玻璃的脆塑性域高效精密切削

研究了单斜压头边位印压玻璃时裂纹产生和扩展规律,根据这一规律设计了玻璃切削刀具。该刀具能同时 利用玻璃的脆性断裂和微塑性对玻璃进行高效精密切削,表面粗糙度Ra达0.344μm,达到甚至超过精磨玻璃时的 质量。如果刀具参数选取得当,能在常规切削用量下获得在玻璃的塑性域内形成的、无微裂纹的加工表面。本文还 研究了玻璃切削刀具特征参数对已加工表面粗糙度的影响。     

Brittle–ductile mode cutting of glass based on controlling cracks initiation and propagation

Owing to brittleness and hardness, functional glass is one of the most difficult to cut materials. This paper proposes a new machining method—brittle–ductile mode machining combining both properties of brittle breakage and plastic flow of glass. Edge-indention experiments are first conducted in order to deduce the laws of crack initiation and propagation in the process of glass cutting, then a single-straight tool with big inclination angle is designed for glass cutting based on the laws of crack initiation and propagation and properties of plastic flow. With this new tool, the lateral and subsurface cracks initiation can be suppressed, and media cracks propagate away from machined surface. At the same time, the requirements for machining glass in ductile manner can be fulfilled. Validation experiments show that highly efficient and precise glass cutting can be achieved at the cutting depth of sub-millimeter level, and an integral and crack-free surface with good finish can be obtained. This method overcomes the process restriction on critical cutting depth and tool feed for ductile regime turning technology and can be transferred to mass production.     

非对称楔形压头印压玻璃裂纹产生与扩展规律的研究

研究了非对称楔形压头印压玻璃时裂纹的产生及扩展规律。根据非对称楔印压玻璃时典型的裂纹照片 ,可明显看出存在加载裂纹、横向裂纹和表面下裂纹 ,并且都偏离印压表面法线方向。试验表明 :加载裂纹的偏角αc 与楔角对称线偏角αa 总是符号相同 ;对于形状相似的压头 ,楔角对称线偏角越大 ,裂纹偏角也越大 ;对双斜压头而言 ,如果楔角不等 ,但楔角对称线偏角相等 ,裂纹偏角仍大致相等。     

球头铣刀高速铣削斜面的三维数值模拟研究

用球头铣刀高速铣削斜面是在三轴加工中心上加工模具时的一种走刀方式。根据球头铣刀高速铣削斜面的特点,建立了在垂直向上和向下、水平向上和向下四种走刀方式下高速铣削45°斜面,以及在垂直向下走刀方式下高速铣削30°、60°、75°斜面的三维有限元模型,以分析不同走刀方式下铣削斜面以及铣削不同角度斜面时切削力和切削温度的变化规律。模拟结果表明,在铣削45°斜面时,采用向上走刀方式较向下走刀方式的切削力幅值小、波动大,且切削温度高;采用垂直向下走刀方式铣削大角度斜面时也出现类似情况。对切削力的实测结果验证了该模型的可靠性。     

光学玻璃的精密加工技术

光学玻璃作为一种典型的脆硬材料,采用普通的加工方法难以进行高效精密加工。本文介绍了光学玻璃的高效精密特种加工技术,对ELID法、激光加工、超声磨削以及精密铣削的最新研究进展进行了综述。采用ELID技术,通过控制加工工艺参数,使砂轮单个磨粒的最大切削深度小于脆性材料的临界切削厚度,实现了脆性材料的塑性加工,并得到精密光滑的表面;在加工非球曲面时,可使零件的精加工抛光量降到最低。最新激光加工技术通过增加预热激光束,极大降低已加工表面的热应力及拉伸应力,使得加工质量有了大幅提高。超声波磨削加工不仅改善了表面完整性,而且提高了加工效率,通过选用适当的刀具和工艺参数,使被加工工件表面粗糙度值比普通磨削降低了30%～40%。光学玻璃精密铣削技术通过优化刀具、加工方式及工艺参数,可提高加工质量和效率、降低加工成本。     

Two-dimensional contour cutting of polycrystalline cubic boron nitride using a novel laser/water jet hybrid process

