氧化铝陶瓷基板紫外纳秒激光打孔工艺研究

氧化铝陶瓷基板作为雷达微波组件的核心部件,其硬脆特性使得传统加工方法在导通孔加工中存在很多限制。激光加工作为一种非接触式高能束加工方法,是氧化铝陶瓷表面孔加工的最优选择。文中主要研究了紫外纳秒激光氧化铝陶瓷表面孔加工中的激光加工参数（包括激光平均功率、扫描速度和扫描次数等）对孔的特征尺寸（包括入口直径、出口直径和锥度）的影响规律,并分析了各种规律产生的相关机理。此研究为雷达微波用电子陶瓷基板的导通孔加工提供了有力的理论依据和技术支持。     

The laser shaping of ceramic by a fracture machining technique

A new laser machining technique for ceramic shaping, based on the concept of fracture mechanics, is proposed in this paper. The principle of fracture machining technique is investigated. A focused laser is used to scribe two groove-cracks at the two intersecting surfaces of the rectangular substrate. Then, a defocused laser beam is applied throughout the length of the groove-cracks to generate a great thermal stress, which makes the two groove-cracks link together. The material removal is due to the linkage of the groove-cracks. Conventional laser machining requires high laser power to evaporate the materials. The high temperature gradient would induce the formation of micro-cracks, which leads to a remarkable reduction in strength. The laser power required in the method proposed is only a tenth of what is required in the conventional method under the same material removal rate, and in addition, the amount of the micro-crack is smaller. The experimental specimens are alumina ceramics, and the laser sources are a CO₂ laser and a Nd:YAG laser. The fracture machining technique can be successfully employed for step shaping and blind corner shaping for a thick ceramic substrate. The relationships of machining parameters such as groove-crack depth, material removal rate, laser scanning speed, and laser power are discussed. Finally, the measurement of the surface roughness and the inspection of crack defects are examined thoroughly.     

Predictive Modeling of Surface Roughness in Grinding of Ceramics

The surface roughness represents the quality of ground surface since irregularities on the surface may form nucleation for cracks or corrosion and thus degrade the mechanical properties of the component. The surface generation mechanism in grinding of ceramic materials could behave as a mixture of plastic flow and brittle fracture, while the extent of the mixture hinges upon certain process parameters and material properties. The resulting surface profile can be distinctively different from these two mechanisms. In this article, a physics-based model is proposed to predict the surface roughness in grinding of ceramic materials considering the combined effect of brittle and ductile material removal. The random distribution of cutting edges is first described by a Rayleigh probability function. Afterwards, surface profile generated by brittle mode grinding is characterized via indentation mechanics approach. Last, the surface roughness is modeled through a probabilistic analysis of ductile and brittle generated surface profile. The model expresses the surface finish as a function of the wheel microstructure, the process conditions, and the material properties. The predictions are compared with experimental results from grinding of silicon carbide and silicon nitride workpieces (SiC and Si₃N₄, respectively) using a diamond wheel.     

Ceramic Response to High Speed Grinding

Material response was investigated with respect to normal grinding forces, surface roughness, and removal mechanisms in grinding of alumina, silicon carbide, silicon nitride, and zircona with a resin-bond 160 μm grit diamond wheel at the grinding speeds of upto 160 m/s. The results reveal that the normal grinding forces decreased significantly with an increase in grinding speed; they also increased substantially with an increase in a complex relation of the ceramic hardness and toughness. High speed grinding produced a reduction in surface roughness for silicon carbide and alumina but gave no improvement for zirconia and silicon nitride. Also the surface roughness in high speed grinding was found to be material-dependent that the ground silicon nitride exhibited much smoother than the other ground ceramics. The influence of grinding speed on material removal mechanisms was analyzed in terms of grinding geometry and ceramic material properties.     

