磨料喷射微细加工应用基础研究--喷嘴设计及加工试验

磨料喷射微细加工是利用高压气体为介质加速磨料对工件形式冲击、冲蚀作用而去除材料的一种特种加工方法，适用于零件微细结构的加工和零件的表现处理。本文主要分析了磨料喷射加工的原理，设计了一套原理性试验装置，通过实验观察分析了磨料喷射加工过程，分析了其加工特性，提出了改进方案。     

微磨料浆体射流抛光技术

近年来,在非传统抛光方法中,微磨料浆体射流抛光由于初始成本,无热损伤,不改变材料力学和物理性能,抛光特性不受工件抛光位置影响,被认为是当前对具有复杂表面的硬脆性材料制品进行超光滑表面加工的最有潜力方法之一.本文详细介绍了微磨料浆体射流抛光技术的应用及特点、装置设计原理及实例、材料去除机理,重点分析了喷射压力等工艺参数对抛光效果的影响,并提出了微磨料浆体射流抛光中有待进一步深入开展的研究工作.     

精密零件的微磨料气射流光整加工

近年来，在非传统去毛刺加工方法中，微磨料气射流去毛刺由于初始成本低、生产效率高、灵活性强、无应力、无热影响区，在精密零件的光整加工中获得了广泛的应用。本文详细介绍了微磨料气射流用于光整加工去毛刺的加工原理、材料去除机理、去毛刺的工艺参数以及对棱边尺寸的影响，并列举了一些微磨料气射流在不同应用领域的加工实例。     

微磨料水射流加工脆性玻璃的冲蚀机理研究

微磨料水射流加工技术正成为制造微细结构零件重要的经济高效的微细加工技术。作者在玻璃上进行微磨料水射流微细槽加工的实验基础上,对微磨料水射流加工的表面形貌、材料冲蚀去除机理及加工工艺性能进行了研究。结果表明,玻璃加工表面沿着槽道的方向形成了波纹状形貌,呈非对称或对称的波形,波纹表面很光滑,波纹图案沿着射流冲击区的径向方向发展。由于黏性流体的阻滞作用,脆性玻璃在微磨料水射流加工过程中,在黏性流区域没有发现任何裂纹,材料的冲蚀去除主要是以塑性断裂的方式为主,形成了光滑的加工表面。适当地控制加工工艺参数,在低压下,微磨料水射流加工是一种用于脆性材料上微细通道的加工切实可行的方法,并可获得良好的加工表面质量。     

磨料浆体射流抛光模具钢的试验研究

通过磨料浆体射流抛光加工SKD12模具钢的试验研究,分析了浆体射流的加工参数与抛光加工工件表面质量之间的关系,得出了各个工艺参数对磨料浆体射流加工质量的影响规律。结果表明:模具钢抛光表面R_a值与磨料尺寸成正比,与工件的初始R_a值无关;走刀速度4 mm/s、喷射压力0.7 MPa、靶距5 mm、磨料浓度75 g/L时工件表面质量最佳;氧化铝磨料比碳化硅磨料抛光质量高;当走刀间距为1.25D时表面粗糙度值最低,且喷嘴直径越大表面R_a值越小。      

采用工件加振方式的微细超声加工特性的研究

通过以ＷＥＤＧ放电加工手段制作微细超声加工用工具,在采用工件加振方式的向细超声加工机上对碳酸玻璃、半导体硅等硬脆材料试件进行微孔加工的实验,来探讨在某一特定加工的实验,来探讨在某一特定加工条件下具材料、工件材料、工件的振幅、加工静载荷、磨料悬浮液浓度、工具长度及工件尺寸等重要因素对加工速度、工具损耗率的影响。为微细超声加工技术的实用化提供参考依据。     

适合复杂曲线加工的低压水刀的开发

低压水刀是应用前混合磨料射流切割技术进行加工,将由喷嘴喷出的磨料射流作为切割刀具.介绍所开发的低压水刀的组成、喷嘴进给的位移量和速度的控制以及数控系统的组成和曲线加工过程的具体步骤,并利用低压水刀对工件进行了实际切割.结果表明:所开发的低压水刀可满足曲线切割的要求,切口光洁整齐,适合各类材料、尤其是板材的曲线加工.     

微磨料空气射流加工玻璃微流道结构研究

采用微磨料气射流加工技术(MAJM),对普通硅酸盐玻璃进行微流道槽加工.对通过掩膜加工与非掩膜加工效果相比较,得出在掩膜加工过程中,由于磨料的二次反弹冲蚀作用,所加工出的槽,槽壁较陡;在掩膜加工过程中,改变喷射距离、喷射压力、喷嘴移动速度和磨料流量四个加工参数,对加工槽的轮廓、加工过程中的材料去除率、磨料的流量效应进行研究,得出当喷射距离为4 mm,喷射压力为0.5 MPa,喷嘴移动速度为1.0 mm/s,磨料流量为0.117 g/s时,加工效果最好.通过倾斜喷射与掩膜加工相结合,研究了磨料磨粒的二次反弹冲蚀现象,为复杂三维微结构的加工,提供了一种新方法.     

