微结构砂轮对不同陶瓷的磨削性能

基于阵列微孔的微结构砂轮和普通砂轮对氧化铝、氮化铝、氧化锆及氮化硅陶瓷材料的不同磨削性能,对比研究不同砂轮和不同陶瓷材料的磨削力、比磨削能、表面粗糙度及表面崩边特征。结果表明:相比普通砂轮,微结构砂轮提高了氧化铝、氮化铝及氧化锆陶瓷的磨削力和比磨削能,降低了表面粗糙度,而对氮化硅陶瓷的磨削力及表面粗糙度影响不明显;相比其他陶瓷,氮化硅陶瓷具有较高的磨削力和比磨削能。从磨削加工表面特征上看,氧化铝、氮化铝陶瓷以脆性去除方式为主,氧化锆以塑性去除为主,而氮化硅则兼具塑性和脆性去除特征;微结构砂轮加工表面崩边尺寸大于普通砂轮的崩边尺寸,氧化铝和氮化铝陶瓷的表面崩边尺寸明显大于氧化锆和氮化硅陶瓷的。      

Experimental investigations of machining characteristics and removal mechanisms of advanced ceramics in high speed deep grinding

Machining characteristics and surface integrity of advanced ceramics, including alumina, alumina–titania, and yttria partially stabilized tetragonal zirconia, were studied under high speed deep grinding conditions. Material removal mechanisms involved in the grinding processes were explored. The material removal in the grinding of alumina and alumina–titania was dominated by grain dislodgement or lateral cracking along grain boundaries. The removal for zirconia was via both local micro fracture and ductile cutting. It was found that under a feed rate of 500 mm/min and for all the wheel speeds used, an increase in the wheel depth of cut (DOC) from 0.1–2 mm slightly improved the ground surface finish, but greatly prolonged the wheel life. This increase did not deepen the subsurface damage layer for the alumina and alumina–titania, but resulted in a slightly deeper damage layer for the zirconia.     

金刚石砂轮磨削轴承用ZrO2 陶瓷表面质量研究

在氧化锆陶瓷磨削中为获得较高质量表面,采用单因素试验研究磨削深度、砂轮线速度、工件进给速度对氧化锆陶瓷精密磨削表面质量的影响规律及材料去除机理,通过超景深三维显微镜以及扫描电子显微镜,观察氧化锆陶瓷试件磨削后的表面形貌,最后用正交试验法进行优选并验证。结果表明:磨削表面的粗糙度随磨削深度、工件进给速度增大而增大,随砂轮线速度增大先减小、后增大。在磨削深度5 μm、砂轮线速度40 m/s、工件进给速度1 000 mm/min的优化组合条件下,磨削3组氧化锆陶瓷的平均表面粗糙度R_a为0.388 9 、0.417 0和0.403 7 μm。      

High speed versus conventional grinding in high removal rate machining of alumina and alumina–titania

High removal rate (up to 16.6 mm³/s per mm) grinding of alumina and alumina–titania was investigated with respect to material removal and basic grinding parameters using a resin-bond 160 μm grit diamond wheel at the speeds of 40 and 160 m/s, respectively. The results show that the material removal for the single-phase polycrystalline alumina and the two-phase alumina–titania composite revealed identical mechanisms of microfracture and grain dislodgement under the grinding conditioned selected. There were no distinct differences in surface roughness and morphology for both materials ground at either conventional or high speed. An increase in material removal rate did not necessarily worsen the surface roughness for the two materials at both speeds. Also the grinding forces for the two ceramics demonstrated similar characteristics at any grinding speeds and specific removal rates. Both normal and tangential grinding forces and their force ratios at the high speed were lower than those at the conventional speed, regardless of removal rates. An increase in specific removal rate caused more rapid increases in normal and tangential forces obtained at the conventional grinding speed than those at the high speed. Furthermore, it is found that the high speed grinding at all the removal rates exerted a great amount of coolant-induced normal forces in grinding zone, which were 4–6 times higher than the pure normal grinding forces.     

