Research on the fabricating quality optimization of the overhanging surface in SLM process

Overhanging surface is inherent geometric restraint during selective laser melting (SLM), which is suitable for various complex parts fabrication. In order to improve the fabricating quality of overhanging surface, a series of experiments were designed to investigate the effects of inclined angle, scanning speed, laser power, accumulated residual stress, and scanning vector length on overhanging surface fabrication. Analysis found that overhanging surface would warp easier when the inclined angle and the scanning speed became smaller and the warping trend will be larger as the laser power became larger. The relationships of laser power, scanning speed, and the critical inclined angle were mutual restraint, that is, larger inclined angle will be designed when the laser power becomes larger and scanning speed gets smaller, or vice versa: the selection of the fabricating parameters will be determined by established inclined angle of the overhanging surface. More serious warp would happen as the processing layers increased as a result of residual stress accumulation, and it was found that longer scanning vector were more helpful to stress accumulation, leading to more serious warp than shorter vector. At last, two effective methods were adopted to optimize overhanging surface fabrication, including adjusting part orientation to improve the inclined angle at the key position, and controlling regional parameters to reduce energy input. Above two ways were adopted to manufacture complex parts with typical overhanging surface, the results proved that adjusting part orientation and controlling regional parameters were effective ways to improve the fabricating quality of overhanging surface. In this study, the basis for building overhanging surface by SLM was provided from the view of process and design, and the preliminary solutions were proposed to manufacture complex metal parts with lower risk.     

双光子三维微结构快速制备技术

建立了一种利用双光子聚合技术快速制备三维微结构的方法,并对加工分辨率进行了研究。通过对高速扫描原理的研究,提出了采用二维振镜与一维压电微移动台相结合,利用跳跃和扫描协同的运动模式,以段段扫描方式进行三维微结构加工的系统来提高其加工速度。实验制备千里马和具有木堆结构的三维光子晶体结构说明,采用上述扫描方式可使其加工速度较点点扫描方式提高10倍至1 000倍。实验结果表明,使用一定的激光功率时,其加工分辨率随曝光时间减小而显著提高,实验得到了50 nm的线宽分辨率,超过文献报道的100 nm的最高值。研究还表明,上述加工方法可实现激光三维微结构的快速制备并具有高分辨率加工的特点。     

Characterization and analysis of weld lines on micro-injection moulded parts using atomic force microscopy (AFM)

In recent years plastic moulding techniques, such as injection moulding, have been developed to fulfil the needs of micro-components fabrication. Micro-injection moulding (μIM) is the process which enables the mass production of polymer micro-systems such as micro-mechanical parts, micro-fluidic systems, micro-optics, micro-components for medical devices, etc. A key factor in micro-polymer based systems is the possibility of designing and therefore replicating very complex geometries, allowing an increasing number of applications and micro-products.Complex geometries bring challenges during the filling stage of the process. Many features cause melt front separation: through holes, presence of pins and cores, changes of thickness, multi-gating systems, existence of micro-inserts, two component injection moulding, etc. When two or more melt flows join each other after separation, a layer between the two original flows will generate and a weld line is formed on the surface of the micro-moulded part. This phenomenon has to be avoided or at least reduced, since in the weld line area the mechanical properties are poorer than in the bulk part, creating strength problems on the final part. Although weld lines are unavoidable, the micro-injection moulding process can indeed be optimized in order to on one hand obtain a good filling of the cavity and on the other hand decrease the size of the weld lines. In this paper, an investigation devoted to the determination of the influence of typical injection moulding parameters on the weld lines’ dimensions is presented, using an atomic force microscope (AFM). Depth and width of weld lines were chosen as parameters to be optimized.     

