Porous polyimide materials(PPI)have interconnected pore structures that can effectively store lubricating oil.However,the presence of these pores will reduce the strength and wear resistance of PPI,resulting in a mutual constraint between its oil content and wear resistance,making it difficult to balance.Therefore,a sandwich type density layered porous polyimide material is prepared using the method of layered cold pressing and constant volume sintering.The outer and inner layers of the material can have different porosities.The outer layer uses a high porosity to increase oil content,while the inner layer uses a low porosity to improve material strength and wear resistance,in order to overcome the problem of difficult balance between oil content and wear resistance.Based on the study of uniform PPI performance with different densities,the pore structure of density layered PPI is designed,and two types of layered PPI are prepared.Their mechanical properties,oil content properties,and friction and wear properties are studied.The results show that compared with uniform PPI,density stratified PPI has a higher oil content(＞15％)and excellent oil retention rate(94.06％)due to the synergistic effect of different porosity in the inner and outer layers,and maintains excellent mechanical and tribological properties.The tensile strength and compressive strength of the 1.0-1.1-1.0 layered material are 41.7 MPa and 374 MPa,respectively.Its friction coefficient(0.078)is close to that of a uniform PPI density of 1.1 g/cm3(0.07),but the oil content of the layered material(15.5％)is much higher than that of the uniform material(11.1％).This sandwich type density layered PPI can balance oil content and wear resistance,providing a new approach for the design of porous materials.

In practical applications, the pocket surface of a porous polyimide (PPI) cage often experiences blackening wear, which may lead to lubrication failure. However, the mechanism of blackening wear is still controversial. In this study, the impact of oxygen concentration on blackening wear was investigated using a sealed double-contact friction tester by controlling the ventilation with argon gas. Then four types of oils, as well as steel balls and Si3N4 balls, were used to study the effect of oil decomposition on blackening wear. Finally, the effect of PPI decomposition was studied under dry friction conditions to obtain high friction temperatures. The results indicate that iron oxides are the primary factors of blackening on the worn surfaces of PPIs, whereas oil and PPI decompositions are minor factors. At an oxygen concentration of 0.1% or when Si3N4 balls are used as rubbing pair materials, there is only slight blackening wear on the worn surface of the PPI. Therefore, the influence of iron oxides on the blackening of worn PPI surfaces is crucial. At low oxygen concentration (0.1%), a relatively high degree of unsaturation of the oil may lead to slight blackening wear of the PPI due to oil decomposition, but its impact is minimal. This study provides necessary insights into the mechanism of blackening wear in PPI cages.

As a commonly used lubricant additive, ZDDP can form antiwear tribofilms on metal surfaces, reduce the wear of rolling elements and grooves, and thus holds potential for application in bearing lubrication. However, in the actual operation of bearings using oil-impregnated porous polyimide (iPPI) as the bearing cage, there are both steel-steel contacts and iPPI-steel contacts. The characteristic of the ZDDP tribofilms under iPPI-steel soft contact remains unclear. Herein, ZDDP was added as a lubricant additive to poly-alpha-olefin oil (PAO4), and its frictional behavior under soft contact (iPPI-steel) and hard contact (steel-steel) at different temperatures was investigated. Results demonstrated that raising temperature promotes ZDDP tribochemical activity and increases the tribofilmaffected area on the steel surface. The formed tribofilm protects the steel surface and reduces wear. FIB-SEM characterization demonstrated that compared with hard contact, the ZDDP tribofilms formed on the steel ball surface under soft contact exhibit stronger continuity and greater thickness, thereby providing more effective protection for the steel ball surface. This study provides necessary insights for the application of ZDDP in bearings with iPPI as the bearing cage.

In engineering, the randomness of assembly experiences, manufacturing errors, and process parameters leads to random connection states and an uneven distribution of contact stress at the assembly interface of an aeroengine rotor, which restricts the high-precision and high-efficiency assembly requirements of these rotors. To address the lack of an evaluation model of the contact characteristics of the rotor assembly interface and the difficulty of establishing the relationship between contact characteristics and assembly performance with multi-random factors, this paper proposes a contact characteristic evaluation method for a rotor assembly interface based on vibration energy flow for the first time. First, based on the structural sound intensity method, the transmission mechanism of the vibration energy flow at the assembly interface is studied from the perspective of vibration energy, and a vibration energy power flow characterization model based on the finite element method is established. Furthermore, the vibration transmission characteristics of the assembly connection interface for different processes and load correlations are analyzed and visualized for characterization. Subsequently, a quantitative evaluation model for the contact state of assembly interfaces is proposed by integrating the gray-level co-occurrence matrix (GLCM). Finally, the feasibility of the model is verified through simulation and experiments. A precise model for the contact characteristics of the aeroengine rotor assembly interface driven by measured data is established, revealing the formation and evolution mechanisms of the vibration transmission characteristics at the connection interface of the aeroengine rotor assembly. This paper discusses the fact that the gray texture features Asm and L parameters can achieve a quantitative evaluation of the connection status of the rotor assembly interface, providing a computational tool for the precise control of the assembly interface connection status of complex equipment such as aircraft rotors.