The effect of ELID grinding on the flexural strength of silicon nitride

Advanced structural ceramics, such as silicon nitride-based materials, are of significant interest due to their excellent physical and mechanical properties. However the cost of grinding these ceramics, an integral part of their fabrication, is very high and can result in surface and subsurface damage to the material. These defects can significantly reduce the strength and reliability of the finished component and are sensitive to grinding parameters. In this investigation, the effect of finish electrolytic in-process dressing (ELID) grinding on the flexural strength of silicon nitride specimens were studied. Kyocera's silicon nitride SN 235, in the form of Modulus of Rupture (MOR) specimens, were ground using the application of ELID grinding with a # 6000 grit sized cast iron bonded diamond (CIB-D) grinding wheel. A significant improvement in the strength of the Si₃N₄ specimens was noted when finish ELID grinding was performed. This was the result of ductile regime grinding using the application of finish ELID grinding. Another method to improve the flexural strength of silicon nitride specimens will also be addressed in this paper.     

Grinding characteristics,material removal and damage formation mechanisms in high removal rate grinding of silicon carbide

Development of advanced ceramics such as silicon carbide has gained significant importance because of their desirable properties. However, their engineering applications are still limited owing to the limitations in developing damage-free and economical machining techniques. It is often desired to increase the machining rate to improve productivity while maintaining the desired surface integrity. The success of this approach, however, requires a fundamental understanding of the material removal and damage formation mechanism in grinding. In this paper, high removal rate grinding of silicon carbide was investigated with respect to material removal and basic grinding parameters using a diamond grinding wheel. The results showed that the material removal was primarily due to the microfracture and grain dislodgement under the grinding conditioned selected. For grain dislodgement removal mode, the relationship for the removal rate in scratching based on a simple fracture mechanics analysis has been established. This research provides valuable insights into the surface and subsurface integrity and material removal mechanism during high removal rate grinding of silicon carbide.     

Li-Ti铁氧体陶瓷精密磨削的试验研究

铁氧体陶瓷的应用因其表面加工质量难以保证而受到很大限制。本文采用80/100#树脂结合剂金刚石砂轮和W 20石墨白刚玉砂轮对Li-Ti铁氧体陶瓷进行了磨削试验。研究了单位宽度磨削力、表面粗糙度和单位宽度材料去除率随磨削参数的变化规律,观察并分析了铁氧体工件磨削后的表面微观形貌。结果表明:Li-Ti铁氧体的表面粗糙度值可达到Ra0.084μm,实际单位宽度材料去除率达到90%,材料以塑性方式去除;采用上述砂轮可实现铁氧体陶瓷的高效精密磨削。     

精密磨削Invar36合金时的磨料选择

本文对白刚玉、铬刚玉和绿色碳化硅三种磨料砂轮磨削Invar36合金时的磨削力、磨削温度、表面粗糙度和磨削比进行了对比分析。结果表明：白刚玉砂轮对Invar36合金的磨削比最高,磨削表面粗糙度较好,但是磨削温度和磨削力也比较高,适用于Invar36合金的粗磨;铬刚玉砂轮磨削时的磨削力最小,磨削温度最低,但是磨削比也比较低,因此适用于易变形零件的精密磨削。     

树脂金刚石砂轮加工氧化铝陶瓷的磨削工艺试验研究

为改善氧化铝陶瓷的磨削效果,分别使用粒度尺寸125~150 μm和38~45 μm的金刚石制备树脂结合剂砂轮,并进行磨削实验,研究表面粗糙度、材料去除方式和材料去除比例随磨削参数的变化规律,观察并分析氧化铝陶瓷磨削后的表面微观形貌。结果表明:氧化铝陶瓷的表面粗糙度可以达到R_a 0.418 μm,材料去除比例可达到95%;用粒度尺寸38~45 μm的金刚石制备的树脂结合剂砂轮在切深≤ 2 μm,工件移动速度为0.15 m/min加工时,材料由延性域的塑性去除转变为脆性去除。优化后的加工工艺为先以磨料粒度尺寸125~150 μm的树脂金刚石砂轮在切深为4 μm时进行初步加工,再用磨料粒度尺寸38~45 μm的树脂金刚石砂轮进行光磨,可以兼顾高效与精密两方面的要求。      

The extrusion freeforming of functional ceramic prototypes

Extrusion freeform fabrication (EFF) and fused deposition of ceramics (FDC) processes are established extrusion-based freeforming techniques capable of fabricating complex shaped monolithic ceramic prototypes by the sequential deposition and solidification of green ceramic feedstock. In these processes, ceramic parts are produced using a commercially available Stratasys 3-D Modeler retrofitted with modified extrusion heads suitable for extruding ceramic materials. The manufactured objects have good dimensional tolerances as well as engineering compositions and microstructures. The process is flexible and can be used for different monolithic ceramic materials such as silicon nitride, alumina, and zirconia.     