Extraction of 5-axis milling conditions from CAM data for process simulation

5-axis milling is widely used in machining of parts with free-form surfaces and complex geometries. Although in general 5-axis milling increases the process capability, it also brings additional challenges due to complex process geometry and mechanics. In milling, cutting forces, tool deflections, and chatter vibrations may reduce part quality and productivity. By use of process simulations, the undesired results can be identified and overcome, and part quality and productivity can be increased. However, machining conditions and geometry, especially the tool–work engagement limits, are needed in process models which are used in these simulations. Due to the complexity of the process geometry and continuous variation of tool–work engagement, this information is not readily available for a complete 5-axis milling cycle. In this study, an analytical method is presented for the identification of these parameters from computer-aided manufacturing data. In this procedure, depths of cut, lead, and tilt angles, which determine the tool–workpiece engagement boundaries, are directly obtained the cutter location file analytically in a very fast manner. The proposed simulation approach is demonstrated on machining of parts with relatively complex geometries.     

A comparison between computational fluid dynamic and Reynolds approaches for simulating transient EHL line contacts

When simulating elastohydrodynamic lubrication (EHL), the Reynolds equation is the predominating partial differential equation for prediction of the fluid flow. Also very few attempts have been carried out using the full momentum and continuity equations separately. The aim of this investigation is to compare two different approaches for simulation of EHL line contacts where a single ridge travels through an EHL conjunction. One of the approaches is based on the Reynolds equation, addressing the coupling between the pressure and the film thickness. The solver uses the advantages of multilevel techniques to speed up the convergence rate. The other approach is based on commercial CFD software. The software uses the momentum and continuity equations in their basic form, enabling numerical simulations outside the contact regions, as well as in the thin film region to be carried out. The numerical experiments show that, under the running conditions chosen, only small deviations between the two approaches can be observed. The results are encouraging from several viewpoints: validation of the codes, the possibilities of further developments of the CFD approach and the justification of using a Reynolds approach under the running conditions chosen.     

A Part Classification System Using a Shape-Analysis Based Heuristic Approach

The classification of the parts for various manufacturing applications is still a labour-intensive and time-consuming process. In this paper, attempts are made to automate some elements of this process using a shape analysis model. In this work, a 24-vector directional template is used to represent the feature elements of the parts (candidate and prototype). Various transformation processes such as deformation, straightening, bypassing, insertion and deletion are used to match the candidate parts with their prototypes. The least-cost paradigm is then adopted to ensure the efficient matching of the candidate with the prototype. Two underlying concepts, namely threshold based deterministic approaches and probabilistic approaches, are considered for the series of transformation processes to map the candidate part with different prototypes. The proposed approaches are applied to classify 100 candidate parts and to classify their prototypes to demonstrate the effectiveness of the system. ID="A1"Correspondance and offprint requests to: M. K. Tiwari, Department of Manufacturing Engineering, National Institute of Foundry and Forge Technology (NIFFT), Hatia, Ranchi 834 003, India. E-mail: mkt09@hotmail.com     

快速成型制作的时间分析及多零件制作的组合布局优化研究

由于快速成型系统的运行成本很高,需要研究缩短零件的制作时间和减小制作成本的方法。基于SOUP600GH光固化成型机,介绍了零件具体的制作过程和制作时间组成,分析了零件制作方向、分层厚度以及激光扫描速度等因素对优化制作效率的影响。通过10组多零件制作实验,对每组单个零件的平均制作时间进行分析对比,指出了多个零件同时制作对提高制作效率的显著作用,进而主要从减少辅助制作时间的角度研究了多零件制作组合布局优化的准则和方法,并用矩形包络简化布置的方法建立了二维布局优化的数学模型。研究表明,多零件制作及其组合布局优化对提高快速成型的制作效率和降低制作成本都具有重要意义。     

多分辨率快速圆检测在抑菌圈测量系统中的应用

本文提出了多分辨率快速圆检测的算法。基于多分辨率的框架,在低分辨率下快速检测圆心和半径的信息,然后映射到高分辨率中,确定圆的边缘和圆心所在的局部区域,减少处理单元的数量,并提出局部单圆验证算法获得精确的圆心和半径信息。本文提出的算法克服了圆检测精度与时空复杂度的矛盾,在高分辨率、多圆、多噪声的情况下,算法的效率下降较少。最后将圆检测算法应用于基于机器视觉的抗生素残留量检测系统中进行抑菌圈检测,结果表明处理时间短、检测精度高。     

