Force prediction models and CAD/CAM software for helical tooth milling processes. I. Basic approach and cutting analyses

The need for reliable quantitative machining performance information for efficient and effective use of machining operations is discussed, as are the recent developments of predictive models and modular software for forces and power in practical operations based on a unified mechanics of cutting approach. The cutting action, comprehensive predictive force models and software modules for peripheral milling, end-milling and slotting operations are developed at three levels of sophistication. The first and basic or ‘ideal case’ model assumes perfectly rigid cutters with no eccentricity and includes all the important process variables, while the second or ‘eccentricity’ model also includes the inevitable eccentricity noted in practice. The third and most sophisticated ‘deflection’ model incorporates both eccentricity and cutter deflection in addition to the many process variables. The necessity to individually study each type of milling operation in order to identify, assess and verify the appropriate predictive model is highlighted in this first paper and the findings for each operation are reported in subsequent parts of this investigation.     

Constrained optimization strategies and CAM software for single-pass peripheral milling

Constrained optimization strategies and computer flow charts for single-pass rough peripheral milling on NC/CNC and conventional machine tools are presented and discussed. Various practical machine tool constraints have been considered, namely the maximum available power, torque and feed force and feed speed and cutting speed limits. The optimization strategies for this common operation have been found to be very complex and require computer assistance. A comparison of handbook recommended and optimal solutions has highlighted the significant benefits of using the latter and the need for minimizing the component loading time and cost to maximize such benefits.     

Times and costs analysis for sheet-metal cutting processes in an integrated CAD/CAM system

The aim of the present article is to develop a detailed time and cost analysis for process planning sheet-metal operations. A special computer module for determining the times and costs in sheet-metal operations has been developed and integrated in a CAD/CAM system which incorporates modules for nesting, toolpath generation, post-processing, etc. The special module allows all the geometrical and technological data from other modules in the CAD/CAM system (e.g. cutting conditions, toolpath parameters, types of material, cutting gases, etc.) required for the cost and time analysis to be automatically included without the need to manually enter the data in the module. This program can also be used as a 'stand alone' module, it has been developed with a graphic programming language (AutoLISP). Case studies are presented to highlight the benefits of using the program during practice.     

A CAD/CAM system for process planning and optimization in LOM (Laminated Object Manufacturing)

Rapid Prototyping (RP) technologies have emerged as a powerful set of manufacturing technologies in recent years. While these technologies invariably provide tremendous time savings over traditional methods for the manufacture of design prototypes, most are still quite inefficient. This paper proposes two ideas: (i), that these processes can be significantly optimized by using better process planning; and (ii), that several of these technologies use similar core planning technologies for optimization. The first hypothesis is verified in this paper by presenting an improved process planning system for one RP technology, Laminated Object Manufacturing (LOM). The second observation led us to develop an open architecture planning system for a host of RP technologies. A testbed software system using these ideas has been developed and is presented in this paper. While the methodologies developed can work with the current industry standard STL format for storing object CAD data, the software is planned purely to work using exact solid models and direct slicing methods.     

烟机异型件CAD/CAM系统的开发与应用

结合企业异型件CAD/CAM系统的开发与应用实际，简要说明了应用CAD/CAM技术是实现烟草机械异型件国产化的必要途径，论述了CAD/CAM系统的开发所依据的技术原理和涉及到的关键技术问题，分析了应用该系统所产生的社会经济效益．     

CAD/CAM技术在机车车辆钣金件展开放样中的应用

对形状复杂的钣金件展开,可通过可展曲面的几何尺寸,用人工通过一系列重复性解析计算求得展开图的尺寸,但工作量大,且难以保证结果的准确性.用CAD/CAM:进行辅助展开放样,既无需现场放样,又不用建立数学模型,就能对复杂构件作更精确的展开放样.     