In the laser/water jet hybrid machining (LWJ), a novel process applicable to brittle materials, the laser beam creates a groove through evaporation and causes solid-state phase transition through heating and shock waves while the water jet performs quenching. Both laser and water jet induce stresses and phase changes that lead to cutting via crack formation and controlled fracture mechanism through the rest of the thickness. While LWJ is very well documented by our group for one-dimensional cutting, it remains as a challenge for two-dimensional cutting because of the changing direction of the crack in relation to the laser beam path. In this paper, a focused continuous wave CO₂ laser (400?W) was combined with abrasive-free water jet at 0.4–1.4?MPa (60–200?psi) to generate and steer the controlled crack in two directions in polycrystalline cubic boron nitride tool blanks. A 42.33-mm/s (100?in./min) cutting speed was used in all the tests. The direction of the cracks generated by LWJ was changed to 60°, 108°, 120°, 135° and made to follow a curve with 1?mm radius in accordance with the standard tool shapes. The cut quality was investigated at the point of change in the crack direction using optical profilometer, Raman spectroscopy, and scanning electron microscopy. Results indicated that successful cuts were made with obtuse angles (120° and 135°) in contrast to acute angles (60°). The crack propagation in the heat affected zone, where the phase transition from c-BN to a new phase has occurred, is responsible for the inability to obtain good quality cuts in the acute angle cases. A preliminary graphical representation that explains the observed experimental results is formulated.     

Effect of process induced variations on machining characteristics of a model epoxy resin system

The present work aims to understand the effect of process induced variation on mechanisms of failure, deformation and damage mechanisms in a model epoxy resin system during machining. Process variations have been introduced for a 5052 Huntsman epoxy resin system by considering three post-cure temperature and cycles, viz., 50°C for 15 h, 80°C for 8 h and 100°C for 4 h. Detailed orthogonal cutting experiments have been carried out at different cutting speeds, rake angles and uncut chip thicknesses. Studies of chip formation characteristics, cutting force signatures and fractography indicate a significant brittle-like behavior with increasing post-cure temperature resulting in discontinuous chips that became more pronounced for a positive rake angle. Concurrently, extensive mechanical characterization under different strain rates and temperatures has been carried out using dynamic mechanical analyzer for the epoxy specimens. In addition, standard tensile tests have also been conducted that indicate a correlation between mechanical properties and post-cure temperature cycles. Results are indicative of a strong correlation between post-cure variations and associated failure, fracture characteristics during machining that can be used as a tool for assessing the in-situ cure characteristics in a composite structure.     

Self-generation of machining precision and its realization in lapping of super precision solid balls

This paper presents the principle of self-generation of machining precision by explaining its basic concept and five necessary conditions for forming a system with self-organization capability. A self-generation system is a kind of system with self-organization capability. The self-generation of machining precision for solid balls with super precision is emphatically explained. From the view-point of self-organization, there are three types of systems including system S1 with the self-regulation capability, S2 with the self-determination capability of goals, and S3 with the self-organization capability. Although they are all closed loop control systems, they have different constructions and functions. Necessary conditions for achieving self-generation of machining precision are given. Establishment of the system for machining solid balls with super precision is discussed. Self-generation of machining precision for solid balls with super precision on the basis of the capability of self-removal of errors is presented. Self-generation includes the ability of self-removal of errors for solid balls, convergence of self-removal of errors, self-generation of precision, and self-generating system for the given. __________ Translated from Chinese Journal of Mechanical Engineering, 2007, 43(9): 75–79 [译自 机械工程学报]     

Cutting heat dissipation in high-speed machining of carbon steel based on the calorimetric method

The cutting heat dissipation in chips, workpiece, tool and surroundings during the high-speed machining of carbon steel is quantitatively investigated based on the calorimetric method. Water is used as the medium to absorb the cutting heat; a self-designed container suitable for the high-speed lathe is used to collect the chips, and two other containers are adopted to absorb the cutting heat dissipated in the workpiece and tool, respectively. The temperature variations of the water, chips, workpiece, tool and surroundings during the closed high-speed machining are then measured. Thus, the cutting heat dissipated in each component of the cutting system, total cutting heat and heat flux are calculated. Moreover, the power resulting from the main cutting force is obtained according to the measured cutting force and predetermined cutting speed. The accuracy of cutting heat measurement by the calorimetric method is finally evaluated by comparing the total cutting heat flux with the power resulting from the main cutting force. __________ Translated from Journal of South China University of Technology (Natural Science Edition), 2006, 34(11): 1–4 [译自: 华南理工大学学报(自然科学版)]     

Characteristics of Inclined Planes According to the Variations of Cutting Direction in High-Speed Ball-End Milling

The recent developments of the manufacturing industry require the machining of freeform surfaces using a ball-end mill. The ball-end mill is geometrically complex. For this reason, there are frequent changes of the contact point between a workpiece and a tool, which changes the machining characteristics when machining a freeform surface. In this study, a comparative evaluation of cutting characteristics will be made for a workpiece with inclined planes at angles of 15°,30°, and 45° each using four possible tool paths in down cutting. Then, tool life will be evaluated for heat-treatment materials of high hardness before obtaining the optimal tool path, which makes machining stable and improves tool life.     