Development of a feature recognition module for tapered and curved base features

This paper presents a feature recognition module which uses the B-rep details extracted from the STandard for Exchange of Product (STEP) format to recognize the manufacturing features on a prismatic part. It adopts the syntactic pattern recognition technique to recognize five classes of features considered in this research by matching the standard pattern strings developed for every class of feature. Using these strings, initially, the types of faces on the prismatic part are determined and edge loops are constructed. The edge loops describe a feature by the information implicit in the details of the edges, vertices, coordinate points, and directions. Using the edge loops and by checking the presence of similar edge loops on parallel faces and the connectivity of faces between parallel edge loops, the final shape of a feature is identified. The developed methodology identifies interacting, tapering, interacting–tapering, curved base features, and tapering cross-sections. Methodologies are presented here to calculate the full dimensional details of all of the features. A case study dealing with complex geometries is presented in the validation of the proposed feature recognizer.     

Dual Material Rapid Prototyping Techniques for the Development of Biomedical Devices. Part 2: Secondary Powder Deposition

Polymeric drug delivery devices play an important role in drug administration. However, the current polymeric drug delivery device fabrication methods lack precision. This impairs the quality of the devices, resulting in a decrease in the efficiency and effectiveness of drug delivery. The concept of building parts layer by layer out of powdered raw materials makes selective laser sintering (SLS) a suitable process for fabricating polymeric matrix drug delivery devices. The current SLS process is not capable of processing two or more materials separately. This work explores the possibilities of using SLS to perform a dual material operation by developing two process models. The two processes can then be integrated to form a dual or multimaterial fabrication technique and act as a foundation for future work in multimaterial applications such as polymeric drug delivery device fabrication. Accordingly, two papers are presented. In this paper, Part 2, the emphasis is on a secondary powder deposition method, which is an electrostatic technique based on electrography. Developed toner on the photoconductor is scraped off using mechanical shearing and is deposited using an electrostatic force by electroplating. Results have shown that by reducing the distance between the photoconductor and surface of deposition, the resolution of the printout can be refined. Other important factors include the efficiency of powder removal from the photoconductor, printing speed, and the traversing speed during deposition.     

基于电场驱动熔融喷射聚合物基复合材料高分辨率3D打印

针对当前聚合物基复合材料（Polymer matrix composites,PMC）成型存在打印分辨率低、打印材料受限、成型结构较为简单、工序复杂等方面的不足和局限性,尤其是还面临难以实现宏/微结构跨尺度高效制造的挑战性难题,提出一种基于电场驱动熔融喷射PMC高分辨率3D打印新工艺。阐述了基于电场驱动熔融喷射PMC高分辨率3D打印的基本原理和工艺流程。通过试验,揭示了主要工艺参数（碳填料含量、施加电压、螺杆转速、打印速度、加热温度等）对于打印件分辨率（精度）和质量的影响及其规律。利用自主搭建的试验平台,并结合试验优化的工艺参数和提出的两种打印模式,实现了多层石墨烯/聚乳酸（Polylactic acid,PLA）和多壁碳纳米管/PLA复合材料微尺度三维网格、多层石墨烯/PLA大高宽比薄壁圆环、多壁碳纳米管/PLA复合材料柔性导电网格以及其他聚合物复合材料3D结构典型工程案例的制造。研究结果表明,提出的电场驱动熔融喷射3D打印能实现高分辨聚合物基复合材料成型（使用内径300 μm喷嘴,实现了分辨率为40 μm的PMC特征结构制造）,而且还具有大面积宏/微结构跨尺度集成制造的优势。     

