry etching. With this principle, it is expected that the smooth and curved surfaces can be made by simple processes and the results can be applied widely, such as optical patterns.