Cryogenic abrasive jet machining of polydimethylsiloxane at different temperatures

The temperature dependence of the solid particle erosion of polydimethylsiloxane (PDMS) using aluminum oxide particles was investigated between the temperatures of ?178 and 17 °C for a variety of angles of attack using a novel cryogenic abrasive jet machining apparatus. It was found that the most efficient machining of PDMS (volume removed per kinetic energy of erodent) occurred at approximately ?178 °C, at angles of attack between 30° and 60° from the surface. A previously developed surface evolution model was used to predict the size and shape of unmasked channels at various temperatures. A good agreement between the predicted and measured channel profiles was obtained when the average blasting temperature was between approximately ?127 and ?178 °C. At ?82 °C, the fit was poorer, probably because of an increase in particle embedding. Although it was demonstrated that PDMS could be machined at temperatures above its glass transition, the erosion rate increased by a factor of more than 10 when the machining temperature was below this point.     

玻璃模压成形用微沟槽磷化镍模具的超精密切削加工

最佳邻接量是高精度加工玻璃模压成形用磷化镍镀层材料微沟槽模具的重要参数。本文提出了一种利用小角度微沟槽交叉切削技术快速确定微沟槽最佳邻接量极限范围的方法。该方法利用沟槽小角度交叉切削材料去除形式与沟槽邻接切削相近的特点,对微沟槽邻接量的极限范围进行预测。首先,以沟槽交叉角度和交叉沟槽深度为变量设定切削条件,得到多组渐变棱;然后,观测交叉渐变棱形貌并结合材料塑性变形法则与脆塑转变理论分析棱边上的材料去除状态;通过观察交叉渐变棱与沟槽邻接脊部在切削过程中去除材料的截面形貌建立二者的关系;最后,分析交叉渐变切入棱与切出棱形貌的差异,确定脆塑转变的邻接量范围。基于上述方法,观测了交叉渐变棱的形貌并进行几何计算,确定磷化镍模具微沟槽邻接切削产生脆性剥离现象的临界邻接量范围为570~720nm。利用微沟槽模具超精密切削加工实验验证了该方法的有效性,加工出了高质量模具并用于微沟槽玻璃模压成形,实现了玻璃微沟槽的精密制造。     

The design and optimization of micro polycrystalline diamond ball end mill for repairing micro-defects on the surface of KDP crystal

Micro-milling is a promising approach to repair the micro-defects on the surface of KH₂PO₄ (KDP) crystal. The geometrical parameters of micro ball end mill will greatly influence the repairing process as a result of the soft brittle properties of KDP crystal. Two types of double-edged micro ball end mills were designed and a three-dimensional finite element (FE) model was established to simulate the micro milling process of KDP crystal, which was validated by the milling experiments. The rake angle of −45°, the relief angle of 45° and the cutting edge radius of 1.5–2 μm were suggested to be the optimal geometrical parameters, whereas the rake angle of −25° and the relief angle of 9° were optimal just for micro ball end mill of Type I, the configuration with the rake angles ranging from 0° to 35°, by fully considering the cutting force, and the stress–strain distribution over the entire tool and the cutting zone in the simulation. Moreover, the micro polycrystalline diamond (PCD) ball end mills adopting the obtained optimal parameters were fabricated by wire electro-discharge machining (WEDM) and grinding techniques, with the average surface roughness Ra of tool rake face and tool flank face ∼0.10 μm, and the cutting edge radius of the tool ∼1.6 μm. The influence of tool's geometrical parameters on the finished surface quality was verified by the cutting experiments, and the tool with symmetric structure was found to have a better cutting performance. The repairing outlines with Ra of 31.3 nm were processed by the self-fabricated tool, which could successfully hold the growth of unstable damage sites on KDP crystal.     

Comparison of the fatigue life of F.F. shaft material according to various environmental temperatures

A rotary bending fatigue test was carried out with two kinds of materials, S43C and S50C, using the front engine and front driveshaft (F.F. shaft) of the vehicle. The specimens were heat-treated using the high frequency induction method (about 1 mm depth and HRC56∼60) and the test environment temperatures were -30 °C (-22 °F), +25 °C (+77 °F), and +80 °C (+176 °F) in order to determine the influence of the heat treatment and the temperatures. The fatigue life increased on the order of +80 °C, +25 °C, and -30 °C regardless of heat treatment. In comparison of the fatigue lives with the basis of the tested result at +25 °C, the fatigue lives of non-heated specimens decreased about 35%, but that of heat-treated specimens decreased by only about 5% at +80 °C, more than at +25 °C. And fatigue life of non-heated and heat-treated specimens were about 110% and 120% higher at -30 °C than that of +25 °C. The initiation of surface microcracks was observed at 0.2 fatigue life ratio in as-received S43C and S50C, but the average crack length in S50C was about 14% longer than that of S43C at the same fatigue life ratio.     