On high-speed turning of a third-generation gamma titanium aluminide

Gamma titanium aluminides are heat-resistant intermetallic alloys predestined to be employed in components suffering from high mechanical stresses and thermal loads. These materials are regarded as difficult to cut, so this makes process adaptation essential in order to obtain high-quality and defect-free surfaces suitable for aerospace and automotive parts. In this paper, an innovative approach for longitudinal external high-speed turning of a third-generation Ti-45Al-8Nb-0.2C-0.2B gamma titanium aluminide is presented. The experimental campaign has been executed with different process parameters, tool geometries and lubrication conditions. The results are discussed in terms of surface roughness/integrity, chip morphology, cutting forces and tool wear. Experimental evidence showed that, due to the high cutting speed, the high temperatures reached in the shear zone improve chip formation, so a crack-free surface can be obtained. Furthermore, the use of a cryogenic lubrication system has been identified in order to reduce the huge tool wear, which represents the main drawback when machining gamma titanium aluminides under the chosen process conditions.     

Scheduling of complex manufacturing systems with Petri nets and genetic algorithms: a case on plastic injection moulds

This paper introduces significant improvements on a previous published work that addresses complex production scheduling problems using Petri nets (PNs) and genetic algorithms (GAs). The PN model allows a formal representation of the manufacturing system and of the special constraints of this kind of system, while the GA generates a near-optimal schedule through the structure provided by the PN. The corresponding manufacturing system is associated with a flexible job shop environment with features such as the fabrication of multiple parts and precedence relationships between such parts and assembly operations, in which the objective is the minimisation of the total weighted tardiness. As part of the modelling stage, a mixed integer linear programming formulation is proposed for this framework. The fabrication of a chess mould in a Colombian company is used in two ways: to introduce a proposed normalisation operator that improves the results by reducing the search space of the GA and to illustrate the use of PN modelling the special aforementioned constraints as well as the encoding of the chromosome used by the GA. The proposed approach was tested on randomly generated instances, and their performance was measure against optimal solutions or solutions provided by algorithms presented in previous work. The results confirm the relevance of this approach to schedule such complex manufacturing systems.     

Reduction of the sheet thickness variation and its negative effects on the accuracy of mini drawn parts using different geometries of tool components

Like in the case of macro deep drawing, the sheet thickness of mini drawn parts, with dimensions smaller than 20 mm and made from very thin sheets, is unevenly distributed and varies from minimum values resulted in the zone of part edge radius to maximum values in the upper zone of part vertical walls. Such variation of sheet thickness can cause for the resulted drawn parts some geometric deviations from their theoretic geometry or it can determine the parts failure. Hence, the main objective of the mini scale deep drawing processes is to obtain an increased accuracy by reducing the sheet thickness variation, or in other words to minimize the values of sheet thinning and thickening. The present paper analyses the results of investigations made by experiment and simulation concerning the use of different geometries of the tool components that permit to control and minimize the sheet thickness variation in the mini cylindrical drawn part zones where this phenomenon can generate negative effects and determine the part inaccuracy. The new geometries of tools were obtained by modifying the state of stress in the deformed sheet using adequate geometries of active surfaces of the die cavity and blank holder plate.     

Determination of fabrication direction to minimize post-machining in FDM by prediction of non-linear roughness characteristics

Rapid Prototyping (RP) is a technology that generates physical objects directly from CAD data. As a prototype can be rapidly built by using this technology, the product cycle is remarkably reduced in manufacturing. However, the surface quality of RP processed parts is not sufficient for general mechanical parts because of the use of the layered manufacturing process. Therefore, additional post-machining processes are required such as grinding and coating. But, these processes are time-consuming and detrimental to the original part’s geometry. In this paper, a methodology for determining fabrication direction which aims to minimize the post-machining process in FDM (Fused Deposition Modeling) is proposed. In order to enhance the accuracy and the computational speed in determining the fabrication direction, a surface roughness model that is considered even non-linear surface roughness characteristics is presented. And, a required post-machining volume is newly introduced as a objective function. Also, a genetic algorithm is applied to obtain a reliable solution. Finally, it is verified that the proposed approach can be very efficient with the developed system.     