超声辅助微细磨料水射流冲蚀K9玻璃的实验研究

目的 提高微细磨料水射流对硬脆材料的加工能力,改善加工表面的形貌和质量.方法 引入超声振动作为辅助手段,使工件在垂直于加工表面方向作小振幅超声频振动.以K9玻璃为加工对象,利用自主设计搭建的超声辅助微细磨料水射流加工装置进行微孔冲蚀加工实验,并以无超声振动时的微孔加工实验作为对照.借助超景深三维显微镜对各实验条件下所加工的微孔进行观测,获取其尺寸和截面轮廓数据,研究超声振动对微孔尺寸、形貌的影响.结果 微孔的深度和顶部直径与射流压力的大小和加工时间的长短呈正相关.超声振动的引入,显著增加了微孔的深度,实验中深度的最大增幅达54.6％,但微孔顶部直径略有减小,最大降幅为8.2％,总体的材料去除量有所提升.塑性冲蚀作用主导了材料的去除过程,微孔的截面呈典型的"W"形.在引入超声振动后,"W"形截面形貌得到了改善,微孔中心凸起部分的材料得到更多的去除,底面平坦程度得到提升.结论 超声振动的引入增强了微细磨料水射流对K9玻璃的冲蚀性能,超声辅助微细磨料水射流加工技术可以实现对K9玻璃等硬脆材料的高质量、高效率加工.     

场致射流微细放电加工的机理研究

提出了一种利用动态场致射流作为工具电极进行微细放电加工的方法。该方法是利用工件和喷嘴之间的电势差形成高压电场,使喷嘴出口的带电液滴同时受到表面张力和电场力的作用,带电液滴形成泰勒锥。在强电场力作用下,泰勒锥顶端产生一束极微细的电解液射流。当场致射流喷射到工件表面附近时,高压电场击穿射流尖端与工件间的气体介质,产生放电现象,工件表面放电点局部材料因放电所产生的热量而熔融、气化,从而产生材料蚀除。     

Influence of kinematic operating parameters on kerf geometry in abrasive waterjet machining of silicon carbide ceramics

Silicon carbide (SiC) is extensively used for manufacturing of highly engineered parts due to its high hardness, low coefficient of friction, wear resistance and high decomposition temperature. However, generating 3D surfaces (e.g. pockets) in such structural ceramics by conventional machining is a difficult task. In this context, abrasive waterjet (AWJ) machining, with its capability to cut any material with low specific cutting forces, seems to be the “ideal” processing technique for such materials; nevertheless machining 3D shapes by AWJ milling is still in its infancy. 3D shapes can be generated by “enveloping” them with successions of jet footprints (kerf geometries) generated by varying the process operating parameters. To enable this, the present work investigates the influence of key kinematic operating parameters (i.e. α-jet impingement angle and v-jet feed rate) on the kerf geometry and its dimensional characteristics. Furthermore, the kerf generation mechanism under multi-pass jet erosion was analysed to get control over erosion depth in multi-pass machining. It was found that by varying α (90°–40°), the symmetric/asymmetric kerf geometry is intimately dependent on the variation of standoff distance (SOD), abrasive particle velocity distributions and their local impact angles accounted across the jet footprint. Variation in v influences the exposure time of material to jet and enhances the erosion capability of abrasives impacting at shallow angle that results in different erosion rates along the kerf profile; this combined effect leads to departure of kerf geometry from simple cosine profile approximation to more elliptical type with the decrease of feed speed. Further, at lower jet feed rates, the depth of erosion increased and the low energy abrasive particles along trailing edge of jet plume get enough time to erode the material that results in variation of slope of kerf walls and hence, overall geometry. Based on these observations, the multi-pass trials showed that the successive passes have to account for both the local impact angles of abrasive particles as well as the actual SOD (SOD+initial kerf depth). In this way, by understanding the influence of key kinematic operating parameters (α and v) on the kerf geometry and its dimensional characteristics, the paper establishes a good basis for developing strategies for controlled 3D AWJ machining of complex shapes.     

Kerf characteristics in abrasive waterjet cutting of ceramic materials

An abrasive water jet (AWJ) can provide a more effective means for precision cutting of ceramic materials as compared with conventional machining methods, but many aspects about this cutting technology are still under flux and development. In this study, experimental techniques based on statistical experimental design principles and theoretical investigations were conducted to study AWJ cutting of alumina-based ceramics. Semi-empirical cutting depth equations are determined for the prediction and optimization of the AWJ cutting performance. Topographical characteristics of uncut-through kerf and the effects of various parameters are discussed. In addition, visualization studies are conducted to develop further understanding of the macromechanics of the AWJ cutting process.     

