激光快速成型致密金属零件的研究

采用激光快速成型技术制备出316L不锈钢薄壁矩形管和663锡青铜扭曲薄壁方管.所成型金属零件的组织均匀、致密,没有缺陷.沿金属薄壁零件高度方向的化学成分分析表明,零件中的化学成分分布均匀,且与金属粉末的化学成分相同,未发生成分偏析.同时,激光快速成型的金属薄壁零件的力学性能与常规加工方法制造出的零件相当.使用表明激光快速成型的金属零件可以满足直接使用要求.     

国外动态

脉冲磁力金属成型在零件成型、焊接和装配方面,金属磁力成型方法应用广泛。复杂、困难、费时的加工过程可以简化,普通方法所不能加工的     

浅析金属粉末选择性激光烧结快速成型技术

介绍了选择性激光烧结技术的工作原理。简述了选择性激光烧结的三种典型金属粉末成型工艺。指出了选择性激光烧结技术成型金属零件所存在的一些问题和选择性烧结技术的发展前景。     

金属喷射成型的最新发展态势

传统粉末冶金工艺，难以制造形状复杂的零件。受塑料喷射成型的启发，在20世纪80年代后期，金属粉末界也开始探索喷射成型技术。经过10多年的探索、研发，金属喷射成型技术取得了很大的进展。从国外的统计资料来看，欧洲、亚洲、美洲金属喷射成型生产都已初具规模，详见表。     

浅析金属粉末选择性激光烧结快速成型技术

介绍了选择性激光烧结技术的工作原理,简述了选择性激光烧结的三种典型金属粉末成型工艺,讨论了选择性激光烧结技术成型金属零件所存在的一些问题。最后总结了选择性烧结技术的发展前景。     

金属零件加工中对工艺设计的应用研究

睡着经济的发展和社会的进步,各种零件的加工工艺越来越完善。特别是随着不同材料和技术的发展,机械加工的工艺水平不断提升。金属零件是日常十分广泛的一种设备,以其强度高、经济实用的特点运用广泛。随着机械加工工艺的不断进步,金属零件的加工也越来越完善,特别是各种工艺的运用。本文主要分析了金属零件加工中各种工艺的运用情况,以此来明确金属零件加工的发展现状以及趋势。     

金属增材制造技术在武器装备的应用和发展

通过对金属光固化3D打印的研究结果和工艺流程进行总结,划分了四种主要的实现途径,即固化烧结法、固化镀膜法、混合固化法和固化模具法,其中固化烧结法是制备金属零件的主要方法,固化镀膜法常用于制备精密电磁设备元件,而混合固化法通常直接固化浆料而无需经过烧结使零件一步成型;归纳了金属光固化3D打印所使用的光敏树脂成分和所制备零件的性能;指出了该技术目前发展还存在浆料中金属与聚合物性质差异、工艺参数研究不足、光敏树脂配方较少等亟待解决的关键科学问题;从研究工艺参数对零件性能的影响、开发新型光敏树脂配方和发明更适用于金属光固化3D打印的设备方面展望了其未来的发展方向.     

日本开发汽车用新型高强度钢板

日本三菱汽车公司为了降低汽车燃料费，与新日铁、住友金属及神户３家钢铁公司共同开发了汽车底盘零件用新型高强度钢板。新钢板为５９０Ｎ（６０ｋｇ级）残留奥氏体高强度钢板。这种钢板具有传统带钢所具有的优良的压力成型性能和高的焊接性以外，还具有高的延伸率，并能适应局部大弯曲、大延伸要求的凸缘成型的要求。这种材料已用于制作新型车种底盘上约８０种零件。所制作的零件与用传统钢板制作的零件相比重量减轻约１２％，每台车重减轻１４ｋｇ。难成型的底盘零件采用高强度钢尚属世界首列。日本开发汽车用新型高强度钢板     

激光快速成型TC4钛合金的力学性能

金属零件的激光快速成型是结合CAD／CAM、高功率激光熔覆和快速原型制造的先进技术。研究了用激光快速成型技术制造TC4钛合金的力学性能，分析了低温退火和热等静压处理对力学性能的影响，并且测量了成型后试件的含氧量，观察了拉伸试件的断口形貌。研究结果表明激光快速成型制造的TC4钛合金的力学性能高于铸造组织的力学性能，达到了锻造组织的力学性能。     