金刚石砂轮双端面磨削氧化铝陶瓷

本研究涉及双端面磨削技术应用于用两片陶瓷结合剂金刚石砂轮同时磨削圆柱形氧化铝陶瓷工件两个端面的技术评价。精细陶瓷(advanced ceramics),例如氧化铝(Al2O3),由于具有高的硬度、抗压强度、耐腐蚀性、导电性、磁导率和脆性而应用广泛。本试验为四因子试验,评价被磨工件的表面粗糙度Ra,采用重量法测定材料去除率,采用激光折射技术测定的平均比例系数来评价被磨工件平面度。本文的研究结果表明,双端面磨削可以在很短的加工时间内获得极高的表面光洁度、高的精度和高的磨除率。     

微粉金刚石钎焊砂轮磨削氧化铝陶瓷的磨削力和表面粗糙度特征

在不同磨削深度、砂轮转速和进给速度组合下,研究微粉金刚石钎焊砂轮磨削氧化铝陶瓷过程的磨削力及工件的表面粗糙度的变化规律,并筛选出低磨削力和低工件表面粗糙度的加工工艺参数。试验结果表明:在微粉金刚石钎焊砂轮的磨削过程中,氧化铝陶瓷主要通过脆性断裂的方式去除;随着磨削深度、进给速度的增加,砂轮在进给方向和切深方向的力以及工件表面粗糙度都上升;随着砂轮转速的增加,进给方向和切深方向的力以及工件表面粗糙度都下降。试验获得的低磨削力和低工件表面粗糙度精密加工工艺参数分别为:磨削深度为1.0 μm,进给速度为12 mm/min,砂轮转速为24 000 r/min和磨削深度为1.0 μm,进给速度为1 mm/min,砂轮转速为20 000 r/min。低磨削力磨削时,微粉金刚石钎焊砂轮受到的X方向和Z方向的磨削力分别为0.15 N和0.72 N;精密加工后的氧化铝陶瓷的表面粗糙度值可达0.438 μm。      

Mechanical spectroscopy of the high-temperature brittle-to-ductile transition in ceramics and cermets

In ceramics such as alumina, zirconia or silicon nitride, the high-temperature “brittle-to-ductile” transition is associated with grain boundary sliding often lubricated by an intergranular glassy film. This dissipative mechanism gives rise to a mechanical loss peak, which turns into an exponential background at higher temperature. When the amount of intergranular glassy phase is higher, the exponential background is globally higher and so is the creep rate. When the mechanical loss peak is due to amorphous pockets surrounded by a rigid skeleton as in silicon nitride, it may account for the toughness improvement by energy dissipation in these glassy pockets, the surrounding skeleton being responsible for creep resistance. Good examples of two-phase materials, in which one phase is responsible for mechanical strength, the other for toughness, are the cermets or the cemented carbides. For instance, in WC–Co, a relaxation peak has been found in the Co binder phase which can be correlated with an increase in toughness, the high-temperature exponential background accounting for the creep behavior of the material.     

Al2O3陶瓷电火花磨削工作液实验研究

考虑到工作液对于非导电工程陶瓷双电极同步伺服电火花磨削新工艺的重要性,以氧化铝陶瓷加工为例,通过实验的方法研究了工作液的种类、浓度对材料去除率和加工表面粗糙度的影响规律,给出了实验步骤,并对实验结果进行了理论分析。综合考虑加工效率、加工质量、成本及环保等因素,在自来水中配制5%体积浓度的DX-1乳化液是比较理想的工作液。考虑单一效果,在自来水乳化液加入0.5%质量的聚乙烯醇作工作液可以提高材料去除率10%以上;使用去离子水作工作液可以得到最好的表面质量。     

Laser milling of ceramic components

Conventional methods of producing ceramic components are based on sintering technology which requires expensive tooling making it uneconomic for small batch fabrication. Laser milling provides a new method of producing parts in a wide range of materials, including ceramics, directly from CAD data. This paper considers the technical capabilities of laser milling when applied to the machining of microcomponents from alumina and silicon nitride ceramics. The main parameters affecting the material removal characteristics of laser milling are reviewed. A new technique for machining alumina components is proposed emphasising the importance of correct set-up design in achieving a high level of accuracy. Process parameters influencing part quality are analysed and guidelines for machine set-ups are formulated. The paper concludes with an assessment of the accuracy of the laser milling process.     