磨料射流铣削工艺参数优化

目的对表面粗糙度和材料去除率作为输出参数的磨料水射流铣削45#钢过程进行研究,旨在寻找最优加工参数。方法对射流去除材料机理进行了分析,设计并进行了以磨料粒度、射流压力、横向进给距离、靶距为加工工艺参数的田氏正交实验。采用Minitab对不同实验参数组合下磨料水射流加工45#钢的表面粗糙度、材料去除效率进行了数据分析,并从材料去除机理方面,对4种加工工艺参数对于铣削表面质量和材料去除效率的影响程度和影响趋势,以及各因素之间的交互作用进行了分析。结果对射流铣削面表面粗糙度影响较显著的因素是横向进给距离,射流压力次之;对于材料去除效率,磨料粒径的影响最显著,横向进给距离次之。结论综合材料去除效率和表面粗糙度值,选出最优加工参数:磨料粒径2000目,射流压力120~160 MPa,喷嘴横移距离1.0~1.5 mm,靶距约30 mm。     

A study of abrasive water jet machining process on glass/epoxy composite laminate

Surface roughness (R_a) and kerf taper ratio (T_R) characteristics of an abrasive water jet machined surfaces of glass/epoxy composite laminate were studied. Taguchi's design of experiments and analysis of variance were used to determine the effect of machining parameters on R_a and T_R. Hydraulic pressure and type of abrasive materials were considered as the most significant control factor in influencing R_a and T_R, respectively. Due to hardness of aluminium oxide type of abrasive materials, it performs better than garnet in terms of both machining characteristics. Increasing the hydraulic pressure and abrasive mass flow rate may result in a better machining performance for both criteria. Meanwhile, decreasing the standoff distance and traverse rate may improve both criteria of machining performance. Cutting orientation does not influence the machining performance in both cases. So, it was confirmed that increasing the kinetic energy of abrasive water jet machining (AWJM) process may produce a better quality of cuts.     

Material removal analysis in abrasive waterjet cutting of ceramic plates

Fine ceramics have been recognized increasingly in structural and functional applications on account of their merits of hardness, corrosion resistance, electromagnetic response and bio-compatibility. Due to the need for dimensional control or production optimization, post-sintering machining can be required. Cutting by conventional means is most often practiced, but the associated heavy tool wear is hard to overcome. A waterjet at transonic speed carrying abrasive particles provides an effective means for hard-material removal. Undesired material fracture at entrance and exit can be reduced significantly by sequential abrasive micro-machining.

The present paper discusses the kerf formation of a ceramic plate cut by an abrasive waterjet. The mechanism and the effectiveness of material removal are studied first. Different materials are found to possess different removal rates in machining and there also exists a critical combination of hydraulic pressure, abrasive flow rate and traverse speed, below which through-cut for a certain thickness cannot be achieved. The wall finish achieved is determined by the mesh size of the abrasives: sufficient hydraulic pressure with fine abrasives will produce a smooth surface comparable to that from grinding. The kerf is slightly tapered with wider entry due to decreased cutting energy with kerf depth. A high-power input per unit length produces a small taper but a wide slot.     

磨料水射流切割工程陶瓷机理分析

高压磨料水射流切割工程陶瓷时，切割破碎物料机理极其复杂。本文以流体力学和材料断裂力学为理论基础，结合试验对工程陶瓷的切割加工进行了研究，为磨料水射流技术在脆性材料加工领域中进一步推广应用提出理论假没。     

Geometrical modelling of abrasive waterjet footprints: A study for 90° jet impact angle

Modelling of abrasive waterjet footprints is of critical importance when aiming to generate controlled freeform surfaces. The paper reports on a geometrical model of the jet footprint (kerf) in maskless controlled-depth milling applications. The model firstly needs to find the material specific erosion (etching) rate that is obtained from the jet footprint by taking the limiting conditions (high jet feed rates) of the model. Once this is found, the jet footprint can be predicted accurately for any jet feed speed. An example of model validation is presented for 90° jet impingement angle against a SiC ceramic as target material.     

Developments in the non-traditional machining of particle reinforced metal matrix composites

The non-traditional machining of particulate reinforced metal matrix composites is relatively new. However, researchers seem to pay more attention in this field recently as the traditional machining of particulate reinforced metal matrix composites is very complex. This research investigates different non-traditional machining, such as electro-discharge, laser beam, abrasive water jet, electro-chemical and electro-chemical discharge machining of this composite materials. The machining mechanism, material removal rate/machining speed and surface finish have been analysed for every machining process. This analysis clearly shows that vaporisation, melting, chemical dissolution and mechanical erosion are the main material removal mechanisms during non-traditional machining. The thermal degradation and the presence of reinforcement particles mainly damage the machined surface. The understanding of electro-discharge, laser beam and abrasive water jet machining is more developed than that of electro-chemical and electro-chemical discharge machining for particulate reinforced MMC.