Cutting force prediction is very important for optimizing machining parameters ahead of the costly physical test. Ball-end milling operation is widely used for machining sculptured surface. ...Mechanistic approach can precisely predict elemental cutting force at each cutting element and integrate them into the cutter tooth with high fidelity to predict the cutting force for ball-end milling operation. However, the intersection between the cutting tool and workpiece could be complicated due to the trochoid motion trajectory of cutting edge and constantly changing workpiece geometry, making it difficult to determine the cutter-workpiece engagement (CWE) and undeformed chip thickness (UCT). In this present research, a modified cutting force prediction model was developed with considering the true trajectory of cutting edge and in-process workpiece geometry in ball-end milling operation. First, a triangular mesh model of the in-process workpiece surface was developed, and its mesh points were continuously updated by the intersection between the vertical reference line of the selected mesh point and the motion trajectory of cutting edge. Secondly, the UCT was calculated directly using the linear distance between a selected point on the cutting edge and the intersection between the radial reference line of the selected point and the triangular mesh of the in-process workpiece surface. Meanwhile, the CWE was expressed as a step function of UCT. Thirdly, a modified mechanistic approach was established by incorporation into the developed UCT and CWE models. The cutting force of ball-end milling operation was predicted with mechanistic approaches. Finally, ball-end milling experiments of AISI P20 steel were carried out for calibrating cutting force coefficients and validating cutting force model. The relative error between the predicted and measured cutting force is less than 15%, which indicates the predicted cutting force is in good agreement with measured cutting force. The works presented in this paper are one important step for optimizing machining parameters and compensating cutting force induced form error, which could improve the surface accuracy and machining efficiency.
Machined surface topography prediction is an important and useful tool for optimizing cutting parameters. However, accurate prediction of machined surface topography in ball-end milling operation has ...been extremely challenging, due to the complexity in tool-workpiece interaction induced by the trochoidal motion of cutting edge and computing burden. In this present research, a modified iterative approach was proposed to solve the intersections between the cutting-edge sweeping surface and the discrete Z-vector model of workpiece, which were used to predict the machined surface topography in ball-end milling operation. Firstly, the accurate model of cutting-edge sweeping surface was established utilizing homogeneous coordinate transformation, in which the tool runout was considered. Secondly, the cutting-edge sweeping surface was dispersed into a series of patches in accordance with equal parameter interval, and the in-cut patch was extracted by using the minimum and maximum axial immersion angle of the cutting edge. Thirdly, the intersection between each in-cut patch and discrete Z-vector was solved using the Newton’s method, which was used to update the endpoint of the corresponding discrete Z-vector. Finally, ball-end milling experiments of AISI P20 steel were carried out to validate the proposed approach as well as investigate the effect of cutting parameters on the machined surface topography and roughness. The predicted machined surface topography and roughness were in good agreement with the measured results. Moreover, the proposed approach needs less computing time than the traditional iterative approaches at the same predicting accuracy. This research also provides guidance for optimizing cutting parameters to control surface quality in ball-end milling operation.
Novel, randomly coupled, soluble, segmented polyimide-polydimethylsiloxane (PI-PDMS) copolymers were prepared from aminoalkyl-terminated polydimethylsiloxane (At-PDMS), 4,4'-oxydianiline diamine, ...pyromellitic dianhydride, and 4,4'-diphenylmethane diisocyanate (MDI). When At-PDMS was introduced into the polyimide chain, the polyimide copolymers exhibited lower dielectric constants and better moisture resistance and mechanical properties. The reductions in the dielectric constant of the PI-PDMS copolymers could be attributed to the incorporation of polydimethylsiloxane (PDMS) into the polyimide chain and the nanopores in the film generated by carbon dioxide evolvement during the reaction. The lowest dielectric constant was 2.58 with 25 wt % PDMS and 5 wt % MDI. In addition, the water contact angles of the resultant copolymers increased from 51 to 109° when the contents of PDMS increased from 0 to 25 wt %.
The manufacturing industry consumes a considerable amount of energy every year, which poses a major challenge to resource consumption and environment problem. To overcome these difficulties, it is ...necessary to understand the machine tools’ power characteristics. The current research aims to investigate the energy consumption of the machine tool and to establish a cutting power model for ball-end milling process. First, a cutting power theoretical model for a ball-end milling cutter was established based on the infinitesimal cutting force. Secondly, a series of experiments were conducted to reveal and validate the mathematical function of spindle power and feed power. Finally, slotting milling experiments were conducted, and a cutting power empirical model was proposed by analyzing the correlation between cutting forces and cutting power. The results showed that the spindle power, feed power, and cutting power could be exactly predicted by the proposed method. Furthermore, the
Z
-axis’s feed power characteristic was revealed that the gravity made the
Z
-axis’s motor transform to the generator when
Z
-axis moved in the downward direction. For cutting power model, the theoretical model and empirical model had the same predictive accuracy, while the empirical model had a simpler form and could be easier applied. The proposed power investigation method provided technical support for the research of the machine tools’ energy consumption characteristics.