A material selection methodology and expert system for sustainable product design

Material selection is one of the main phases of product design process that has great impact on the manufacturing of sustainable products. One of the best approaches of material selection for sustainable products is life cycle engineering (LCE). But LCE is a costly and cumbersome task and it is not economic to perform this task for a large number of proposed materials in order to choose the most suitable one for a sustainable product. Instead, it is more reasonable to make a preliminary filtering on the proposed materials and obtain a shorter list of candidate materials and then perform LCE on alternatives which are obtained from preliminary filtering. Since environmental friendliness of materials is a critical sustainability issue, so it is a good criterion for preliminary filtering of alternatives. In this paper, a new methodology is proposed to support preliminary filtering of alternatives from environmental viewpoint. The methodology uses the knowledge of experts in the field of eco-design. The knowledge is translated to decision making rules and a decision tree is developed to guide the choice. In order to use the capabilities of frame-based systems, an object-oriented approach for representation of knowledge is also proposed. Moreover, a prototype hybrid expert system based on the proposed methodology called material selection expert system for sustainable product design is developed to support the task of preliminary filtering. Finally, a case study from tire manufacturing industries is presented to show the validity of the proposed system. The results show that the system can determine the appropriate candidate materials and hence improve the possibility of manufacturing of more sustainable products. Eliminating alternatives that do not have the necessary conditions for sustainable product leads to a large saving in time and cost of the LCE evaluation process     

Injection moulding parameters influence on weight quality of complex parts by means of DOE application: Case study

Injection moulding is a very popular plastic transformation process to produce complex parts, since a mould is capable to reproduce different shapes, and also due to its economic advantages for large series. However, defects can appear into the pieces, leading to reject them in the quality control.In order to control these defects, it is necessary to know the influence of the injection parameters on the quality of the part. Several researchers applied Design of Experiments (DOE) methods to injection process, with good results for test or lab specimens, but many industrial parts usually have more complex geometries or singularities.This paper introduces a case study focused on the application of DOE in a complex part because it has an integrated hinge. In this case study, the weight and pressure curves (hydraulic and specific) are analysed depending on the variation of process parameters. The authors would show that the analysis has found a strong influence of the geometry on the results which sometimes are different to the expected ones.In authors’ opinion, the use of this procedure it still is a challenge, and this example could assist future attempts to create new expert systems in injection moulding.     

Deburring precision miniature parts

Precision parts demand care not only in the generation of dimensions and surfaces, but also in subsequent finishing operations. Deburring and edge finishing are two areas often given little consideration by those designing or machining such parts. Due to the lack of data and difficulty involved, it is common for deburring of precision parts to require up to 30% of the total part costs, and even more when the parts are small.Some basic design and fabrication guidelines are available as a result of recent research which provide a scientific method for specifying edge quality and choosing appropriate deburring processes. The basic constraint to deburring and edge finishing is minimising burr size and defining actual edge quality requirements     

Thermal expansion of a fused quartz tube in a dimensional stability test facility

A facility to monitor the dimensional stability of structures of arbitrary size or shape under varying temperature and pressure conditions is described. Real-time linear displacements are measured with a modified Michelson laser interferometer to a resolution of less than one part in 10(7) and an accuracy of approximately 2 parts in 10(7) for approximately 1 m gauge lengths. Verification of the system accuracy with a quartz tube required considerations of its fabrication and compositional characteristics.     

Frequency-shift vs phase-shift characterization of in-liquid quartz crystal microbalance applications

The improvement of sensitivity in quartz crystal microbalance (QCM) applications has been addressed in the last decades by increasing the sensor fundamental frequency, following the increment of the frequency/mass sensitivity with the square of frequency predicted by Sauerbrey. However, this sensitivity improvement has not been completely transferred in terms of resolution. The decrease of frequency stability due to the increase of the phase noise, particularly in oscillators, made impossible to reach the expected resolution. A new concept of sensor characterization at constant frequency has been recently proposed. The validation of the new concept is presented in this work. An immunosensor application for the detection of a low molecular weight contaminant, the insecticide carbaryl, has been chosen for the validation. An, in principle, improved version of a balanced-bridge oscillator is validated for its use in liquids, and applied for the frequency shift characterization of the QCM immunosensor application. The classical frequency shift characterization is compared with the new phase-shift characterization concept and system proposed.