塑料模具设计的内涵与方法

塑料模具的设计牵涉到方方面面,设计塑料模具应按一定的设计程序进行,并对几个设计要点必须予以足够重视,这样才能保证模具的设计制造质量.塑料模具设计不仅仅是结构设计还包括模具材料及其热处理选择,选择正确与否对模具的使用性能及其寿命将产生重大影响.模具设计与模具失效紧密相关,为了尽量避免模具失效,应充分研究分析塑料模具的失效机制,并在模具设计上采取相应的防范措施.     

基于不同粗糙度Ra与Rz的FV520B-I超高周疲劳失效研究

粗糙度Ra及Rz这两种粗糙度都会对高强度钢FV520B-I的超高周疲劳行为产生明显的影响.首先,以FV520B-I不同粗糙度的超声疲劳试验结果为基础,得到不同粗糙度情况下的失效试件的断口特征.结合超声疲劳试验结果、失效试件断口特征及能谱检测结果,分析粗糙度Ra对FV520B-I超高周疲劳失效机理的影响.其次,以粗糙度R...     

刀具状态与切削过程的优化

刀具磨损是机械加工过程中普遍存在的一种自然现象,研究了刀具磨损状态对已加工表面质量的影响,主要是后刀面磨损量对工件表面粗糙度、残余应力和加工硬化的影响,同时也探讨了切削速度与表面粗糙度的关系,并对这些影响产生的机理进行了讨论.     

Study of plowing and friction at the surfaces of plastic deformed metals

Experimental and analytical investigations of plowing and friction were conducted at the surfaces of well-polished lead, aluminum, copper, nickel, molybdenum, and tungsten to study the mechanism of the load/penetration dependency. The experimental tests were performed with a Nano-Indenter XP of MTS and a Scanning Probe Microscope (SPM), Nanoscope IIIa of Digital Instruments. In addition to make indentation and measure the hardness and Young’s modulus, the indenter was used to make scratches at the surface of metals under different normal load while the penetration depth and frictional force encountered during the scratching were recorded. The SPM, operated mostly in the contact mode, was used to examine the scratch profile. Under the test conditions, plastic deformation dominated at the surfaces of the metals. An analytical model was established to express plastically deformed contacts, based on plowing of a conical-shaped indenter with a hemispherical tip at a plastic deformed surface. Penetration depth and scratched volume were calculated, which is in good agreement with experimental observation. The frictional coefficient μ was also calculated with the model, which accounted for plowing as well as the adhesion force between the indenter and surface. Beside fair agreement of experimental data and calculated values on μ under the loads applied, the model indicated a dramatic rise in friction coefficient under very low loads, which was not observed in the tests. The discrepancy was discussed, and it was believed that the dramatic increase in μ is for the calculated μ and may be due to the assumed dominant contribution of adhesion force in actual contact load with decreasing external load, and it appears only the adhesion energy Δγ is significant. The actual adhesion energy Δγ between our diamond indenter and metal surface in our test condition might be smaller than the value used in calculation.     

基于AutoCAD的塑料模标准件参数化图形库的开发

介绍了在AutoCAD软件平台下,以Access软件建立数据库管理系统,利用参数化和VBA语言开发塑料模标准件参数化图形库,并用实例介绍了开发过程.该系统的建立与使用能缩短模具设计的周期和提高工作效率.仿此能进行其它专业的参数化图库的开发.     

Wheel-rail wear simulation

This paper declares the method for the computation of the wheel-rail surface degradation in a curve where the major surface degradation phenomenon is a combination of wear and plastic deformation. Simulating the form change of the wheel-rail contacts help to identify the risk of severe or catastrophic wear resulting from increased train speeds and axle loads and can help in determining more efficient maintenance schedules for track and rolling stock. The method was previously used to simulate the form change in a two-roller contact. The progress is made in the terms of general geometry modelling, which makes differences in the various contact configurations. The normal contact problem is analysed using the modified Winkler method and calibrated using the results from FEM modelling of the wheel-rail contact with elastic-plastic material model. A piecewise approach and stick-slip analysis of the rolling-sliding contact solves the tangential problem. A linear wear law is used in the wear computation. The form change for a typical two-point contact in a low radius curve was analysed and discussed.     

Durability improvement method for plastic spur gears

An experimental investigation of power-transmission plastic spur gears was performed by inspecting both the characteristics of wear and durability, and a durability improvement method is proposed that either drills an internal hole or inserts a steel-pin in the internal hole of the gear tooth, and this proposed method was verified. In the case of acetal gears, the amount of wear was observed to increase with the development of plastic deformation, and an increase in tooth stiffness occurred due to the brittle material property of acetal. On the other hand, in the case of nylon gears, the proposed method was shown to reduce the tooth temperature compared to the original gear, thus reducing the amount of wear and prolonging service life. Hence, the proposed method was proven to be practically applicable to plastic gears made from soft polymers that show visco-elastic properties such as nylon.     