Life prediction for fatigue of T800/5245 carbob-fibre composites: II. Variable-amplitude loading

This is the second of two papers describing the fatigue response of a [(±45,0₂)₂]_s laminate of the T800/5245 composite system, a modern aerospace material consisting of high-failure-strain, intermediate-modulus carbon fibres in a toughened bismaleimide resin system. In the first paper, the fatigue response in repeated tension, repeated compression, and mixed tension-compression was determined at constant stress levels over a wide range of R values. The results of those constant-amplitude experiments were then used to define a programme of four- and two-block variable-loading experiments in an attempt to derive predictive methods for such loading conditions. Formulae have been developed to predict life under non-linear cumulative damage conditions and empirical data derived to validate the procedures.     

Dissolution processes,hydrolysis and condensation reactions during geopolymer synthesis: Part II. High Si/Al ratio systems

The mechanisms of speciation of aluminate and silicate phases during dissolution and condensation stages of alumino-silicate geopolymer reactions characterised by Si/Al ≥ 3, have been investigated and the results compared to predictions of the partial charge model. Solid-state nuclear magnetic resonance (NMR) traces indicate that free [Al(OH)₄]⁻ species, present in lower silicate formulations such as Si/Al ≤ 1, do not occur in the present systems, suggesting that the condensation reaction between [Al(OH)₄]⁻ and silicate species is fairly quick and is consumed as soon as it is formed. This observation is also consistent with both calorimetric measurements and model predictions, as the condensation time increased exponentially with increased Si/Al ratio in the geopolymeric phase, indicating again that the high content of Al species in the gel phase greatly enhanced the condensation rate. The experimental observations suggest that the condensation process in these systems occurs in two stages: (a) quick condensation between aluminate and silicate species; followed by (b) a slow condensation stage solely involving silicate species.     

Effect of interfacial adhesion and statistical fiber strength on tensile strength of unidirectional glass fiber/epoxy composites. Part. II: comparison with prediction

An analytic model by Curtin and Takeda (Curtin WA, Takeda N. Tensile strength of fiber-reinforced composites: I. Model and effects of local fiber geometry. Journal of Composite Materials 1998;32(22):2042–59; Curtin WA, Takeda N. Tensile strength of fiber-reinforced composites: II. Application to polymer matrix composites. Journal of Composite Materials 1998;32(22):2060–81) is used to predict the ultimate tensile strength (UTS) of unidirectional (UD) glass fiber/epoxy composites with different interfacial adhesion and statistical fiber strength. Data for the fiber strength σ_c at the critical fiber length δ_c for five kinds of treated fibers are used for predicting UTS, which is obtained from both single fiber composite (SFC) and single fiber tension (SFT) tests. σ_c from SFC is attained using the Curtin theory on the fragmentation of SFC, while that from SFT is determined using a linear extrapolation of SFT data. Under good interface adhesion, the predicted UTS values based on the SFC data show the best agreement with measured ones at various fiber volume fractions, but a higher predicted value is obtained if the interface failure is matrix-controlled. For poor interfacial adhesion, the predicted UTS values are rather high compared to experimental ones due to the ineffective stress transfer. The predicted values based on the SFT data are much higher than the measured value for good interfacial adhesion.     

Hertzian flaw analysis and models for the prediction of flexural fracture strength of Al2O3 and Al2O3/SiCp nanocomposites

A study is presented comparing the statistics of observed crack-originating flaws on fracture surfaces of samples of Al2O3 and its composites (having 5 and 15 vol % SiC particle, SiCp) with those determined by the Hertzian indentation analysis. Cracks originating from Vickers microindents are also examined using transmission electron microscopy (TEM). Critical flaws determined by the Hertzian analysis predict experimental fracture strengths reasonably well when Orowan's model of obtaining the latter is used. This model is supported by microstructural features, which strongly suggest blunt crack-tips. The critical flaw sizes of alumina and the 5 vol % SiCp composite are found to be practically the same. Hence the explanation of the higher strength of the composites (relative to alumina) based on flaw size is improbable. The composite with 15 vol % SiCp is tougher and has a lower fracture strength in comparison with those of the 5 vol % SiCp composite. Therefore an increase in toughness does not satisfactorily explain the strengthening trend. The change in the mode of fracture and the interspacing distances (implicitly the heights) of the fracture steps are suggested as the main factors that control strengthening in these materials. © 1998 Chapman & Hall     

