三维打印快速原型机技术分析

快速成型技术是综合计算机、激光、新材料、CAD/CAM集成等技术而形成的一种全新的制造技术,是高科技的产物,技术含量较高。本文介绍了三维打印机的工作原理及各部分的组成,并对机械系统、数控系统、分层软件和成型材料等4个方面进行了技术分析。该成型机成型速度快;采用标准打印头;支持多种材料;支撑材料粉末可以重新利用,材料浪费极少;操作简单。     

Increased accuracy by using dynamic finite element method in the constrain-surface stereolithography system

The E-DARTS apparatus is a commercial rapid prototyping (RP) system that uses the constrain-surface stereolithography (SL) technology. The advantages of the type SL system are saving resin and apparatus fees, although its accuracy needs to be increased. To find the best scanning path planning is one solution to improve the accuracy of the built part. In this paper, the diagnostic H-4 parts have been fabricated and simulated according to different path plans. The critical dimensions of the built H-4 diagnostic parts are also measured and compared with the analytical results, showing that the best path plan for building the H-4 diagnostic part is the contour-out path. In addition, it has been shown that using the skip skill in raster fill is also effective for improving the full filling of the big or long area.     

Metal filled resin for stereolithography metal part

A new route to produce metallic parts through stereolithography is explored in this work. Stereolithography of metallic materials consists of a UV curable metallic suspension prepared with a pre-polymer acting as the binder material, a photo-initiator, metallic powder and additives. The critical material and process parameters are investigated in order to identify appropriate photosensitive metallic suspensions for stereolithography, based on their rheological and photochemical properties. Two different types of resins, unsaturated polyester and epoxy resin were considered in this study, to get a better understanding of free radical, cationic and hybrid polymerisation mechanisms, being the photo-curing reactions carried out at different light intensities. The powder used was either tungsten carbide (WC) or cobalt (Co) with different powder sizes.     

基于光固化的直接陶瓷成形工艺

文章把光固化技术应用于陶瓷成形,提出了一种新型的直接陶瓷成形工艺-陶瓷光固化工艺。通过实验研究发现,陶瓷浆料粘度、固化厚度对陶瓷素坯的成形过程有决定性作用;陶瓷粉末的体积分数决定了陶瓷素坯的收缩率。为减少陶瓷素坯收缩率,必须提高陶瓷粉末的体积分数。实验表明,陶瓷浆料粘度小于3000MPa·s,固化厚度大于200μm,能够满足该工艺的要求。陶瓷粉末体积分数大于40%,能够得到低收缩率的陶瓷零件。     

Estimation of machine tool feed drive inclination from current measurements and a mathematical model

Leveling is an important part of a machine tool installation process because it significantly influences the product quality, machine tool accuracy, and machine lifetime. Conventional leveling procedures are performed by skilled engineers using leveling instruments such as spirit or electronic levels. It is difficult to monitor the level of a machine tool because an accurate leveling instrument is expensive and difficult to install. Therefore, a novel methodology for estimating the inclination angle of a machine tool feed drive is proposed in this paper to overcome the difficulties of leveling. The proposed methodology utilizes motor current measurements and a new mathematical model of the machine tool feed drive that considers the inclination. Experimental results showed that the proposed method successfully estimates the inclination angle and enhances the accuracy of the machine tool feed drive model by considering the inclination effects.     

Rapid fabrication of alumina-based ceramic cores for gas turbine blades by stereolithography and gelcasting

Injection moulding is accepted as one of the most important methods for shaping complex ceramic cores, which are used to form intricate internal cooling passages of gas turbine blades. But the relatively long lead time and high costs involved in the fabrication of hard tooling render it uneconomical for new products development and low-volume production. In the study, a rapid prototyping process is developed to fabricate complex-shaped alumina-based ceramic core by combining stereolithography (SL) with gelcasting. SL is utilized to fabricate an integral sacrificial resin mold, and gelcasting is utilized to form a wet ceramic core green body through polymerization of aqueous ceramic slurry. The freeze-drying process is adopted to treat the wet green body surrounded by the resin mold, the drying shrinkage is decreased, and the generation of crack can be prevented. The sintering shrinkage of ceramic core is controlled by adding magnesium oxide power and developing a novel sintering process. After the resin mold is burnt out, the complex-shaped alumina-based ceramic core is obtained.     

单官能团单体对光固化成型用树脂基氧化铝浆料流变性和光敏性能的影响

从分子结构和官能团的角度研究了单官能团单体对光敏树脂基氧化铝浆料流变性能和光固化性能的影响。以双官能团单体1,6-己二醇二丙烯酸酯（HDDA）和三官能团单体三羟甲基丙烷三丙烯酸酯（TMPTA）为原料,按照HDDA:X:TMPTA=6:3:1的体积比加入单官能团单体X,通过室温磁力搅拌制备出光敏树脂,研究了单官能团单体X和树脂的流变性能。采用机械球磨法制备了30%~50%（体积分数）固相含量的光敏树脂基氧化铝浆料,实现了基于立体光刻（SL）技术的3D打印并制备出了氧化铝坯体。本研究确定了3种具有亲水性和高光固化活性的单官能团单体,即丙烯酰吗啉（ACMO）、丙烯酸2-苯氧乙酯（2-PHEA）和丙烯酸羟乙酯（HEA）,优化了光敏树脂,使其具有高活性和高固化精度,可用于制备流变性和光固化性能优异的氧化铝浆料。     