An elastic-plastic stress analysis in silicon carbide fiber reinforced magnesium metal matrix composite beam having rectangular cross section under transverse loading

In this work, an elastic-plastic stress analysis has been conducted for silicon carbide fiber reinforced magnesium metal matrix composite beam. The composite beam has a rectangular cross section. The beam is cantilevered and is loaded by a single force at its free end. In solution, the composite beam is assumed perfectly plastic to simplify the investigation. An analytical solution is presented for the elastic-plastic regions. In order to verify the analytic solution results were compared with the finite element method. An rectangular element with nine nodes has been choosen. Composite plate is meshed into 48 elements and 228 nodes with simply supported and in-plane loading condations. Predictions of the stress distributions of the beam using finite elements were overall in good agreement with analytic values. Stress distributions of the composite beam are calculated with respect to its fiber orientation. Orientation angles of the fiber are chosen as 0°, 30°, 45°, 60° and 90°, The plastic zone expands more at the upper side of the composite beam than at the lower side for 30°, 45° and 60° orientation angles. Residual stress components ofσ _x andτ _xy are also found in the section of the composite beam.     

Topography and microstructure of the cutting surface machined with abrasive waterjet

Abrasive waterjet (AWJ) technology has been widely used for cutting materials in precision machining. The present paper reports the surface topography and microstructure of the cutting surfaces machined by AWJ. Four different kinds of ductile metallic materials were used for preparation of specimens. With the AWJ processing technique, smooth surfaces were easily obtained with a lower surface roughness about 2 to 3 μm. By comparing the microhardness of the specimens with the control surface sample obtained by wire electrodischarge machining, it is found that there is no heat-affected zone on the cutting surfaces machined by AWJ. By observing the surface morphology and microstructure, the features of friction and wear marks are revealed. The results show that a smooth cutting surface is more easily obtained on hard materials, while erosions on soft material surfaces are more serious. All scratches have a clear consistent direction, under the action of mechanical abrasive wear.     

Selection of the Machining Inclination Angle in High-Speed Ball End Milling

High-speed machining is a key issue for current die and mould manufacturing. Though this technology has great potential for high productivity, tool wear accelerated by high cutting speeds and hard materials is a barrier. In this work, we attempted to reduce tool wear by controlling the machining inclination angle between the tool and the workpiece. To do this, the range of cutting angles engaged in the cutting using a ball end cutter is obtained from the boundary lines describing machined sculptured surfaces represented by the cutting envelop condition and the geometric relationships of successive tool paths. Then, the chip cross-sectional area and chip length can be obtained from the calculated cutting edge and the rotational engagement angle. The simulation results showed that a machining inclination angle of 15° was good enough from the point view of machineability, and this value was verified by a cutting experiment using high-speed ball end milling.     

Selection of an optimal parametric combination for achieving a better surface finish in dry milling using genetic algorithms

In machining, coolants improve machinability, increase productivity by reducing tool wear and extend tool life. However, due to ecological and human health problems, manufacturing industries are now being forced to implement strategies to reduce the amount of cutting fluids used in their production lines. A trend that has emerged to solve these problems is machining without fluid – a method called dry machining – which has been made possible due to technological innovations. This paper presents an experimental investigation of the influence of tool geometry (radial rake angle and nose radius) and cutting conditions (cutting speed and feed rate) on machining performance in dry milling with four fluted solid TiAlN-coated carbide end mill cutters based on Taguchi’s experimental design method. The mathematical model, in terms of machining parameters, was developed for surface roughness prediction using response surface methodology. The optimization is then carried out with genetic algorithms using the surface roughness model developed and validated in this work. This methodology helps to determine the best possible tool geometry and cutting conditions for dry milling.     

Development of meso-scale milling machine tool and its performance analysis

To overcome the shortcomings of current technologies for meso-scale manufacturing such as MEMS and ultra precision machining, this paper focuses on the investigations on the meso milling process with a miniaturized machine tool. First, the related technologies for the process mechanism studies are investigated based on the analysis of the characteristics of the meso milling process. An overview of the key issues is presented and research approaches are also proposed. Then, a mesoscale milling machine tool system is developed. The subsystems and their specifications are described in detail. Finally, some tests are conducted to evaluate the performance of the system. These tests consist of precision measurement of the positioning subsystem, the test for machining precision evaluation, and the experiments for machining mechanical parts with complex features. Through test analysis, the meso milling process with a miniaturized machine tool is proved to be feasible and applicable for meso manufacturing. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42(11): 162–167 [译自: 机械工程学报]     

高硅氧与石墨黏合件铣削加工工艺研究

针对高硅氧和石墨材料切削加工的特点,以典型尖劈组件为研究对象,从尖劈组件的结构特点和所用材料特性着手,分析探讨了影响其加工质量及尺寸精度的主要因素。通过加工工艺试验,得出了合理的安装定位方式、加工方法、切削刀具材料以及切削参数,为类似零件的加工提供了重要的参考价值。