Production schedule of concretes for maximum profit

Three numerical examples illustrate both the types of profit problem related to concrete production that can be solved by linear programming, and several optimization techniques. It is shown that linear programming can provide not only the production schedule for maximum profit under a set of existing conditions but also it can point in the direction of the most efficient changes of the existing conditions for increased production and profit.     

Development of a component-based machining centre selection model using AHP

Machining centres are widely used in manufacturing companies all over the world. Since investments in machining centres are long-term and expensive, selection of the most appropriate machining centre is an important decision for manufacturing companies. There has been considerable effort spent in developing crisp and fuzzy multi-criteria decision-making (MCDM) models that use technical specifications provided by machining-centre manufacturers such as, axis size, power, spindle speed, tolerance, repeatability, cutting-tool change time, and number of cutting tools along with other economical and commercial factors. However, the technical specifications are directly taken from machining-centre manufacturers’ catalogues without checking their correctness, adequacies, or ability to represent the areas that are used for measurement. In such a case, one cannot be sure whether the outcomes are sound or not without a detailed check of the technical specifications, which can only be performed after actual usage of the machine itself. To overcome all such problems, an analytic hierarchy process (AHP) model that evaluates the machining centre components is developed in this paper. The new component-based AHP model is then compared with two MCDM models that use only technical specification values.     

Optimization of machining conditions for multi-tool milling operations

The variables affecting the economics of machining operations are numerous and include machine tool capacity, required workpiece geometry, cutting conditions of velocity, feed rate, depth of cut and many others. This paper describes a procedure to calculate the machining conditions for milling operations according to minimum production cost as the objective function. Optimum values of machining conditions for each pass are determined based on the objective function criteria by circular direction search method which is specifically developed for this purpose. The effects of constraints on the objective function can be evaluated by graphical representation of the objective function and the constraints in the developed software.     

Formulation and solution of problems of tool positioning on a single machining centre

We extend previous work on the construction of a computer technique used to formulate and solve a tool positioning problem concerning the efficient use of a single machining centre. The problem is formulated as an integer programming model. The problem is to identify which pockets of a circular tool magazine should be used to accommodate specific tools, during machine setup, so as to minimize the makespan of a given sequence of operations. We now analyse the more realistic situation in which it is assumed that the given sequence of operations is to be carried out repeatedly. Consequently, the pockets of the magazine must contain the same classes of tools at the end of each cycle of operations as they did at the beginning, so that the process can be repeated in an identical fashion. The extended problem is also formulated as an integer programming model, capable of being solved using commercially available software. Problems of a realistic size can then be used to set up operating conditions for a machining centre     

Tool replacement policies for a machining centre producing multiple types of products with distinct due dates

This paper focuses on a tool replacement problem to determine tool replacement schedules in a machining centre that produces multiple types of products with given due dates using multiple types of tools. For the problem, we develop new tool replacement policies with the objective of minimizing the sum of tool purchasing costs, material costs, and the tardiness penalty costs of not meeting due dates. In these policies, tool replacement intervals or exact times for tool replacements are determined using the information on the accumulated actual processing time and the processing time of the operation. The suggested policies are compared with other policies that are used in practice or suggested in previous research through a series of computational experiments on a number of test problems. Results of the computational tests show that the new replacement policy gives better performance than existing policies.     

Process planning for reliable high-speed machining of moulds

A method of generating NC programs for the high-speed milling of moulds is investigated. Forging dies and injection moulds, whether plastic or aluminium, have a complex surface geometry. In addition they are made of steels of hardness as much as 30 or even 50 HRC. Since 1995, high-speed machining has been much adopted by the die-making industry, which with this technology can reduce its use of Sinking Electrodischarge Machining (SEDM). EDM, in general, calls for longer machining times. The use of high-speed machining makes it necessary to redefine the preliminary stages of the process. In addition, it affects the methodology employed in the generation of NC programs, which requires the use of high-level CAM software. The aim is to generate error-free programs that make use of optimum cutting strategies in the interest of productivity and surface quality. The final result is a more reliable manufacturing process. There are two risks in the use of high-speed milling on hardened steels. One of these is tool breakage, which may be very costly and may furthermore entail marks on the workpiece. The other is collisions between the tool and the workpiece or fixtures, the result of which may be damage to the ceramic bearings in the spindles. In order to minimize these risks it is necessary that new control and optimization steps be included in the CAM methodology. There are three things that the firm adopting high-speed methods should do. It should redefine its process engineering, it should systematize access by its CAM programmers to high-speed knowhow, and it should take up the use of process simulation tools. In the latter case, it will be very advantageous to use tools for the estimation of cutting forces. The new work methods proposed in this article have made it possible to introduce high speed milling (HSM) into the die industry. Examples are given of how the technique has been applied with CAM programming re-engineered as here proposed, with an explanation of the novel features and the results.     