Experimental study on grinding force and grinding temperature of Aermet 100 steel in surface grinding

This paper investigates grinding force and grinding temperature of ultra-high strength steel Aermet 100 in conventional surface grinding using a single alumina wheel, a white alumina wheel and a cubic boron nitride wheel. First, mathematical models of grinding force and grinding temperature for three wheels were established. Then, the role of chip formation force and friction force in grinding force was investigated and thermal distribution in contact zone between workpiece and wheel was analyzed based on the mathematical model. The experimental result indicated that the minimum grinding force and the maximum grinding force ratio under the same grinding parameters can be achieved when using a CBN wheel and a single alumina wheel, respectively. When the phenomenon of large grinding force and high grinding temperature appeared, the workpiece material would adhere locally to the single alumina wheel. Grinding temperature was in a high state under the effect of two main aspects: poor thermal properties of grinding wheel and low coolant efficiency. The predicted value of grinding force and grinding temperature were compared with those experimentally obtained and the results show a reasonable agreement.     

蓝晶石在树脂高速砂轮制造中的应用

本文介绍了蓝晶石作为活性材料和补强材料在树脂高速砂轮制造中的应用。在砂轮使用速度80 m/s的条件下,对不同粒度、不同配方的蓝晶石补强的磨钢坯锆刚玉砂轮性能进行了测试和分析。结果表明:采用蓝晶石作为砂轮补强材料制造的规格600 mm×75 mm×203 mm磨钢坯砂轮,通过了使用速度为80m/s的回转强度3 820 r/min检测,满足了用户使用要求。文中还介绍了蓝晶石应用于高速砂轮制造中的条件,并对蓝晶石作为砂轮活性填料在钛合金磨削中的作用进行了论述。     

氮化硅陶瓷磨削表面质量的建模与预测

目的提升氮化硅陶瓷加工质量和效率,提高粗糙度模型预测精度。方法提出塑性与塑-脆性去除转变临界切深hc1和塑-脆性与脆性转变临界切深hc2,然后对原有模型进行修正,并引入塑性去除粗糙度修正系数φ1、τ1和塑-脆性去除粗糙度修正系数φ2、τ2,建立基于不同去除方式的粗糙度Ra预测模型,后通过磨削实验对系数进行求解,并得出磨削参数对粗糙度和表面形貌的影响。结果塑性去除粗糙度修正系数φ1=5.872×10^-6、τ1=0.1094,塑-脆性去除粗糙度修正系数φ2=1.299×10^-5、τ^2=0.1582。砂轮线速度vs由30 m/s增大到50 m/s,粗糙度Ra由0.366μm减小到0.266μm,去除方式由脆性断裂向塑性变形转变,表面质量变好。磨削深度ap由5μm增大到45μm,粗糙度Ra由0.252μm增大到0.345μm,去除方式由塑性变形向脆性断裂转变,表面质量变差。工件进给速度vw由1000 mm/min增大到9000 mm/min,粗糙度Ra由0.227μm增大到0.572μm,去除方式由塑性变形向脆性断裂转变,表面质量变差。模型预测值与实验值的相对误差δ在2.1%~8%之间。结论在加工中应控制磨削深度和工件进给速度,适当提高砂轮线速度,以保证加工精度和效率。基于不同去除方式的粗糙度预测模型,可较为精准地预测实际加工情况。     

氮化硅陶瓷的残余应力和抗弯强度特性

利用X射线衍射方法测量了经不同磨削的氮化硅陶瓷表面残余应力及其对抗弯强度的影响。结果表明 ,磨削工艺所引入的残余应力是拉应力 ,显著降低陶瓷抗弯强度。