Optimal designing of multiple deferred state sampling plan for assuring percentile life under Weibull distribution

Continuous carbon fiber reinforced silicon carbide ceramic matrix composites (C/SiC) are promising materials in aerospace and space optical fields due to their excellent properties. However, poor machining quality resulted from surface/subsurface breakage is hard to meet precision requirements of some components. With an objective to study surface/subsurface breakage formation mechanism and improve machining quality of C/SiC composites, ultrasonic assisted grinding (UAG) and conventional grinding (CG) tests with a defined diamond grain distribution brazed grinding wheel were conducted. The surface/subsurface breakage types and formation mechanism were studied by comparative analysis of grinding force, micro-morphology of grinding surface/subsurface, and ground surface roughness. The results showed that main breakage types of different angle fibers in ground surface were lamellar brittle fracture and pit group originating from fracture and pullout of fibers, while breakage types of different angles fibers in ground surface were brittle fracture. Compared to CG, these breakages were reduced by UAG in varying degrees because it can reduce grinding force that determined fiber breakage. Consequently, because of the lower fiber breakages, the ground surface roughness Sa obtained by UAG was lower than CG and the maximum reduction was 12%.     

Tribological behaviour of steel‐alumina sliding pairs under boundary lubrication conditions

The tribological behaviour of oil‐lubricated steel‐alumina sliding pairs was investigated using a ball‐on‐disc tribometer at room temperature. Commercial bearing balls of 10 mm diameter were mated to 99.7% Al₂O₃ discs, and additive‐free mineral oil was fed into the contact area. The sliding speed and the applied normal load were varied, and the initial surface roughness of the Al₂O₃ disc was altered using different polishing and grinding procedures. The results showed that the surface roughness of the ceramic discs dominated the tribological behaviour under the given experimental conditions. The sliding speed as well as the normal load showed less effect on the friction behaviour, but the amount of wear depended strongly on the normal load. From the results it was concluded that improvement of the surface roughness and optimised surface machining of the ceramic material can be essential for improving the tribological performance for boundary‐lubricated steel‐ceramic sliding pairs.     

Automated surface finishing of plastic injection mold steel with spherical grinding and ball burnishing processes

This study investigates the possibilities of automated spherical grinding and ball burnishing surface finishing processes in a freeform surface plastic injection mold steel PDS5 on a CNC machining center. The design and manufacture of a grinding tool holder has been accomplished in this study. The optimal surface grinding parameters were determined using Taguchi’s orthogonal array method for plastic injection molding steel PDS5 on a machining center. The optimal surface grinding parameters for the plastic injection mold steel PDS5 were the combination of an abrasive material of PA Al₂O₃, a grinding speed of 18000 rpm, a grinding depth of 20 μm, and a feed of 50 mm/min. The surface roughness R_a of the specimen can be improved from about 1.60 μm to 0.35 μm by using the optimal parameters for surface grinding. Surface roughness R_a can be further improved from about 0.343 μm to 0.06 μm by using the ball burnishing process with the optimal burnishing parameters. Applying the optimal surface grinding and burnishing parameters sequentially to a fine-milled freeform surface mold insert, the surface roughness R_a of freeform surface region on the tested part can be improved from about 2.15 μm to 0.07 μm.     

超声振动磨削陶瓷材料高效去除机理研究

基于压痕断裂力学,在工件横向施振超声振动平面磨削单颗磨粒受力分析基础上,建立了材料去除率综合数学模型;并就超声振动和普通磨削进行了对比试验研究。研究结果表明超声振动磨削陶瓷材料去除率与被加工材料的种类、磨削深度、砂轮磨粒粒度、超声振动的振幅以及磨削条件有着密切关系。同样磨削条件下,超声振动磨削陶瓷材料去除率是普通磨削的1.7~3.2倍,与理论模型相符合。试验结果表明超声振动磨削可以获得良好的加工表面,工件横向施振超声振动磨削是一种精密、高效加工新工艺。     

Optimization of machining parameters in the abrasive waterjet turning of alumina ceramic based on the response surface methodology

A study on the radial-mode abrasive waterjet turning (AWJT) of 96 % alumina ceramic is presented and discussed. An experimental investigation is carried out to explore the influence of process parameters (including water pressure, jet feed speed, abrasive mass flow rate, surface speed, and nozzle tilted angle) on the material removal rate (MRR) when turning 96 % alumina ceramic. The experiments are conducted on the basis of response surface methodology (RSM) and sequential approach using face-centered central composite design. The quadratic model of RSM associated with the sequential approximation optimization (SAO) method is used to find optimum values of process parameters in terms of surface roughness and MRR. The results show that the MRR is influenced principally by the water pressure P and the next is abrasive mass flow rate m _a . The optimization results show that the MRR can be improved without increasing the surface roughness when machining 96 % alumina ceramic in the radial-mode abrasive waterjet turning process.     