Application of the TOC thinking processes to challenging assumptions of profit and cost centre performance measurement

The interaction of the measurement criteria of cost centres and profit centres, and the resultant effect on organizational profit is examined by applying the Theory of Constraints thinking processes. Three cases are described based on the assumptions that a profit centre should maximize profit and a cost centre should at least recover its costs. These cases illustrate that there will exist conflict between profit centres and cost centres due to disagreement about transfer pricing and hourly tariffs; that some outsourcing decisions taken in isolation can lead to a spiral of declining competitiveness; and that the attempts by a cost centre to maximize cost recovery leads to a lower profit for the organization. The thinking process logic trees show that these negative effects are caused by the application of wrong measurement criteria.     

'Dose per unit content' functions: a robust tool for the interpretation of bioassay data

The purposes of this study were to investigate the influence of the consequences of the lack of primary bioassay information and to elaborate approaches which could improve the reliability of dose assessments. The aggregated time-dependent functions 'dose per unit organ (excretion) content' z(t) have been proposed in this study as a convenient and reliable tool for bioassay. The analysis of the variation of z with changes of AMAD has demonstrated the existence of areas of the relative invariance of z, which permits the selection of one (reference) function z for the whole area of stability. Within the framework of such an approach an arbitrary set of bioassay data can be approximated by the linear combination F(t) = sum(i) E(i)/z(t - tau(i)), where F(t) = function of time t, which approximates the observed bioassay time trend; tau(i) = time shift of the acute intake i; E(i) = effective dose, associated with the acute intake i (the two last parameters are results of the approximation procedure).     

Process planning for multi-axis NC machining of free surfaces

Process planning for the manufacture of free surfaces is mainly concerned with determination of machining configuration. In this paper, we investigate the machining configuration problem stated as: For a given surface model, find (1) The minimum number of control axes, (2) The minimum range of the rotational axes, and (3) The workpart setup orientation. In deriving the solution algorithm, we ensured implementability by casting the problem into an algebraic domain. Using a digitized visibility map, called the binary spherical map, the machining configuration problem can be solved in a unified fashion without falling into numerical complexity. The solution algorithms are implemented and validated via computer simulations, indicating they can be implemented on the CAD/CAM system as a process planner.     

Lifetime replacement policy in discrete time for a single unit system

We consider, in discrete time, a single unit system which operates for a period of time represented by a general distribution. This unit is subjected to failures during operations. Some of these failures are repairable and the unit is repaired in the repair facility. When the unit experiences a non-repairable failure then it has to be replaced with a new one. We consider a replacement policy based on the lifetime of the unit. This policy can be studied from two different approaches. The first approach, named Model I, is to replace the unit by a new one when the unit attains a predetermined lifetime. The other approach, named Model II, is to close repair facility when the lifetime of the unit attains a predetermined quantity. For each model, we obtain the stationary distribution and some performance measures of interest.     

Measurement of maximum time interval error for telecommunicationsclock stability characterization

Maximum time-interval error (MTIE) is historically one of the main time-domain quantities considered for the specification of clock stability requirements in telecommunications standards. In this paper, MTIE is first introduced according to its formal definition. Then, the main issue of its experimental measurement is pointed out: the heavy computational effort in most cases of practical interest. Therefore, two suitable methods to face up to this issue are herein discussed, summarizing the state of the art of MTIE measurement techniques in telecommunications. A new effective technique is proposed, with the aim to provide an easy but accurate way to test the compliance of telecommunications clocks with MTIE standard masks. Several results, measuring clocks deployed in telecommunications networks, are provided     

Predictive analytics for truck arrival time estimation: a field study at a European distribution centre

Distribution centres (DCs) are the hubs connecting transport streams in the supply chain. The synchronisation of coming and going cargo at a DC requires reliable arrival times. To achieve this, a reliable method to predict arrival times is needed. A literature review was performed to find the factors that are reported to predict arrival time: congestion, weather, time of day and incidents. While travel time receives considerable attention, there is a gap in literature concerning arrival vs. travel/journey time prediction. None of the reviewed papers investigate arrival time: all the papers found investigate travel time. Arrival time is the consequence of travel time in combination with departure time, so though the travel time literature is applicable, the human factor involved in planning the time of departure can affect the arrival time (especially for truck drivers who have travelled the same route before). To validate the factors that influence arrival time, the authors conducted a detailed case study that includes a survey of 230 truckers, a data analysis and a data mining experiment, using real traffic and weather data. These show that although a ‘big data’ approach delivers valuable insights, the predictive power is not as high as expected; other factors, such as human or organisational factors, could influence arrival time, and it is concluded that such organisational factors should be considered in future predictive models.     