注射成型TiAl金属间化合物

与传统的金属材料相比 ,Ti Al金属间化合物密度低 ,熔点高 ,有较高的高温强度 ,有望用作新一代的结构材料。但 Ti Al金属间化合物一般较脆 ,加工性极差 ,在加工成品率和尺寸精度上也有很大问题。因此要实用还有待于新的低成本大批量生产加工方法的开发。金属粉末注射成型 (MIM)是生产形状复杂零件的高精度制造方法 ,可大量生产高密度高强度的近净形烧结体。为此 ,用 MIM工艺系统地研究了注射成型 Ti Al的基础材料性能及不同组分材料的性能。使用的是燃烧合成法制造的 Ti Al合金粉末 ,几种不同组分的性能如表 1所示。表 1　 Ti Al粉末…     

Metabolism of [ring-U-14C] agaritine by precision-cut rat, mouse and human liver and lung slices

Agaritine [(beta-N-[gamma-L(+)glutamyl]-4-hydroxymethylphenylhydrazine] is present in the common cultivated mushroom Agaricus bisporus and several agaritine derivatives have been shown to produce tumours in experimental animals. In this investigation the metabolism of [ring-U-14C]agaritine has been studied in precision-cut rat, mouse and human liver slices and in precision-cut rat and mouse lung slices. To confirm the functional viability of the tissue slice preparations, the metabolism of 7-ethoxycoumarin was also studied. Liver and lung slices from all species metabolized 50 microM 7-ethoxycoumarin to 7-hydroxycoumarin, which was conjugated with D-glucuronic acid and sulfate. Incubation of rat, mouse and human liver slices, and rat and mouse lung slices with 25 microM [14C]agaritine resulted in a time-dependent formation of metabolite(s), which bound covalently to tissue slice proteins. Agaritine metabolite covalent binding was greater in mouse liver than in rat and human liver slices and was greater in mouse lung than in rat lung slices. No correlation was observed between agaritine metabolite covalent binding and tissue slice gamma-glutamyltransferase activity. Additional studies with mouse liver slices showed that [14C]agaritine was also metabolized to a number of unknown polar metabolites. These results demonstrate that agaritine can be metabolized by enzymes present in mammalian liver and lung.     

Myenteric neurons with different projections have different dendritic tree patterns: a morphometric study in the pig ileum

Species differences in the biotransformation of the antiemetic tropisetron, a potent 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist, were evident in liver slice incubates of human, rat and dog, and reflected the species differences observed in vivo with respect to the relative importance of individual pathways. The dominant biotransformation pathway of tropisetron (10 microM) in human liver slices was formation of 6-hydroxy-tropisetron, whereas in rat liver slices it was 5-hydroxy-tropisetron, and in dog liver slices N-oxide formation. Initial rates of tropisetron metabolite formation in the liver slices (8 mm in diameter, 200 +/- 25 microns thickness) of human (83 +/- 61 pmol/h/mg slice protein), rat (413 +/- 98 pmol/h/mg slice protein) and dog (426 +/- 38 pmol/h/mg slice protein) would predict less of a first-pass effect in humans compared to the rat or the dog. For human and rat, the prediction matched well with the species ranking of tropisetron bioavailability; however, for dog the in vitro data overestimated the apparent first-pass effect. The jejunum is not expected to contribute to the first-pass effect in humans, since human jejunum microsomes did not metabolize tropisetron. The major organ of excretion for tropisetron and its metabolites is the kidney, but the contribution of the kidney to the overall metabolism of tropisetron would be small. Species independent N-oxide formation (2-12 pmol/h/mg slice protein) was the major pathway in human, rat and dog kidney slices, and was comparable to N-oxide formation in the rat and human liver slices but was 1/10 the rate in dog liver slices. This study has demonstrated that the liver is the primary site of tropisetron biotransformation, and the usefulness of organ slices to characterize cross species differences in the dominant biotransformation pathways.     