Evaluation of Y2O3 surface machinability using ultra-precision lapping process with IED

Prospects of Y₂O₃ have been more extended as a great promising and creditable material for optical, electronic and mechanical purposes. Y₂O₃ has been more observed as a fine ceramic which has great material properties: high light transparency, excellent thermal resistance and chemical inertness. But in terms of effective application of Y₂O₃, its hard and brittle nature needs to be overcome during the surface machining process. Therefore, the surface machining control of Y₂O₃ should be conducted carefully. The evaluation for stable and continuous machining should also be investigated in various industrial fields as there are only limited studies on the subject. The lapping process with in-process electrolytic dressing (IED) is widely used for surface machining of hard and brittle materials. In this study, Y₂O₃ surface machinability was evaluated by using the ultra-precision lapping process with IED method by changing three major variables: applied force, wheel speed and machining time. The most suitable value of Ra 92nm surface roughness was acquired with smooth surface quality from the following machining condition: 7kg of applied force, 60rpm of wheel speed and 30minutes of machining time. After the lapping process, the machining tendency and surface characteristics were analyzed with fracture toughness and Vickers hardness for the evaluation of Y₂O₃ surface machinability. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Eun-Sang Lee received B.S. and M.S. degrees in Mechanical Engineering from INHA University in 1985 and in 1987. After that time, he received a Ph.D. degree from Korea Advanced Institute of Science and Technology in 1998. Dr. Lee is currently a Professor at the School of Mechanical Engineering at INHA University in Incheon, Korea. His research fields are ultra-precision manufacturing, electro chemical micro machining and development of semiconductor wafer polishing system.     

Face Grinding Surface Quality of High Volume Fraction SiCp/Al Composite Materials

The existing research on SiCp/Al composite machining mainly focuses on the machining parameters or surface morphology.However,the surface quality of SiCp/Al composites with a high volume fraction has not been extensively studied.In this study,32 SiCp/Al specimens with a high volume fraction were prepared and their machining parame-ters measured.The surface quality of the specimens was then tested and the effect of the grinding parameters on the surface quality was analyzed.The grinding quality of the composite specimens was comprehensively analyzed taking the grinding force,friction coefficient,and roughness parameters as the evaluation standards.The best grinding parameters were obtained by analyzing the surface morphology.The results show that,a higher spindle speed should be chosen to obtain a better surface quality.The final surface quality is related to the friction coefficient,surface roughness,and fragmentation degree as well as the quantity and distribution of the defects.Lower feeding amount,lower grinding depth and appropriately higher spindle speed should be chosen to obtain better surface quality.Lower feeding amount,higher grinding depth and spindle speed should be chosen to balance grind efficiently and surface quality.This study proposes a systematic evaluation method,which can be used to guide the machining of SiCp/Al composites with a high volume fraction.     

Study on the grinding behavior of laser-structured grinding in silicon nitride ceramic

Silicon nitride ceramics are extremely difficult and time-consuming to be machined with conventional methods, such as turning and grinding. Laser-assisted machining has been a field of extensive research during the past decade, as it is a promising solution to enhance the machinability of many difficult-to-cut materials, including silicon nitride ceramics. To enhance the processing precision of silicon nitride ceramic grinding, in this work, a method of laser structuring the surface of silicon nitride is proposed. The laser process allows to precisely control the dimensions of the generated features. Therefore, different patterns with equal silicon nitride surface area are produced in order to study the influence of the pattern geometry on the grinding behavior of the silicon nitride. Grinding performance of the structured silicon nitride is tested. The influences of grinding parameters, such as wheel speed and feed rate, are analyzed for their effects on the grinding force, surface roughness. It is found that the procedure of laser-structured silicon nitride has a strong influence on the grinding results. The grooves obtained by laser-structured silicon nitride are favorable for the flow of coolant, and the cracks generated inside the grooves weak the material locally. The laser-structured silicon nitride generally allows for a reduction of grinding forces by up to 63%, and it can effectively reduce the wear of the tool.     