Porous polyimide (PPI) possesses interconnected micro-pores capable of storing lubricant oil. However, the strength of PPI was weakened by pores, resulting in a decrease in wear resistance. Herein, organic silicon coating (OSC) was used to strengthen the PPI surfaces. The oil storage capacity and tribological performance of the coated PPI with varying coating coverages were investigated. Results demonstrated that PPI surfaces were effectively protected by the OSC. Particularly noteworthy was the substantial reduction in friction coefficient by 50.9 wt.% and wear rate by 55.8 wt.% observed under a high load of 100 N (103.19 MPa) with a 79.31 wt.% coating coverage. Improving surface strength and shrinking surface pore size are the two beneficial effects of the OSC. On the one hand, the OSC has high hardness and excellent density, which improves the wear resistance of PPI surfaces. On the other hand, the OSC reduces the surface pore size of PPI, improves the load-bearing capacity of the oil film, and thus reduces wear. This study provides a viable approach for strengthening the wear resistance of porous polymer materials.

Optical freeform surfaces (OFS) have been extensively employed as core components in advanced optical systems for their excellent performances. However, the surface complexity and the high surface accuracy do impose challenges to the processing of OFS, especially the surface form maintaining or control during polishing. As one of the promising ultra-precision machining technologies to fabricate OFS, the flexible ball-end tool (FBET) polishing becomes available due to its attractive technical advantages. Nevertheless, there are still lack of more comprehensive insights on material removal mechanisms for FBET polishing incorporating the curvature effect, particularly from a microscopic scale, which is of great significance to determine the surface quality and form control in ultra-precision polishing process. In this paper, different from those published macro-scale Preston law-based models, a micro-scale material removal model is developed based on the mutual interaction of the slurry, polishing pad and curved workpiece among the FBET polishing interfaces with micro-contact theory and tribology theory, wherein various parameters embodied in FBET polishing are formulated quantitatively, such as slurry characteristics, pad properties, tool features, processing conditions, as well as workpiece curvature effect. The FBET is designed and adopted to conduct the spot polishing experiments within the concave curvature radius range from 75 mm to 225 mm, wherein the curvature radius range from 225 mm to 800 mm is theoretically chosen as an extension of this research. The predicted results agree well with the experimentally measured section profiles of polishing spots, thereby demonstrating the correctness and effectiveness of the proposed model. Furthermore, the effective relative velocity U together with the separation gap d between reference plane and workpiece surface are known as the two key parameters to account for the material removal mechanisms, and the latter is figured out to be the sensitive one to the curvature effect rather than the former. Through the analysis of key parameters, the established model is capable of helping to strengthen the understanding of material removal mechanisms for FBET polishing with the consideration of curvature effect, addressing those cannot be interpreted by the classical Preston equation previously, which is meaningful for precision control of material removal during polishing of OFS.

Pore size is critical to the oil-storage performance and tribological properties of porous polyimide (PPI). To study the effect of pore size, four PPIs with different pore sizes and similar porosities were fabricated. The mechanical, oil-absorption, and tribological properties of the PPIs were investigated. According to the results, PPIs with larger pores demonstrate faster oil absorption and a higher oil-filling rate. However, larger pores contribute to a rougher surface and lower oil retention. These dual effects result in PPIs with larger pores displaying a low friction coefficient at low speeds but a high friction coefficient at high speeds. The effect of pore sizes on elastohydrodynamic (EHD) film and Stribeck curves were discussed from seepage effect and viscoelasticity of PPI, respectively. The permeability of the four PPIs was calculated based on mercury intrusion test results. Larger pores lead to higher permeability of PPI at lower pressure, which makes it easier to reduce thickness of EHD film, causing high friction and wear. The damping effect of PPIs, rather than a viscous flow, results in a slight increase in friction coefficient at high speed under micro-oil lubrication. Considering the tribological and oil-absorption properties, the preferred particle size of polyimide molding powder is 25-48 mu m. [DOI: 10.1115/1.4067905

