Computer Aided Tolerance assignment

Tolerances are basic to the production of every part. This is because perfect parts cannot be produced with existing processes and machines. The determination of tolerances for the individual parts of a functional assembly is critical, but not trivial. Numerous approaches are suggested in past literature for (analytical) tolerance allocation. With the advent of total automation, more attempts are being made to computerize manual design tasks. Tolerance design, assignment and allocation can also be fully automated if the assembly function can be estimated by the computer.

In the present paper, an attempt is made to computerize tolerance assignment. A simple example of a two piece assembly, viz., a fit, is used to demonstrate the developed methodology. A feature extraction is first performed from both detail and assembly drawings. Then, probable assembly interfaces are determined using a rule based procedure. Consequently, tolerances are assigned to the basic dimensions of each feature and to the assembly interfaces using a tolerance database and user interaction. More complex analysis for tolerance allocation is also under study.     

Applying the critical path method to manufacturing routing

Traditionally the critical path method (CPM) has been used primarily as an a'priori planning and scheduling device. Its applications have typically been limited to one-shot projects, usually with a long period of completion time. This paper proposes taking these ideas to continuous production systems, and to implement the CPM not just at the outset but throughout the process. The algorithm calls for repeatedly calculating the critical path through the production process and routing parts so as to remain off this path. Before the model is presented, some basic ideas are introduced from group technology (GT) and CPM. After the presentation of the model, two potential implementations with the usage of computer are proposed.     

Magnetohydrodynamic stability of boundary layers along a flat plate with pressure gradient

Summary The purpose of the paper is to consider theoretically the characteristics of steady two-dimensional magnetohydrodynamic boundary layer flow past a flat plate with pressure gradient in the presence of transverse magnetic field and its stability problem. The boundary layer equation is transformed into a non-similar one and numerical solutions are obtained by the difference-differential method. The neutral stability curves for wavelike disturbances of Tollmien-Schlichting type are then presented for the velocity profiles obtained above. Numerical results for the magnetic parameter and pressure gradient parameter are given for the velocity profiles, coefficient of skin friction, displacement thickness and the critical Reynolds number.With 10 Figures     

中国台湾电信市场现状

台湾电信市场的开放大致分四个阶段,从1995年起,陆续开放了移动通信、卫星通信及固定通信等多种业务。固网市场,2001年新世纪资通、台湾固网和力霸宽频电信的加入打破了中华电信的独家垄断,开始形成四强竞争的新局面。移动领域,1997年底6家运营商8张民营执照的发放开始了该领域史无前例的竞争。在2001年1月,台湾大哥大、远致电信、亚太行动宽频、联邦电信和中华电信获得了3G执照,累计竞标金额达488.99亿元(新台币)。     

浅析数据挖掘与企业市场营销战略

数据挖掘是客户关系管理的重要组成部分,而客户关系管理的核心是营销管理。在高度信息化的社会的今天,数据挖掘在市场营销决策中起到越来越重要的作用,通过它可以实现对客户深度的把握,研究老客户,发现新客户,让企业实时把握住市场动态,及时地调整企业的营销策略,以在激烈的市场竞争中立于不败之地。     

直馏汽油异构化装置的运行

长庆油田公司第二助剂厂新建的 70kt a直馏汽油异构化装置 ,采用二个反应器 ,以常压直馏汽油为原料 ,采用非临氢重整催化剂 ,生产的异构化汽油的研究法辛烷值约 90 ,但改质汽油收率较低 ,仅 65 %左右     

Improvement of the engineering properties of asphalt pavements using a ‘soft’ compaction technique (AMIR-Compaction)

In most countries of the world asphalt pavement of road networks represents the biggest single investment in the transportation system. In Canada, asphalt pavement built over the past decade is worth more than 70 billion dollars (in 1984 dollars). In order to maintain the current road network at the present level of service and prevent it from further deterioration, over 6 billion dollars is needed anually.

Traditionally, asphalt overlays are widely used to rehabilitate existing deteriorated pavements. Unfortunately the new overlays have been observed to fail in a relatively short time. Thus the investment in overlays is lost.

Recent research based on the concept of relative rigidity has indicated that the rapid deterioration of new asphalt overlays is directly related to current construction equipment. It has been shown analytically and experimentally that steel rollers used in compacting the asphalt layer will result in surface cracks during construction. Traffic and environmental influences will accelerate the failure of the new layer.

This paper presents the results of a testing programme evaluating the engineering properties of asphalt slabs compacted by a new method using a compactor termed AMIR. The results showed that the AMIR compactor will prevent the formation of constitution cracks resulting in an increase of indirect tensile strength of 10% and an increase of direct tensile strength of up to 60% when compared to steel roller compacted asphalt slabs.     

EFFECT OF FINE GRINDING ACTIVATION ON LEACHING BEHAVIOUR OF SCHEELITE CONCENTRATE

The influence of mechanical activation on the leaching behaviour of scheelite was studied bymeans of fine grinding in an attritor and subsequently HCl leaching in presence of PO_4~(3-).Results showed that after fine grinding in the attritor,the reaction rate of scheelitewith HCl-Na_3PO_4 solution was remarkably increased,the extraction of W increased fromabout 8 to 99%.The IR spectra and X-ray diffraction analysis indicated that in addition toan enlargement of surface area the fine grinding action had made also changes of fine struc-ture and reactivity of solid surface,hence the leaching process of scheelite can be carried outunder mild leaching conditions.     

CHARACTERISTICS OF INTERNAL FRICTION AND MODULUS ASSOCIATED WITH NON-EQUILIBRIUM DIFFUSION-TYPE PHASE TRANSFORMATION IN EUTECTOID Al-Zn ALLOY

The characteristics of the low frequency internal friction and the modulus effect associatedwith the non-equilibrium spinodal pretransformation and the following discontinuous trans-formation was investigated in an as-quenched eutectiod Al-Zn alloy.It was observed that theloss of the stability in the lattice,which corresponded to the large-amplitude long-wavelengthstatic concentration wave in the non-equilibrium spinodal pretransformation,did not induceany effect of localized soft modulus.Although there are two aging internal friction peaks inphase transformation which correspond to the appearance and disappearance of the coherencyin spinodal pretransformation and the maximum of the interface area in the discontinuoustransformation respectively,the effect of localized soft modulus did not take place yet.     

内部信息不对称下IT项目外包决策风险测度

从企业内部信息不对称的角度对项目外包决策风险进行定量化研究,通过内部信息不对称事件发生的概率、内部信息不对称度、内部信息不对称对外包决策的损失及内部信息不对称对决策产生风险的可管理性4个方面建立了IT项目外包内部信息不对称的风险度函数,并结合具体实例进行了应用分析,分析结果对于企业今后在外包决策时进行风险控制具有一定的借鉴意义。