Performance studies of multilayer hard surface coatings (TiN/TiCN/Al2O3/TiN) of indexable carbide inserts in hard machining: Part-I (An experimental approach)

In recent years, hard machining using CBN and ceramic inserts became an emerging technology than traditional grinding and widely used manufacturing processes. However the relatively high cost factors associated with such tools has left a space to look for relatively low cost cutting tool materials to perform in an acceptable range. Multilayer coated carbide insert is the proposed alternative in the present study due to its low cost. Thus, an attempt has been made to have an extensive study on the machinability aspects such as flank wear, chip morphology, surface roughness in finish hard turning of AISI 4340 steel (HRC 47 ± 1) using multilayer coated carbide (TiN/TiCN/Al₂O₃/TiN) insert under dry environment. Parametric influences on turning forces are also analyzed. From the machinability study, abrasion and chipping are found to be the dominant wear mechanism in hard turning. Multilayer TiN coated carbide inserts produced better surface quality and within recommendable range of 1.6 μm i.e. comparable with cylindrical grinding. At extreme parametric conditions, the growth of tool wear was observed to be rapid thus surface quality affected adversely. The chip morphology study reveals a more favorable machining environment in dry machining using TiN coated carbide inserts. The cutting speed and feed are found to have the significant effect on the tool wear and surface roughness from ANOVA study. It is evident that, thrust force (Fy) is the largest component followed by tangential force (Fz) and the feed force (Fx) in finish hard turning. The observations yield the machining ability of multilayer TiN coated carbide inserts in hard turning of AISI 4340 steel even at higher cutting speeds.     

Effects of Abrasive Types on Grinding of Chopped Strand Mat Glass Fiber-Reinforced Polymer Composite Laminates

A grindability study of chopped strand mat glass fiber reinforced polymer laminates (CSM GFRP) has been carried out to evaluate the effects of abrasive types on grinding force ratio and area roughness at varying grinding parameters such as speed, feed and depth of cut. Performances of alumina (Al₂O₃) and cubic boron nitride (CBN) wheels were compared. Both wheels delivered the maximum grinding force ratios at low speed, high feed and low depth of cut. Alumina wheel produced smoother surface when grinding at low speed, low feed and high depth of cut. CBN wheel, on the other hand, gave smoother surface at high feed and low depth of cut conditions, regardless of speed. With CBN wheel, it is likely that a single grinding condition exists that maximizes grinding force ratio and minimizes area roughness. The findings indicate that CBN wheel exhibited higher grinding force ratio than alumina grinding wheel in general. CBN grinding wheel also outperformed alumina grinding wheel by producing smoother ground surface in most cases.     

表面微观形貌参数尺度独立性的研究

表面微观形貌的表征主要采用传统粗糙度参数和分形参数等多种参数综合描述,尺度独立性是衡量表面形貌表征参数的重要指标。研究了传统粗糙度评定参数和分形维数等表面微观形貌表征参数的尺度独立性。以准分子激光加工,平磨、外圆磨、研磨等磨削机加工表面轮廓为对象,分析了取样长度和采样间距对传统粗糙度参数和分形维数的影响。结果表明,传统粗糙度参数受取样长度和采样间距影响较大,而分形参数与尺度独立性的相关性与加工方法有关系,微细加工表面微观形貌受取样长度和采样间距的影响比机加工表面要小,准分子激光等微细加工表面的分形参数具有尺度独立性。     

An experimental study of ultrasonic vibration-assisted grinding of polysilicon using two-dimensional vertical workpiece vibration

An experimental study of polysilicon grinding with ultrasonic vibration assistance was presented. The two-dimensional (2D) vertical vibration was applied on the workpiece directly and vibrated perpendicular to both the workpiece and grinding wheel. The grinding forces were measured using a three-component dynamometer, and the surface conditions were examined using a surface profilometer and a laser microscope. The experimental results showed that the grinding force and surface roughness with ultrasonication were much less than those in conventional grinding. In the case of ultrasonication, the wheel speed and worktable feed rate would have a more positive effect on the grinding force decrement/increment, especially for the tangential force while the wheel depth of cut had a negative effect. The surface condition of the ground polysilicon surface was improved with the assistance of ultrasonication. This research indicated that the 2D ultrasonic vibration-assisted grinding technique can be an effective method for the high-efficiency machining of hard brittle polysilicon material.     