As one of the crucial functional units in ultra-precision machines, the hydrostatic guideways have been commonly adopted due to their own superiority. Although the existed analysis approaches can enable researchers to understand the influence of various design parameters on motion accuracy of hydrostatic guideways, the corresponding imperfections remain to be captured easily. In this paper, targeted at avoiding those defectiveness as much as possible, the kinematic theory based quasi-static analysis model with less simplification is developed directly, wherein the profile pattern difference between main and vice guide rails induced by the manual lapping technology is taken into consideration, and the general structure of hydrostatic guideways extracted from Z axis of the ultra-precision grinding machine UPG80 is determined as the research object. Three CASE studies are proposed orderly to verify the correctness and effectiveness of the established analytical model, and the results demonstrate that the variation trends of the theoretically calculated vertical straightness errors are in good accordance with those of the experimentally measured. Furthermore, the fluctuation amplitude deviation between the predicted and the measured motion accuracy does occur in CASE 3, which should be attributed to the accumulated thermal effect revealed via an experimental platform of hydrostatic guideways with similar structure type to the research object. It also is figured out that, the variation of three components of guide rails’ profile errors caused by the thermal accumulation leads to the fluctuation amplitude deviation reflected in CASE 3, and the level of influence can be known as Amplitude component ( E) > Phase component ( φ) Upside wavelength component ( λ up ) > Downside wavelength component ( λ down ). This study can serve as a valuable foundation for improving the motion accuracy of hydrostatic guideways and is also confirmed to be valuable to the peer designers.

316L stainless steel has been extensively employed in the manufacturing of medical equipment and biomedical implants because of its good ductility, corrosion resistance and biocompatibility, etc. However, there has always been a non-neglected problem of low polishing precision and efficiency in the whole machining chain for such parts, hence, it is difficult to meet the batch demand of the market for 316L stainless steel with high-precision surface. Based on the principle of magnetic field-assisted batch polishing (MABP) proposed by our research team previously, a novel chemical magnetic field-assisted batch polishing (CMABP) method here is developed by adding chemical reagents (i.e., the mixture of oxalic acid and hydrogen peroxide) in the preparation process of regular magnetic brush, desiring and expecting to further realize the polishing of 316L stainless steel with higher precision and efficiency simultaneously. The preliminary experimental results demonstrated that the value of surface roughness Sa after CMABP became smaller and the material removal rate increased comparing to that after MABP, which did verify the potential advantage of the established CMABP approach. In detail, CMABP experiments with pH value and H2O2 concentration as variables were carried out quantitatively. The results suggested that, within the set range of pH value (from 2 to 7) and H2O2 concentration (from 0.3 wt% to 2.0 wt%), when pH was chosen as 4 and H2O2 concentration was adjusted as 2.0 wt%, the value of Sa after CMABP was the minimum, which could be 38% lower than that of MABP approximately. Nonetheless, material removal rate reached to the maximum, which could be around 168% more than that after MABP, when pH and H2O2 concentration were determined as 3.0 and 2.0 wt%, respectively. Additionally, the discrepancy between the chemical and the regular magnetic brushes were detected and analyzed comparatively both at macro and micro scales. Also, the products on the surface of 316L stainless steel, such as the weak-binding layer and the passive layer, were discovered and taken to interpret the experimental phenomena of the surface roughness and material removal rate varying with the content of chemical reagents in CMABP, thereby revealing the material removal mechanisms correspondingly and interestingly. This work is capable of providing valuable reference undoubtedly for batch precision polishing of 316L stainless steel and other significant functional materials.

To improve the tribological properties of porous polyimide (PPI), ZDDP-mixed PAO4 was impregnated in PPI (denoted as ZPPI), and the tribological properties of ZPPI under single- and double-contacts were investigated. In the single-contact of ZPPI-steel, a rough and thick tribofilm was formed on the steel ball, which could protect the steel surface but resulted in large fluctuations in the friction coefficient. In the double-contact of ZPPI-steel-steel, ZDDP formed a uniform and thinner tribofilm on steel surfaces, leading to a lower friction. ZDDP could inhibit the formation of iron oxides significantly in the double-contact, while the antioxidant effect of ZDDP in the single-contact of ZPPI-steel was not obvious. ZnS and ZnO generated from ZDDP were adsorbed in the ZPPI pores, which aggravated the blackening of the ZPPI worn surface.