Sweeping filters and tooth rotation energy estimation (TREE) techniques for machine tool condition monitoring

This paper presents a method for the condition monitoring of the milling cutting process based upon a combination of two techniques; sweeping filters and tooth rotation energy estimation (TREE). Existing spindle speed and spindle load signals from the machine are used thus avoiding the need for any additional sensors. The sweeping filter technique determines the frequency components of the spindle signal using low cost hardware. The filter's cut off frequency is swept across a range of frequencies and its output is acquired and analysed in real time. The variations of individual tooth energies estimated by the TREE technique in the time domain are used to verify the results. The hybrid approach created is based on the verification of any indicated faults before making a final conclusion about the health of the cutting tool. This provides a robust and reliable tool monitoring system that is able to identify tool breakage in real time during machining operations.     

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.     

基于PMAC的商用五轴联动电火花加工数控系统

研制了一种基于可编程运动控制器PMAC的五轴联动电火花加工数控系统。其采用全闭环速度模式的控制体系,具备实现电火花成形加工控制中包括间隙电压检测、伺服进给回退运动、多轴联动、主轴高速抬刀运动及各类摇动等的多项关键技术。该数控系统已应用于商用五轴联动电火花成形加工机床,通过大量的样件加工实验,验证了其良好的控制与加工性能。同时按商业化标准完善了数控系统,推动了其产业化进程。     

利用光固化快速成形技术和凝胶注模工艺制备变周期电磁晶体

提出了一种光固化快速成形技术及凝胶注模工艺制备变周期电磁带隙晶体的工艺路线,结构材料是氧化铝陶瓷.研究了该工艺制备得到的电磁带隙晶体的微现形貌,及其在8～13 GHz微波段的带隙特性,并对比了不同比例拉伸后的变周期结构和标准结构的微波带隙特征.测试结果发现,与同等外形结构尺寸的周期性结构相比,变周期金刚石EBG结构的带...     

Laser curing of silver-based conductive inks for in situ 3D structural electronics fabrication in stereolithography

A hybrid stereolithography (SL)/direct print (DP) system has been developed and previously described that fabricates three-dimensional (3D) structural electronic devices in which component placement, interconnect routing, and system boundaries are not confined to two dimensions as is the case with traditional printed circuit boards (PCBs). The resulting increased level of design and fabrication freedom provides potential for a reduction in both volume and weight as well as the capability of fabricating systems in arbitrary and complex shapes as required to conform to unique application requirements (e.g., human anatomy, airframe structures, and other volumetrically-constrained mechanical systems). The fabrication of these devices without intermediate part removal between SL and DP processes requires in situ curing of DP-dispensed silver-based inks to sufficiently cure the inks prior to continuing additional SL fabrication. This paper describes investigations into the laser curing process using the two laser wavelengths, 355 nm and 325 nm, which have been used in commercial SL machines. Various laser curing parameters, including energy (laser power and scan speed), scanning location, and laser wavelength were investigated. The trace resistances and structural changes in the SL substrate and printed trace were compared for each experiment to determine the most preferred laser ink curing method. Furthermore, oven curing of partially laser cured ink traces was investigated as a means for minimizing the number of in situ laser passes required to embed ink traces during SL fabrication. The laser curing process was repeated for a wide variety of conductive inks, having different structure, composition, and curing properties to determine if certain inks were more responsive to laser curing and if the ink curing results could be generalized. A statistical study was conducted under the hypothesis that laser curing of inks at 325 nm wavelength would be better, due to lower silver reflectance, as compared to 355 nm wavelength. Results indicated that particulate silver based conductive inks can be successfully cured in situ using SL lasers with various laser curing parameters. Curing ink traces at high laser power and slow scan speeds with the laser beam located on the substrate adjacent to the ink channel resulted in the most effective ink curing but resulted in discoloration of the ink and/or charring of the SL substrate. Comparatively, when laser power was reduced sufficiently to eliminate the charring, lower effective ink curing was achieved. Irradiating the laser directly on the ink did not damage the ink or the substrate, while providing low trace resistances, and represents the most viable laser curing alternative to achieve acceptable trace resistance without charring the SL substrate. The results further indicated that partial laser curing of ink using a reduced number of laser passes with subsequent oven cure seem to work effectively and may decrease overall manufacturing time. SL lasers with low power (<100 mW) may not be effective for curing conductive inks that have high viscosities and require high curing temperatures. Finally, a statistical study determined that 325 nm is more effective for direct curing of the ink as compared to the 355 nm laser.     