Optimization of machining conditions for turning cylindrical stocks into continuous finished profiles

The optimization problem involving straight turning operations for bar components with constant finished diameters has received extensive attention. In the real-world turning processes on a computer numerical control (CNC) machine, the cylindrical stocks are frequently machined into their desired continuous profiles. Such turning processes require not only straight turning but also face turning, taper turning and circular turning to complete the removal of stock. However, machining models proposed in the literature do not simultaneously consider these turning operations to optimize machining conditions (parameters). This study formulates a machining model to optimize the machining conditions for turning cylindrical stocks into continuous finished profiles, thereby extending the applications of machining optimization. The usefulness of the developed machining model is finally established through a test example.     

Optimal machining conditions with costs of quality and tool maintenance for turning

Although there is a voluminous literature on machine tool economics, the cost of machining quality has received little attention. In this paper, we develop a timedynamic economic model for single-pass turning. The model incorporates considerations on the stochastic nature of tool-life and such tool maintenance activities as tool replacement and tool regrinding. We model the quality cost of tool-cutting in terms of deviation from target roughness and deviation from target dimension. The cost of deviation is either the Taguchi type under continuous assumption or in terms of the cost to the entire workpiece under discrete assumption. The connection between quality cost and tool maintenance cost is explicitly addressed. Essentially, quality cost as well as machining cost is a function of two sets of decisions: machining conditions as defined by the choice of cutting speed and feed rate (depth of cut is a constant in single-pass operations), and the condition of the cutting tool as defined by the tool retirement and regrinding policy. The cost of tool failure is also incorporated.     

Determination of grinding conditions for renewal of a wheel cutting ability allowing for its variation during the machining process

The authors discuss the determination of rigid-mode grinding conditions with a periodic electric discharge action on the wheel working surface in a separate zone, taking into account the in-process variation of the wheel cutting ability. The calculation is based on the mathematical relations that describe variation of the wheel cutting ability in elastic-mode infeed grinding with a constant workpiece-to-wheel pressing force, where the process kinematics is similar to that of the rigid-mode grinding. The workpiece speed is determined for a specified machined surface roughness. The workpiece-to-wheel pressing force is chosen such that the surface layer of the workpiece material should undergo no phase-structural transformations. The variations of the wheel cutting ability during the rigid-mode grinding are taken into account through the use of the equations that describe the variations of the wheel's current limited cutting ability in the elastic-mode grinding. Based on the discussion of various methods of calculation of one of the grinding parameters—depth of cut—the authors have found its value ensuring that no phase-structural transformations will occur in the surface layer of the workpiece material under maximum feasible removal rates.     

缩短空分设备开车时间的优化操作

简介了KDON-1500/1500型空分设备的主要技术参数,详细介绍了在空分设备开车时冷却、积液和调纯三阶段以及间断制氧阶段所采取的优化操作措施,缩短空分设备的开车时间,达到节能降耗的目的。     

Uncertainty analysis of the weighted equivalent lung dose per unit exposure to radon progeny in the home

A parameter uncertainty analysis has been performed to derive the probability distribution of the weighted equivalent dose to lung for an adult (w(lung) H(lung)) per unit exposure to radon progeny in the home. The analysis was performed using the ICRP Publication 66 human respiratory tract model (HRTM) with tissue weighting factor for the lung, w(lung) = 0.12 and the radiation weighting factor for alpha particles, wR = 20. It is assumed that the HRTM is a realistic representation of the physical and biological processes, and that the parameter values are uncertain. The parameter probability distributions used in the analysis were based on a combination of experimental results and expert judgement from several prominent European scientists. The assignment of the probability distributions describing the uncertainty in the values of the assigned fractions (ABB, Abb, AAI) of the tissue weighting factor proved difficult in practice due to lack of quantitative data. Because of this several distributions were considered. The results of the analysis give a mean value of w(lung) H(lung) per unit exposure to radon progeny in the home of 15 mSv per working level month (WLM) for a population. For a given radon gas concentration, the mean value of w(lung) H(lung) per unit exposure is 13 mSv per 200 Bq.m(-3).y of 222Rn. Parameters characterising the distributions of w(lung) H(lung) per unit exposure are given. If the ICRP weighting factors are fixed at their default values (ABB, Abb, AAI = 0.333, 0.333, 0.333; w(lung) = 0.12; and wr = 20) then on the basis of this uncertainty analysis it is extremely unlikely (P approximately 0.0007) that a value of Hw/Pp for exposure in the home is as low as 4 mSv per WLM, the value determined with the epidemiological approach. Even when the uncertainties in the ABB, Abb, AAI, values are included then this probability is predicted to be between 0.01 to 0.08 depending upon the distribution assumed for describing the uncertainties in the ABB, Abb, AAI, values. Thus, it is concluded that the uncertainties in the HRTM parameters considered in this study cannot totally account for the discrepancy between the dosimetric and epidemiological approaches.