低压烧结温度对一步法制备超细晶WC-Co基硬质合金组织及性能的影响

采用等离子球磨技术制得W-C-10Co-0.9VC-0.3Cr_3C_2纳米复合粉体,并利用单向模压成型法将其压制成生坯,再经低压烧结一步法制备成硬质合金。研究表明,等离子球磨3h所获得的复合粉体呈片层状形貌,并且成分分布均匀。在1 380℃及1 400℃烧结时,由于等离子球磨的特殊作用,VC、Cr_3C_2对WC晶粒长大抑制作用突显。1 380℃烧结制备的硬质合金,致密度为99.2%,WC平均晶粒尺寸为250nm,硬度和横向断裂强度分别为92.3HRA和2 443 MPa,具有最佳的WC晶粒尺寸与致密度配合,以及最佳的综合力学性能。     

(Mg2B2O5w+ND)/ZK60镁基复合材料的摩擦磨损性能研究

在湿球磨条件下以600 r/min高能球磨混粉,并将球磨后的粉末经过热压烧结-热挤压成型制备(Mg2B2O5w+ND)/ZK60镁基复合材料。研究了(Mg2B2O5w+ND)/ZK60镁基复合材料在不同载荷和转速下的干摩擦磨损性能。结果表明:干摩擦条件下,材料的摩擦系数随着滑动距离的增加会经历跑和阶段和稳定阶段;材料的质量磨损率随着转速的增大而降低,随着载荷的增大而增大,且基体镁合金的质量磨损率始终低于复合材料。随着摩擦载荷和转速的增加,材料的摩擦系数减小,然后逐渐趋于平稳。混杂增强的镁基复合材料相比基体合金具有更低的摩擦系数。     

Effect of High‐Energy Ball Milling on Mechanical Properties of the Mg–Nb Composites Fabricated through Powder Metallurgy Process

New biocompatible and biodegradable Mg–Nb composites used as bone implant materials are fabricated through powder metallurgy process. Mg–Nb mixture powders are prepared through mechanical milling and manual mixing. Then, the Mg–Nb composites are fabricated through cold press and sintering processes. The effect of mechanical milling and Nb particles as reinforcements on the microstructures and mechanical properties of Mg–Nb composites are investigated. The mechanical milling process is found to be effective in reducing the size of Mg and Nb particles, distributing the Nb particles uniformly in the Mg matrix and obtaining Mg–Nb composite particles. The Mg–Nb composite particles can be bound together firmly during the sintering process, result in Mg–Nb composite structures with no intermetallic formation, lower porosity, and higher mechanical properties compared to composites prepared through manual mixing. Interestingly, the mechanical properties of manually mixed Mg–Nb composites appear to be even lower than that of pure Mg.

     

难加工材料铣削力预测研究进展

为了降低难加工材料铣削过程中的加工变形,改善表面加工质量,对加工过程中的铣削力进行预测是必须的。从难加工材料特性及实验现象出发,分别针对端铣刀和球头铣刀将现有铣削力预测方法及其进展进行解析。从现有的研究分析,对于端铣刀铣削力的研究主要集中于切屑形成、最小能量与斜角切削机理,而对于球头铣刀,主要研究微元切削力、刀具接触区域与切屑流动方向对预测结果的影响。从研究趋势上看,对端铣刀和球头铣刀铣削力预测模型理论的研究均有进展,但对铣削过程中状态参数的研究逐渐成为了近年来的研究热点。     

Effect of particle size on quality of crab meatballs using enzymatically deproteinized crab by-products

The production of crab meatballs generates large amount of crab shell waste, it is therefore necessary to develop a green, economical and environmentally friendly process to vaporize the waste. This study was aimed at investigating the applicability of microwave heating combined with ultrasonic field-assisted alkaline protease (MUSED) (50 ℃, pH = 9.0, 14025.67 U/g, 4.21 h and liquid/material = 14.41:1) for pretreatment of ball-milled crab shells. The ball milling efficiency of the crab shell powder pretreated by MUSED was observed to increase by 50 % compared to the control group, with the final average particle size of D₄ = 4.88 ± 0.20 um. High calcium solubility and low energy consumption of the ball-milled powder increased dietary calcium bioavailability and reduced the potential for high calorie intake. The addition of 6 % (w/w) crab shell powder treated by MUSED improved the texture of the crab meatballs (CM-D₄) and gave the product enhanced crab flavor relative to the control group. Moreover, the lower cooking loss of CM-D₄ resulted in significant retention of nutrients (p < 0.05). The crab shell powder treated by MUSED method was more efficient in ball milling, which improved the quality of crab meatballs while relieving environmental pressure.     

园弧槽无相同直径刀具时的近似铣削

提出了一种在铣削开式园弧槽无相同直径铣刀时,用小直径铣刀代替的近似铣削方法,并给出了有关公式及误差估计式。     

受模糊干扰的耦合型颤振的模糊稳定分析

在耦合型颤振的分析中考虑了模糊不确定性因素的影响,利用模糊数学分析方法详细探讨了受模糊干扰的耦合型颤振的模糊稳定性分析问题,给出了关于耦合型颤振的模糊稳定性切削阈的可能性分布及其置信水平表达式。     

铲齿成形铣刀重磨误差的分析和重磨前角的优化

本文先提出了γｆ＞０的铲齿成形铣刀因重磨而引起的廓形高度误差的计算方法,分析了重磨误差的规律。在此基础上又进一步提出了重磨前角的修正和优化。     

Global optimization of tool path for five-axis flank milling with a conical cutter

In this paper, optimum positioning of the conical cutter for five-axis flank milling of slender surfaces is addressed from the perspective of approximating the tool envelope surface to the data points on the design surface following the minimum zone criterion recommended by ANSI and ISO standards for tolerance evaluation. Based on the observation that a conical surface can be treated as a canal surface, i.e. envelope surface of one-parameter family of spheres, the swept envelope of a conical cutter is represented as a sphere-swept surface. Then, an approach is presented to efficiently compute the signed distance between a point in space and the swept surface without constructing the swept surface itself. The first order differential increment of the signed point-to-surface distance with respect to the differential deformation of the tool axis trajectory surface is derived. By using the distance function, tool path optimizations for semi-finish and finish millings are formulated as two constrained optimization problems in a unified framework, and a sequential approximation algorithm along with a hierarchical algorithmic structure is developed for the optimization. Numerical examples are given to confirm the validity and efficiency of the proposed approach. Comparing with the existing approaches, the present one improves the machining accuracy greatly. The rationale developed applies to general rotary cutters.     

基于解耦控制的同步传动技术的应用研究

对龙门移动式镗铣床同步传动不一致性问题进行研究,用两台直线电机作为龙门柱纵向进给的传动机构,分析了扰动与输出之间存在的耦合,设计出一种解耦控制器,并用龙门框架不平行时所产生的应力变化进行补偿。仿真结果表明,系统性能良好,并能快速实现同步运行。