Photoinduced superhydrophilicity and photocatalytic properties of ZnO nanoplatelets

The present work is devoted to the investigation of photoinduced superhydrophilicity (PSH) and photocatalytic oxidation (PCO) activity of quasi-2D zinc oxide nanoplatelets obtained by Chemical Vapor Deposition (CVD). In the case of PCO, the degradation of a fatty compound layer (methyl stearate) was chosen as a test reaction. The peculiar textural and morphological features of such systems resulted in a PSH behavior and in a PCO activity appreciably higher than those of a reference commercial Pilkington^® Activ^TM Glass. Relevant results are presented and discussed as a function of the structure and morphology of these systems, whose control enables a direct tailoring of the functional response.     

The laser forming of metallic components using particulate materials

Direct fabrication technology, which utilizes computer-aided design solid models to automatically control the manufacture of functional piece parts, is rapidly gaining popularity as a means to significantly reduce the time to market of new concepts. Since the introduction of stereolithography in 1982, several different rapid prototyping technologies have evolved using surrogate rather than actual materials of construction. Most recently, researchers have begun to develop laser-based methods to obtain fully dense metallic components directly from a computer-aided design solid model. Each of these methods is unique, but possesses aspects that are similar to the others. Many of these methods hold a great deal of promise for applications; however, none have been developed into a commercial product.     

Simultaneous deep drawing and cold forging of multi-material components: Draw-forging

A new process combining cold forging and deep drawing is introduced for forming multi-material components. The components consist of a cold extruded core with a deep drawn and redrawn cup acting as shell. Process mechanics, failures, and process window are investigated for a steel-aluminium pairing. The joining mechanisms between the steel shell and the aluminium core is of force- and form-fit type. The joining strength is larger than 40% of the shear yield stress of the weakest material. Alternative material pairings, chip-cores, double stepped shafts, and deep drawing with sequential backward cup-extrusion, are explored demonstrating the technological potential of the process.     

Quantifying the degree of particle melt in Selective Laser Sintering

This research highlights the fact that individual particles are melted to different degrees during Selective Laser Sintering^® (SLS) of Nylon 12. Many particles comprise an un-melted core, surrounded by a melted and crystallised mass that bonds with other particles. Methods to quantify the Degree of Particle Melt (DPM), including Differential Scanning Calorimetry (DSC) analysis and optical microscopy analysis, are compared against each other and against mechanical properties of parts manufactured under different conditions. The results show that the derived DPM has a close correlation with mechanical properties. This represents a new depth of understanding of the SLS process.     

基于西门子840D SL系统快速I/O的并联控制应用

针对大型飞机部件加工中多台数控机床同步加工时存在的加工质量风险难题,基于西门子840D SL系统中的快速I/O功能,提出一种多台设备电气、程序控制判断方法。该方法能实现多台设备的并联互锁功能,有效解决了多台数控设备同步加工时存在的加工质量风险问题,为实现大型飞机部件数字化加工应用提供了参考。     

Introduction to CFRP-metal hybrids for lightweight structures

Intrinsic hybrids present a new approach to join metal and CFRP, to produce multi-material components which utilise the particular advantages of the involved materials. Due to the intrinsic hybridisation, no additional process steps are required and the total weight of the component can be reduced. The present special issue was initiated within the priority programme 1712 of the German Research Foundation and gives a global view of current research activities in the field of lightweight-optimised CFRP-metal hybrids. Various contributions to production technology, material science and mechanics are discussed.     

Structural Integration of Sensors/Actuators by Laser Beam Melting for Tailored Smart Components

Laser beam melting (LBM), an additive laser powder bed fusion technology, enables the structural integration of temperature-sensitive sensors and actuators in complex monolithic metallic structures. The objective is to embed a functional component inside a metal part without losing its functionality by overheating. The first part of this paper addresses the development of a new process chain for bonded embedding of temperature-sensitive sensor/actuator systems by LBM. These systems are modularly built and coated by a multi-material/multi-layer thermal protection system of ceramic and metallic compounds. The characteristic of low global heat input in LBM is utilized for the functional embedding. In the second part, the specific functional design and optimization for tailored smart components with embedded functionalities are addressed. Numerical and experimental validated results are demonstrated on a smart femoral hip stem.     

Kinetic modeling of adsorption of vanadium and iron from acid solution through ion exchange resins

This study assessed the adsorption process and the reaction kinetics involved in the selective recovery of vanadium from an acid solution containing iron as an impurity. Four commercial resins were studied: Lewatit® MonoPlus TP 209 XL, Lewatit® TP 207, Dowex? M4195 (chelating resin) and Lewatit® MonoPlus S 200 H (strong cationic exchange resin). To investigate the effect of time on the adsorption process, batch experiments were carried out using the following initial conditions: pH 2.0, 298 K, and a proportion of 1 g of resin to 50 mL of solution. The variation of pH over time was analyzed. Chelating resin released less H⁺ ions as the adsorption occurred, resulting in a lower drop of pH when compared to S 200 H resin. Ion adsorption by the resins was also evaluated through FT-IR and SEM?EDS before and after the experiments. Among the evaluated kinetic models (pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models), the pseudo-second order model best fits the experimental data of the adsorption of vanadium and iron by all of the four resins. M4195 resin showed the highest recovery of vanadium and the lowest adsorption of iron. Kinetic data, which are fundamental to industrial processes applications, are provided.