知识结构图是提高课程教学质量的有效手段.结合课程选定的教材,从课程整体内容和章节内容两方面设计了机械专业"机械制造技术基础"课程的知识结构图.以工艺规程为课程教学主线,以汽车发动机的制造过程为工程实例,构造出将毛坯加工成零件并完成装配的工作内容,设计和制作出了"机械制造技术基础"课程整体教学内容的知识结构图,通过课程的整体知识结构图,将课程中的加工方法、机床、刀具、夹具、切削用量、加工质量检测、加工工艺以及装配工艺等内容,分别与教材的六个章节建立了联系.同时,针对课程的各章节教学内容,设计了课程各个章节的知识结构图,以"第四章机床夹具原理与设计"为例,说明了"机械制造技术基础"课程中章节知识结构图的设计方法.所建立的知识结构图有助于指导学生以全局角度了解"机械制造技术基础"课程的知识结构,理解教材各个章节所学知识之间相互关系和知识用途,能够以生动、有趣的图片描述课程每章应该掌握的知识内容以及知识点之间的关系,从而帮助学生以简单、轻松、有趣的方式系统学习和掌握各章的知识内容,有助于提高课程教学质量.

Binderless tungsten carbide (B-WC) has become a typical material for mold inserts due to its super mechanical and thermal properties. However, it is a typical hard-brittle material that is difficult to implement precision and high-efficiency polishing. This paper answers this challenge using a semi-rigid bonnet (SRB) tool, together with systematic theoretical and experimental investigation on its material removal. First, both polishing spots generation and uniform polishing experiments were conducted to demonstrate the polishing performance and material removal characteristic of SRB on B-WC substrates. Afterwards, the tool influence function model of SRB was established and verified experimentally, which enables the accurate prediction of surface generation during polishing. Finally, the surface and subsurface integrity of a B-WC substrate before and after SRB polishing was demonstrated. The results indicate that SRB is effective for fast polishing of B-WC with superior surface and sub-surface qualities. This discovery also paves the way for the application of SRB for the polishing of other hard materials. The developed material removal model can be a theoretical basis for the prediction of surface generation during the polishing process.

超精密机床是国家相关重大工程实现预期目标的装备保证.为实现示范线全流程的效率目标,本课题组研制了超精密磨削机床UPG80,采用液体静压技术以保证整机加工精度.本文聚焦液体静压导轨运动误差分析及节流控制技术研究.

超大口径超精密机床研制是大口径光学元件加工的必要基础,超大口径超精密机床在大行程、长工作周期的加工过程中,由于导轨发热引起的机床热形变将严重影响运动部件的直线度与光学元件的加工精度.利用ANSYS Workbench软件进行热-结构耦合仿真,对所设计的龙门式大口径磨削机床、5轴柔性气囊抛光机床进行了热形变分析,得到了导轨生热对机床整体热形变的影响规律.针对现有的磨削、抛光机床进行温度-直线度监测实验,探究了热形变对磨削机床所用液体静压导轨与抛光机床所用直线导轨运动直线度的影响规律,实际测量结果表明机床液体静压导轨的油膜生热对导轨运动直线度有较大影响.

Optical surfaces with high quality have been widely applied in high-tech industries for their excellent performances. To precision manufacture those surfaces efficiently and effectively, various machining technologies involved become extremely crucial. As one of the promising ultra-precision machining technologies, inflated or solid elastic tool polishing has attracted more attention for its own superiority. However, there is still lack of understanding on material removal mechanisms especially with the consideration of curvature effect, and it is of great importance to determine the surface quality and form control in ultra-precision polishing process. In this paper, originating from the famous macro-scale Preston equation, the curvature effect-based material removal model in polishing using a flexible ball-end tool has been developed successfully on the basis of two key sub-models, one is the generic model of effective relative velocity and the other refers to the semi-experimental contact pressure model. A series of spot polishing experiments subsequently are conducted on concave surfaces with a curvature radius range from 75 mm to 225 mm. The experimentally measured section profiles of polishing spots do match well with the predicted data, which verifies the effectiveness of the proposed material removal model. On the measured polishing spots, it is also observed that there have two nonuniform material removal phenomena, one is analyzed along the central axis and the other is discussed by two regions symmetrical about the central axis. Compared with the effective relative velocity, it is found that, the contact pressure is more sensitive to curvature effect by investigating the variation of maximum removal depth within a broader curvature radius range from 75 mm to 1000 mm. This study can provide a valuable foundation for polishing optical surfaces with deterministic removal.