Economic restructuring changes the distribution of labor earnings and family incomes, with implications for schooling and future incomes. The potential magnitude of the schooling effect is examined ...in the first chapter for a major economic restructuring, China's state-owned enterprises (SOEs) reform. This study exploits variations in children's exposure to the policy change and in the shock intensity across sectors where these children's parents initially worked. The empirical results show that the shock enlarged the earning gap between SOEs and non-SOE public organizations (hereinafter referred to as non-SOEs) and reduced SOE children's high school and college attendance, compared with their non-SOE peers. The second chapter examines to what extent and how upper secondary education affects sex selection. To study this link, I exploit an event that disrupted the normal operation of high school education during China's Cultural Revolution. Urban high schools in China were suspended for two years from 1966 to 1968. When the high school reopened, the schooling years were shortened from 3 to 2 years and the education quality plunged. I examine the impact of school closure and degradation in education quality on sex selection with the Regression Kink Design. The empirical results show that lacking good-quality education significantly increases future sex selection. In the third chapter, I investigate whether parents' education affects their children's early childhood skill acquisition. To identify a causal effect, I exploit the introduction of the CSL as an instrument for parents' education. I find that the CSL considerably increased years of schooling and cognitive skills, and reduced incidences of teenage birth. I also find more years of mother's education lower children's age of developing their skills of walking, speaking, counting, and getting independent, while more years of father's education are associated with children's earlier age to develop skills of speaking and independence. Further investigation suggests that the effect of parents' education is more likely to work through its impact on parents' nurturing style than on other channels such as the changes of family income or fertility pattern.
A class of ultra low dielectric constant polymethylsilsesquioxane (PMSQ) films with T
8(Me
4NO)
8 polyhedral oligomeric silsesquioxanes (T
8 POSS) as double-effective porogen was studied. Through the ...Me
4NO
− groups of T
8 POSS attacking the Si–O–Si chains of PMSQ, the POSS will be connected to the PMSQ crosslink system. POSS has the cage structure, which acted as the closed pores (≤
1.5
nm). On the other hand, the Me
4NO
− groups served as the sacrificial template. When they decomposed after annealing, the open pores were then left in the films. The introduction of T
8 POSS can greatly decrease the dielectric constant of PMSQ, and effectively improve its mechanical strength owing to T
8(Me
4NO)
8 interconnected with PMSQ. These continuous and smooth films were prepared by spin-coating with thickness in the range of 60–200
nm. The dielectric constant of the films could be controlled by adjusting the proportion of porogen. These films showed good mechanical strength and ultra low dielectric constant. In particular, a POSS/PMSQ film with ultra low dielectric constant of 1.6 and modulus of 7
GPa had been prepared on silicon wafer by spin-coating.
Objective The study is to investigate the associations between visibility, major air pollutants and daily counts of hospital admission in Shanghai, China. Methods Daily data on hospital admission, ...visibility, and air pollution during 2005‐2008 were obtained from the Shanghai Insurance Bureau （SHIB）, Shanghai Meteorological Bureau, and Shanghai Environmental Monitoring Center, respectively. The generalized additive model （GAM） with penalized splines was used to examine the associations between daily visibility and hospital admission. Results Among various pollutants, PM 2.5 showed strongest correlation with visibility. Decreased visibility was significantly associated with increased risk of hospital admission in Shanghai. An inter‐quartile range decrease in the 2‐day （L01） moving average of visibility corresponded to 3.66% （95%CI： 1.02%, 6.31%）, 4.06% （95%CI： 0.84%, 7.27%）, and 4.32% （95%CI： 1.67%, 6.97%） increase of total, cardiovascular, and respiratory hospitalizations, respectively. Conclusion Our analyses provide the first piece of evidence in China, demonstrating that decreased visibility has an effect on hospital admission, and this finding strengthens the rationale for further limiting air pollution levels in Shanghai.
A new idea for reuse of the cathode materials of lithium-ion batteries (LIBs) is investigated to develop an environmentally friendly process for recycling spent batteries. LiCoO₂ is re-synthesized ...from spent LIBs by leaching and a sol-gel method calcined at high temperature. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are employed to study the reactions occurring calcination that are responsible for the weight losses. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to determine the structures of the LiCoO₂ powders. It was found that a pure phase of LiCoO₂ can be obtained by the re-synthesis process. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are used to evaluate the electrochemical properties of the LiCoO₂ powders. The discharge capacity of re-synthesized LiCoO₂ is 137 mAh g⁻¹ at the 0.1 C rate, and the capacity retention of the re-synthesized LiCoO₂ is 97.98% after 20 cycles at the 0.1 C rate, and 88.14% after 40 cycles. The results indicate that the re-synthesized LiCoO₂ displays good charge/discharge performance and cycling behavior.
Lithium–sulfur batteries have been regarded as promising candidates for energy storage because of their high energy density and low cost. It is a main challenge to develop long-term cycling stability ...battery. Here, a catalytic strategy is presented to accelerate reversible transformation of sulfur and its discharge products in lithium–sulfur batteries. This is achieved with single-atomic iron active sites in porous nitrogen-doped carbon, prepared by polymerizing and carbonizing diphenylamine in the presence of iron phthalocyanine and a hard template. The Fe-PNC/S composite electrode exhibited a high discharge capacity (427 mAh g–1) at a 0.1C rate after 300 cycles with the Columbic efficiency of above 95.6%. Besides, the electrode delivers much higher capacity of 557.4 mAh g–1 at 0.5C over 300 cycles. Importantly, the Fe-PCN/S has a smaller phase nucleation overpotential of polysulfides than nitrogen-doped carbon alone for the formation of nanoscale of Li2S as revealed by ex situ SEM, which enhance lithium-ion diffusion in Li2S, and therefore a high rate performance and remarkable cycle life of Li-sulfur batteries were achieved. Our strategy paves a new way for polysulfide conversion with atomic iron catalysis to exploit high-performance lithium–sulfur batteries.
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