Transition of elevated-temperature wear mechanisms and the oxidative delamination wear in hot-working die steels

Dry sliding wear tests of H13 and H21 steels were performed at 400 °C. The wear mechanisms and their transitions were studied, and an oxidative delamination wear was suggested. A mild oxidative wear prevailed with oxide fatigue delamination under less than 3.54 MPa. Under 3.54-5.31 MPa, the oxidative wear prevailed with oxide fatigue delamination and the oxidative delamination wear. As the pressure surpassed 5.31 MPa, a severe wear prevailed with the oxidative delamination wear and the plastic extrusion. The oxidative delamination wear meant that the delamination occurred inside the matrix underneath tribo-oxides with long-ditch delamination and belt-like wear debris.     

FEM analysis of erosive wear

Surface damage caused by the impact of dispersed particles in gas or liquid flow is called “erosion”. Much attention has been paid to this phenomenon as one of the most serious problems to be solved, particularly concerning pipe-bends or valves in pneumatic conveying systems. But the phenomena of erosive wear are so complicated and vary depending on the factors of not only the kinds of material, hardness, shapes, sizes and mechanical properties of the particles, but also of blasting angles and velocity.

For the purpose of this study, mild steel was prepared and erosion wear tests were carried out. Steel grits were impacted against target materials at different incident angles. The results showed that the wear losses varied markedly as a function of the impact angles, and that the maximum wear occurred at specific angles. Maximum wear occurred at 20–30° for mild steel, and 60° for ductile iron. This impact angle dependence of wear was simulated by Tabor’s theory and FEM which could analyze the plastic deformation of alloy surface as a result of a single particle impact. In the case of both mild steel and ductile cast iron, it was found that the impact angles play a very important and valid role in the corrosion process.     

Friction coefficient and wear mode transition in micro-scale abrasion tests

The purpose of this work was to conduct ball-cratering wear tests to monitor both normal and tangential forces. Balls of 52100 steel, a specimen of H10 tool steel and an abrasive slurry prepared with silicon carbide particles and distilled water were used. Optical microscopy analysis of the worn craters revealed the presence of only grooving abrasion. However, a more detailed analysis conducted by SEM has indicated that different degrees of rolling abrasion have also occurred along the grooves. The results also showed that the normal force plays an important role in the scattering of the values of the friction coefficient.     

A generalized fretting wear theory

Combined impact-sliding fretting wear is a complex phenomenon due to the random nature of the excitation force and the self-induced tribological changes. Available models, which relate wear losses to the process variables, are empirical in nature and bear no physical similarity to the actual mathematical and physical attributes of the wear process. A generalized fretting wear theory is presented to mathematically describe the fretting wear process under various modes of motion; impact, sliding and oscillatory. This theory, which is based on the findings from the fracture mechanics analysis of the crack initiation and propagation processes, takes into consideration the simultaneous action of both the surface adhesion and subsurface fatigue mechanisms. The theory also accounts for the micro-, and macro-contact configuration of the fretting tribo-system. The closed form solution requires the calibration of a single parameter, using a limited number of experiments, to account for the effect of environment and the support material. The model was validated using experimental data that were reported for Inconel 600 and Incoloy 800 materials at room and high temperature environment, and for different types of motion. The results showed that model can accurately predict wear losses within a factor of ±3. This narrow range presents better than an order of magnitude improvement over the current state-of-the-art models.     

冲压模具凸凹模间隙控制与调整方法研究

模具凸模和凹模之间的间隙将直接影响制件的质量和模具的使用寿命,合理控制凸、凹模间隙并使其均匀是装配的关键。笔者深入探讨了冲压模具装配前需注意的问题,分析研究了凸、凹模间隙的控制与调整方法,并提出了模具使用后间隙变化的调整修配措施,对模具装配生产实践具有指导意义。     

TRIZ理论在螺旋输送机磨损问题中的应用研究

在对TRIZ理论解决技术系统矛盾问题理论深入研究的基础上,认为技术矛盾和物理矛盾是可以相互转化的。改进目前TRIZ理论解决矛盾问题的一般流程,提出在应用TRIZ理论解决技术系统矛盾过程中,应该尽量将技术矛盾转化为物理矛盾,能更好的抓住矛盾问题的本质特征,使解决问题的思路更清晰。针对螺旋输送机因细小物料挤入轴承座而造成的严重磨损问题,把技术矛盾转化为物理矛盾,通过分离原理与创新原理的综合应用,提出了用马蹄形法兰代替盘形法兰解决问题的创新性方案,有效的解决了问题。