A brazed chip breaker capable of controlling the chip curling and flow is proposed on the rake face of a poly-crystalline diamond (PCD) tool to obtain ideal chip shape of aluminum alloy materials. Two new position pa-rameters, the breaker-point distance and the rotation angle of chip breaker, are proposed for positioning the chip breaker on the rake face of PCD turning tool. Influences of two position parameters of the chip breaker on the chip curling and chip flow direction are studied through finite element simulations and cutting experiments. The appropriate breaker-point distance can improve the up-curling and back-flow of the chip, and control the chips flow to the tool flank face to form a C-shaped chip. After setting the appropriate breaker-point distance, increasing the rotation angle of chip breaker can promote the trend of side-curling and side-flow of the chip, which is beneficial to the formation of short helical chip. Based on the chip-breaking criterion and the geometric relationship between the chip breaker and tool rake face, the equations of two position parameters of chip breaker are established, and effective chip breaking can be achieved within the reasonable range of chip breaker position parameters calculated by the established equations. The proposed chip breaker which position pa-rameters are convenient to measure and install can be brazed on turning and drilling tools to obtain needed chip shape of aluminum alloy materials.

The development of high-reliability, high-precision large-scale CNC ultra-precision grinding machines is essential for the efficient processing and manufacturing of large-diameter optical components. In this paper, we studied the reliability and the precision-maintenance of the ultra-precision grinding machine tool experimentally. First, the subsystems with poor performance were identified based on former operating data, which turned out to be the hydrostatic spindle subsystem and the feed subsystem. Then, we set up specific experimental platforms for these two subsystems to study the thermal deformation and thermal characteristics. The temperature difference between the inflow and outflow oils of the hydrostatic systems is used as the key parameter to model the accuracy evolution. Our results may provide a method to reveal the relationship between the thermal characteristics and the operating parameters of the subsystems, and therefore compensate the thermal error of the whole ultra-precision grinding machine.

Hydrostatic guideways are widely applied in ultra-precision machine tools, and motion errors undermine the machining accuracy. Among all the influence factors, the thermal effect distributes most to motion errors. Based on the kinematic theory and the finite element method, a 3-degrees-of-freedom quasi-static kinematics model for motion errors containing the thermal effect was established. In this model, the initial state of the closed rail as a "black box" is regarded, and a self-consistent setting method for the initial state of the guide rails is proposed. Experiments were carried out to verify the thermal motion errors simulated by the finite element method and our kinematics model. The deviation of the measured thermal vertical straightness error from the theoretical value is less than 1 μm, which ensured the effectiveness of the model we developed.

在激光核聚变、大型天文望远镜等国家大光学工程及各种光机电产品的驱动下,高面形精度、高表面质量、多结构型式光学组件的需求量日益增加,因此,先进光学制造技术显得尤为重要.主要综述了近十年来光学超精密加工技术的发展情况,主要包括超精密车削、磨削和抛光技术.根据光学组件的材料特性、结构特征和加工要求等,阐述了超精密加工技术的具体研究进展,包括传统技术的迭代更新与新型技术的研制开发,并针对典型应用进行举例.最后,展望了超精密光学加工技术的发展趋势.希望能为光学制造领域后续深入研究提供参考.

Aspheric optics has been widely employed in some high-tech industries for its superiority. In order to achieve the ultra-precision machining of these aspheric surfaces, the large optical ultra-precision grinding machine becomes crucial because it determines the efficiency of the whole process. As the key functional unit in ultra-precision machine tool, the hydrostatic guideways are commonly adopted for the excellent performance. However, the motion errors of hydrostatic guideways have a direct influence on the accuracy of the machined workpiece, and some analysis approaches have been reported correspondingly. Although the existed analysis models do work, their imperfections also can be easily captured. Accordingly, a novel analysis model with less imperfection is deserved to be developed. In this paper, the kinematic theory is utilized to establish the quasi-static analysis model for motion errors in closed hydrostatic guideways. Through the large ultra-precision grinding machine designed by our research group, the consistently good agreement between the predicted results and the measured experimental data are obtained. Furthermore, it is found that the motion accuracy is more sensitive to the profile error of the guide rail bearing the external load rather than that of the other guide rail in the closed hydrostatic guideway. The presented research is supposed to be valuable to the peer designers.