The biotransformation of the ergot derivative CQA 206-291 in human, dog, and rat liver slice cultures and prediction of in vivo plasma clearance

Liver slice cultures from humans, dogs, and rats were used to investigate the biotransformation of the dopaminergic ergot agonist CQA 206-291 and to predict pharmacokinetic values for hepatic intrinsic clearance and plasma clearance. CQA 206-291 was extensively metabolized in the liver slice cultures and in vivo. The HPLC metabolite patterns from the liver slice cultures were similar for all three species, indicating the occurrence of the same metabolic pathways for CQA 206-291 biotransformation. The rate of formation of CQ 32-084, a pharmacologically active N-deethylated metabolite, exceeded that of metabolite d, a primary metabolite, by 1.4 fold in human liver slices, and by 1.7 fold in rat liver slices. In dog liver slice cultures, metabolite d formation exceeded CQ 32-084 formation by 1.3 fold and was formed at a statistically significantly greater rate (3 fold) than in either human or rat liver slices. The metabolism of ergots like CQA 206-291 by human fetal liver was also demonstrated in this study. However, the prominent metabolite from fetal and adult human liver microsomes was metabolite d with minor amounts of CQ 32-089 being formed. A major route of excretion for the metabolites of CQA 206-291 is the kidney, yet the kidney does not contribute to the metabolism of CQA 206-291. Kidney slices derived from humans, rats, and dogs did not metabolize CQA 206-291 within 24 hr. CQA 206-291 intrinsic clearance was derived from the half-life of parent drug disappearance in the liver slice and hepatocyte cultures, and from the ratio of Vmax/Km of human and rat liver microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)     

A light and electron microscopic study of cytoplasmic phospholipase A2 and cyclooxygenase-2 in the hippocampus after kainate lesions

Tamoxifen, the major adjuvant drug treatment for estrogen-dependent breast cancer, has been shown previously to affect both estrogen-dependent and calcium/calmodulin-dependent pathways. In the current study, we developed an in vitro slice system to study the effects of tamoxifen on ATP levels in hypothalamic (HTH) and preoptic areas (POA) of the rat brain. Baseline data showed that, following a 2-h incubation, HTH and POA slices had comparable ATP levels to hippocampal slices, a system used extensively by researchers examining the metabolic responsiveness of the hippocampal region (HPC) of the brain. HTH-POA slice ATP levels remained steady for 2, 4 and 6 h, but fell to 11% of initial levels by 12 h. Neurons from HTH-POA slices incubated for 4 h appeared healthy and demonstrated robust protein synthesis as measured autoradiographically by incorporation of [3H]leucine. We explored the effects of tamoxifen (TAM), fluphenazine (FLU) and estradiol (E2) on ATP levels in HTH and POA slices. The effects of TAM were complex: a 4-h incubation with 10-6 M TAM led to decreased ATP levels in HTH (but not POA), and a 4-h incubation with 10-8 M led to increased ATP levels in POA (but not HTH); a 15-min exposure to 10-6 M TAM decreased ATP levels in POA (but not HTH) slices, while the exposure of slices to the lower concentration of TAM was without effect in either area. As with higher concentrations of TAM, 4-h incubation with 10-6 M FLU decreased ATP levels in HTH (but not POA), while incubation with E2 did not affect slice ATP levels. These data are consistent with the hypothesis that both TAM and FLU alter ATP levels in HTH slices via calmodulin- or calcium-mediated processes.     

Waldeyer''s ring lymphomas: an epidemiological study of 55 cases

In vitro accumulation of p-aminohippurate (PAH) was investigated in "intact" human renal cortical slices of normal kidney tissue and in tissue slices of renal cell carcinoma (RCC). The technique used was established in preliminary experiments on rat kidney tissue slices. In principle, the accumulation capacity is comparable in renal tissue slices of both species (slice to medium accumulation ratios between 4 and 8). In man sex differences in accumulation capacity do not exist. But, as shown in detail for rats, accumulation capacity drops with age. Tissue slices of RCC are unable to accumulate PAH actively; slice to medium ratio reaches about 1 and indicates passive PAH uptake only. Surprisingly, in tumors of stage pT1 PAH uptake is lowest. perhaps as a sign of PAH transport out of the cells. There is no difference between peripheral and central parts of RCC. Age and sex are without influence on PAH uptake in RCC tissue slices. Interestingly, the accumulation capacity of "intact" tissue of kidneys infested with RCC also depends on the severity of the tumor (stage, diameter), but not on grading and formation of metastases.     

