基于岭回归的数控机床温度布点优化及其热误差建模

提出一种基于岭回归分析的数控机床温度布点优化方法.数控机床热误差建模一般采用多元线性回归方法,在多元线性回归模型中,隐含着要求解释变量之间无强相关性的假定.然而在实际的建模中,各自变量与因变量之间的相互关系并不与简单相关系数所反映的情况完全吻合.通过岭迹对温度变量进行优化选择,实现了温度测点优化布置,并选用适当的岭参数k建立了数控机床热误差的多元线性回归优化模型,提高了热误差模型的精确性和鲁棒性.     

Thermo-physical and thermal cycling properties of plasma-sprayed BaLa2Ti3O10 coating as potential thermal barrier materials

Increased turbine inlet temperature in advanced turbines has promoted the development of thermal barrier coating (TBC) materials with high-temperature capability. In this paper, BaLa₂Ti₃O₁₀ (BLT) was produced by solid-state reaction of BaCO₃, TiO₂ and La₂O₃ at 1500 °C for 48 h. BLT showed phase stability between room temperature and 1400 °C. BLT revealed a linearly increasing thermal expansion coefficient with increasing temperature up to 1200 °C and the coefficients of thermal expansion (CTEs) are in the range of 1 × 10^− 5–12.5 × 10^− 6 K^− 1, which are comparable to those of 7YSZ. BLT coatings with stoichiometric composition were produced by atmospheric plasma spraying. The coating contained segmentation cracks and had a porosity of around 13%. The microhardness for the BLT coating is 3.9–4.5 GPa. The thermo-physical properties of the sprayed coating were investigated. The thermal conductivity at 1200 °C is about 0.7 W/mK, exhibiting a very promising potential in improving the thermal insulation property of TBC. Thermal cycling result showed that the BLT TBC had a lifetime of more than 1100 cycles of about 200 h at 1100 °C. The failure of the coating occurred by cracking at the thermally grown oxide (TGO) layer due to severe oxidation of bond coat. Based on the above merits, BLT could be considered as a promising material for TBC applications.     

Thermal and mechanical properties of perovskite-type barium hafnate

Polycrystalline samples of the barium perovskite-type oxide, BaHfO₃ were prepared by solid-state reactions from HfO₂ and BaCO₃ powders. The thermal expansion coefficient, heat capacity, thermal diffusivity, thermal conductivity, elastic modulus, Debye temperature, and micro-Vickers hardness were measured. The crystal structure of BaHfO₃ is of the cubic perovskite type with the lattice parameter 0.4171 nm at room temperature. The sample bulk density is 91% of the theoretical density. The average linear thermal expansion coefficient is 6.93 × 10⁻⁶ K⁻¹ in the temperature range between 300 and 1500 K. The Young's modulus equals 194 GPa. The thermal conductivity at room temperature is 10.4 Wm⁻¹K⁻¹.     

基于模拟退火遗传算法优化BP网络的数控机床温度布点优化及热误差建模

在热误差建模中,温度测点的优化选择至关重要。提出了运用相关性方法,分析测点温度与主轴热漂移之间的关系,找到相关性较高的测点位置,实现温度布点的优化选择。在此基础上采用模拟退火遗传算法（ GSA）优化BP神经网络的方法建立热误差模型,并通过实验验证。结果表明：优化的热误差模型能够跳出局部最优而达到全局最优解,得到的误差模型拟合值更加接近实测误差值;基于GSA优化的BP网络模型较传统的神经网络模型有较高的精度及更强鲁棒性。     

Thermal Expansion and Phase Stability Investigations on Cs-Substituted Nanocrystalline Calcium Hydroxyapatites

The high-temperature phase stability of Ca_10−x Cs _x (PO₄)₆(OH)₂, (x = 0–3) compositions synthesized by various wet chemical methods was investigated. The thermal expansion property of Ca₁₀(PO₄)₆(OH)₂ (abbreviated as CaHAp) and Cs-substituted CaHAp was measured by high-temperature XRD and dilatometry. The average crystallite size of the powders synthesized by wet chemical methods was found to be 10–50 nm range as shown by XRD and TEM. Up to 30 mol% Cs loading was observed to show only the apatite phase by XRD when the apatite powder was nanocrystalline in nature. However, high-temperature stability of the Cs-substituted system is limited to ≤5 mol%. Cs₃(PO₄) is observed to be separated out on heating the material above 773 K for compositions substituted with more than 5 mol% of Cs in the Ca-sublattice. The coefficient of thermal expansion measured by HTXRD is α_a = 12.42 × 10⁻⁶ K⁻¹, α_c = 14.98 × 10⁻⁶ K⁻¹; and α_a = 12.62 × 10⁻⁶ K⁻¹, α_c = 12.57 × 10⁻⁶ K⁻¹ for CaHAp and Ca_9.78Cs_0.2(PO₄)₆(OH)_1.96, respectively, in the temperature range of 298-1083 K. Bulk thermal expansion measurements are seen to be in agreement with the lattice expansion results.     