Experimental analysis on Nd:YAG laser micro-turning of alumina ceramic

Laser micro-turning is a micro-machining strategy to machine cylindrical workpiece of hard-to-process materials such as ceramics. Laser micro-turning method is in high demand in the present high-precision manufacturing industries because of its wide and potential uses in various engineering fields such as automobile, electronics, aerospace, and biomedical applications, etc. In the present research, the experimental analysis of Nd:YAG laser micro-turning of cylindrical-shaped ceramic material has been made to explore the desired laser output responses, i.e., depth of cut and surface roughness by varying laser micro-turning process parameters such as lamp current, pulse frequency, and laser beam scanning speed. Single laser beam has been utilized for successful micro-turning operation. Experimental results revealed that the laser machining process parameters have great influences for achieving desired laser micro-turned depth and surface roughness characteristics during laser micro-turning of alumina ceramics. SEM and optical photographs have also been analyzed for better understanding of the laser micro-turning process for different parametric settings.     

准分子激光加工参数对表面形貌影响的模糊分析

采用准分子激光微细加工方法 ,选用不同的工艺参数加工Al2 O3 陶瓷材料试件。通过表面轮廓仪测量并计算表面形貌统计参数。分析了激光加工工艺参数对表面形貌的影响 ,利用模糊分析方法 ,就激光器的放大器电压、激光脉冲频率、激光扫描速度等工艺参数对表面形貌轮廓均方根值Rq 的影响进行了评价。结果表明 ,Rq 值随激光器的放大器电压和激光脉冲频率的增大而增大 ,随激光扫描速度的增大而减小。分析得出 ,激光加工工艺参数对表面形貌的影响程度不同 ,由大到小依次为激光扫描速度、激光脉冲频率、放大器电压。因此 ,可以通过合理地选择工艺参数获得所需求的表面形貌 ,为表面微观形貌修饰提供了参考依据。     

光学自由曲面反射镜模芯的镜面成型磨削

采用精密修锐修整的圆弧形粗金刚石砂轮在CNC精密磨床上进行了数控成型磨削加工,实现了高效镜面磨削。分析金刚石砂轮圆弧形轮廓的成型修整原理,建立了圆弧形修整的数控模式。通过建立曲面数控成型磨削的行走轨迹算法,实现了自由曲面的圆弧包络成型磨削加工。分析了磨削工艺参数和砂轮出刃形貌参数与超光滑表面形成的作用机制,进行了镜面磨削试验并检测表面微观形貌和粗糙度,分析实现镜面磨削的脆/塑性磨削转换机理。理论分析表明,降低砂轮行走速度,提高砂轮转速以及改善出刃形貌可以获得纳米级粗糙度的超光滑磨削表面。试验结果显示,先将砂轮修锐修整再控制砂轮行走速度小至15 mm/min时,表面粗糙度小于10 nm以下,且微观加工表面没有发生脆性破坏,形成镜面。加工高速钢自由曲面时,面形误差(PV值)可以达到10 μm以下,表面粗糙度R_a可以达到约16 nm。实验结果表明:利用数控技术和粗金刚石砂轮可以实现自由曲面模芯的高效镜面磨削加工,保证了高精度的光学自由曲面反射镜注塑模芯。     

C/SiC复合材料组织对磨削力与加工表面质量的影响

采用树脂结合剂金刚石砂轮对C/SiC复合材料与SiC陶瓷进行了平面磨削加工试验,通过对比两种材料的磨削力及磨削加工表面质量,分析了C/SiC复合材料组织与其磨削加工特性的 关系。研究结果表明,C/SiC复合材料中碳纤维及SiC基体皆以脆性断裂方式实现材料去除;与SiC陶瓷的加工表面(其表面粗糙度值Ra为0.2~0.3μm)相比,C/SiC复合材料磨削时由于碳纤维层状断裂、拔出及其与SiC非同步去除现象导致其加工表面粗糙度值较高, Ra为0.8~1.0μm;C/SiC复合材料磨削力较小,是相同工艺参数下SiC陶瓷材料磨削力的35%~76%。