3,3'-Diindolylmethane induces CYP1A2 in cultured precision-cut human liver slices

1. The effect of 3,3'-diindolylmethane (DIM), an indole derivative derived from cruciferous vegetables, on cytochrome P450 (CYP) isoforms in the CYP1A and CYP3A subfamilies has been studied in 72-h cultured human liver slices. 2. In cultured human liver slices 50 microM DIM induced 7-ethoxyresorufin O-deethylase and to a lesser extent 7-methoxyresorufin O-demethylase activities. 3. Western immunoblotting of liver slice microsomes was performed with antibodies to rat CYP1A2 and human CYP3A4. Compared with control liver slice microsomes (dimethyl sulphoxide-only treated), DIM induced levels of CYP1A2 but had little effect on levels of CYP3A4. The treatment of human liver slices with 2 microg/ml of the polycholorinated biphenyl mixture Aroclor 1254 also resulted in an induction of levels of CYP1A2, but had no effect on CYP3A4. 4. These results demonstrate that DIM induces CYP1A isoforms in cultured human liver slices. Some variability in the magnitude of induction of enzyme activities by DIM was observed in four human liver samples examined. For 7-ethoxyresorufin O-deethylase, the magnitude of induction by 50 microM DIM ranged from 2.3- to 19.3-fold. 5. These results demonstrate that cultured human liver slices can be used to evaluate the effect of chemicals derived from cruciferous and other vegetables on CYP isoforms.     

Olfactory epithelial organotypic slice cultures: a useful tool for investigating olfactory neural development

An in vitro slice culture was established for investigating olfactory neural development. The olfactory epithelium was dissected from embryonic day 13 rats; 400 microns slices were cultured for 5 days in serum-free medium on Millicell-CM membranes coated with different substrates. The slices were grown in the absence of their appropriate target, the olfactory bulb, or CNS derived glia. The cultures mimic many features of in vivo development. Cells in the olfactory epithelium slices differentiate into neurons that express olfactory marker protein (OMP). OMP-positive cells have the characteristic morphology of olfactory receptor neurons: a short dendrite and a single thin axon. The slices support robust axon outgrowth. In single-label experiments, many axons expressed neural specific tubulin, growth-associated protein 43 and OMP. Axons appeared to grow equally well on membranes coated with type I rat tail collagen, laminin or fibronectin. The cultures exhibit organotypic polarity with an apical side rich in olfactory neurons and a basal side supporting axon outgrowth. Numerous cells migrate out of the slices, of which a small minority was identified as neurons based on the expression of neural specific tubulin and HuD, a nuclear antigen, expressed exclusively in differentiated neurons. Most of the migrating cells, however, were positive for glial fibrillary acidic protein and S-100, indicating that they are differentiated glia. A subpopulation of these glial cells also expressed low-affinity nerve growth factor receptors, indicating that they are olfactory Schwann cells. Both migrating neurons and glia were frequently associated with axons growing out of the slice. In some cases, axons extended in advance of migrating cells. This suggests that olfactory receptor neurons in organotypic cultures require neither a pre-established glial/neuronal cellular terrain nor any target tissue for successful axon outgrowth. Organotypic olfactory epithelial slice cultures may be useful for investigating cellular and molecular mechanisms that regulate early olfactory development and function.     