Variation of the lattice parameter and thermal expansion coefficient of (U,Dy)O2 as a function of DyO1.5 content

Thermal expansions of (U,Dy)O₂ solid solutions were investigated between room temperature and 1673 K by using a thermo-mechanical analyzer. The lattice parameter of (U,Dy)O₂ pellets is lower than that of UO₂ and it decreases as Dy content increases. The linear thermal expansion and average thermal expansion coefficients of (U,Dy)O₂ are higher than that of UO₂. For the temperature range from room temperature to 1673 K, the average thermal expansion coefficient values for UO₂ and (U_0.8Dy_0.2)O₂ are 10.97 × 10⁻⁶ and 11.37 × 10⁻⁶ K⁻¹, respectively.     

An extremely low thermal conduction ceramic: RE9.33(SiO4)6O2 silicate oxyapatite

Complex rare-earth silicate oxyapatite RE_9.33(SiO₄)₆O₂ (RE = La, Nd, Sm, Gd, Dy) ceramics have been synthesized and their thermal conduction characteristics investigated. When evaluated using a steady-state laser heat-flux technique under conditions ranging from room temperature to 1000 °C the materials demonstrated very low thermal conductivities (0.96–1.49 W m^–1 K^–1), especially Gd_9.33(SiO₄)₆O₂, which shows a value of 1.10–1.14 W m^–1 K^–1 in the measured temperature range. Phonon mean free path and Raman spectra were used to investigate the thermal transfer mechanism. The source of low thermal conductivity was determined to be the strong intrinsic scattering in the crystal cell, which is due to the phonon mean free path being on the inter-atomic level. Furthermore, a connection between the full width at half maximum Raman spectra and the thermal conductivity of RE_9.33(SiO₄)₆O₂ ceramics at room temperature was established. The insensitivity of the thermal conduction properties to temperature for RE_9.33(SiO₄)₆O₂ ceramics have allowed it to show great potential in high temperature thermal insulation applications.     

Crystal structure of single phase and low sintering temperature of α-cordierite synthesized from talc and kaolin

Cordierite body with the formulation of 2.8MgO·1.5Al₂O₃·5SiO₂ was prepared from talc and kaolin as the basic raw materials. Following glass crystallization technique the glass powder was successfully heat treated at 900 °C for 2 h to form a single-phase α-cordierite. The crystal structure of α-cordierite was analysed using X-ray diffraction technique and the Rietveld structural refinement method. Differential thermal analysis (DTA), Fourier-transform infrared (FTIR), field emission scanning electron microscopy (FESEM), coefficient of thermal expansion (CTE) and dielectric properties were also performed. Results show that the materials crystallized as a hexagonal structure with space group of P6/mcc and the room temperature lattice parameters are a = 9.743742 (Å) and c = 9.389365 (Å). FTIR analysis on the glass revealed that only silicate species is the only unit that exists in the glass network. DTA also confirmed that α-cordierite completely formed after 13.5 min of isothermal heating at 900 °C. Coefficient of thermal expansion of synthesized α-cordierite is 2.5 × 10⁻⁶ °C⁻¹. The dielectric constant is between 5.0 and 5.5 for 1 MHz and 1.8 GHz, respectively, and the dielectric loss is in the range 10⁻². FESEM micrographs revealed that the material is fully densified.     

基于SSA-BP的电主轴热误差优化建模

为解决某加工中心电主轴的热误差补偿问题，建立预测精度高、鲁棒性强的热误差补偿模型。搭建实验台，利用美国雄狮回转误差分析仪采集电主轴的温度场和热误差数据。介绍麻雀搜索算法(SSA)原理、具体优化流程。采用SSA优化BP神经网络的权值和阈值，建立SSA-BP神经网络预测模型。与之前建立的BP神经网络预测模型相比，优化后预测效果更优，为电主轴热误差建模提供新的思路。     

High-temperature stability, structure and thermoelectric properties of phases

Polycrystalline perovskite-type CaMn_1-xNb_xO₃ phases (with x=0.02,0.05,0.08 and 0.10) were investigated with regard to their structure, microstructure and thermal stability as a function of temperature. The studied phases revealed a complex microstructure at room temperature with 90° twinned domains. At high temperatures, the manganate phases underwent a structural transition from orthorhombic to cubic symmetry, as confirmed by in situ high-temperature X-ray powder diffraction and electron diffraction data. Thermogravimetric heating/cooling studies showed a reversible thermal reduction/reoxidation process that occurred above a defined transition temperature. A possible mechanism relating the high-temperature structural transition and the thermal reduction process of slightly substituted CaMnO₃ phases was proposed. The thermal reduction process resulted in a change in the Mn³⁺/Mn⁴⁺ concentrations in the Mn sublattice, and therefore in a modification of the transport properties. A comprehensive study examined the impact of both phenomena on the electrical and thermal transport properties.