Thermal performance prediction models for a pulsating heat pipe using Artificial Neural Network (ANN) and Regression/Correlation Analysis (RCA)

Pulsating heat pipe (PHP) is one of the prominent research areas in the family of heat pipes. Heat transfer and fluid flow mechanism associated with PHP are quite involved. The analytical models are simple in nature and limited in scope and applicability. The regression models and Artificial Neural Network (ANN) are also limited to a number of input parameters, their ranges and accuracy. The present paper discusses the thermal performance prediction models of a PHP based on ANN and RCA approach. Totally 1652 experimental data are collected from the literature (2003–2017). Nine major influencing input variables are considered for the first time to develop the prediction models. Feed-forward back-propagation neural network is developed and verified. Backward regression analysis is used in RCA-based regression model. Linear and power-law regression correlations are developed for input heat flux in terms of dimensionless Kutateladze (Ku) number, which is a function of Jakob number (Ja), Morton number (Mo), Bond number (Bo), Prandtl number (Pr) and geometry of a PHP. The prediction accuracy of present regression models (R²?=?0.95) is observed to be better as compared with literature-based correlations.     

Investigation on the competing effects of clay dispersion and matrix plasticisation for polypropylene/clay nanocomposites. Part II: crystalline structure and thermo-mechanical behaviour

In view of the structure–property relationship, the mechanical property enhancement of polypropylene (PP)/clay nanocomposites can also be associated with the alterations of their crystalline structures and behaviour in addition to the general interpretation of intercalation/exfoliation level and uniform dispersion of more rigid clay platelets with higher aspect ratios in the PP matrix. Wide-angle X-ray diffraction (WAXD) was utilised to evaluate the effects of clay content, maleated PP (MAPP) content (MAPP as the compatibiliser) on PP crystalline structures of nanocomposites. Furthermore, the melting and crystallisation behaviour of PP/clay nanocomposites was also investigated by conducting differential scanning calorimetry (DSC). The thermo-mechanical properties were characterised via dynamic mechanical thermal analysis (DMTA). It is observed that enhancement of mechanical properties are mainly affected by the preferred orientation of PP crystals, the growth of α-PP phase and effective nucleating agent role of additional clay while the excessive amount of MAPP becomes detrimental to these crucial aspects, which is also evidently revealed in DMTA measurements.     

Application of the network alteration theory for modeling the time-dependent constitutive behaviour of rubbers.: Part II. Further evaluation of the general theory and experimental verification

In part I of this paper (E.G. Septanika, L.J. Ernst, 1998. Application of the network alteration theory for modeling the time-dependent constitutive behaviour of rubbers. Part I. General theory. Mech. Mater. 30, 253–263), a general time-dependent constitutive model for rubber materials has been developed, based on combination of the general rubber hyperelastic theory and the microstructure alteration theory. Besides, Mullin's effect is included into the model by employing Simo's rubber hysteresis theory. In this second article a further evaluation of the developed model is presented. First, the eight non-Gaussian chain model of Arruda and Boyce is chosen to describe the rubber hyperelastic behaviour. Second, the full range of the alteration process is described using a general reaction law. The experimental characterization of both the time-independent and the time dependent parameters is performed for a modified Natural Indonesian Rubber (modified SI-Rubber). Finally, numerical examples are presented to illustrate the capability of the proposed model. It appears that the present model is capable of describing the time dependent irreversible deformation behaviour of rubber-like materials, i.e. large (irreversible) deformation, stress-relaxation, creep, permanent set and aging induced flexibility changes.     

A general dynamic simulation model for evaporators and condensers in refrigeration. Part II: simulation and control of an evaporator: Modèle général dynamique pour évaporateurs et condenseurs frigorifiques. Partie II: Simulation et régulation d'un évaporateur

A mathematical model of an evaporator based on one-dimensional partial differential equations representing mass conservation, and tube wall energy has been formulated. These equations are then restructured and linked to a program data base of all major refrigerants and refrigerant mixtures. The result is a simulation model of an evaporator that is general and flexible. The model is tested over a wide range of operating conditions and a simple controller is implemented to demonstrate the effectiveness of the model for controller and systems design.