Age-related thickening of basement membrane in stria vascularis capillaries

Several studies have examined the activity of neurons in hypothalamic tissue slices. The present experiments studied relationships between neuronal activity (firing rate and thermosensitivity) and tissue survival as a function of time and slice thickness. Rat hypothalamic tissue slices were sectioned at different thicknesses (350, 450, and 600 microm) and maintained in an oxygenated interface chamber which was perfused with artificial cerebrospinal fluid (ACSF). Electron and light microscopy were used to examine tissue morphology at different depths from the slice surfaces, and extracellular recordings were used to measure each cell's spontaneous activity and response to changes in temperature. Tissue damage was most evident at tissue layers nearest the gas-exposed surface. At 9 h in the chamber, 350 microm thick slices showed subtle changes in morphology with little difference between the gas-exposed and ACSF-exposed surfaces. In the 450 and 600 microm thick slices, tissue degeneration became more evident with increased damage at the gas-exposed surface. This damage extended fully into the tissue of the 600 microm section. There were no differences in firing rate or thermosensitivity between 350 and 450 microm slices; but in 600 microm slices, there were fewer spontaneously active neurons, although these neurons had a higher mean thermosensitivity. Based on the incidence of spontaneous activity and morphological integrity, the results suggest that electrophysiological experiments using 350 microm slices are preferable to experiments using thicker slices.     

Visualization and Analysis of Microstructure in Three-Dimensional Discrete Numerical Models

A computer program has been developed to allow for the virtual slicing of irregularly spaced and irregularly shaped three-dimensional image data. The program was used to virtually slice three-dimensional particle assemblies from discrete element method (DEM) simulations, allowing, for the first time, direct comparison to two-dimensional slices extracted from solidified physical specimens. Based on slices obtained from the numerical specimens, it is possible to compare quantitatively numerical microstructure directly to its physical analog, which should lead to greatly improved calibrations of granular mechanics models, and could facilitate the calibration of models across all scales of interest rather than solely at specimen boundaries. Improved confidence in the ability of the DEM to realistically simulate the microstructure of granular assemblies (through improved multiscale calibration) should result in increased confidence in microstructural parameters measurable in numerical simulations but inaccessible in the laboratory. Algorithm development within the framework of the open-source Visualization Toolkit is described and performance of the algorithm is quantified for two platforms. Results from virtual slices of a test assembly with regular particle packing are verified against known analytical solutions. A slice of a more complex assembly comprised of nearly 40,000 spheres is quantified statistically and compared to an analogous slice from a physical specimen of uniform sand.     

Three-window transformation cross-talk correction for simultaneous dual-isotope imaging

A newly developed cross-talk correction method for simultaneous dual-isotope SPECT imaging was tested in a canine model. The method is based on the assumption that the transformations, which modify the primary energy window images into the scatter images as viewed in the other energy windows, are known. These transformations were found by measuring the point spread functions (PSFs) in two different energy windows for both isotopes in water. The dual-isotope correction method is described by two convolution equations which were applied in frequency space. The equations take into account the different spatial distributions of the primary and scatter cross-talk photons. The new enhancement of the method was in applying restoration filters to the resulting corrected images. Three separate studies were acquired in our dog study: two single-isotope and one dual-isotope study. The single isotope images were used as references. The contrast between the left ventricle cavity (LVC) and the myocardium was used in transaxial and short-axis slices as a parameter to evaluate results of dual-isotope correction method with restoration. The change in contrast in the dual-isotope corrected images in both energy windows, i.e., Tc-99m primary window (140 keV) and Tl-201 primary window (70 keV), was significant. The only exception was for the short-axis Tc-99m window images. The corrected 140 keV dual-isotope short-axis slice had the contrast of 0.60 vs 0.58, which was the value in the noncorrected dual-isotope short-axis slice. For dual-isotope 140 keV transaxial slice, the contrast changed from 0.72 to 0.82 after correction. In comparison, for single-isotope Tc-99m 140 keV transaxial slice, contrast changed from 0.62 to 0.84 after restoration correction. There was less change in contrast in the short-axis Tc-99m 140 keV slice, i.e., from 0.56 to 0.61. In the Tl-201 primary window for the transaxial slices the improvement of contrast was from 0.38 to 0.64, and for short-axis slices from 0.22 to 0.32 after correction. In the same 70 keV energy window for single-isotope Tl-201 images, contrast improved from 0.61 to 0.69 and from 0.35 to 0.38 for transaxial and short-axis slice, respectively, after applying restoration correction. In conclusion, the presented dual-isotope correction method with restoration improves the quality of the simultaneous rest Tl-201/stress Tc-99m sestamibi SPECT imaging.